Effectiveness of Water Alternating Gas Injection (WAG) for Oil Recovery in the Niger Delta

Abstract

Many reservoirs on discovery have weak primary drive mechanisms an thus, are augmented with either water injection or gas injection for pressure maintenance to improve recovery. Unfortunately, using either water or gas injection has proven not to be sufficient to reduce the residual oil saturation, thus leaving behind substantial volume of unrecoverable hydrocarbons. Hence, one of the options that has been engineered to optimally reduce the residual oil saturation is the water-alternating gas injection which has been proven due to its capacity to increase both oil displacement and sweep efficiency. This research investigates the effectiveness of Water-Alternating-Gas injection in comparison with Waterflooding or Gas injection standalone methods for optimal oil recovery using a field in the Niger Delta as a case study. The Eclipse Simulator was used to simulate the Field oil efficiency (FOE), Field oil production total (FOPT) and the field water cut (FWCT) for WAG injection and compared with that of Waterflooding and Gas injection. From the results, WAG injection had an FOE (recovery factor of 34%), FOPT of 76.46 MMSTB and a FWCT of 26% while waterflooding alone has an FOE of 26.65%, FOPT of 57.62MMSTB and a FWCT of 47.58% respectively. The FOE, FOPT and FWCT of gas injected were estimated to be 21.35%, 47.89MMSTB, and 9.2% respectively. From the results, it could be inferred that WAG injection technique proved to be the most effective recovery technique in maximizing oil recovery, based on its recovery performance, having the highest recovery factor and a minimal water cut, compared to waterflooding and gas injection as standalone technique.