Managing Well Performance Under Reservoir Uncertainty: Case Study of a Niger Delta Well

Abstract

Managing well performance under reservoir uncertainty requires robust definition of the operating limits of the well. It also requires flexibility for reacting to observed performance trends and adjusting the well operating envelope to guarantee safe operations and stable production. BAJE-8 experienced anomaly in production performance occasioned by exposure of part of the drain hole to a gas pocket near the gas cap. The well definition carried uncertainty in fluid contact and there was also inability to map intra-reservoir faults and shales around the proposed landing depth of the drain hole. Uncertainty in the size of the gas pocket also led to the inability to accurately predict the timing of the blowdown. Prudent reservoir management enabled by proactive well monitoring and surveillance led to timely review and modification of operating conditions of the well when abnormally high GOR was observed from the well. The strategy was to blowdown the gas cap while monitoring changes in the well parameters with expectation that parameters would normalize once the gas pocket is blown down. The GOR and FTHP showed a peak in performance and steadily declined within the 6-month period of blow down. The blowdown pushed the well performance parameters towards the previously predicted ranges prompting modification of the operating envelope. This rollercoaster well performance occasioned by subsurface uncertainty lasted for some 6 months and was successfully managed. The well performance now aligns with predictions and the well has sustained production in the last 18 months.