Visualization and Measurement of CO2 Flooding in Porous Media Using MRI

CO2 flooding is used extensively as a commercial process for enhanced oil recovery. In this study, the visualization of CO2 flooding in immiscible and miscible displacements in a high-pressure condition was studied using a 400 MHz MRI system. For CO2 immiscible displacement, the phenomenon of CO2 channelling or fingering was obviously due to the difference in fluid viscosities and densities. Thus, the sweep efficiency was small, and the final residual oil saturation was 37.2%. For CO2 miscible displacement, the results showed that pistonlike displacement occurred, and the phenomenon of the miscible regions and CO2 front was obvious. The viscous fingering and gravity override caused by the low viscosity and density of the gas were restrained effectively, and the velocity of the CO2 front was uniform. The sweep efficiency was high, and the final residual oil saturation was 13.5%, indicating that CO2 miscible displacement could recover more oil compared with CO2 immiscible displacement. Finally, the average velocity of the CO2 front was evaluated by analyzing the oil saturation profile. A special core analysis method was applied to in situ oil saturation data to directly evaluate the effect of viscosity, buoyancy, and capillary pressure on CO2 miscible displacement.