Experimental and theoretical investigation of the impact of crude-oil on the wettability behavior of calcite and silicate due to low salinity effect

Abstract

Wettability alteration is recognized as the main responsible mechanism for enhanced oil recovery during low salinity water flooding (LSWF) in both carbonates and sandstones. However, there is still a lack of understanding about the possible role of oil type on rock wettability alteration during LSWF. In the current study, contact angle (CA), interfacial tension (IFT), and zeta potentials for both oil/brine and rock/brine interfaces are measured for rock/brine/crude oil systems in a wide range of salinity of seawater. Two different crude oil samples and both calcite and silicate as good end-members of carbonate and sandstones are investigated. For oil A, the CA decreases with brine dilution; however, for oil B, the CA showed almost the opposite trend vs. salinity. The increased water-wetness of silicate compared to calcite surface was more highlighted in lower salinity. The results of zeta potentials showed that diluting seawater (SW) reduced the zeta potentials of rock/brine and oil/brine in all systems. The changes in zeta potential suggest that more dilution shall lead to more water-wetness, which is not in agreement with the CA behavior of two minerals in the case of crude oil B. Based on the augmented Young-Laplace equation, it was demonstrated that there is a good correlation between the IFT and the wettability, especially for calcite minerals. To shed light on the competition between the IFT and the EDL force, a comprehensive model was created to predict the CA results by coupling the surface complexation model (SCM), the DLVO theory, and the Young-Laplace equation. The coupled model successfully predicted the experimental contact angle for both crude oil and rock samples. Analyzing the disjoining pressure curves showed that due to the attractive EDL forces of calcite rocks, the oil/brine IFT solely controls the calcite wettability behavior with salinity. However, for silicate substrates, the high repulsive EDL forces are the main reason for the rock water-wetness at low salinity brines.