Study on Main Controlling Factors of CO2 Enhanced Gas Recovery and Geological Storage in Tight Gas Reservoirs

Tight gas reservoirs, as important unconventional natural gas resources, face low recovery rates due to low porosity, low permeability, and strong heterogeneity. CO2 Storage with Enhanced Gas Recovery (CSEGR) technology combines CO2 geological storage with natural gas development, providing both economic and environmental benefits. However, the main controlling factors and influence mechanisms remain unclear. This study utilized the PR-EOS to investigate CH4, CO2, and natural gas physical properties, established a numerical simulation model considering CO2 dissolution and geochemical reactions, and explored the influence of injection scheme, injection rate, production rate, and shut-in condition on CO2 enhanced recovery and storage effectiveness through orthogonal design. Results show that CO2 exhibits significant differences in compressibility factor, density, and viscosity compared to natural gas, enabling piston-like displacement. Intermittent injection slightly outperforms continuous injection in recovery enhancement, while continuous injection provides greater CO2 storage capacity. The ranking of the significance of different influencing factors for enhanced oil recovery is as follows: injection rate > production rate > injection scheme > shut-in condition. For the effect of geological storage of CO2, it is as follows: injection rate > injection scheme > production rate > shut-in condition. During gas injection, supercritical, ionic, and dissolved CO2 continuously increase while mineral CO2 decreases, with storage mechanisms dominated by structural and residual trapping. The study provides scientific basis for optimizing CO2 flooding strategies in tight gas reservoirs.