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Environmental Impact Assessment for drilling of an
exploratory well in the NELP-VII block MB-OSN-2005/3
of
Western Offshore Basin
Corporate Health, Safety and Environment Management
New Delhi
November 2015
Acknowledgement
Environmental Impact Assessment and Risk assessment report for proposed exploratory drilling activity
in MB-OSN-2005/3 in Western Offshore Basin has been prepared by the HSE Team of Western Offshore
Basin, Mumbai under the guidance and support from the Corporate HSE, ONGC, New Delhi. The primary
baseline data with the analytical observations has been provided by IPSHEM, Goa. The report
incorporates the offshore environmental baseline data acquired under the project Western Offshore
Environment Monitoring conducted and carried out by IPSHEM, Goa.
We express our sincere gratitude to Shri A.K. Dwivedi, Director (Exploration), I/c HSE, ONGC for his
encouragement and support in preparation of this report. Our sincere thanks are due to Shri G.C. Katiyar,
ED-Basin Manager, Western Offshore Basin and Shri S. Ganesan, GGM-HOI, IPSHEM for providing
guidance during the course of this work.
Project Team
Contents
SL.NO. PAGE NO.
CHAPTER 1 INTRODUCTION 1
1.1 PURPOSE 1
1.2 IDENTIFICATION OF THE PROJECT PROPONENT & THE
PROJECT 2
1.3 SCOPE OF STUDY 4
CHAPTER 2 TERMS OF REFERENCE 5
2.1 POINTWISE COMPLIANCE OF TOR 5
CHAPTER 3 PROJECT DESCRIPTION
3.1 TYPE OF THE PROJECT 10
3.2 LOCATION OF PROJECT 11
3.2.1 CRZ REGULATION APPLICABILITY 13
3.2.2 DRILLING WELL LOCATION 13
3.3 PROPOSED PROJECT SCHEDULE FOR APPROVAL AND
IMPLEMENTATION 14
3.4 TECHNOLOGY AND PROCESS DESCRIPTION 14
3.4.1 SOURCE OF WATER 19
3.4.2 WATER USAGE PLAN 19
3.4.3 WASTEWATER GENERATION & DISCHARGE 20
3.4.4 CHEMICAL REQUIREMENTS AND THEIR STORAGE AT RIG 21
3.5 LITIGATIONS & COURT DIRECTIONS / ORDERS 22
3.6 ASSESSMENT OF NEW AND UNTESTED TECHNOLOGY 22
3.7 CLIMATOLOGY & METEOROLOGY OF THE ARABIAN SEA 23
CHAPTER 4 DESCRIPTION OF ENVIRONMENT 30
4.1 STUDY AREA 30
4.2 STUDY COMPONENTS 30
4.3 BASELINE ENVIRONMENT 31
4.3.1 OBJECTIVES AND SCOPE OF THE STUDY 31
4.3.2 SCOPE OF WORK 31
4.3.3 METHODOLOGY 32
4.3.4 ASSOCIATION OF BIOLOGICAL EXPERTISE 33
4.3.5 DESCRIPTION OF STUDY AREA AND SAMPLING
LOCATIONS 34
4.3.6 EQUIPMENT USED FOR SAMPLING: 36
4.3.7 METHODOLOGY FOLLOWED FOR HYDROGRAPHICAL AND
CHEMICAL PARAMETERS 38
4.3.7.1 HYDROGRAPHICAL PARAMETERS 38
4.3.7.2 CHEMICAL PARAMETERS 39
4.3.8 RESULTS AND DISCUSSION 41
4.3.8.1 TEMPERATURE 41
SL.NO. PAGE NO.
4.3.8.2 PH 41
4.3.8.3 SALINITY 41
4.3.8.4 TURBIDITY 41
4.3.8.5 TOTAL SUSPENDED SOLIDS 42
4.3.8.6 DISSOLVED OXYGEN DO 42
4.3.9 BIOLOGICAL MONITORING OF OFFSHORE STATIONS 46
4.3.9.1 METHODOLOGY OF BIOLOGICAL ANALYSIS 46
4.3.9.1.1 COLLECTION AND ANALYSIS OF CHLOROPHYLL-A 46
4.3.9.1.2 COLLECTION AND ANALYSIS OF PHYTOPLANKTON: 46
4.3.9.1.3 ZOOPLANKTON COLLECTION AND ANALYSIS 47
4.3.9.1.4 FISH & FISHERY 48
4.3.9.2 RESULTS AND DISCUSSION 49
CHAPTER 5 ANTICIPATED ENVIRONMENTAL IMPACTS AND
MITIGATION MEASURES 79
5.1 ENVIRONMENTAL IMPACTS IDENTIFIED 79
5.1.1 IMPACTS ON MARINE WATER AND SEDIMENT: 80
5.1.2 GENERATION & IMPACTS OF NOISE 82
5.1.3 MARINE ECOLOGICAL IMPACTS 84
CHAPTER 6 ENVIRONMENTA MANAGEMENT PLAN 85
6.1 MUD MAKE-UP AND MUD & CUTTINGS DISPOSAL 85
6.2 MEMBERSHIP OF COMMON DISPOSAL FACILITIES 85
6.3 MEASURES TO HANDLE OILY WASTE DISCHARGES 85
6.4 SEWAGE TREATMENT AND DISPOSAL 89
6.5 SOLID WASTE HANDLING 89
6.6 SPENT OIL HANDLING 87
6.7 OIL HANDLING FROM WELL TEST OPERATIONS 87
6.8 NOISE ABATEMENT MEASURES 87
6.9 MEASURES TO MINIMIZE DISTURBANCE DUE TO LIGHT
AND VISUAL INTRUSIONS 88
CHAPTER 7 ANALYSIS OF ALTERNATIVES (TECHNOLOGY AND SITE)
7.1 DRILLING LOCATIONS 89
CHAPTER 8 ENVIRONMENTAL MONITORING PROGRAMM 91
8.1 BUDGET AND PROC. SCHEDULES OF ENVIRONMENTAL
MONITORING 91
CHAPTER 9 ADDITIONAL STUDIES
9.1 RISK ASSESSMENT 92
9.1.1 STAGES FOR WHICH RISK ASSESSMENTS ARE
UNDERTAKEN 92
9.1.1.1 OBJECTIVE OF QRA 93
9.1.1.2 RISK ASSESSMENT METHODOLOGY 94
9.1.1.3 HAZARD IDENTIFICATION 95
SL.NO. PAGE NO.
9.1.1.4 FREQUENCY ANALYSIS 95
9.1.1.5 CONSEQUENCE ANALYSIS 96
9.1.1.6 RISK EVALUATION 97
9.1.2 KEY RISKS INVOLVED 98
9.1.2.1 BLOWOUTS 99
9.1.2.2 COLLISIONS INVOLVING MODU (JACK-UP DRILLING RIG) 101
9.1.2.3 HELICOPTER CRASHES 102
9.1.3 RISK MITIGATION MEASURES 104
9.1.3.1 WELL PLANNING & DESIGN 104
9.1.3.2 SELECTION OF EQUIPMENT, SYSTEMS AND PEOPLE 108
9.1.3.3 TESTING AND MAINTENANCE OF CRITICAL EQUIPMENT 109
9.1.3.4 SELECTION OF SUPPORT SERVICES 110
9.1.3.5 ENSURING MARINE INTEGRITY 110
9.1.4 H2S EMISSION CONTROL PLANS 112
9.1.4.1 DETECTION AND ALARM SYSTEMS 112
9.1.4.2 VISUAL WARNING SIGNS 113
9.1.4.3 MUSTER STATION AND ESCAPE ROUTE 113
9.1.4.4 VENTILATION 113
9.1.4.5 H2S KICK CONTROL 113
9.2 DISASTER MANAGEMENT PLAN 114
9.2.1 PURPOSE & SCOPE OF THE PLAN 114
9.2.1.1 UPDATING AND EXERCISES 115
9.2.1.2 DISASTER MANAGEMENT PREPAREDNESS 115
9.2.1.3 ON SCENE COORDINATOR 110
9.2.1.4 SITE CONTROL ROOM 116
9.2.1.5 COMMUNICATION 116
9.3 OIL SPILL RISK ASSESSMENT 117
9.3.1 OIL SPILL SCENARIOS 117
9.3.1.1 MARINE & COASTAL FEATURES SENSITIVE TO OIL SPILLS 117
9.3.1.2 ASSESSMENT OF RISKS DUE TO OIL SPILLS 118
9.3.1.3 OIL SPILL CONTINGENCY PLAN 118
9.3.1.4 PROJECT NEED & BENEFITS 124
CHAPTER 10 ENVIRONMENT MANAGEMENT PLAN 126
10.1 SELECTION OF DRILLING LOCATION AND NAVIGATIONAL
PATH WAYS 126
10.2 ATMOSPHERIC EMISSIONS 127
10.3 STORAGE AND HANDLING OF CHEMICALS AND SUPPLIES 127
10.4 MANAGEMENT OF DRILL CUTTINGS & DRILLING MUD 128
10.5 OILY WATER DISCHARGES AND OTHER WASTES 129
10.6 MANAGEMENT MANUAL 131
Sl.No. Page no.
10.7 MANAGEMENT SYSTEM PROCEDURES AND
DOCUMENTATION 132
Chapter 11 ORGANISATIONAL STRUCTURE AND IMPLEMENTATION
FRAME WORK 135
11.1 CAPITAL AND RECURRING COST FOR ENV. POLLUTION
CONTROL MEASURES 136
11.2 DISCLOSURES OF CONSULTANTS ENGAGED 136
11.3 EIA CONSULTANT ENGAGED 136
11.4 AGENCY ENGAGED FOR CRZ MAPPING 136
Chapter 12 BIBLIOGRAPHY 137
ANNEXURE-I TOR ISSUED BY MOEF&CC FOR THE NELP VII BLOCK MB-
OSN-2005/3 (SCANNED COPY) 142
ANNEXURE-II LETTER FROM DGH (SCANNED COPY) 150
ANNEXURE-III EQUIPMENT AND APPLICABLE STANDARDS 151
ANNEXURE-IV COMPARATIVE ECOTOXICITIES 154
Team from Project Proponent
EIA Sector
Number as per
NABET
2
Name of
Sector
Offshore & On land oil & gas
exploration, development &
production
EIA Coordinator
Name Dr. J.S.Sharma
Signature & Date
Period of Involvement October, 2015 onwards
Contact Information ONGC, CHSE, SCOPE Minar, 8th Floor, Laxmi Nagar,
New Delhi. Mobile:9868282230
Functional Area Experts
Sl.
No.
Name Functional Area
1. Dr. J.S.Sharma I. Air Pollution Control II. Water Pollution
III. Solid and Hazardous Waste IV. Air Quality Modelling
2 Mr. Ravi Misra,DGM(Geology) i. Geology ii. Hydrology
3 Dr. (Mrs) Archana Yadav Ecology and biodiversity
4 Mr. D. K. Trivedi,CE(P) Noise & vibration
5 Mr. Amlan Chakraborty,CE(Mech.) Risk & Hazards
6 Mr. H J Godbole, EE(Env.Engg.) Water Pollution
7 Mrs. Vineeta Kumari Sattawan Ecology and biodiversity as
Associate
8 Sh S K Lijhara Assisted as EIA Coordinator
Executive summary
ONGC has acquired NELP-VII block MB-OSN-2005/3 as operator with 70% PI while the rest
30% is retained by Essar Energy. The exploratory block MB-OSN-2005/3 was initially awarded to M/s
Essar Energy as Operator along with M/s Noble Energy with 50% PI each. However, M/s Noble Energy
backed out from the consortium therefore, M/s Essar Energy became the sole operator with 100% PI.
Later on, a firm-out agreement was signed between ONGC and Essar Energy on 24.12.2014 whereby
ONGC acquired NELP- block MB-OSN-2005/3 during the phase-II (04.08.2013 to 03.02.2016) of
operation with commitment of drilling one exploratory well as per the Minimum Work Programme (MWP).
The NELP-VII Block MB-OSN-2005/3 is located in the southwest of the Mumbai High-DCS
platform of Mumbai Offshore Basin, having an area of 1685 km2. Two wells, viz., SM-1-1 and SM-1-2
were drilled in the early nineties on the western flank of the block. It is approximately 44 km north-north-
east due SM-86 structure and about 80 Km north-west of D-1 hydrocarbon bearing structure. Deep water
nomination block BB-OS-DW-1 lies in the west of the block. The block is located in the shallow water
western offshore
The Production Sharing Contract (PSC) requires to conduct EIA studies and obtain its approval
from MoEF&CC. It is also emphasized in the PSC that the contractor shall conduct its petroleum
operations with due regard to and concern with respect to protection of the environment and conservation
of natural resources.
The area in and around the block had been extensively explored for hydrocarbon prospectivity.
To assess the baseline environmental status of the block, data from the adjacent area and wells have
been gathered and analysed by IPSHEM, ONGC, Goa. In addition, secondary information on
meteorology, biological characteristics of nearest beaches and coastal area and ocean hydrography have
been obtained from literature reviews and information available in the public domain.
The baseline data comprise of chemical characteristics, dissolved oxygen, nutrients like nitrate,
nitrite, phosphate and silicate and presented briefly in the following lines.
Temperature is found to vary from 26.2-28.3 °C respectively, the average being 27.31 °C. The
surface layer showed higher temperature at all the sampling stations varying from 26.0-26.9 °C The
observed range of temperature variation is well in normal limits for the coastal waters.
pH is found to vary from 7.12-8.30 the average pH values were detected of 7.78 and 7.67
respectively. No particular trend is followed regarding the distribution of pH, though all the observed pH
values are well within normal limits.
Salinity around the points of observation depict variation from 31.5-37.5 PSU the average salinity
values were detected of 34.4 PSU and 35.57 PSU respectively. The observed salinity values are similar
to those observed at the reference stations and the values are well within acceptable limits.
Turbidity is found to varfy from 4.6 – 16.8 NTU and 3.4 – 17.4 NTU respectively and an average
turbidity values were detected of 10.31 NTU and 9.02 NTU respectively. The variation of turbidity has
followed no trend and the observed turbidity indicate normal values for the seawater at the site.
TDS vary from 10-38 mg/l and 9-34 mg/l respectively with an average of 24.98 mg/L and 18.63
mg/L respectively. However comparing the values with reference point; disturbance of operational activity
cannot be concluded. The observed values are within normal limits for the coastal seawater
Dissolved Oxygen (DO) concentrations are considered to be very vital parameter to assess the
health of the marine environment especially where exploration and production activities are in progress.
DO variation from 3.24-5.38 mg/l and 3.25-5.34 mg/l respectively with an average 4.42 mg/l. It is observed
that all obtained values are most similar to the values obtained at reference station values and well within
acceptable limits for the coastal seawater.
Nutrients - Phosphate– Phosphorus (PP)’s variation is from 0.042–0.84 μmol/l and 0.045–0.75
μmol/l respectively with an average PP values at 0.21 μmol/l. The vertical variation of phosphates at these
stations showed no regular trend of phosphorous. The values observed however are normal for the
coastal seawater.
Nitrite–Nitrogen have been found to vary within the range of 0.008 – 0.026 μmol/l with an average
value 0.017 μmol/l. The Nitrite – Nitrogen values follow no particular trend and they are similar at all the
observation columns. The values observed are well within normal acceptable limits. Nitrate – Nitrogen,
on the other hand, vary from 0.015 – 4.5 μmol/l. The Nitrate – Nitrogen values follows no particular trends
and values are at lower side. The values are within normal acceptable limits.
Silicates is found to vary from 0.12-0.57 μmol/L and 0.16-0.45 μmol/L respectively. The observed
values are normal for the coastal seawater. Petroleum Hydrocarbons (PHC) values come under non
detection level. The distribution of PHC in the sediment samples has shown minute contamination, though
all observed valued values are acceptable limits.
Sediment Quality - The Total Phosphorous and Total Nitrogen’s concentration was measured in
the sediment samples has shown variation from 19.7—40.2 μg/g, the average being 29.2 μg/g and 25.2
μg/g respectively. The Total Organic Carbon’s concentration was measured to vary from 1.9% to 4.7%
and 2.0% to 4.2% respectively and an average values were detected of 3.0% and 3.0%μg/g respectively.
The PHC’s concentration in the sediment samples has shown variation from 45.62– 86.74 mg/g with an
average of 64.055 mg/g. The values are within acceptable limits. The texture of sediment samples has
been analyzed and it has been observed that the composition of clay varies from 30% -42% with average
value of 36.71%.
The meteorological and climatological environment has been assessed from secondary data
available in the public domain and scouting the literature. The average rainfall in the Arabian sea is of the
order of 1-2 mm /day while the mean wind speed lies in the range of 6.1 to 6.8 m/sec. Maximum and
minimum value of mean air temperature in the Arabian Sea is of the order of 30.2 ºC and 24.4 ºC,
respectively. Mean air temperature of the area of exploratory block lies in the range of 26.5 ºC to 27.5 ºC.
It is observed that monthly frequency of depression, cyclonic storm and severe cyclonic storm in the
Arabian Sea was highest for June followed by November and May in a year.
In addition, potential impacts on the environment have been assessed and duly incorporated in
the report. ONGC has an elaborate Disaster Management Programme (DMP) with an exhaustive manual
of disaster management methodologies that are capable of taking care of an eventuality of any magnitude
with the primal objective to impact the environment the least. Activities related to exploratory drilling,
namely, operational discharges like sanitary waste water, food waste and residuals, washing fluids (deck
drainage, rig floor washing etc.), cooling water, non-routine discharges that may be caused by ballast
water, chemical spills has the potential to impact marine water quality.
ONGC is committed to protect the environment through improving the effectiveness of
management and reporting systems and ensuring the reduction of local environmental impact from
operations by improving environmental performance and implementing initiatives for the conservation of
biodiversity and the resource recovery and reuse. ONGC places high emphasis on health and safety
aspects of workers and staff and will ensure that all activities will be conducted in a safe and skillful
manner with staff appropriately trained and equipment maintained in safe condition. ONGCs QHSE
management system entails continuous monitoring to be carried out for various aspects of the project,
environmental, safety and health impacts and the performance of EMP implementation.
Pre-drill EIA for the NELP block MB-OSN-2005/3
1
Chapter -1
INTRODUCTION
1.1 PURPOSE
The exploratory block MB-OSN-2005/3 was awarded to M/s Essar Energy as Operator along
with M/s Noble Energy with 50% PI each. Afterward, M/s Noble Energy backed out from the consortium
therefore, M/s Essar Energy became the sole operator with 100% PI.
Later on, a firm-out agreement was signed between ONGC and Essar Energy on 24.12.2014
whereby ONGC acquired NELP- block MB-OSN-2005/3 as operator with 70% PI while Essar Energy with
30% PI. As per the Minimum Work Programme (MWP), presently phase-II is going on from 04.08.2013
to 03.02.2016 with commitment of drilling one exploratory well. In this regard, EC is required at the earliest
possible to start the drilling operation in time to complete the exploratory well before the due date i.e.
03.02.2016 for which EIA study of the block is required. The NELP-VII Block MB-OSN-2005/3 is located
in the southwest of the Mumbai High-DCS platform of Mumbai Offshore Basin, having an area of 1685
sq. km. The water depth within 3D seismic area, where prospects are likely to be drilled, ranges from 90
m to 100 m. Well SM-1-2 is near western boundary of the block. It is approximately 44 Km north of SM-
86 structure and about 80 Km north-west of D-1 hydrocarbon bearing structure. Deep water nomination
block BB-OS-DW-1 lies in the west of the block. The block is located in the shallow water area. (Fig-1.1:
Location Map).
It may be emphasized that the EIA notification 2006, which requires prior Environmental
Clearance from the Ministry of Environment & Forest (MOEF&CC), before carrying out exploratory
drilling, is not applicable in the block as the block is located beyond territorial waters (beyond the
stipulated 12 nautical miles). However, the Production Sharing Contract (PSC) requires conducting of
EIA studies and obtaining its approval from MOEF&CC. It is also emphasized in the PSC that the
contractor shall conduct its petroleum operations with due regard to and concern with respect to
protection of the environment and conservation of natural resources.
ONGC had applied for EC in Form-I to MoEF&CC on 11.06.2015. The project was discussed
in 44th Reconstituted Expert Appraisal Committee (Industry-2) on 21.07.2015 Terms of Reference (ToR)
for the preparation of Environmental Impact Assessment has been issued by MoEF&CC to ONGC vide
F NoJ-11011/171/2015- IA II (I) dated 31.08.2015 (Annexure-I).
Pre-drill EIA for the NELP block MB-OSN-2005/3
2
Fig. 1.1: Location Map showing position of NELP Block MB-OSN-2005/3
1.2 IDENTIFICATION OF THE PROJECT PROPONENT & THE PROJECT
ONGC is a premier national hydrocarbon E & P company having Maharatna status. ONGC
was founded in the year 1956 to power a new born republic making rapid strides towards growth and
development. Discovering 6 (six) out of 7 (seven) oil and gas producing basins, adding 8.6 billion tons of
oil and gas reserves, it has led India’s quest for national energy security. Today ONGC is the world’s
No.3 Exploration and Production Company. With a recoverable reserve of 2.0 billion tons of oil equivalent,
ONGC’s daily production of over 1.22 million barrels per day contributes over 69% of India’s domestic oil
equivalent production. It is the country’s trust in our vision that makes us largest exploration and mining
lease holder in the country. Fuelled by the desire to build a strong energy foundation for tomorrow, we
have gone beyond the seven seas. ONGC’s wholly owned subsidiary ONGC Videsh Ltd(OVL) is the
Pre-drill EIA for the NELP block MB-OSN-2005/3
3
nation’s biggest E&P multinational, managing 35 overseas hydrocarbon properties in 16 countries, with
a cumulative investment of over US$22 billion. Winning hearts and awards world over, ONGC is one of
the fortune World Most Admired Companies of 2014. ONGC is the Top Energy Company of India as per
the coveted Platts Top 250 Global Energy Company ranking 2014. In FY 2014-15, ONGC made 22 oil
and gas discoveries (in the areas operated by ONGC). Of these, 10 discoveries were made in new
prospects whereas 12 were new pool discoveries. Out of 22 discoveries, 12 discoveries were made in
onshore areas; 7 in shallow water offshore and 3 were in deep-water. 7 were oil discoveries, 6 were oil
& gas bearing and 9 were gas discoveries. In FY 2014-15, ONGC achieved crude oil production of 22.264
MMT. (Excluding JV share). ONGC’s JV share of crude oil production was 3.679 MMT. Thus total crude
oil production (including condensate) was 25.943 MMT (excludes ONGC Videsh share). In FY 2014-15,
ONGC achieved Natural Gas production of 22.02 BCM. (excluding JV share). ONGC’s JV share of natural
gas production was 1.50 BCM. Thus total natural gas production was 23.52 BCM (excludes ONGC
Videsh share). During the year 2014-15, ONGC acquired 605.9 GLK/LK of 2D and 9176.5 SKM of 3D
seismic data. A total of 371 wells were drilled out of which 103 were exploratory wells and 268
development wells. ONGC accreted Initial in place hydrocarbon reserves of 215.65 MMToe & Ultimate
reserves of 70.98 MMToe (3P).
As for as oil discoveries done by ONGC is concerned, it has made 14 oil and gas discoveries
in domestic fields (operated by ONGC). Out of these, 12 discoveries were made in the new prospects
whereas 10 were new pool discoveries. Nine discoveries were made in NELP blocks and thirteen in the
nomination blocks.
Mangalore Refinery & Petrochemical Ltd. (MRPL) and ONGC Videsh Limited (OVL) are two
fully owned direct subsidiary of ONGC. OVL is the biggest Indian multinational, with 40 oil & Gas projects
(9 of them producing) in 16 countries i.e. Vietnam, Sudan, Iraq, Iran, Russia, Myanmar, Libya, Cuba,
Colombia, Nigeria, Nigeria Sao Time JDZ, Egypt, Brazil, Syria and Venezuela. OVL recorded highest-
ever Net Profit of Rs. 39,291 million. ONGC Videsh achieved Oil Production of 5.533 MMT & Natural Gas
production of 3.341 BCM for FY 2014-15.
On an average, ONGC drills about 20 exploratory wells every year in the Arabian Sea. The
Western Offshore area has been the main contributor of domestic hydrocarbon production in India. This
endeavor will continue in the Block MB-OSN-2005/3 which is located in the Mumbai Offshore, having an
area of 1685km2. The cost of drilling a well is estimated at approximately ₹ 124 crores. The project block
is located in Arabian Sea due southwest off the state of Maharashtra.
The only well which will be drilled by the ONGC is in this block is about ~138 nm from the
coast. Offshore rigs (MODU) will be deployed for the proposed drilling. ONGC has its centralized
warehouse/ stores at Nhava. Accordingly, all the material will be brought to the site from Nhava supply
Pre-drill EIA for the NELP block MB-OSN-2005/3
4
base by sea route through Offshore Supply Vessel (OSVs). However, the personnel will be transported
to the rig by helicopters from the Juhu Helibase, Mumbai.
1.3 SCOPE OF STUDY
Terms of Reference (ToR) assigned by MoEF&CC would be the basis of scope of EIA study along with
understanding of the project and its implication, assessing the marine physical environment where the project
would be located and probable interactions that are expected to occur as a result of execution of the project.
The scope of work includes:
Review of regulatory and institutional framework to ensure that ONGC is aware of regulatory
obligations and make compliance while undertaking project activities.
Collate and analyze primary and secondary data on environmental components like
meteorology, marine water quality, levels of pollution, marine and coastal ecology, etc.
Assess potential environmental impacts that may arise as a result of the project and
evaluate them.
Table 1.2.1: Project at Glance
Sl. No. Parameter Particulars
1 Area Shallow offshore due south and southwest Mumbai, 1685 km2
2 No. of Wells 01
3 Depth of the wells (m) 2500 m
4 Water Depth (Bathymetry) (m) ~ 90 to ~ 100 m
5 Distance from the Coast (m) 138 nm
6 Water Consumption 40 m3/day
7 HSD consumption 60 kl / day
8 Drill Cuttings 3 – 8 m3 / day, i.e., about 20 – 50 bbls / day
9 Cost of the Project ₹ 124 crores
10 Sensitive Areas No sensitive or legally protected areas lie in the close vicinity of the block which is located about 250 km southwest off the coast of Mumbai, Maharashtra.
Pre-drill EIA for the NELP block MB-OSN-2005/3
5
Chapter-2
Terms of reference
2.1 POINTWISE COMPLIANCE OF TOR:
Terms of Reference (ToR) for the preparation of Environmental Impact Assessment issued
by MoEF to ONGC vide F No. J-11011/171/2015-IA-II (I) dated 31st August 2015 has been duly
addressed in EIA-EMP Report. Summary of the same is tabulated below:
TABLE 2.1: COMPLIANCE WITH TERMS OF REFERENCE PROVIDED BY 44th EXPERT
APPRAISAL COMMITTEE (INDUSTRY-2) OF MOEF
Sl Points of TOR Issues Addressed In EIA-EMP and RA Report
1 Executive summary of the
project
Executive summary included in EIA report of the project (p.
i-iii)
2 No. of exploratory wells for
which environmental
clearance is accorded and
no. of new wells proposed
during expansion. Status and
no. of the wells which are
completed and closed.
Environment Clearance has not been accorded so far this
block. ONGC plans to drill 1 (one) exploratory well in this
block.
3 Project Description and
Project Benefits;
Initially the exploratory block MB-OSN-2005/3 was
awarded to M/s Essar Energy as operator along with M/s
Noble Energy with 50% PI each. However, M/s Noble
Energy left the consortium thereby M/s Essar Energy was
having 100% PI with it. Later, a firm-out agreement was
signed between ONGC and Essar Energy on 24.12.2014
whereby ONGC agreed to acquiring the NELP-VII block
MB-OSN-2005/3 as operator with 70% PI while Essar
Energy would retain 30% PI. As per the Minimum Work
Programme (MWP), during the Phase-II, from 04.08.2013
to 03.02.2016, it is committed to drill one exploratory well in
the block. The block comprises of an area of 1685 Km2. It is
a shallow water offshore block in the West Coast of India.
(Chapter 3, p. 10-23)
4 Cost of project and period of
completion
₹. 124 crores, Time of completion : 4-5 Months
Pre-drill EIA for the NELP block MB-OSN-2005/3
6
5 Employment to generated Well will be drilled hiring a Jackup or a Floater (MODU)
drilling rig.
6 Distance from coast line The block is located on the continental shelf west off the
coast of Mumbai about 250 km from the coast.
7 Details of sensitive areas
such as coral reef, marine
water park, sanctuary and
any other eco-sensitive area.
No sensitive areas such as coral reef, marine water park,
sanctuary and any other eco-sensitive area lie within 10 km
from the block boundary.
8 Recommendation of SCZMA/
CRZ Clearance as per CRZ
notification dated 6th January
2011 (if applicable).
CRZ notification is not applicable on this project, as the
block is beyond territorial waters. (Section 3.2.1, p.14)
9 Details of support
infrastructure and vessel in
study area.
Operational personnel shall be commuted to and fro to the
rig by helicopter from the service base at Juhu-Helipad,
Mumbai. The material will be transported to the rig by OSVs
from the Nhaba Supply base-the frequency of OSVs shall
depend on the actual requirement, never more than once
per day.
10 Climatology and meteorology
including wind speed, wave
and currents, rainfall etc.
Section 3.7, p. 23 – Climatology and Meteorology of
Mumbai Offshore.
11 Details on establishment of
Base line on air quality of
areas immediately affected
by the exploratory drilling and
also particularly with
reference to hydrogen
sulphide, sulphur dioxide
NOx and background levels
hydrocarbons and VOCs.
Baseline data on marine water quality generated by
analysis of 23 water samples gathered in and around the
project area and the probable drilling location. (Chapter 4,
p.30).
12 Details on estimation and
computation of air emissions
(such as nitrogen oxide,
sulphur dioxides, carbon
mono oxides, hydrocarbons,
VOC, etc.) resulting from
flaring, DG set, combustion
etc. during all project phases.
(Chapter 4, p.30).
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13 Base line data collection for
surface water for one season
leaving the monsoon season
within one Km for each
exploratory well, particularly
in respect of oil content in
water sample and sediments
sample.
Baseline data on marine water quality generated by
analysis of 23 water samples gathered in and around the
project area and the probable drilling location. (Chapter 4,
p.30).
14 Fisheries study w.e.t.
benthos and marine organic
material and coastal
fisheries.
(Chapter 4, p. 30).
15 Source of fresh water.
Detailed water balance ,
waste water generation and
discharge.
The average daily water consumption will be about 40
m3/day and will be supplied from Nhava supply base of
ONGC. Wastewater generation from the drilling well is
expected to be around 10 m3/day. The dirty oil from bilge
fluid will be periodically sent to shore in drums or special
containers by supply vessels deployed for the purpose.
(Section 3.4.2; p.19, Section 3.4.3, p.20-Waste Water
Generation and Discharge)
16 Noise abatement measures
and measures to minimize
disturbance due to light and
visual intrusions in case of
project site closed to coast.
Discussed under Section 5.1.2, p.82
17 Procedure for handling oily
water discharges from deck
washing, drainage systems,
bilges etc.
Section 10.5 - Oily Water Discharges and Other Wastes,
p. 129
18 Procedure for preventing
spills and spill contingency
plans
Section 10.5, p. 129
Chapter 11, p.135
19 Procedure for treatment and
disposal of produced water
During well testing oil is stored in storage tanks, gas is
flared, and water is discharged to sea after treatment. Oil is
transported to base facility.(Section 3.4.3,p.21)
20 Procedure for sewage
treatment and disposal and
also for kitchen waste
disposal.
Section 6.4 - Sewage Treatment and Disposal, p.86
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21 Details on solid waste
management drill cutting,
drilling mud and oily sludge
produced sand, radioactive
materials, other hazardous
materials, etc including its
handling options during all
project phases.
Section 6.2, p.85 – Membership of Common Disposal
facilities.
The disposal of the drill cuttings will be conforming to the
guidelines pertaining to the “Disposal of Drill Cuttings and
Drilling Fluids for Offshore Installations” provided by the
Ministry of Environment & Forests (MoEF) G.S.R. 546(E)
August 2005.
22 Storage of chemicals on site Section 3.4.4 – Chemical Storage at Rig, p-21
23 Commitment for the use of
WBM and synthetic oil based
mud in special case
ONGC is committed to using only Water Based Mud (WBM)
for the offshore exploratory drilling operations. However,
synthetic oil based mud (SOBM) will be used to combat
specific hole problems. Refer to Mud System and Cuttings,
p.18.
24 Details of blowout preventer
installation
It is standard oil-well drilling practices to install BOP at the
well head (section 3.1-Technology and Process
Description, p.17).
25 Risk assessment and
mitigation measures
including whether any
independent reviews of well
design, construction and
proper cementing and casing
practices have been followed
Risk assessment – Section 9.1, p.92
26 Handling of spent oils and oil
from well test operations.
Section 6.6 Handling of spent oil, p.87
Section 6.7 - Oil Handling From Well Test Operations, p.87
27 H2S emissions control plans,
if required
Section 9.1.4, p.112
28 Details of all environment and
safety related documentation
within the company in the
form of guidelines, manuals,
monitoring programmes
including Occupational
Health Surveillance
Programme etc.
Section 10.7–Management System Procedure and
Documentation, p.132
29 Restoration plans and
measures to be taken for
decommissioning of the rig
After drilling and initial testing, if the well does not contain
commercial quantities of hydrocarbon, the site is
decommissioned to a safe and stable condition and
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and restoration of on-shore
support facilities on land
restored. Open rock formations are sealed with cement
plugs to prevent upward migration of wellbore fluids. The
casing wellhead and the top joint of the casings are cut at
the ground level and capped with a cement plug. The
hazardous waste will be sent to authorize hazardous waste
disposal facility.
30 Documentary proof for
membership of common
disposal facilities, if required
The solid waste generated on the rig will be segregated and
stored in colour coded bags. The solid waste will be
transported back using support vessels or with the rig, to
the Nhava supply base of ONGC. At Nhava supply base the
segregated waste will be treated separately. Hazardous
waste, if any, will be sent to authorized hazardous waste
recyclers and disposal facility.(Section 6.2 – Membership of
Common Disposal Facilities, p.85)
31 Any litigation pending against
the project or any directions /
order passed by any Court of
Law against the project. If so,
details thereof.
Not Applicable.
32 Total capital and recurring
cost for environmental
pollution control measures.
Section 11.1, p.136 - Capital and Recurring Cost for
Environmental Pollution Control Measures
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Chapter 3
PROJECT DESCRIPTION
3.1 TYPE OF THE PROJECT
Initially the exploratory block MB-OSN-2005/3 was awarded to M/s Essar Energy as Operator
along with M/s Noble Energy with 50% PI each. Due to withdrawal of M/s Noble Energy, M/s Essar Energy
was having 100% PI with it. Later on, a farm out agreement between ONGC and ESSAR for JV
partnership was signed on 24th December 2014 with ONGC as operator. The participating interest of
ONGC is 70% and for ESSAR 30%. Vide letter No. DGH/PSC/ (MB-OSN-2005/3)/Phase-
II/Assignments/2015 dated 28th April 2015, MOPNG has approved the proposed assignment of 70% to
ONGC and transfer of ownership (Letter from DGH: Annexure - II).
Geological Setup:
The Block MB-OSN-2005/3 falls in the Shelf Margin block of Mumbai Offshore Basin. Shelf
Margin is demarcated to the east by Paleocene shelf edge, to the west by West Margin basement arch,
to the north by Saurashtra Arch and to the south by Vengurla Arch. Major structural elements within the
block from north to south are Saurashtra low to the north, followed by Alibagh saddle to the south of it
(DCS platform and south Bombay low fall just to the east of it), Murud low, Mahabaleshwar high and
Rajapur low to the south. The shelf is characterized by NNW-SSE trending parallel sets of longitudinal
faults giving rise to series of horst-graben features.
Basement associated anticlinal highs of Paleocene-Eocene sequence and tilted fault blocks
of oligo-miocene section formed due to gravity slide are the two main structural styles in the block.
The generalized litho-stratigraphy (Fig. 3.1) of the shelf margin block is established based on
the information of the wells SM-1-1 and SM-1-2, following the framework of lithostratigraphic classification
of Mumbai offshore basin. In general the area received dominantly finer clastic of claystone and and
shale except for medium to thick carbonate deposits of Eocene and upper Miocene times which are
laterally less extensive.
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Fig.3.1: Generalized stratigraphy of the Shelf margin area
3.2 LOCATION OF PROJECT
The initial 2D seismic interpretation indicates six probable locations for drilling wells as shown
in the Map at Fig. 3.2 and Fig. 3.3 given below. However, initially, only one well is to be drilled, out of
identified 6 prospects. The exact position of the well would be decided on the basis of 3D interpretation
of seismic data being acquired in the block.
Water depth and TD of well
Water depth (bathymetry map. Fig. 3.4) of the 3D area (within the block) where prospects are
identified and to be drilled, falls within the range of 90 m to 100 m. The total depth of the well to be drilled
will be 2500 m.
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Fig.3.2: Tentative Prospects shown in 3D area
However, the tentative details of the well location is as follows:
Table 3.1 : Tentative details of the well location
Horizontal/Vertical Vertical well
Deep/Shallow Shallow water
Bathymetry 90-100 m
Target Depth 2500 m
Mud to be used Water based (SOBM if necessity arises)
Objective Mio-Pliocene sequences
Co-ordinates of location X: 638204.80
Y: 2092770.06
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Fig. 3.3: Block Map with tentative prospects.
Fig-3.4 Map indicating coastal land near the block MB-OSN-2005/3
The geographical coordinates of the boundary of the NELP exploratory block MB-OSN-2005/3 are
provided in the Table 3.2.
MAP INDICATING COASTAL LAND NEAR BLOCK MB-OSN-2005/3
MAP SHOWING THE BAATHYMETRY OF THE AREA
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TABLE 3.2.: Geographical coordinates of Block MB-OSN-2005/3.
Longitude Latitude
Pt. Deg. Min. Sec. Deg. Min. Sec.
A 70 05 11.27 19 04 16.54
B 70 20 17.00 19 06 56.00
C 70 45 53.78 18 30 17.00
D 70 35 00.00 18 30 17.00
E 70 35 00.00 18 40 00.00
F 70 21 07.13 18 40 00.00
A 70 05 11.27 19 04 16.54
3.2.1 CRZ Regulation Applicability
The block MB-OSN-2005/3 is located beyond 12 nautical miles from the coast line, CRZ
regulations, therefore, is not applicable.
3.2.2 DRILLING WELL LOCATION
One exploratory well RMBSO53NAA-A with geographical coordinates X: 638204.80 Y:
2092770.06 has been planned to be drilled in the NELP-VII block MB OSN-2005/3 as per the committed
MWP. Since the block lie in the shallow offshore at a distance of over 250 km southwest off the coast of
Mumbai, the stipulation and the guidelines by MoEF&CC that no drilling within 1 km from coastline i.e.
Low Tide Line (LTL) is not applicable in the case.
3.3 PROPOSED PROJECT SCHEDULE FOR APPROVAL AND IMPLEMENTATION
The project activities for the proposed offshore drilling processes have been divided into three
phases- Mobilization of drilling rig, Drilling and finally Decommissioning. Drilling activity under normal
conditions would continue for about 40-60 days to drill one well. Casing will be lowered in the well drilled
and tested by perforation if indications of hydrocarbons are noticed. The well will be sealed for further
development if the prospect so discovered is found to be a successful hydrocarbon bearing structure.
3.4 TECHNOLOGY AND PROCESS DESCRIPTION:
The different phases, as mentioned above, for the exploratory drilling are
Mobilization of the drilling rigs
Drilling and testing
Decommissioning
These phases are explained in the subsequent sections. A flow chart describing the major phases of
‘Oil exploration’ is sketched in the Fig. 3.5.
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Drilling and testing phase
Seismic data acquisition is the initial process of Exploitation of hydrocarbons followed by
processing and interpretation for identification of viable prospect. The prospect so identified is required
to be probed by drilling to ascertain the accumulation and, in the eventuality, the extent of the prospect.
Wells are drilled, offshore or onshore, using a rig and ancillary tools and equipment.
There are two basic categories of offshore drilling rigs; those that can be moved from place
to place, allowing for drilling in multiple locations, MODU (Mobile Offshore Drilling Unit), and those rigs
that are temporarily or permanently placed on a fixed platform (Platform Rigs). In the present case, the
water depth of proposed location is about 90-100 meter therefore, drilling will be done by deploying a
floater rig where in a rig is mounted on a ship. ONGC will use Mobile Offshore Drilling Unit (Floater/Jack
up Rig, Fig. 3.6, Fig. 3.7) for drilling the well.
Fig 3.5: Flow chart describing in nutshell the ‘Oil Exploration Process’
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Fig. 3.6: Typical picture of jack-up rig
Fig 3.7: Typical picture of floater rig
Initial Well Construction
Offshore wells are drilled in sections, with the diameter of each section decreasing with
increasing depth. Lengths and diameters of each section are determined prior to drilling and depend on
geological conditions through which the well is to be drilled. The conduit or pipe section will be set in
place by jetting operations. Drilling starts with spudding a hole of diameter 26" on the sea bed, followed
by lining it with a metal casing of 20". The above structural section is likely to be drilled using sea water.
Next hole will be of 17-1/2" diameter and casing will be 13-3/8". Further hole will be of 12-1/2" diameter
with 9-5/8" casing.
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Well head equipment is installed thereafter followed by marine riser including the Blowout
Preventer (BOP, Fig. 3.8). The blowout preventer is a large underwater assembly of control valve that
prevents high pressure from the well escaping through the water and oil column into the surface at the
derrick floor. The release of this pressure is called a “blowout” and can result in an explosion and could
cause large scale damage to the environment. If a blowout were to occur with a BOP in place, giant
valves inside it seal off the well, containing any excessive pressure and putting it back into the ground.
Maintaining the BOP and continually testing it is a very high priority for both ONGC and its drilling
contractor.
The BOP is placed on top of the wellhead (the top of the well), which is why it is important to
make sure the casing is properly cemented in place. A marine riser is a type of offshore drilling tool that
is used as a temporary extension connecting the oil well to the rig.
Picture from Google images
Fig. 3.8: A Typical drawing of a BOP (Blow Out Preventer)
As drill pipe is lowered down through the marine riser, through the BOP, into the wellhead,
and then further down into the well, drill fluid or mud (fluid that helps clear the rock bits or “cuttings” that
are being chipped away when drilled) is pumped back up through the pipe annulus and out through the
drill bit. The mud eventually circulates around up through the marine riser and back to the surface of the
oil rig. As each section is drilled, casing is run and cemented into place ready for drilling the next smaller
diameter section. Operations continue in this way until target depth is reached.
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Mud System and Cuttings
During drilling operations, the drilling fluid (or mud) is pumped through the drill string down to
the drilling bit and returns via the drill pipe – casing annulus up to surface back into the circulation system.
After separation of drill cuttings /solids through solids control equipment, the mud is circulated back.
Drilling fluid is essential to drilling operations in order to:
Control down-hole pressure
Lift soil/rock cuttings from the borehole bottom and carry them to settling pit
Prevent cuttings to settle rapidly.
Prevent caving
Seal the borehole wall to reduce fluid loss. (Formation of filter cake)
Cool and clean the drill bit and lubricate drill bit, bearings, mud pumps and drill pipes
ONGC is committed to using Water Based Mud (WBM) for the offshore exploratory drilling
operations. However, synthetic oil based mud (SOBM) will be used to address specific down-hole issues,
if so warranted. Otherwise, keeping in view the environmental factors in the backdrop, only water based
mud is proposed to be used in the drilling the exploratory wells in the block. Water-based mud is made
up of clay (bentonite) and water; it may include barite, a heavy mineral to increase specific gravity of the
mud system. Chemical additives are mixed in to stabilize the drilling fluid during use, and to reduce
corrosion and bacterial activity. Chemical additives viz. glycols and salts may be used in conjunction to
mitigate potential problems related to hydrate formation.
The mud is subjected to continuous testing for its physical parameters, namely, density,
viscosity, yield point, water loss, pH value, etc. to ensure that drilling operations are successful and
continued without any down-hole complication. The mud will be prepared onsite (drill location) using
centrifugal pumps, hoppers and treatment tanks.
Drill-cuttings that circulate back to the surface will be separated from drilling mud using control
equipment comprising of linear motion vibrating screens called shale shakers, hydro-cyclones (including
de-sanders and de-silters), and centrifuges to mechanically separate cuttings from the mud. Once
cuttings have been separated, drilling fluid will be processed or reused after further treatment. The total
mud-circulation is depicted in a sketch in Fig. 3.9.
The time taken to drill a bore hole depends on the depth of the hydrocarbon bearing formation
and the geological conditions, but it is commonly of the order of 50 to 60 days. Where hydrocarbon
formations is found, initial well tests—possibly lasting for another 20 to 30 days—are conducted to
establish flow rates and formation pressure.
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Fig. 3.9: Typical drilling fluid circulation system
After drilling and initial testing, the rig is usually dismantled and moved to the next site. If the
exploratory drilling has discovered commercial quantities of hydrocarbons, a wellhead valve assembly
may be stalled. If the well does not contain commercial quantities of hydrocarbon, the site is
decommissioned to a safe and stable condition and restored to its original state. Open rock formations
are sealed with cement plugs to prevent upward migration of fluids. The casing wellhead and the top joint
of the casings are cut at the ground level and capped with a cement plug.
3.4.1. Source of Water
Water requirement in a drilling rig is mainly meant for preparation of drilling mud apart from
washings and domestic use. The average daily water consumption is of the order of 40 m3/day will be
drawn from Nhava supply base of ONGC (which is a main material supply base for offshore installations
of western region) along with other materials through sea route. Nhava supply base of ONGC receives
water from Industrial Development Corporation of Maharashtra Limited (CIDCO).
3.4.2. Water Usage Plan
The average daily water consumption is about 40 m3/day including water requirement for mud
preparation, washing and domestic activities. Wastewater generation from the proposed drilling activity
is from domestic activity @ 80 percent of the domestic water requirement and from washing @100
percent of the washing water requirement. Thus, wastewater generation from the drilling well is expected
to be 9 m3/day (Table 3.3).
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TABLE 3.3: WATER USAGE PLAN
Sr. No. Particulars Water requirement (m3/day)
Water Requirement
1 Mud preparation 20
2 Washing activities 5
3 Shale Shaker 10
4 Domestic purpose 5
Total water requirement 40
Wastewater generation
1 Domestic activity 4
2 Washing 5
Total Wastewater Generation 9
Typical drill rig module (schematic) is shown in figure below.
Fig. 3.10: A sketch of a typical drilling rig module
3.4.3. Wastewater Generation & Discharge
Waste water generated at the rig will be of three types and its disposal methodologies are
explained in the subsequent sections. The International Convention for the Prevention of Pollution from
Ships (MARPOL) is the primary regulations/ guidelines on prevention of pollution of the marine
environment by ships. The Convention includes regulations aimed at preventing and minimizing pollution
from ships - both accidental pollution and that from routine operations.
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Bilge Fluids
Bilge fluids are a mix of sea water, petroleum products and other brackish material that settles
to the bottom of a ship. The collection and disposal system for this fluid will be done in compliance with
the International Convention for Prevention of Pollution from Ships, 1973 as modified by the protocol of
1978 (MARPOL 73/78). The rig will be having provision to collect bilge fluids into a sludge tank and then
to a water/oil separator. Separated oil will then be diverted into "dirty oil" tank, where exhaust oil from
engine lubricant change is collected. The dirty oil will be periodically sent to shore in drums or special
containers by supply vessels. Separated water can be directly discharged overboard, provided that oil
content does not exceed 15 ppm as per MARPOL standards.
Deck Drainage
Drainage water generated from precipitation or routine operations, such as deck, rig floor and
equipment cleaning will be routed to separate drainage systems on the rig. This includes drainage water
from process/non-process areas that could be contaminated with oil. These waste fluids will be collected
by gravity in a tank and subsequently pumped into tanks installed below the main deck. The tank will be
periodically emptied, pumping waste fluid to the supply vessel for shipment to shore. Waste water,
wherever feasible, can be recycled to condition new mud and hence may be connected to the mud tanks
circulating system.
Grey and Black Water
Grey and Black Water is generated from showers, toilets, laundry and kitchen facilities on the
rig and will primarily contain waste material, paper, soap, etc. Rig operations will typically result in the
generation of sewage and wastes. Once collected through headers, they will be passed through a sewage
treatment plant (STP). The wastes will then be passed through a screen of less than 25 mm diameter
and an extended aeration system prior to their discharge into the marine environment. Sewerage
treatment on-site will be carried out in compliance with MARPOL 73/78 requirements.
3.4.4. Chemical Requirements and their storage at rig
Chemicals are required for preparation of WBM, giving the drilling mud the desired
characteristics to facilitate drilling at different depths. A variety of drilling chemicals and additives are
stored on the drilling rig with storage places clearly marked with safe operating facilities and practices.
Some of the common drilling and cementing fluid, chemicals likely to be used during drilling includes
cement, surfactants, de-foamers, lignin, inorganic salts, bentonite and barite, etc. as elucidated in the
Table 3.4.
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TABLE 3.4: CHEMICALS USED FOR PREPARATION OF DRILLING FLUIDS
S. No. Name of Chemical S. No. Name of Chemical
1 BARYTES 21 MOD. GUAR GUM
2 BENTONITE 22 PAC-LV
3 BIOCIDE 23 PAC-RG
4 CAL. CARB, COARSE 24 PGS
5 LIME STONE POWDER (Marble) 25 PHPA
6 CAL. CARB, MICRONISED 26 POT. CHLORIDE
7 CAL.CHLORIDE 27 RESINATED LIGNITE
8 CAUSTIC SODA 28 SAW DUST
9 CITRIC ACID 29 SODIUM BICARBONATE
10 CMC 30 SODA ASH
11 COMMON SALT 31 SP. FLUID (N.W.)
12 DEFOAMER 32 SP. FLUID (W)
13 DRILLING DETERGENT 33 SUL. ASPHALT
14 E.P. LUBE 34 THERMOGEL
15 GLYCERENE 35 WALNUT SHELL
16 HEC 36 XC-POLYMER
17 HYDRATED LIME 37 ZINC CARBONATE
18 IRONITE SPONGE 38 GLYCOL
19 LIGNITE 39 SOBM
20 MICA FLAKES
3.5. LITIGATIONS & COURT DIRECTIONS / ORDERS
There is no litigation pending against the project or any directions/order passed by any Court
of Law against the project. The project has been awarded to ONGC (70%) as the operator in partnership
with Essar Energy (30%) by the Ministry of Petroleum and Natural Gas (MoPNG), Govt. of India under
NELP VII.
3.6. ASSESSMENT (FOR RISK OF TECHNOLOGICAL FAILURE) OF NEW AND UNTESTED TECHNOLOGY
Over five decades of its existence ONGC has grown to be one of the largest E&P companies
in the world in terms of reserves and production. ONGC as an integrated Oil & Gas Corporate has
developed in-house capability in all aspects of exploration and production business, i.e., Acquisition,
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Processing and Interpretation (API) of Seismic data, drilling, work-over and well stimulation operations,
engineering and construction, production, processing, refining, transportation, marketing, applied R&D
and training, etc.
ONGC has planned to use Floater Drillship type mobile offshore drilling unit on hire-contract
basis for the Block MB-OSN-2005/3. The drilling technology and process to be used by ONGC, as
described in Section 3.4, is well established in Indian conditions. ONGC has used this technology and
process in many of its offshore exploration and drilling projects. No new or untested technology will be
used in the present case of drilling in MB-OSN-2005-3. ONGC generally use SOPs that are tested and
are used worldwide. The rigs to be used in the proposed exploratory block will be hired globally from
experienced vendors to ensure standard tested technologies. Thus the risk of technological failure of new
and untested technology does not arise.
3.7 Climatology & Meteorology of the Arabian Sea
Climate and meteorology of a place can play an important role in the implementation of any
developmental project. Meteorology (weather and climate) plays a key role in understanding local air
quality as there is an essential relationship between meteorology and atmospheric dispersion involving
the wind speed/direction, stability class and other factors. The block falls in the Mumbai offshore of
Maharashtra. Mumbai offshore experiences tropical monsoon climate with an average rainfall of
approximately 14 inches. The temperature ranges from 2ºC in the winter to 45 ºC in the summer. The
following are the well-defined seasons of the region:
Summer: February to June
Monsoon: July to September
Winter: October to January
The average rainfall during the last 10 years has been more than 300 mm. The general weather
conditions are not good for agriculture harvest.
Average rainfall
Average rainfall of the proposed exploratory block is in the range of 1mm to 2 mm /day as per ‘Physical
Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado, from their Web site at
http://www.esrl.noaa.gov/psd/’.
Maximum value of average rainfall in the region is 8.3 mm/day and minimum value is 0.045 mm/day.
Figure 3.14 given below reciprocates the mean rainfall of the area in mm/day.
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FIG. 3.11: WIND PATTERN OF INDIAN OCEAN
Mean Wind Speed
As per Physical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado, from
their Web site at http://www.esrl.noaa.gov/psd/, mean wind speed measured in m/sec for the period of
January 2011 to December 2011 for the study area lies in the range of 6.1 to 6.8 m/sec. Minimum and
maximum value of the same in the region is 3.5 m/sec and 9.98 m/sec. Figure 3.13 given below shows
the mean wind speed (m/s) of the Arabian sea.
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FIG. 3.12: MEAN RAINFALL (MM/DAY)
FIG. 3.13: MEAN WIND SPEED (M/S)
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“V” component of Wind
"V" component represents the north-south component. The positive V component answer indicates a
southerly component to the wind, or in other words, a wind that blows from south to north. A negative V
component would mean that the wind is blowing from north to south. Mean value of V component of wind
in the region of proposed exploratory block lies in the range of -1m/s to 0 m/s as per ‘Physical Sciences
Division, Earth System Research Laboratory, NOAA, Boulder, Colorado, (http://www.esrl.noaa.gov/psd/).
Figure 3.14 below shows the V component of wind speed (m/s) showing the tentative location of block.
Fig.3.14: Mean V component of the wind
“U” Component of Wind
The "U" component represents the east-west component of the wind. The minus sign in front of the U
component answer indicates an easterly component to the wind, or in other words, a wind that blows
from east to west. A positive U component would mean that the wind is blowing from west to east.
According to Physical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado
(http://www.esrl.noaa.gov/psd/), mean value of u component of wind, averaged over January 2011 to
December 2011 in the region of proposed exploratory block lies in the range of 2 m/s to 3.5 m/s. Figure
3.15 given below shows the U component of wind speed (m/s) of the Arabian Sea indicating the tentative
location of block.
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Mean Air Temperature
Maximum and minimum value of mean air temperature in the Arabian Sea is of the order of 30.2 ºC and
24.4 ºC, respectively. Mean air temperature of the area of exploratory block lies in the range of 26.5 ºC
to 27.5 ºC as per data available with Physical Sciences Division, Earth System Research Laboratory,
NOAA, Boulder, Colorado. Figure 3.15 given below indicates the mean air temperature of the Arabian
Sea showing tentative location of block.
FIG. 3.15: U COMPONENT OF WIND (M/S)
Mean Sea Surface Temperature
Maximum and minimum value of mean sea surface temperature in the Arabian Sea is of the order of 30.8
ºC and 26.04 ºC, respectively. Mean air temperature of the area of exploratory block lies in the range of
27 ºC to 27.5 ºC as per data available with Physical Sciences Division, Earth System Research
Laboratory, NOAA, Boulder, Colorado.
Tides
The tides in the offshore area are of mixed semi-diurnal type with a large diurnal inequality. The tidal
range in the gulf is about 4 m at the mouth and increase to around 7 m in the inner gulf. This macro-tidal
range is associated with strong water flows during ebb and flood tides. The gulf waters behave as
homogeneous one-layered structure due to high tidal range, low run-off from land, shallow depth and
irregular bottom topography – all suitable for turbulent flow field; however the impacts of the complex
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physiographic features on the shelf circulation and shelf sediment dynamics remain unexplained. This
behaviour of the gulf is in sharp contrast to the estuaries on the west coast of the India, which show
seasonal stratification, sometimes with salt –wedge formation associated with the height of the two
monsoons. Figure given in Fig 3-11 indicates the mean sea surface temperature of the Arabian Sea
showing tentative location of block.
FIG. 3.16: MEAN AIR TEMPERATURE (ºC)
FIG. 3.17: MEAN SEA SURFACE TEMPERATURE (ºC)
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Circulation
Circulation in the gulf is mainly controlled by tidal flows and bathymetry. Strong currents normally occur
during mid-tide, i.e. 2-3 hrs. before and after low and high tides. The spring currents are 60-65% stronger
than the neap currents. The surface currents are moderate (0.7 to 1.2 m/s), but increases considerably
(2.0-2.5 m/s) in the central portion of the gulf. The bottom currents are periodically strong with bimodal
directions generally parallel to the uneven bottom contour. The associated tidal currents are fairly strong
and bimodal in nature having two dominant directions – upstream during flood and downstream during
ebb in all-encompassing oscillatory motions.
The circulation pattern in the near shore areas however is modified considerably due to the presence of
creeks and inlets.
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Chapter- 4
DESCRIPTION OF ENVIRONMENT
This chapter describes the existing environmental settings in the block MB-OSN-2005/3 and
its immediate surroundings comprising of physical environment, namely, air, water and land components,
the biological environment. Attributes of the physical environment were assessed primarily through
collection and analyses of surface water samples by IPSHEM, ONGC Goa. Records and literature
available in public domain were studied for amassing information about physical and ecological features
of marine environment.
4.1. STUDY AREA
The NELP VII Block MB-OSN-2005/3 is located in the southwest of the Mumbai High-DCS
platform of Mumbai Offshore Basin, having an area of 1685 km2 having 90-100 meter bathymetry range.
The distance between block boundary and the coastal area is about 138 NM.
4.2. STUDY COMPONENTS:
Components for the EIA study of the proposed exploratory block include Climate &
Meteorology, Physico-chemical parameters of sea surface water and ecologically sensitive marine areas.
The details of the study parameter, its study area and study components are given in Table 4.1.
TABLE 4.1: DETAILS OF STUDY COMPONENTS, STUDY AREA AND STUDY PARAMETER
Sr. No. Study Components Study Area Study Parameters
1. Climate & Meteorology MB-OSN-2005/3 and Mumbai high offshore
Wind pattern, ocean currents, rainfall, wave height and direction.
2. Physico-Chemical characteristics of marine surface water
MB-OSN-2005/3 block area within 1 km2 from the proposed drilling locations.
Physical parameters – pH, Salinity, temperature. Chemical Parameters – Oil & Grease, Total Petroleum Hydrocarbon (TPH), Petroleum aromatic Hydrocarbon (PAH)
3 Ecology MB-OSN-2005/3 and Mumbai high offshore
Marine ecology for the Mumbai Offshore and coastal areas near the block.
4 Marine Sensitive Areas No sensitive areas fall within 1 km from the project activity area.
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4.3. BASELINE ENVIRONMENT
Introduction
Oil and Natural Gas Corporation Limited (ONGC) started oil exploration activities in western
offshore region in the early 70's. After the discovery of oil at Bombay High in 1974, from the first offshore
rig - Sagar Samrat, ONGC increased its attention towards Bombay High. True to expectations, ONGC
has delineated several major and minor oil fields on the western continental shelf.
During the various phases of development of Oil and Gas fields in western offshore, ONGC
has deployed several drilling rigs and commissioned process complexes besides more than a hundred
unmanned platforms. Strict controls by the Government necessitated ONGC to device plans to minimize
impacts from the offshore activities on the environment.
Though ONGC developed its own self control strategies in the initial phases of oil field
development by following international norms and practices, enactment of environment legislation and
regulation by the Ministry of Environment & Forests (MoEF) culminated in closer scrutiny of operations
by both governmental and non-governmental agencies. The Government also imposed several
conditions viz. incorporating preventive measures in the design, emergency preparedness for accidental
pollution and regular environment monitoring around the installations.
The first such environment monitoring was carried out by IPSHEM, Goa as a two season
study (post monsoon season and pre monsoon season) during November 1994 and March 1995. As the
variation of result is not significant, it was decided to carry out once in a year and since the year 2003,
the offshore environment monitoring around the ONGC’s installations in the western offshore region is
being conducted every year regularly.
4.3.1 Objectives and Scope of the Study
As mentioned above, ONGC as per the directives of the Government has started regular
environment monitoring around its installations in the western offshore region, to identify if there are any
impacts on the marine life due to its oil field activities. The objectives of the study are;
To generate a data bank of various important parameters by monitoring the water column
near the offshore installations and beyond 6 km from the installations, can be considered as
reference points.
To assess the spatial and temporal effects on marine benthic communities by sea bed
monitoring.
4.3.2 Scope of work
Collection of water samples in water column for monitoring hydrographical chemical and
biological characteristics including pollutants like hydrocarbons and heavy metals.
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Collection of sediment samples for quantifying hydrocarbon deposition, heavy metal
concentrations and benthic biota.
Collection of a few samples of zooplankton and fish in the vicinity of oil fields to understand
and estimate the possible bioaccumulation of pollutants.
The monitoring strategy including the fixing of sampling stations was guided by the Paris
Commission Guidelines (1987) and practices adopted in Gulf of Mexico (EPA - 1985). The
ocean monitoring methods adopted in India (Anon, 1994) were also taken into account while
designing the monitoring programme.
The Paris convention seeks to prevent pollution of the marine environment by virtually all
substances that can reach sea. All types of human activities are regulated within the
framework of this convention. The convention, in its meeting during June 1988 adopted the
guidelines framed by the Norwegian Pollution Control Authority for standardizing the
monitoring programme of offshore oil and gas platforms. These guidelines are called Paris
Commission (PARCOM) guidelines.
In general, the parameters to be studied and the frequency of monitoring are decided by the
local authorities. These guidelines are useful in fixing of sampling stations around the
platforms. The guidelines are based on the overall objective of environmental monitoring,
namely to assess the effects and extent of the spreading of oil and chemicals discharged
from the offshore industry into the marine environment.
4.3.3 Methodology
The task of offshore environment monitoring is needed the coordination of various agencies like,
A survey vessel to go around the offshore area for sample collection, analysis on board and
preservation of some samples;
A biological team for collection and interpretation of marine biological samples;
Fixing of sampling stations around offshore installation — these were governed by the Paris
commission guidelines as detailed above.
The survey vessel would cruise to the locations where samples were desired as per the given
geographical coordinates (lat/long) were collected and preserved for analysis. The typical sample
collection sketch conforming to international standards is shown in Fig. 4.1.
In view of this, IPSHEM adopted the following methods to execute the project.
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Fig. 4.1: Typical lay out of sampling stations based on Paris Commission Guidelines
4.3.4 Association of Biological Expertise:
Agency, having well experienced in Offshore Environment Monitoring and engaged in all
types of Oceanographic studies like Physical, Chemical, Biological and Geological studies
was approached for this study. A senior scientist working in the Biological division of the
agency was associated for the biological part of the study. He has carried out similar
biological work in the past in the coastal and offshore marine environment.
Cruise Vessel
A research vessel scrutinized by ONGC offshore security and offshore Defense Advisory
Group was hired by the agency. It should have bow and stern thrusters, auto steering
system, radio communication and satellite telephone etc. in addition to GPS and Radar for
accurate positioning of the vessel. It will be equipped with computerized weather monitoring
system and a well-set laboratory for analysis and preservation of samples. The cruise route
and the sample locations along the cruise route is depicted in the Fig. 4.2.
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4.3.5 Description of study area and Sampling locations:
The sampling stations around these installations were fixed based on Paris Commission
Guidelines, 1989 and was also guided by the following criteria.
Pipeline network in the immediate vicinity of the platform
Sea state and maneuverability of the vessel near the installation
In this study, two locations viz. Location-1 and Location-2 were covered to know the environmental status
of specific portion of Western Offshore. The sampling locations around all these locations are given
below.
Fig. 4.2: Cruise Sailing Route
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Coordinates of the Sampling stations
Approach
towards
Installation/
Direction
Distance from
the location
Sample
number Location Code Latitude Longitude
North- 1
2 km RA4-1 RA4/2/1 19007’26” 70056’24”
1 km RA4-2 RA4/1/1 19006’53” 70056’39”
0.5 km RA4-3 RA4/0.5/1 19006’32” 70056’37”
South West -2
2 km RA4-4 RA4/2/2 19005’38” 70055’26”
1 km RA4-5 RA4/1/2 19005’48” 70056’13”
0.5 km RA4-6 RA4/0.5/2 19006’04” 70056’26”
South East-3
2 km RA4-7 RA4/2/3 19005’29” 70057’27”
1 km RA4-8 RA4/1/3 19005’44” 70056’48”
0.5 km RA4-9 RA4/0.5/3 19005’58” 70056’48”
Reference Point >6 Km RA4-10 RA4/6/1 19002’38 70057’15”
Coordinates of the Sampling stations
Installation Latitude Longitude
Location -2 19014’26” 70058’52”
Approach
towards
Installation/
Direction
Distance from
the location
Sample
number Location Code Latitude Longitude
North- 1
2 km RGD-1 RGD/2/1 19015’28” 70058’47”
1 km RGD-2 RGD/1/1 19015’01” 70058’47”
0.5 km RGD-3 RGD/0.5/1 19014’44” 70058’57”
South West -2
2 km RGD-4 RGD/2/2 19013’35” 70058’20”
1 km RGD-5 RGD/1/2 19013’54” 70058’32”
0.5 km RGD-6 RGD/0.5/2 19014’14” 70058’37”
South East-3
2 km RGD-7 RGD/2/3 19013’37” 70059’46”
1 km RGD-8 RGD/1/3 19013’52” 70059’17”
Installation Latitude Longitude
Location-1 19006’05” 70056’26”
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0.5 km RGD-9 RGD/0.5/3 19014’09” 70059’08”
Reference Point >6 KM RGD-10 RGD/6/1 19010’52” 70059’05”
4.3.6 Equipment used for Sampling:
Mechanical Instruments
Electro-hydraulic winch
Hydrographic winch
Van Veen Grab
Single arm davits
Nishkin Bottle Sampler
Plankton nets
Electronic Instrument
Echo Sounder
CTD
DGPS
AWS
UPS
pH meter
Spectrophotometer
Spectroflouro meter
Computer
Sampling of water
All Seawater samples were collected from three levels of the water column-surface (1 m below
the surface), mid depth and near bottom (3 - 4 m above the sea bed) using PVC Niskin type samplers of
5 L capacity. Depth measurements were made to the nearest 1 m using a digital counter attached to the
pulley and counter checked by marking the cable.
Sampling of sediments
A Van Veen grab of 25 cm x 30 cm dimension and approximately 1.5 kg capacity having a
penetration depth of 10 cm was used for collection of sediments. This medium version of the grab was
used to prevent likely damage to pipelines etc. in case of any accidental strike on flow lines.
Sampling of plankton and benthos
Zooplankton samples were collected with a modified Heron-Tranter (HT) net; having 0.25m2
mouth areas and 330m mesh size. A horizontal haul of similar plankton net of 60 mesh size was used
for collection of mixed plankton. The collections were made during the period sunrise to sunset only.
Storage and Preservation
Samples of sea water (1 L) were preserved in polythene bottle after addition of metal free
hydrochloric acid for further analysis of heavy metals in the laboratory. Two aliquots of 1 L, each were
filtered through GF/F filters (pore size 0.70pm) and extracted with 10mL of 90% acetone under cold dark
conditions after an extraction period of 18 to 20 hours. The extract (g.L -1) was determined using
fluorometer. Column chlorophyll-a (mg m-2) was calculated by integrating the depth values.
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Zooplankton samples were preserved in 5% neutral formalin for further identification and
quantification. Sediment samples were made to stand in 5% buffered Rose- Bengal formalin for 24 hours
and then sieved onboard the vessel using standard sieves for collection of benthic organisms. The fauna
thus collected were stored in 4% neutral formalin for subsequent analysis. Samples for sediments were
also collected in aluminum foil and preserved at -20° C for hydrocarbon analysis. Another set of sediment
samples were collected in pre washed polythene bags and preserved at room temperature for grain size
analysis and the determination of heavy metals. Samples of fish and fish tissues were collected onboard
in aluminum foils and polythene bags and stored at -20° C for subsequent determination of hydrocarbons
and heavy metals in the laboratory.
Analytical Methods
Immediately after collection, seawater samples were analyzed for pH and nutrients (Nitrate,
Nitrite, Phosphate and Silicate). Nutrients were analyzed using chemical methods (Grasshoff, 1987).
Petroleum Hydrocarbons were extracted immediately after collection of seawater onboard the vessel
from 500 ml of seawater with spectroscopic grade n-hexane and the extract was preserved at 5°C for
further analysis in the laboratory.
Parameters like temperature, salinity, dissolved oxygen were determined, onboard the vessel,
using the CTD profiler and the values were double-checked using manual methods.
At each of the station, zooplankton was collected, by deploying a Heron-Tranter net fitted with
calibrated TSK flow meter at the mouth area. The net was towed horizontally at a uniform speed of 1.5
knots for five minutes. After initial processing onboard the ship, zooplankton samples were further studied
for population density, biomass, faunal composition and taxon diversity by using standard procedures.
Sea bottom dwelling organisms or benthos were collected, at each of the station, by lowering
a Van Veen Grab having penetration depth of 10 cm and variable surface coverage of 587.5 cm2 (small
grab) and 1035 cm2 (large grab). Meiobenthos sampling was done by using a plexiglass core of 4.5 cm
diameter. Macrobenthos samples were processed onboard the vessel, by sieving through 500 micron
stainless steel mesh screen for 48 hours whereas the samples for meiobenthos were passed through a
63 micron sieve. Organisms - meio and macro were treated with Rose Bengal stain and further preserved,
in 5% seawater formalin.
Bottom deposits were classified into dominant sediment type by visual touch-on method. Silty
- clay followed by sand were the dominant sediment types.
The methods followed for analyzing various parameters have been taken from standard books
on the subject of seawater analysis and conform to US EPA standards.
Winds
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The meteorology of the study area is governed by the monsoon system inducing alternating
winds and currents. The Northeast monsoon winds (November-February) are rather moderate, compared
to the Southwest monsoon winds (June to September). The meteorological data recorded in the vicinity
of these two stations are given in table No: 1.
Sediment characteristics
The continental shelf of western offshore region is approximately 140 nautical miles of the
coast of Mumbai. The shelf is distinguished as an inner and outer part, the demarcation being the 60 m
isobaths (Nair & Hashmi, 1980). The inner shelf is dominated by recent terrigenous deposits while the
outer shelf is characterized by relict oolite sand (Satyaprakash and Agarwal, 1981). The sedimentary
cover of the continental shelf exhibits a seaward succession of increasing granulometry from clay to silt
and sand (Nair and Hashmi, 1980)
The sediment samples collected at various locations during the present study also revealed
that the sediments were not uniformly distributed in the study area.
4.3.7 Methodology Followed for the analysis of Hydrographical and Chemical Parameters
4.3.7.1 Hydrographical Parameters
Temperature
Temperature was measured using the centigrade thermometer with a graduation of 0 - 100
°C. This is an important parameter since the characteristics of water column like the density, viscosity,
solubility, of gases and dissolved oxygen are related to temperature of the water column. The variation
in temperature of a water body has great impact upon the biological productivity. The organism including
fishes show limited tolerance for variation in temperature for processes such as feeding, reproduction
and movement. Distribution of aquatic organism is greatly influenced by water temperature.
During the survey it was revealed that the water column experienced homogeneous and
uniform distribution of temperature indicating that the impact of the offshore operation on the thermal
regime of the water column is insignificant.
pH
pH was measured using a portable pH meter ( Systronics) with an accuracy of ± 0.01 pH units.
pH meter was first calibrated with standard pH buffers of pH 7.0 and pH 4.0.
Salinity
Salinity was measured directly by Systronics water analyzer with an accuracy of 0.1ppt. Prior to the
sample, standard seawater was used to calibrate the salinometer.
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Turbidity
Turbidity was measured by Nephelometric method and the results are expressed in
Nephelometric Turbidity units (NTU). This method was based on a comparison of an intensity of light
scattered by the sample under defined conditions with the intensity of light scattered by a standard
reference suspension under the same conditions. The greater the intensity of the scattered light, the
higher is the turbidity. Standard turbidity suspensions for calibration were prepared by using hydrazine
sulphate and hexamethylene tetramine and the analysis were carried out using turbidity meter.
Suspended Solids
A known volume of seawater was filtered through a pre-weighed 0.45m Millipore filter paper.
This paper was dried till constant weight was obtained. The difference in initial weight and the weight
after filtration and drying was taken and the amount of suspended solids calculated.
4.3.7.2 Chemical Parameters
Dissolved Oxygen
Dissolved Oxygen (DO) was measured directly by Systronics water analyzer with an accuracy of
0.1ppm. The values of DO are expressed in mg/L.
Nutrients
Phosphate — Phosphorus
Dissolved reactive phosphate was measured by the method of Murphy & Riley in which the
seawater samples were made to react with acidified molybdate reagent and reduced using ascorbic acid.
The absorbance of the resultant blue complex was measured at 880 nm using HACH (DR- 3900)
spectrophotometer.
Nitrite — Nitrogen
Nitrite was measured by the method of Bendschneider and Robinson wherein the nitrite in
the samples was determined by diazotising with sulfanilamide and coupling with N (1-Naphthy)-ethylene
diamine-dihydrochloride. The absorbance of the resultant azo-dye was measured at 543 nm by a HACH
(DR- 3900) spectro-photometer.
Nitrate — Nitrogen
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Nitrate in the samples was first reduced quantitatively to nitrite by heterogeneous reduction
by passing the buffered seawater samples through an amalgamated cadmium column and the resultant
nitrite was analyzed as above. The measured absorbance was due to the initial nitrite in the sample and
nitrite obtained after the reduction of nitrate. Necessary correction was therefore made for any nitrite
initially present in the sample.
Silicates
The determination of silicates in seawater was based on the formation of a yellow
silicomolybdic acid when a nearly acidic sample was treated with a molybdate reagent. The yellow
silicomolybdic acid was reduced to an intensely colored blue complex using ascorbic acid as the
reductant and the colour was measured spectrophoto metrically.
Petroleum Hydrocarbons
Dissolved / dispersed petroleum hydrocarbons were extracted from seawater with Methylene
Chloride followed by GC- FID Analysis using Thermo (GC- 1000) GCFID.
Sediment
Total Phosphorus
The organic phosphorus was converted into inorganic form by digestion of sediment with
perchloricacid and the phosphorous was estimated using standard methods applicable for the
estimation of inorganic phosphate phosphorus by spectrophotometric method.
Total Nitrogen
Total nitrogen was estimated by the persulphate oxidation technique in which the nitrogen
compounds were converted to nitrates by alkaline persulphate at 115 °C (in an autoclave under
pressure) and the resultant NO3 was reduced to NO2 by passing through the cadmium amalgamated
column. Finally the NO2 was estimated by diazotization and coupling with aromatic amines and
measured at 543 nm by a spectrophotometer.
Total Organic Carbon
Total carbon present in organic material in sea sediment is estimated with the help of muffle furnace
using semi- quantitative method and finally total organic carbon is calculated in percentage.
Petroleum Hydrocarbons
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Dried sediment sample was digested with the perchloricacid and PHC was measured with Thermo (GC-
1000) GC-FID.
4.3.8 RESULTS AND DISCUSSION
Drilling Rig-Abban Ice and Drilling Rig-GD Chayya are retitled as Station-1 and Station-2
respectively during the following discussion to avoid complexity. The data of chemical characteristics,
dissolved oxygen, nutrients like nitrate, nitrite, phosphate and silicate as recorded around these stations
of Western offshore are presented in following Tables.
4.3.8.1 Temperature
Sampling Points around the station-1 and Station-2 have shown temperature’s variation from
26.2-28.3 °C and 26.2-28.3 °C respectively and an average temperatures were detected of 27.31 °C and
27.11 °C respectively. The surface layer showed higher temperature at all the stations, which decreased
towards the bottom. At station-1 reference point, temperature was varying from 26-26.9 °C whereas at
station-2 reference point, temperature was 26.1-26.8 °C. The observed range of temperature variation is
well in normal limits for the coastal waters.
4.3.8.2 pH
Sampling Points around the station-1 and Station-2 have shown pH’s variation from 7.12-8.3
and 6.75-8.25 respectively and an average pH values were detected of 7.78 and 7.67 respectively. At
station-1 reference point, pH was varying from 7.21-8.28 whereas at station-2 reference point,
temperature was 7.1-8.26. No particular trend is followed regarding the distribution of pH, though all the
observed pH values are well within normal limits.
4.3.8.3 Salinity
Sampling Points around the station-1 and Station-2 have shown salinity’s variation from 31.5-
37.5 PSU and 31.6-38.4 PSU respectively and an average salinity values were detected of 34.4 PSU and
35.57 PSU respectively. At station-1 reference point, salinity was varying from 33.8-36.8 PSU whereas
at station-2 reference point, salinity was 36.7-37.5 PSU. The observed salinity values are similar to those
observed at the reference stations and the values are well within acceptable limits.
4.3.8.4 Turbidity
Sampling Points around the station-1 and Station-2 have shown turbidity’s variation from 4.6
– 16.8 NTU and 3.4 – 17.4 NTU respectively and an average turbidity values were detected of 10.31 NTU
and 9.02 NTU respectively. At station-1 reference point, turbidity was varying from 8.4-10.9 NTU whereas
at station-2 reference point, turbidity was 4.6-9.6NTU. The variation of turbidity has followed no trend and
the observed turbidity indicate normal values for the seawater at the site.
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4.3.8.5 Total Suspended Solids
Sampling Points around the station-1 and Station-2 have shown the Total Suspended Solids
(TSS)’s variation from 10-38 mg/L and 9-34 mg/L respectively and an average TSS values were detected
of 24.98 mg/L and 18.63 mg/L respectively. At station-1 reference point, TSS was varying from 20-41
mg/L whereas at station-2 reference point, TSS was 13-16 mg/L. The vertical variation of suspended
solids shows no characteristic trend, however comparing the values with reference point; disturbance of
operational activity cannot be concluded. The observed values are within normal limits for the coastal
seawater
4.3.8.6 Dissolved Oxygen DO
Dissolved Oxygen (DO) concentrations are considered to be very vital parameter to assess
the health of the marine environment especially where exploration and production activities are in
progress. The measured DO concentrations around station-1 and station-2 have almost shown
predictable a variation depends on depth at which sample was collected (In general, DO concentrations
are decreased when depth is increased).
Sampling Points around the station-1 and Station-2 have shown the DO’s variation from 3.24-
5.38 mg/L and 3.25-5.34 mg/L respectively and an average DO values were detected of 4.42 mg/L and
4.30 mg/L respectively. At station-1 reference point, DO was varying from 3.52-5.38 mg/L whereas at
station-2 reference point, DO was 3.67-4.67mg/L. Subsequently, studying all these experimental results
carefully, it is observed that all obtained values are most similar to the values obtained at reference station
values and well within acceptable limits for the coastal seawater.
Nutrients
i. Phosphate - Phosphorous
Sampling Points around the station-1 and Station-2 have shown Phosphate– Phosphorus
(PP)’s variation from 0.042–0.84 μmol/L and 0.045–0.75 μmol/L respectively and an average PP values
were detected of 0.21 μmol/L and 0.21 μmol/L respectively. At station-1 reference point, PP was varying
from 0.10-0.19 μmol/L whereas at station-2 reference point, PP was 0.16-0.19 μmol/L. The vertical
variation of phosphates at these stations showed no regular trend of phosphate phosphorous. The values
observed however are normal for the coastal seawater.
ii. Nitrite – Nitrogen
Sampling Points around the station-1 and Station-2 have shown Nitrite – Nitrogen (NN)’s
variation from 0.008 – 0.026 μmol/L and 0.007 – 0.027 μmol/L respectively and an average NN values
were detected of 0.016 μmol/L and 0.015 μmol/L respectively. At station-1 reference point, NN was
varying from 0.013-0.017 μmol/L whereas at station-2 reference point, NN was 0.015-0.016 μmol/L. The
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Nitrite – Nitrogen values follows no particular trends and they are similar at all the stations and at all the
water columns. The values observed as well within normal acceptable limits
iii. Nitrate - Nitrogen
Sampling Points around the station-1 and Station-2 have shown Nitrate – Nitrogen (NN)’s
variation from 0.015 – 4.5 μmol/L and 0.022 – 0.67 μmol/L respectively and an average NN values were
detected of 0.85 μmol/L and 0.30 μmol/L respectively. At station-1 reference point, NN was varying from
0.014-0.34 μmol/L whereas at station-2 reference point, NN was 0.037-0.043 μmol/L. The Nitrate –
Nitrogen values follows no particular trends and values are at lower side. The values are within normal
acceptable limits.
iv. Silicates
Sampling Points around the station-1 and Station-2 have shown Silicate’s variation from 0.12-
0.57 μmol/L and 0.16-0.45 μmol/L respectively and an average Silicate values were detected of
0.31μmol/L and 0.29 μmol/L respectively. At station-1 reference point, Silicate was varying from 0.28-
0.51 μmol/L whereas at station-2 reference point, Silicate was 0.29-0.35 μmol/L. The observed values
are normal for the coastal seawater.
v. Petroleum Hydrocarbons (PHC)
Sampling Points around the station-1 and Station-2 have shown (Table-4.1) PHC’s
concentration very minimal at majority of points which comes under non detection limit. At both the
reference stations also, the PHC comes under non detection level.
The distribution of PHC in the sediment samples at and around the both stations has shown
(Table.7) minute contamination, though all observed valued values are acceptable limits.
Sediment Quality
Total Phosphorous and Total Nitrogen
The Total Phosphorous and Total Nitrogen’s concentration was measured in the sediment
samples collected around the sampling points of station-1 and Station-2 has shown variation from 19.7—
40.2 μg/g and 8.6—30.1 μg/g respectively and an average values were detected of 29.2 μg/g and 25.2
μg/g respectively. At station-1 reference point, the concentration was 92.4 μg/g whereas at station-2
reference point, it was 64.2 μg/g.
Total organic carbon
The Total Organic Carbon’s concentration was measured in the sediment samples collected
around the sampling points of station-1 and Station-2 has shown variation from 1.9% to 4.7% and 2.0%
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to 4.2% respectively and an average values were detected of 3.0% and 3.0%μg/g respectively. At station-
1 reference point, the concentration was 3.1% whereas at station-2 reference point, it was 1.4%.
PHC content in Sediment
The PHC’s concentration was measured in the sediment samples collected around the
sampling points of station-1 and Station-2 has shown variation from 45.62– 86.74 g/g and 42.81– 89.67
g/g respectively and an average values were detected of 64.055 g/g and 69.42 g/g respectively. At
station-1 reference point, the concentration was 34.51g/g whereas at station-2 reference point, it was
46.52g/g. Though all the stations are contaminated with PHC’s, the values are within acceptable limits.
Sediment textures
The texture of sediment samples collected around the station-1 and station-2 has been
analyzed systematically and it has been observed that the composition of clay varies from 30% -42% and
57% -80% respectively with average value of 36.71% and 69.7% respectively. At station-1 reference
point, it was 31% whereas at station-2 reference point, it was 36%.
Table - 4.1:: Meteorological parameters
Sr. No. Parameter Unit Location: 1
Date : 26.10.13
Time : 07:30 am
Location: 2
Date : 26.10.13
Time : 01:45 pm
1 Latitude - 19° 05’ 69” N 19° 13’ 157” N
2 Longitude - 70° 57’ 46” E 70° 57’ 714” E
3 Speed Knots 1.2 1.3
4 Heading ° C 220 15
5 Coarse ° C 214 10
6 Depth m 84 79
7 Wind Crest m/sec 2.7 3.4
8 Wind Speed m/sec 7.72 8.75
9 Wind Direction - NE NE
10 Air Temp. °C 30 29
11 Pressure mbar 1009.3 1010.7
Table-4.2 :: Hydrographical Parameters of Sea Water Column around Offshore Stations
Location: 1
Station Distance from Station Depth Temp Salinity pH Turbidity Suspended solids
°C PSU pH Unit NTU mg/l
1 0.5 km S 28.3 33.4 7.94 5.9 24
Pre-drill EIA for the NELP block MB-OSN-2005/3
45
M 27.7 32.5 7.21 4.6 20
B 27.5 31.5 7.51 7.6 36
2 1 km
S 27.8 35.9 7.68 11.2 19
M 27.5 34.8 8.14 10.6 17
B 27 33.4 7.14 12.7 15
3 2 km
S 27.6 35.6 7.65 5.4 25
M 27.2 33.2 7.58 8.3 27
B 26.9 31.6 8.16 15.4 16
4 0.5 km
S 27.4 33.8 8.14 12.6 23
M 27.1 35.6 8.16 14.3 10
B 26.9 33.9 7.95 12.5 18
5 1 km
S 27.5 34.5 8.16 11.6 29
M 26.7 36.8 8.13 13.8 37
B 26.2 37.5 7.79 11.4 28
6 2 km
S 27.9 34.6 7.54 12.6 36
M 27.4 36.8 8.15 5.6 38
B 27 34.2 7.68 8 21
7 0.5km
S 27.5 32.1 7.45 14.7 16
M 27.8 36.7 8.3 6.8 18
B 26.9 34.7 7.54 5.6 28
8 1 km
S 27.4 31.7 7.68 8.4 26
M 27.6 36.8 7.84 11.2 19
B 27.1 32.9 7.31 13.5 34
9 2 km
S 27.6 34.7 8.19 16.8 25
M 27.2 32.8 8.02 9.8 31
B 26.7 36.8 7.12 7.5 37
R R
S 26.9 33.8 8.28 8.4 20
M 26.4 35.7 8.09 10.9 21
B 26 36.8 7.21 9.6 41
Location: 2
Station Distance from Station Depth Temp Salinity pH Turbidity Suspended solids
°C PSU pH Unit NTU mg/l
1 0.5 km
S 27.9 34.2 6.75 14.3 16
M 27.4 31.7 7.42 3.6 10
B 26.7 36.1 7.21 4.6 19
Pre-drill EIA for the NELP block MB-OSN-2005/3
46
2 1 km
S 27.3 34.8 7.52 12.7 24
M 26.8 35.9 7.31 4.8 27
B 26.2 37.4 8.24 6.9 14
3 2 km
S 27.5 36.7 7.98 4.7 18
M 27 37.8 7.42 6.4 16
B 26.8 35.9 7.86 8.2 14
4 0.5 km
S 27.3 34.2 7.81 12.3 24
M 26.8 36.7 7.58 10.2 29
B 26.5 32.7 7.68 9.5 27
5 1 km
S 27.8 31.6 7.24 5.6 16
M 27.2 32.7 8.25 4.6 16
B 26.7 33.7 8.12 3.4 16
6 2 km
S 27.2 37.6 8.2 4.7 15
M 26.7 36.9 7.86 5.8 21
B 26.3 34.8 7.25 4.5 12
7 0.5km
S 28.3 35.9 7.61 6.7 24
M 27.5 37.4 7.82 13.8 10
B 26.7 35.9 7.95 15.6 14
8 1 km
S 27.9 36.8 8.13 17.4 16
M 27.3 37.1 7.43 13.8 28
B 26.8 36.4 8.1 14.8 34
9 2 km
S 27.7 38.4 7.51 12.9 24
M 27.2 36.4 7.62 11.8 10
B 26.7 34.8 7.41 10.2 9
R R
S 26.8 36.7 7.1 9.6 13
M 26.4 37.5 8.26 4.6 14
B 26.1 36.9 8.2 7.6 16
S-Surface, M-Middle, B- Bottom, R-Reference
Table-4.3 :: Chemical Parameters of Sea Water Column around Offshore Stations
Location: 1
Statio
n
Distance from
Station
Dept
h
Dissolved
oxygen
Nutrients
Nitrite-
N
Nitrate-
N
Phosphate-
P
Silicate-
Si
mg/l mg/l mg/l mg/l mg/l
1 0.5 km
S 5.32 0.019 0.22 0.042 0.43
M 4.6 0.014 2.51 0.12 0.45
B 3.5 0.013 0.39 0.19 0.23
2 1 km S 5.24 0.018 0.21 0.12 0.25
Pre-drill EIA for the NELP block MB-OSN-2005/3
47
` M 4.65 0.018 3.45 0.084 0.26
B 3.24 0.009 0.21 0.14 0.28
3 2 km
S 5.31 0.012 0.29 0.21 0.19
M 4.38 0.021 4.51 0.24 0.24
B 3.65 0.014 0.25 0.23 0.37
4 0.5 km
S 5.31 0.019 0.87 0.21 0.42
M 4.7 0.013 2.6 0.074 0.2
B 3.8 0.014 0.18 0.14 0.26
5 1 km
S 5.37 0.02 0.24 0.19 0.27
M 4.57 0.025 2.63 0.84 0.19
B 3.68 0.017 0.54 0.21 0.32
6 2 km
S 5.1 0.008 0.19 0.16 0.25
M 4.63 0.01 0.015 0.17 0.16
B 3.57 0.011 0.16 0.18 0.36
7 0.5km
S 4.75 0.015 0.28 0.25 0.31
M 3.85 0.021 1.3 0.24 0.36
B 3.52 0.02 0.28 0.29 0.45
8 1 km
S 4.75 0.008 0.54 0.27 0.29
M 4.67 0.026 0.015 0.26 0.23
B 3.57 0.013 0.19 0.095 0.32
9 2 km
S 5.26 0.022 0.42 0.27 0.31
M 4.6 0.024 0.017 0.16 0.26
B 3.68 0.012 0.53 0.18 0.27
R R
S 5.38 0.016 0.32 0.19 0.34
M 4.6 0.013 0.014 0.16 0.35
B 3.52 0.017 0.34 0.1 0.29
S-Surface, M-Middle, B- Bottom, R-Reference
Location: 2
Statio
n
Distance from
Station
Dept
h
Dissolved
oxygen
Nutrients
Nitrite-
N
Nitrate-
N
Phosphate-
P
Silicate-
Si
mg/l mg/l mg/l mg/l mg/l
1 0.5 km
S 5.26 0.019 0.46 0.23 0.26
M 4.87 0.023 0.61 0.16 0.42
B 3.97 0.027 0.31 0.17 0.16
Pre-drill EIA for the NELP block MB-OSN-2005/3
48
2 1 km
S 4.36 0.016 0.2 0.24 0.34
M 4.24 0.019 0.29 0.36 0.12
B 3.56 0.012 0.34 0.26 0.21
3 2 km
S 4.85 0.018 0.38 0.75 0.18
M 4.25 0.013 0.25 0.16 0.31
B 3.52 0.014 0.29 0.23 0.51
4 0.5 km
S 5.34 0.021 0.34 0.16 0.42
M 4.37 0.014 0.36 0.075 0.31
B 3.67 0.007 0.38 0.19 0.42
5 1 km
S 5.21 0.009 0.21 0.52 0.21
M 4.37 0.012 0.27 0.21 0.35
B 3.59 0.015 0.25 0.16 0.14
6 2 km
S 4.92 0.017 0.29 0.19 0.26
M 4.25 0.019 0.23 0.089 0.49
B 3.61 0.016 0.25 0.23 0.25
7 0.5 km
S 4.86 0.015 0.21 0.25 0.27
M 4.23 0.012 0.049 0.21 0.34
B 3.64 0.008 0.67 0.075 0.32
8 1 km
S 5.3 0.014 0.41 0.15 0.39
M 4.31 0.007 0.022 0.045 0.34
B 4.13 0.014 0.54 0.19 0.46
9 2 km
S 4.67 0.019 0.24 0.12 0.35
M 3.69 0.024 0.041 0.069 0.33
B 3.25 0.02 0.16 0.095 0.25
R R
S 4.38 0.013 0.38 0.19 0.28
M 4.67 0.16 0.037 0.18 0.39
B 3.67 0.015 0.43 0.16 0.51
S-Surface, M-Middle, B- Bottom, R-Reference
Table - 4.4 :: Petroleum Hydrocarbon (mg/L) in water samples
Station Depth 0.5 km 1 km 2 km 0.5 km 1 km 2 km 0.5 km 1 km 2 km R
1 2 3 4 5 6 7 8 9 10
Location-1
S ND ND ND ND ND ND ND ND ND ND
M ND ND ND ND ND ND ND ND 0.24 ND
B ND ND ND ND ND ND ND ND ND ND
Location-2 S ND ND ND ND ND ND ND ND ND ND
Pre-drill EIA for the NELP block MB-OSN-2005/3
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M ND ND 0.18 ND ND ND ND ND ND ND
B ND ND ND ND ND ND ND ND ND ND
Table - 4.5 :: Total Nitrogen (µg/g), Total Phosphorous (µg/g) and Organic carbon (%) in sediments
ABAN ICE (Loc-1)
Distanc
e
Total
Phosphoru
s
Total
Nitroge
n
Total
Org.
Carbon
GD
Chayya
(Loc-2)
Distance
Total
Phosphoru
s
Total
Nitrogen
Total
Org.
Carbo
n
( Km) µg/g µg/g % ( Km) µg/g µg/g %
1 0.5 27.2 66.4 4.7 1 0.5 20.7 57.8 2.6
2 1 36.1 52.1 2.6 2 1 9.4 67.5 2
3 2 21.3 78.3 3.2 3 2 18.9 86.9 3.4
4 0.5 30.6 88.4 3.6 4 0.5 8.6 43.7 2.1
5 1 40.2 73.5 2 5 1 23.2 76.1 4.2
6 2 19.7 51.8 1.9 6 2 15.8 51.4 3.7
R R 25.2 92.4 3.1 7 0.5 11.2 39.3 2.9
8 R 30.1 64.2 1.4
R-Reference
Table - 4.6 :: Sediment Texture Analysis around Sampling Stations
Location1 Distance
(Km)
Silt Clay Location 2 Distance
( Km)
Silt Clay
% % % %
1 0.5 42 39 1 0.5 27 73
2 1 39 35 2 1 39 60
3 2 36 30 3 2 42 57
4 0.5 40 36 4 0.5 21 79
5 1 49 42 5 1 36 68
6 2 44 38 6 2 26 80
R R 36 30 7 0.5 29 71
8 R 31 62
R-Reference
Table - 4.7:: Petroleum Hydrocarbon (μg/g) in sediment samples
Station 0.5 km 1 km 2 km 0.5 km 01 km 02 km 0.5 km 01 km 02 km R
1 2 3 4 5 6 7 8 9 10
ABBAN 86.74 75.62 45.62 72.34 46.87 57.14 - - - 34.51
CHAAYA 87.68 76.58 86.64 48.67 53.89 42.87 89.67 - - 46.52
Heavy Metal concentrations
Pre-drill EIA for the NELP block MB-OSN-2005/3
50
Various heavy metals are present in small concentrations in the marine environment. Metal
pollution in the seas is invisible and insidious and does not attract enough attention as compared to oil
pollution, unless catastrophic events like the Minamata case of Japan occurs (which was due to Mercury
poisoning). In aquatic environments – metals can be termed as ‘conservative pollutants’, which once
added to the environment are there forever and cannot be broken down to harmless substances by
bacterial action as many of the organic pollutants are. Most of them are however, perfectly natural
substances occurring in seawater, though often in extremely low concentrations. They are leached or
introduced into the aquatic systems as a result of the weathering of soils and rocks, from underwater
volcanic activities, and from a variety of manmade sources, which involve mining, processing or use of
metals or substances that contain metal contaminants. This is which changes the natural concentrations
of metals in seawater resulting in a ten or even a hundred fold increase near the source of an effluent
discharge. Although many metals are poisonous at quite low concentration, they are often vital as trace
elements. Hence, while manganese, copper, iron, zinc etc. are considered essential micronutrients,
mercury, cadmium and lead are not required for any important biological function by any organisms and
are termed as non-essential elements.
Generally speaking, except at a few places, metal pollution in the sea is not and never was at
dangerous levels, but the potential threat it offers is sufficient to merit a careful watch, in terms of
monitoring programs. Metals once introduced in the seawater, either naturally or as contaminants
undergo various alternatives. Apart from dilution and dispersion there are biogeochemical processes
which remove metals from the seawater, or in other words reduce the concentrations of the added metal
in seawater. These are precipitation, adsorption by suspended matter and absorption by organisms. It is
the last process that includes removal by zooplankton ‘debris’ and other organisms which is of prime
concern to man. This has led to much interest in determining the levels of heavy metals in a wide variety
of commercially important marine fishes more as a food hygiene study.
Because of these factors, monitoring the concentrations of heavy metal in water, sediments
and fishes is very important. The toxicity limits (LC50 values) of some heavy metals towards fish in the
open sea are given below:
Table - 4.8 :: Heavy metal and Toxicity Limit
Metal Toxicity Limit (µg/L)
Chromium >10000
Zinc >1000
Cadmium 6400 – 16400
Mercury 67
Lead >1000
Pre-drill EIA for the NELP block MB-OSN-2005/3
51
Since the concentration of heavy metals in seawater is very low (usually in the parts per billion
levels), accurate determination of their concentration is a very delicate and cumbersome task. The
analytical methods using normal flame atomic absorption cannot detect the low concentrations of heavy
metals in seawater (in µg – ng ranges) and do not give reproducible results. Hence all the seawater
samples were analyzed using inductively coupled Plasma emission spectrophotometer (ICP- OES)
available at IPSHEM.
The heavy metal contents in sediments were analyzed after digestion with hydrofluoric acid
and perchloric acid, using same ICP- OES available at IPSHEM. These methods were standardized and
calibrations done using standard metal solutions and standard reference samples. The same equipment
was used for the determination of heavy metals.
Heavy Metals in Seawater
The range of concentration (in µg/L) of heavy metals viz. Zinc, Iron, Cadmium, Lead, Barium,
Manganese, Chromium and Mercury in the sea water sampled at surface, mid depth and bottom of
various sampling stations around Rig.Abban-Ice and Rig.GD Chayy are given in Table 14. Ranges of
some significant heavy metals like Zinc, Iron, Manganese and Lead which are usually present in higher
concentrations (in ppb) than the other heavy metals, and which require close watch from pollution point
of view, have been tabulated.
Table - 4.9 :: Heavy Metal Concentrations at Reference Stations
Heavy Metal Range of Concentration (µg/L) Heavy Metal
Range of Concentration (µg/L)
Ba 1.5-2.2 Mn 0-12.6
Cd 0.2-0.5 Pb 1.25-3.22
Cr 1.6-2.5 Zn 2.7-8.3
Fe 0.23 % - 0.43% Hg 5.8-9.9
The distribution of heavy metals in water column did not reveal any clear pattern either
vertically or horizontally. The spatial distribution also did not yield any clear trend of either enrichment or
depletion.
For some of the heavy metals, the ranges of concentrations (µg/L) in the Indian Ocean have
been reported by various authors is given in Table:4.10.
Table - 4.10 :: Heavy metals concentration in the Indian Ocean
Authors Fe Mn Zn
Sen Gupta et.al. (1978) 7.2 – 66.9 - 0.5 – 42.4
Pre-drill EIA for the NELP block MB-OSN-2005/3
52
Sanzgiri and Moraes (1979) 8.5 – 96 1.8 – 80 1.2 – 29.7
Braganca and Sanzgiri (1980) 6.2 – 131.5 1.8 – 40.8 2.4 - 20
Though the iron contents in seawater recorded in this study are relatively higher in
concentration comparable to the standard values as described above, the concentrations observed in the
reference stations around Bombay High are quite identical to the values recorded near the installations.
This is inferred that there is no enrichment in the heavy metal concentration due to oil field activities in
spite of the fact that the drilling mud discharges and the disposal of produced water are sources of heavy
metals around an oil field installation. Literature review gives an idea of concentration of heavy metals in
various oceans of the world, which is given in Table:4.11
Table - 4.11 :: Concentration (µg/l) of heavy metals in oceans of the world
Metal Open
N.Atlantic
Continental
Coastal
Northern and
Central North sea
Western Atlantic Shelf
Cd 0.002– 0.007 0.04 – 0.068 0.014 – 0.026 0.022
Cu 0.064– 0.096 0.346– 0.666 0.15 – 0.30 0.252
Mn 0.033– 0.073 0.40 – 1.04 0.027 – 0.673 1.155
Another exhaustive study records following values for heavy metals (values in µg/L):
Table - 4.12:: Concentration (µg/l) of heavy metals in oceans of the world
Metal Open ocean Coastal, Bay and Estuary
Cd Pacific = 0.02 – 0.04
Norwegian sea = 0.02 – 0.025
North sea = 0.2 – 0.4
Cr Pacific = 0.06 – 1.26
Mediterranean = 0.07 – 0.97
North sea = 0.4
Cu Pacific = 0.3 – 2.8
North sea = 0.208
Norwegian sea = 0.08 – 0.1
North sea = 2.82 – 9.7
Fe Pacific = 140 – 320 Sea water = 3.2 – 3.4
Pb Pacific = 0.6 – 0.8 North sea = 1.8 – 7.44
Mn Open ocean = 0.018
Hg Atlantic = 0.021 – 0.078
Zn Pacific = 1.9 – 3.0 North sea = 7.0 – 22.0
Pre-drill EIA for the NELP block MB-OSN-2005/3
53
Though, it is observed that values in open oceans are less than those found near the oil
installations, as per data available for the permissible limits of heavy metals in coastal marine water, as
given bellow, it can be safely concluded that the values observed near Bombay High and other fields are
very much below the toxicity limits for metals given in the literature.
Table - 4.13 :: Limits of Heavy metal concentrations
Heavy Metal Limit (ppb) Heavy Metal Limit (ppb)
As 200 Cu 3000
Hg 10 Zn 15000
Pb 2000 Ni 5000
Cd 2000 Mn 2000
Cr 2000 Fe 3000
(Source: Kerala pollution control board: www.keralapcb.org/)
Table - 4.14 :: Heavy metals in sea water
Station Distance Depth Barium Cadmium Chromium Iron Manganese Lead Zinc Mercury
ABBAN from station µg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L
1
0.5 km
S 2.058 0.261 2.437 48.96 2.408 0 1.961 2.908
M 1.582 0.182 2.346 34.79 1.534 0.37 4.341 7.749
B 1.742 0.273 2.657 35.81 1.498 0 5.369 4.929
2
0.5 km
S 1.51 0.247 2.246 31.83 2.685 0 5.515 4.844
M 2.214 374 2.521 36.49 2.383 0 3.558 19.93
B 1.154 0.265 1.48 23.48 1.847 1.626 3.54 10.12
3
0.5 km
S 1.246 29.24 1.666 27.55 2.014 1.189 10.8 41.65
M 1.2 0.222 1.586 45.9 2.928 1.529 4.31 10.09
B 1.25 0.306 1.637 25.47 2.019 0.902 3.709 7.597
4
1 km
S 1.709 0.307 2.989 32.95 1.771 0.081 4.142 16.67
M 1.608 0.288 2.367 48.6 1.676 0.371 13.18 12.86
B 1.727 0.321 2.497 62.52 2.292 1.074 4.285 5.66
5
1 km
S 1.297 9.208 1.608 21.81 2.734 1.389 4.728 8.942
M 1.35 0.351 1.765 36.75 4.461 2.072 9.043 8.806
B 1.229 0.642 1.65 21.46 2.437 1.826 7.336 7.42
6
1 km
S 1.152 0.277 1.773 24.54 4.095 1.773 2.677 5.171
M 1.397 0.294 1.71 19.59 6.541 2.503 7.441 11.52
B 1.384 0.399 1.788 33.62 9.47 3.305 3.476 8.123
2 km S 2.614 0.395 2.872 57.97 8.334 1.67 12.41 11.89
Pre-drill EIA for the NELP block MB-OSN-2005/3
54
7
M 2.113 0.463 2.422 36.85 7.693 1.613 8.028 7.906
B 1.41 0.307 2.527 38.86 12.31 3.014 3.789 10.66
8
2 km
S 1.592 0.243 2.725 34.67 10.31 1.221 4.821 13.15
M 1.86 0.288 2.348 39.05 8.979 1.327 7.861 8.639
B 1.315 0.26 1.668 42.54 2.226 1.972 4.996 7.81
9
2 KM
S 0.104 828 0.989 21.61 2.947 1.36 2.945 6.47
M 1.48 252.6 1.592 28.49 6.423 2.578 7.363 0
B 1.913 0.452 1.744 28.26 12.59 3.215 6.466 10.09
10
R
S 1.533 0.399 2.132 33.11 11.33 2.974 8.142 9.931
M 2.163 0.323 2.469 42.55 8.569 1.531 8.277 5.803
B 1.913 0.452 1.744 28.26 12.59 3.215 6.466 7.316
S-Surface, M-Middle, B- Bottom, R-Reference
Table: 4.14 Heavy metals in sea water (contd.)
Station Distance Depth Barium Cadmium Chromium Iron Manganese Lead Zinc Mercury
GD- CHAYYA
from station µg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L
S 2.825 0.407 4.449 75.82 8.457 0.833 6.407 10.54
1 0.5 km M 1.115 0.134 1.44 20.55 10.23 0 1.642 6.995
B 2.024 0.482 3.173 45.28 3.297 0.508 12.08 2.213
S 1.637 0.176 3.128 24.68 1.552 0 1.344 8.202
2 0.5 km M 1.159 0.212 1.555 26.8 10.32 2.226 8.017 7.028
B 1.417 0.159 1.528 25.31 1.351 0.211 8.604 10.38
S 1.427 0.202 1.462 19.04 1.323 0 5.657 17.39
3 0.5 km M 1.306 0.15 1.447 39.55 1.681 0.583 4.938 6.973
B 1.297 0.192 1.819 61.99 1.454 1.759 9.217 7.776
S 1.16 0.115 1.474 22.29 1.114 0 4.748 9.406
4 1 km M 1.207 0.184 1.45 18.95 1.424 0.128 1.186 7.992
B 1.891 0.126 1.559 23.28 1.114 0 6.82 2.973
S 1.7 0.275 2.877 32.9 1.121 0 5.565 8.928
5 1 km M 0.961 0.123 1.235 15.81 1.203 0 6.303 7.038
B 3.197 0.696 0.982 1.59 1.63 32.18 0.28 4.449
S 1.121 0.192 1.566 30.36 1.282 0 5.021 7.01
6 1 km M 6.621 2.069 0.749 1.903 1.619 28.09 6.208 6.89
B 1.086 0.175 1.438 28.3 1.096 0.069 3.282 8.88
S 1.902 0.405 3.19 33.31 1.427 0.442 5.899 4.484
Pre-drill EIA for the NELP block MB-OSN-2005/3
55
7 2 km M 1.134 0.077 1.196 14.41 1.06 0 5.926 7.05
B 1.752 0.303 2.736 35.41 3.382 1.056 5.902 6.77
S 2.024 0.411 3.111 32.53 2.087 0.413 9.842 7.718
8 2 km M 1.134 0.077 1.196 14.41 1.06 0 5.926 7.05
B 1.752 0.303 2.736 35.41 3.382 1.056 5.902 6.77
S 2.024 0.411 3.111 32.53 2.087 0.413 9.842 7.718
9 2 KM M 1.374 0.114 1.239 26.7 0 1.291 6.946 8.317
B 1.032 0.144 1.695 24.03 0.646 1.765 1.088 8.012
S 1.322 0.243 1.79 25.77 0.504 2.208 2.661 8.534
10 R M 1.106 0.228 1.666 22.6 0.847 2.7 4.921 6.404
B 1.272 0.186 1.558 28.35 0 1.249 7.754 8.858
S-Surface, M-Middle, B- Bottom, R-Reference
Heavy metals in sediments
Heavy metal concentrations in sediments sampled around the installations in Bombay High
South are given in Table 15. Concentrations of Zinc, Copper, Cobalt, Lead, Chromium, Nickel and Barium
are given in units of µg/g (ppm) while that of iron in percentage of dry weight.
Table: 4.15 Heavy metals in sea sediments
Staion Barium Cobalt Chromium Copper Iron Nickel Lead Zinc
ABBAN µg/g µg/g µg/g µg/g %(w/w) µg/g µg/g µg/g
1 0.117 0.008 0.093 0.035 46.9 0.022 0.015 0.027
2 0.111 0.008 0.096 0.039 49.2 0.022 0.017 0.022
4 0.113 0.008 0.092 0.032 46.79 0.021 0.016 0.02
5 0.135 0.009 0.093 0.045 46.1 0.027 0.026 0.026
7 0.105 0.007 0.076 0.03 43.07 0.018 0.022 0.012
8 0.127 0.007 0.075 0.028 40.48 0.021 0.014 0.01
10 0.08 0.006 0.064 0.031 36.04 0.016 0.018 0.01
Table: 4.15 Heavy metals in sea sediments (contd.)
Staion Barium Cobalt Chromium Copper Iron Nickel Lead Zinc
CHAYYA µg/g µg/g µg/g µg/g %(w/w) µg/g µg/g µg/g
1 0.108 0.009 0.078 0.022 40.4 0.037 0.013 0.045
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56
2 0.085 0.013 0.076 0.017 38.31 0.054 0.068 0.023
3 0.078 0.018 0.085 0.014 43.79 0.067 0.052 0.016
4 0.074 0.016 0.087 0.013 44.02 0.02 0.036 0.02
5 0.161 0.025 0.149 0.039 82.66 0.067 0.059 0.041
7 0.102 0.012 0.087 0.017 47.02 0.068 0.136 0.033
8 0.097 0.003 0.0991 0.018 46.93 0.054 0.086 0.034
10 0.207 0.032 0.108 0.034 49.13 0.075 0.047 0.045
4.9 BIOLOGICAL MONITORING OF OFFSHORE STATIONS
4.9.1 Methodology of Biological analysis
4.9.1.1 Collection and analysis of Chlorophyll-a
For chlorophyll-a (Chl-a), water samples were collected from surface and bottom according
to the standard protocols. One litre of water from each depth was filtered through GF/F filters (pore size
0.7 µm), and extracted with 10 ml of 90% acetone under cold dark conditions after an extraction period
of 18 to 20 hours. The extract (µg.l-1) was determined using fluorometer. Column Chl-a (mg m-2) was
calculated by integrating the depth values.
4.9.1.2 Collection and analysis of Phytoplankton:
Single celled plant communities floating in the surface water are collectively termed as
phytoplankton. The communities mainly comprise of diatoms and dinoflagellates. They form the first link
in the oceanic food chain. This food web is the most complex as it constitutes of 5 or more links. Almost
entire marine life directly or indirectly depends on the microscopic algae, found at the surface. Due to the
availability of food source, most of the animals either live in this region or migrate towards the surface in
search of food. As such, the top layer of the ocean is considered as most diverse and highly productive.
Diatoms are estimated to contribute up to 45% of the total oceanic primary production (Mann,
1999). Diatoms and dinoflagellates serve as food for the zooplanktons like molluscs, tunicates and also
for small fishes. One of the significant roles of phytoplankton is in the ocean’s carbon cycle. Feeding of
the zooplanktons on these producers marks the entry of photosynthetically fixed carbon into the food
web. This carbon gets accumulated as biomass or detritus or provides energy. Organic matter being
denser than sea water tends to sink, leading to the transport of carbon from surface to the bottom (called
biological pumping) which subsequently acts as food source for bottom living organisms.
Dinoflagellates when present in large number give rise to “red tide” (as the colour of the water
is changed). At such times they are known to produce neurotoxins. These toxins are fatal to fishes and
Pre-drill EIA for the NELP block MB-OSN-2005/3
57
also to the humans consuming such fishes. They can flourish well in phosphate rich conditions (as a
result of anthropogenic activity), as well as in increasing temperatures due to global warming. Hence,
they are also considered as environmental indicator.
Samples were collected 1m below the surface and 2-3 m above the seabed using Niskin
sampler. All the samples were fixed by adding Lugol’s iodine and 5% formalin solution. In laboratory, the
phytoplankton samples were concentrated to 25ml using a siphoning tube. The tube consists of a 10 µm
Nytex filter at one end. This concentrated sample was then taken in 3 aliquots of 1ml each, on Sedgwick-
Rafter Counting Chamber for taxonomic identification and quantification of the phytoplankton (cells per
liter). Olympus BX 41 inverted binocular microscope was used for identification and counting.
The total number of phytoplankton cells present in a litre of water sample calculated using the
formula:
N= n x v x 1000 / V
Where,
N: total number of phytoplankton cells per liter of water filtered.
n: average number of phytoplankton cells in 1 ml of plankton sample.
v: volume of plankton concentrate (ml)
V: volume of total water filtered (l).
Water samples for estimation of chlorophyll were collected from surface and bottom using
Niskin’s sampler. A known quantity of water sample (1 L) was filtered through GF/F Whatman filter paper.
Chlorophyll was extracted using 10ml of 90% acetone in cold condition after a period of 18 – 20 hours.
The acetone extract was read on fluorometer.
The data for the phytoplankton was analyzed using MS-Excel package and Primer. Primer
was mainly used for analyzing diversity. Attempts have been made to estimate the natural variability of
phytoplankton especially that of diatoms and dinoflagellates, in the surface and bottom water.
4.9.1.3 Zooplankton collection and analysis
Zooplankton samples were collected with a modified Heron-Tranter (HT) net; having 0.25m2
mouth areas and 330m mesh size. A calibrated TSK flow meter was fitted at the net mouth to measure
the volume of water filtered. The stratified horizontal vertical haul of 5 minutes in the upper 10-15 m water
depth was sampled. All the samples were preserved in 5% neutralized formaldehyde solution. The
zooplankton biomass was later estimated by displacement volume method and readings were converted
for 100m3. Different zooplankton taxa were sorted from an aliquot of the sample, identified and
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enumerated under stereoscopic zoom binocular microscope. The numbers were calculated for the whole
samples and given for 100m3 of water.
Sediment sampling for benthic communities, estimation of sediment chlorophyll-a and organic
carbon
Bottom dwelling organisms or benthos were collected, at each stations, by lowering a van
Veen grab. Sub-sampling for meiofauna was done using Plexiglas core of 4.5 cm diameter. The standard
height of corer that is used for sampling is 5 cm. All the sub-samples were preserved in 5% buffered Rose
bengal formalin solution.
Meiobenthos: The meiofauna in the sediment were separated using a 63-micron sieve and placed in plastic bottles
for detailed identification. The meiofauna taxa were picked using a sorting needle and temporary glycerol mounts
were made on glass slides. All specimens were identified up to group level following identification key of Higgins
and Thiel (1988), under a stereo zoom binocular microscope.
Macrobenthos: The sediment samples were collected by van Veen grab (area: 0.11 m-2; Plate 1). Metallic
quadrant of 151510 cm was used for macrofaunal sub sampling from grab sample and preserved in 5% buffered
formalin rose Bengal solution. Aminimum of 2-5 replicates were taken from each station.
All the macrofauna samples were sieved on-board after 48hrs of collection using 500µ size mesh
sieve in filtered seawater and material retained on sieve mesh were fixed in 5% formalin Rose Bengal. In
the laboratory, all the fauna was sorted, identified upto the lower possible level under the microscope.
Biomass (wet weight) was measured by blotting the sample on a blotting paper and weight was taken by
direct weighing on balance. The biomass was calculated in g m-2.
4.9.1.4 Fish & Fishery
Experimental fishing was done along three transects, in the depth zone of 30 - 50 meters.
Fish and shellfish samples were obtained with modified beam trawl, specially designed for deep-water
trawling.
Finfish and shellfish samples were brought in iceboxes to the field laboratory and kept frozen
for further study. Species-wise sorting was done following FAO species identification sheets for fisheries
purposes, western Indian Ocean (Fisher and Bianchi, 1984). Each sorted sample then counted, weighed
and preserved in 70% alcohol for further analysis. Fishes were identified up to species level Species
occurrence (total number of species); abundance (number of fishes and catch rate per hour) was
calculated.
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59
4.9.2 Results and Discussion
Location-1 Coordinates: 19006’05” E 70056’26”
Date of sampling: 26th October 2013
Time of sampling: 6:00 - 12:00
Sampling stations 1 2 3 4 5 6 7 8 9 R
Depth in meter 84.6 83.8 84.2 84.7 84.1 84.8 83.5 84.4 84.7 84.2
Secchi disc depth in meter Not measured as sea was rough
Sampling Station Coordinates
Latitude Longitude
RA-1 19007’26” 70056’24”
RA-2 19006’53” 70056’39”
RA-3 19006’32” 70056’37”
RA-4 19005’39” 72014’44”
RA-5 18032’01” 72015’09”
Sampling Station Coordinates
Latitude Longitude
RA-6 18032’12” 72015’21”
RA-7 18031’43” 72016’30”
RA-8 - -
RA-9 18032’12” 72015’50”
RA-10 18037’16” 72016’50”
Biological parameters sea water column around Location -1
Chlorophyll-a
In the sub surface water chlorophyll-a was varying from 1.98-2.83-mg/M3 and in the above
bottom water, chlorophyll –a concentration was varying as 0.55-0.98 mg/m3.
Phytoplankton Population
For evaluation of Phytoplankton population in the surroundings of the Rig ABBAN -4 Sampling
was conducted from 10 sampling locations within 2km radius from the rig. The phytoplankton community
of the sub surface water and above bottom water near the rig was represented by two species Blue green
Algae, (Richelia intracellularis and Trichodesmium sp.),9 species of Diatoms ;10 species of
Dinoflagellates and one member of green algae (Pterosperma sp). Phytoplankton of the sampling stations
at sub surface layer was varying from 166- 210 units/ L with an average of185.2 units/L (SD 16.41).
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Phytoplankton from the above bottom samples are very high compare to the other installations
sampled. Phytoplankton population from the various locations around Rig was varying from 54-84 units
/L. with an average of 67.6 units/L (SD. 12.06).
Zooplankton Population
Zooplankton sample collected from the sub surface layer in different sampling locations
around the Rig, ABAN-4. Zooplankton population near the rig ABBAN-4 was represented by 8 groups of
plankton; Tintinids, Polychaete worms, Molluscan larvae, Cindaria( Medusa and Polyp). Molluscans,
Urochordata copepods and Arrow worms. Among these holoplankton of this region Protozoans Tintinids
was dominant group followed by Copepods and Urochordata members. The zooplankton density was
varying from 78-130 N/L at an average of 108.8 (S.D-15.78) among these sampling stations. The biomass
of zooplankton by displacement volume was varying from 0.14ml/m3- 0.14 ml/m3.
BENTHIC COMMUNITIES
Chlorophyll content in the sediment
Chrophyll content in the sediment extracted in acetone was below detectable limits.
Benthic organisms
The Mieo benthic organism collected along with sediments by using the Vanveen grabs were
represented by 2 groups of meio fauna , Nematode worms, Polychate worms.The total number of meio
benthic organisms were varying from 0 -0.14/ 10 cm2.The macro benthic organisms were represented by
the same four groups the abundance was varying from11-55 no/M2.
Table: 4.16 (a) :: Phytoplankton variation in abundance and Diversity of marine phytoplankton in sub
surface water between the sampling stations near Location1
Sampling
Station
Surface water Above Bottom water
Abundance
In units/L
No of Species
observed /total
species
% of
diversity
Abundance
In units/
No of Species
observed /total
species
% of
diversity
1 166 20/23 86.95 76 13/23 56.52
2 190 22/23 95.65 78 14/23 60.86
3 210 21/23 91.30 78 16/23 69.56
4 198 19/23 82.60 84 13/23 56.52
5 164 19/23 82.60 72 12/23 52.17
6 200 21/23 91.30 56 13/23 56.52
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7 170 21/23 91.30 62 12/23 52.17
8 200 19/23 82.60 68 12/23 52.17
9 178 20/23 86.95 48 12/23 52.17
R 176 20/23 86.95 54 13/23 56.52
Table: 4.16(b) Abundance of phytoplankton near Location 1
Installation Surface No of Sampling
location
Group of
phytoplankton
Range
Units/L
Mean
units/L SD
Location-1
Sub surface
10
Blue green algae 50-84 63.6 13.12
Green algae 2-12 5.8 3.58
Diatoms 40-80 64.6 12.03
Dinoflagellates 34-62 51.2 9.43
Total phytoplankton 164-210 185.2 16.41
Above
bottom
10
Blue green algae 10-26 15.4 4.90
Green algae 0 0 0
Diatoms 22-48 39.2 8.85
Dinoflagellates 6-18 13.0 12.56
Total phytoplankton 48-84 67.6 12.06
Table: 4.17(a) Variation in abundance and Diversity of marine Zooplankton in sub surface water between the sampling stations near Location 1
Sampling Station Abundance N/L No of Species/ group/total species % of diversity
1 130 15/16 93.75
2 124 14/16 87.5
3 112 12/16 75.0
4 126 14/16 87.5
5 106 14/16 87.5
6 96 12/16 75.0
7 106 13/16 81.25
8 98 14/16 87.5
9 78 14/16 87.5
R 112 16/16 100
Table: 17(b) Abundance of Zooplankton near Rig ABBAN
Installation Surface No of Sampling locations Range N/L Mean N/L SD
Location-1 Sub surface 10 96-130 108.8 15.78
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Table.4.18: Systematic Account of Phytoplankton in the sea near Location1
GROUP PHYLUM CLASS ORDER FAMILY GENUS/SPECIES #
BLUE GREEN ALGAE
(Desikachary, 1959)
CYANOPHYTA
CYANOPHYCEAEA
NOSTOCALES
NOSTOCACEAE Sub Family Anabanae
Richelia intracellularis
B1
OSCILLATORIACEAE Trichodesmium sp B2
Oscillatoria sp. B3
DIATOMS (Hendey,1937)
BACILLARIOPHYTA CHRYSOPHYTA
BACILLARIOPHYCEAE
ORDER BACILLARIALES Sub Order COSCINODISCACEAE
COSCINODISCACEAE
Coscinodiscus sp. D1
SUB ORDER BIDDULPHINEAE
BIDDULPHIACEAE Eucambia sp. D2
Biddulphia sp. D3
CHATOCERACEAE Chaetoceros costatus D4
SUB ORDER: RHIZOSOLENIINEAE RHIZOSOLENIACEAE Rhizosolenia sp. D5
SUB –ORDER FRAGILARINEAE FRAGILARIACEAE Synreda sp. D6
SUB ORDER NAVICULINEAE
NAVICULACEAE Navicula sp. D7
BACILLARIACEAE Nitzschia sp. D7
DINO FLAGELLATES
PYRROPHYTA
DESMOPHYCEAE
GONYAULACALES
CERATIACEAE
Ceratium breve F1
Ceratium furca F2
Ceratium fusus F3
Ceratium triops F4
CLADOPYXIDACEAE Cladopyxis F5
GONIODOMATACEAE Alexandrium sp. F6
PYROCYSTACEAE Pyrocystis sp. F7
PERIDINIALES PROTOPERIDINIACEAE Protoperidinium sp. F8
NOCTILUCALES NOCTILUCACEAE Naoutiluca F9
GYMNODINIALIS POLYKRIKACEAE Polkrikos sp. F10
GREEN ALGAE CHLOROPHYTA PARSINOPHYCEAE CHLORODENTRALES HALOSPHAERACEAE Pterosperma sp. G1
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Table: 4.19.Quantitative evaluation of marine phytoplankton in sub surface water near Location-1 GENUS/SPECIES Abundance in units/cells / l of marine water from different sampling stations Rep. by group and individual genus/species
1 2 3 4 5 6 7 8 9 R TOTAL AVG %of Group % Total SD
B BLUE GREEN ALGAE
B1 Richelia intracellularis 32 52 60 64 38 58 46 60 44 48 502 50.2 78.93 27.10 10.47
B2 Trichodesmium sp 4 8 6 10 4 8 6 10 6 8 70 7.0 11.00 3.77 2.16
B3 Oscillatoria sp 6 4 12 10 8 2 4 6 10 2 64 6.4 10.06 3.45 3.50
Total Blue green algae units/l 42 64 78 84 50 68 56 76 60 58 636 63.6 34.34 13.12
I DIATOMS
D1 Coscinodiscus sp. 10 8 2 4 0 4 8 6 2 4 48 4.8 7.43 2.59 3.15
D2 Eucambia sp. 12 4 8 0 2 6 2 8 4 10 56 5.6 8.66 3.02 3.86
D3 Biddulphia sp. 12 10 16 10 8 10 14 12 10 8 110 11.0 17.02 5.94 2.54
D4 Chaetoceros costatus 4 8 12 6 10 14 4 8 12 10 88 8.8 13.62 4.75 3.42
D5 Chaetoceros sp. 6 4 2 2 6 8 10 2 4 2 46 4.6 7.12 2.48 2.84
D6 Rhizosolenia sp. 16 18 12 10 14 8 12 10 12 8 120 12.0 18.57 6.48 3.26
D7 Synreda sp. 12 8 10 4 8 6 12 10 6 2 78 7.8 12.07 4.21 3.32
D8 Navicula sp. 6 4 2 0 0 4 2 8 10 12 48 4.8 7.43 2.59 4.13
D9 Nitzschia sp. 2 4 8 4 2 8 10 8 2 4 52 5.2 8.04 2.80 3.01
Total Datoms units/L 80 68 72 40 50 68 74 72 62 60 646 64.6 34.88 12.03
II DINO FLAGELLATES
F1 Ceratium breve 8 12 10 10 6 8 4 10 12 16 96 9.6 18.75 5.18 3.37
F2 Ceratium furca 4 8 10 12 6 10 2 6 8 4 70 7.0 13.67 3.78 3.16
F3 Ceratium fusus 0 4 0 6 0 10 2 0 4 0 26 2.6 5.08 1.40 3.40
F4 Ceratium triops 8 4 10 6 10 12 8 12 10 12 92 9.2 17.96 4.97 2.69
F5 Cladopyxis 0 4 2 4 0 6 0 0 0 6 22 2.2 4.29 1.18 2.57
F6 Alexandrium sp. 6 2 0 0 10 6 12 8 6 10 60 6.0 11.71 3.24 4.21
F7 Pyrocystis sp. 0 6 8 10 12 8 2 4 4 2 56 5.6 10.93 3.02 3.86
F8 Protoperidinium sp. 4 8 10 6 8 2 4 8 4 2 56 5.6 10.93 3.02 2.79
F9 Naoutiluca 2 0 4 0 2 0 0 0 0 0 8 0.8 1.56 1.56 1.39
F10 Polkrikos sp. 2 6 4 8 2 0 4 0 0 0 26 2.6 5.08 1.40 2.83
Total Dinoflagellates units/L 34 54 58 62 56 62 38 48 48 52 512 51.2 27.65 9.43
G GREEN ALGAE
G1 Pterosperma sp. 10 4 2 12 8 2 2 4 8 6 58 5.8 100 3.13 3.58
Total Green Algae Units/L 10 4 2 12 8 2 2 4 8 6 58 5.8 3.13 3.58
Total phytoplankton units/l 166 190 210 198 164 200 170 200 178 176 185.2 185.2 16.41
Chlorophyll –a Content mg/m3 2.61 2.55 1.98 2.22 2.44 2.17 2.83 2.24 1.98 2.12 0.28
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Table: 4.20. Quantitative evaluation of marine phytoplankton in above bottom water near Location-1
GENUS/SPECIES Abundance in units/cells / l of marine water from different sampling stations Representation by group and individual genus/species
1 2 3 4 5 6 7 8 9 R TOTAL AVG %of Group % Total SD
B BLUE GREEN ALGAE
B1 Richelia intracellularis 12 8 10 16 6 4 6 8 12 10 92 9.2 59.74 13.6 3.55
B2 Trichodesmium sp 6 4 8 10 12 6 4 4 4 4 62 6.2 40.26 9.17 2.89
B3 Oscillatoria sp 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Total Blue green algae units/l 18 12 18 26 18 10 10 12 16 14 154 15.4 22.78 4.9
I DIATOMS
D1 Coscinodiscus sp. 6 6 4 2 10 8 4 6 4 8 58 5.8 14.79 8.58 2.39
D2 Eucambia sp. 4 6 2 8 4 2 6 10 6 4 52 5.2 13.26 7.69 2.52
D3 Biddulphia sp. 10 8 12 16 8 12 10 8 4 2 90 9 22.96 13.31 4.02
D4 Chaetoceros costatus 6 4 2 2 0 4 2 0 0 2 22 2.2 5.61 3.25 1.98
D5 Rhizosolenia sp. 10 8 8 12 6 4 8 8 4 10 78 7.8 19.89 11.54 2.57
D6 Synreda sp. 0 0 0 0 2 0 0 0 0 0 2 0.2 0.51 0.29 0.63
D7 Navicula sp. 2 4 2 0 4 2 0 4 2 0 20 2 5.1 2.95 1.63
D8 Nitzschia sp. 10 12 8 6 14 4 4 6 2 4 70 7 17.85 10.35 3.91
Total Datoms units/L 48 48 38 46 48 36 34 42 22 30 392 39.2 8.85
II DINO FLAGELLATES
F1 Ceratium breve 0 0 2 0 0 0 4 2 2 2 12 1.2 9.23 1.77 1.39
F2 Ceratium furca 0 2 2 4 0 0 0 0 0 0 8 0.8 6.15 1.18 1.39
F3 Ceratium fusus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
F4 Ceratium triops 4 6 6 4 2 6 8 10 4 2 52 5.2 40 7.69 2.53
F5 Cladopyxis 0 0 4 0 0 0 0 0 0 0 4 0.4 3.08 0.59 1.26
F6 Alexandrium sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
F7 Pyrocystis sp. 2 4 4 2 0 2 0 0 2 4 20 2 15.38 2.96 1.63
F8 Protoperidinium sp. 4 6 4 2 4 2 6 2 2 2 34 3.4 26.15 5.02 1.64
F9 Naoutiluca 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
F10 Polkrikos sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Total Dinoflagellates units/L 10 18 22 12 6 10 18 14 10 10 130 13 100 69.08 12.56
G GREEN ALGAE
G1 Pterosperma sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Total Green Algae Units/L 0 0 0 0 0 0 0 0 0 0 0 0 0 0
TOTAL PHYTOPLANKTON UNITS/L 76 78 78 84 72 56 62 68 48 54 676 67.6 - 12.06
CHLOROPHYLL –a Content mg/m3 0.98 0.78 0.67 0.55 0.66 0.9 0.9 0.8 0.64 0.6 0.14
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Table: 4.21. Systematic account of marine zooplankton in the subsurface water near –Location1
GROUP PHYLUM CLASS ORDER FAMILY GENUS/SPECIES #
TINTINIDS PROTOZOA
CILIOPHORA
SPIROTRICHEA TINTINNIDA TINTINNIDAE Eutintinnus sp. T1
Amphorides sp..
XYSTONELLIDAE Favella SP.
POLYCHAETE WORMS
ANNELIDA POLYCHAETA PHYLLODOCIDA LOPADORHYNCHIDAE Lopadorhynchus sp.
P1
MOLLUSCANS MOLLUSCA GASTROPODA MESOGASTROPODA ATLANTIDAE Atlanta sp. MO1
COPEPODS
ARTHROPODA
CRUSTACEA
SUB CLASS COPEPODA
CALANOIDA CALANIDAE Canthocalanus sp. C1
ACARTIIDAE Acartia sp. C2
CENTROPAGIDAE Centropages sp. C3
CYCLOPOIDA ONCAEIDAE Oncaea sp. C4
HARPACTICOIDA ECTINOSOMATIDAE Microsetella sp. C5
POLYP CNIDARAIA HYDROZOA
HYDROIDA
THECATA CAMPANULARIIDAE Clytia sp. P1
HYDROIDOMEDUSAE CNIDARAIA HYDROZOA
Proboscoida Campanulariidae Obelia sp. M1
UROCHORDATA CHORDATA
SUB PHYLUM UROCHORDATA
APPENDICULARIA OIKOPLEURIDAE Oikopleura sp. U1
FRITILLARIIDAE Fritillaria sp. U2
ARROW WORMS CHAETOGNATHA SAGITTOIDEA APHRAGMOPHORA SAGITTIDAE Sagitta sp. A1
NUPLIUS LARVAE ARTHROPODA
SUB PHYLM CRUSTACEA
COPEPODA - - Nauplius larvae L1
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Table.4.22: Quantitative evaluation of marine zooplankton in sub-surface water near Location1
GENUS/SPECIES Abundance in n/l marine water from different sampling stations Representation by group and individual genus/species
1 2 3 4 5 6 7 8 9 R TOTAL AVG % of Group % of Total SD
T TINTINIDS
T1 Eutintinnus sp. 22 14 16 30 14 18 20 24 12 16 186 18.6 51.38 17.09 5.50
T2 Amphorides sp.. 12 10 8 12 18 6 10 12 8 10 106 10.6 29.28 9.74 3.27
T3 Favella SP. 4 8 10 6 12 4 2 8 10 6 70 7.0 19.34 6.43 3.16
Total Tininids N/L 38 32 34 48 44 28 32 44 30 32 362 36.2 33.27 6.89
P POLYCHAETE WORMS
P1 Lopadorhynchus sp. 2 4 4 2 2 6 2 2 4 4 32 3.2 100 2.94 1.39
Polychaete worms N/L 2 4 4 2 2 6 2 2 4 4 32 3.2 2.94 1.39
MO MOLLUSCANS
MO1 Atlanta Sp. 4 0 0 2 0 0 0 2 0 6 14 1.4 100 1.29 2.11
Molluscans total N/L 4 0 0 2 0 0 0 2 0 6 14 1.4 1.29 2.11
C COPEPODS
C1 Canthocalanus sp. 8 2 6 4 2 4 6 2 4 2 40 4.0 12.19 3.67 2.10
C2 Acartia sp. 10 14 8 18 6 12 10 4 6 8 96 9.6 29.27 8.82 4.19
C3 Centropages sp. 4 2 4 2 2 2 8 2 4 6 36 3.6 10.98 3.30 2.06
C4 Oncaea sp. 12 16 10 8 12 6 12 10 4 8 98 9.8 29.88 9.00 3.45
C5 Microsetella sp. 6 8 12 4 10 4 6 2 2 4 58 5.8 17.68 5.33 3.32
Total copepods N/L 40 42 40 36 32 28 42 20 20 28 328 32.8 30.14 8.54
MY CNIDARAIA
MY1 Clytia sp. 4 2 2 4 2 2 6 2 2 2 28 2.8 77.77 2.57 1.39
MY2 Obelia sp. 0 0 0 2 0 0 0 0 2 4 8 0.8 22.22 0.74 1.39
Total cindarians N/L 4 2 2 6 2 2 6 2 4 6 36 3.6 3.30 1.69
UROCHORDATA
U1 Oikopleura sp. 10 8 6 4 2 4 8 4 6 2 54 5.4 72.97 4.96 2.67
U2 Fritillaria sp. 4 2 0 0 4 4 0 2 2 2 20 2.0 27.03 1.84 1.63
Total Urochordata N/L 14 10 6 4 6 8 8 6 8 4 74 7.4 6.80 2.98
A ARROW WORMS CHA ETOGNATHA
A1 Sagitta sp. 2 4 0 0 2 4 2 0 0 2 16 1.6 100 1.47 1.57
ARROW WORMS TOTAL NO/L 2 4 0 0 2 4 2 0 0 2 16 1.6 1.47 1.57
L NUPLIUS LARVAE
L1 Nauplius larvae of Copepods 26 30 26 28 18 20 14 22 12 30 226 22.6 100 20.77 6.46
LARVAE TOTAL N/L 26 30 26 28 18 20 14 22 12 30 226 22.6 20.77 6.46
ZOOPLANKTON TOTAL N/L 130 124 112 126 106 96 106 98 78 112 1088 108.8 15.78
BIOMASS DISPLACMENT VOLUMEml / m3 0.14 0.12 0.12 0.12 0.12 0.10 0.12 0.14 0.12 0.12 0.011
Pre-drill EIA for the NELP block MB-OSN-2005/3
67
Table.4.23 Quantitative evaluation of macro fauna near the near Location-1
TAXA
ABUNDANCE IN N/M2 DIFFERENT SAMPLING STATIONS REPRESENTATION BY GROUP
1 2 3 4 5 6 7 8 9 R TOTAL MEAN % OF
COMPOSITION SD
POLYCHATES 11 22 11 0 0 11 22 0 11 11 99 9.9 32.24 8.12
NEMATODES 11 11 22 11 0 0 22 11 11 32 131 13.1 42.67 9.89
CRUSTACEANS 0 0 22 0 11 22 0 22 0 0 77 7.7 25.08 10.43
TOTAL NUMBERS
N/ m2 22 33 55 11 11 33 44 33 22 44 307 30.7 14.48
BIOMASS gm/m2
4.17 4.46 8.75 0.75 2.73 6.08 7.1 3.41 4.19 5.26 2.26
Table 4.24 Macro fauna taxon diversity near the rig – Abban
STATION NUMBER OF TAXA TOTAL DENSITY N/m2 % OF DIVERSITY
1 2/3 22 66.6
2 2/3 33 66.6
3 3/3 55 100
4 1/3 11 33.3
5 1/3 11 33.3
6 2/3 33 66.6
7 2/3 44 66.6
8 2/3 33 66.6
9 2/3 22 66/6
R 2/3 44 66.6
Location-2
Geographical coordinates :: 19014’26” E 70058’52”N
Date of sampling: 26th October, 2013 Time of sampling: 14:00-
19:30
Sampling Stations 1 2 3 4 5 6 7 8 9 R
Depth in meter 79 78.8 79.7 79.4 78.7 79.4 79.4 78.9 79.3 78.3
Sechi disc
depth in meter Not measured as sea was rough
R – Reference station
Pre-drill EIA for the NELP block MB-OSN-2005/3
68
Sampling Station Coordinates
Latitude Longitude
RGD-1 19038’06” 71024’51”
RGD-2 19037’33” 71024’40”
RGD-3 19037’17” 71024’43”
RGD-4 19036’03” 71023’42”
RGD-5 19036’31” 71024’17”
Sampling Station Coordinates
Latitude Longitude
RGD-6 19036’46” 71024’28”
RGD-7 19036’20” 71025’50”
RGD-8 19036’41” 72025’22”
RGD-9 19036’47” 72025’03”
RGD-10 19038’16” 72028’47”
Biological parameters in sea water column around Location-2
Chlorophyll-a
In the sub surface water chlorophyll-a was varying from 1.98-2.83-mg/M3 and in the above
bottom water chlorophyll –a concentration was below detectable limit.
Phytoplankton Population
For evaluation of Phytoplankton population in the surroundings of the Rig G.D Chayya.
Sampling was conducted from 9 sampling locations within 2km radius from the rig. The phytoplankton
community of the sub surface water and above bottom water near the rig was represented by two species
Blue green Algae, (Richelia intracellularis, Trichodesmium sp.),9 species of Diatoms and 10 species of
Dinoflagellates. Phytoplankton of the sampling stations at sub surface layer was varying from 178-254
units/ L with an average of 211.2 units/L (SD 23.70).
Blue green algae Richelia intracellularis was present in large number in the sub surface water
along with one associated diatom Rhizosolenia sp. These two algae were the dominant among the
phytoplankton in the surface water around these region. Phytoplankton from the above bottom samples
the various locations around Rig was very low varying from 24-58 units /L. with an average of 44.0 units/L
(SD. 11.07).
Zooplankton Population
Zooplankton samples were collected from the sub surface layer in different sampling locations
around the Rig G.D. Chayya. Zooplankton population near the rig was represented by 6 groups of
plankton; Tintinids copepods, Cindararians (medusa and polyp), Urochordata members and arrow
worms. Among these, Protozoans Tintinids was dominant group followed by Copepods, The zooplankton
density was varying from 56-100 No/L with an average value of 81.2 N/L (S.D-14.70) among the sampling
stations. The biomass of zooplankton by displacement volume was varying from 0.02ml/m3- 0.05 ml/m3.
Pre-drill EIA for the NELP block MB-OSN-2005/3
69
BENTHIC COMMUNITIES
Chlorophyll content in the sediment
Chlorophyll content in the sediment extracted in acetone was below detectable limits.
Benthic organisms
The Mieo benthic organism collected along with sediments by using the Vanveen grabs were
represented by 2 groups of meio fauna, Nematode worms, Polychaete worms, The total number of meio
benthic organisms were varying from 0 -0.06 / 10 cm2.The macro benthic organisms were represented
by Nematode worms, Polychaete worms and crustaceans groups but the abundance was s varying from
11 -55 no/M2.
Table: 24 (a) Phytoplankton variation in abundance and Diversity in subsurface and above bottom water
between the sampling stations near Location-2
Sampling
Station
Surface water Above Bottom water
Abundance
In units/L
No of Species observed
/total species
% of diversity Abundance
In units/L
No of Species observed
/total species
% of diversity
1 232 20/22 90.90 58 10/22 45.45
2 218 18/22 81.81 60 9/22 40.90
3 188 18/22 81.81 50 9/22 40.90
4 202 16/22 72.72 42 6/22 27.27
5 188 19/22 86.36 46 7/22 31.81
6 254 17/22 77.27 38 7/22 31.81
7 222 16/22 72.72 38 5/22 22.72
8 228 17/22 77.27 50 6/22 27.27
9 202 14/22 63.63 24 5/22 22.72
R 178 15/22 68.18 34 5/22 22.72
Pre-drill EIA for the NELP block MB-OSN-2005/3
70
Table: 24 (b) Abundance of phytoplankton near Location2
Installation Surface No of Sampling location
Group of phytoplankton
Range Units/L
Mean units/L
SD
Rig
G.D hayya (Loc-2)
Sub surface 10
Blue green algae 48-88 67.6 15.22
Green algae 2-12 7.2 3.12
Diatoms 72-114 91.4 10.28
Dinoflagellates 26-68 45.0 11.39
Total phytoplankton 178-254 211.2 23.70
Above bottom 10
Blue green algae 8-22 13.4 4.2
Green algae 2-4 0.6 1.28
Diatoms 10-26 16.8 4.99
Dinoflagellates 4-22 13.2 5.81
Total phytoplankton 24-58 44.0 11.07
Table: 25 (a) Variation in abundance and Diversity of marine Zooplankton in sub surface water between
the sampling stations near Installation Location -2
Sampling
Station
Abundance N/L No of Species/ group/total species
% of diversity
1 80 17/20 85
2 94 18/20 90
3 82 17/20 85
4 66 14/20 70
5 56 17/20 85
6 64 16/20 80
7 86 15/20 75
8 90 16/20 80
9 94 16/20 80
R 100 18/20 90
Table: 25 (b) Abundance of Zooplankton near Location-2
Installation Surface No of Sampling locations
Range
N/L
Mean
N/L
SD
Rig
G.D Chayya (Loc-2)
Sub surface 10 56-100 81.2 14.70
Pre-drill EIA for the NELP block MB-OSN-2005/3
71
Table: 4.26: Systematic account of marine phytoplankton in the subsurface water in the sea near Location-2
GROUP PHYLUM CLASS ORDER FAMILY GENUS/SPECIES #
BLUE GREEN
ALGAE (Desikachary,
1959)
CYANOPHYTA
CYANOPHYCEAEA
NOSTOCALES
NOSTOCACEAE Sub Family Anabanae
Richelia intracellularis
B1
OSCILLATORIACEAE Trichodesmium sp B2
DIATOMS (Hendey,1937)
BACILLARIOPHYTA CHRYSOPHYTA
BACILLARIOPHYCEAE
ORDER BACILLARIALES Sub Order
COSCINODISCACEAE COSCINODISCACEAE Coscinodiscus sp. D1
SUB ORDER BIDDULPHINEAE
BIDDULPHIACEAE Eucambia sp. D2
Biddulphia sp. D3
CHATOCERACEAE Chaetoceros costatus D4
Chaetoceros sp. D5
SUB ORDER: RHIZOSOLENIINEAE
RHIZOSOLENIACEAE Rhizosolenia sp. D6
SUB –ORDER FRAGILARINEAE
FRAGILARIACEAE Synreda sp. D7
SUB ORDER NAVICULINEAE
NAVICULACEAE Navicula sp. D8
BACILLARIACEAE Nitzschia sp. D9
DINO FLAGELLATES
PYRROPHYTA
DESMOPHYCEAE
GONYAULACALES
CERATIACEAE
Ceratium breve F1
Ceratium furca F2
Ceratium fusus F3
Ceratium triops F4
CLADOPYXIDACEAE Cladopyxis F5
GONIODOMATACEAE Alexandrium sp. F6
PYROCYSTACEAE Pyrocystis sp. F7
PERIDINIALES PROTOPERIDINIACEAE Protoperidinium sp. F8
NOCTILUCALES NOCTILUCACEAE Naoutiluca F9
GYMNODINIALIS POLYKRIKACEAE Polkrikos sp. F10
GREEN ALGAE CHLOROPHYTA PARSINOPHYCEAE CHLORODENTRALES HALOSPHAERACEAE Pterosperma sp. G1
Pre-drill EIA for the NELP block MB-OSN-2005/3
72
Table: 4.27: Quantitative evaluation of marine phytoplankton in sub surface water near Location-2
GENUS/SPECIES Abundance in units/cells / l of marine water from different sampling stations Rep. by group and individual genus/species
1 2 3 4 5 6 7 8 9 R TOTAL AVG %of Group. % Total SD
B BLUE GREEN ALGAE
B1 Richelia intracellularis 60 48 42 76 40 78 68 84 60 48 604 60.4 89.35 28.59 14.93
B2 Trichodesmium sp 12 8 4 10 12 0 14 4 8 0 72 7.2 10.65 3.40 4.75
Total Blue green algae units/L 72 56 46 86 52 78 82 88 68 48 676 67.6 15.22
I DIATOMS
D1 Coscinodiscus sp. 8 4 0 0 4 8 6 2 0 10 42 4.2 4.59 1.98 3.52
D2 Eucambia sp. 8 10 4 12 6 10 8 12 10 2 82 8.2 8.97 3.88 3.15
D3 Biddulphia sp. 12 14 10 10 6 4 16 12 14 12 110 11.0 12.03 5.21 3.49
D4 Chaetoceros costatus 10 18 12 8 16 4 12 10 12 8 110 11.0 12.03 5.21 3.82
D5 Chaetoceros sp. 8 0 0 4 0 0 0 0 0 0 12 1.2 1.31 0.56 2.56
D6 Rhizosolenia sp. 42 28 36 24 34 40 30 32 46 50 362 36.2 39.60 17.14 7.82
D7 Synreda sp. 4 0 12 2 4 6 0 0 0 2 30 3.0 3.28 1.42 3.60
D8 Navicula sp. 12 8 6 2 4 12 6 4 2 4 60 6.0 6.56 2.84 3.46
D9 Nitzschia sp. 10 12 8 10 12 16 10 14 8 6 106 10.6 11.59 5.02 2.83
Total Datoms units/L 114 94 88 72 86 100 88 86 92 94 914 91.4 43.28 10.28
II DINO FLAGELLATES
F1 Ceratium breve 10 12 8 10 16 14 22 10 14 8 124 12.4 27.55 5.87 4.08
F2 Ceratium furca 4 4 2 0 2 4 10 4 0 0 30 3.0 6.66 1.42 2.86
F3 Ceratium fusus 2 0 6 0 6 0 4 6 0 0 24 2.4 5.33 1.14 2.65
F4 Ceratium triops 6 8 2 4 6 4 0 2 6 10 48 4.8 10.66 2,27 2.86
F5 Cladopyxis 0 4 0 0 2 0 0 0 0 0 6 0.6 1.33 0.28 1.28
F6 Alexandrium sp. 4 6 2 0 8 4 6 10 6 4 50 5.0 11.11 2.36 2.72
F7 Pyrocystis sp. 0 4 0 0 0 0 0 0 0 0 4 0.4 0.88 0.19 1.2
F8 Protoperidinium sp. 4 8 12 10 2 6 14 8 6 2 72 7.2 16.0 3.41 3.81
F9 Naoutiluca 4 0 8 2 0 6 0 0 0 0 20 2.0 4.44 0.94 2.82
F10 Polkrikos sp. 6 12 8 6 4 10 12 4 8 2 72 7.2 16 3.41 3.24
Total Dinoflagellates units/L 40 58 48 32 46 48 68 44 40 26 450 45.0 21.31 11.39
G GREEN ALGAE
G1 Pterosperma sp. 6 10 6 12 4 8 4 10 2 10 72 7.2 100 3.41 3.12
Total Green Algae Units/L 6 10 6 12 4 8 4 10 2 10 72 7.2 100 3.41 3.12
Total phytoplankton units/l 232 218 188 202 188 254 222 228 202 178 2112 211.2 23.70
CHLOROPHYLL –a Content mg/m3
2.61 2.55 1.98 2.22 2.44 2.17 2.83 2.24 2.12 1.98 0.28
Pre-drill EIA for the NELP block MB-OSN-2005/3
73
Table.4.28: Quantitative evaluation of marine phytoplankton in above bottom water near Location-2
GENUS/SPECIES Abundance in units/cells / l of marine water from different sampling stations Representation by group and individual genus/species
1 2 3 4 5 6 7 8 9 R TOTAL AVG %of Group. % Total SD
B BLUE GREEN ALGAE
B1 Richelia intracellularis 10 20 12 16 18 10 12 16 8 10 132 13.2 98.51 30.0 3.82
B2 Trichodesmium sp 0 2 0 0 0 0 0 0 0 0 2 0.2 1.49 0.45 0.6
Total Blue green algae units/l 10 22 12 16 18 10 12 16 8 10 134 13.4 4.2
I DIATOMS
D1 Coscinodiscus sp. 2 0 4 0 0 0 0 0 0 0 6 0.6 3.57 1.36 1.28
D2 Eucambia sp. 0 2 0 0 0 0 0 0 0 0 2 0.2 1.19 0.45 0.6
D3 Biddulphia sp. 6 8 2 10 4 2 0 4 2 6 44 4.4 26.19 10.0 2.93
D4 Chaetoceros costatus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
D5 Chaetoceros sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
D6 Rhizosolenia sp. 18 12 10 6 12 8 10 16 10 14 116 11.6 69.04 26.36 3.44
D7 Synreda sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
D8 Navicula sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
D9 Nitzschia sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Total Datoms units/L 26 22 16 16 16 10 10 20 12 20 168 16.8 38.18 4.99
II DINO FLAGELLATES
F1 Ceratium breve 8 2 6 0 4 6 4 6 2 2 40 4.0 30.30 9.09 2.36
F2 Ceratium furca 2 6 6 4 2 2 8 2 2 2 36 3.6 27.27 8.18 2.15
F3 Ceratium fusus 0 0 2 0 4 0 0 0 0 0 6 0.6 4.54 1.36 1.28
F4 Ceratium triops 4 4 4 4 0 0 4 0 0 0 20 2.0 15.15 4.54 2.0
F5 Cladopyxis 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
F6 Alexandrium sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
F7 Pyrocystis sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
F8 Protoperidinium sp. 2 4 4 0 2 6 0 6 0 0 24 2.4 18.18 5.45 2.33
F9 Naoutiluca 2 0 0 0 0 4 0 0 0 0 6 0.6 4.54 1.36 1.28
F10 Polkrikos sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Total Dinoflagellates units/L 18 16 22 8 12 18 16 14 4 4 132 13.2 330.0 5.81
G GREEN ALGAE
G1 Pterosperma sp. 4 0 0 2 0 0 0 0 0 0 6 0.6 100 1.36 1.28
Total Green Algae Units/L 4 0 0 2 0 0 0 0 0 0 6 0.6 - - 1.28
Total phytoplankton units/l 58 60 50 42 46 38 38 50 24 34 440 44.0 - - 11.07
Chlorophyll –a Content mg/m3 ND ND ND ND ND ND ND ND ND ND 0.26
Pre-drill EIA for the NELP block MB-OSN-2005/3
74
Table - 4.29: Systematic account of marine zooplankton in the subsurface water near Location-2
GROUP PHYLUM CLASS ORDER FAMILY GENUS/SPECIES #
TINTINIDS PROTOZOA CILIOPHORA
SPIROTRICHEA TINTINNIDA TINTINNIDAE Eutintinnus sp. T1
Amphorides sp..
XYSTONELLIDAE Favella SP.
RHABDONELLIDAE Rhabdonella sp.
CODONELLIDAE Tintinnopsis acuminata
COPEPODS
ARTHROPODA
CRUSTACEA
SUB CLASS COPEPODA
CALANOIDA CALANIDAE Canthocalanus sp. C1
ACARTIIDAE Acartia sp. C2
CENTROPAGIDAE Centropages sp. C3
CYCLOPOIDA ONCAEIDAE Oncaea sp. C4
HARPACTICOIDA ECTINOSOMATIDAE Microsetella sp. C5
POLYP CNIDARAIA HYDROZOA HYDROIDA
THECATA CAMPANULARIIDAE Clytia sp. P1
HYDROIDOMEDUSAE CNIDARAIA HYDROZOA
Proboscoida Campanulariidae Obelia sp. M1
UROCHORDATA CHORDATA SUB PHYLUM
UROCHORDATA
APPENDICULARIA OIKOPLEURIDAE Oikopleura sp. U1
FRITILLARIIDAE Fritillaria sp. U2
ARROW WORMS CHAETOGNATHA SAGITTOIDEA APHRAGMOPHORA SAGITTIDAE Sagitta sp. A1
NUPLIUS LARVAE ARTHROPODA SUB PHYLM CRUSTACEA
COPEPODA - - Nauplius larvae L1
Pre-drill EIA for the NELP block MB-OSN-2005/3
75
Table.4.30: Quantitative evaluation of marine zooplankton in sub surface water near Location-2
GENUS/SPECIES Abundance in n/l marine water from different sampling stations Representation by group and individual genus/species
1 2 3 4 5 6 7 8 9 R TOTAL AVG % of Group % of Total SD
T TINTINIDS
T1 Eutintinnus sp. 8 6 10 4 2 10 6 8 10 12 76 7.6 32.47 9.36 2.93
T2 Amphorides sp.. 0 2 0 0 0 0 4 0 0 6 12 1.2 5.13 1.48 2.04
T3 Favella SP. 4 10 6 2 4 2 6 10 2 4 50 5.0 21.37 6.16 2.86
T4 Rhabdonella sp. 2 0 0 2 6 4 0 0 0 2 16 16 6.84 1.97 1.95
T5 Tintinnopsis acuminata 10 8 12 6 4 2 8 12 10 8 80 8.0 34.18 9.85 3.09
Total Tininids N/L 24 26 28 14 16 18 24 30 22 32 234 28.82 5.66
C COPEPODS
C1 Canthocalanus sp. 4 8 6 2 4 6 10 6 12 6 64 6.4 21.33 7.88 2.8
C2 Acartia sp. 6 12 2 4 2 6 6 4 10 12 64 6.4 21.33 7.88 3.55
C3 Centropages sp. 2 4 2 0 2 2 0 6 8 4 30 3.0 10.0 3.69 2.40
C4 Oncaea sp. 10 6 8 12 6 2 8 12 4 2 70 7.0 23.33 8.62 3.49
C5 Microsetella sp. 8 6 6 10 4 2 6 8 10 12 72 7.2 24.0 8.86 2.85
Total copepods N/L 30 36 24 28 18 18 30 36 44 36 300 30.0 - 36.94 7.95
M CNIDARAIA
M1 Clytia sp. 2 0 2 0 0 0 0 0 0 2 6 0.6 75.0 0.74 0.92
M2 Obelia sp. 0 2 0 0 0 0 0 0 0 0 2 0.2 25.0 0.25 0.6
Total cindarians N/L 2 2 2 0 0 0 0 0 0 2 8 0.8 - 0.98 0.98
U UROCHORDATA
U1 Oikopleura sp. 6 10 8 12 6 8 10 2 8 10 80 8.0 83.33 9.85 2.68
U2 Fritillaria sp. 0 4 2 0 4 0 0 4 2 0 16 1.6 16.67 1.97 1.74
Total Urochordata N/L 6 14 10 12 10 8 10 6 10 10 96 9.6 - 11.82 2.33
A ARROW WORMS CHA ETOGNATHA
A1 Sagitta sp. 2 4 2 0 2 6 2 4 2 2 26 2.6 100 3.20 1.56
ARROW WORMS TOTAL NO/L 2 4 2 0 2 6 2 4 2 2 26 2.6 - 3.20 1.56
L NUPLIUS LARVAE
L1 Nauplius larvae of Copepods 16 12 16 12 10 14 20 14 16 18 148 14.8 100 18.23 2.85
LARVAE TOTAL N/L 16 12 16 12 10 14 20 14 16 18 148 14.8 - 18.23 2.85
ZOOPLANKTON TOTAL N/L 80 94 82 66 56 64 86 90 94 100 812 81.2 - 14.70
BIOMASS DISPLACMENT VOLUMEml / m3
0.04 0.04 0.03 0.02 0.03 0.04 0.05 0.04 0.04 0.05 - - - - 0.008
76
Table.4.31: Quantitative evaluation of macro fauna on rig near Location2
TAXA
ABUNDANCE IN N/M2 DIFFERENT SAMPLING STATIONS REPRESENTATION BY GROUP
1 2 3 4 5 6 7 8 9 R TOTAL MEAN % OF
COMPOSITION SD
POLYCHATES 0 0 11 0 11 22 0 11 11 11 77 7.7 27.02 7.42
NEMATODES 22 11 32 11 11 22 11 0 22 22 164 16.4 57.54 9.15
CRUSTACEANS 0 0 11 0 0 11 0 0 0 22 44 4.4 15.44 7.69
TOTAL NUMBERS NO/
m2 22 11 54 11 22 55 11 11 33 55 285 28.5 - 19.39
BIOMASS gm/m2
3.01 1.39 5.68 1.82 4.60 8.66 1.39 1.07 4.03 7.21 2.64
Table.4.32: Macro fauna taxon diversity of the rig Near Location-2
Station Number Of Taxa Total Density No/m2 % Of Diversity
1 1/3 22 33.3
2 1/3 11 33.3
3 3/3 54 100
4 1/3 11 33.3
5 2/3 22 66.6
6 3/3 55 100
7 1/3 11 33.3
8 1/3 11 33.3
9 2/3 33 66.6
R 3/3 55 100
Fish and Fisheries
Coastal fishery is an important commercial activity as it plays a vital role in regional and
national economy of a maritime state. However, coastal fishery is facing many problems largely due to
the increased level of pollution and management. It has been successfully demonstrated that coastal
pollution can seriously affect the fishable stocks. Consequently, significant efforts are put in assessing
fishery resources both on the regional as well as local level. In this context, the presence or absence of
particular fish species and their standing stock has been widely used as a biological indicator of the
degree of pollution.
The success of any fishery depends upon the prevailing' physicochemical and biological
conditions and hence the study of environmental factors is important for the assessment of fishery
77
resources. The effect of effluent or waste disposal in the aquatic environment inevitably includes
modifications and changes in the physico-chemical and biological characteristics of the ecosystem.
These changes are more pronounced in the semi-enclosed water bodies such as estuaries and bays
where water circulation is limited. The toxic effluent once discharged into the environment produces
characteristic response and sometimes mortality among the biota including fish and fishery. Such
responses can be measured on the biological scale. Hence, evaluation of biological productivity
(microbes, phytoplankton, zooplankton and benthos) of an ecosystem is an integral part of any
environmental impact assessment. Such studies are concerned with identifying, predicting and evaluating
the environmental effects of waste water/effluent discharge. It employs the scientific methodologies and
techniques for collecting baseline data which at later stage will be useful in planning and decision making.
Experimental fishing was done along two transects, at 30~ 50 m water depth zone Finfish and
shellfish samples were brought in iceboxes to the field laboratory and kept deep frozen for identification.
Samples of each species were sorted, counted and weighed. Fishes were identified up to species level
following FAO species identification sheets for fisheries purposes, western Indian Ocean (Fisher and
Bianchi, 1984). Species occurrence (total number of species), abundance (number of fishes and catch
rate per hour) were calculated.
Abundance and density
The relative abundance (total fish number and biomass) and number of demersal fishes
caught in the selected area is presented below. A catch rate of 120 kg/hr and 65 kg/hr was obtained in
depth zones of 50 m and 30 m, respectively. Even though the weight was higher, trawl catch obtained
from 50 m depth zone was of poor quality and mainly consisted of gastropods, jellyfish etc., Hence, only
catch from 30 m depth zone was considered for detailed fishery assessment.
Species Occurrence
The fish community was typical of Indio-Pacific type. The demersal fish assemblage was
dominated in terms of abundance by members of the family, Penaeidae (19.4%), Trichiuridae (16.2%),
Portunidae (15%) Scienidae (14%), Synodontidae (7%), Leognanthidae (5.8%) and Cynoglossidae
(5.4%) were the main contributos. Others such as families Tetradontidae, Carcharinidae together
contributed to the remainder of the catch (~ 13%). Different crustacean and molluscan species were
recorded in the trawl catch. Amongst crustaceans, prawns were the most dominant. Prawns belonging to
family Penaeidae, Solenoceridae, Sergestidae, Sicyonidae consistently occurred. Crustacean species in
order to the abundance were Acetus Indiicus, Deep sea shrimp, Solenocera sp. and Metapenaeus sp
and crab species (Porunus sp. and Charybdis sp.). While two species Charybdis annulata and
Cryptopodia angulata were reported first time from the Mumbai High region.
78
The high population density of bottom fauna (demersal fish and benthos) in the study area
reflects on the high biological productivity and rich fishing grounds. The occurrence of large number of
juveniles in the trawl samples indicate that the area may serve as nursery ground for commercially
important fin and shellfishes. Furthermore, high occurrence of decapod larvae, fish eggs and larvae in
zooplankton samples substantiates it. The mean catch rate of 80 kg/hour is well comparable to some of
the nearshore fishing grounds along the west coast of India (Parulekar et al., 1982).
Table 4.33: Relative abundance in the fishes during the sampling
# Scientific name Common name Relative abundance
no/Haul
Relative Biomass gm/ haul
1 Combionella buitendijki Jelly fish 20 -
2 Octopus sp. Octopus 12 3500
3 Sepia elliptica Cuttle Fish 7 560
4 Loligo duvauceli Indian squid 4 450
5 Penaeus indicus Indian White Prawn 12 1000
4 Penaeus monodon TigerPrawn 20 800
5 Eugomphodus Taurus Sand Tiger Shark 2 1400
6 Carcharhinus dussumieri White Cheeked Shark
1 1100
7 Sardinella longiceps Sardine 12 1800
8 Congresox telabonoides Common Ell 2 600
9 Hardpodon nehereus Bombay Duck 32 3000
10 Trichiurus lepturus Ribbon Fishes 4 400
11 Lepturacanthus savla Ribbon Fishes 2 300
12 Arius sp. Arius sp. 4 1500
13 Rastrelliger kanagurta Indian Mackerel 10 2500
79
Chapter 5
ANTICIPATED ENVIRONMENTAL IMPACTS
& MITIGATION MEASURES
5.1. ENVIRONMENTAL IMPACTS IDENTIFIED:
This section identifies and attempts at assessing the aspects arising due to drilling activity which may
have environmental (Physical and Biological). The following factors which were analyzed for the impact
study based on secondary data constituting the baseline study of.
Offshore air and noise quality
Marine water quality & temperature
Biological environment
Benthic community
Marine micro-organisms, fish, reptiles, mammals, seabirds
Marine ecology
Occupational safety of personnel
Environmental aspects (based on phases of activities pre drilling, drilling, decommissioning
and potential accidental events) and impacts on offshore environment have been taken into consideration
in line with standard management system terminology. It is imperative that an environmental or socio-
economic impact may result from any of the project activity.
Disposal of Drill Cuttings and Residual WBM:
Drill cuttings, composed of rocky substrate like shale, clay, sandstone, etc. are produced
during the drilling process and are separated from the mud. Typically, the solid medium used in the drilling
mud is barite (barium sulfate) as weighing agent, with bentonite clays as a thickener. Drilling mud also
contains a number of chemicals that are added depending on down-hole formation conditions.
Thoroughly washed drill cuttings are dispersed into the sea.
ONGC instituted a study on the drill cuttings and their toxicity through CRRI (Central Road
Research Institute, New Delhi) which reveals that there is no toxicity in any of the samples
of drill cuttings analyzed and the drill cuttings were found to be inert in nature.
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Mud system analyses data has been found to be much below the prescribed toxicity limit;
the relevant portion from the report published by Institute of Drilling Technology, ONGC,
Dehradun is annexed at Annexure – IV at the end of the report.
Impacts on Marine Water and Sediment as given below.
5.1.1. Impacts on Marine Water and Sediment:
Number of activities related to various phases of the proposed drilling activity has the potential
to impact marine water quality and consequently marine ecology adjacent to the drilling locations. Some
marine water quality impacts will also occur along corridors that are proposed to be used for providing
logistic support to the drilling rig, though they are anticipated to be minimal. Some near shore activities
like handling of chemicals and oil may also impact marine environment. The important potential
anticipated impacts to marine environment are discussed under the following major heads:
Physical presence of the drilling rig
Disposal of drill cuttings and WBM
Operational discharges like sanitary waste water, washing fluids (deck drainage, rig floor
washing, etc.,), cooling water,, etc.,
Non-routine discharges that may be caused by ballast water, chemical spills, etc.
Food waste and residuals.
Impacts on Marine Water Quality:
The main physical impacts on seawater from the discharge of cuttings and drilling fluids are
associated with a localized increase in water turbidity (due to increase in suspended solids) in the vicinity
of discharge point and minor changes in local water quality.
Impact on Benthic Fauna:
The main impact on benthic fauna will be from physical smothering and restricted to areas
where cuttings are deposited. Studies suggest that biological effects of WBM contaminated cuttings will
be confined within 100 m from well location (Effects of Exploratory Drilling Discharges on the Benthos.
Gillmor R. B. Et al.). Re-colonization of biota and recovery will be well established within a year after
disposal has stopped.
Under less energetic wave and current conditions, impacts recovery may take more time;
however taking into account that project site is located in high waters of Arabian Sea characterized by a
high energy environment, impacts on benthos due to smothering and physical disturbance are anticipated
to be minimal and of short duration.
Toxic effects on marine species of this substratum are also not anticipated due to low toxicity
of mud formulation to be used for the proposed project. Data from previous studies indicate that major
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biological changes in benthic communities mostly extend to a maximum of 500 – 1000 m (GESAMP,
1993); in addition to minor detectable changes extending to a maximum of about 3 – 5 km from the drilling
location (Gray et al., 1999).
Discharge of Grey and Black Water
It is estimated that Drilling rig operations will result in the generation of about 10 m3/day of
sewage and wastes from kitchen, shower and laundry area. Sewage will be subsequently discharged
into marine environment after passing it through a screen less than 25 mm diameter prior to discharge.
It is likely that such discharge can result in localized organic enrichment in the vicinity of the discharge
point that in turn can result in potential oxygen depletion in the discharge plume resulting in some minor
disturbance to the marine ecosystem close to point of discharge - treatment/maceration of effluents will
be carried out in compliance with MARPOL 73/78 requirements.
Water currents would also assist dilution and dispersion of discharged material and would
eventually restore oxygen and nutrient levels to background conditions. Impacts on marine water quality
and marine organisms are therefore considered to be significantly low.
Disposal of Bilge Fluids and Drainage Water
Bilge and drainage waters generated on Drilling rig have the potential to be contaminated with
oily wastes. Drilling rig will be having designated containment and bounding zones where oil products will
be used and stored. While no wastes will be routinely discharged by deck drains, wash down of the decks,
rig floor, pipe rack,, etc., may result in minor quantities of chemical residues (primarily oil and grease)
entering into the marine environment. Drainage water discharges would therefore contain very low levels
of oil and would be readily dispersed after discharge resulting only in some minor localized impact on
marine species. Bilge fluids generated will be treated on-site on Drilling rig in water/oil separator. Effluents
of separated oil will be shipped to onshore periodically in special drums/containers whereas effluent of
separated water will be discharged in sea. Concentration of oil in water discharged will be restricted in
accordance with the International Convention for the Prevention of Pollution from Ships, 1973, as
modified by the Protocol of 1978 (MARPOL 73/78). Meeting requirements for disposal of oil or oily
mixtures at sea, any impact arising from discharge of such treated effluent is therefore considered to be
negligible.
Disposal of Kitchen & Food Wastes
Kitchen & Food waste generated from drilling rig would be macerated (by passing it through
25 mm screen) and discharged directly to water column. Large-scale discharges of organic material can
result in increased biological productivity in the vicinity of the discharge point with a resultant reduction in
dissolved oxygen in receiving waters. Given the limited number of personnel that would be onboard rig
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(i.e. maximum 100) combined with the anticipated level of dispersion and mixing of wastes in water
column, it is considered that impacts on marine water ecosystem from discharge of such wastes may be
incrementally positive.
Non Routine Discharges
Ballast Water Discharges
The discharge of ballast water from vessels coming into the area can be categorized as a
non-routine discharge and may lead to introduction of exotic species contained in ballast water and
displacement of native species. Discharge of ballast water from Drilling rig and vessels, while in the area
of operations, may also lead to release of low levels of oils and chemicals into marine environment.
Although the probability of ballast water being discharged during the project is considered to be high,
scope of impact will be local with intensity of such impact varying from low to medium. However, it will be
ensured that any discharge of ballast water would be carried out following international maritime guidance
and legal requirements.
5.1.2. Generation & Impacts of Noise
Major noise generating sources during offshore drilling and testing activities will:
Rotary drilling equipment as part of rig;
Diesel engines for power generation;
Mud pumps;
Cranes and material handling equipment;
Supply vessels and helicopter movement
As drilling activity is continuous, part of noise associated with the functioning of rig and ancillaries will
be generated only during drilling hours.
Sound pressure levels associated with drilling are the highest with maximum broadband (10 Hz to 10
kHz) energy of about 190 dB re 1μPa @ 1 m.
Noise Impacts
Project related activities including offshore drilling will lead to considerable local level emission
of noise that may have significant impact on the occupational health of drilling crew and personnel housed
on the drilling rig. Potential impacts on noise quality may arise from air borne noise generated during
drilling operations of rotary drilling equipment, diesel engines for power generation and mud pumps,
leading to perceptible increase in ambient noise levels in immediate vicinities. Noise is also likely to be
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generated during rig mobilization and also during operation of supply vessels and helicopter. However,
noise so generated will be comparable in level to other drilling related activities and would be continuous
in places (drilling location and ports) and intermittent along transportation routes. The value range of
noise generated from various sources during offshore exploratory drilling operations is as follows:
Helicopter : 103 to 105 dB(A)
Diesel Generators : 60 to 70 dB(A)
Mud Pumps at the Rig : 90 to 100 dB(A)
Upper Decks : 65 to 73 dB(A)
Control Room & Quarters : 50 to 60 dB(A)
In addition, drilling would also result in generation of underwater noise which has the potential
to affect the marine ecology in and around the drill locations. The quantum of noise, its quality and related
impacts and their significance is discussed in the following paragraph.
Atmospheric Noise Emanated from Rig and DG Sets Drilling rig and associated machinery,
including high power DG sets, mud pumps, shakers, etc., will emit very high noise during drilling
operations. Typical noise levels emanated from drilling rig and DG sets are of the order of 95 – 100 db
(A) and 100 -105 db (A) respectively.
Moreover, as drilling is a continuous (24x7) activity, such noise will be emitted during both
daytime and nighttime and may lead to significant impact on drilling crew on rig, unless proper mitigation
measures are implemented. The offshore project block is located in shallow sea but at a considerable
distance from the coastal area, so the above impacts are expected to be localized and have potential
effect only on workers at site.
Noise Emanated from Supply Vessels and Helicopter Movement
Supply vessels and helicopters will be deployed for transportation of resources (water, fuel
and equipment, etc.) and personnel to the drilling rig respectively. This will result in an incremental
increase of noise levels because of additional maritime traffic along the supply routes. However, noise
levels increase will be intermittent having only localized impacts along the corridor of no or low
significance. Also, since there exist predefined shipping routes near to Nhava base, it is expected that
marine animals in this region are accustomed to noise generated from passing vessels. Although vessel
activity along the shipping route between shore and offshore block would increase, it is expected that if
animals initially displayed avoidance behavior, they would eventually return to the affected area once
they become accustomed to the increased noise levels or once noise source had moved or ceased.
Taking into account limited movement of such vessels and helicopters any cumulative noise related
impacts arising from vessel activities are therefore considered to be negligible.
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In addition, noise impacts are measured in terms of logarithmic equivalent (LeQ) averaged
over hours, considering transient nature of project and intermittent plying of transport vessels and
helicopters (moving sources), no significant impact is envisaged.
5.1.3. Marine Ecological Impacts
Impacts from Physical Presence of Rig
Drilling rig to be utilized for the offshore exploratory project is a Jack-up type of MODU, which
will be stationed at each of the drilling locations. Underwater structures and apparatus like risers will be
sunk from rig to the sea floor to enable drilling operations. It is a well-established fact the such sub-sea
structures can provide new stable areas for marine flora and fauna to colonize. Development of colonies
may in fact be beneficial for the local fish populations. In this event, the structures may attract marine
species to the area as the structures in effect form artificial reefs where fish can seek food, shelter and
protection. Such positive effects have been confirmed by research studies conducted on fish population
near offshore installations. Such studies have revealed that fish growing around the manned and
unmanned installations were found to grow better than those caught at a remote site unaffected by
manmade structures (Mathers et al., 1992b). It was also found that fish caught around the man-made
installations were in good condition with no evidence of lesions or other defects on their skin (Mathers et
al., 1992b).
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Chapter-6
ENVIRONMENTAL MANAGEMENT PLAN
6.1. MUD MAKE-UP AND MUD & CUTTINGS DISPOSAL:
As has been elucidated earlier that the mud system used in drilling by ONGC is largely inert
in nature and contains no toxicity, the same will be disposed of into the sea only after drying and on being
washed thoroughly as per standard legal guidelines. In addition, WBM mud system will be used following
the 2005 guidelines/ notification of MoEF and accordingly, the rate of discharge of discharge of the drill
cuttings into the sea will be <= 50 bbls per hour
Mitigation measures for discharge of mud cuttings will include the following:
Strict compliance with regulatory provisions relating selection of drilling fluid chemicals,
separation of drilling fluid from cuttings and proper washing of drill cuttings;
Design of disposal mechanism to ensure sufficient dispersal of discharged cuttings, thereby
causing minimal impacts on marine water productivity; and
Monitor effective functioning of outfall equipment during operations.
6.2. MEMBERSHIP OF COMMON DISPOSAL FACILITIES:
The solid waste generated on the rig will be segregated and stored in colour coded bags. The
solid waste will be transported back using support vessels or with the rig, to the Nhava supply base of
ONGC. At Nhava supply base the segregated waste will be treated separately. Hazardous waste, if any,
will be sent to authorized hazardous waste recyclers and disposal facility.
6.3. MEASURES TO HANDLE OILY WASTE DISCHARGES
Bilge and drainage waters generated on the rig may have the potential to be contaminated
with oily wastes. Drilling rig will be having designated containment and bunding zones where oil products
will be used and stored. While no wastes will be routinely discharged by deck drains, wash down of the
decks, rig floor, pipe rack, etc., may result in minor quantities of chemical residues (primarily oil and
grease) entering into the marine environment. Drainage water discharges would therefore contain very
low levels of oil and would be readily dispersed after discharge resulting only in some nominal localized
impact on marine species.
Bilge fluids generated will be treated on-site on the rig, in water/oil separator. Effluents of
separated oil will be shipped to onshore periodically in special drums/containers with effluent of separated
86
water being discharged in sea. Concentration of oil in water discharged will be restricted to less than 15
ppm in accordance with the International Convention for the Prevention of Pollution from Ships, 1973, as
modified by the Protocol of 1978 (MARPOL 73/78). Impact due to disposal of oil or oily mixtures at sea,
arising from discharge of such treated effluent is therefore considered to be negligible.
Mitigation Measures
Typical mitigation measures include:
Use of well-maintained oil/water separator;
Operational controls covering materials storage, wash-downs and drainage systems;
Maintaining a high level of housekeeping on board;
Use of only low toxicity chemicals on board; and
Design an adequate storm water drainage system to allow oily waste and contaminated
liquid waste, if any, to be collected and contained separately from clean storm water
6.4. SEWAGE TREATMENT AND DISPOSAL
Black Water also known as sewage will be generated from toilets on the rig and will primarily
include faecal material and urine. Rig operations will typically result in the generation of 9 m³ of sewage
per day. Once collected through headers, they will be passed through a sewage treatment plant (STP).
The wastes will then be passed through a screen of less than 25 mm diameter and an extended aeration
system prior to their discharge into the marine environment. In this case also, sewerage treatment on-
site will be done in compliance with MARPOL 73/78 requirements.
6.5. SOLID WASTE HANDLING
Combustible and non-combustible wastes routinely generated at offshore facilities will be
segregated at source and shipped to shore for re-use, recycling, or disposal. Efforts will be made to
eliminate, reduce, or recycle wastes at all times.
A waste stream inventory for the proposed offshore exploratory drilling project will be compiled
to identify predicted wastes for the spectrum of activities throughout the lifetime of the project. Overall,
the project waste management strategy will be adopting an effective solid waste treatment hierarchy.
However, the ultimate responsibility for effective waste disposal lies firmly with ONGC, who will ensure
that the project contractor(s) have adequate training and follow stipulated waste management procedures
for minimizing, handling and storing waste; that meet acceptable standards; and audits are carried out to
ensure these are achieved. Detailed waste management procedures will be put in place and all personnel
employed at on the rig will receive formal waste management awareness training, particularly regarding
the proper waste segregation, storage and labeling procedures and potential recycling of waste.
87
6.6. SPENT OIL HANDLING
Spent oil collected during the various activities of the offshore drilling on drilling rig will be
collected and stored separately in the labeled containers. These containers will then be sent to onshore
Nhava supply base from where it will be finally sent to the authorized hazardous treatment facility.
6.7. OIL HANDLING FROM WELL TEST OPERATIONS
Once drilling operations are completed and if sufficient indications of hydrocarbons are
noticed while drilling, the well may be tested by perforations. It is estimated that well testing period would
be about 1-2 days per well. Well testing will be carried out in accordance with Well Testing Program to
safely meet program objectives. During well testing oil will be stored in storage tanks, gas will be flared
up. Oil will be transported to base facility.
6.8. NOISE ABATEMENT MEASURES
The following mitigation measures will be adopted for noise reduction during the proposed offshore exploratory
drilling
Install sufficient engineering control on machineries (like mufflers, enclosures,, etc.,.) to
reduce noise and vibration emission levels at source;
Ensure that staff mobilized for the project is trained to use Personnel Protective Equipment
(PPE) like ear plugs/muffs and aware of noise related safeguards at workplace;
Identify areas sensitive for marine life such as feeding, breeding, calving, and spawning
areas in close proximity to the drill locations;
Undertake planning of navigational route for the drilling rig and supply vessels to avoid
Potential Fishing Zones and sensitive habitats in Arabian Sea;
Undertake proper preventive maintenance of supply vessels, helicopters and DG sets to
reduce noise levels;
Monitor presence of any sensitive species in the study area prior to the onset of any
exploratory activity;
Maintain relatively safe speed for vessels transporting equipment and fuel to the project site
in Arabian Sea;
6.9. MEASURES TO MINIMIZE DISTURBANCE DUE TO LIGHT AND VISUAL INTRUSIONS
The physical presence of the drilling rig is also to be felt at night because of the illumination
at night by deck and navigational lights. Other possible sources of illumination will be flaring conducted
for a short period of time during well testing phase. Artificial lighting and well testing flares may result in
the attraction of marine species leading to their disorientation and confusion behaviour. However, such
88
behaviour is particularly observed in hatchelling turtles, female turtles and sea birds. Lights on the rig
may also result in the sea birds concentrating on the immediate vicinity of the rig; however the operation
is short term in nature and is not likely to have a significant impact. As physical presence at drilling location
is intrinsically linked with the proposed drilling activities, and the fact that the adverse environmental
impacts are minimal, no mitigation measures are proposed to further reduce the impacts. However, a
reconnaissance survey will be carried out before the finalization of the drill locations to ensure that the
area is not the point of convergence or gathering for any sensitive marine species.
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Chapter 7
ANALYSIS OF ALTERNATIVES (TECHNOLOGY & SITE)
ONGC as an integrated oil and gas Corporate has developed in-house capability in all aspects
of exploration business i.e., Acquisition, Processing & Interpretation (API) of Seismic data, drilling, work-
over and well stimulation operations, engineering, construction, production, processing, refining,
transportation, marketing, applied R&D and training, etc. Wherever possible alternatives with respect to
rig, mud, on-site support base, and drilling locations are considered and best possible option is selected.
7.1. DRILLING LOCATIONS
The main objective of the exploratory drilling in block MB-OSN-2005/3 is to identify the block
area that contains oil and/or gas. The prospective drilling areas for the block is selected on the basis of
the 3D seismic survey. Based on the interpretation of 3D seismic data (acquisition ensued), specific
drilling locations are finalized. Before finalization of drilling locations information on the stability of surface
sediments and potential subsurface hazards (e.g. shallow gas formations) are gathered to ensure the rig
not to encounter problems when positioning or drilling the surface hole.
MoEF, through its ToR for this block, has asked ONGC for commitment on no drilling within
1 km from coastline. The exploratory drilling locations in the block MB-OSN-2005/3 is over 250 km from
the coast, thus MoEF requirement/ stipulations are met with spontaneously.
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Chapter 8
ENVIRONMENTAL MONITORING PROGRAM
Monitoring is one of the most important components of a management system. ONGC’s IMS
(Information Management System) requires continuous monitoring to be carried out for environmental,
safety and health impacts and the performance of EMP implementation, etc. Monitoring indicators have
been developed for each of the activities considering the mitigation measures proposed. Real time
measurements of these indicators will be carried out during drilling and data will be submitted to MoEF
as per statutory requirements of MoEF.
ONGC is required to record daily discharge of drill cuttings & drilling fluids in sea and also to
monitor the effluent quality. Compliance report will be prepared and it will be submitted to MoEF on 6
monthly basis or as per the conditions specified by MoEF.
Monitoring results would be documented, analyzed and reported internally to Offshore Drilling
Supervisor, Wells Operations Manager and HSE Coordinator. Monitoring requirements have been
described in the following Table 8.1. Frequency of monitoring and responsibility of carrying out the
monitoring have also been presented in the table.
TABLE 8.1: ENVIRONMENTAL MONITORING PROGRAM
Sr.
No. Particular Criteria/Regulation
Parameter to be
monitored
Frequency
of
Monitoring
Responsibility
1
Lo
cati
on
of
dri
llin
g w
ells
ONGC shall be drilling the
exploratory wells much
beyond 5 km from the coast
(nearest being 42 km SSW,
thus meeting the MoEF
requirement.
Drilling locations Once before
start of
drilling
activity.
Drilling HSE
Team
2
Qu
alit
y o
f se
a w
ater
Physico-chemical
characteristics of marine
surface water
Physical parameter – pH,
Salinity, temperature,
Chemical parameter – Oil
& Grease, Total
Petroleum, Hydrocarbons
(TPH), Petroleum
Aromatic Hydrocarbons
(PAHs)
Once in 24
hrs.
if no toxicity is
found, then
once in a
week.
Drilling HSE
Team
91
3
Use
of
mu
d ONGC is committed to using
of only Water Based Mud
(WBM) for the offshore
exploratory drilling
operations.
Quantity & characteristics
of mud to be used
Toxicity as per CPCB
guidelines.
Once every
year
Drilling HSE
Team
4
Wat
er
Usa
ge
Commitment to use an
average of 40 m3/day of
water during the drilling
period
Monitor the quantity of
water being used in
vessel
Drilling HSE
team
5
No
ise
Gen
erat
ion
Noise levels to which drilling
crew is exposed
Noise monitoring at rig Weekly, as
per CPCB
guidelines
Drilling HSE
team
6
Dri
llin
g
Mu
d a
nd
Cu
ttin
gs
Drilling Mud
Quantity & Characteristics Once for
each well as
per CPCB
guidelines
Drilling HSE
team
Drill cuttings Quantity
7
Eff
luen
ts
Drilling Effluents
Residual chlorine (Cl2)
after treatment
Weekly, as
per CPCB
guidelines
Deck drainage
Sanitary wastes- volume &
regular quality
as per MARPOL
8.1. DETAILED BUDGET AND PROCUREMENT SCHEDULES OF ENVIRONMENTAL MONITORING
ONGC has regular procurement plans for various operations related to hiring of drilling rig
services and associated facilities. These also include various aspects related to environmental
management measures. Thus procurements related to EMP are inbuilt in the procurement requirement
of ONGC.
Various man power requirements are provided by Drilling HSE, Basin HSE and Corporate
HSE teams of ONGC.
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Chapter 9
ADDITIONAL STUDIES
9.1 RISK ASSESSMENT
ONGC plans to drill one exploratory well and the exploratory drilling will be taken up in the
Block MB-OSN-2005/3 having an area of 1685 km2, and bathymetry ranging from ~90 to ~100 m, during
this phase of exploration.
Drilling will be performed using a self-contained Mobile Offshore Drilling Unit (MODU), a Jack-
up / Floater rig capable of performing shallow water drilling. Well testing will be conducted in the event of
discovery of hydrocarbon at such formation to establish hydrocarbon potential in terms of flow rates and
reservoir pressure. Following drilling and well testing activities, wells will be permanently abandoned or
sealed off for further development. Once well has been secured and all necessary equipment has been
retrieved, MODU will be mobilized to the next drill location.
The Risk Assessment encompasses identification of risks involved in the drilling process and
the associated activities in the drilling program, and assessment of probability of certain consequences.
9.1.1. Stages for which risk assessments are undertaken
Exploration drilling activity can be broken up into a series of stages during which different risk
assessments are undertaken:
Pre-operational assessments and regulatory approvals
Well design
Selection of rig, equipment and services
Pre-mobilization, mobilization
Drilling
De-mobilization
The Risk Assessment ascribed here has been undertaken prior to commencing of drilling
operation, and as part of the regulatory requirements, involving evaluation and disclosure of major risks
to the members of the Expert Appraisal Committee (EAC) of MoEF and other regulators, and
demonstrates that the exploratory wells, in principle, can be drilled in a manner not resulting in harm to
individuals or damage to the environment.
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This assessment relies on environmental and social sensitivities associated in the region,
data on past accidents in the oil and gas industry, information on past E&P activities undertaken by ONGC
in general and specifically in this area / region, and HSE management systems of ONGC. This study
however has certain limitations for the absence of sufficient details of the Drilling Rig or associated
support systems to be deployed for the proposed exploratory drilling program.
This report on Quantitative Risk Assessment (QRA) aims at providing a systematic and
syntactic analysis of the major risks that could arise as a result of offshore exploration activities of ONGC
in the MB-OSN-2005/3 block.
The QRA process outlines rationale behind the identified risks based on their significance and
also provides for appropriate preventive and risk mitigation measures. It is anticipated that the results of
the QRA would provide valuable inputs for the overall project planning, ONGC’s existing IMS and the
DSS (Decision Support System) for effectively addressing the identified risk to ensure that the project
risks stay at ‘As Low As Reasonably Practicable (ALARP)’ levels at all times during project
implementation. In addition, the QRA will also help in assessing risks arising from potential emergency
situations like a large oil spill and develop a structured Emergency Response Plan (ERP) to restrict
damage to personnel, infrastructure and the environment.
The risk study for the offshore project has considered all aspects of operation of the MODU
and other associated activities during the exploratory phase. Oil spills, loss of well control / blow-out,
vessel collisions, process leaks and helicopter crashes constitute the major potential hazards that may
be associated with the project. External and environmental risk factors (e.g., collisions with passing
merchant vessels, severe weather and seismic events) were considered in the assessment. However,
the risks or hazards associated with development and production program of exploratory wells has been
precluded for it being beyond the scope of the study.
The following section describes the methodology of the risk assessment study and then
presents the assessment for each of the potential risk separately.
9.1.1.1 Objective of QRA
The overall objective of the QRA is to identify the main contributors of major risks arising from
the offshore project which in turn will help in understanding the nature of hazards, evaluate and prioritize
them keeping in mind the ALARP principle and then suggest practicable targets for risk reduction, if any.
The specific objectives of this risk assessment are to:
Identify potential risk scenarios that may arise from operation of supply ships, helicopter
transport, etc.
94
Analyze the possible likelihood and frequency of such risk scenarios by reviewing historical
accident data.
Predict the consequences of such potential risk scenarios and if consequences are high,
establish the same by through application of quantitative simulations.
Recommend feasible preventive and mitigation measures as well as provide inputs for
drawing up an Emergency Response Plan (ERP) for the project.
The objectives of the QRA meet the criteria set for risk assessment for offshore operations in the
Petroleum and Natural Gas (Safety in Offshore Operations) Rules, 2008.
9.1.1.2 Risk Assessment Methodology
Risk associated with offshore oil and gas activities has two main elements - the risk of an
event happening - an oil spill, and the probability that that it will impact a receptor, such as an ecologically
sensitive area. For the purposes of this assessment, a risk ranking methodology based on likelihood and
consequence has been developed in line with specific criteria defined by ONGC for this project, and
represented in the form of a risk matrix.
The risk matrix is a widely accepted and standardized method of semi-quantitative risk
assessment and is preferred over purely quantitative methods, given its inherent limitations to define a
risk event with certainty. The application of this tool has resulted in the prioritization of the potential risk
events for the proposed drilling operations thus providing the basis for drawing up risk mitigation
measures leading to formulation of plans for risk and emergency management. The overall approach is
summarized in the Figure 9.1
FIGURE 9.1: RISK ASSESSMENT METHODOLOGY
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9.1.1.3 Hazard Identification
Hazard identification for the purposes of the QRA comprised of a review of the project and
associated activity related information provided by ONGC. In addition, guidance provided by knowledge
platforms/portals of the upstream oil & gas industry including OGP, ITOPF and DNV as well as historical
information available with ONGC were used to identify the potential hazards that may arise out the
proposed project activities.
Primarily, six major categories of hazards that can be associated with the project have been dealt with
in detail. They are as follows:
Oil Spills
Blowouts
Collisions
Helicopter crash
Process leaks
Process and non-process fires / explosions
Other possible hazard scenarios like chemical spills, falls, etc. has not been considered for
detailed assessment as preliminary evaluation has indicated that the overall risk that may arise out of
them is or negligible. In addition, it is understood that the causative factors and mitigation measures for
such events can be adequately taken care of through existing safety management procedures and
practices of ONGC.
It must also be kept in mind while evaluating the QRA that many of the hazards identified are
sometimes interrelated with one hazard, often has the ability to trigger off another hazard through a
domino effect. For example, a large oil spill in most instances is caused by another hazardous incident
like a blowout, a process leak or a collision. This aspect has been considered while drawing up hazard
mitigation measures and such linkages (among hazards) has also been given due Importance for
managing hazards and associated risks in a composite manner through ONGC safety management
system and the Emergency Response Plan.
9.1.1.4 Frequency Analysis
The analysis of frequencies of occurrences for the key hazards is important to assess the
likelihood of hazards during the lifecycle of the project. With relevance to the risk assessment study of
the proposed offshore exploratory project, major information sources viz. statistical data, historical
records and global offshore industry experience were considered for the frequency analysis of the major
identified risks.
The following accident databases and published oil industry databases have been consulted for arriving
at probable frequencies of identified hazards for the purpose of this QRA:
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The Worldwide Offshore Accident Databank (WOAD) – world’s most extensive database of
offshore accidents and incidents maintained by DNV;
SINTEF Offshore Blowout Database - a compilation sponsored by 6 operators and 2
consultants;
CAA Helicopter Data – statistics published by the UK Civil Aviation
Accident Data published by DNV Technica
Environmental & Safety Performance of E & P Industry published by oil & gas producers
OGP;
Oil Spill Statistics published by International Tankers Owners Pollution Federation (ITOPF)
Likelihood Ranking Criteria Definition
E Higher than 1 occurrences/year
D Between 10-1 to 1 occurrences/year
C Between 10-4 to 10-3 occurrences/year
B 10-3 to 10-1 occurrences/year
A Between 10-6 to 10-4 occurrences/year
0 0 Lower than 10-6 occurrences/year
9.1.1.5 Consequence Analysis
In line with the frequency analysis, hazard prediction / consequence analysis exercise has
been done to assess the resulting effects in the event of an accident and their likely impact on project
personnel, infrastructure and environment. The consequences of accidental events on the marine and
social environment have been studied to evaluate any major impact to the aforesaid environment. Overall,
the consequence analysis takes into account the following aspects:
Magnitude of impacts in terms of area involved
Stakeholder concern
Impact on ecology/biodiversity
Time period for natural recovery and cleanup in case a risk scenario unfolding
The following criteria for consequence rankings have been drawn up in context of the possible
environmental consequences in the event of the risk events unfolding during the drilling operations:
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TABLE 9.1: SEVERITY CATEGORIES AND CRITERIA
Environment Severity
Ranking Criteria Definition
Major International Impact
5
International stakeholder concern
Impact on licenses / acquisitions
More than 5 years for natural recovery
More than 5 months for clean-up Reduction of
biodiversity
Impact on special conservation areas.
Involved area > 100 km2 – Spill= 5000 MT
Major National Impact 4
National stakeholder concern
Impact on licenses
2-5 years for natural recovery
Up to 5 months for clean-up
Threatening to biodiversity
Impact on interesting areas for science.
Involved area < 100 km2 – Spill= 700 MT
Local Impact 3
Regional stakeholder concern
1-2 years for natural recovery
1 week for clean-up
Threatening to some species
Impact on protected natural areas.
Involved area < 10 km2 - Spill = 100 MT
Minor Impact 2
Some local stakeholder concern
1 year for natural recovery
Impact on small no of not compromised species.
impact on localized ground
Involved area < 1 km2
Spill = 10 MT
Slight Impact 1
No stakeholder impact
Temporary impact on the area.
Involved area < 0.1 km2
Spill < 1 MT – no sensitive impact on ground
9.1.1.6 Risk Evaluation
Based on ranking of likelihood and frequencies, each identified hazard has been evaluated
based on the likelihood of occurrence and the magnitude of consequences. The significance of the risk
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is expressed as the product of likelihood and the consequence of the risk event, expressed as
“Significance = Likelihood X Consequence”.
The figure below Illustrates all possible product results for the four likelihood and
consequence categories and the Fig. 9.2 and Fig. 9.3 assign risk significance criteria in three regions that
identify the limit of risk acceptability according to the policy and the strategic objectives. Depending on
the position of the intersection of a column with a row in the risk matrix, hazard prone activities have been
classified as low, medium and high thereby qualifying for a set of risk reduction / mitigation strategies.
FIGURE 9.2: RISK MATRIX & ACCEPTABILITY CRITERIA
Likelihood of Occurrence
Sev
erity
of C
onse
quen
ce
O A B C D E
1 Continuous Improvement
2 Risk Reduction
Measures
3
4 Intolerable Risk
5
FIGURE 9-3: RISK CATEGORIES AND SIGNIFICANCE CRITERIA
Risk Criteria Definition
Low (Continuous improvement The level of risk is broadly acceptable and no Specific control measures are required.
Medium (Risk reduction measures) The level of risk can be tolerable only once a structured review of risk reduction measures has been carried out.
High (Intolerable risk) The level of risk is not acceptable and risk control measures are required to move the risk figure to the previous regions.
9.1.2. Key Risks involved
The key accidental scenarios corroborating safety and environmental risks due to offshore exploratory
drilling program in the current region are:
Fire and Explosion due to Blowouts and other reasons
Accidents during sea transport of materials and supplies
Accidents during air transport of personnel
Oil Spills
Risk and consequence of oil spills are included in separate section, while blowouts and other risks
relating to air and sea side transport accidents are included in the following sub sections.
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9.1.2.1 Blowouts
A blowout in a hydrocarbon exploration activity can be defined as any uncontrolled flow of
formation fluids from the reservoir to the surface, due to formation pressure exceeding the hydrostatic
pressure of the mud or fluid column and failure of blowout prevention measures. For an offshore drilling
activity, blowout events may occur at the drill ship level or subsea and may result in pool /jet fires, vapour
cloud explosions or sometimes may lead to release of toxic gases like Hydrogen Sulphide.
Blowouts during offshore operations may be initiated during both drilling and development
phase and also as a result of external causes viz. earthquakes, ship collision, and structural collapse. In
the context of the proposed project, offshore operations will be limited to exploratory drilling and testing.
Therefore, any incidence of blowout during the aforesaid phases may occur as a result of loss of well
control due to formation fluid entry into well bore, well head damage or loss of containment. The
underlying causes of most of the blowout incidents (excluding external causes) occurring worldwide can
be interpreted as organizational and managerial. An analysis of blowout causes into such factors
attempted for the Marintek database (NSFI 1985) revealed that the main causal factors were improper
maintenance, operational failures and inadequate supervision.
Blow Out Frequency Analysis
Blowout frequency estimates are obtained from a combination of incident experience and
associated exposure in a given area over a given time period. Due to limited offshore oil & gas related
activities in the offshore region, blowouts that have occurred at other offshore locations worldwide have
been considered for the blowout frequency analysis. Input data for the frequency analysis of blowout
events were taken from DNV’s database, viz., WOAD (World Offshore Accident Database). Review of
blowout frequencies from the database reveals a frequency 1.1 X 10-2 per operation per year for drill
ships (comparable to the MODU to be deployed for the drilling activity) compared to Jack Up Rigs (9.8 X
10-3), and Fixed Platforms (9.3 X 10-4).
Since the proposed project involves only exploratory drilling, measurement of exposure for
blowout incidents has been determined by considering blowout frequencies during drilling and by the
platform type. The blowout frequency for the proposed 6 wells have been obtained by multiplying the
blowout frequencies per well year by the no of wells drilled, and the time taken for drilling each well.
Estimated frequency for blowout for the proposed drilling operation in exploratory block MB-
OSN-2005/3 is: Probability for blowout from ONGC drilling operations = 1.1 X 10-2 (prob/ year / drilling
operation) X 1(no of drills) X 0.2 (time taken for each drill in yrs) = 0.2 X10-2
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Blow Out Consequences and Effects
A blowout incident can take a variety of different forms, ranging from a minor leak which can
be stopped within minutes, to a major release which continues out of control for days or even months.
The consequences of a blowout event will to a large extent depend on how the blowout scenario evolves
and the following possible scenarios are likely:
release of oil resulting in a slick or spill on the sea
release of drilling fluids and resulting spill leading to contamination of marine environment
release of toxic / flammable gas which may have deleterious/detrimental effect on the drill
ship personnel
ignition of the flammable gas / oil released resulting in a jet of fire, pool of fire or an explosion
Ignition of released oil and gas can possibly result in considerable harm. With historical data,
40% of blowout incidences to have led to significant damage to the drill ship / platform (WOAD database)
and resulted in associated fatalities amongst drilling crew and support personnel present on the ship /
platform. Also, ignition has been recorded world over, on an average, in about 30% of the blowout cases
(SINTEF offshore blowout database). However, on the positive side, with improvement of offshore drilling
technology, number of offshore blowouts occurrences has significantly gone down in the last decade.
A public domain database maintained by DNV for all offshore hazards including 312 blowouts worldwide
from 1970-96.
Risk Ranking for Blowouts
Likelihood Ranking - C
Consequence Ranking - 4
Risk Ranking - 4C (High)
Preventive and Mitigation Measures
Blowouts being events which may be catastrophic to any well operation, it is essential to take
up as much a preventive measures as feasible. Following measures would be implemented:
Necessary active barriers (e.g. Blowout Preventer) will be installed to control or contain a
potential blowout.
Close monitoring of drilling activity would be done to check for signs of increasing pressure,
viz., shallow gas formations.
Adequate precautionary measures to be taken in case of a natural event like earthquake or
a cyclone.
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9.1.2.2 Collisions Involving MODU (Jack-up Drilling Rig)
A collision event is considered for the risk assessment for the impacts on MODU by other drill
ships or other marine vessels working nearby or passing by it. The following possibilities have been taken
into consideration:
support vessels which approach the MODU under their own power including supply vessels,
standby vessels, etc.
Collisions may vary from minor bumps to rare but highly damaging full-speed collisions. The
frequency for such incidences is strongly dependent on the severity of the collisions
included. The types of collisions possible in this are as follows:
On arrival – where the visiting vessel fails to stop when it reached the platform;
Manoeuvering – where the vessel misjudges a turning or approach manoeuver, and the hits
the MODU at a relatively low speed
Drifting – where the vessel loose power or suffers a failure of dynamic positioning and drifts
into the platform because of winds or waves.
The collision frequency would be expected to vary roughly in proportion to the number of
visits, particularly for supply vessels, which are again of a similar pattern. The frequency of collisions will
also depend on the weather conditions prevailing in the offshore region near the coast during the drilling
period, especially for minor collisions. As exact vessel movement data for the ONGC India operations
are not available at this time, an average vessel movement (Technica, 1987) of about 3.6 vessels / week
has been assumed.
Assuming the number of visits to the MODU as 5.0 vessels per week, the typical overall
frequency of moderate to severe collision by a support vessel with the MODU can be taken as 1.0X10-4
per visit. Estimated frequency for support vessel collision for the proposed drilling operation in exploratory
block MB-OSN-2005/3 is:
Total number of visits = 5 / 7 X 210 = 150
Frequency for collision = 1.0 X 10-4 X 150 = 1.5 X 10-2
Collisions Involving MODU and Passing Vessels
Collisions with offshore oil structures involving passing vessels are generally very rare (about
5 % of all reported collisions) but can be potentially very damaging. Probabilities for passing vessel
collisions can be estimated from historical experience. However, the frequencies are uncertain and
statistically insufficient as only few passing vessel collisions have has been reported. Historical data have
limited value because they are often unable to reflect local traffic levels with reasonable degree of
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accuracy and also because the sea has few formally defined shipping lanes and ships tend to follow
informal lanes voluntarily between ports.
Collisions Involving Supply and Other Vessels
There is a negligible probability of supply vessels colliding with other commercial vessels on
route to the MODU while maneuvering near to the Nhava base. These collisions may happen because
of navigational difficulties or because of prevailing traffic density near JNPT. However, the traffic on local
routes is highly regulated and controlled. So the possibility of such collisions happening is considered to
be minimal.
Consequences and Effects
The analysis of collision consequences is generally based on the principle of conservation of
energy. The incident kinetic energy of a vessel on a collision course can be transferred to the MODU
during the impact. The magnitude of energy transfer will depend on the mass of the vessel and on the
square of its speed at the time of impact. However, in the case the collision is as a result of a glancing
blow from a support vessel, where the vessel brushes against the platform, the kinetic energy transfer is
minimal and is expected to cause minimal damage to the MODU. The impact of a full-on collision may
however be more severe and may lead to structural damage to the MODU. The risk to personnel manning
a platform / drill ship from a collision in terms of fatalities or injuries has been historically found to be very
low, if not resulting in a catastrophic incidence like a blowout. It should be noted that the MODU would
be connected to the drilling apparatus at the sea bottom; a collision involving high energy transfer may
lead to a rupture or leak in the riser resulting in a process leak or a blowout.
Risk Ranking for Vessel Collision
Likelihood Ranking - C
Consequence Ranking - 3
Risk Ranking - 3C (Medium)
Preventive and Mitigation Measures
A Vessel Management Plan will be formulated and implemented to reduce collision risk, both vessel–
vessel and MODU–vessel and will address the following:
Mandatory 500 m safety zone around platform;
Operational restrictions on visiting vessels in bad weather;
Defined vessel no-go areas within safety zone; and
Agreed approach procedures to platform by supply and safety vessels.
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9.1.2.3 Helicopter Crashes
The journey to and from offshore installations has historically been one of the main reasons
for accidental death or injury to many offshore workers. For the ONGC India drilling activities, crew
transport to and from the MODU will be taken care of by helicopter for its speed, convenience and good
operability under rough weather conditions.
Frequency Probability
Several approaches exist to analyze probability of helicopter crash risks. The most common
approach involves the use an overall Fatal Accident Rate (FAR) value (e.g. SINTEF 1990). However,
there are certain inherent deficiencies in adopting this approach in spite of the fact that it provides
convenient risk numbers. A more reasonable approach involves the use of individual risk approach as a
product of 3 components:
Frequency of helicopter accidents per flight;
Proportion of accidents which involve fatalities;
Proportion of personnel on board in fatal accidents who become fatalities.
Taking this approach and considering historical data from the UK sector which is available, while
accounting for both the flying time and number of flying stages involved, the Individual Risk per journey
can be calculated as Individual Risk (IR) per journey = 1.7 X 10-6 X flying time (hours) + 2.7 X 10-7 X No.
of stages per journey.
Consequences and Effects
Helicopter crashes with offshore oil & gas exploration and production have happened routinely
in the past, especially in the North Sea offshore operations in Europe, with some resulting in fatalities or
injuries to crew members. In addition to the risk posed to the helicopter occupants, accidents involving
helicopters can also cause damage to the drill ship itself by way of crashing into the ship during take-off
or landing or by an accident when the helicopter is on the helideck. However, the consequence of such
risk may be considered to be small compared to the other risks sources on the MODU.
Risk Ranking for Helicopter Crash
Likelihood Ranking - BC
Consequence Ranking - 3
Risk Ranking - 3B (Medium)
Preventive and Mitigation Measures
Following preventive and mitigation measures will be adopted with respect of helicopter operations:
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Air worthiness of helicopter to be checked by competent authority before helicopter is hired
by ONGC India.
ONGC India should ensure that the pilot/pilots who will be operating have got appropriate
training on similar craft.
Effective arrangements for coordination would be developed with air traffic control room at
Nhava base, as also in the MODU;
Helicopter operations to be restricted during night time and during bad weather conditions.
All employees who are supposed to travel on helicopters would be receiving basic training
on rescue and survival techniques in the case of a helicopter crash at sea.
9.1.3. Risk Mitigation Measures
9.1.3.1 Well Planning & Design
Exploration wells are designed to manage the uncertainty in the true nature of the well to be
drilled. The possibility of shallow gas, uncertainty in pore-pressure and temperature, porous and
permeable intervals, weak formations, etc. all need to be assessed, and the well design and drilling
program developed to cater for ‘worse-case’ scenarios. Offset well data, computation modeling and site
specific survey data allow the geoscientists to provide the drilling engineers with information on the likely
range (probabilistic) and maximum values of key design parameters. The drilling engineer designs the
well (and the associated drilling programme) on the basis of maximum anticipated values.
Explicit risk assessment, in terms of assigning quantitative probabilities of failure to all parts
of the well design, does not feature in the design of a typical exploration well. However, risk assessment
is implicit within the design process, specifically through the adoption of operational manuals and
procedures and industry recognized design approaches by ONGC.
ONGC and other private E&P operators such as RIL have in the past undertaken drilling
activities in the offshore region around the coast of Maharashtra. This has led to a fair amount of
geological information and offset well data from the region, based on which ONGC will be able to plan
and design exploratory wells in the block, with minimal uncertainties and therefore higher probability of
avoiding accidental scenarios such as blowouts.
As per ONGC’s Management Systems of Offshore Drilling and HSE, and in compliance with
Petroleum and Natural Gas (Safety in Offshore Operations) Rules 2008, ONGC will ensure that:
A Well programme describing the individual activities and the equipment to be used will be
prepared prior to starting well activities
The management system with associated processes, resources and operational
organization will be established;
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Steering documents, including technical documents for drilling and well testing operations,
will be made available, in an updated version and the operational personnel shall be
acquainted with it.
Commissioning process prior to startup of facilities for first time or after technical
modifications will be completed
Well barriers:
During drilling and other related well activities, there will at all times be at least two
independent and tested well barriers after surface casing a in place. Well barriers will
be designed in such a manner that unintentional influx, cross flow to deformation
layers and outflow to the external environment is prevented.
Well barriers will be designed in such a manner that their performance can be verified.
If a barrier fails, during drilling and other related well activities, no other activities will
be undertaken in the well than those to restore the barrier.
When a well is abandoned, the barriers would be designed to provide integrity for the
longest period of time in such a manner, inter alia, that outflow from the well or
leakages to the external environment do not occur.
ONGC will choose well location and well path on the basis of well parameters of
importance, including occurrence of shallow gas, other hydrocarbon bearing
formation layers and distances to adjacent wells and to ensure that it is possible to
drill a relief well from two alternative locations. The well path will be known at all times.
ONGC will ensure that the necessary actions are planned including setting of casing above
all known shallow gas hazard zones to handle occurrence of situations of shallow gas or
other formation fluids.
During drilling and well activities, drilling and well data will be collected and monitored to
verify the well prognoses, in order that necessary actions may be taken and the well
programme may be adjusted, if necessary.
Well control:
Well control equipment will be designed, installed, maintained, tested and used so as
to provide for well control.
In the case of drilling of top hole sections with riser or conductor, equipment with
capacity to conduct shallow gas and formation fluid away from the facility, until the
personnel has been evacuated, will be installed.
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Floating facilities shall have an alternative activation system for handling critical
functions on the blow out preventer.
Accumulator for surface and subsurface well control equipment will have minimum
useable fluid capacity as per industry standards in order to perform closing and
opening sequences as applicable to secure the well.
The pressure control equipment used in well interventions will have remote control
valves with locking devices.
The well intervention equipment will have a remote control blind or shear ram as close
to the Christmas tree as possible
If well control is lost, ONGC will ensure that it shall be possible to regain the well
control by direct intervention or by drilling a relief well.
ONGC will prepare an action plan describing how the lost well control can be regained
ONGC will set operational limitations in relation to controlled well flow
Securing of wells before abandoning
All wells will be secured before they are abandoned in such a manner that well
integrity remains intact for the period abandoned.
With regard to subsea completed wells, the well integrity will be ensured if the wells
are planned to be temporarily abandoned
Radioactive sources will not be left behind in the well.
In case it is not possible to retrieve the radioactive sources and these have to be left
in the well, ONGC will follow proper abandonment procedure as per guidelines of the
Department of Atomic Energy, Government of India.
Compensator and disconnection systems:
Design of compensator systems will be based on robust technical solutions so that
failures do not lead to unsafe conditions.
Floating facilities shall be equipped with a disconnection system that secures the well
and releases the riser before a critical angle occurs
Drilling fluid system:
The drilling fluid system will be designed in such a manner that it will mix, store,
circulate and clean a sufficient volume of drilling fluid with the necessary properties
to ensure the drilling fluid’s drilling and barrier functions.
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The high pressure part of the drilling fluid system with associated systems will in
addition have capacity and working pressure to be able to control the well pressure
at all times.
Availability of sufficient quantity of drilling fluid weighting material to subdue the well
at any time during the drilling operation will be ensured
Cementing unit:
The cementing unit will be designed in such a manner that it will mix, store and deliver
as exact volume as possible of cement with the necessary properties to ensure full
satisfactory anchoring and barrier integrity
The unit will be designed in such a manner that remains of unmixed chemicals as
well as ready-mixed cement is handled in accordance with the applicable
environment regulations.
If the cementing unit with associated systems is intended to function as backup for
the drilling fluid system, it shall have capacity and working pressure to be able to
control the well pressure at all times.
Casings and anchoring will be such that the well integrity is ensured and the barrier functions
are provided for the life time of the well.
Equipment for completion and controlled well flow
Equipment for completion will provide for controlled influx, well intervention, backup
well barrier elements and plug back activities.
Completion strings will be equipped with necessary down hole equipment including
safety valves
During controlled well flow, the surface and down hole equipment will be adapted to
the well parameters.
Equipment for burning of the well stream will be designed and dimensioned in such
a manner that combustion residues shall not cause pollution of the marine
environment
ONGC will ensure that controlling well pressure through the work string and the well
flow through the choke manifold at any time
9.1.3.2 Selection of Equipment, Systems and People
Assessing the Ability of the Drilling Rig to Perform the Required Operation
The water depth, environmental conditions, reservoir and geophysical properties will dictate
the type of rig and equipment required to perform the drilling operation. Highly technical risk assessments
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will be undertaken both to demonstrate that the rig is capable of providing an acceptable working
environment, and to determine the limits to which certain operations will be undertaken.
During this phase, the ability of the equipment and systems on the rig to provide a suitable
barrier(s) to well control incidents will be reviewed (e.g., pressure rating and functionality of the BOP).
The ability of a drilling rig to operate at the specific location will be assessed, usually through the
application of an industry recognized site assessment practice. (e.g., Site Specific Assessment of Mobile
Jack-Up Units). The objective being to ensure that the risk of (for example) a structural or mooring failure
does not exceed ONGC’s and the regulator’s risk acceptance requirements.
The risk assessment process is, to an extent, embodied within the relevant design and
assessment standards applicable to the particular type of drilling rig. However, detailed, site-specific risk
assessments support the application of these standards, for example the analysis of borehole data to
establish the risk of a punch-through. Where a drilling rig is deemed to be operating close to the limits of
its operating envelope, more detailed risk assessments may be warranted.
The requirements of the following applicable standards for the listed equipment shall be met
to demonstrate that drilling systems are in compliance with requirements of the Petroleum and Natural
Gas (Safety in Offshore Operations) Rules, 2008 and Drilling Rig (MODU) is thus fit for purpose:
Fire and explosion risk assessment on MODU includes hazards from the wells and well testing
operations. Following fire and explosion hazards related to wells are generally considered:
Subsea shallow gas blow out
Shallow gas blow out in cellar deck
Blow out at drill floor
Subsea blowout
HC gas release / ignition in mud processing area
Fire and explosion in well testing areas
Well programs needs to be designed taking into consideration the anticipated hazards as
listed above. MODUs should conform to conventions and codes of International Maritime Organization
(IMO). Fire and explosion risk management at MODU can be ensured by meeting the requirements of
these codes. Following issues have been taken into consideration by MODU code:
Structural fire protection layout plan for decks and bulkheads
Protection of accommodation spaces, service spaces and control stations
Means of escape
Fire pumps, fire mains, hydrants and hoses
Fire extinguishing systems in machinery spaces and in spaces containing fired processes
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Portable fire extinguishers in accommodation, service and working spaces
Arrangements in machinery and working spaces
Fire detection and alarm system
Gas detection and alarm system
Fireman’s outfit
Provisions for helicopter facilities
Fire control plan
Ensuring fit for purpose status of fire extinguishing appliances (operational readiness and
maintenance is detailed in MODU Code 2009)
Number and type of portable extinguishers provided on the MODU would be based on the fire hazards
for the spaces protected.
9.1.3.3 Testing & Maintenance of critical equipment
Blowout preventer and other pressure control equipment is the most critical equipment to
avoid major accidents during drilling. Therefore the blow out preventer will be pressure tested regularly
in order to maintain its capability of carrying out its intended functions. The blow out preventer with
associated valves and other pressure control equipment on the facility shall be subjected to a complete
overhaul and shall be recertified at regular intervals based on original equipment manufacturer’s
recommendations and international standards and recommended practices.
Contractor Management (Drilling Contractor)
Management of major incident risks are by the drilling contractor on the MODU is of interest
to ONGC, and will, therefore, ensure that all major incident risks have been assessed and suitable
controls put in place to reduce the risks to as low as reasonably practicable (ALARP). Pre-mobilization
and pre-drilling assessments will be undertaken by ONGC to ensure that the risk to an individual worker
is as low as reasonably practicable. Typically this is demonstrated through the analysis and summation
of all the individual risks and how they impact different classes of offshore personnel.
The major incident risks for which some level of risk assessment is undertaken normally include:
Hydrocarbon releases resulting in fires, explosions or asphyxiation
Structural failure (environmental overload, foundation failure, seismic etc.)
Mooring failure (loss of station keeping and secondary impacts)
Ship Collision
Helicopter operations
Lifting operations and dropped objects (with major incident potential)
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The nature of the risk assessment exercise undertaken for each of the risk types varies from
analysis of past incident data, to the detailed assessment of blast overpressure resulting from
hydrocarbon releases of varying sizes and from different locations.
9.1.3.4 Selection of Support Services
The proposed drilling operations will require some level of 3rd party support services which
typically include helicopter operations, standby and supply vessels, services and equipment on the rig,
onshore supply base and so on. Associated with each of these activities some level of risk assessment
will be undertaken by ONGC. These risk assessments will, for example, drive the need to develop
‘bridging arrangements’ between the contractors that contribute to the management of a particular activity
and the risks that arise from it. However, since ONGC is an experienced E&P operator owning and/or
contracting such support services – Risk Management is built in selection, supervision, and monitoring
these support services.
9.1.3.5 Ensuring Marine Integrity
1. Stability:
ONGC will ensure that floating facilities are in accordance with the requirements contained
in the applicable standards concerning stability, water tightness and watertight and weather
tight closing means on mobile offshore units.
There will be weight control systems on floating facilities, which will ensure that weight,
weight distribution and centre of gravity are within the design assumptions and equipment
and structural parts will be secured against displacements to affect stability.
2. Anchoring, mooring and positioning:
Floating facilities will have systems to enable them to maintain their position at all times and,
if necessary, be able to move away from the position in the event of a situation of hazard
and accident.
Dynamic positioning systems will be designed in such a manner that the position can be
maintained in the event of defined failures and damage to the system, in case of accidents.
During marine operations, necessary actions will be taken in such a manner that the
probability of situations of hazard and accident is avoided and those who take part in the
operations are not injured.
Requirements will be set to maintaining position in respect of vessels and facilities during
implementation of such operations, and criteria will be set up for commencing and
suspension of activities.
3. Collision risk management
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The Offshore Installation Manager will be the overall authority for safe operations within the
safety zone of installation.
ONGC will ensure that a collision risk management system is implemented and maintained
wherein following shall be inter alia included –
suitability of attendant vessels and off take tankers and competence of their crew;
assessment of probability of collision peculiar to the installation and its location;
provision of necessary risk reduction and control measures;
appropriate procedures and communications for managing operations of attendant
vessels developed jointly with marine service providers;
provision of appropriate equipment and procedures for detecting and assessing the
actions of vessels intruding into the safety zone;
provision of competent personnel with an appropriate level of marine knowledge;
provision of appropriate evacuation and rescue procedures and facilities; and
regular audit and updating of the above systems.
4. Control in the safety zone
The master of the attendant vessel or off take tanker will comply with instructions of the
Offshore Installation Manager when in a safety zone.
The master of the attendant vessel or off take tanker will be responsible for safety of his
crew, the safe operation of attendant vessel or off take tanker and for avoiding collision with
the installation or associated facilities.
5. Operations in rough weather conditions
The operator will ensure safe working in adverse weather and tidal conditions and identify
the rough weather conditions when the operations are to be discontinued and evacuations
carried out, as required.
The operator will ensure that transfer of personnel and cargo between the vessel and
installation is carried out under safe weather conditions and such transfers should be
stopped during adverse or unsuitable weather conditions
6. Cargo management
The operator will ensure optimization of cargo trips, from and to the shore, and cargo handling time at
installation by efficient planning of cargo supplies through containerization, pre-slinging of cargo etc.
9.1.4. H2S Emission Control Plans
H2S production is not envisaged in these wells, but due to exploratory nature of the wells, contingency
plan for emergencies are provided herewith:
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9.1.4.1 Detection and Alarm Systems
The system comprises of H2S sensors located at pre-determined points. In air conditioned or
ventilated areas, detectors will be installed at the fresh air inlets (ducts, entrance ways etc.). Outside,
detectors are required to be installed on gas carrying equipment (well nipple, shale shaker, mud, pits,
drillers’ stands etc.).
The alarm systems are located near potential leaks, such as the shaft gland connection,
flanges etc. It is pure alarm system with two warning stages and cannot trigger emergency shutdown
alone. The two levels of alarm are as follows:
10 ppm H2S level alarm triggers a light signal but does not indicate danger for all. At this
stage persons are instructed to stand by to check the installation after announcement on
public address system (PA) by the tool pusher, otherwise, to proceed to the upwind side
20 ppm H2S high level triggers a sound alarm and also red light on the control panel.
Emergency alarm is sounded by two short rings of bell intermittently. At this stage breathing
equipment is to be used immediately and the hazard area be vacated unless the tool pusher
give other instruction or announcement over the Public Address System.
H2S Conditions H2S (ppm) measure from Danger
to Life Action
Open air Core/Drill string
Normal operations No H2S potential None None
Watch Potential H2S None Monitor
Alert 1 - 19 NA None Monitor, use PA as needed
Danger 20 - 49 >20 Moderate Stop coring operation
Emergency >50 NA Extreme Evacuate to safe areas
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9.1.4.2 Visual Warning Signs
In case of high level H2S alarm, the following warning signs should be displayed to alert helicopter and
vessels in the vicinity of the drilling rig.
Red flag 90cm X 60 cms on each side of the rig.
Danger boards painted yellow with black lettering 30 cms high indicating "DANGER H2S".
9.1.4.3 Muster Stations and Escape Route
Since H2S is heavier than air, it is likely to settle down at lower levels particularly in still air or
in light winds and cut off the natural escape route to the boat landing; in this situation following is
practiced:
Sufficient stair cases on the upwind side of prevailing winds for escape route up the stairs
or down to the lifeboat.
Muster stations for operating personnel in the event of gas alarm areas, in the open on the
upper deck which can be kept free of H2S by the wind.
9.1.4.4 Ventilation
Forced air ventilation to disperse any accumulation of H2S will be provided by fans (bug blower) at the
following points:
Shale shaker
Working platforms
Control rooms
9.1.4.5 H2S Kick control
The control of H2S kick may be achieved either by bulldozing gas back into formation or
circulating it out. The actual method to be adopted will depend upon the condition of the well. When a
gas kick occurs, estimate the quantity of H2S present taking adequate precautionary measures of wearing
self-contained breathing apparatus (SCBA). The following procedure is to be adopted:
Close BOP, monitor SIDPP, SICP & pit gain.
If the concentration is high and cannot be circulated out due to H2S hazard in atmosphere,
bulldoze the gas into formation by pumping through kill line.
Raise mud wt. and pH as required.
Load H2S scavenger like zinc carbonate and ironite sponge as may be necessary in the
active mud pit.
Circulate the gas through choke and degasser and burn off the gas.
The following factors are needed to be kept in view:-
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All persons on the drilling floor, shale shaker area, mud pump and tank should put on
self-contained breathing apparatus when the kick is to be circulated out.
Persons who are not required for the control operation are withdrawn to a safe area,
where adequate ventilation is arranged.
Frequent checks with portable H2S gas detector are to be made.
Supply vessels will be directed to stay upwind on power and maintain continuous
radio and visual watch.
9.2. DISASTER MANAGEMENT PLAN
Oil & Natural Gas Corporation Limited is the premiere national oil company engaged in the
exploration and production (E&P) of crude oil and natural gas from offshore as well onshore assets in
Indian and abroad. The inherent risk in the oil well drilling and production are well known and the
management of the risks calls for systematic planning, adopting engineering practices and positive
attitude towards safety & environment protection. It was therefore, necessary to develop a Disaster
Management Plan (DMP) to facilitate necessary actions to meet emergency scenarios.
9.2.1. Purpose & Scope of the Plan
The disaster management plan would serve the following purpose
To set out the appropriate course of action to mitigate the impact of an emergency event.
The plan provides for a procedure allowing all those involved to mobilize their resources in
an orderly way and to react in time effectively.
To respond immediately to an emergency event to prevent its escalation to a disaster and
also the response in the event of such an escalation. The scope of the plan is to cover all
the emergency situations which can influence the risk under the following situations
Disasters due to natural causes Disasters due to manmade causes (external)
Floods Civil disturbances
Tsunami Terrorist Attack
Hurricane Hostage Crisis
Earthquake Bomb threats
Tornado Potential Offshore Vessel Collision
Lightning Helicopter crash on Helideck in Offshore
Disasters due to manmade causes (operational)
Helicopter crash-Ditch in sea
Fires Helicopter Emergency landing
Oil/gas well blowouts Office/Offshore accommodation fire
Toxic gas releases, Dropped object incidents
Oil / Chemical spills, Emergencies to offshore installations
Hydrocarbon Release Diving Incidents
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Explosions (unconfined, confined) Man Overboard incidents
The emergency situations mentioned above can escalate to such an extent that the required
level of response would be beyond ONGC’s own resources available within an Asset and intervention of
corporate level will be necessary to mobilize additional resources not only from various other work centres
of ONGC, but even from outsourcing services internationally. In such cases, DMP shall be activated by
the CMD, ONGC as and when, in his opinion, a national and/or international level intervention is required
for handling the crisis.
9.2.1.1 Updating and Exercises
The disaster management plan shall be updated as and when required but at least once in a
year. Also, the plan will be exercised under the chairmanship of the CMD once every year to test the
communication system, action plan and the response of all key agencies within ONGC, govt. of India and
outside resources. Accordingly, a Disaster, scenario will be simulated and the ‘Emergency Coordinators’
as defined by the plant will be required to act in a predetermined way to deal in real time with the situation.
The outcome of the exercise will be taken as input to updating the plan and improve on the lacunae, if
any, on the front of preparedness as well as to plug the loopholes to meet with emergencies of any extent
feasible. The exercise shall include the National Crisis Management Committee. If in any case the
exercise cannot be carried out due to operational reasons the same shall be done as a table top exercise.
9.2.1.2 Disaster Management Preparedness
In case of emergency, Emergency Response Plan (ERP) is activated by the installation
manger. He shall immediately bring it into the notice of the Asset/ Basin Manager/ Chief of Services for
mobilization of resources, should the emergency warrants so, beyond the capability of the installation/
rig/ vessel, as well as to activate the Disaster Management Plan constituting a part of the Regional
Contingency Plan (RCP). In order of affixing the responsibility, the Senior most Asset Manager shall be
the Chief Emergency Coordinator (CEC). In case of his absence the next Senior Asset Manager shall be
the CEC. The CEC shall, on the gravity of the emergency, inform the CMD, Director (HR)-CCEC, Director-
concerned and Director-I/C HSE for intervention of Corporate Disaster Management Group (CDMG).
Corporate Disaster Management Group (CDMG) will come into action in the following
situation when in case of an Offsite emergency, likely to have effect beyond the installation premises or
an emergency originated from outside the premises of the installation which is likely to effect the
operations of the installation and requires corporate intervention.
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9.2.1.3 On scene Coordinator
Initial Phase
One who is close enough to the scene of emergency may exercise emergency co-ordination in the
initial phase. Accordingly, the Installation Manager will assume the role of On-Site Coordinator (OSC).
Intermediate Phase
The Chief Emergency Coordinator (CEC) at Asset level may appoint a person, normally stationed at
base to take over the task of OSC at Site Control Room (SCR).
Function
The OSC will make an assessment of the situation; the type and quantity of assistance
required and communicate the same to the Asset ECR. The OSC will mobilize the resources available at
the site, deal with the situation and take such actions as directed by the Chief Emergency Coordinator at
the Asset/ Basin/ Plant. He will transmit situation reports (SITREPS) at regular interval prefixing a
numerical sequence to each message.
9.2.1.4 Site Control Room
Location
The Site Control Room will function at the installation depending upon situation. Alternate site control
room will be set up at the closest installation.
Mobilization
The On-Scene Co-coordinator (OSC) will set up SCR as soon as he becomes aware of the emergency
situation.
Function
To make situation reports (SITREPS) from time to time and take steps to fight the emergency. Determine
the type of assistance required & mobilize the same through ECR.
9.2.1.5 Communication
As effective communication is crucial for the overall success of the operation, a
communication flow-chart for such scenario is outlined herewith. In the event of a terrorist act, timely,
accurate communications will be critical for the success and survival. Timely response during emergency
is extremely important.
CEC at the work center must communicate immediately as per the flow chart for first
information in case any emergency is likely to come to the notice of media. This is to ensure that the
management has an authentic update of the emergency to reply to the media.
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9.3. OIL SPILL RISK ASSESSMENT
9.3.1. Oil spill scenarios
Exploration drilling in offshore areas implies a risk for acute spills to sea. Major incidents are
blowouts during drilling into the reservoir zone. Minor incidents include small spills of crude oil (well
releases), diesel (from the rig or from supply vessels) or hydraulic oil (from the rig). With respect to
environmental risk and oil spill emergency preparedness, the dimensioning incident is a blowout.
The oil spill scenarios have been assessed to classify into:
Most probable spill scenario
Maximum likely spill
Worst case spill
TABLE 9.3.1: OIL SPILL SCENARIOS
Spill Scenario Classification Qty. of oil spilled
Spill due to Rupture of flow lines/ hose during transfer of
diesel from supply vessel to the Drilling Rig (as such these
transfer hoses are likely to have auto shut off valve, but
presuming a scenario where this auto shut off valve is non-
functional and is manually shut off after a reaction time of
15 min)
Most probable
spill scenario
100 MT
(Instantaneous)
Spill of diesel due to collision between supply vessel and
the Jack-up drilling rig and damage to diesel storage in the
supply vessel
Maximum likely
spill
700 MT
(Instantaneous)
Spill of crude oil / condensate due to well blowout which
takes 2 days to cap
Worst case
spill
5000 MT (over a
period of 2 days)
9.3.1.1 Marine & Coastal Features Sensitive To Oil Spills
The block MB-OSN-2005/3 is approximately at a distance of over 160 km off the coast of
Mumbai where no ecologically sensitive areas in the exploration area lie. However, the Marine National
Park and the Marine Sanctuary that lie in the gulf will not come in the specific activities for exploratory
drilling in the block MB-OSN-2005/3. Besides this, the Maharashtra coastline comprises of significant
mangrove patches which could also be sensitive to oil spills in case of large oil spill. The well proposed
to be drilled in this block which is closest to this coast is at a distance of over 160 km.
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9.3.1.2 Assessment of Risks Due To Oil Spills
In absence of sufficient met-ocean data and an oil spill trajectory model validated to Indian
metocean conditions, the assessment of risks due to oil spills is made on the basis of logical analysis.
Quantitative spill trajectory models have not been used as part of this assessment. This assessment is
with respect to seasonal trend of coastal currents. A recent study on “Intra-seasonal variability of coastal
currents in India” (by SSC Shenoi, INCOIS – Dec’10) indicates that except during the period June to
October of the year, sea currents around the coast (excluding the gulf) are pre-dominantly towards the
northwest. During the monsoon period (i.e., Jun to Oct), the currents are predominantly towards
southeast.
Considering this, accidental spills from the proposed oil and gas drilling activity in this block
are not likely to hit the coast during the weather window generally chosen for deploying offshore rigs and
undertaking drilling activities. Moreover the nearest well (from the coast) proposed to be drilled is at a
distance of over 160 km from the coast. Therefore the risk of oil spills due to the proposed exploratory
drilling activities in this block is negligible / nil. However, considering the coastal sensitivities, ONGC
understands that preparedness to respond to oil spills during exploratory drilling program is key for
exploratory drilling.
9.3.1.3 Oil Spill Contingency Plan
Since accidental spills of crude oil and oil based products pose risks to human health and
environment, ONGC will make every effort to prevent accidental oil spills and to clean them up quickly in
case such accidental spill occurs.
The entire offshore facilities are designed, installed and operated in such a way, so as to
minimize possibility of any accidental oil spills. Facilities and resources supplied by outsourced agencies
also meet international pollution prevention design and operation standards. Oil spill risks are identified
and measures to prevent and contain oil spills have been outlined in contingency plan given below:
To establish response procedures for oil spills
To combat, contain, recover, cleanup and dispose of the spilled oil
To provide training and drill schedule for keeping the system in place, and
To meet statutory requirements
Activation of plan starts with notification of “Oil Spill” and spill assessment. Immediate action
is taken to disconnect the source. Further action is taken based on Short Term and Long Term strategies
for spill containment.
Oil Spill Response
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In any marine oil spill response, mobilization of resources depends on a number of factors.
One of the most critical ones is the time taken to activate this plan and mobilize equipment & resources
to the scene of the spill. To ensure efficiency in response initiation, a tiered response approach is adopted
by ONGC in line with NOSDCP and Oil Industry Safety Directorate (OISD) guidelines. This plan takes
into account the response time needed to mobilize, transport and deploy increasing amounts of resources
to the scene of a spill, depending upon the severity of oil spill.
The size, location and timing of an oil spill are unpredictable and different situations require
different responses. The severity of an oil spill incident is largely based on the quantity of oil spilled and
its distance from the shore. With increasing size of spill and decreasing distance from shore the number
of outside agencies involved and urgency of their notification increases and so does the resources
required and degree of organization needed. Based on past experience of oil spills, the strategy and
guidelines for dealing with different sizes of oil spills, Tier wise classification of resources have emerged.
But these tier levels were varying from place to place and company to company based on different
interpretations. In India, considering these differences, guidelines has been provided by Oil Industry
Safety Directorate (OISD), Ministry of Petroleum & Natural Gas to enable oil companies to plan their
respective tiered response strategy.
ONGC follows a 3-tier approach for oil spill response: Tier 1, 2 and 3. These are explained in
following sections.
Tier I:
In line with the standard industry practice, ONGC is prepared to mitigate spills of importance
from routine operations (Tier-1), while oil spill situations of higher magnitude are dealt with industry co-
operation and external intervention. Oil spill is considered as Tier 1 when it is less than 100T and is up
to 500 m around its installations. ONGC will immediately respond to combating such oil spill incidents
and will continue to provide equipment, material, trained manpower, sampling efforts, and vessels.
ONGC’s IMR (Inspection, Maintenance & Repair) Division is operating four numbers of Multi
Support Vessels (MSV) in the Western Coast. One of the functions of MSVs is to handle oil spills. The
following facilities exist with ONGC.
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TABLE 9.3.2: OIL SPILL RESPONSE EQUIPMENT WITH IMR, ONGC (TIER –I FACILITY)
Sl.
No.
Item Availability
in the field
At Nhava Remarks
1 Oil Spill
Dispersants
20 M3 Type-II OSD available on MSVs and at Nhava
Store.
2 Heavy Duty
Containment
Booms
500Mtrs each
(M-36, HAL
Anant &
Seamac-II)
500 mtrs
(S/Sevak)
MSV S/Sevak-500 mtrs of heavy duty oil
containment boom (Make -Lamor), kept at
Nhava Supply Base
MSV Mal-36-500 mtrs available on board
(Make-Seacurtain)
MSV HAL Anant -500 mtrs available on board
(Make-Canadyne).
Seamac-II-500 mtrs available on board
(Make –Kepner)
3 Skimmer Sets 3 (M-36, HAL
Anant &
Searnac-II)
1 (S. Sevak) MSV S/Sevak (Make- Lamor),
MSV HAL Anant (Make-Canadyne),
Malviya-36 (Make-Seavac HD Delta),
Seamac-II (Make-Kepner)
4 Ship Borne
Dispersant
Spray System
7 sets One each on S/Sevak, and Prabha and five
on chartered vessels-Hal
Anant, Mal-36., Mal-25 Mal-27 and Seamac-
II
Tier II:
Oil spill is considered as Tier II when it is more than 100T but less than 700T. ONGC will
immediately inform Coast Guard about such oil spill incidents as they are the national agency for ensuring
marine environment security in India.
Coast Guard is involved in protection and preservation of the environment and prevention and
control of pollution. Being the national coordinator in oil spill response, it has a variety of responsibilities
under the National Oil Spill Disaster Contingency Plan (NOS-DCP). It is the coordinator for oil spill
response in the entire maritime zones of India with specific allocation for direct response functions in the
maritime zones outside the port limits and notified areas around offshore oil facilities.
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TABLE 9.3.3: POLLUTION RESPONSE EQUIPMENT HELD AT COAST GUARD POLLUTION
RESPONSE TEAM (WEST), MUMBAI
Sl.
No.
Pollution Response Equipment at PRT ( West),
Mumbai
Qty. (No.) Remarks
1 RO Boom OSA 2000 with deck Reel 4 200 m each
2 RO Boom Powerpack (old) 2
3 RO Boom Powerpack (New) 2
4 Vikoma Hi-Sprint Boom with deck Reel 4
5 Vikoma PN Diesel Hydraulic Powerpack 3
6 Vikoma Hi-Sprint Boom air blower (Echo) 2
7 Vikoma air Blower (Honda) 2
8 Vimkoma Sentinal Boom 1
9 Vikoma Sential boom 1
10 Ro Boom 610 (16 x 25) 16
11 Air Blower for sl. No. 10 5
12 Boom Washing Chamber 1
13 Fresh water Chemical Pump for Sl No. 12 2
14 Power pack for Sl. No. 12 1
15 Ro ser (Settling Tank) 1
16 RoC kean Unit 1
17 Beach Cleaning equipment 1
18 Hot water cleaner (KEW) 4
19 Hot water cleaner (L&T) 1
20 CCN-100 off loading pump 1
21 Power pack for Sl. No. 20 1
22 TC-3 Aerial spray unit with bucket 3
23 TC-3 Areal Spray Arm set 5
24 Spill Spray Pump 4
25 Spill Spray Arm (set) for Sl. No. 24 5
26 Wide Spray System 2
27 OMI Oil Mop MK-II-9D 2
28 SS-50 Disk skimmer (Vimoma) 4
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29 Power Pack for OMI Sl. No. 28 4
30 Welosep Vertex Skimmer 2
31 Power Pack for Sl. No. 30 2
32 Desmi DEstroil Skimmer Ds-250 4
33 Powerpack for Sl. 32 4
34 Desmi Destroil Skimmer DS 210 2
35 Powerpack for Sl. 34 - 02 2
36 Dunlop Salvage Barge 100 M3 2
37 Dunlop Salvage Barge 30 M3 3
38 Linductor Oil recovery 2
39 Vikoma Sea Devil Skimmer 3
40 Powerpack for Sl. 3 3
41 Hydraulic Control for Sl. 39 - 03 3
42 Hydraulic hand pallet 3
43 Hydraulic power pack lifter drum lifter 1
44 Hand trolley 1
45 Hand trolley 1
46 Fork lift 1
47 SeaVac Heli Skimmer 1
48 Pallet Stacking System (Ex Jay=24 & Ex Godrej=32) 56
49 Container top for OSA 200 Boom reel 3
50 Oil Spill response kit 1
51 Seavac 330 Heli skimmer system 1
52 RO Boom 1
53 DS 250 Skimmer 1
54 Spill Spray equipment 1
55 Spray Pod 2
56 Spray Pod 8 750 SQN at Daman.
57 IR/UV System 2 -do
58 TC-3 Bucket with boom S/N 7584 1 841 SQN at Daman
59 Oil Water separator 1 At Vadinar
60 Petrol Engine General Purpose 1
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61 Rop Mop skimmer(Diesel engine & power pack) 2
62 Oil Spill Kit with accessories 2
63 Dunlop Dragon Barge 30 Ton .3
64 Sea Curtain Boom 24000 m
65 Sea vac Heli skimmer 1
66 High Pressure Steam Jet Cleaner 2
67 TC-3 Bucket 1 CGAE Goa
68 TC-3 Bucket 1 800 SQN at Goa
69 TC-3 Bucket 1 Vera flight at Kochi
Source: National Oil Spill Disaster Contingency plan (short title: NOS-DCP), 2006 (Updated),
Ministry of Defense, Government of India, CGBR 771, (Edition 2006)
Tier III:
Oil spill is considered as Tier III when it is more than 700T. Globally there are a select few
industry cooperative, international Tier 3 Response Centers. Their location was originally influenced by
the occurrence of major oil spills from shipping, these being perceived as the greatest risk. Since then
their service remit has evolved and the membership and capability have changed. While stockpiles of
equipment remain a key feature, emphasis has grown on the provision of expert staff for a range of
preparedness and response services.
For combating oil spills of this magnitude, ONGC has obtained membership of International
agency i.e. M/S OSRL (Oil Spill Response Limited), UK. The membership is continually renewed annually
to cover all ONGC’s offshore operations from the threat of major oil spills. OSRL is having expertise in
handling the disaster of any higher magnitude. They are capable of deploying their services in minimum
response time anywhere in emergency.
Strategy during first Six Hours
Depending upon nature of emergency at sea and weather conditions booms will be laid
around source of spill for containment. Recovered oil will be stored for further disposal as per laid down
procedures. If some quantity of oil has spread prior to deployment of booms or some oil has slipped away
during containment and recovery process, following factors will be taken into consideration prior to taking
decision on application of dispersant:
Spilled oil shall not be more than 4 hours old
Oil is moving towards shoreline
Spilled crude characteristics are amenable to use of dispersants
Prevailing weather conditions are conducive to dispersant applications.
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Prior approval from Coast Guard for use of dispersant will be obtained.
Spraying of Dispersants
During rough weather, monsoon, low visibility or in case of delayed deployment of equipment,
the spraying of dispersants is considered one of the options, because this strategy needs very less
reaction time (resource mobilization time) and can be initiated by the boat/vessels crew operating in the
area. Spray of dispersants can be done through Helicopters also.
Response equipment such as Containment Booms will be deployed for protection of
Maharashtra coastal belt, the creeks and mangroves along the Maharashtra coast, and sensitive pilgrim
/ tourist area of Dwarka and Bet Dwarka, to deflect spills towards other areas of the shoreline where it
shall cause less harm to the environment.
Shore Cleanup
Despite best efforts to contain and recover spilled oil, there is always a likelihood of spilled oil
reaching shorelines. Shoreline cleanup technique will be practiced for the left over oil as per topography
of the coastline.
9.3.1.4 PROJECT NEED & BENEFITS
The hydrocarbons sector plays vital role in the economic growth of the country. Oil and gas
continue to play a pre-eminent role in meeting a part of the energy demands of the country. Growth of
the economy would lead to spontaneous growth in energy consumption. Economists opine that there the
GDP and per capita energy consumption is a directly proportional. The hydrocarbon sector, therefor,
plays a crucial role in the energy security for the country.
As per the Hydrocarbons Vision – 2025 of the Ministry of Petroleum & Natural Gas, Govt. of
India, inter alia, is – ‘to assure energy security by achieving self-reliance through increased indigenous
production and investment in equity oil abroad.’ The medium term objective for E & P Sector of the country
includes:
Continue exploration in producing basins.
Aggressively pursue extensive exploration in non-producing and frontier basins for
knowledge building' and new discoveries.
Venturing into deep-sea offshore areas of the Indian basin for newer finds.
The rapid economic growth of the country and rising population result in the considerable
increase in demand of petroleum products. The gap between supply and availability of crude oil,
petroleum products as well as gas from indigenous sources is likely to increase over the years.
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The growing demand and supply gap would require increasing emphasis on E&P sector to
pace keep with demand-supply relationships.
At present, India meets about 30% of petroleum requirements from all of its resources. It is,
therefore, impertinent to expedite exploration activities to minimize our dependence on the imports and
to ensure the energy security of our country.
In view of the unfavorable demand-supply balance of hydrocarbons in the country, ONGC has
been intensifying its E&P activities in Indian basins to improve on the domestic productivity of oil and gas
as well as make equity oil available by acquiring gas assets overseas with a focus on oil security.
The Western Offshore area has been the main contributor of domestic hydrocarbon
production the Indian exchequer. The recent finds and discoveries have given new vistas and the
likelihood of finding potential hydrocarbon pools is quite high here in the basin.
Block MB-OSN-2005/3 is located in the Western Offshore basin and is proposed by ONGC
for exploratory drilling to explore for the liquid gold. In view of prognosticating the feasibility of presence
as well as tapping hydrocarbon, this offshore exploratory project is of immense domestic and national
importance.
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Chapter 10
ENVIRONMENT MANAGEMENT PLAN
The Environmental Management Plan is a site specific document for ONGC’s Offshore Drilling
Project in Arabian Sea developed to ensure that the project can be implemented in an environmental
sustainable manner and where all contractors and related stakeholders understand the potential
environmental impacts and risks arising from the proposed project and take appropriate actions to
properly manage them.
The EMP will be taken as a guide to optimize its management of all aspects of ONGC’s
activities in the MB-OSN-2005/3 Block in the Arabian Sea and activities related to the operations of its
onshore project base at Nhava. The EMP describes inter alia the actions in terms of:
Regulations and Standards
Best Practices and guides
Local Environmental and Social Sensitivities
International Conventions and National Policies
10.1. SELECTION OF DRILLING LOCATION AND NAVIGATIONAL PATH WAYS
Proper site selection and routing of navigational pathways for drilling rig and supply vessels
can result in preventive mitigation measures that may considerably reduce impacts arising out of the
proposed project. The Project planning team will work in close cooperation with the HSE Department to
look at preventive options early in the project life cycle based on findings of the EIA study. This will ensure
optimizing the need for “end-of-the-pipe” solutions to the extent feasible. Some of the proposed mitigation
measures that need to be adopted are discussed below.
Setting of Exploratory Block and Drill Locations
As has been elaborated earlier, there exists no designated marine protected areas or marine
archaeological sites in and around the project block. The project location, therefore, is not bound by any
national and international siting regulations. Occurrence of sensitive species in close proximity or within
the block will also govern the selection of drilling locations. If sensitive species viz. sea turtles are
anticipated in the block area, their presence will be monitored in accordance with the international sighting
guidelines for marine mammals.
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Selection of Navigational Pathway for Drilling Rig & Supply Vessels
ONGC will be giving due weightage to the impacts that may arise due to movement of supply
vessels (SOVs) and drilling rig, which will be documented prior to the exploratory operations and planned
taking into account MARPOL designated sensitive areas and also marine habitats protected by national
legislation. Appropriate measures will be adopted by the project proponent to avoid migratory routes of
turtles and ecologically and culturally sensitive coastal areas during vessel movement. In addition,
consultations with different stakeholders (Directorate of Fisheries, Coast Guard, Port Management
Board, etc.) will be carried out to aid in the routing of supply vessels from the logistic base.
10.2. ATMOSPHERIC EMISSIONS
There are a number of sources of atmospheric emissions (both point sources and fugitive
emissions) from the proposed offshore project. The primary air pollutant emission source for the proposed
project is DG sets. Five DG sets for meeting power requirement (~600 KW/day) will be in operation during
the exploratory period with estimated fuel consumption of 15 Kl/day/rig. The following specific mitigation
measures are recommended:
All equipment would be operated within specified design parameters during drilling
operations and fully trained personnel will be utilized to maintain and test the systems;
The project will monitor and record fuel use for compressors and generator sets.
The emissions from DG sets will be in accordance with the guidelines in MARPOL.
Valves, flanges, fittings, seals and packing considering safety and suitability requirements
will be selected to reduce gas leaks and fugitive emissions. Additionally, leak detection and
repair programs will be implemented;
Flaring of gas during well testing will be minimized and restricted to a short duration;
Flare combustion efficiency will be maximized by controlling and optimizing flare
fuel/air/steam flow rates to ensure the correct ratio of assist stream to flare stream; and
Dry, dusty materials (chemicals), mud etc. would be stored in bags or sealed containers;
10.3. STORAGE AND HANDLING OF CHEMICALS AND SUPPLIES
ONGC will ensure proper storage and handling of chemicals and other supplies at the onshore
facility at Nhava base, prior to their shipment to the rig. A good working inventory will help minimize
impacts that may arise due to such handling and storage. All loading and unloading activities will be
carried out as close as feasible to the storage facilities.
It will be ensured that lids of all containers containing volatile substances/chemicals are
properly fitted.
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All chemical storage areas to have proper bunds so that contaminated run-off cannot escape
as runoff into the nearby coastal areas. Regular inspections to be undertaken for the storage areas to
detect any indication of leakage, decomposition or other unsafe storage conditions and corrective actions
initiated accordingly.
Adequate Personal Protective Equipment (PPEs) shall be provided to all workers involved in
handling of hazardous materials.
10.4. MANAGEMENT OF DRILL CUTTINGS & DRILLING MUD
The offshore exploratory drilling project is likely to generate a considerable amount (Total
volume during drilling of the well ~ 700 m3) of drill cuttings. The disposal option for such drill cuttings
generated from offshore drilling will primarily be governed by the type of drilling mud (water or oil based)
utilized for the exploratory drilling. The disposal of the drill cuttings to be conforming to the guidelines
pertaining to the “Disposal of Drill Cuttings and Drilling Fluids for Offshore Installations” provided by the
Ministry of Environment & Forests (MoEF) G.S.R. 546(E) August 2005. Drill cuttings disposal will be
monitored to check compliance of these guidelines.
Oil based mud will not be used unless and until warranted otherwise, and only water based
mud will be used.
To mitigate specific hole problems if SOBM is used, ONGC will ensure that it has less than
1% of aromatic content and will use with intimation to MoEF
Chemical additives used in the mud will be biodegradable (mainly organic constituents) with
a toxicity of 96 hr. LC 50 Value > 30,000 mg /l as per missed toxicity or toxicity test conducted
on locally available sensitive sea species
Hexavalent chromium compound will not be used in drilling mud. Alternative chemical in
place of chrome lignosulfonate will be used.
Except in emergency situations, bulk discharge of drilling mud in offshore will not be
undertaken. Drilling mud will be recycled to a maximum extent.
Discharge of thoroughly washed drill cuttings separated from mud & unusable portion of
mud will be discharged into sea intermittently, at an average rate of 50 bbl/hr/well to have
proper dilution & dispersion without any adverse impact on marine ecology and
environment.
Drill cuttings will not be discharged in sensitive areas notified by the Ministry of Environment
and Forests.
Disposal of drill cuttings associated with high oil content from hydrocarbon bearing formation
will have oil content < 10 gm/kg.
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The drill cuttings wash water will be treated to conform to limits notified under EPA, before
disposal into Sea. The treated effluent will be monitored regularly.
Use of environmental friendly technology emerging due to substitution of DF or disposal
technology will be brought to the notice of MoEF and regulatory agencies and a prior
approval from Ministry of Environment and Forests will be taken
Barite used in preparation of drilling mud will not contain Hg> 1 mg/kg and Cd> 3 mg/kg.
Daily discharge of drill cuttings and drilling mud to offshore will be recorded, daily effluent
quality will be monitored and compliance reports to be submitted half-yearly to the Ministry
of Environment and Forests.
10.5 OILY WATER DISCHARGES AND OTHER WASTES
In addition to drill cuttings and unused drilling mud, the proposed exploratory drilling
operations would also result in the generation of other routine and non-routine waste streams. These
waste steams will primarily comprise of bilge fluids, ballast water, cooling water, deck drainage and food
and sanitary waste and needs to be disposed and managed in compliance with best industry practices
and international requirements to avoid any impacts arising from the same.
The waste streams which are routinely generated at offshore facilities are listed below along
with their recommended disposal measures and management alternatives:
Ballast Water
The drilling rig will be having a Ballast Water Record Book and ONGC has formulated ballast
water management procedures to a given standard. These procedures will serve as an effective
management tool in reducing the risk arising from ballast-mediated invasion. The process involved will
reduce the density of coastal organisms in ballast tanks which may be able to invade a recipient port,
replacing them with oceanic organisms with a lower probability of survival in near shore waters.
Cooling Water
In regard to the disposal of cooling water, available alternatives will be evaluated and, where
practical, the seawater intake depth will be optimized to reduce the need for use of chemicals. Appropriate
screens will be fitted to the seawater intake if safe and practical. Deck Drainage water generated from
precipitation, sea spray, or routine operations, such as deck and equipment cleaning, will be routed to
separate drainage systems on offshore facilities of the drilling rig. This includes drainage water from
process areas that could be contaminated with oil (closed drains) and drainage water from non-process
areas (open drains).
The following management measures will be followed:
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Chemicals, oils and wastes will be stored in the designated storage areas on the drilling rig
where appropriate spill cleanup materials (e.g. absorbents, containers) are maintained in
accessible locations;
In the event of a chemical or oil spill, absorbents will be used to remove spill material prior
to any washing activities;
Absorbent material, used for cleanup, will be containerized and sent to shore as hazardous
waste;
Bunding will be provided for those areas/activities where there is an increased risk of
oil/chemical spill (e.g. fuel transfer);
Material Safety Data Sheets will be made available for all chemicals used on the drilling rig
(which also includes spill response requirements);
Chemicals used will be assessed for environmental impacts prior to their purchase (e.g. fully
biodegradable detergent); and
Slops water will be discharged via an IMO approved Oil-in-water (OIW) meter as per
MARPOL requirement.
Food Waste
Food waste generated from the kitchen will be, at a minimum macerated to levels less than
25 mm as per the legal requirements prior to their discharge in the marine environment. It will also be
ensured that cleaning agents (detergents) used in the accommodation block are fully biodegradable and
inspection undertaken on a regular basis to conform to operability and performance.
As far as practicable, typical combustible and non-combustible wastes routinely generated at
offshore facilities will be segregated at source and shipped to shore for re-use, recycling, or disposal.
Efforts will be made to eliminate, reduce, or recycle wastes at all times.
The project waste management strategy being adopted to be effective solid waste treatment
hierarchy.
ONGC would ensure that the project contractor(s) have adequate training and follow
stipulated waste management procedures for minimizing, handling and storing waste; waste disposal
contractor(s) use facilities for treatment and the disposal of waste is acceptable to mitigate damage to
the environment to the permissible limit and standards.
Audits are carried out to ensure these are achieved.
Detailed waste management procedures will be put in place and all personnel employed at
the drilling rig will receive formal waste management awareness training, particularly regarding the proper
waste segregation, storage and labeling, procedures for recycling of waste.
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Quality, Occupational Health, Safety and Environmental Policy
Comply with all applicable occupational, safety, environmental legal and other requirements
of the organization.
Commitment for continual improvement in Quality, Occupational Health, and Safety and
Environmental management and performance.
Prevention of pollution due to release of hydrocarbon and other waste.
Ensure safe operations and prevent loss of property.
Protection of employees, contractual persons and persons living in adjacent areas of the rig
from the foreseeable work hazards.
Optimize the use of natural and other resources.
Maintain safe and healthy work environment.
Provide quality product and service to the customer’s satisfaction in the drilling / servicing
of well in offshore for production of hydrocarbons consistent with national and international
standards.
Be always alert and equipped to respond to emergencies and disasters by having an
updated “Emergency Response Plan” and “Disaster Management Plan”.
Equip employees and contractors with the awareness, information, instructions, and
Supervision Skills needed for safe working, quality of operation and environmental
management.
Identify and maintain the processes needed for effective implementation of the “Quality
Management System”.
10.6 MANAGEMENT MANUAL
Management of the rig describes the relevant management systems for quality occupational
health, safety, and environment in the QHSE management system manual. The management system
manual of rig establishes and maintains a quality manual that includes:
The scope of the quality management system includes all the elements of the ISO
The documented procedures for the management of quality management system have been
established for;
1. Commitment to the relevant clauses of ISO Standard
Needed by the various sections of Rig listed as documents of internal origin (DIO), these
are:-
MM manual,
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Book of delegated powers,
R & P Regulations,
ONGC Chemistry lab procedures,
ONGC Emergency Plan (EMP).
Cementing manual,
Drilling Operational manual
Code of Safe practices Vol. I & II
Procedures needed for implementation of various clauses also referred to as Quality System
Procedure (QSP)
Check lists for the various key operations and these may be maintained by the concerned
personnel or demonstrated by them.
The details of the procedures and method of operations are developed based on the
competency of the complexity of the operations. The method of presentation of procedures aims at
enhancing the understanding of operation being done and realization of the services of drilling and testing
or the working over of wells at all stages of operation/manufacturing.
Review
The management system manual is generally reviewed at least once in a year. The review
can even be carried out in part or whole in a shorter period when the need for the same is felt due to audit
observations, change of system, change of equipment, change of management etc. The review is carried
out based on the inputs provided by a nominated manual development team. Records of such reviews
are maintained by MR/Dy MR.-QHSE.
10.7 MANAGEMENT SYSTEM PROCEDURES AND DOCUMENTATION
The rig management team documents, implements and maintains procedures for ensuring
requirements for quality, occupational health, safety, and environment in accordance with the installation
and ONGC’s stated policies. The following procedure manuals have been documented:
QHSE/DS/SSK/CPM-Common procedure manual
QHSE/DS/SSK/SPM-Safety procedure manual
QHSE/DS/SSK/QPM-Quality procedure manual
QHSE/DS/SSK/EMS/OM/01 to 04-Environment Management System and Aspect
Manual
QHSE/DS/SSK/RR- Risk Register
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Management system documentation is in the form of a written QHSE management manual
(QHSE/DS/SSK/MM).
Implementation, Operation, Infrastructure and Work Environment
The Drilling Services has determined, provided and maintained the infrastructure needed to
achieve conformity to services requirements. Infrastructure includes machineries, man power, plants,
equipment (both hardware and software) for exploratory or work over drilling operations. ONGC also
maintains marine and air logistics services, catering services, communication and information systems
for satisfactory performance in its drilling operation.
Work Environment in offshore comprises 12 hours shift duty, 14 days on-off work period
(24x7), accommodation for offices, staff and contract personnel etc. Environmental factors such as
temperature, humidity, illumination, wind speed, ventilation and weather conditions are taken care.
Resource, Roles, Responsibility & Authority
The roles, authorities and responsibilities are defined, documented and communicated to all
concerned staffs to facilitate effective QHSE Management. The Management provides essential
resources for manpower, technology and finance required for establishment, implementation
maintenance, improvement and control of QHSE Management System.
Documentation / Control of Documents
The OHSAS and EMS management system documentation includes
The OHSAS and EMS Policy and objectives and targets.
Description of scope of OHSAS and EMS.
Description of main elements of OHSAS and EMS and their interaction and reference to
related documents.
Documented procedure and records required by QMS, OHSAS and EMS standards.
Documents, including records, determined by Drilling services to be necessary to ensure
the effective planning, operation and control of processes that relate to management of its
OHSAS risk and environmental issues.
The details of the Occupational health, Safety, Environment and Quality management system
documentation are as below:
QHSE Management manual (QHSE/DS/SSK/MM) - This manual provides the outline for the
quality, occupational health, safety and environment management systems and describes
the commitment to adoption of elements as per the requirement of ISO9001, OHSAS18001
and ISO14001.The manual also provides the cross references to the relevant procedures.
134
Common Procedure Manual (QHSE/DS/SSK/CPM) - This manual, inter alia, defines the
detailed procedure of applying each element defined in the QHSE Management manual.
Quality Procedure Manual (QHSE/DS/SSK/QPM) - This manual contains all the quality
procedures (operating work instructions) to address the significant quality issues.
Environment Aspect Manual (QHSE/DS/SSK/EMS/AM): This manual provides
The list of environmental aspects (QHSE/DS/SSK/EMS/AM/01)
Evaluation and significant environmental aspects (QHSE/DS/SSK/EMS/AM/02)
Objective and Targets (QHSE/DS/SSK/EMS/AM/03)
Environment management program (QHSE/DS/SSK/EMS/AM/04)
Risk Register (QHSE/DS/SSK/RR): This manual provides the master list of
Risk Assessment criteria (QHSE/DS/SSK/RR/RAC/01)
Objectives (QHSE/DS/SU/RR/OBJ/04)
Occupational and safety hazards & Evaluation (QHSE/DS/SSK/RR/HIE/02)
List of significant risk (QHSE/DS/SSK/RR/SSK/03)
Legal Register (QHSE/DS/SSK/LR/)
This register will contain the list of applicable legislation, acts, Regulations Company’s
code etc. with reference to QHSE.
135
Chapter 11
ORGANIZATIONAL STRUCTURE
AND IMPLEMENTATION FRAMEWORK
In addition to regular operational roles & responsibilities defined for the drilling services, all
personnel directly or indirectly have a role to play towards an effective environment management in the
project. Personnel responsible for environment management at the drilling project will be responsible for
implementing the HSE policy and the environment management plan. The drilling services shall co-
operate with government agencies, regulatory authorities and other stakeholders who may have
environmental concerns associated with the project.
Various key personnel involved in the oil spill in the organization and communication have
been shown in a hierarchical manner in the following Figure 11-1.
FIG. 11.1: OIL SPILL ORGANIZATION AND COMMUNICATION
136
ONGC would also set up a Safety Committee in the MODU headed by the Well Operations
Manager as stipulated by the OISD Rules. The Safety Committee would meet once a week and will
function with the following mandate:
Discuss work related health, safety and environmental issues and make suggestions for
improvement;
Undertake safety and housekeeping inspections of the MODU with a view to identify
deficiencies and recommend corrective measures;
Promote development of safety attitude amongst employees.
11.1 CAPITAL AND RECURRING COST FOR ENVIRONMENTAL POLLUTION CONTROL MEASURES
ONGC has regular procurement plans for various operations related to hiring of drilling rig
services and associated facilities. These also include cost related to various aspects related to
environmental management measures. Thus procurements related to EMP are inbuilt in the procurement
requirement of ONGC.
11.2 DISCLOSURES OF CONSULTANTS ENGAGED
For carrying out the environmental impact assessment study of the proposed oil exploration
block MB-OSN-2005/3 in Mumbai offshore, various institutions/agencies have been working in
coordination with each other.
11.3 EIA CONSULTANT ENGAGED
No consultant has been engaged for the present study. Corporate HSE (Health Safety &
Environment) Department, ONGC, 8th floor, Scope Minar, South Tower, Laxminagar, Delhi – 110 092 is
accredited to carry out EIA studies and the present study has been carried out under their active
supervision & guidance. The primary data has been provided by Institute of Petroleum Safety, Health and
Environment Management (IPSHEM), ONGC, Betul, Goa-403 723.
11.4 AGENCY ENGAGED FOR CRZ MAPPING
Since the block MB-OSN-2005/3 block of Western offshore lies much beyond 12 nautical
miles, the nearest point of the boundary lies at a distance of over 255 km (~ 138 nautical miles) no CRZ
regulation was applicable in the block and therefore, CRZ mapping was not mandatory.
137
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Annexure – I
ToR issued by MoEF&CC for the NELP VII block MB-OSN-2005/3 (Scanned copy)
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143
144
145
146
147
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149
Annexure – II
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Annexure - III
EQUIPMENT AND APPLICABLE STANDARDS
Sl. No.
Equipment Verification retirements Reference Standard
1 Drilling structure, Derick floor, sub structure, lifting equipment.
A. Derrick / structures i. Structures have been designed and fabricated by manufacturers as per API Spec 4F or equivalent. This verification should include structural safety level (refer sections 6 and B.6 of API Spec 4F). ii. Different categories’ inspection(s) of derrick, structures and drill floor have been carried out as per section 6 of API RP 4G or equivalent and OEM’s recommendations, besides Non Destructive Examination (NDE) as considered necessary. Chairmen cum managing director iii. Repair and modification of structures (if carried out, based on inspection) have been carried out as per section 7 and 8 respectively of API RP 4G or equivalent and OEM’s recommendations. Quality control of repair and modification has been ensured in line with requirements of section 11 of API SPEC 4F or equivalent. B. Drilling equipment i. Installation, inspection and maintenance of IC engines have been carried out as per API Spec 7C-11F or equivalent and OEM’s recommendations. For minimizing potential fires and/or explosions in the operations of IC engines requirements given in Appendix A of API Spec 7C-11F or equivalent, are being followed. Functional testing of safety devices and emergency stop function has been carried out. ii. Design, inspection and operating limits of drill stem components is as per API RP 7G or equivalent. iii. Design of drilling equipment (rotary equipment, slush pumps, power tongs and draw works) is as per API Spec 7K or equivalent. iv. Inspection, maintenance and repair of rotary equipment, slush pumps, power tongs and draw works has been carried out as per API RP 7L or equivalent and OEM’s recommendations. Inspection has included NDE and/or opening of equipment as considered necessary. Functional testing of safety devices and emergency stop function has been carried out. v. Design of drilling hoisting equipment is as per API Spec 8A and API Spec 8C or equivalent. vi. Inspection, maintenance and repair of hoisting equipment are as per API RP 8B or equivalent and OEM’s recommendations. Inspection of hoisting equipment has focused on structural integrity and personnel protection. Category III and IV inspection has included NDE / MPI and/or opening of equipment as considered necessary. Functional testing of safety devices and emergency stop function has been carried out.
API Spec 4F (3rd Edition 2008) API RP 4G (3rd Edition, 2004) API RP 4G(3rd Edition, 2004) API Spec 4F (3rd Edition 2008) API Spec 7C-11F (5th Edition 1994) API RP 7G API Spec 7K API RP 7L API Spec 8A and API Spec 8C API RP 8B
151
vii. Minimum requirements and terms of acceptance of steel wire ropes as per API Spec 9A / ISO 10425 or equivalent are being followed. viii. Field care (inspection) and use of wire rope and evaluation of rotary drilling line has been carried out as per API RP 9B or equivalent. ix. Inspection of piping and piping systems has been carried out as per API RP 570 and API RP 574. x. Pressure vessels have been inspected externally and internally; thickness measurement / crack detection tests have been carried out as deemed necessary. Pressure testing at a pressure equal to maximum allowable working pressure has been carried out. Safety valves / instrumentation have been tested.
API Spec 9A / ISO 10425 API RP 9B API RP 570 and API RP 574
2 Well Control Systems: blow out preventers, diverters, marine risers, choke and kill system, control systems for well control equipment.
A. Design of drill through equipment / blowout prevention equipment – ram and annular blowout preventers, hydraulic connectors, drilling spools, adaptors etc. is as per API Spec 16A / ISO 13533 or equivalent. Records of maintenance (including major inspection as per section 17.10.3 of API RP 53 and OEM’s recommendations) have been reviewed. Installation and testing (complete performance testing including functional and pressure tests) of blow out control equipment is being carried out in line with API RP 53 or OISD-RP-174 or equivalent. B. Design and maintenance of diverter systems is as per API RP 64 or equivalent. Inspection and testing of diverter systems has been carried out as per API RP 64 or OISD-RP-174 or equivalent. C. Design of choke and kill systems are as per API Spec 16C or equivalent. Pressure testing of choke and kill systems is being carried out in line with API RP 53 or OISD-RP-174 or equivalent. Flexible choke and kill lines and choke manifold are inspected as per section 17.10.3 of API RP-53(3rd Edition 1997) and OEM’s recommendations. D. Design of control systems for well control equipment and diverter equipment is as per API Spec 16D and API RP 53 or equivalent and performance requirements/ testing, inspection and maintenance is as per API RP 53 or OISD-RP-174 or equivalent and OEM’s recommendations. E. Marine drilling riser systems for floating drilling operations have been selected, operated and maintained in line with API RP 16Q or equivalent. Design, manufacture and fabrication of marine drilling riser system and associated equipment used in conjunction with a subsea blowout preventer (BOP) stack are as per API Spec 16F or equivalent. Design and standards of performance for marine drilling riser coupling is as per API Spec 16R or equivalent. Risers and riser couplings / joints are being inspected for wear, cracks and corrosion; thickness measurement has been carried out as required.
API Spec 16A (3rd Edition 2004) / ISO 13533 (2001) API RP 53 (3rd Edition 1997) or OISD-RP-174 API RP 64 or OISD-RP-174 API Spec 16C API RP 53(3rd Edition 1997) or OISD-RP-174 API Spec 16D and API RP 53 API RP 53 or OISDRP-174 API RP 16Q API Spec 16F / API Spec 16R
3 Man riding equipment Selection of man riding equipment is done ensuring that equipment is suitable for man riding operations, and the equipment are inspected and maintained regularly
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4 Station keeping systems: anchoring, mooring, dynamic positioning, compensator and disconnection systems.
Verify that MODU’s station keeping and stability characteristics are suitable for the environmental (including sea bed and soil conditions) and operating conditions envelope. Inspection and maintenance of mooring hardware is as per API RP 2I or equivalent and OEM’s recommendations; and design, manufacturing and maintenance of synthetic fiber ropes for offshore mooring is as per API RP 2 SM or equivalent.
API RP 2SK (for station keeping) MODU code (for stability) API RP 2I API RP 2 SM
5 Drilling fluid handling and cementing system
Physical condition of the equipment is satisfactory and instrumentation, safety alarms and pressure safety valves are being tested regularly.
6 Electrical Systems A. Design and maintenance of electrical systems is as per IMO MODU code meeting requirements of industry standards API RP 500 or API RP 505. B. Inspection and functional testing of emergency power system is being carried out.
MODU code API RP 500 API RP 505
7 Safety systems (exclude items which are covered by MODU safety certificate, provided the rig has valid MODU safety certificate
A. Inspection and testing of the following safety systems is being carried out periodically: − Fire detection system − Gas detection system – HC and H2S − Drilling operations related alarm system − Lifesaving appliances − SCBA − Gas measuring devices − Firefighting system − Communication systems B. Safety systems are as per MODU code requirements, as applicable.
8 Cranes (If classed certificate notation does not cover cranes)
A. Design and testing of pedestal mounted offshore cranes are as per API Spec 2C or equivalent. B. Operations and maintenance of offshore cranes are as per API RP 2D or equivalent. Inspection has focused on structural integrity and includes: − Blocks and sheaves − Wire ropes and end attachments − Hooks − Bearings − Shackles − Securing arrangements − Support structure − Axle pin and housing C. Inspection and function testing has included: − Correct adjustment of brakes − Resistance measurement of electrical systems − Leakages in hydraulic systems D. Load charts have been verified by carrying out load tests as per applicable requirements. Functional testing of safety devices and emergency stop function are being carried out
API Spec 2C API RP 2D
9 Helideck (If classed certificate notation does not cover helideck)
Inspection has included: − Structural integrity of deck and supporting structure − Surface of deck − Obstacles and marking − Safety net − Fire safety arrangements
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Annexure - IV
COMPARATIVE ECOTOXICITIES
Comparative ecotoxicitities (96 hrs LC50 values) of SPP of 15 different system drilling fluids
for one species of sensitive pawn (Penaeus monodon) and one species of fish (Mugil cephalus) are
summarized in the following table.
Comparative 96 hrs LC50 values (ppm) of different WBM samples in response to species of prawn (Penaeus monodon) and fish (Mugil cephalus).
Sample
No. Drilling Fluid System
Test Species Permissible
Limit* P. monodon M. cepjalus
Clay Free Non Damaging System ppm (%) ppm (%) (%) or (ppm)
1 KCL-PHPA System 103,100 10.31 113700 11.37 >3.0% or >30,000
2 CL-CLS System 77,700 7.77 77800 7.78 >3.0% or >30,001
3 HTHP System 84,100 8.41 87800 8.78 >3.0% or >30,002
4 Biopolymers System (TSP) 97,200 9.72 83600 8.36 >3.0% or >30,003
5 KCL-KOH-K-Lignite System 81,900 8.19 93000 9.30 >3.0% or >30,004
6 Potassium Formate System 62,100 6.21 53000 5.30 >3.0% or >30,005
7 KCL-Polyol System 58,600 5.86 47600 4.76 >3.0% or >30,006
8 Sodium Formate System 37,100 3.71 46000 4.60 >3.0% or >30,007
9 Low Lime System 102,400 10.24 121900 12.19 >3.0% or >30,008
10 Choline Chloride based System 120,200 12.02 112500 11.25 >3.0% or >30,009
11 Mixed metal oxide System 55,100 5.51 56600 5.56 >3.0% or >30,010
12 HGS System 50,900 5.09 48700 4.87 >3.0% or >30,011
13 Silicate Mud System 44,100 4.41 46100 4.61 >3.0% or >30,012
14 Low Toxic mineral Oil based Mud
system
255,200 25.52 261100 26.11 >3.0% or >30,013
*Permissible limit (96 hrs LC50) as specified by the Ministry of Environment and Forests, Govt. of India vide G.S.R. 546 (E)- dated 30th August, 2005 is >30,000 mg/l or >3.0%
The 96 hrs LC50 values of 15 water based drilling fluid systems to post larvae of black tiger
prawn (Penaeus monodon) were found to be range from 37,100 ppm (3.71%) for KCL-Polyol System to
255,200 ppm (25.52%) for Silicate Mud System drilling respectively. On the other hand, 96 hrs LC50
values of different drilling fluid systems tested using larvae of grey mullet (Mugil cephalus) were found to
be range from 46,000 ppm (4.60% for KCL-Polyol System to 261,100 ppm (26.11%) for Silicate Mud
System, respectively.
The determined median lethal concentrations (96 hrs LC50 values) for all the drilling fluids to
two tested species fell within the acceptable criterion of >30,000 mg/l (>3.0%) as stipulated by
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EPA/MoEF. Further, the of toxicity indices of 15 drilling fluid sample supplied by Institute of Drilling
Technology (IDT) of Oil and Natural Gas Corporation Limited (ONGC), Dehradun was assessed by
comparing the median lethal concentrations (96 hrs LC50 values) obtained for post larvae of prawn and
fish larvae against the Toxicity rating classification system used by EPA/NPDES (Table below).
Toxicity testing classification system used by EPA/NPDES
Category Median lethal concentration (LC50)
Non-toxic (NT) >100,000 mg/l
Practically Non-toxic (PNT) 10,000-100,000 mg/l
Slightly-toxic (ST) 1,000-10,000 mg/l
Moderately-toxic (MT) 100-1,000 mg/l
Toxic 1-100 mg/l
Very toxic < 1 mg/l
(Hindwood et al., 1994)
The toxicity indices determined for prawn post larvae and fish larvae belonged to the ‘Non-
toxic’ category as per the toxicity testing classification used by EPA/NPDES (Table 36). Therefore, it is
concluded that based on acute toxicity test results on local sensitive sea species, the water based drilling
fluid sample provided by The Institute of Drilling Technology (IDT) of Oil and Natural Gas Corporation
Limited (ONGC), Dehradun is acceptable to EPA/NPDES/BAT/MoEF for its use and discharge in
offshore/onshore drilling operations.
Source: Institute of Drilling Technology (in-house Report 2013).