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.

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