Experimental and Numerical Simulation Study on Enhancing Gas Recovery with Impure CO2 in Gas Reservoirs

To achieve carbon peaking and carbon neutrality goals, using CO(2 )to enhance natural gas recovery has broad application prospects. However, the potential for CO2 to increase recovery rates remains unclear, the mechanisms are not fully understood, and the cost of purifying CO2 is high. Therefore, studying the effects of impure CO2 on natural gas extraction is of significant importance. This study investigated the effects of injection timing and gas composition on natural gas recovery through high-temperature, high-pressure, long-core displacement experiments. Based on the experimental results, numerical simulations of CO2-enhanced gas recovery and sequestration were conducted, examining the impact of impurity gas concentration, injection timing, injection speed, and water saturation on recovery efficiency. The results indicate that higher impurity levels in CO2 increase gas diffusion, reducing the effectiveness of natural gas recovery and decreasing CO2 sequestration. Earlier injection timing improves recovery efficiency but results in a lower ultimate recovery rate. Higher injection speeds and water saturation levels both effectively enhance recovery rates.