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Planning complex well designs for multilateral and extended reach wells presents substantial challenges for optimizing well construction, drilling risks, and economics. The subject well of this case study is located in a prolific onshore field in Abu Dhabi; the field has been producing for many years, giving rise to pore pressure uncertainties between different reservoir sublayers. The primary challenges are associated with reducing drilling time for the future development program while delivering optimized drilling performance and cost effective openhole side tracks with rotary steerable system (RSS) bottomhole assemblies (BHA), eliminating extra trips, and enabling accurate formation evaluation and precise well placement. Goals included optimizing drilling parameters in accordance with rig capabilities, addressing anti-collision concerns, optimizing mud weights to mitigate differential sticking, maximizing reservoir exposure in thin reservoir sublayers, and minimizing the surface footprint. Close collaboration between the operator and the directional drilling/logging-while-drilling (LWD)/geosteering service provider was a key component of developing a fit-for-purpose solution. This solution consists of a comprehensive feasibility study using historical field data, a detailed pre-planning process that includes well and BHA design; anti-collision; and optimizing sidetrack points, LWD configuration, and tool downloads for longevity. The well plan incorporated a trilateral design with optimized trajectories for minimizing dogleg severity (DLS) and borehole tortuosity in the horizontal laterals while cutting the poor porosity layers that separate the targeted four thin reservoir sublayers. The mother bore trajectory also included humps (building the inclination from 89° to 91°, then returning to 89° within 50 ft with 4° DLS) to facilitate openhole sidetracks without the need to pull out of the hole (POOH). The BHA included a RSS with azimuthal density, neutron porosity, gamma ray, and propagation resistivity tools. The alternative BHA included azimuthal deep resistivity and acoustic LWD sensors to meet complex drilling, geosteering, and petrophysical data gathering requirements. A formation tester while-drilling sensor was also included to provide accurate pore pressure measurements to optimize mud weight in real time. Continuous (24/7) real-time operation support provided drilling performance monitoring and analysis, and facilitated geosteering services. Three horizontal laterals of 5,000 ft each were successfully drilled with openhole sidetracks without POOH for the first time in the United Arab Emirates. Mud weights were optimized by reductions from 78 to 70 pcf, and 100% reservoir exposure was attained in all three laterals. Finally, significant improvement in production and cost savings, as compared to traditional single lateral designs, prompted a review of the future development drilling program. This paper presents a step change from traditional field development drilling techniques in terms of well construction. Similar well designs are currently being implemented to benchmark drilling, well placement, and petrophysical data gathering requirements for future development drilling to maximize asset value. |
