Factors and Mechanisms Governing Wettability Alteration by Chemically Tuned Waterflooding: A Review

Enhanced oil recovery (EOR) techniques are aimed at improving the recovery efficiency of mature oil fields in secondary and tertiary recovery modes. In particular, chemically tuned waterflooding (CTWF) has been a rising EOR technique toward improving oil recovery from rocks that are difficult to produce due to their initial wetting state, e.g., oil-wet and intermediate-wet. With an increasing oil-wetting affinity of a reservoir rock, extraction of oil becomes more challenging. As such, wettability alteration has been identified as the primary mechanism for oil recovery from oil-wet and intermediate-wet rock types. Recently, researchers have attempted to categorize the factors and mechanisms governing wettability alteration by CTWF. Multiple studies have identified the importance of brine salinity and ion composition on promoting wettability alteration to a more favorable water-wet state. Reservoir temperature, the surface charge of the rock, and the surface active components of crude oil are also reported to influence wettability alteration and therefore oil recovery from waterflooding. In this paper, we present an extensive literature review on the subject of wettability alteration, with an emphasis on experimental work conducted on carbonate and sandstone rocks, as they constitute the majority of the oil reserves in the world. The purpose of this review paper is to synthesize the current state of knowledge regarding the factors and mechanisms that govern wettability alteration by CTWF and, through this exercise, set the platform to pose new research questions.