Concerns about global warming have urged the researchers to carry out various carbon capture utilization and storage attempts, among which low salinity carbonated water (LSCW) injection have attract much attention recently. Carbonated water and low salinity water both affect the wettability of crude oil on rock surface, which is crucial to ultimate oil recovery. However, it is still unclear how the wettability will change when combining low salinity water and carbonated water together. Accordingly, to assess and quantify the degree of possible wettability alteration initiated by LSCW, a series of contact angle experiment using the axisymmetric drop shape analysis (ADSA) technique for the captive bubble case under real reservoir pressure (16.0 MPa) and temperature (80℃) is conducted. The effect of brine salinity, CO2 dissolution level and aging time is also well considered for the crude oil-brine-reservoir rock system. Based on analysis of oil adhesion on rocks and rock surface dissolution by LSCW, geochemical modeling is conducted to investigate the mechanism of wettability alteration by LSCW. Results indicate that both brine salinity and CO2 dissolution level have significant effect on the wettability. A reduction in contact angle by carbonated water is observed as compared with formation brine. A decrease in the salinity of carbonated water further enhanced the water wetness of the reservoir rock. Surface complexation modelling results show that the interaction of LSCW with kaolinite dominated sandstone surface reduces the zeta potential of the rock surface as compared with formation brine and carbonated water alone. Meanwhile, an expansion of electric double layer from about 0.373 nm to 2.056 nm occurs. The cation exchange phenomenon during low salinity water injection is also triggered by LSCW. We believe these changes are the dominant mechanisms that make the rock submerged in LSCW become more water wet. Such wettability alteration will favorably affect oil recovery and CO2 storage when LSCW is injected into an oil reservoir at high pressures. This work may offer an experimental and theoretical basis to water-chemistry design for the implementation of pilot projects of LSCW flooding in low permeability reservoirs in Ordos Basin.
