Customized Integrated Approach for Increasing Reservoir Understanding and Lowering Costs: Case Study, Deepwater Gulf of Mexico

Abstract

In the deepwater Gulf of Mexico (GOM), an operating company planned to drill and log a challenging wellbore in a mature field within the Upper Tertiary set of target sands. High levels of depletion as well as extremely tight pore pressure margins were anticipated. The operator and the service company's drilling and evaluation (D&E) integrated teams developed a highly collaborative environment from the early planning stage of the project, aligning people and processes and enabling applications. Regional knowledge from an archived geomechanical model was updated during collaborative planning sessions, enabling both parties to have a consistent understanding of the subsurface challenges to correctly drill and log each interval. Potential wellbore instability issues were mitigated using a proactive geomechanics analysis and hydraulics management from an integrated real-time operations center (iROC). Formation compressional slowness from a logging-while-drilling (LWD) sonic system was used, updating the geomechanical model for accurate real-time pore pressure and wellbore stability analysis. Additionally, the sonic system was used for top-of-cement (TOC) evaluation behind the intermediate casing to satisfy the Bureau of Safety and Environmental Enforcement (BSEE) requirements to differentiate fully bonded pipe from free pipe. Geosteering services from real-time log response correlations and at-bit geological predictions were used to correctly geostop for an intermediate casing point before pressure regression. An LWD formation pressure system provided pressure tests over various depth intervals, providing excellent fluid gradient determination for the primary target sand package. An LWD azimuthal density system delivered high-quality borehole images within the 16 ½-in. borehole section, providing dip information for geological correlation to seismic. Further, the azimuthal density image system resolved the interbedded shale/sand sequences, allowing dip analysis for geological model correlation within the reservoir. Challenges for this wellbore included shallow water hazards, wellbore instability, setting intermediate casing above the sand targets, and the depleted reservoir section. The deployment of specific technologies with associated unique applications discussed in detail within this paper led to superior well construction execution under time (8 days) and under budget (USD 4 million).