Coupled simulation study of CO2 adsorption in coal matrix based on CT-derived representative elementary volume (REV)

To enhance the safety and reliability of geological CO2 sequestration, this study proposes a finite element coupling simulation method based on representative elementary volume (REV) models reconstructed from industrial CT imaging. The objective is to simulate gas migration and stress response within the coal matrix under CO2 adsorption conditions. The authentic three-dimensional internal structure of coal was acquired via industrial CT scanning, and the optimal REV scale was determined as 60 × 60 × 60 voxels through gradient error analysis. A multi-physics coupling model incorporating seepage, adsorption, and mechanical behavior was established and implemented on the COMSOL platform to perform numerical simulations under varying adsorption durations and injection pressures of 6 MPa. The results indicate that the adsorption-induced swelling of the matrix leads to a redistribution of internal stresses, exhibiting a directional transfer from fractures toward the matrix. The stress response of the coal demonstrates a nonlinear “increase-then-decrease” trend: the fracture domain stress increases from 0.66 to 0.73 MPa in the first day and then decreases to 0.54 MPa at 7 days. These findings offer both technical support and theoretical foundations for elucidating the multi-field coupling mechanisms in coal during CO2 sequestration and for the development of robust numerical simulation methodologies.