Implications of Long Core Experiments in Oil Recovery Enhancement During Carbon Dioxide-Water Alternating Gas Injection

In this paper, several long core-flooding experiments for simulating the CO2 Water-alternating-gas (WAG) injection were performed and the oil recovery factor under various crucial parameters such as injection pressure, slug size, and water cut was observed. During CO2-WAG injection, the general oil mobilization and recovery factors were further investigated under varying injection pressures and WAG injection timing (the water cut in the produced fluid reaching 0, 50, 75, and 98% after water flooding). The MMP slim tube experimental results revealed that the Minimum-miscible-pressure (MMP) is about 32.43 MPa which means that gas can be miscible in the crude oil to reduce the viscosity and improve the displacement efficiency. Moreover, it was also observed that with the increase of water cut in the produced fluid (that is to conduct waterflooding longer and to perform CO2-WAG later), the ultimate recovery factor after CO2-WAG decreased. The oil recovery factor increased with the injection pressure and had a maximum value of 60.96% when the injection pressure is 34 MPa. A significant increase of the oil recovery factor was achieved when the injected CO2 could be miscible with the crude oil. Smaller slug sizes would be more efficient during the CO2-WAGinjection due to more opportunity for injected CO2 to be contacted, mixed, and dissolved with the residual oil, higher oil mobility ratio, and lower oil viscosity.