Unlike saline aquifers and depleted reservoirs, where CO2 storage relies primarily on structural and residual trapping within a largely passive rock matrix, coal seams store CO2 through direct adsorption onto the coal matrix itself, coupling storage capacity directly to swelling-induced permeability decline. This coupling makes coal seams a mechanistically distinct and comparatively underconstrained CCS target relative to conventional geological formations.Accurate characterization of coal pore structure is essential for predicting CO2 adsorption, transport, swelling, and injectivity loss during carbon capture and storage. NMR cryoporometry and T2 relaxometry are used to determine pore-size distributions and surface relaxivity across micro- and mesopore scales. These experimental data are combined with density functional theory calculations to quantify fluid–solid interactions, adsorption-induced stresses, and coal-matrix swelling. The resulting nanoscale constitutive relations are incorporated into a multiscale homogenization framework to derive effective poromechanical and transport properties at the reservoir scale. The integrated model links pore-scale adsorption and solvation forces to cleat closure, permeability reduction, and the progressive decline of CO2 well injectivity.