Enhanced Oil Recovery Through Synergy of the Interfacial Mechanisms by Low Salinity Water Alternating Carbon Dioxide Injection

During this study, a comprehensive investigation of low salinity water alternating CO2 injection was performed for enhanced oil recovery in oil-wet carbonate reservoirs. A synergy of interfacial mechanisms such as IFT, wettability alteration, CO2 solubility, oil swelling, water shielding effect, and rock dissolution was considered in two and three-phase systems. Results showed that the monovalent ions, such as NaCl or KCl, inhibit the dissolution of carbon dioxide in brine in excess of divalent salt solutions, e.g. CaCl2 or MgCl2 due to the salting-out effect. In addition, more water shielding effect was observed in low salinity formation water than it in low salinity seawater. The significant change in the reservoir wettability of oil/brine/CO2 system compared to oil/brine referred to the CO2 solubility in brine which could cause stronger carbonated water in the reservoir. Consequently, the low salinity alternating CO2 injection overpowers the late-production problem that occurred commonly in conventional WAG injection.