Improving the Performance of Smart Waterflooding Through Surfactant-Assisted Process for a Carbonate Oil Reservoir

Abstract Enhanced oil recovery (EOR) techniques utilizing low-salinity water (LSW) are advancing owing to their favorable technical and economic viability. LSW flooding entails the injection of a modified-composition brine into oil reservoirs with a lower concentration of the potential determining ions (PDIs), specifically Ca2+, Mg2+, and SO42− ions compared to high-salinity connate water or injected seawater. Achieving an optimum concentration of the PDIs in the injected water provides further potential for enhancing oil recovery, which is denoted as smart waterflooding. Surfactants can be used to reinforce the smart waterflooding performance by reducing oil-water interfacial tension (IFT) and enhancing the rock surface wettability alteration. In this research, a comprehensive laboratory study is conducted to investigate the optimum surfactant-assisted smart water formulation for a carbonate rock. The initial step of this study involves the evaluation of fluid-fluid interactions using IFT via spinning drop tensiometer. The subsequent step involves studying the rock-fluid interactions using zeta potential experiments, wettability alteration in a specifically-designed HPHT imbibition cell and reservoir-condition HPHT coreflooding tests in composite cores. The results of IFT experiments showed more effective oil-water interactions of the smart brine when the sulfate concentration increased. The zeta potential experiments using the streaming potential method showed a clear trend of yielding more negative values for the smart water solutions when the surfactant was added to the system. The rock surface charge was found sensitive to the sulfate concentration and by adsorption of this ion, the positive charge of the rock surface is reduced. The presence of the surfactant in smart water system has improved the wettability alteration mechanism and reduced the contact angle by 12° which indicated the further alteration of wettability of the carbonate rock from oil-wet to water-wet. The outcomes of the coreflooding revealed an additional oil recovery of 7.72% achieved via the addition of the A-1 surfactant to smart waterflooding. The findings of this study are expected to enhance the understanding of the application of smart waterflooding in carbonate reservoirs and the future perspective of hybrid application of water-based EOR processes.