CO_2 flooding is considered not only one of the most effective enhanced oil recovery(EOR) methods,but also an important alternative for geological CO_2 storage.In this paper,the visualization of CO_2 flooding was studied using a 400 MHz NMR micro-imaging system.For gaseous CO_2 immiscible displacement,it was found that CO_2 channeling 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 CO_2 miscible 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 CO_2 front was uniform.The sweep efficiency was so high that the final residual oil saturation was 33.9%,which indicated CO_2 miscible displacement could enhance oil recovery more than CO_2 immiscible displacement.In addition,the average velocity of CO_2 front 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.
Zhao Yuechao SongYongchen Liu Yu Jiang Lanlan Zhu Ningjun
