Study on CO₂ Injection in Tight Sandstone Gas Reservoirs to Enhance Recovery and Burial Mechanism

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.