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 ($V_{L,C{O}_2}$) to Langmuir volume of CH₄ ($V_{L,C{H}_4}$), initial reservoir pressure, CO₂ injection rate (R_i), and the staring time of CO₂ injection (T_s,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 $V_{L,C{O}_2}/V_{L,C{H}_4}$ and T_s,i, while positively related to the initial reservoir pressure and R_i. The CO₂ storage volume is positively related to $V_{L,C{O}_2}/V_{L,C{H}_4}$, R_i, and T_s,i, while shows no significant correlation with the initial reservoir pressure. These findings offer valuable insights for parameter optimization of the CO₂-ESGR process.