Design Execution and Evaluation of Advanced Completions in Deepwater West Africa

Abstract

Abstract Deepwater wells in offshore West Africa traverse through a complicated faulted block with sand bodies ranging in 10s of meters of thickness. A horizontal or deviated configuration allows wells to intersect and produce from multiple sand formations at once. This also brings in complexity of segmentation along the wellbore with chances of either tapping into gas cap or potential gas build up in zones around the wellbore in time which could render the well uneconomical. The study provides insight into designing advanced well completions in offshore West Africa wells with Autonomous Inflow Control Devices (AICDs) under various challenging reservoir conditions that enable maximizing the producing life of the wells. Subsurface characterization and engineering models were used to predict well performance under various conditions creating the expectation envelope of possible scenarios in pre-drilled planning phase using a digital-twin model of the well. When the wells were drilled, real time data of wellbore geometry, sand interval lengths, permeability and fluid phase saturations were estimated which were used to revalidate, revise, and optimize the design of lower completions including placement of packers and AICDs. Further, compaction well operability limits were defined using the geomechanical analysis to provide guidance on the well start-up without formation collapse. Once the wells were turned on for production, the digital twin models were recalibrated, and drawdown was readjusted for optimizing production performance. The study presents two wells’ case studies with completely different production strategies – one with existing gas cap and other with potential gas cap build in time. The engineering approach allowed designing lower completion in both the wells and without which the wells would otherwise be dominant gas producers in their producing life (early or later) and become inoperable with gas handling constraints at surface. Efficient design maximized oil productivity and allowed reservoir fluid influx control for efficient reservoir maintenance. Production of gas was suppressed by over 600% and an equivalent increase in oil production was achieved with the optimized completion design. Integrated subsurface understanding, reservoir characterization, completion engineering and execution of advanced completions in the wells maximized the oil productivity and delay the gas influx into the well. The engineering workflow designed in the study has become the framework of decision making in designing lower completions for future wells with complex zonal segmentation of reservoir or potential gas/ water influx in time.