Shale Gas Production and CO₂ Storage of CO₂-ESGR Based on the Stress–Strain–Sorption Behavior of Shale

The CO2-enhanced shale gas recovery (CO2-ESGR) technique is a promising method for enhancing shale gas production and sequestering of CO2. In this study, a two-component gas flow model in shale reservoirs considering the stress–strain–sorption behavior of shale during the CO2-ESGR process was developed. Using this model, the impact of the parameters of the ratio of Langmuir volume of CO2 (VL,CO2) to Langmuir volume of CH4 (VL,CH4), initial reservoir pressure, CO2 injection rate (Ri), and the staring time of CO2 injection (Ts,i) on the CO2-ESGR process was analyzed by numerical simulation. The results indicate that the sustained reduction in reservoir porosity and permeability during primary production is dominated by the effect of effective stress changes. Following CO2 injection, reservoir porosity and permeability decrease rapidly in the CO2 sweep region mainly due to the CO2/CH4 adsorption-induced differential swelling, while it is still dominated by effective stress changes outside the CO2 sweep region. CH4 production is negatively related to VL,CO2/VL,CH4 and Ts,i, while positively related to the initial reservoir pressure and Ri. The CO2 storage volume is positively related to VL,CO2/VL,CH4, Ri, and Ts,i, while shows no significant correlation with the initial reservoir pressure. These findings offer valuable insights for parameter optimization of the CO2-ESGR process.