On the CO2 storage potential of cyclic CO2 injection process for enhanced oil recovery

Abstract

In this study, the potential of cyclic CO2 injection process was examined for CO2 storage and enhanced oil recovery. For this purpose, a detailed phase behavior study on the light crude oil–CO2 and brine–CO2 systems was conducted. CO2 solubility in the oil and brine samples as well as oil swelling factor as a result of CO2 dissolution were experimentally measured. The equilibrium interfacial tension of the crude oil–CO2 system was also determined by applying the axisymmetric drop shape analysis (ADSA) technique for the pendant drop case. Furthermore, the minimum miscibility pressure (MMP) of CO2 with crude oil was calculated by means of vanishing interfacial tension (VIT) technique and found to be MMP=9.18MPa. Thereafter, series of cyclic CO2 injection tests were designed and carried out at constant temperature of T=30°C and various operating pressures in the range of Pop=5.38–10.34MPa to cover immiscible and miscible conditions. The results showed that 40–50% of the injected CO2 was stored in the porous medium mainly through residual and solubility trappings’ mechanisms. It was found that during immiscible injection condition (i.e., Pop<MMP), higher amount of CO2 can be stored in the porous medium at higher operating pressures. The results also revealed that optimum potential of CO2 storage is almost at operating pressures near the MMP, while beyond that pressure, the CO2 storage capacity was not substantially increased. From the enhanced oil recovery point of view, the oil recovery factor was significantly improved when operating pressure increased and reached its maximum value at miscible condition (i.e., Pop⩾MMP). During the immiscible injection scenario, mechanisms involved in oil production were mainly oil swelling and reduction of interfacial tension. However, the light component extraction was the major production mechanism contributing to the oil recovery during miscible injection process.