Experimental investigation of synergistic effect of non-ionic surfactant and smart water injection methods for enhanced oil recovery from carbonate reservoirs

In the water-based EOR methods, surfactants and smart water injection methods usually are employed to reduce the water-oil interfacial tension and altered the rock wettability, respectively. The main objective of this study is to employ the combination effects of non-ionic Surfactants (including KEPS 80 and Behamid D) and Smart water Flooding to alter the wettability and interfacial tension (IFT) towards the most favorable conditions. Contact angle, spontaneous imbibition, capillary pressure (Pc), and relative permeability (kr) experiments were performed at various concentrations of the surfactants and ions using carbonate rock to identify the various mechanisms occurring in the Surfactant and Smart water (SSW) flooding process and also to determine the additional oil recovery. The optimum concentrations of surfactant and positive ions (Mg2+, Ca2+) were also obtained. In this regard, concentrations of the employed ions were optimized for altering the carbonate rock surface wettability toward the water-wet. The optimum surfactant concentrations obtained by Mohammadshahi et al. (2019) were also used, in this study. After obtaining the optimum concentrations, some promising aqueous solutions were designed for Amott cell, relative permeability, and capillary pressure experiments using the combination of surfactant and ions. Amott cell tests were implemented for comparing the ability of different aqueous solutions such as base water (Brine with 30,000 ppm NaCl), surfactant solution, smart water, and SSW solution in the oil recovery from the cores. Subsequently, relative permeability and capillary pressure experiments were performed. The results of contact angle experiments depicted that brine containing 24,000 ppm NaCl +6000 ppm Mg2+ yielded the lowest contact angle among the studied samples. In the spontaneous imbibition tests, the oil recovery was obtained to be 7.6% for the base water, 9.5% for the smart water (24,000 ppm NaCl + 6000 ppm Mg), 15.09% for the surfactant solution (1500 ppm KEPE in 30,000 NaCl), and 20.8% for the SSF water. The relative permeability and capillary pressure tests have demonstrated the change of residual oil saturation and wettability of rock while using the SSW method compared to other techniques (i.e. base water, surfactant injection, smart water flooding). Finally, the results indicated that the combination of smart water and surfactant injection could lead to a much higher recovery factor than each method alone.