Deepwater managed pressure drilling technology in block OML137 of Addax

Block OML137 of Addax is located at Nigeria offshore, with the water depth of 83 to 496 m. The formation pressure coefficient of the lower well section is 1.92 g/cm3, and the breaking pressure coefficient is 2.10 g/cm3, so the safe density window is relatively narrow, about 0.18 g/cm3. The target zone cannot be reached by conventional drilling. Managed Pressure Drilling (MPD) technology can resolve narrow MW window problem effectively. So it is necessary to conduct MPD adaptability evaluation and optimization to provide theoretical basis for scientifically selecting well, selecting section, optimizing MPD method, and parameter design. The adaptability evaluation method for MPD in Block OML137 was established, namely “Three-step Evaluation System”, including necessity, feasibility and economy evaluation. The method and system of pressure control were optimized, fine flow model of MPD was set up, and the principles of deepwater MPD parameter design and the design method of bottom hole constant pressure were put forward. The equipments were coordinated in accordance with the optimized pressure control system. The technique was applied to Well Asanga-2, which supplied a reference for future pressure control treatment.