This paper presents how cased-hole formation testing technology solves the mystery of fluids distribution in a reservoir in a South China Sea well with very challenging operational conditions. Two wireline cased-hole formation testers were deployed together on more than 7000 m of drilpipe, which would be one of the world's longest such operations in a highly deviated well. The significant oil column that was identified results in a completely new picture of the field.The L#4 through L#8 formations of the Wenchang Group in A-fieldwere originally believed to be gas pay. But the big question whether this belief was correct was suddenly raised when oil was identified in a deeper zone right beneath L#8 by a mini-drillstem test (DST) conducted in an appraisal and development well looking for gas. Because the L#4-L#8 formations were already cased, a cased hole formation tester was identified as the best approach to characterize the vertical fluid distribution across the column and acquire pressure measurements and PVT samples from each zone. But the operational conditions are extremely tough: more than 7000 m of pipe-assisted operation required in a highly deviated well, zero tool failure tolerance due to the time-consuming and costly long pipe-conveyance operation offshore, and thermal expansion of this long drillpipe in a nonhomogeneously distributed high-temperature profile along the wellbore could potentially jeopardize the formation tester operation.Careful planning, smooth operation, and real-time technical support ensured flawless execution of the cased-hole formation testing. Oil instead of gas was identified from three sands to make a big oil column that exceeded everyone's expectations. Well testing showed #,#00 bbl/day of oil production with a restricted choke. More significantly, this breakthrough discovery has opened a brand new exploration and development area and has a significant impact on field development planning. This paper gives a detailed description of how this great success was achieved and a summary of technical findings from petrophysics and reservoir engineering points of view. Distinguishing features of the oil properties have been observed, which has triggered a deeper investigation of the regional petroleum system, PVT behaviors, and production and development optimization. The preliminary results of these investigations are also discussed.
The horizontal wells side-track campaign at CACT’s H fields in South China Sea has been very successful and challenging over the last two years. Horizontal wells are well-recognized in developing thin-oil column within multi-stacked reservoir by exposing wellbore to maximum reservoir contact and drainage area. The lateral targets and remaining oil reserves are in attic thin oil columns in clean sands and shaly sands. Since the oil column is thin at the top of a clean sandstone reservoir with strong bottom water drive, early water break through can occur even when the lateral is well placed on the top of the reservoir. To further optimize the reserves recovery, horizontal trajectories are placed near the top of the reservoir, and the well is completed with stand-alone screen combines with downhole inflow control devices (ICD’s). This combination provides the horizontal well optimum completion for draining and further prolongs the life of the well. The application of the field-adjustable nozzles based on real-time Logging-while-Drilling (LWD) data updates into ICD’s predrilled model, together with the precise well placement have enabled horizontal wells to be economically developed in a thin oil-bearing layer. In this paper, some of the technical assessment and collaboration workflow between the multi disciplinary team of technology users and service providers, enrooting to the successful implementation of the first nozzle-type ICD’s installation and Distance-to-Boundary Well Placement technology in China will be highlighted. The success of the first ICD’s well completions installation was proven with better Productivity Index (PI) based on initial well performance. The first ICD’s well produced ~100% oil for almost two months since early Mar 2009. Meanwhile, a second ICD’s well with thinner net oil pay produced 100% oil for 20 days clearly showed the benefit of ICD later when water break through and increased to 85%. The mentioned integrated Nozzle-ICD’s design with precise Distance-To-Boundary Well Placement solution have shifted the conventional application of ICD’s, which is hardware-orientated, from being dictated one-way by hardware supplier, towards a holistic reservoir-centric design. It has become an operation that keeps all-party informed and always in communication. The "real-time" add-value of LWD and well placement data in updating the predrilled ICD’s well model has benefitted horizontal wells inflow control design. This integrated and reservoir-centric solution has optimized horizontal well application successfully in one well, but facing some reservoir and structural challenges in another well; which has provided valuable lesson-learned for future drilling.
The Huizhou (HZ) 25-4 oil field, in the Pearl River Mouth basin of the South China Sea, has multiple oil-bearing zones. To economically exploit this discovery, it was decided to use the already existing HZ 19-2 platform. This platform was located 6 km southwest of the target, which meant drilling extended reach wells to the target. The small drilling package on the platform, the need for extended reach drilling (ERD), and the stress directions contributed to the complexity of the drilling. To accommodate the stresses and the target, the well trajectories require more than 90° azimuth change toward the end. To reach the target, the well path must cross a fault and cut through geologically unstable formations. To optimally drain the thin oil- bearing sands, the well needs to be placed horizontally in the target, making these complex ERD wells. The paper presents the integrated approach to optimization between the operator and the contractor to drill these challenging wells. The paper details the challenges of planning, executing, and refining the process of drilling consecutively more complex ERD wells, each with a progressively higher ERD ratio. The integrated approach involves various teams from engineering, subsurface, and operations support working closely to efficiently execute these complex wells. In addition, the paper examines the performance of new emerging technologies such as the continuous circulating system to address the wellbore instability caused by changes in equivalent circulating density (ECD) and the use of lightweight aluminum drillpipe to minimize torque, drag, and side forces. To minimize true vertical depth (TVD) uncertainty, a high-accuracy survey program combined with logging while drilling (LWD) were used to optimally land and place the well horizontally while minimizing tortuosity.
An operator in offshore South China planned to develop a new oil field comprising multiple thin oil-bearing zones. It was decided to develop the field by upgrading an existing drilling rig on a platform rig 6 km away to drill extended reach horizontal wells. The objective was to place long lateral drains in a thin-pay reservoir. However, the foreseen risk of high drilling torque against the backdrop of the drilling rig that has maximum 42,000 ft-lbf drilling torque capacity limited this option. In addition, subsurface challenges constrained the ability to access the target reservoir optimally for production and reserve recovery optimization.The latest fit for purpose logging-while-drilling applications were used to overcome the drilling challenges-limited rig capacity and subsurface challenges-in these extended reach horizontal wells and to optimize ultimate recovery and the economics of each additional well drilled. The efforts were performed in real time while drilling and aimed to place the well optimally within the thin pay zone by delineating and mapping the top and bottom pay zone boundaries simultaneously. With this ability, the lateral could be placed accurately without making unnecessary trajectory adjustment that can result in additional drilling torque.Two wells were completed successfully. Application of the technology resulted in significantly higher production compared to the set target. The reserve recovery was optimized by placing the well 0.5 m below the top. The drilling torque was minimized, thus increasing the ability to drill farther and capture additional reserves. Significant savings in total drilling cost were attained by ensuring smooth drilling operations free from unnecessary adjustment and sidetracks. A similar approach could address the challenges in other, similar complex and hard to reach reservoirs targeted in exploration and development activities in offshore operations.
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