IADC/SPE 155440

Drilling Performance Optimization on Malaysia's First Coiled Tubing Drilling Pilot Project: A Case Study A.A. Abdul Rahman, SPE, N.E. Hamzah, SPE, and N. Ahmad Fauzi, SPE, PETRONAS CarigaliSdn. Bhd; and H. El-Hariry, SPE, J.R. Jenie, SPE, and Y. Chaari, SPE, Schlumberger

Copyright 2012, IADC/SPE Asia Pacific Drilling Technology Conference and Exhibition This paper was prepared for presentation at the IADC/SPE Asia Pacific Drilling Technology Conference and Exhibition held in Tianjin, China, 9–11 July 2012. This paper was selected for presentation by an IADC/SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the International Association of Drilling Contractors or the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the International Association of Drilling Contractors or the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the International Association of Drilling Contractors or the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of IADC/SPE copyright.

Abstract This paper presents a general discussion of the phases necessary to undertake coiled tubing drilling (CTD) project in a new area: conceptual design during the feasibility study, equipment planning and preparation, detailed engineering, and operational challenges during execution. The actual operations and performance results for these phases are given for the first CTD pilot project undertaken in Malaysia. CTD can provide significant economic benefits when applied in the proper field setting. In addition to potential cost advantages, it can provide other benefits: safer and more efficient pressure control, faster tripping time, smaller footprint and weight, faster rig-up and rig-down, reduced environment impact, operations with fewer personnel, and high-speed telemetry. In the Malaysia project, where it was applied to the drilling of directional through-tubing reentry wells requiring casing exit methods and high dogleg capability, it provided the flexibility to access compartmentalized bypassed pockets in the reservoir. Drilling for the CTD project was started in February 2011 and completed in August 2011; three out of four wells were drilled and completed in the target formation. The challenges faced during the beginning of the execution phase were used as lessons learned and contributed to a fast learning curve, leading to delivery of the last three wells within budget. The drilling campaign demonstrated the ability of CTD to reach small, bypassed pockets that are difficult to produce economically with conventional reentry drilling techniques. This success has opened the door for CTD of other numerous idle wells [in same field or just in Malaysia in general?], which can result in efficient recovery of the bypassed oil. This is especially important for the offshore environment of Malaysia because platforms require a significant investment that is usually not justified for such marginal reserves. Introduction The application of coiled tubing drilling (CTD) can be divided into two main categories: grass roots and through-tubing reentry sidetracks. The grass roots application is driven by the efficiency provided by a hybrid CTD rig, combining advantages from the conventional rig and CT unit in one mobile package. This method has seen significant growth in the last few years, mainly in North America and Canada but recently in Australia. Through-tubing reentry sidetracks gained popularity in the early1990s. The majority of the work was performed in Alaska with the specific driver of accessing bypassed reserves without removing existing completions. This process allows the operator to tap the hydrocarbon quickly without a workover rig. With experience and new technologies, this method has matured to become a proven alternative to conventional drilling. More than 90% of the case histories published in literature are from land applications, with Alaska, USA, being the leader, followed by the Middle East, Far East and Asia, and Latin America CTD in the offshore environment is a totally different scenario, although offshore lifting cost is significantly higher than that on land. According to Abdul Rahman et.all (2012), few projects have qualified as a success, and none of them became sustainable operations. This result is mainly due to one-off projects that did not have enough candidates to generate a learning curve. Also, Abdul Rahman et .al (2012) determined that the failure impact of this method in offshore applications was

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significantly higher than on land application. A combination of these factors dimmed the potential of this application for production enhancement in the offshore environment. A major operator in the South China Sea continuously tried to find ways to increase production from its mature fields but had difficulties finding cost-effective ways to develop the small bypassed reserves that were uneconomical to drill with conventional rigs (Abdul Rahman et al. 2012). The CTD method is evaluated as one of the technologies that can bring value to the company. The approach proposed is to set the candidate criteria based on case histories and commitment to multi-well campaigns with a proven method of CTD from similar projects, engage expertise in this application, and manage the project in such a way that all lessons learned are captured and applied accordingly within the campaign. This paper will describe the overall CTD pilot project experience in offshore Malaysia, starting from feasibility study, equipment planning and preparation, execution, results, lessons learned and overall project achievement to date. Feasibility Study As an economical solution to monetize marginal hydrocarbons, CTD needs to fit this requirement by optimizing all aspects of resources, candidate selection, execution approaches, and contingency preparation. In this project, at early stages the candidate reservoirs were selected from a database of mature and bypassed reservoirs based on the potential remaining hydrocarbons that could be produced; this volume had to exceed the threshold of 0.5 million standard barrel oil per day. The minimum net pay thickness was set as 10 m minimum to allow kickoff and landing in the same layer. A study was conducted to determine the re-entry spotsin the existing well. The optimization plans were detailed out, based on the following considerations, but not limited to; - Existing completion: The main criterion was the size. Because of the size of the bottomhole assembly, 3!-in. completions

were the main target. Complexity and restrictions were also considered; dual completions cost more and require more time to determine the correct side of the window to exit. Restrictions will generate more intervention runs to flush the inner diameter so that the drilling assembly can be run in.

- Window exit spot: The main objective was to exit from the existing tubing -casing and land the open hole in the same sand layer. CTD offers this benefit through its capability to build angle up to 45°/100ft dogleg severity. Example:A single exit window is less challenging than a dual or triple one.

- Number of potential candidates from the same platform: The higher the number, the more drastic will be the reduction in exposure to logistics hazards and the more time will be saved. A separate study was performed to determine if the platform facility needed modification for structural strengthening.

- Open hole length: Because of the additional drag in open hole, candidates were assessed for potention to reach target. A threshold of 1000 m was determined based on rules of thumbs for CTD applications in other locations.

- Torque and drag: The tortuosity of the open hole and its orientation to the main bore affect frictions. These parameters can compromise the target if the openhole section is relatively long.

From the pool of 17 candidates initially, a systematic ranking system was created based on lateral length, engineering assessment, platform size/condition and casing exit method. Five wells were selectedand located on twomainplatforms. The subsequent topics discussed here are related to the preparation and optimization done in planning and executing these five (5) wells.

Equipment planning and preparation Based on the feasibility study, in support from a subsequent platform & offshore facilities assessment, the suitable surface equipment for the CTD campaign was selected. Major criteria for all equipment selection were the zone rating and the load distribution. All electric, diesel and hydraulic driven equipment closed to the zoned area as per platform hazardous area layout were Zoned II. This requirement added more complexity to equipment selection,availability in the market and compatibility. Surface equipment is composed of equipment similar to that of conventional operations: mud circulating system, drilling and conveying system, and pressure control equipment. Fig. 1 shows the process and instrumentation diagram.

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Fluid Pumps

Fluid Pump 2

Fluid Pump 1

1111

Tank

Solids Tank

Turbine Flow Meter

Flow Meter

Annular BOP

Combi BOP

Batch MixerStorage Tanks

Solids Handling Equipment

Choke Manifold

Mud Gas SeparatorPressure Control

Equipment

Coiled Tubing Injector Head Coiled Tubing Reel

Fig 1: Process and instrumentation diagram

• Pressure control equipment - Dual combination CT BOP: With a function similar to a BOP in conventional drilling, the CT BOP is for pressure control

in case of contingency work or well control situation. The order of the rams is slightly different from that in the BOPS used for standard drilling: o Upper ram: Combined shear and blind ram to cut and hold CT pipe and completion [string] under maximum

allowable surface pressure. o Lower ram: Combined pipe and slip ram to hold CT pipe in tension and seal against flow direction. BOP design considerations are mainly the drilling assembly size, maximum potential wellhead pressure, temperature rating, and rating for sour environment. The model selection also took into consideration the relatively small dimension of the BOP, which must have a larger diameter than the piston for passage of the well slot hatches.

Annular BOP: This BOP is an additional barrier for sealing against the CT and is the main barrier to seal across the completion, the BHA, or any unconventional shape or size of the drilling assembly during deployment or reverse deployment of relatively long tools. Design considerations are mainly the pressure rating, completion and BHA assembly sizes, and type of fluid used. See Fig. 2 for configuration of CT wellhead stack up.

Top of wellhead to main deck

Main deck

Note: Skid beam sits on

platform beam

2.19 m

Lower Deck

Top of Xmas tree

Tubing Hanger Flange

11.31 m

Fig 2: CTD wellhead stack up

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• Drilling and Conveying System: CT equipment for drilling applications is custom built to accommodate the workload, which is higher than that for standard intervention services. - CT reel: The reel stores the CT pipe, similarly to the stand for pipe joints used in conventional drilling. The reel is

equipped with a pumping manifold and swivel that offer the advantage of continuous pumping during the tripping in and out of the drilling assembly. During the design phase, the reel weight and footprint are considered for crane and platform structure limitation. The reel is normally the heaviest equipment for an offshore environment, so a methodical structural engineering assessment needs to be performed to ensure the platform crane can lift the reel and place it in the desired location.

- Injector head and gooseneck: This equipment feeds the pipe into the well during tripping in or retrieves it during tripping out. The injector head is equipped with hydraulic motors, brakes, and chains that convert the hydraulic power generated by the CT powerpack to a mechanical motion. During the design phase, the injector head rating is determined based on pulling and snubbing capacity and pipe size to be used. The gooseneck will ensure a smooth pipe feed from the reel to the injector head: the curvature will avoid kinked pipe at the entry of the chains.

- CT pipe: This pipe is designed to convey the drilling assembly in a “sliding” mode at all times. This continuous “pipe” provides continuous pumping while tripping in and out of the well. For pipe selection and design, several key parameters must be considered, including but not restricted to the following:

o Existing completion restrictions. o Designed pump rates for optimal hole cleaning. o Expected differential pressures. o Expected pulling and snubbing forces. o Expected sour environment. o Drilling assembly design: wired or non-wired BHA.

- CTD structure with jacking capability: A CTD substructure serves multiple purposes: to supportthe CT injector head

without crane attachment, to provide a platformto offload across an area acceptable for the deck on which it is placed, to serve as a platform for working on pressure control and injector components, and to provide 3D movement of the injector head for deployment and retrieval of the BHAs without removing the substructure from its original position. Deployment and retrieval of CT BHAsare two of the most critical activities in CTD operations, and hence the ability to do this task faster while maintaining all safety considerations is crucial.

• Mud circulating system: - Fluid Pumps:

The CTD pumps for the project required lower flow rates and higher pressures than those for standard pumps and were required to pump continuously; these requirements led to a need for special CTD pumps. Regular mud pumps that work with high flow rate and low pressure cannot be used for CTD. Type of drilling mud,rheology, CT size, and pumping rate required to achieve proper holecleaning are key inputs for CT job simulation to determine the hydraulic horsepower requirement. Considering the need for continuous and long pumping hours, a minimum 50% more horsepower was required from the CTD pumps.

- Batch Mixer

A zoned batch mixer with double stainless steel compartments and equipment with hooper are used to mix the mud to the design specifications. The batch mixer is equipped with paddles to promote mixing capabilities that set the mud properties to the design parameters before transferring it to the active mud circulating system. The batch mixer is also used to mix any other contingency fluid, such as cement, fluid loss pills, or even acid. The batch mixer compartments can also be used for storage. The centrifugal pumps can be used as feeding or booster pumps for the main mud pumps

- Solids Control Equipment

Solids control in drilling mud is crucial in maintaining hole-cleaning ability. It also significantly affects the applicable weight on bit transferred to the end of the CT BHA, and thus the ability of reaching target depth. Shale shakers, de-sanders, centrifuge pumps, active pits, storage tanks, and mud gas separator are part of the circulating system and solids control package. For CTD applications, an integrated fit-for-purpose modular system was developed based on those with proven performance in different locations. The significant advantage of CTD reentry sidetracking is the lower mud volume required compared to that needed for conventional rigs; therefore, the footprint of this equipment is relatively small.

Detailed Engineering

The pilot project time and cost were optimized by splitting the execution into a pre-CTD campaign and CTD campaign using a purpose-built package. The pre-CTD program was designed to prepare the CTD candidate wells for sidetracking. This was

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done while mobilizing the CTD package into the country. The well preparations use the conventional CTU, slickline, and electric line equipment to plug and abandon the well and set the whipstock.

Pre-CTD Campaign

The campaign had the following main objectives: - To ensure integrity of the Christmas tree and its capacity to sustain working pressure during drilling phases. - To check the condition of the existing completion and the way forward for any additional intervention needed before

commencing drilling. - To prepare for well integrity during through-tubing exit by creating a permanent seal between the formation and the

casing/tubing annulus. - To ensure a homogenous wellbore ID for whipstock setting success. - To set the whipstock for the window exit.

Depending on the well status and initial completion, several scenarios for the pre-CTD work can be designed. A typical pre-CTD process can include but is not restricted to the following: - Mill out nipples to allow window milling and drilling BHAs to pass through to the predesigned kickoff point. - Cement jobs and cement assessment: Performed based on the window exit position.

o Single-window exit: Through-tubing cement bond log to check the cement status behind casing or liner. o Dual- or multiple-exit window: Set tubing punch, bridge plug, or cement retainer using wireline or CT depending on

the well deviation, followed by a cement squeeze in the tubing/casing annulus. o Cement bond log to ensure good cement portion above the kickoff point.

- Drift and gauge run using caliper. - Set the whipstock with e-line orienting tool to set in planned direction

CTD Campaign The CTD program was planned with three main steps; each step hada key objective: window milling; drill the build and tangent sections, and completion. - Window milling: The objective was to provide access to the formation. The plan was to make two runs, the first to create

a window in the tubing and or casing and the second to dress or ream the window. - Drill the build and tangent sections: This openhole operation was planned with two drilling BHAs: The first was designed

to drill the build section to the landing point with bent housing. The second was designed to drill the tangent section with reduced-angle bent housing to planned final depth.

- Completionand well reinstatement: Openhole logging was performed to determine the gas/oil contact (GOC) and placement for the swellable packer; an additional loggingrun was needed to determine reservoir saturation, and an additional hole-conditioning run was made with the drilling BHA to prepare the openhole for the liner. The plan was to make up predrilled liner fora predetermined depth withswellable packers for isolation, run it to total depth, and then release it in the openhole. Drilling mud was to be displaced with diesel and slickline would be used to open the gas lift mandrels prior to production.

Trial Run for Actual Performance During planning and preparing for this CTD project offshore Malaysia, it was deemed necessary to perform a mock test involving all service providers. The setup is shown in Fig. 3. - The dedicated area for the platform was simulated in the yard. Equipment was spotted as if it were on the platform with

regards to escape routes because personnel become familiar with the equipment positions. Specific needs were addressed at early stage, including cable lengths, lengths of hoses and extensions, and the direction the container doors open. The main test performed was the interface of all related personnel or teams for different stages: milling the window, drilling the build section, openhole drilling, and completion running.

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Fig 3: Pilot project yard setup for mock test

- Drilling program and specific procedures were developed, internally and peer reviewed before approval bytechnical experts

- Heavy lifting simulations were performed in the yard. All certifications were prepared, filed and shared with Operator HSE department. Lifting plans were made for mobilization (boat layout and platform layout). The objective was to optimize the lifting sequences, hazards exposure and extended platform shut down time for heavy lifting as per Operator safety standards.

- Heavy lift also simulated offshore to ensure the crane can be operated within the specified weight, area and reach - Structural Engineer was involved to ensure actual layout is in conformity with the facilities load distribution model. - The CTD team developed a quality hazard assessment and risk control to prevent and mitigate service quality issues. - CTD team developed the bridging document to comply with both Operator and Service Company standards.

Project Execution Pre-CTDcampaign

The main challenge was the time frame allocated to perform the whole pre-CTD campaign simultaneously with the ongoing preparation of the CTD campaign. The last stepof the pre-CTDcampaign on the second platform were handovertoCTD team to execute the as part of CTD campaign. Even though pumping cement through wired coiled tubing pipe is not a common practice, however during this pilot project, after taking into consideration of HSE risk of swapping reels, and major heavy lifting operation which impact on the production, this option was planned well in advanced as a contingency, in case the need arise and in actual give an advantage of 16% time savings of the operating time.

CTD Campaign

- A CTD project requires a working force of about 50 people who must be accounted in the platform personnel on board

(POB) as additional personnel. The pre-CTD phase, performed by a conventional CT package, was also managed indirectly by the CTD team. It was foreseen as important that the drilling requirement s to be delivered from the Pre CTD should be monitored by CTD team.Based on case histories and lessons learned from previous CTD projects it is crucial for the CTD team to build a standard requirement to be achieved during pre-CTD campaign.

- Mobilization and rig up:

The complexity of the lifting sequences was different from the first to the second platform. Taking into account the crane position and capacity, the CTD team planned for a smooth transition between demobilization and mobilization from the first to the second platform. The optimization includes:

o Boat-loading sequence was based on platform layout: lifting sequences in the platform will be from the farthest equipment to the closest.

o Platform loading sequences were based on the layout approved by structure engineers and on crane limitation and job steps. Chemicals take up a big space on the platform, so they were managed in a timely manner: Only

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necessary chemicals were kept on board (cement and cement additives for two plugs, and lost circulation material). The remaining chemicals were sent to a nearby platform; they were not kept on supply boats because of the continuous movement of these assets.

o The second platform had less space than the first one; however, based on the layout design from the first platform, most of the correction factors were adjusted. Crane limitation in reach for the second platform was less than for the first one, which induced the need for intermediate lifts and intermediate equipment to skid heavy lifts to the final position.

Despite all these challenges, performance indicators were showing an ascendant learning curve. - Reduce allowable space for rig up: 20% less usable space on the second platform, made the rig up tighter with respect

toHSE requirement. - Rig-up and spud time: 30% of the rig-up and spud time was saved byuse of an additional boat.The first boat was

loaded during demobilization as the last boat was offloaded during rig-up in the second platform Execution phase The execution phase of any through tubing CTD well can be divided into three distinct phases: Window milling, Drilling, and Completion. Below are the highlights of the various optimization initiatives that contribute to the significant improvement in the learning curves for all three (3) phases: Window Milling:This is the first operation of the CTD package. This phase is timed from the first milling BHA passes the Christmas tree until the last milling BHA returns to surface. Window milling operation evolution shows an improvement in execution time compared to plan for most of the wells. This improvement was mainly due to the lessons learnt from the second well in sequence, where the milling BHA was unable to create window for dual casing exits. This triggers an increased focus on the details of the milling operation for the dual casing exit specifically. Gathering the overall experience for single and dual casing exit operation, a thorough risk assessment was done at each step to ensure all operational risks are covered. All the improvement initiatives and options were covered in the detailed drilling program for each well. This drilling program was peer reviewed rigorously within the technical and operational communities involved in the project. It was discussed in the pre-spud meeting with all relevant parties and furthermore, a dedicated pre-operations review done few days before the execution where lessons learnt and best practices from the previous window milling operations highlighted. Some of the lesson learned from window milling phase are:

- Ensure correct placement of Whipstock with the use of multi finger caliper and LIB. If whipstock is found to be off-centered, run backup whipstock on top of existing, hence to ensure enough room for kick off during planning stage.

- Time mill is very effective window milling technique for CTD, this was enhanced with 100psi maximum differential pressure across the bit

- Use of real time differential pressure from the BHA during window milling, this significantly improve the milling time milling efficiency (as low as 25psi increment)

- The selection of diamond speed mill and string reamer was perfect fit for window milling with Coiled Tubing, out of 4 casing exits (2 of them were dual exits), none of them were under gauge more than 1/16”. Also, the window profile was smooth, no difficulties whatsoever with CTD BHA, logging or completion (including swell-able packers)

- It is proven that for dual casing exit, it has to be milled in 2 runs, with straight motor for milling thru the tubing, and swap to bent motor to mill the casing. This will ensure that the bent motor will not tracking down the annulus between tubing and casing.

- To mill the pilot hole for setting whipstock, it was proven that the diamond speed mill and string reamer made a very smooth profile, this was confirmed with multi finger caliper run

Overall, the window milling time was cut by approximately 75% (from 4.48 days to 1.13 days) from the first to last well of the campaign.

Drilling: The figure 4 shows how the Performance Indicators has improved on individual well basis, showing the impact of understanding the local drilling environment, requirement and practices. Well#1 performance was severely hindered by the lack of understanding of the impact of shaly sand formations against the capability of CTD technology. This resulted in a number of unplanned operations related to mitigating stuck pipe incidents. Immediate measures were taken to build on the lessons learnt. These could be summarized as:

- Adopting a synthetic based drilling fluid to insure maximum inhibition within the environmental considerations is achieved.

- Introducing more conservative drilling practices by increasing the frequency of wiper trip sections drilled at the beginning of the drilling sections and building confidence as drilling progressed deeper.

- Changed wiper trip philosophy to be based on hole angle (up to 30deg. Inclination) rather than wiper trip to shoe. This is a hole cleaning practice adopted from conventional drilling in highly deviated / extended reach wells where above 30deg. inclination cutting beds tend to accumulate on the low side of the hole and need to be mechanically removed.

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- Handling weight transfer issues by supporting the drilling momentum gained during the first lateral drilling penetrations. By keeping the ROP at a higher values, around 50 m/hr, weight transfer issues can be avoided or delayed to the last few feet as per planned. This cannot marginalize the positive effect of straightening the pipe from time to time in the lateral section to reset the compression ability of the coiled tubing pipe. In addition to these mechanical effects, rheology of the drilling fluids was monitored closely to help achieving good drilling performances. Circulating the mud through centrifuge helped in reducing the low gravity solids, which can reduce circulating pressure at the same pumping rate and help improves the carrying capacity of the mud.

- Optimized well trajectory and drilling practices in drilling potential weak zones (i.e. depleted reservoir, inter-bedded shale, etc.).

- Measure cuttings volume compare to theoretical hole volume for indication of hole cleaning effectiveness - Conservative hole cleaning approach – wipertrip to window every 20 m drilled. After 100m drilled, tripped to 30deg

inclination. Build confidence according to well condition. - During planning, the HiVis and LoVis sweep pills were planned to help hole cleaning. On the execution, it was

noticed that the wiper trips were adequate to clean the hole and these sweep pills were actually changed the mud properties over time in this small volume mud application, thus this sweep pills were ceased from the hole cleaning practices

- Uniform hole geometry (3 !” OD – 2.992” ID tubing with 2.7” x 3” openhole) from surface to TD. - Differential sticking issue was overcome by the following;

o Maintain drilling at higher ROP (30-50m/hr) o Keep pipe moving at all times. o Reduce ECD as low as possible without compromising hole stability.

The results of these improvement measures were clear when drilling well#2 where the DDPTF was reduced by approximately 65%. A further improvement introduced afterwards was related to the drilling practices adopted to minimize the differential sticking issues while drilling. As the operation continues, with proper monitoring of the fluid properties and good drilling practice, confidence level on the operation was build and improve gradually according to the well condition. The frequency and length of wiper trip section was reduced and the frequency of differential stuck event was also reduced significantly. This results in the betterment of drilling duration and the drilling practice was established suited for the field.

Completion: Before completion phase starts the wells had to be logged to determine the Gas Oil Contact (GOC) and a conditioning trip was performed to ensure the well is ready for completion. The completion string consists of 2-3/8” pre-drilled liner, with swell-able packers to isolate the gas and was run at the end of the coil tubing string to bottom. Several challenges was faced to ran in the completion string down to depth for the second and third well, mainly due to high overbalanced, higher friction factor and deviation from original well trajectory. However, between third and fourth well, with the TD is almost similar, there is an improvement in terms of percentage of liner coverage in open hole and the timing associated with the operation. This is due to the improvement in the overall completion fluid design i.e reducing static mud weight during running the completion and reducesswell-able packer assembly length, which contributes to the success. The flexibility inherent to this completion string design enabled making changes from well to well to capitalize on the lessons learnt to ensure the completion is run safely to bottom. The main change on the swell-able packer was the adjustment of the seal length to the minimum accepted length to form an effective seal while reducing the risk of swell-able packer stuck while running in hole with tight tolerance clearance in the original design.

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Fig 4: Performance Indicators for Execution Phase

Overall Project Highlights - This was the first CTD and completion operation through 3!-in. tubing offshore Malaysia.[This implies there may have

been other operations using different size tubing] - 0 lost-time incidents over 160 days: no accident or incident. - Economic recovery of bypassed reserves, which is not always possible with conventional sidetrack technology. - Successful milling oftwo exits through casing usingtwo BHAs (one with bent housing and one with straight housing). [are

there two exits, or one exit through two casing sizes? If the latter, dual-casing exit is correct. If the former, two exits is correct]

- Set 2.625-in. mono-bore whipstock inside cement, and milled through it. - Well trajectory with maximum deviation of 61°/30m. - Drilled 927m of horizontal open hole. - Instantaneous ROP of 50m/h (maximum). - Established best practices for holecleaning and drilling. - Proved suitability of synthetic-based mud as drilling fluid in reservoir section: minimum formation damage and wellbore

stability Conclusions • Using CTD for reentry sidetracking in offshore environment isa feasible alternative to the conventional rotary drilling to

recover bypassed reserves. • A multi well campaign is a must to capitalize on best practices, and lessons learned; and improve the performance through

drilling optimization initiatives • A systematical approach is required to ensure that the project does not deviate from a normal CTD operating envelope.

This is the key to a successful CTD campaign • Peer review with respective subject matter experts during planning and execution is the key factor to capture and address

concerns and suggestion for optimum project deliverables • The presence of consistent project team in offshore and office, regular communication and real-time data to onshore from

all parties are very important for continuous improvement and intervention of operation • A consistent learning and build confidence curve was elaborated during the execution phase based on the mentioned

lessons learned from well to well as shown in Fig

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Fig 5: Well Objectives Trending

Acknowledgements The authors thank PETRONAS CarigaliSdnBhd and Schlumberger management for their support and the approval to publish the paper.

References

1. ICoTA Publication Introduction to Coiled Tubing, History, Applications, and Benefits 2. DeWitt, Ron, “Technical Feasibility Assessment for Coiled Tubing Drilling” 3. A.A. Abdul Rahman, SPE; , N.E. Hamzah, SPE; N. Ahmad Fauzi; N. Safiin, SPE; M.Z. Khalid, SPE; N. Syaifullah,

SPE; PETRONAS CarigaliSdn. Bhd; J.R. Jenie, SPE; H.E. Hariry, SPE; Schlumberger, “Case History: Pilot Project with Coiled Tubing Drilling in Offshore South China Sea”, SPE/ICoTA 154371

4. A. A. Abdul Rahman, SPE; N. Ahmad Fauzi; N. E Hamzah, SPE; PETRONAS CarigaliSdn, Bhd; and Y. Chaari, SPE; I. Sorman, SPE; J. R. Jenie, SPE; Z. Marsaleh, SPE; D. MacDonald, SPE; Schlumberger, “Successful Cementing Through Coiled Tubing E-Line: An Economical Solution for Coiled Tubing Drilling Applications”, SPE/ICoTA 154234