Leadon Decommissioning Programmes - gov.uk · Title: Leadon - Decommissioning Programmes Date 24/01/14 1. All of the subsea wells will be plugged and abandoned in accordance with

Doc No: LEA-LEA108-SU-RE-0019 Page 1 of 61

Title: Leadon - Decommissioning Programmes Date 24/01/14

Leadon Decommissioning Programmes

Consultation Draft Programmes - December 2013

LEA-LEA108-SU-RE-0019



Document Reference

LEA-LEA108-SU-RE-0019

R2 61

Rev Total Sheets

System : LEA108

Change Number : 5318

Title:

Draft Leadon Decommissioning Programmes

Maersk House

Crawpeel Road

Altens Industrial Estate

Aberdeen

AB12 3LG

Telephone: 01224 242000

www.maerskoil.com



DOCUMENT CONTROL

REVIEW AND APPROVAL

Prepared by Ross McNeill / Martin Simms/ Vincent Petitfils

Reviewed by Doug MacLeod

Approved by Glenn Corr

REVISION RECORD

REV. DATE REVISION DETAILS

R1 24/01/14 Issue for Public Consultation

DISTRIBUTION LIST

1 Department of Energy & Climate Change (DECC)

2 Scottish Fishermen’s Federation (SFF)

3 National Federation of Fishermen’s Organisations (NFFO)

4 Northern Ireland Fishermen’s Federation (NIFF)

5 Global Marine Systems Ltd (GMS)



TABLE OF CONTENTS

LIST OF ABBREVIATIONS ..................................................................................................... 5

TABLE OF FIGURES .............................................................................................................. 7

LIST OF TABLES .................................................................................................................... 7

1.0 EXECUTIVE SUMMARY ................................................................................................ 8

2.0 BACKGROUND INFORMATION ................................................................................... 16

3.0 SCOPE OF DECOMMISSIONING ................................................................................. 21

4.0 INVENTORY OF MATERIALS ....................................................................................... 29

5.0 REMOVAL AND DISPOSAL OPTIONS ......................................................................... 32

6.0 SELECTED REMOVAL AND DISPOSAL OPTIONS ..................................................... 40

7.0 WELLS .......................................................................................................................... 42

8.0 DRILL CUTTINGS ......................................................................................................... 43

9.0 ENVIRONMENTAL STATEMENT .................................................................................. 44

10.0 INTERESTED PARTY CONSULTATIONS ..................................................................... 46

11.0 COSTS ........................................................................................................................... 48

12.0 SCHEDULE ................................................................................................................... 49

13.0 PROJECT MANAGEMENT AND VERIFICATION.......................................................... 50

14.0 DEBRIS CLEARANCE & AS LEFT SURVEY ................................................................ 51

15.0 MONITORING AND MAINTENANCE ............................................................................. 52

16.0 SUPPORTING STUDIES AND REFERENCES .............................................................. 53

APPENDIX 1 – REFERENCE DRAWINGS ............................................................................. 54

APPENDIX 2 – SPOOLS DETAILS ......................................................................................... 55

APPENDIX 3 – COMPARATIVE ASSESSMENT MATRICES ................................................. 57

APPENDIX 4 – WELL PLUG AND ABANDONMENT OPERATIONS ..................................... 60

APPENDIX 5 - FEED PROCESS FOR DECOMMISSIONING OPTION .................................. 61



LIST OF ABBREVIATIONS

ALARP - As Low As Reasonably Practical CAPEX - Capital Expenditure CDTM - Controlled Depth Tow Method CEFAS - Centre for Environment Fisheries & Aquaculture Science CO2 - Carbon Dioxide COP - Cessation of Production DECC - Department of Energy and Climate Change DSV - Diving Support Vessel DTI - Department for Trade and Industry EHS - Environmental Health and Safety EIA - Environmental Impact Assessment ES - Environmental Statement FEED - Front End Engineering & Design FPSO - Floating Production Storage and Offloading ft - Feet GMS - Global Marine Systems Ltd GPIII - Global Producer III GVI - General Visual Inspection HCV - Heavy Construction Vessel HP - High Pressure Hs - Significant Wave Height IMO - International Maritime Organisation IR - Individual Risk JIP - Joint Industry Project JNCC - Joint Nature Conservation Committee Kg - Kilogram Km - Kilometre KN - Kilonewton LAT - Lowest Astronomical Tide LTOBM - Low Toxicity Oil Based Mud LSA - Low Specific Activity m3 - cubic meters MCA - Marine & Coastguard Agency MEG - Monoethylene Glycol MLS - Midline Structure mm - millimetre MODU - Mobile Offshore Drilling Unit MONS - Maersk Oil North Sea UK Limited NBR - North Bundle Replacement NFFO - National Federation of Fishermen’s Organisations NIFF - Northern Ireland Fishermen’s Federation NORM - Naturally Occurring Radioactive Material NOX - Nitrogen Oxide OBM - Oil Based Mud OSPAR - Convention for the Protection of the Marine Environment of

The North East Atlantic P&A - Plug and Abandonment PLL - Potential Loss of Life ppm - Parts per million



psi - Pounds per Square Inch PL - Pipeline No. ROV - Remotely Operated Vehicle RQ - Risk Quotient SAC - Special Area of Conservation SFF - Scottish Fishermen’s Federation SOX - Sulphur Oxide SWL - Safe working load Te - Tonne ToP - Top of Pipeline UKCS - United Kingdom Continental Shelf WIL - Well Intervention Vessel WO - Work Over WPA - Well Plug & Abandonment



TABLE OF FIGURES

FIGURE 1: FIELD LOCATION IN UKCS ..................................................................................................................... 13 FIGURE 2: FIELD LAYOUT....................................................................................................................................... 14 FIGURE 3: ADJACENT FACILITIES ........................................................................................................................... 15 FIGURE 4: AS INSTALLED LEADON FACILITIES ....................................................................................................... 16 FIGURE 5: LEADON CURRENT STATUS .................................................................................................................. 17 FIGURE 6: LEADON FIELD IN RELATION TO BERYL ALPHA ..................................................................................... 17 FIGURE 7: AVERAGE ANNUAL LANDINGS BY SPECIES (TONNES) FOR ALL UK AND FOREIGN VESSELS 2007-2008

WITH ICES RECTANGLE 48F1 ........................................................................................................................ 19 FIGURE 8: FISHING EFFORT (DAYS FISHED) FOR ALL UK AND FOREIGN VESSELS 2007-2008 WITHIN ICES

RECTANGLE 48F1 ......................................................................................................................................... 20 FIGURE 9: TYPICAL TOWHEAD (LEFT) AND RISER BASE ........................................................................................ 21 FIGURE 10: VIEW OF THE TWO BUNDLE SECTIONS .............................................................................................. 22 FIGURE 11: TOWHEADS AND MIDLINE STRUCTURE ............................................................................................. 23 FIGURE 12: GAS IMPORT FLOWLINE ..................................................................................................................... 24 FIGURE 13: LEADON DECOMMISSIONING SCHEDULE .......................................................................................... 49

LIST OF TABLES

TABLE I: INSTALLATIONS BEING DECOMMISSIONED .............................................................................................. 9 TABLE II: INSTALLATIONS SECTION 29 NOTICE HOLDER’S DETAILS ........................................................................ 9 TABLE III: PIPELINES BEING DECOMMISSIONED ................................................................................................... 10 TABLE IV: PIPELINES SECTION 29 NOTICE HOLDER’S DETAILS .............................................................................. 10 TABLE V: SUMMARY OF DECOMMISSION PROGRAMMES ................................................................................... 12 TABLE VI: LIST OF ADJACENT FACILITIES ............................................................................................................... 14 TABLE VII: YEARLY SIGNIFICANT WAVE HEIGHT IN THE LEADON AREA (UKDMAP, 1998) .................................... 18 TABLE VIII: STRUCTURE DETAILS ........................................................................................................................... 22 TABLE IX: BUNDLES DETAILS ................................................................................................................................. 23 TABLE X: GAS IMPORT FLOWLINE DETAILS ........................................................................................................... 24 TABLE XI: CROSSING DETAILS ................................................................................................................................ 25 TABLE XII: FLEXIBLE BURIAL EXTENTS AT NBR CROSSING ..................................................................................... 25 TABLE XIII: SPOOL DETAILS ................................................................................................................................... 25 TABLE XIV: DECOMMISSIONED RISER DETAILS ..................................................................................................... 26 TABLE XV: SUMMARY OF THE LEADON WELLS ..................................................................................................... 27 TABLE XVI: STRUCTURE MATERIAL AND CHEMICAL SUMMARY ........................................................................... 29 TABLE XVII: CONDITIONING STATUS SUMMARY - BUNDLES – PL1841 & PL1842 ................................................. 29 TABLE XVIII: BUNDLE MATERIAL AND CHEMICAL SUMMARY ............................................................................... 30 TABLE XIX: GAS IMPORT FLOWLINE MATERIAL AND CHEMICAL SUMMARY ........................................................ 30 TABLE XX: SPOOLPIECE & JUMPER MATERIAL AND CHEMICAL SUMMARY.......................................................... 30 TABLE XXI: MATTRESS AND GROUT DETAILS ........................................................................................................ 31 TABLE XXII: PREFERRED DECOMMISSIONING OPTIONS ....................................................................................... 32 TABLE XXIII: DISCOUNTED BUNDLE OPTIONS ....................................................................................................... 34 TABLE XXIV: EXTRACT FROM QUANTITATIVE IMPACT MATRIX ............................................................................ 35 TABLE XXV: EXTRACT FROM CONFIDENCE RATING MATRIX ................................................................................. 36 TABLE XXVI: COMPARATIVE ASSESSMENT II RESULTS .......................................................................................... 36 TABLE XXVII: NATURAL BUILD-UP SUMMARY ....................................................................................................... 38 TABLE XXVIII: POTENTIAL LOSS OF LIFE FOR PERSONNEL AND OTHER USERS OF THE SEA .................................. 39 TABLE XXIX: SUMMARY OF COMMITMENTS MADE WITHIN THIS ES TO ENSURE IMPACTS TO THE

ENVIRONMENT FROM THE PROPOSED DECOMMISSIONING ACTIVITIES ARE MINIMISED AS FAR AS PRACTICABLE ................................................................................................................................................ 45



1.0 EXECUTIVE SUMMARY

1.1 Combined Decommissioning Programmes

This document contains two decommissioning programmes for (i) the Leadon Field installations and (ii) the Leadon Field Pipelines. Additionally, the plug and abandonment activities for the wells will be outlined.

1.2 Requirement for Decommissioning Programmes

1.2.1 Installations

In accordance with the Petroleum Act 1998, the Section 29 Notice Holders (see Table 2) are applying to the Department of Energy and Climate Change to obtain approval for decommissioning of the installations detailed in Section 2 of this programme.

1.2.2 Pipelines

In accordance with the Petroleum Act 1998, the Section 29 Notice Holder is applying to the Department of Energy and Climate Change to obtain approval for decommissioning the pipelines detailed in Section 2 of this programme. Subject to concluding public, stakeholder and regulatory consultation the decommissioning programmes are submitted in full compliance with national and international regulations and the DECC guidelines. The schedule for the main project outlined in this document is planned to begin in 2014.

1.3 Introduction

The Leadon Field is located on the United Kingdom Continental Shelf (“UKCS”), approximately eight (8) kilometres east of the Beryl Field and twenty five (25) kilometres from the Gryphon Field. The Leadon Field straddles UKCS Blocks 9/14a and 9/14b. The Leadon Field was discovered in 1979 by the British National Oil Corporation and then developed following the drilling of an appraisal well by Kerr-McGee in 1998. Production from the field commenced in 2001. A cessation of production application was submitted in 2004 and approved in 2006 and the FPSO and mooring system were removed in 2006 by agreement with DECC under correspondence. The Leadon Field was produced via the floating production storage and offloading vessel (“FPSO”) known as Global Producer III (“GPIII”): crude oil was exported by offshore tanker loading; and fuel gas was imported via a four (4) inch flexible flowline connected to the Beryl Alpha platform. The Subsea infrastructure consists of two drill centres. Drill Centre A (North towhead) has seven production wells and two water injectors and is linked to a mid-line structure, close to the FPSO location by a 42.5in bundle section. Drill Centre B (South Towhead) consists of three production wells, two water injectors and two aquifer wells and is linked to the mid-line structure by a 47.5in bundle section. With safety and the environment at the centre of the decision making process, a comprehensive assessment of available decommissioning options for the remaining infrastructure concluded the following:



1. All of the subsea wells will be plugged and abandoned in accordance with Oil and Gas UK and Maersk Oil well abandonment guidelines and standards.

2. The FPSO (Global Producer III) mooring system were removed in 2006 by agreement with DECC under correspondence.

3. The structures, spool-pieces, control jumpers and associated equipment will be removed and returned to shore for recycling or disposal. Risers were removed from site in 2007 and disposed of onshore in agreement with DECC.

4. The bundle will be left in-situ with the ends made safe through the use of rock-dump and its over-trawlability confirmed.

5. All Concrete mattresses will be recovered where considered safe to do so.

Following public, stakeholder and regulatory consultation, the decommissioning programmes are submitted without derogation and in full compliance with DECC guidelines. The decommissioning programmes explain the principles of the project and are supported by an environmental assessment.

1.4 Overview of Installations / Pipelines Being Decommissioned

1.4.1 Installations

Installations Being Decommissioned

Field name Leadon Block 9/14 Number of

platforms 1

Distance from

nearest UK

coastline (km)

305km Distance to

median (km) 8km

Platform

type FPSO

Number of

subsea

installations:

6 Riser bases Drill cuttings

piles:

Cuttings piles fall

below the OSPAR 2006/5

thresholds1

Dead weight

(Te): 85,943

Jacket

weight (Te): NA

Number of

wells (Total): 18

Production

type: Oil/Gas

Water depth

(m):

120 Platform: 0

Subsea: 18

Table I: Installations Being Decommissioned

1) Based ‘Technical Review of Data from around Maersk Oil’s North Sea fields with regard to OSPAR Recommendation 2006/5’ [3] there were only 2 wells known to have been drilled with OBM, these were both some distance apart and cannot be seen as contributing to a single drill cuttings pile as defined by the OSPAR Recommendation.

Installations Section 29 Notice Holder’s Details

Section 29 Notice Holder Registration Number Equity Interest (%)

Maersk Oil North Sea UK Limited

03682299 0% (Operator)

Maersk Oil UK Limited 00946986 100%

Table II: Installations Section 29 Notice Holder’s Details



1.4.2 Pipelines

Pipelines Being Decommissioned

Number of pipelines / umbilicals 2 bundles (PL1841

&PL1842) and a gas import flowline (PL1895)

See: Table IX: Bundles

Details and Table X: Gas Import Flowline Details

Structures 3 Manifolds (North and South towheads and Midline structure).

See Table VIII: Structure Details

Table III: Pipelines Being Decommissioned

For section 29 purposes the towheads and midline structure are considered part of the

bundles. They form therefore part of the pipelines programmes and the riser bases form

part of the installations programme. The towheads, midline structure and riser bases will

henceforth be referred to as ‘structures’ for the remainder of the document.

Pipelines Section 29 Notice Holder’s Details

Section 29 Notice Holder Registration Number Equity Interest (%)

Maersk Oil UK Limited 00946986 100%

Table IV: Pipelines Section 29 Notice Holder’s Details

1.5 Summary of Proposed Decommissioning Programmes

Summary of Decommission Programmes

Selection Option Reason for

Selection Proposed Decommissioning Solution

1. Topsides

N/A N/A N/A

2. FPSO

Removal and re-use

Vessel suitable for re-use.

Disconnected (following agreement with the Department of Trade & Industry (governing body at the time) per letter dated 22

nd June 2006) and

relocated to the Donan Field, UKCS, in 2006

3. Subsea Installations

Riser bases to be removed

To leave a clear seabed

Riser bases will be removed to shore for disposal / recycling



4. Pipelines, Bundles, Flowlines & Umbilicals

Towhead structures

to be removed


Towhead structures will be removed to shore for disposal / recycling. The towheads structures are expected to be disconnected from the bundle using cutting tools and cut into smaller loads for recovery.

Flowlines, spools, grout, mattresses

and control jumpers all to be

removed


Flowline, spools, mattresses, grout and control jumper all to be removed to shore for disposal / recycling

Risers Already removed Risers were removed from site in 2007 and disposed of onshore in agreement with DECC

Bundle to be rendered

overtrawlable and left in place

Significantly reduced risk to personnel, reduced seabed

disturbance, minimal environmental impact

and minimal cost burden to tax payer

Conservative assessments of the anticipated degradation rate of the carrier pipe indicate that it will not become susceptible to trawler board strike until after a period of 60 years.

As a result of this assessment and the assessed physical risks to decommissioning project personnel and the environmental impact at this time of any proposed pipeline bundle removal operation, the Operator’s proposal is, in respect of the short to medium term, that the 4.2km pipeline bundle, consisting of two sections 42.5” diameter and 47.5” diameter respectively will be decommissioned in-situ, with the cut ends rock dumped.

A periodic survey routine will be agreed with relevant stakeholders. Overtrawlability trials will also be established to monitor and minimise the risk presented by the bundle to other users of the sea.



5. Well Abandonment Operations

Wells to be abandoned in

accordance with Oil &Gas UK

and Maersk Oil UK guidelines for the suspension

and abandonment of

wells

Meets DECC regulatory

requirements

Operations are subject to on-going engineering and as such, the finalised methods may differ from those described in this document.

A final decision on the P&A campaign and schedule will be made following a commercial tendering process, the timing of which will be between 2014 and 2019 depending on MODU market capacity and availability.

A PON5/OPPC/MCAA/Consent to Locate application and any other permits and consents under the relevant regulations will be submitted in support of works carried out

6. Drill Cuttings

Leave in place to degrade naturally

Cuttings piles fall below the OSPAR 2006/5 thresholds

Left undisturbed on seabed

7. Decommissioning interdependencies

The P&A activities require the completion of diving activities to fully disconnect the trees from the bundle structures.

Table V: Summary of Decommission Programmes



1.6 Field Location/Layout and Adjacent Facilities

Figure 1: Field Location in UKCS



Figure 2: Field Layout

List of Adjacent Facilities

Owner Name Type Distance/

Direction Information Status

Apache Beryl Alpha

Valve structure

7.3km West A 4” gas import flexible flowline (PL1895) is tied-into the mid-line structure of the Leadon bundle and is connected to the Apache operated Beryl Alpha SSIV. There is no expected impact other than entering in the Beryl 500m zone. There are 7 crossings with pipelines, all of these being unaffected by the decommissioning activities.

Operational (see 3.2.2)

Table VI: List of Adjacent Facilities



Figure 3: Adjacent Facilities

1.7 Industrial Implications

In planning and preparing for executing the Leadon decommissioning strategy, Maersk Oil as operator of the Leadon Field and on behalf of the Section 29 Notice Holders has undertaken the following:

Published project information and contact details on the DECC website: www.gov.uk/oil-and-gas-projectpathfinder

Contributed to the preparation of a Joint Industry Project report providing a comprehensive description of the bundle technology as well and the decommissioning options available.

Working with Decom North Sea and other industry bodies in engagement sessions with the decommissioning supply chain on issues relating to the Leadon Decommissioning programme. In particular, a high-level description of the Leadon Decomissioning programme was presented at the Offshore Decommissioning Conference in October 2013.



2.0 BACKGROUND INFORMATION

2.1 Leadon Development

The Leadon field is situated in block 9/14 of the North Sea, approximately 190 miles North - North-East of Aberdeen in a water depth of 120m.

The field was developed in 2001 by Kerr McGee with two drill centres, North and South Leadon, situated 4.2km apart connected by two bundle sections. Production is via an FPSO, Global Producer III, positioned at the midpoint of the bundle.

Figure 4: As installed Leadon facilities

2.2 Current Status

The Leadon field was acquired by Maersk Oil in 2005 and cessation of production was granted in 2006.

Some preparation work has already been undertaken for decommissioning of the Leadon facilities, with the FPSO and associated mooring system removed and reused at the Donan development in 2006 and the flexible risers recovered and disposed of in 2007. The current layout of the facilities is detailed in Figure 5. Currently, there is a permanent guard vessel at Leadon to patrol exclusion zones and the former 500m safety zone of the FPSO.



Figure 5: Leadon Current Status

2.3 Adjacent Facilities

The 4” gas import flexible flowline (PL1895) which ties into the mid line structure at Leadon runs to a valve structure within the Apache operated Beryl Alpha 500m zone, 7.3km to the west of Leadon. The flexible crosses a number of pipelines within the Beryl Alpha 500m zone.

Figure 6: Leadon Field in relation to Beryl Alpha



2.4 Environmental Data [1]

2.4.1 Seabed and Bathymetry

Along the bundle route the seabed shallows gently towards the south. Water depth ranges from 120 metres LAT to 116.4 metres LAT, the steepest gradient is measured to be 1:400, 0.14 degrees. Similarly, there is little change in water depth along the length of the flowline from Beryl.

Side scan sonar data shows the seabed in the area to be of low reflectivity with very few features. The sediments are loose clayey sand, identified as Holocene Witch Ground formation. This is interspersed with areas of firm to stiff clayey gravelly sands of the Ferder Formation. Anchor scars are present within these areas, but not visible within the Witch Ground areas, which suggests finer sediments are being redistributed by seabed currents. Throughout the area there are small depressions, characteristic of the Witch Ground, however these are of insignificant height. In addition, Leadon is not within a known area of Pockmark occurrence, the closest being in Block 9/19, 15 to 20 kilometres to the south.

2.4.2 Oceanography and Meteorology

Tidal currents in the northern North Sea area are generally weak and are readily influenced by other factors such as winds and density driven circulation. This results in a relatively atypical pattern to the tidal currents. Maximum tidal rates at the location are 0.26 and 0.10 metres per second respectively for spring and neap tides. The combination of the general circulation and the tidal currents result in relatively unpredictable currents at any given time, due to the influence of prevailing winds.

The wave climate in the northern North Sea is a combination of background swell and local wind generated waves. Waves vary seasonally. Table 7 shows wave height frequency in the Leadon area.

10% Exceedance 25% Exceedance 50% Exceedance 75% Exceedance

4.0 metres 3.0 metres 2.5 metres 1.5 metre

Table VII: Yearly significant wave height in the Leadon area (UKDMap, 1998)

Wind directions are variable in this area of the North Sea, but predominantly blow from the south and south-west. Northerly winds occur most frequently during the spring and early summer. There is a marked seasonal variation with stronger winds prevailing during the autumn and winter. The maximum hourly mean wind speed, with an average recurrence of 50 years at 10 meters above still water level, is between 37 and 38 metres per second in this area.

2.4.3 Protected Sites, Marine Protected Areas

Annex I Habitats in the Vicinity of the Leadon infrastructure There are no designated Annex I habitats in the vicinity of the Leadon infrastructure.

Annex II Species in the Vicinity of the Leadon Infrastructure Of the species listed in Annex II, common seals generally forage around their haul-out sites and are not normally found more than 60 kilometres from shore. Similarly, grey seals are mainly distributed around and between haul-out sites and foraging areas.



Given the distance of the field from the coastline, it is unlikely that common or grey seals will be present in the vicinity of the proposed decommissioning activities.

Bottlenose dolphins are rare in the northern North Sea and reported to be infrequently recorded in the JNCC atlas of marine mammal distribution sighting effort. In addition, the JNCC (2003) holds no records of sightings of bottlenose dolphins in the vicinity of blocks 9/13 and 9/14.

Harbour porpoises have been observed in the vicinity of the Leadon infrastructure, but only in February and June to August. Hence, the harbour porpoise may be found in the vicinity of the field, but only seasonally and in relatively low numbers.

2.5 Commercial Fisheries

The Leadon infrastructure lies within ICES Rectangle 48F1. Species fished in Rectangle 48F1 are predominantly pelagic (mackerel, herring and sprat) with mackerel accounting for 52 per cent of the total catch by weight (3,698 tonnes between 2007 and 2008). Demersal species (cod, haddock, monkfish and whiting) and Nephrops make up the remaining total catch with haddock accounting for 26 per cent of the total catch by weight (1857 tonnes between 2007 and 2008), as illustrated Figure 7.

Figure 7: Average Annual Landings by Species (tonnes) for all UK and Foreign

Vessels 2007-2008 with ICES Rectangle 48F1

The main fishing method utilised over ICES Rectangle 48F1 is bottom pair trawls, which account for 49 per cent of vessel utilised, bottom otter trawls and Scottish seines are also utilised over the Rectangle and account for 20 per cent and 27 per cent of vessels utilised, respectively. SGMD cumulative fishing effort data for ICES Rectangle 48F1 over the 2007 to 2008 period are shown in Figure 8.



Figure 8: Fishing effort (days fished) for all UK and Foreign Vessels 2007-2008 within

ICES Rectangle 48F1

2.6 Shipping and Ports

The majority of shipping activity in the area is a result of fishing and oil related activities. Ships utilising the northern North Sea, at long distances from any ports are unlikely to follow set shipping routes, so it is difficult to estimate the exact level of shipping intensity in this area. However, a shipping study carried out for the Leadon installation activities identified 8 shipping routes within 1 nautical mile of the field, with a combined annual traffic density of 587, corresponding to less than 2 vessels per day.

2.7 Military Activity

Blocks 9/13 and 9/14 do not lie within a designated military exercise area.

2.8 Dredging and Dumping Activity

No commercial or capital dredging is undertaken in the area, nor are there sites licensed for disposal of dredged material within Blocks 9/13 or 9/14.

2.9 Tourism and Leisure

The tourism industry will not be impacted by decommissioning if the Leadon field.



3.0 SCOPE OF DECOMMISSIONING

To reflect the offshore execution process, three work scopes may be considered: Scope 1: Spools, Flowline, Riser bases and Mattresses Scope 2: Bundle and Structures Decommissioning Scope 3: Well Plug & Abandonment The first scope, which can be considered as standard operations, will remove mattresses, grout bags, spools, control jumpers, gas-lift flowline and riser bases. The second scope to remove the towheads and mid-line structures and rock-dumping exposed bundle ends requires significant engineering and operational preparation. The final scope is to plug and abandon all wells in the Leadon area. The three scopes are largely independent and may be completed over multiple campaigns subject to appropriate rig and vessel availability.

3.1 Installations

3.1.1 FPSO

The Global Producer III is considered retrospectively in the installations programme as it was removed from site and relocated to the Donan field in 2006. The FPSO is a monohull type ship, 217.8m in length, 38m wide with 17m draught. The dead weight tonnage is 85,943Te.

3.1.2 Structures

At each of the drill centres, the bundle is terminated in a towhead structure that incorporates all of the connections between the flowlines and the individual wells. A similar midline structure (MLS) is located halfway along the bundle length which contains the connections between the bundle and the riser bases. These structures are integral to the bundle. In addition to the towheads and MLS, six gravity riser base structures clustered around the MLS are to be considered. None of the structures are piled.

Figure 9: Typical towhead (left) and riser base



Description Dim’s (m) Weight

in Air (Te) Quantity Scope

North towhead 29 x 6.6 x 4.6 307 1 2

Midline structure 41 x 6.1 x 4.5 282 1 2

South towhead 26 x 6.6 x 4.6 275 1 2

Riser Base – 12” Aquifer 6.2 x 6.0 x 6.1 95 1 1

Riser Base – 12” Production 6.2 x 6.0 x 6.1 95 1 1

Riser Base – 6” Gas Lift 5.9 x 5.3 x 6.1 79 1 1

Riser Base – 6” Gas Import 5.9 x 5.3 x 6.1 79 1 1

Riser Base – 8” test 5.9 x 5.3 x 6.1 79 1 1

Riser Base – Umbilical 4.8 x 4.0 x 3.5 59 1 1

Table VIII: Structure Details

3.2 Pipelines, Flowlines, Risers and Controls

3.2.1 Bundles

The North and South drill centres are connected by two bundle sections, bundle A (PL1841) and bundle B (PL1842). The bundles consist of various flowlines and control systems that bring services and production to and from the wells.

Figure 10: View of the two bundle sections

The pipeline bundles consist of an assembly of pipelines including production, gas-lift, water injection and test lines in addition to control tubes and cables housed within a carrier pipe. The carrier pipe provides buoyancy to support the weight of the pipelines and internals during the towing operation and mechanical protection after installation. This pipe is flooded during the installation process and remains sea water filled. The assembly of pipelines and controls are maintained in position by a series of clamped spacers which are positioned at defined offsets along the length of the bundle. Each spacer is mounted on rollers which allow the longitudinal movement required during manufacture and installation.



Item Description Length

Weight

in Air

(Te)

Quantity Scope

PL1841 Bundle A (North)

42.5" Diameter Bundle • 16” Production (18”Sleeve) • 8” Test (10”Sleeve) • 10” Water Injection • 6” Gas Lift • Control tubes and cables run on 200w x 100h cable ladder

2117m 1934 1 2

PL1842 Bundle B (South)

47.5" Diameter Bundle • 12” Production (16”Sleeve) • 8” Test (10”Sleeve) • 12” Water Injection • 16” Aquifer • 4” Gas Lift • Control tubes and cables run on 200w x 100h cable ladder

2137m 2382 1 2

Table IX: Bundles Details

The bundle sections are exposed on the seabed and are designed to be overtrawlable. Since installation in 2001, a degree of backfill has occurred, although it is not completely buried at any location. The 2011 biennial Maersk Asset GVI (General Visual Inspection) Survey [10] identifies no areas of freespan and a comparison of the bundles’ burial status [16] since installation indicates that the lines are stable. The 2013 GVI survey was undertaken in July 2013 and the results are anticipated by December 2013.

Figure 11: Towheads and midline structure

3.2.2 Flowlines

A 7.3km, 4” gas import flexible flowline (PL1895) runs between a valve structure within the Beryl A 500m zone and the Leadon MLS. The flowline is laid in an open trench which has accumulated a degree of natural backfill since installation. The line remains filled with hydrocarbon gas at ambient pressure with a 50m MEG slug injected at the Leadon end of the flexible.



Gas Import Flowline – PL1895

Length 7315m

I.D. / Nominal Diameter 101.6mm / 4”

O.D. 138.9mm

Weight in Air (empty) 20.71kg/m

Weight in Air (filled) 29.62kg/m

Table X: Gas Import Flowline Details

The flowline crosses several lines within the Beryl 500m zone and is itself crossed in one location by the Apache operated Skene North Bundle Replacement (NBR). The crossings are generally constructed from grout bags positioned to provide a smooth ramp over the product to be crossed. Where the flexible exits the trench at Beryl A, the flowline is stabilised by ‘stitch mattressing’, an installation procedure where a number of concrete mattresses are placed at defined intervals. At Leadon the exposed end of the flowline is protected by continuous concrete mattressing to the MLS.

Figure 12: Gas Import Flowline



Crossing

Description PL No. Operator Crossing

Easting Northing

32” Oil to SPM3 PL381 Apache Under 417 450 6 601 744

SS48 6” Gas Lift PL354 Apache Under 417 370 6 601 725

*Skene (NBR) PL1840 Apache Over 417 334 6 601 712

Skene Bundle PL1840 Apache Under 417 299 6 601 704

SS48 6” Flowline PL353 Apache Under 417 264 6 601 693

Buckland Bundle PL1696 Apache Under 417 246 6 601 689

SS48 Umbilical N/A Apache Under 417 205 6 601 678

Table XI: Crossing details

The Skene NBR crosses over the 4” flexible. At this crossing point the flexible has been jetted to 0.6m (natural backfill) over a 50m length between the following points:

Description Easting Northing

Start of Burial 417 308 6 601 708

End of Burial 417 359 6 601 721

Table XII: Flexible burial extents at NBR crossing

3.2.3 Spool-pieces and Control Jumpers

In total approximately 100Te of spoolpieces and jumpers are to be decommissioned ranging in diameter from 2” to 12”. These spoolpieces and jumpers are currently protected by concrete mattresses. A list of spools and figures showing their location can be found in Appendix 2.

Location OD & Wall

Thickness

(mm)

Qty Spools

& Jumpers

Total

Length

(m) From To:

North Towhead

Wells P4,P3,P9,

P6,P10,P5,P8

168.3 x 14.3 9 201.61

60.3 x 5.5 9 201.61

Well: W1 168.3 x 11 2 39.61

88.9 x 7.6 2 39.61

Midline Structure

6” Imp Gas & Gas Lift Spool

168.3 x 11 6 296.38

12” Aquifer Spool

323.9 x 21.4 3 121.81

12” Prod Spool 323.9 x

21.4/14.3 3 116.03

8” Test Spool 219.1 x

15.9/11.1 3 129.03

South Towhead

Wells: P1, P2, AQ2, P7

168.3 x 14.3 6 155.31

60.3 x 5.5 6 155.31

Well: W2 168.3 x 11 1 20.59

Table XIII: Spool Details



3.2.4 Risers

Details of the risers at the Leadon field are shown in the table below. These are covered retrospectively in this programme as they were removed from site in 2007 and recycled/disposed of onshore.

Pipeline

Number

Description Length

(m)

PL1842.5 12” Flexible Aquifer Riser(South Drill Centre) 191

PL1841.1 12” Flexible Production Riser(North Drill Centre) 191

PL1842.1 12” Flexible Production Riser(South Drill Centre) 191

PL1842/1.4 12” Flexible Water Injection Riser(North/South Drill Centre) 191

PL1841.3 6” Flexible Gas Lift/Injection Riser(North Drill Centre) 191

PL1843 6” Flexible Import Gas Riser(Future Well) 191

PL1841.2 8” Flexible Riser(North Drill Centre) 191

PL1842.2 8” Flexible Riser(South Drill Centre) 191

Table XIV: Decommissioned Riser Details

3.3 Wells

The Leadon field was developed with the drilling of 18 wells, drilled in the Northern and Southern Clusters. The following table summarises the registration names and status of each well:



Registration

Number Field or Prospect Status

O&G UK Guidelines

Categories

Cat. 1,

2.1, 2.2, 3

or 4

Cat. 1 or

2a-2e

09/14a-A11 Leadon North Suspended 30"

Wellhead 1 2b

9/14a-9 Leadon North P4 - Disconnected 3 2b

9/14a-N1z Leadon North P9 - Disconnected 3 2b

9/14a-N2 Leadon North P3 - Disconnected 3 2b

9/14a-N3y Leadon North P5 - Disconnected 3 2b


9/14a-N5 Leadon North W1 - Disconnected 3 2b

9/14a-N6y Leadon North P8 - Disconnected 3 2b


9/14b-S1z Leadon South P2 - Disconnected 3 2b

09/14b-S2 Leadon South Suspended

wellhead with tree 3 2b

09/14b-S3 Leadon South Suspended 30"

conductor 1 2b

9/14b-S3a Leadon South P1 - Disconnected 3 2b

9/14b-S4 Leadon South W2 - Disconnected 3 2b

9/14b-S5 Leadon South AQ2 - Disconnected 3 2b

09/14a-S6 Leadon South Suspended 18 3/4"

wellhead 3 2b

9/14b-S7 Leadon South P7- Disconnected 3 2b

09/14b-W3 Leadon South Suspended 30"

conductor 1 2b

Table XV: Summary of the Leadon wells

3.4 Materials on the Seabed

3.4.1 Concrete Mattresses & Grout

Mattresses are used for spool-piece and jumper protection as well as flexible flowline stabilisation and crossing construction. In total there are 202 mattresses and approximately 2000 grout bags on site at Leadon, all of which are expected to be recovered and transferred onshore as part of decommissioning scope 1.



3.4.2 Drill Cuttings

After analysis of the drilling data it was concluded that Leadon did not require further assessment, based on the following:

• Only two of the wells in the Leadon field are known to have been drilled with

OBM discharge to sea. • These two wells were drilled at some distance from each other and cannot be

seen as contributing to a single cuttings pile as defined by the OSPAR recommendation.

• Although a number of wells have been drilled where the drilling history was

unavailable, these were all either single well sites or drilled after the cessation of OBM discharge which is definitively known as being the 1st January 2001 in any field operated by Maersk Oil.

3.4.3 Debris

The latest survey (2011) of the Leadon facilities [10] identifies no significant items of debris to be considered.



4.0 INVENTORY OF MATERIALS

The following sections list the infrastructure and equipment to be decommissioned under the decommissioning programmes. A complete and comprehensive inventory [8] has been produced in support of the programme and should be referred to if further information is required.

4.1 Subsea Installations The following table details the materials to be decommissioned under the installations programme.

Towheads / MLS Riser Bases

Materials Carbon Steel 864Te 483.92Te

Aluminium-Zinc-Indium Alloy 10.6Te - depletion 3.868Te - depletion

Chemicals Seawater Treated With

TROS 650 At 1600ppm 36m

3 9m

3

Table XVI: Structure Material and Chemical Summary

4.2 Pipelines, Flow Lines and Umbilicals

The following sections list the infrastructure and equipment to be decommissioned under the pipelines programme.

4.2.1 Conditioning status

Prior to disconnection of the GPIII FPSO in 2006, a comprehensive flushing campaign was carried out from the topside facility. The infrastructure was flushed and dosed in order to maintain integrity of the system through to decommissioning or potential reuse of the facilities. The current status of the lines is detailed in Tables XVII-XX:

Description Status Pressure Chemical dosing

Bundle - Carrier Pipe As Installed Subsea ambient 50ppm biocide

Bundle - Production Flushed <30ppm Subsea ambient 1600ppm TROS 650

Bundle – Gas Lift Flushed <30ppm Subsea ambient 1600ppm TROS 650

Bundle – WI / Aquifer Flushed <30ppm Subsea ambient 1600ppm TROS 650

Structures Flushed <30ppm Subsea ambient 1600ppm TROS 650

Control System Gas Lift & Service

Flushed Subsea ambient 1600ppm TROS 650

Control System Chemical

Flushed Subsea ambient 1600ppm TROS 650

Control System Hydraulic

Transaqua HT2 filled

Subsea ambient N/A

Control System Electrical

Shrouded plastic compound

N/A N/A

Spoolpieces Flushed <30ppm Subsea ambient 1600ppm TROS 650

Flowlines Hydrocarbon Gas

Filled Subsea ambient Slug MEG / water

Control Jumpers As per Control System

Table XVII: Conditioning Status Summary - Bundles – PL1841 & PL1842



Bundle A (North) Bundle B (South)

Materials

Carbon Steel 1902.63 Te 2349.5 Te

Stainless Steel 15.564 Te 14.5Te

Duplex Stainless 5.288 Te 3.723 Te

Copper 1.864 Te 1.881 Te

Aluminium-Zinc-Indium Alloy 8.316 Te-depletion 10.458 Te-depletion

LDPE Foam Insulation 59 m3 92 m

3

Ballast Chains – Carbon Steel 117.5 Te 150.5 Te

Chemicals

Seawater Treated With TROS

650 At 1600ppm 438.278 m

3 609.00 m

3

Transaqua 1.022 m3 1.032 m

3

Carrier Pipe Contents

Approx 1125m3 of

seawater treated with

biocide at 50ppm

Approx 1375m3 of

seawater treated

with biocide at

50ppm.

Oil Residue 8.79kg 6.3kg

Table XVIII: Bundle Material and Chemical Summary

Materials

Carbon Steel 80.30 Te + End

fittings

Stainless Steel 42.00 Te

Polyethylene TP11 14.77 Te

Polyethylene TP14 11.12 Te

Chemicals Hydrocarbon Gas *57m3

*Note: Volume calculated at standard temperature and pressure.

Table XIX: Gas Import flowline material and chemical summary

Materials

Carbon Steel 65.074Te

Duplex 26.35Te

Syntactic Polyurethane Insulation 4.975m3

Chemicals Seawater Treated With TROS 650 At 1600ppm 31.204m

3

Residual Oil 0.48kg

Table XX: Spoolpiece & Jumper Material and Chemical Summary



4.2.2 Materials on the Seabed

Concrete Mattresses and Grout

Location Size Weight Qty Total

Weight Material

North Towhead

6 x 2 x 0.15m

4Te 30 120Te Concrete with polypropylene rope block ties.

South Towhead

6 x 2 x 0.15m


Mid Line structure

6 x 2 x 0.15m


Midline structure

6 x 3 x 0.15m


4” Flexible – Beryl location

5 x 3 x 0.30m


Grout Bags N/A 25kg N/A 50Te (est.)

Set Grout

TOTAL 202 1068Te

Table XXI: Mattress and Grout Details

4.2.3 NORM / LSA

There is no historical evidence of Naturally Occurring Radioactive Material (NORM) being present at the Leadon field in either the previously recovered flexible risers or the topside process vessels, therefore it is not anticipated any radioactive material will be encountered. However, as part of the preparations for the decommissioning operations, appropriate measures will be implemented to check the equipment as it is brought back to the vessel.



5.0 REMOVAL AND DISPOSAL OPTIONS

The proposed decommissioning solution was developed through an extensive programme of continual assessment which included screening sessions, comparative sessions and Peer Review [7] involving appropriate industry representatives and stakeholders. In support of the review and decision-making process numerous supporting studies and analyses were undertaken.

Particular focus was placed upon the decommissioning solution for the bundle, which was subject to a more in-depth review. An overview of the FEED study process is detailed graphically in Appendix 5.

5.1 Re-Use and Phasing

Since cessation of production Maersk have explored resale and redevelopment opportunities for the Leadon facilities. As such the FPSO, Global Producer III, and associated mooring system was removed from site to be re-used in the Donan field.

It has not been possible to identify a suitable use for the remaining subsea infrastructure, therefore the remaining infrastructure will be decommissioned. The following sections describe the options considered for decommissioning.

5.2 Decommissioning Options

With the exception for the bundle, all infrastructure on site was considered to be a candidate for full removal therefore there was no requirement to consider the option to leave on site. A summary is presented in Table XXII:

Installations

FSPO Global Producer III To be reused on the Donan Field

Towhead structures Removal to shore for disposal and recycling

Riser bases Removal to shore for disposal and recycling

Pipelines

Flowline Removal to shore for disposal and recycling

Spools and control jumper Removal to shore for disposal and recycling

Risers Removal to shore for disposal and recycling

Mattresses and Grout Removal to shore for disposal and recycling

Table XXII: Preferred Decommissioning Options

5.3 Bundle Decommissioning Options

It is recognised that the bundle decommissioning is the most challenging part of the planned programmes. Bundle decommissioning is currently recognised as a general industry problem, and there is no common approach to the disposal of bundles of similar size. A number of options for bundle decommissioning were considered during the preparation of the decommissioning programme. In particular, the options to trench or tow the bundle have been discounted for the following reasons.



5.3.1 Trenching Options

Historic instances of burial of bundles of a comparable size after installation are unknown. The large diameter, heavy bundle exceeds the capacity of virtually all equipment currently available on the market including the largest evolution ploughs, mechanical trenchers and jet trenchers. Other trenching methods, such as mass flow excavation, can be slower especially in stiff virgin soils; and they do not have the capacity to backfill the excavated trench which means large quantities of remedial rock dump are required making them prohibitively expensive when compared to other trenching methods or simple blanket rock dumping. In order to further assess the options for burial of the bundle a study was completed into burial equipment capability and availability as well as a geotechnical and trenching assessment of the Leadon soils [6]. This study concludes there is no suitable equipment currently available for the burial of the 47.5” diameter bundle, consequently it would not be recommended to attempt to bury the bundle using the methods reviewed. In addition, consultation with the SFF has indicated that large spoil heaps of stiff clay that can result from cutting deep trenches or from incomplete or insufficient backfilling operations represent a significant hazard for fishermen. This has been evidenced by the loss of the FV Harvest Hope which capsized on 28th August 2005 after snagging her trawl gear/nets on boulder clay from a pipeline trench [6]. Excavating trenches up to 2.5m deep for larger diameter products, such as bundles, further increases this risk as a greater volume of excavated material is produced and hence is more problematic to re-deposit in the trench, now occupied by the bundle. For these reasons and the results of the comparative assessment the decommissioning options that involve trenching are discounted due to the high level of safety, technical and commercial risk.

5.3.2 Bundle Tow

The key issue with regard to bundle tow is the technical and safety challenges involved. No bundle has ever been refloated and towed. In theory it may be possible to dewater a bundle carrier pipe and attach trim chains, however configuring the bundle weight to make Controlled Depth Tow Method (CTDM) possible is a major challenge [11]. To achieve the required level of accuracy (0.2%) for the buoyancy distribution in an offshore subsea environment would be a major challenge and not deemed practicable, particularly as the bundle condition and weight will have changed since installation. In addition, dewatering the carrier pipe, although possible, also presents some issues. If small pockets of water remain within the bundle carrier they will tend to migrate to the lowest point of the bundle causing the bundle to bow, with the belly of the bundle unable to be lifted from the seabed. The reasons for discounting bundle towing as a viable option are further detailed in Leadon Decommissioning Bundle Tow Summary [12]. These options were assessed among others as part of an Option Screening Session [15] and first comparative assessment [9]. The following options were discounted:



Item Option Reasons for discounting

1 Rock dump entire bundle

including towheads and MLS

Due to the length of the bundle and the size of the towheads the anticipated rock quantity and the height of the berm, in particular at the towhead and mid line structure, would be significant, leading to potential issues with regard to over-trawlability. The option to remove the towhead structures and rock dump the remaining bundle sections (only) was taken forward for further review as part of the pipelines programme.

2

2) Refloat bundle, including

towheads and MLS and:

For all of the following cases, concerns remain over the feasibility of refloating the bundle and towheads namely remaining fatigue life and strict trim tolerances.

2A - Tow into a pre-cut trench

A limited range of equipment is available for creating a trench suitable for this diameter. The resulting berms would be a potential hazard for the other sea users. Not compliant with decommissioning regulations.

2B - Tow bundle to shore (reverse installation)

This operation has never been attempted before and would certainly raise issues when crossing over third party assets. There is no available reception facility for the bundle.

2C - Tow to reuse location No reuse opportunities identified.

2D - Tow to deep sea disposal site

Not compliant with decommissioning regulations

3 Trench bundle in current location There is no suitable equipment currently available for the burial of the 1200mm diameter bundle [6].

4 Remove towheads & tow bundle sections to shore

The towheads and midline structure provide a dedicated mechanism to control the ballast of the bundle during installation. Without the structures in place there is no reliable method to recreate a controlled buoyancy method for large free filling bundles; another major technical issue would be to control the movement of the internals of the bundle during refloating and tow. Anticipated issues when crossing over third party assets. There is no available reception facility for the bundle.

Table XXIII: Discounted Bundle Options

5.3.3 Further Appraisal - Comparative Assessment II

Following the screening session and the first comparative assessment, a second comparative assessment [14] was undertaken which concentrated on:



Cut & remove bundle sections This operation involves the deployment and diver positioning of diamond wire cutting equipment at pre-determined points along the bundle. Cutting operations are controlled from the surface. The length of each section and lifting methodology are subject to the vessel used for recovery but would be expected to be between 20 and 25m. Once cutting operations are complete, divers will prepare equipment for recovery. Prior to recovery, the internals of the bundle will have to be secured in place.

Decommission bundle in place & protect bundle ends This option involves removal of the towheads and MLS then protecting the ends of the remaining bundle sections to leave them in an overtrawlable condition.

Comparative Assessment II [14] was held with a focus on these two remaining bundle decommissioning options. The comparative assessment utilised a combination of quantitative and qualitative methods to assess each of the decommissioning options.

In order to accurately categorise the impact of each decommissioning option the assessment criteria have been quantified at five levels of impact; very low, low, medium, high, and very high as per the example in Table XXIV: Extract from Quantitative Impact Matrix

ASSESSMENT

CRITERIA IMPACT

1 2 3 4 5

Safety Very Low Low Medium High Very High

Risk to offshore personnel

First Aid case or no specific

treatment

Medical Treatment

Case

Restricted Work Case

Day Away from Work Case

Multiple long term injuries or

fatality

Table XXIV: Extract from Quantitative Impact Matrix

The scoring for environmental impact has been based on the assessment criteria stated in the Environmental Statement for Leadon Decommissioning [1].

Once the impact of the item has been rated, the confidence in that rating will also be

categorised. The level of confidence is again divided into; very low, low, medium, high,

and very high as per the table below which is extracted from the Comparative

Assessment Matrix.



Confidence Rating

Very Low 5 Limited definition and understanding of methodology, hazards or equipment. Very high level of uncertainty.

Low 4 Basic definition and understanding of methodology, hazards or equipment. High level of uncertainty.

Medium 3 General definition and understanding of methodology, hazards or equipment. Moderate level of uncertainty.

High 2 High level definition and understanding of methodology, hazards or equipment. Low level of uncertainty.

Very High 1 Detailed definition and understanding of methodology, hazards and equipment. Very low level of uncertainty.

Table XXV: Extract from Confidence Rating Matrix

The matrices used for the comparative assessment are presented in Appendix 3. The results of the comparative assessment are shown in Table 24 below.

Assessment

Criteria Matters to be considered

Assessment

Leave In Place Cut and Recover

Score Average Score Average

Safety

Risk to personnel - topsides 2

2.4

9

6.6

Risk to Personnel - subsea 2 12

Risk to other users of the sea 6 2

Risk to those on land 1 9

Risk to 3rd party assets 1 1

Environment

Physical Presence 6

2.7

1

2.1

Seabed Disturbance 4 1

Noise & Vibration 2 6

Atmospheric Emissions 2 2

Marine Discharges 1 1

Solid Waste 1 1

Minor Loss of Containment 3 3

Technical

Technical challenge 1

1.8

8

11.8 Level of diving intervention 3 15

Weather Sensitivity 2 15

Risk of major project failure 1 9

Societal

Fisheries impacts 6

4.0

1

6.3 Amenities 3 12

Communities 3 6

Reputation Risk to company 9 9.0 2 2.0

Ongoing

liability Ongoing liability

9 9.0

2 2.0

Economic Economic 6 6.0 20 20.0

Average Comparative

Assessment Score 3.4

6.3

Table XXVI: Comparative Assessment II Results



The assessment found that the “leave in place” option was judged to be the best

option in eleven of the criteria assessed, compared to “full removal” being judged as

the best option in six of the criteria. This was also reflected in the overall average

comparative scores, where “leave in place” was scored at 3.4 compared to 6.3 for “full

removal”. Of note, when considering safety, in place was assessed as being the

preferred option in 4 of the 5 criteria.

One of the key considerations during this comparative Assessment was the impact on

other sea users, and the following points were considered:

5.3.3.1 Interaction with other users of the sea

It is not envisaged that the infrastructure decommissioned in place will impact on the safety of navigation, due to its relatively low height above mean seabed level of approximately 2 metres when compared with the water depth (120m).

It is recognised there are concerns that large diameter pipelines and bundles represent an increased risk to other users of the sea. Specifically that a larger obstacle increases the likelihood of fishing gear becoming snagged. The risk of fishing gear snagging has been under discussion in both Norway and the UK for a number of years and considerable effort and resources have been spent attempting to document the effect. A number of overtrawl trials have been performed on pipelines ranging from 28” to 46” including the 40” Zeepipe and 44” Langeled lines. These concluded that no problems were registered by any of the trawlers used for the trial programmes [22]. In addition a Joint Industry Programme (JIP) [23] was initiated in 2005 at the request of the then DTI to confirm that the 46” Exxon Mobil Skene bundle did not present an increased hazard compared to existing unburied pipelines. This JIP concluded that:

• There is no fundamental safety problem in overtrawling large diameter pipelines and that the risks to fishermen are no greater than overtrawling smaller pipelines.

• The pipeline provided no worse obstacle to fishing gear than that from other natural features, debris and artefacts present on the seabed.

During operational discussions with SFF [17], dated 03/11/2009, it was stated that due to the rocky seabed conditions in the Leadon area, it is likely that any fishing vessels would employ rock hopper gear. This type of fishing equipment reduces the potential for snagging on subsea obstructions. In order to ensure that the Leadon bundle sections do not represent a hazard to fishing activities, a series of trial trawl sweeps will be performed over the bundle sections and the installed end protection. The structure and frequency of these trials will be agreed in consultation with the SFF and DECC. These trials may also be performed on the bundle sections in advance of the full decommissioning activities to ensure that the proposals within these programmes are validated. A concern expressed by the SFF was with regard to the long term breakup of the bundle carrier pipe if left in situ and exposed as this would represent a snagging



hazard for fishing gear. A study was undertaken to review the corrosion rate of the bundle and to assess the long term protection strategy [5]. The conclusion of this study was that even a conservative assessment of the corrosion profile of the bundle gives a period of 60 years before the bundle carrier pipe loses 55% of its wall thickness and therefore becomes vulnerable to a trawler strike. Wall thickness checks on the bundle will form part of the on-going monitoring campaign to ensure that mitigation is in place prior to the carrier pipe becomes a snagging hazard.

5.3.3.2 Freespan Assessment

The 2011 biennial asset inspection survey [10] of the bundle reports no freespan area along the bundle length. In addition, a comparison [16] between the surveys undertaken in 2006 and 2009 shows that the natural build-up has increased along the bundle.

Natural build-up along the

bundle

Bundle

Section 2006 2009 Difference

North 18.6% 21.2% +2.6%

South 7.3% 13.5% +6.2%

Table XXVII: Natural Build-up Summary

On the basis of this historical survey data, it is not anticipated that any areas of freespan will develop over time.

5.3.4 Quantitative Risk Assessment

In conjunction with the qualitative assessment, an additional quantitative risk assessment was carried out in order to assess the PLL (Potential Loss of Life) for the two bundle decommissioning options [21]. In the findings below the PLL is expressed as the expected number of fatalities to over the pipelines lifetime and as an average annual number of fatalities. The quantitive risk assessment has been developed considering the effects specifically to fishermen as no other sea users have been identified as having a direct interaction with Leadon infrastructures. The PLL value is based on a statistical approach using a combination of the following relevant factors:

Pipeline Hooking Fatality Rate

Leadon Pipeline Factor: Leadon bundle length vs. cumulative length of North Sea pipelines

Rock Dumping Factor: Risk mitigation factor based on the additional protection to other users of the sea by the removal of snagging points

Freespan Mitigation Factor: Risk mitigation factor based on the regular bundle inspections and planned remedial action, if required.



Full Removal Bundle left in-situ

Risk to Personnel (fishermen) shown as Potential Loss of Life (PLL)

5.21E-2 2.80E-2

Table XXVIII: Potential Loss of Life for Personnel and Other Users of the Sea

As evidenced in the summary table above there is a significantly increased risk to personnel associated with the bundle cut & recover option. This is shown to increase the risk of incident or accident by 86% compared with leaving the bundle in-situ. The main reason for the increase in PLL is the additional man-hours required to complete the scope of work, both onshore and offshore, including diving activities. The additional risk to personnel associated with cut and recover of the bundle is not justifiable considering the negligible residual impact of leaving the bundle in-situ. This increase in risk is not in accordance with the programme objectives to perform the decommissioning workscope with risks ensured as ALARP (as low as reasonably practicable). A second assessment [21] was to evaluate the risk for the other users of the sea and to ensure that risks are ALARP. The main risk to ‘other users of the sea’ from leaving the Leadon pipelines in situ is from trawl gear snagging on the pipelines. The most likely scenarios for trawl gear snagging on a pipeline are:

A de-stabilised trawl board (dragged on its back along the seabed) approaches a pipeline on the seabed or a free spanning pipeline with a small gap. The trawl board may dig under the pipeline and get hooked.

The crossing angle with the pipeline is less than 45° and the pipeline is free spanning. The warp line lifts the trawl board off the seabed; it slides along the pipeline, becomes, de-stabilised, turns over and slides underneath the pipeline until becoming wedged on the span shoulder.

The PLL value was calculated from a combination of the following parameters:

Recorded occurrences of trawl gear snagging on subsea pipelines

Bundle length as a percentage of the total North Sea pipeline length

Expected lifespan of the pipeline

Risk reduction from mitigation measures pre-rock dump*

Risk reduction from rock dumping

* For the purposes of assessment it was assumed that if no suitable recovery method had been found the bundle would be completely rock-dumped after 60years

In the case of leaving the bundle in-situ, a long term and persistent risk remains for the fishermen from the potential snagging of their fishing gear on the bundle. The PLL per annum for fishermen, directly attributable to fishing over the bundle left in situ, is 2.21E-5 (0.000021) per annum or 1 in 45,000 years [25].



6.0 SELECTED REMOVAL AND DISPOSAL OPTIONS

6.1 Installations

6.1.1 FPSO

The FPSO, Global Producer III has been removed from site and is now in use on the Donan Field.

6.1.2 Structures

All subsea structures in the field will be completely removed and recovered onshore for recycling and / or disposal. It is expected that the structure sections will be offloaded at a specialist decommissioning facility where they will be cleaned and upwards of 95% of the material recycled

6.2 Pipelines, Umbilicals and Flowlines

6.2.1 Spoolpieces and Control Jumpers

All spoolpieces and control jumpers in the field will be completely removed and recovered to shore for recycling and / or disposal by a recognised and licensed decommissioning and disposal contractor. It is anticipated that up to 95% of the recovered material may be recycled.

6.2.2 Flexible Flowline PL1895

Prior to disconnection stich mattresses will be removed and the line will be purged to removed residual hydrocarbon gas. The flexible flowline will be removed from site to be decommissioned onshore. It is anticipated that the flowline would be largely recycled with over 95% of the multi-layer material recovered including metals and plastic.

The flexible will be cut as close as practicable to either side of the already buried 50m section (to ensure minimal jetting is required). The ends of the 50m section which will remain in place under the Apache operated Skene NRB will be lowered to a depth of 0.6mToP (to the top of the pipeline).

6.2.3 Concrete Mattresses and Grout

In line with DECC Guidance, all mattresses and grout will be recovered from the seabed for disposal onshore.

6.2.4 Pipeline Bundles PL1841 & 1842

It is proposed that the bundle sections will be left in situ. To ensure a smooth transition from the bundle ends to the seabed it will be necessary to rock dump the bundle ends.

As the UKCS decommissioning market develops, the safety and efficiency of bundle recovery techniques and equipment are expected to improve to a level that makes complete removal of the Leadon bundle viable. The decommissioning of large bundles is considered as an industry problem and it is foreseen that as the number of bundles to be decommissioned increases there will be a combined industry effort to develop effective decommissioning solutions. Maersk Oil is committed to becoming a driving force towards developing a complete bundle recovery solution and is currently involved in a Joint Industry Project (JIP) exploring bundle decommissioning options.



Failing that, Maersk Oil will take appropriate action to leave the bundle in a condition safe for all sea users over the long-term. In this event it is anticipated that the pipeline bundle would be fully rock dumped after 60years based on the bundle corrosion assessment [5].

Any potential rock dumping is expected to take place at a point when the integrity of the bundle carrier pipe is such that an impact may result in the creation of a snagging hazard. The maximum quantity of rock that may be placed on the bundles to provide complete protection is estimated to be between 69000 to 84000Te.

6.3 Naturally Occurring Radioactive Material (NORM)

There is no historical evidence of NORM being present at the Leadon field in either the previously recovered flexible risers or the topside process vessels, therefore it is not anticipated that any radioactive material will be encountered. Should any radioactive material be detected the items will be packaged, handled and transported following appropriate procedures. Once the contaminated material is returned to the designated decommissioning facility, it will be cleaned of LSA/NORM which will then be stored prior to being transported to a licensed facility for disposal.

6.4 Recycling / Disposal

Prior to commencement of the decommissioning project operations, a Waste Management Plan shall be developed. The Waste Management Plan shall specify all the waste issues associated with the project.

It is intended that the recovered infrastructure will be returned to shore and transferred to a recognised decommissioning facility which will have all necessary approvals and licenses in place and possess the capability to recycle a vast proportion of the recovered material.

It is expected that the structures, flowline, spoolpieces and control jumpers would be cleaned before being largely recycled.

The concrete mattresses and set grout will be cleaned of any bio foul and most likely sent to landfill as they are not readily recyclable.

It is anticipated that the facility will be in the UK and as such no potential transfrontier shipment of waste issues are expected. The final contractor for the onshore receipt and disposal of the Leadon infrastructure will be selected following a commercial tendering process.



7.0 WELLS

The Leadon field comprises 18 wells split between the North and South drill centres. Drill Centre A (North 9/14a) has seven production wells as well as one water injector and one suspended well. Drill Centre B (South 9/14b) consists of three production wells, one water injector, one aquifer and four suspended wells. Details of the wells are summarised in Part 3.4.

The wells which remain to be abandoned will be plugged and abandoned in accordance with Oil and Gas UK and Maersk Oil Guidelines for the Suspension and Abandonment of Wells, Version 4, July 2012.

Conductor strings will be cut in accordance with Oil and Gas UK Guidelines for the Suspension and Abandonment of Wells, Version 4, July 2012. A PON5/OPPC/MCAA/Consent to Locate application will be submitted in support of any such work that is to be carried out.

A final decision on the P&A campaign and schedule will be made following a commercial tendering process. P&A operations are not expected to begin before mid-2014 with a 6 year period to abandon all Leadon wells. The number of wells to be plugged and abandoned each year will be subject to MODU market capacity and availability.



8.0 DRILL CUTTINGS

In order to provide a response to the implementation of OSPAR Recommendation 2006/5 on a ‘Management Regime for Offshore Cuttings Piles’ a technical review of Maersk’s North Sea fields was completed [3].

The report presents an analysis of data gathered from a range of sources including environmental reports and discharge histories. This data has been used to predict the likely levels of oil loss and persistence over time, as outlined in the Recommendation, for each of Maersk’s relevant fields.

After analysis of the drilling data it was concluded that several fields, including Leadon, did not require full Stage 1 screening. For Leadon this assessment was made on the following bases:

• Of the wells drilled in the Leadon field, only two are known to have been drilled with OBM discharge to sea.

• These two wells were drilled at some distance from each other and cannot be

seen as contributing to a single cuttings pile as defined by the OSPAR recommendation.

Although a number of wells have been drilled where the drilling history was unavailable; these were all either single well sites or drilled after the cessation of OBM discharge which is definitively known as being the 1st January 2001 in any field operated by Maersk Oil.



9.0 ENVIRONMENTAL STATEMENT

A full Environmental Statement (ES) [1] was prepared in order to review the environmental impacts associated with Leadon decommissioning. The key environmental sensitivities arising from the review of the existing environment are as follows:

• Fish spawning ground for saithe (Pollachius virens) and Norway pout

(Trisopterus esmarkii). • Fish nursery area for haddock (Melanogrammus aeglefinus), Norway pout and

blue whiting (Micromesistius poutassou). • Seabird vulnerability in the vicinity of the Leadon infrastructure is very high

during October (1 out of 4 on the JNCC scale), during January and July seabird vulnerability is high (2 out of 4) all other months of the year are rated as moderate or low seabird vulnerability (3 or 4 out of 4), however, there is no data available for the months of February, March and December

• White-beaked dolphin harbour porpoise and minke whale have been observed in the vicinity of the Leadon infrastructure, predominantly during the summer months;

• Fishing in Blocks 9/13 and 14 targets both demersal and pelagic species and occurs all year round with a peak in effort during March and in August and October;

• Shipping density is expected to be low within Blocks 9/13 and 9/14 (approximately 2 to 3 vessel per day).

It was found that although there will be some environmental impact during each phase of the decommissioning programmes, adverse long term environmental impacts from the activities will be negligible. In addition, incremental cumulative impacts of the activities will be minimal and there will be no transboundary effects. A summary of the commitments detailed within the ES are shown in Table 27:



No. Summary of Commitments as Detailed within the Environmental Statement

1. Prior to operations commencing, the appropriate notifications will be made & maritime notices posted.

2. All vessel activities will be in accordance with national & international regulations. Appropriate navigation aids will be used to ensure other users of the sea are made aware of the presence of vessels.

3. Operations are planned to take place outside the main period of fish spawning to limit impacts on fish stocks.

4. If the bundles are left in situ and rock placement is required, the rock berms will have a slope of 1 in 3 to minimise impact on trawling activity.

5. Where rock placement is required it will be kept as close to the required area as possible, by the use of a fallpipe or equivalent to place the rock, monitored by a dedicated ROV.

6. Noise disturbance will be limited by utilising suitable vessels for the operations. The cutting operations are expected to be the highest source of sound.

7. The use of large vessels has been limited by cutting structures offshore and the number of cuts has been optimised to limit the time spent in the field .

8. Diamond wire cutting equipment will be used to make the subsea cuts rather than explosives.

9. Maersk will ensure that contract specification and control processes require all equipment and generators to be well maintained and operated.

10. In order to minimise the uptake of resources, the amount of recovered material sent for recycling will be maximised as much as is technically and financially viable.

11. All vessels will implement appropriate Waste Management Plans and store and dispose of all solid wastes onshore accordingly.

12. In order to minimise this risk of oil spill from the Leadon wells, barrier testing will be completed on the wellheads to ensure that a proven double block and bleed is in place prior to breaking containment.

Table XXIX: Summary of Commitments Made within the Environmental Statement [1] to

ensure Impacts to the Environment from the Proposed Decommissioning Activities are

Minimised As Far As Practicable



10.0 INTERESTED PARTY CONSULTATIONS

10.1 Public Consultation Process

The formal consultation process will begin with the submission of the Consultation Draft of the Decommissioning Programmes. Prior to the submission, dialogue has been established with the SFF and DECC with regard to the proposals. The SFF have consulted with their membership on the proposed decommissioning strategy and their response is included overleaf.

Further consultation and communication will be undertaken and followed up with the resubmission of the Consultation Draft. The consultation process will include notices being placed in local and national newspapers and with the Decommissioning Programmes placed on the Maersk Oil website. In addition a copy of the Decommissioning Programmes will be available at Maersk Oil’s Aberdeen office for inspection by members of the public.

As well as making the programmes publicly available, copies will be sent to the following statutory consultees for comment:

• Scottish Fishermen’s Federation (SFF) • National Federation of Fishermen’s Organisations (NFFO) • Northern Ireland Fishermen’s Federation (NIFF) • Global Marine Systems Ltd (GMS)

Any comments from this process will be addressed in the final submission of the programmes.



SFF Email to Maersk Oil UK dated 19/09/2013:

Thank you for your email of 10th September and the Leadon Decommissioning presentation attached. I can confirm that the presentation was discussed during the course of the SFF’s internal committee meetings of 12th September 2013. The committee appreciated being provided with the presentation which it found very informative. The committee was pleased to note that the planned ‘Subsea Scopes I and II’ involve the removal of all subsea structures, flexible flowlines, spool pieces, control jumpers and concrete mattresses. With regard to the remaining two pipeline bundle sections, it was noted that given the restraints of current technology, Maersk’s selected decommissioning option is to rock cover the bundle ends and immediately thereafter for overtrawlable trials to take place. It was further noted that continuous integrity monitoring of the remaining bundles would be put in place; including the undertaking of periodical overtrawlable trials. As discussed at the SFF/Maersk meeting of 30th August, it remains the case that the preferred option for the SFF is the cutting and recovery of the bundles to shore. However, given the restraints of current technology as advised by Maersk at this meeting (and as highlighted in the Leadon Decommissioning presentation) and on the understanding that the described overtrawlable trials are performed at time of decommissioning and periodically thereafter, I can advise that, subject to agreement being reached on the frequency of the periodic overtrawlable trials, the SFF would be prepared to support this course of action in the interim period until such time as future compatible technologies (which Maersk advised they are proactively seeking) become available with which to recover the Leadon bundles. Kind regards, Steven Steven Alexander Director of Business Development Scottish Fishermen's Federation 24 Rubislaw Terrace Aberdeen AB10 1XE



11.0 COSTS

11.1 Cost Estimate Basis

The outline budget cost estimate is based on the decommissioning methodology proposed within this programmes; namely, removal of all subsea structures, flexible flowlines, spoolpieces, control jumpers and concrete mattresses while leaving the bundle sections in place. The cost estimate includes the following aspects:

• Project Management & Engineering (Operator & Contractor) • Offshore execution • Onshore receipt, handling, recycling and disposal • Weather downtime • Contingencies in line with the risk and uncertainty of the Work • Ongoing monitoring and maintenance activities

11.2 Cost Estimate

The details of the cost estimate are commercially sensitive and will ultimately form part of a competitive tendering process and as such are not included here. These details however will be made available to DECC as part of the approval process of the decommissioning programmes.

Preparatory work will be commenced in 2014 to allow for disconnection of the spool pieces and control jumpers from the trees, as well as potentially preparing other items of infrastructure for early recovery should synergies be identified with ongoing projects.



12.0 SCHEDULE

The schedule for decommissioning activities at Leadon is shown below.

The windows outlined for subsea infrastructure decommissioning and plug and abandonment of the wells do not indicate continuous work but rather show the anticipated timescale for decommissioning activities whilst allowing for a flexible approach with decommissioning contractors to achieve the most efficient and cost effective solution.

A final decision on the P&A schedule will be made following a commercial tendering process, the timing of which will be between 2014 and 2019 depending on MODU market capacity and availability.

The ongoing liability to monitor and maintain the bundle is shown below as starting on completion of Subsea Scope II and P&A activities. To ensure there is no risk to the users of the sea a guard vessel will remain on location until this time.

Figure 13: Leadon Decommissioning Schedule



13.0 PROJECT MANAGEMENT AND VERIFICATION

A Maersk Oil Project Management team has been appointed to manage sub-contractors for the decommissioning activities. Maersk Oil standard procedures for operational control and hazard identification and management will be used. Maersk Oil will monitor and track the process of consents and the consultations required as part of this process. Any changes in detail to the offshore removal programme will be discussed with DECC.

13.1 Stakeholder Management

In order to ensure a successful decommissioning process, the many stakeholders must be identified and managed throughout the life of the project. These interested parties along with methods and frequency of communication have been outlined in the Leadon Decommissioning Stakeholder Management Plan [13].

13.2 Independent Verification

In line with the DECC guidelines [2], to ensure transparency and correctness of the process applied to develop this decommissioning programmes, an independent expert verification was commissioned [20]. This review concluded that the Programme has been developed in line with current DECC guidance.

13.3 Audit

Through the project duration, audit requirements will be outlined in project specific Quality and EHS plans. The level of auditing will be consistent with Maersk internal procedures.

Certain offshore activities will be subject to review and approval by a Marine Warranty Surveyor. These items will be identified to potential contractors as part of a commercial tendering process.

13.4 Decommissioning Close out Report

A report detailing the decommissioning works carried out will be compiled and issued to DECC within 4 months of the completion of offshore operations. This report will include:

• As left status of the Leadon field. • Any deviations from the decommissioning programmes and how approval for

these was gained. • Debris clearance details and results of any seabed soil sampling. • Details of the ongoing monitoring regime for Leadon. • A comparison of actual costs against those predicted during the planning of the

decommissioning project. • Commitment to carry out the first post-decommissioning environmental survey

and Leadon site survey in agreement with DECC



14.0 DEBRIS CLEARANCE & AS LEFT SURVEY

14.1 Debris Clearance

Recent surveys [10], [16], of the Leadon facilities have identified minimal debris accumulation through the operating life of the field. In order to ensure that this debris along with any arising from the decommissioning activities is identified and recovered; debris surveys by ROV will be conducted in several key areas:

• North drill centre (500m radius) • South drill centre (500m radius) • Mid line structure (500m radius) • North & South Bundle sections (200m corridor) • 4” gas import flowline route (200m corridor)

Upon the verification of the seabed clearance by an independent organisation a clearance certificate will be provided by SFF and presented to DECC along with the decommissioning closeout report.

14.2 As Left Surveys

To ensure detailed as built records for the Leadon decommissioning project, extensive surveys will be carried out of the areas where infrastructure has been removed to ensure that the seabed has been restored, as much as possible, to its natural state as well as of those items that have been decommissioned in place. The post-decommissioning survey will include a debris clearance survey along a 200mtr corridor of the bundle and a 500mtr radius around drill centres. These videos will form part of the as-built dossier compiled by the subsea decommissioning contractor and subsequently will be included as part of the close out report. Seabed samples will be taken at the locations of equipment removed from site (locations to be agreed with DECC) to confirm if the seabed is returning to its original condition. As part of the final operations at Leadon seabed samples shall be taken around the drill centre sites. Should analysis of these samples identify residue from drill cuttings then additional samples will be obtained in 12 months time as part of the ongoing monitoring regime.



15.0 MONITORING AND MAINTENANCE

15.1 Monitoring Regime

A carefully planned and structured monitoring regime will be required to ensure that the Leadon infrastructure decommissioned in place is maintained in a safe condition. It is anticipated that the first survey will be carried out 12 months after completion of the decommissioning works. This will be discussed and agreed with DECC following submission of the close out report. Thereafter Leadon will become part of Maersk’s ongoing UKCS survey operations which at present are conducted every two years for operational assets. The frequency of surveys may be revised based on survey results with the agreement of DECC. In the Leadon case it is proposed that the outcome of the initial 12 month survey and the condition of the infrastructure decommissioned will be used to perform a risk based assessment (using DNV Integrity Management of Submarine Pipelines DNV-RP-F116). This assessment will provide the basis of discussion with DECC to come to an agreement for the ongoing monitoring regime to be employed. An important part of these subsequent surveys will be to monitor the wall thickness of the bundle carrier pipe as well as the burial status and development of any areas of freespan. It is anticipated that the burial status will continue to improve and as such it is unlikely that any freespan will develop. However the burial status and wall thickness will be monitored at designated reference points. This will ensure that the corrosion profile of the bundle is consistent with that predicted in the corrosion assessment [5] and the burial status is well understood. As part of Maersk’s ongoing liability for the Leadon infrastructure, trial trawl sweeps of the bundles and the installed protection will be completed periodically. The procedure for these trials and their frequency will be planned and agreed in conjunction with the SFF and DECC. The ends of the 50m section which will remain in place under the Apache operated Skene NRB will be lowered to a depth of 0.6mToP. The ownership and decommissioning liability for this 50m section will be agreed with relevant stakeholders. If initial soil samples taken as part of the as left survey identified drill cutting residue then the sampling will be repeated 12 months after decommissioning operations. The comparison of the two sets of data and consultation with DECC and other stakeholders will dictate whether further sampling is required and to what extent.



16.0 SUPPORTING STUDIES AND REFERENCES

REF DESCRIPTION DOCUMENT NUMBER Date

[1] Leadon Environmental Statement (05/2010)

LEA-LEA108-SU-RE-0012 March 2010

[2] Guidance Notes: Decommissioning of Offshore Oil and Gas Installations and Pipelines under the Petroleum Act 1998

URN 09D/734;

Version 6 March 2011 March 2011

[3]

Technical Review of Data from around Maersk Oil’s North Sea fields with regard to OSPAR Recommendation 2006/5

ERT 1868 April 2008

[4] Leadon Decommissioning Options Comparative Risk Assessment

5079630/029/029/RP001/A May 2010

[5] Bundle Corrosion and Long Term Protection Assessment

LEA-LEA108-SU-RE-0015 February 2010

[6] Leadon Decommissioning Burial Equipment Study


[7] Leadon Decommissioning FEED Study Report

LEA-LEA108-SU-RE-0002 April 2009

[8] Leadon Decommissioning Inventory LEA-LEA108-SU-IR-0002 March 2009

[9] Leadon Decommissioning Comparative Assessment Report

LEA-LEA108-SU-RE-0004 March 2010

[10] Maersk UK 2011 ROV Inspection Campaign

Various files July 2011

[11] Technical Note: Surface Towing LEA-LEA108-SU-TN-0006 March 2009

[12] Bundle Tow Summary LEA-LEA108-SU-RE-0016 August 2010

[13] Leadon Decommissioning: Stakeholder Management Plan

LEA-LEA108-PM-RE-0001 September 2009

[14] Comparative Assessment II Report LEA-LEA108-SU-RE-0020 February 2012

[15] Leadon Decommissioning Option Screening Summary


[16] Bundle Survey Comparison 2006 - 2009 LEA-LEA108-SU-RE-0011 February 2010

[17] Maersk / SFF Minutes of Meeting 03.11.09

C122-MOM-002 November 2009

[18] Conditioning Philosophy: Requirements prior to Decommissioning

LEA-LEA108-SU-TN-0003 March 2009

[19] Maersk HAZID Report LEA-LEA108-SA-HD-0001 July 2010

[20] Independent Review of Process to Evaluate Leadon Decommissioning Options.

LEA-LEA108-SU-RE-0013 October 2010

[21] Other Users of the Sea PLL Study LEA-CR5318-LEA108-SU-RE-

5000 September 2013

[22]

Constructing the World’s Longest Subsea Pipeline, Langeled Gas Export, Leif Solberg and Erling Gjertveit, Statoil, 2007

OTC 18962 2007

[23] Overtrawling of Large Diameter Pipelines JIP, Jee

JIP07 R11A summary rpt Public 20-APR-05



APPENDIX 1 – REFERENCE DRAWINGS

DRAWING No. TITLE

GP3-5318-SU-GA-0001-01 Towhead / Bundle Arrangement

GP3-5318-SU-GA-0002-01 Midline Structure Piping / Controls Arrangement

GP3-5318-SU-GA-0003-01 North Towhead Piping / Controls Arrangement

GP3-5318-SU-GA-0004-01 South Towhead Piping / Controls Arrangement

GP3-5318-SU-LA-0001-01 Field Layout

GP3-5318-SU-LA-0002-01 Field Layout Midline Structure

GP3-5318-SU-LA-0003-01 Field Layout North Towhead Area

GP3-5318-SU-LA-0004-01 Field Layout South Towhead Area

GP3-5318-SU-LA-0005-01 Field Layout Beryl Platform Area

LEA-LEA108-SU-SK-004 4” Gas Import Pipeline – Pipeline Works Schematic

LEA-LEA108-SU-SK-005 4” Flexible Flowline Crossings at Beryl



APPENDIX 2 – SPOOLS DETAILS

As per section 29 notice, the following spools will be decommissioned:

PL1841. I(J )P3 PL1841. I( J)P4 PL1841. I(J )P5

PL1841. I(J ) P8 PL1841. I(J )P9 PL1841. I( J)PIO

PL1841.2(J)P4 PL1841.2(J)P5 PL1841.2(J)P6

PL1841.2(J)P9 PL1841.2(J)PIO PL1841.3(J)P3

PL1841.3(J)P5 PL1841.3(J)P6 PL1841.3(J)P8

PL1841.3(J)PIO PL1841.4(J)W14 PL1841. I(J )P6

PL1841,2(J)P3 PL1841.2(J)P8 PL1841.3(J)P4

PL1841.3(J)P9

PLU1841.5(J)P5 PLU1841.5(J)P3 PLU1841.5(J)P4

PLU1841.5(J)W11 PLU1841.5(J)P8 PLU1841.5(J)P9

PLU1841.5(J)P6 PLU1841.5(J)W14 PLU1841.5(J)PIO

PL1842.1(J)P1 PL1842.1 (J)P2 PL1842.1 (J)P7

PL1842.2(J)P2 PL1842.2(J)P7 PL1842.3(J)P1

PL1842.3(J)P7 PL1842.3(J)AQlI PL1842.3(J)AQ2

PL1842.4(J)W13 PL1842.5(J)AQI PL1842.5(J)AQ2

PL18422(J)Pl PL1842.3(J)P2

PLU1842.6(J)P2 PLU1842.6(J)P7 PLU1842.6(J)W12

PLU1842.6(J)AQI PLU1842.6(J)AQ2 PL1842.4(J)W12

PLU1842.6(J)PII PLU1842.6(J)W13 PLU1842.6

Leadon North Towhead Spool Details and Layout



Leadon Mid Line Structure Spool Details and Layout

Leadon South Towhead Spool Details and Layout



APPENDIX 3 – COMPARATIVE ASSESSMENT MATRICES







APPENDIX 4 – WELL PLUG AND ABANDONMENT OPERATIONS

MODU Operations

• Locate over well. Re-enter well (e.g. Run guidewires. Remove debris cap, RU and run WO string. Run Manifold connector and latch to wellhead. PU controls to SS tree. Pull tree cap) (Assumes BOP hopping)

• Bullhead tubing contents to formation • Lubricate annulus to kill fluid • Unseat tubing hanger. Circulate well. • Recover upper completion (+/- 6,000ft) • Run bridge plug to upper completion and pressure test • Pull running string • Run cementing string • Lay a cement plug on top of bridge plug • Pull cementing string • Lay a cement plug on top of bridge plug • Pull running string • Pull BOPs, pull Xmas tree, Run BOPs • Back out packoff. Cut production string at 13.3/8" shoe @ 2200ft. Circulate

LTOBM from annulus. Retrieve casing. • Set bridge plug above casing cut and pressure test. • Pull running string • Run cementing string • Lay a cement plug on top of bridge plug • Pull cementing string • Prepare BOPs to hop • Prepare to skid to next well

WIV Operations

• Establish WIV over well. Rig up and run abrasive cutter • Sever 13.3/8" and 30" below seabed and recover to surface • Prepare to move WIV



APPENDIX 5 - FEED PROCESS FOR DECOMMISSIONING OPTION

Documents

Leadon Decommissioning Programmes - gov.uk · Title: Leadon - Decommissioning Programmes Date 24/01/14 1. All of the subsea wells will be plugged and abandoned in accordance with