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The BZ25-1S oil field, a marginal producer, is located in Bohai Bay, China. The depositional environment is predominantly a fluvial meandering river system deposited at different geological times that crisscross each other. Most of the primary oil was produced from directional wells and a few horizontal wells beginning in 2004. As of today, only 9.9% oil recovery and a 0.91% annual oil recovery factor with 70% water cut has been recorded. The relatively narrow river sand channel, highly disconnected sand bodies, and an irregular well pattern all contributed to the lower overall development effect. A multidisciplinary study focused on the following: Determine reservoir facies using sequence stratigraphy and depositional facies analysis coupled with well logs; Analyze channel distribution and channel geometry using high-resolution seismic interpretation; Rebuild a high-resolution geological model integrating all relevant information. An optimized horizontal well drilling program based on the results of this comprehensive study was launched in 2013. A total of 60 wells containing 52 horizontal wells were planned in this block to enhance oil recovery. The new planned horizontal wells were required to be optimally placed within the complex channel sand, which dramatically changes vertically and laterally across the field. Meanwhile, the trajectory needs to be placed as close as possible to the target roof to reduce or delay water production; however, there is a high risk for real-time horizontal well geosteering if the trajectory only relies on the rebuilding the geological model and using conventional logging-while-drilling (LWD) tools. A new real-time geosteering model was required and needed additional detailed information about the subsurface to reduce the geometry and formation property uncertainties. The innovative multilayer boundary detection technology was deployed to optimize the trajectory placement, avoiding drilling hazards and water zones, eliminating sidetracks, and minimize well construction costs and risk. The rotary steerable drilling system with near-bit measurement capability provides improved and accurate trajectory control in unconsolidated sands. Multiple well case studies will be presented in this paper. Several important results that had been observed during execution of this project will be highlighted, including: Optimize the redevelopment plan, including the target selection and well planning based on the comprehensive studyClearly identify the geometry of the complex channel sand and their interfaces, and update the information about the current fluid contactIdentify the optimum horizontal well placements in the sweet zones to enhance production performance on the first attempt while reducing drilling risks and significantly saving costs. The authors conclude that the complex channel sand reserve recovery program was enabled through detailed comprehensive geological study, well planning optimization, and horizontal well drilling with advanced LWD technologies. The best practices can also address other similar reservoir development programs. |
