Experimental Study on CO2 Injection to Enhance Recovery and its Storage Characteristics in Low Permeability Gas Reservoirs

This study explores the effectiveness of CO2 injection for enhancing methane (CH4) recovery and its storage characteristics in low permeability gas reservoirs. Conducted under controlled conditions of 90°C and 10 MPa, experiments employed a CO2 injection rate of 0.4 mL/min to assess displacement efficiency between dry cores and cores saturated with bound water. The results indicate that the presence of bound water significantly delays CO2 breakthrough by approximately 0.15 PV compared to dry cores, leading to a longer transition zone as CO2 first dissolves in the bound water before effectively displacing CH4. In wet cores, initial effective displacement of CO2 is minimal, resulting in a lag in CH4 recovery rates. However, the final CH4 recovery rate in wet cores is slightly higher than that in dry cores due to the ability of bound water to occupy smaller pores, facilitating the displacement process. Additionally, CO2 storage efficiency is evaluated through retention rates and storage ratios. The presence of bound water enhances CO2 retention, significantly increasing retention rates during injection. The dissolved CO2 in formation water accounts for a substantial portion of the pore volume, indicating improved solubility at higher pressures. In conclusion, this research demonstrates that CO2 injection not only improves CH4 recovery but also serves as a viable method for geological CO2 storage in gas reservoirs, with recovery rates ranging from 88.37% to 96.29% and breakthrough times between 0.62 PV and 0.88 PV.