Simulation Study on IWAG Assisted by Low Salinity Water Injection for Light Oil Reservoirs

Water alternating gas (WAG) injection is a widely practiced Enhanced Oil Recovery (EOR) technique for light oil reservoirs. On the other hand, various researches have documented that using the Smart water concept can further enhance the oil recovery obtained from water-flooding. Although, there was extensive researches conducted on each of the WAG and the smart water techniques separately, yet there are a very few researches conducted on using the smart water concept as the injection water in WAG technique. Previous laboratory core flooding researches have shown that reducing the salinity of the injection water in miscible WAG process would decrease the ultimate oil recovery. The published literature attributed that to the fact that reducing the salinity of the injection water would increase the solubility of the injected gas in water and thus reducing the amount of available gas to be soluble in oil.
Reservoir simulation processes were utilized in order to study the effect of using the smart water as the injection water in IWAG technique for light oil reservoirs. A synthetic model with 7,500 grid cells was used to evaluate the performance of several injection scenarios involving low salinity water and WAG techniques under the conditions of light oil reservoir at the depth of -6,000 ft. with oil API of 45°. The thickness of the reservoir is 30 ft.
The simulated results showed that using low salinity water as the injection water in immiscible WAG process would increase the oil recovery by 3.5% of the original oil in place (OOIP) than when using conventional high salinity water for light oil reservoirs. The results obtained from the simulation processes do not contradict the laboratory experiments results because of two main reasons. The first reason is that the simulation operations were based on immiscible WAG processes while the core flooding experiments were based on miscible WAG processes, and the second one is due to the gravity effects. During core flooding operations, gravity effects are minimal, while it was taken in consideration during the simulation processes.
Another important discovery by the reservoir simulation operations is that using a slug of low salinity water followed by high salinity drive water has much higher recoveries than conventional high salinity water flooding, and that adjusting the slug size can obtain recoveries almost as high as continuous low salinity water injection