LAUSR

Abstract This investigation is conducted on one of the southern Iranian oil fields, which experiences a fault on its gas cap. Therefore, no traditional gas injection and normal water injection for pressure maintenance is suggested. The target is set to inject special compatible and proper type of chemicals in each single well to avoid the pressure increase for the risk of oil and gas spill. Two different sources of aqueous phases, namely formation brine and sea water were used to find the effects of different brine composition on the main mechanisms of releasing the trapped oil, interfacial tension (IFT) and wettability alteration. The obtained results reveal that both the ionic liquid (IL) based surfactants and new synthesized commercial surfactants are not only able to tolerate harsh conditions (250,000 ppm) of salinity but also have the ability to reduce the IFT more effectively (from 19 to 0.07 mN m− 1). As the salinity is increased, ionic liquid ([C12mim] [Cl]) showed lower critical micelle concentration (CMC) of about 50 ppm, which shows that the IL use for EOR is economically feasible. The contact angle measurements also indicate the possibility of activating wettability alteration mechanism. Consequently, the core flooding tests revealed more oil recovery efficiency of 8% and 22% based on original oil in place (OOIP) and residual oil in place, respectively for the solely IFT reduction cases. The oil recovery efficiency for the tertiary oil recovery process was increase up to 12% and 35%, based on OOIP and residual oil in place, respectively, which clearly clarifies the effectiveness of soaking to exploit the wettability alteration mechanism.