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.

The sustained and relatively high value of oil and natural gas has resulted in an unprecedented level of drilling activity and implementation of innovative methods to recover as much hydrocarbon as possible, and as quickly as possible. The resulting demand for conventional drilling rigs for programs has forced the rates high and the availability low, making use of the units difficult to justify for use in declining fields with less significant amounts of recoverable product. The by-passed reserves remaining accessible in these depleted fields exist in volumes worthy of pursuit, but must be done economically. In many fields, operators, either intentionally or unintentionally, bypass pay zones during initial development by focusing only on the best zones. Accessing bypassed thinly laminated formations can be economically attractive but poses several challenges, especially due to aged platforms and completion string in place, also offshore environment is adding its own challenges. Coiled Tubing Drilling (CTD) has yet to establish itself in an offshore environment. Numerous one-off projects have been tried, but commitment was never made to a number of wells to see through the learning curve and realize the potential of the application. Offshore South China Sea have a huge quantity of candidates on existing installations, installations that, due to water depths and sub sea conditions require large, expensive rigs to drill or re-enter wells. Technically the wells can be accessed with coiled tubing with drilling parameters seen regularly in other projects. The challenges for this pilot project will be equipment specification and set up, efficiently exiting the casing, and management of wellbore stability in open hole drilling and completion techniques. The main objective of this pilot project is to bring proven technology to offshore environment to access small bypassed reserves economically and provide an alternative to conventional drilling. The well candidates were selected with strict work scope to avoid going beyond the regular CTD application to ensure learning curve and lessons learned can be implemented throughout the project and achieve the objective. This paper will described the preparation, execution, achievement and lessons learned from this 4 wells pilot project in offshore South China Sea.

Peninsular Malaysia has a number of fields where reserves are not economical to be further exploited using conventional drilling methods. With the increase in oil prices over the last few decades, an operator decided to embark on a new drilling technique of using acoiled-tubing drilling (CTD) unit to successfully access a bypassed reservoir. One of the candidates chosen for the project was Well D in which the completion includes 3½-in. tubing in 7-in. production casing. The challenge in this well was to place the whipstock through the cased tubing before drilling operations could be performed because there was no through-tubing (3½-in.) whipstock design for 7-in. casing available on the market. The placement of the whipstock was crucial due to the existence of a shale zone uphole through which it was to be drilled thatwould createa borehole stability issue. The other reasons taken into considerations were to avoid dual-casing exit and the potential associated complications as well as to provide a uniform wellbore to create adequate annular velocity for cuttings transportation to the surface. The team proposed an atypical solution to assist whipstock setting by plugging the entire 7-in. production casing column until the end of tubingwith cement.Once the cement was hardened and tested, a directional drilling assembly with a 2.8-in. speed mill was used to mill a pilot hole through the cement plug, boring along the high side of the casing. Next, a caliper log was run on slickline to confirm hole diameter, and a whipstock wasthen runinto the pilot hole and set with it facing toward the casing. These operations were successfully performed by a rig-less CTD package.The milling assembly was run smoothly and the sidetrack window was effectively cut prior to drilling the target sand. The successful case study presented summarizes in detail the technique used to mill such a wellbore, the challenges presented, and considerations madein designing the job, which proved to becorrect and accurate on the first attempt.

Cementing through coiled tubing electric line (CT e-line) is not a common practice; this application is highly recommended in Coiled Tubing Drilling (CTD) applications using the existing CT e-line pipe to achieve a better time performance for sidetracking a well since using the CTD technique is mainly based on economical evaluation. Several considerations need to be taken into account while designing the job and performing the operation. The relatively high density and viscosity fluid can lead to bird nesting the cable due to high friction and excessive slack inside the pipe; it can also affect the integrity of the cable as well as the performance of the bottomhole assembly (BHA). The interface between cement and other fluids pumped through CT e-line pipe can be also affected. A review on a feasibility study of cementing through CT e-line that was performed in 2003 in Alaska highlights all the concerns, challenges, and potential issues that can be encountered during a cementing job through CT e-line, best practices, lessons learned, and way forward to implement this technique. This review is supported by two successful case histories performed in Malaysia CTD campaign applying this technique for different objectives: remedial cementing for casing and tubing sealing in a deviated well and remedial cement plug for window recovery. By implementing cementing through CT e-line, the effective job time was improved by avoiding swapping pipes in an offshore environment where the logistic, safety, and space accommodation is a huge challenge. The use of CTD as an economical sidetracking technology was reinforced by making the CT e-line pipe universally utilized in all the project steps, even for running and setting completion.

Agile activated circulation sub is presented, with design advantage of being able to open and close numerous times and there is no limitation to the number of tools run in the string. The tools now being field tested are designed to perform complete needed cycles in one trip, with the total number of cycles limited only by the battery life. The standalone tool system activated by sensing its environment (Flow, Pressure or RPM), working internal logics before being in a position to receive surface signal to operate in desired mode. The tool has application in any well where it operates the first position for partial bottom-hole-assembly (BHA) bypass increasing annular flow and second, full bypass, position for dumping lost-circulation-materials (LCM) or fast wellbore clean up, the final, downhole barrier isolate drill string above the tool from downhole pressure in well control situation. Restrictive BHA limits the flow rate and annular velocity required to clean the hole during drilling or displacement operations. BHA restrictions can also limit the size and concentration of LCM and wellbore strengthening material needed to seal troublesome zones. The tool helps driller reduce risks associated with hole cleaning by improving annular fluid velocity with the ability of running multiple tools in same BHA in hole cleaning mode. Each tool can be operated independent of all other tools, allowing driller to optimize hole cleaning hydraulics, as well, tools can be configured with suitable side port nozzle to achieve the desired pressure drop and flow split according to well program. The tool presents advantages over the industry's current system is that there are no restricting ball seats, flow chokes or ball catcher subs in the tool. This paper presents the design, engineering, testing, field trial results, application and function of this new circulation valve The novelty of the tool is in the ability provided for driller to overcome circulating challenges efficiently and effectively irrespective of tool depth or well profile in reasonable time using variation of RPM, or variation of flow rate. When circulation is not possible or when string is stuck, the tool can be operated to assist driller resume circulation using pump pressure without need for flow.