CO ₂ –CH ₄ Adsorption-Induced Volumetric Deformation and Its Impact on the Permeability of Shale

CO 2 -enhanced shale gas recovery (CO 2 -ESGR) has been demonstrated to be a promising method for increasing shale gas production and simultaneously achieving CO 2 storage. During the CO 2 -ESGR process, the permeability of shale reservoirs is an important parameter significantly influencing the shale gas production and the CO 2 sequestration efficiency. However, the quantitative relationship between CO 2 and CH 4 competitive adsorption induced differential deformation, and its impact on the permeability of shale is not yet fully understood. In this study, experimental investigations of pure gas (CH 4 and CO 2 ) and binary gas (CH 4 /CO 2 = 3:1, 1:1, and 1:3) adsorption-induced volumetric deformation and the subsequent permeability changes on shale were conducted. The results show that under the constant effective stress conditions, adsorption-induced shale deformation increased with the increase of gas pressure for pure CO 2, CH 4, and their gas mixtures, while the permeability of shale shows a tendency of first decreasing rapidly, followed by a slow decrease, and then increasing slightly. In addition, binary CO 2 /CH 4 gas adsorption-induced deformation increased with the increase of the mole fraction of CO 2, leading to the decrease in the permeability of shale with the increase of the CO 2 mole fraction, which means a significant permeability loss as the CO 2 adsorption-induced swelling increases. In addition, with the increase of the CO 2 mole fraction, the impact of the slippage effect on the permeability of shale decreased. The final slight rebound in the permeability of shale can be attributed to the dynamic variation of the Biot coefficient of effective stress in shale caused by adsorption. The results can provide theoretical support for optimization of the engineering parameters of CO 2 -ESGR.