Optimization and Modeling of Contact Angle via Response Surface Methodology in Wettability Alteration Process of Carbonate Rocks by Smart Water

One of the recently developed methods of enhanced oil recovery in carbonate reservoir is smart water flooding. Smart water can alter the wetting state of carbonate rocks from oil-wet to water-wet and increase oil production. In this study, we have investigated the effect of smart water composition on the carbonate rock wettability at different aging temperatures and pH’s through measuring the contact angle. The response surface methodology was utilized for the design of experiments. The results show that Mg+2, SO4-2, and K+ ions have important roles in wettability alteration due to interaction with carboxylic acids adsorbed on the rock surface. Not only Mg+2 and SO4-2 ions but also, inactive ions such as K+ influenced the wetting state of carbonate rock. Furthermore, an increase in temperature could cause more water wetting state and more activity of ions in solution. In addition, increasing pH could decrease the contact angle because of reduction in positive surface charge of carbonate rock surface. However, when pH was close to 8, the contact angle was raised probably due to the precipitation of Mg+2 ion.