Visualization of CO2 and oil immiscible and miscible flow processes in porous media using NMR micro-imaging

COflooding is considered not only one of the most effective enhanced oil recovery(EOR) methods,but also an important alternative for geological COstorage.In this paper,the visualization of COflooding was studied using a 400 MHz NMR micro-imaging system.For gaseous COimmiscible displacement,it was found that COchanneling or fingering occurred due to the difference of fluid viscosity and density.Thus,the sweep efficiency was small and the final residual oil saturation was 53.1%.For supercritical COmiscible displacement,the results showed that piston-like displacement occurred,viscous fingering and the gravity override caused by the low viscosity and density of the gas was effectively restrained,and the velocity of COfront was uniform.The sweep efficiency was so high that the final residual oil saturation was 33.9%,which indicated COmiscible displacement could enhance oil recovery more than COimmiscible displacement.In addition,the average velocity of COfront was evaluated through analyzing the oil saturation prof ile.A special core analysis method has been applied to in-situ oil saturation data to directly evaluate the local Darcy phase velocities and capillary dispersion rate.