Can Low Salinity Wastewater Act as Smartwater for Improved Oil Recovery in Carbonates?

Abstract This study comprises an experimental evaluation of different brine compositions for waterflooding applications in carbonate reservoirs. In particular, the low-salinity wastewater obtained from a gas plant is benchmarked against the conventional high-salinity injection water and SmartWater (diluted high-salinity injection water). Such a study is essential to promote wastewater reuse in waterflooding projects and achieve improved oil recovery. The detailed characterization of interfacial properties, as well as static oil recovery tests, were conducted using high-salinity injection water, SmartWater, and wastewater. To understand electrostatic interactions between interfaces, the zeta-potentials of oil/brine emulsions and calcite nanoparticle/brine suspensions were measured at 25°C and 70°C. Furthermore, oil-brine interfacial tension (IFT) and contact angle measurements were carried out at reservoir conditions (70°C and 2200 psi). The contact angles of captive oil bubbles were examined on both aged reservoir rock and crystalline calcite. Incremental hydrocarbon recovery was studied through two multi-stage Amott cell experiments at 70°C. The zeta-potential results indicate a generally negative effective charge at both the oil/brine and the calcite/brine interfaces. Additionally, an electric double layer (EDL) collapse with increasing salinity and temperature is observed for both interfaces. The reduction in zeta-potential magnitude is accompanied by a decrease in electrostatic repulsion between the two interfaces, promoting oil-wet behavior. This observation is confirmed by the contact angle results, which display a wettability transition from a water-wet state for wastewater and SmartWater to an oil-wet state for high-salinity injection water. The normalized incremental recovery from spontaneous imbibition also showed this wettability trend, with both wastewater and SmartWater resulting in an almost similar 50% normalized oil recovery increment after high salinity water imbibition. These results clearly demonstrate the ability of low-salinity wastewater to act as SmartWater in carbonates. This work has demonstrated, for the first time, the potential of wastewater as a "SmartWater" for improved oil recovery in carbonates. Consistent trends were obtained from zeta potentials, contact angles, and spontaneous imbibition results to confirm the wettability alteration capability of wastewater to achieve a higher oil recovery. These findings would eventually promote wastewater recycling/reuse and environmental sustainability in waterflooding projects.