Active aquifer is one of the most common driving forces in a producing oil reservoir. But invasion of water from the aquifer into reservoir and raising the level of WOC cause a volume of oil to be remained in water-invaded zone, which is significant in most cases.

As a research, we studied on a field case with an active aquifer which has been encroached the oil zone till abandonment condition. As a remedy, after abandonment of the reservoir, we inject a miscible gas (CO2) to recover the remaining oil. It works like a one-cycle WAG injection, in which, water injection has been done naturally by aquifer and we continue the process by gas injection.

We investigated different gas injection scenarios to inspect the effect of this method on recovery of the oil remained in water invaded reservoir. This study shows that it is possible to increase the recovery factor considerably by choosing the right gas injection scenario. The feasibility study based on economical and surface facilities considerations would help us to select the best scenario.

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