Evaluation of the use of Water Alternated Gas Injection for Enhanced Oil Recovery

Hydrocarbon production from underneath naturally fractured sandstone formations will reach a mature phase of production where natural pressure can no longer force fluids to the surface facilities, therefore, a cost-effective enhanced oil recovery (EOR) approach is required to recover the remaining oil. Water alternated gas(WAG) injection is a promising EOR method that utilize the combine advantage of water and gas injection to achieve better mobility control, improved sweep efficiency and overall recovery from the given reservoir. In this study, a miscible WAG to a core flood model using numerical simulation techniques (Eclipse Reservoir Simulator – Black Oil Model Option) was investigated. A case study reservoir X was produced for 15 years using three wells after initial forecast showed that natural depletion could not sustain production from the earliest time of production. With different simulation scenarios that represent specific case of WAG ratio, optimal WAG ratio using oil recovery factor was selected and used to perform   twelve (12) simulation runs to ascertain the influence of WAG cycle period on oil recovery factor. The most effective WAG cycle scenario was 90W-30G with oil recovery factor of 0.54684 (54.68 %) and cumulative production of 14.987MMSTB, while 30W-90G gives the lowest oil recovery factor and cumulative production of 0.47468 (47.47%) and 12.996MMSTB respectively. Hence, higher water cycling period is required for better oil recovery. Also, lower water to gas injection rates (WAG ratio) enhances the recovery of oil from the reservoir. Results reveals that despite predicted higher recovery factor, lower WAG ratio showed a potential of relatively poor pressure maintenance which can impact future recovery from the reservoir