Experimental Evaluation of Treated Produced Water for Improved Oil Recovery in Carbonates

Abstract This study comprises an experimental investigation and comparison of different brine compositions for waterflooding applications in carbonate reservoirs. In particular, a novel zero liquid discharge (ZLD) brine, which is obtained from produced water treatment and features no significant salinity, is benchmarked against conventional high salinity injection water. Such a study is essential to promote produced water reuse in waterflooding projects and achieve improved oil recovery. A detailed characterization of interfacial properties as well as static and dynamic oil recovery tests were conducted using high salinity injection and treated produced water. To understand electrostatic interactions between interfaces, 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 aged reservoir rock and crystalline calcite. Incremental hydrocarbon recovery was studied through a multi-stage Amott cell experiment and a high-pressure, high-temperature (HPHT) core flood 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 ZLD treated produced water to an oil-wet state for high-salinity injection water. The incremental recovery from spontaneous imbibition also showed this wettability trend. ZLD water resulted in an oil recovery increment equal to the recovery by high salinity water imbibition. Finally, the core flood revealed the full potential of ZLD treated water, yielding an incremental oil recovery of 4-5% after high salinity water injection in a carbonate core. This work has demonstrated, for the first time, the potential of treated produced water for improved oil recovery in carbonates. Consistent trends were obtained from zeta potentials, contact angles, spontaneous imbibition, and core floods to confirm the wettability alteration capability of treated produced water to achieve incremental oil recovery. These findings would eventually promote produced water recycling/reuse and environmental sustainability in waterflooding projects.