Experimental study of the effect of CO2 on rock seepage characteristics

Abstract

The influence of different phase states of CO2 on the seepage characteristics of different rocks is one of the most important factors to enhance shale gas exploitation, such as CO2 fracturing and displacement, and achieve CO2 geological storage. Rock soaking experiments with different CO2 phase states were carried out to compare and analyze the influence of permeability, contact angle, starting pressure gradient and other seepage characteristic parameters of sandstone and shale before and after soaking. Research shows: After soaking in liquid and supercritical CO2, the permeability and contact angle of sandstone and shale increase in varying degrees, and the starting pressure gradient decreases in varying degrees. After soaking in liquid CO2, the permeability of sandstone and shale increased by 1.71% and 12.88% respectively, the contact angle increased by 3.23% and 7.47% respectively, and the starting pressure gradient decreased by 3.02% and 5.88% respectively. After supercritical CO2 immersion, the permeability of sandstone and shale increased by 37.37% and 48.82% respectively, the contact angle increased by 19.27% and 36.80% respectively, and the starting pressure gradient decreased by 35.39% and 39.34% respectively. Compared with sandstone, the seepage characteristics of shale after soaking in liquid and supercritical CO2 have greater changes; Compared with liquid CO2, the seepage characteristics of sandstone and shale change more after supercritical CO2 soaking. With the increase of supercritical CO2 soaking time, the contact angle of sandstone slightly increases, while that of shale obviously increases. Compared with liquid CO2, the change of seepage curves of sandstone and shale after supercritical CO2 soaking is more different.