Ion-induced oil–water wettability alteration of rock surfaces. Part II: Base interactions between oil and solid

Following the first part of this study, herein, we focus on the oil-wet rock surfaces formed by the adsorption of polar molecules via base interactions. The effects of ions on the oil–water wettability of quartz surfaces and the mechanism behind the phenomenon are revealed through contact angle measurements and surface characterization. The results indicate that the ions can greatly alter the wettability of the surface to become more water-wet only when the salt solutions are alkaline, with a maximum decrease of approximately 20° in the water contact angle. NaCl and KCl solutions are more effective than CaCl 2 and Na 2 SO 4 solutions. In alkaline solutions, the hydroxyl ions can deprotonate the octadecylamine molecules to weaken their interactions with the surfaces, such that the cations can displace the adsorbed octadecylamine and lead to large desorption from the surfaces. Finally, a quantitative model is established to describe the ion-induced wettability alteration.