To study the mechanism of CO2 injection in tight sandstone gas reservoirs for enhanced recovery and geological storage, we conducted experimental studies based on the reservoir conditions in West Sichuan. These studies focused on the properties of CO2 and CH4, their adsorption and diffusion under high temperature and high pressure, the interactions of CO2 with tight sandstone and formation water, and the displacement efficiency of the CO2 injection in long core samples. The results show that under reservoir conditions, the adsorption capacity of CO2 in tight sandstone is nearly four times higher than that of CH4, and its diffusion capacity is also four times higher. This enables CO2 to replace adsorbed CH4 through competitive adsorption. Due to the greater density of CO2 compared to CH4, gravitational differentiation causes CO2 to sink below CH4, pushing CH4 upward in the reservoir. This process facilitates the sequestration of CO2 and enhances the recovery of natural gas. Additionally, CO2 injection dissolves feldspar and calcite in dense sandstone minerals, generating kaolinite, iron dolomite, and chlorite. The dissolution effect exceeds precipitation, leading to an increase in permeability by 73.25 to 91.15% and an increase in porosity by 0.65 to 0.72%. This improves the reservoir's seepage characteristics, reduces the minimum flow pressure of liquids in the pores, decreases water-phase trapping damage, and ultimately increases gas recovery. This study provides technical guidance for the efficient development of tight sandstone gas reservoirs and geological storage of CO2.
© 2025 The Authors. Published by American Chemical Society.