Improving Chemical Composition of Smart Water by Investigating Performance of Active Cations for Injection in Carbonate Reservoirs: A Mechanistic Study

Laboratory experiments have shown that smart water (low salinity water with electrolyte additive) can improve the carbonate reservoir wettability toward a favorable condition to enhance oil recovery. Several hypotheses have been introduced in previous studies to explain the underlying mechanisms, but there are still some contradictions among those mechanisms. In this research, throughout a comprehensive laboratory study, we investigated cationic surfactant to explore why the conventional method of reducing the salinity of injection solutions is not always effective. Then for the preparation of smart water, several conclusive remarks are introduced for more effective application in carbonate reservoirs. In our experimental study, first, the effect of change in electric charge was studied using zeta potential measurement. From the generated lab data, an equation was developed for the zeta potential at the calcite-brine and oil-brine interfaces. Next, the effect of cationic surfactant on wettability alteration was tested. It was observed that the required time to activate the wettability alteration was significantly reduced from around 63 days to approximately 40 days in the presence of cationic surfactant. In addition, we showed that the interfacial tension between oil and water is changed by both reducing the salinity and cationic surfactant additive. Furthermore, using Attenuated Total Reflectance (ATR), it was observed that the negatively functional groups of oil were adsorbed on the calcite surfaces confirming that the crude oil properties were essential parameters in this EOR method. Finally, we developed a geochemical model that shows calcite's solubility is not the only factor for the wettability alteration mechanism. (C) 2021 Elsevier B.V. All rights reserved.