Relative contribution of wettability Alteration and interfacial tension reduction in EOR: A critical review

Interfacial tension (IFT) reduction and wettability alteration (WA) are important enhanced oil recovery (EOR) mechanisms that help displace residual oil from the reservoir. Many studies have been done to investigate the effect of IFT reduction and WA on EOR processes. Most of the studies suggested a combination of IFT reduction and WA from oil-wet to water-wet as the principal mechanism for increased oil recovery. However, some studies hold different opinions regarding the optimal IFT and wettability modification. This work discussed the relative contribution of IFT reduction and WA for different residual oil categories and in different types of reservoirs. In this review, the residual oil is divided into five categories depending on its locations and forms: oil film, dead-end oil, pore throat oil, residual oil clusters, and trapped oil droplets. The factors affecting IFT reduction and WA on residual oil recovery separately or simultaneously are reviewed. It was noted that IFT reduction alone increases residual oil recovery in all wettability cases. However, the effect of WA differs due to different initial wetting state. This review will help in the best possible designing of the chemical EOR (cEOR) method by considering the effect of IFT reduction and WA in line with the effect of the relative amount of each residual oil category, the magnitude of the capillary force, the aspect ratio, and gravity and viscous forces.