Uncovering Smart Water Flooding Mechanisms in Carbonate Reservoir Rocks by Integrating the Impact of Zeta Potential on Wettability Alteration

Injection of smart water into reservoirs for recovery enhancements remains a low-cost and an environmentally safe method of enhanced oil recovery (EOR). However, a definitive explanation for the incremental recovery enhancement, or lack thereof, is far from established and the research, therefore, continues to be very active. This study investigates the effect of divalent ion-based modified brines on wettability alteration in carbonate reservoirs. The focus is on analyzing wettability alteration via integrating precise quantitative zeta potential measurements and contact angle analysis. Experiments were carried out on carbonate core-plug samples analyzing the impact of various brines, including formation brine, seawater, low salinity, and engineered smart water. Specific formulations were prepared using softened seawater with multiple dilution factors and optimized phosphate and hexametaphosphate concentrations. To establish the baseline wetting state, core-plug samples were aged with the respective light crude oil and formation brine from a giant Abu Dhabi carbonate oilfield. Wettability alteration confirmed by changes in contact angles was recorded over a span of 72-80 h with each of the tested brines. Zeta potential measurements were performed utilizing a reproducible approach on the same core-plug samples at all stages of the experiments. The integrated measurements presented important conclusions on the effect of ionically modified smart brines on wettability alteration.