PETRONAS Carigali and Schlumberger IPM have formed an alliance to develop a field in offshore Malaysia. Due to space limitations, a platform extension was installed to accommodate three additional conductor sharing wellheads (CSW). Project challenges include limited CSW pass-through, well collision risk, highly unconsolidated formations in the angle building section, directional control and shallow gas zones. To avoid well-to-well collision caused by poor directional control, a pilot hole must be drilled under the conductor to provide good directional control in the unconsolidated sandstone. The pilot hole must also mitigate shallow gas risk. To achieve the reservoir hole size and accommodate dual gravel-pack completions, the pilot hole must be opened from 8–1/2" × 16" to allow subsequent hole section drilling. The project team had to design a BHA that could efficiently deliver the objectives with minimal rig time. To solve the challenges a new hole opening methodology would be required. The pre-drill analysis included studies in: BHA durability/dynamic stability to ensure good hole quality; hydraulics and fluid dynamics to deliver proper cooling and hole cleaning; optimized combination of hole opening technologies. To reduce reaming runs/bit trips, a dynamic modeling system was employed to quantitatively analyze the interaction of various downhole tools and optimize the BHA configuration/drilling parameters. The modeled dual eccentric PDC hole-opening BHA was run and successfully solved the challenges, mitigated risks and met the required drilling objectives for completing the six CSW wells. A post-drill simulation analysis was performed to analyze the dynamic downhole BHA behavior with the actual operating parameters. The authors will explain how the BHA was developed and successfully used in the field to solve the unconsolidated formation challenge. Survey method and challenges of drilling through the conductor sharing wellhead are also discussed.

A novel workflow methodology that covers the entire cycle of field development maximizes the production potential and can increase reserves in stacked reservoirs. The approach will potentially reduce associated costs, risks, and uncertainties, in spite of complex geological structures and drainage patterns. The new workflow encompasses planning from concept selection to preparation of well proposals during the implementation work. Scalable to any given size of hydrocarbon prospect and number of infill wells, the computational method incorporates cross-disciplinary software (geomodeling and seismic packages) as well as reservoir, production, completion, and drilling software. Linkage between the disciplines is close and conducted iteratively, operating in parallel instead of the common sequential and decoupled approach. The method has been successfully tested in a brown field with 165 stacked reservoirs. Reserves increased significantly compared to the offset field development plan (FDP), while water production was significantly reduced. The optimized drainage pattern for the whole field also revealed significant future workover potential in shallower reservoirs, maximizing contingency and lifetime value of infill wells. Introduction Stacked reservoirs are a common occurrence among subsurface hydrocarbon accumulations. In them, each wellbore penetrates many prospective reservoirs that can range, depending on the field size and number of reservoirs, from a few into the hundreds. Technical and reservoir management considerations usually make every wellbore capable of producing from only a limited completion interval. Hence, the main objective should be to optimize not only the areal drainage pattern but also the vertical scheme. This makes the process highly complex and iterative and thus represents a complex, multidimensional optimization problem. In the current standard industry practice, the full production potential of these reservoirs is often not realized because of poor integration among individual discipline software platforms, limitations in hardware and software, and a generally too serial workflow. Trajectories are typically derived by the drilling engineer to target individual single reservoirs, disregarding the opportunities existing in the entire stack. Stacked hydrocarbon reservoirs are characterized by a varying number of reservoirs with different properties and characteristics, includingAreal and vertical extent of the individual reservoirsHydrocarbon type and propertiesReservoir quality and drive mechanismOptimum production and reservoir management strategyOptimum well type (vertical, horizontal, multilateral) and completion requirements Fig. 1 illustrates the nature of such hydrocarbon accumulation by means of an offshore oil field, which spans vertically about 5,500 ft with more than 165 individual reservoirs. Existing wellbore trajectories are shown as lines; oil-bearing zones are green; gas-bearing zones, red; and parts of the encroaching aquifer and the connate water, blue.

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.