Simultaneous water and gas (SWAG) injection is one of the effective secondary/tertiary enhanced oil recovery methods which can boost the sweep efficiency of a CO2/EOR project dramatically. Moreover, geological storage of CO2 in depleted or mature oil reservoirs is considered as a long-term controlling method of CO2 emissions into the atmosphere. This paper applies a defined objective function to co-optimize oil production of SWAG injection process and its CO2 storage efficiency. A compositional simulation study was carried out to examine the effect of various CO2-water ratios in SWAG process in different miscibility conditions on sweep efficiency, ultimate oil production and the stored CO2 in the reservoir during the process. Simulation results show that oil recovery can be increased 13-36% OOIP in SWAG injection compared to water flooding and continuous CO2 injection while SWAG optimum gas fraction is a direct function of reservoir pressure. Moreover, CO2 storage capacity when CO2 is injected simultaneously with water is 30-70% of the injected CO2 and this value decreases by miscibility. However, in CGI both oil production and CO2 storage increase with miscibility. The simulation results also reveal that the CO2 storage efficiency of near miscible SWAG and CGI process are almost the same.


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