SPE-171852-MShh

SPE-171852-MS

Innovative and Cost-Effective Coring Technique Extended Coring for LongIntervals of Multiple Zones with World Record – Case Histories from theUAE

M.Hegazy Gehad, ADCO, SPE, UAE; Adel M. Salem, American University in Cairo (AUC), Egypt;Shedid A. Shedid, Consultant & Professor; Muhammad N. Aftab, Ali Muhammad, and Reyami Mazin Al, ADCO;Wahab Hazem and Farouk Mohamed, Baker Huges, UAE

Copyright 2014, Society of Petroleum Engineers

This paper was prepared for presentation at the Abu Dhabi International Petroleum Exhibition and Conference held in Abu Dhabi, UAE, 10–13 November 2014.

This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contentsof the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflectany position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the writtenconsent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations maynot be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.

Abstract

Continuous core acquisition across formations of interest to perform quantitative and qualitative analysisis extremely important for exploration geologists and reservoir engineers. Measurements performed oncores are typically calibrated against well logging data for accurate and better reservoir interpretations.However, the coring cost is directly proportional to coring technique, core length and a significant part ofcoring cost is associated with rig time. In deep formations, the coring cost becomes extensively high dueto multiple trip times required after each conventional coring run (90 ft). The best way to minimize thecoring cost is to reduce the rig time efficiently achieved by reducing the number of trips required toacquire core.

Abu Dhabi Oil Company for Offshore Oil Operations (ADCO) has recently investigated differentcoring scenarios and technologies to optimize the coring operation time. An innovative and cost effectivesolution was developed and applied as a result of this investigation by Extended Coring (Long Barrel)which meets ADCO’s objective of continuous coring across formations of interest. This procedurereduced number of trips, rig time and eventually drilling cost. The extended coring (Long Barrel) can berun in lengths from 120 ft to 810 ft with proper timing and planning for the jobs.

This paper describes ADCO’s new strategy of extended coring (long barrel) acquisition based onformation’s geological description. The case histories of extended coring in different formations in 8 ½”and 6” hole size sections, the core handling procedures applied and lessons learned in a continuousiterative process to optimize drilling cost in future operations are presented and analyzed.

Introduction and Literature ReviewAs global energy demand continues to rise and production of unconventional oil declines, furtherdevelopment of low permeability oil recovery processes and technologies is needed to meet future energydemands. The value of core samples to enhance reservoir evaluation and completion strategies has longbeen recognized. Coring has early been recognized as very desirable to provide both qualitative and

quantitative geological and mechanical data necessary for reservoir characterization and management,completion decisions, drilling, and other applications. The difficulty has been identified in justifying thecoring cost. The solution to the cost problem of core quality and ensuring that the core is representativeof the reservoir is to obtain more and sometimes longer cores in the minimum possible time.

Core analysis has been widely divided into Routine Core Analysis (RCAL) and Special Core Analysis(SCAL), as shown by Shedid (2013). When the drilled formation become more complex of low and verylow permeability, special core analysis has become necessary for better evaluation of the formationunderdevelopment (Aboud et al., 2008).

It is important to have a comprehensive understanding of heterogeneity and structural complexity of thereservoir under development. The main sources for better description of complex heterogeneous reservoirsinvolve special core analysis, well logging, and well testing (Shedid, 2014). Coring goal is to obtain corerepresentative of the formation of interest while minimizing the physical and chemical alteration of therock during coring process. Earlier the target was to core a low Invasion core samples to minimize thephysical and chemical alteration of the rock but recently with the demand to core long interval it was alsorequired to save rig time without affecting the core quality.

The main applications of coring tight gas/oil reservoir can be summarized as: (1) definition ofunconventional gas/oil reservoirs, (2) Identification of cost-effective coring and core characterizationprograms for basin-scale model development and sampling strategies, and (3) Understanding the chal-lenges and defining progressive drilling and completion strategies, (Shedid, 2014).

The cost effective cutting of large intervals of continuous core in dolomitic formations requiresoptimization of existing coring practices (Bretches et al., 1993). This study indicated that coring costs canbe reduced as much as 38% when innovative techniques are applied to the coring operation with regardto core barrel spacing, core barrel modification, and proper bit selection to include the use of suitablecoring bits. Another major problem of coring is Health, Safety, and Environment concerns. Briner et al(2010) succeed in coring sour ones in the South Rub Al-Khali. They considered the HSE aspects, the mudsystem and core barrel vibrations by close monitoring to guarantee good core recovery with a maximumof H2S scavenged. Special attention was also given to the cores after recovery to ensure no poisonous gasis released in an uncontrolled manner. Moran et al (1989) cored samples in 1.0 meter length. Thesesamples were collected from Shelf in the south to Baffin Bay in Canada. Coring long core to be morerepresentative is another difficult task in coring process.

Some studies indicate that the overall cost of coring is influenced more by higher rig costs, due toadditional trip time and slower penetration rates, than by charges made by the penetration rates, than bycharges made by the coring companies for their tools and services. Filshtinsky and Quinn (1983) presentedthree coring tools to reduce coring cost and make it economically feasible, including (1) non-jammingcore barrel, (2) downhole motor coring system, and (3) wireline downhole motor coring system. Today,several advanced technologies have been developed and used in this study to reduce the coring cost.

Conventional core barrels collect and containerize a column of core material in an inner barrel that canbe made of non-disposable steel or disposable materials such as aluminum, fiberglass, or thin-walled steel.In 2008, Hall et al (2008) presented a new tool as a one-piece aluminum inner barrel liner system toprotect and containerize core material during coring operations with conventional and wireline corebarrels.

Commonly exploration and appraisal objectives are different than the development objectives wherethe cores are one of the main targets to measure the rock properties of very low permeability. Geo-mechanical measurements become one of the goals to design the well completion for future fracturingwhere studding the layers above and below the main reservoir become very important to insure theisolation. An example of conventional coring technique is shown in Figure 1, below. Comparison ofconventional and extended coring is listed in Table 1.

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ADCO Exploration and development teams request to have many cores for early studies and also toovercome the conventional way of higher rig time and consequentially higher required cost. These tworeasons of attaining representative very log core at minimum costs were the main incentives of the authorsto undertake this study.

Problem StatementThis study was important to achieve the required cores meanwhile not affecting the ongoing planning.Many techniques were reviewed and evaluated such as extended coring, wire line coring and side wall

Figure 1—Examples of Conventional Coring Technique.

Table 1—Extended Coring Summery

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core to achieve the objective. Considering the risk, rock size and quality are the main targets followed bythe operation cost. Based on the above comparison of coring operations, which shown more complexprocess due to the following reasons:

● Limited technology.● Limited Core Size.● Less Core Quality.● Higher Operation risk due to high H2S.● More Operation cost.

The General Coring GoalsMajor and general goals of coring process of a formation under development are summarized to be asbelow:

● Obtaining representative core of the formation to be developed while minimizing the physical andchemical alteration of the rock during coring process.

● Providing great care and concern to reduce time associated with high cost.

Current ADCO Coring Technique

● Cut cores with maximum 90 – 120 ft length● The average core trips were ranged from 2 to 3 days based on the core depth and

H2S % value.● Considering three different examples for the existing core objectives.

ADCO New Goals

● Unconventional reservoirs “high uncertainties and long intervals”: to minimize theuncertainties it was recommended to cut long core intervals 800 ft to 1200 ft.

● Conventional reservoirs: it was recommended to cut the dense between the layersfor frac geo-mechanical studies within same cost and time effective program.

● Getting the long coring without affecting the company budget and business plan(number of wells/year)

Coring Techniques and Study OutcomesThis study was important to extract the required cores and not affecting the ongoing planning. Manytechniques were reviewed such as extended coring, wire line coring and side wall core to achieve theobjective. It was important to minimize the risk, keep rock size and quality, and also reduce the operationcost. The main current coring techniques involve:

● Extended coring: Applied in areas where the core length is more than 120 ft● Wire Line coring: Used when coring, drilling operation are in sequence.● Side wall core : In exploration wells where hydrocarbon indication after drilling

New System SelectionBaker Hughes Extended Coring System (Long Barrel) is designed to be able to core longer interval above90 ft where the system is consisting of the followings:

➢ Core Barrel (HT Series) core barrel, which is 30 ft in length of each joint incorporated with 4 ftstabilizer, the assembly can be made up till 840 ft. in one run, Figure 2.

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➢ Low Invasion bits were recommended, Fig-ure 3.

➢ The core barrel is incorporated with LongDistance Adjustable (LDA) system, Figure4, for the following:

A) Adjusting the thermal expansion of theinner barrels without lifting the assemblyafter picking up.

B) Swivel assembly which has the ball seatfor the flow diversion.

C) Pressure relief plug to allow releasing anytrapped gas while pulling out of the hole.

Inner parts

➢ The System can be made up with Aluminuminner barrel with different lengths, Figure 5.

➢ Aluminum tube might be vented or normaldepending on the reservoir conditions.

➢ LaserCut Liner (Core Quick View) and / orJambuster Liner can be made up easily on thesystem.

➢ Minimum ID Gage, Figure 6

✓ Reduced Disturbance✓ Reduced Core Fluidization✓ Improved Protection

➢ Force Balance Technology➢ Wear Knots – reduce depth of cut, limits

aggressiveness

✓ Lateral Movement Mitigate (LMM),building up of blade behind & around thegauge cutters, limits lateral motion, reduc-ing bit whirl

✓ Increased Stability

Extended coring systems can be used in vertical& deviated hole with interbedded formations as wellas the system can be used a combined Jambustersystem which is used for highly interbedded forma-tions:

Protecting the Core for Enhanced Reservoir DataThe JamBuster anti-jam coring system incorporates telescoping inner core barrel sleeves into the provenBaker Hughes HT- Series heavy duty core barrels to eliminate the effects of core jamming. With theJamBuster system, two concentric inner core barrel sleeves automatically telescope if a core becomesjammed in the core barrel. Coring continues without interruption.

Figure 2—Core Barrel Design

Figure 3—Low Invasion Bits

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ApplicationsJamBuster is especially effective in difficult coring applications:

– Coring fractured formations– Coring through a slanted formation fault– Coring interbedded shale’s and expanded clays– Extended coring system.

Proven Results and AnalysisSystem effectiveness has been demonstrated repeatedly:

– Core barrel efficiencies (percent of barrel filled) of 70% to 100% can be obtained

Figure 4—LDA assembly

Figure 5—Integration of Aluminum Inner barrel with PRCV helps in releasing trapped gas and pressure while POOH with the core barrel in highgas wells/high H2S %.

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– Three-jam capacity reduces coring trips by at least two-thirds, core sample milling is eliminated– Offset comparisons with conventional systems show twice the length of core recovered with

JamBuster.

JamBuster can be run with new generation core bits and Core-Guard low invasion coring systems, and canbe combined with the Baker Hughes Gel Coring technology. Core diameters of 2 1/8” to 4 1/2” can beobtained with the various barrel configurations.

Baker Hughes JamBuster anti-jam system, Figure 7, can reduce the costs associated with coring andproduce quality core samples.

Figure 6—BHC-406C Core Bit

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ADCO and Baker Hughes – Achievements in the UAE

ConclusionsBased on the executed field coring jobs and the developed analysis, the following conclusions are drawnas follows:

Case 1, Well X-71, Top Drive Rig

Plan:Conventional:Extended Coring Outcome:

Was to cut 480 core across conventional formations – 8 ½” vertical hole90 ft barrel, 6 runs and rig time planned was 15 days482 ft core was cut in two runs with 100% recovery, excellent core conditionFirst run was 180 ft. and second run was 300 ft core length5 days for coring operationLongest core run in conventional formations with 34% H2S.Saved 10 days of rig time with 400,000 USD

Many lessons were learned in the first coring runs in ADCO.



Was to cut 540 ft. Core across deep and tight formations, 6�vertical hole.90 ft barrel, 6 runs and rig time planned was 21 days350 ft core was cut in two runs with 65% recovery, excellent core conditionFirst run was 270 ft and run was 80 ft core length11 days for coring operationSaved 10 days of rig time with 500,000 USDMany lessons were learned in this first 6� coring runs in ADCO

World record pf longest core run 270 ft in 6.0 inch hole



Was to cut 420 ft. Core across three layers with 20 deg. Inclination.90 ft barrel, 5 runs and Rig Time planned was 13 days422 ft core was taken with 101% recovery, excellent core conditionAchieved in one run6 days actual coring operationSaved 7 days of rig time with 450,000 USDLongest core run in 20 degree deviated hole

World record of longest core run 422 ft in 20 deg deviated hole



Was to cut 780 ft core across five formations90 ft barrel, 9 runs and rig time planned was 27 days780 ft core was taken in two runs with 100% recoveryExcellent core conditionAchieved in 2 runs (390 ft each)8 days actual coring operation

Saved 19 days of rig time with 900,000 USD

Case 5, Well X-64, Kelly Rig


Was to cut 1150 ft core across tight formations90 ft barrel, 13 runs and Rig Time planned was 26 days100% recovery and excellent core conditionAchieved in 5 multiple coring runs from 156 to 287 ft core length16 days actual coring and drilling operationsSaved 10 days of rig time with 400,000 USD

World record of longest Core run 287 ft with Kelly Rigs

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1. A new technology has been proven as the first time in the UAE tight/inclined reservoirs. Inaddition, an innovative coring strategy based on the requirements has been developed and appliedsuccessfully.

2. Remarkable cost and time saving were achieved with zero operation Non-Productive Time (NPT)and/or no safety concerns.

3. The first longest core through 8.5� wellbore slanted hole, the first longest core through 6� hole, andthe first longest core through Kelly rig are carried out successfully as the worldwide records.

4. Extended coring has proven its ability to core with long barrel to reduce rig time and to reduce theoverall time of the reservoir exposure to the drilling fluid. This allows better quality of wire linedata to be obtained especially when sampling and pressure record runs are required.

5. Extended coring reduces the overall time of the core sample exposure to the drilling fluids whichalso lead to a reliable routine and special core analyses.

6. Extended core reduces the number of trips required for coring, which effectively reduces and eveneliminates negative Health, Safety and Environment (HSE) concerns and consequently removesexpected risk involved. This method also reduces the overall cost of the rig which allows wells toput on production faster and allows calibrating the drilling plan.

RecommendationThe following recommendations are important to be considered in the future coring jobs:

1. Extended Coring services need to be planned prior to the jobs to ensure Maximum benefit of thetools.

2. Extended Coring Services need to be selected as per Core Analysis Program, i.e. Extended Coringassembly with LaserCut System allows repaid access to the core sample to be able to do all thecore analysis services at well Site.

3. Extended Coring System can be assembled with JamBuster System to be able to core inter-beddedformation without pullout of hole incase jam occurs / or Suspected.

4. When coring in formation with High H2S and CO Gas, Extended Coring Can be used with vented

Figure 7—JamBuster System (Anti-Jamming System) used with Extended System

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inner barrel to allow the gas to escape while pulling out of hole.

AcknowlegementsThe authors would like to thank ADCO, ADNOC Management and Baker Hughes for their support andthe permission to publish.

Nomenclature

LDA Long Distance Adjustable systemLMM Lateral Movement MitigateRCAL Routine Core AnalysisNPT Non Productive TimeSCAL Special Core Analysis

References1. Shedid A. Shedid, (2013), “Coring and Core Analysis: Routine and Special Core Analysis (RCAL

& SCAL)” HOT Eng Manual, Venia, Austria.2. Shedid A. Shedid, (2014), “Characterization Number (CN): Field Applications and Analytical

Evaluation of Reservoir Characterization Techniques,” Petroleum Technology Development Jour-nal.

3. Aboud, R., et alet al., (2008), “Effective Stimulation of Carbonate Reservoirs around the Worldby Creating Multiple Drainage Holes,” Paper IPTC 11993 presented at the International Petro-leum Technology Conference held in Kuala Lumpur, Malaysia, 3–5 December.

4. D.C. Bretches, J.E. Shields, C. A., Harder, and F. W. Hagins, (1993), “Permian Basin Coring CostCut by One-Third Over a Long Cored Interval Using Innovative Coring Techniques,” SPE 26346,SPE Annual Technical Conference and Exhibition, 3–6 October, Houston, Texas.

5. Andreas P. Briner, Rajendra Chitnis, Abdul-Hameed Azzouni Rajendra Chitnis, and Vishal Vyas(2010), “Sweet Success In Sour Coing” SPE-128007-MS, North Africa Technical Conference andExhibition, 14–17 February, Cairo, Egypt.

6. K. Moran, D.J.W. Piper, L.A. Mayer, R.C. Courtney, A.H. Driscoll, F.R. Hall (1989), “ScientificResults of Long Coring on the Eastern Canadian Continental Margin” OTC paper -5963-MS,Offshore Technology Conference, 5/1/1989, Houston, Texas.

7. Michael Filshtinsky and Joel Quinn, (1983), “New Tools Improve the Economics of Coring”SPE-12092-MS, SPE Annual Technical Conference and Exhibition, 5–8 October, San Francisco,California.

8. Larry M. Hall, Bob Wilso, and Alan G. Norrie (2008) “Novel Liner System Improves CoringPerformance, Rig Safety, and Wellsite Core Processing,” SPE-113294-MS, SPE Indian Oil andGas Technical Conference and Exhibition, 4–6 March, Mumbai, India.

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