Supercritical CO(2) Interaction Induced Pore Morphology Alterations of Various Ranked Coals: A Comparative Analysis Using Corrected Mercury Intrusion Porosimetry and Low-Pressure N(2) Gas Adsorption

[Image: see text] Enhanced coal bed methane (ECBM) recovery via CO(2) geological storage (CGS) involves CO(2) adsorption and CH(4) desorption from coal pores, gas diffusion, and flow through coal matrix and cleats, which are closely related to coal pore morphology. To characterize and quantify the alterations of pore morphology of different ranked coals treated by supercritical CO(2) (ScCO(2)), CGS was simulated with a custom-built high-pressure ScCO(2) geochemical reactor at 10 MPa and 35 °C for sub-bituminous coal, bituminous coal, and anthracite, respectively. The bituminous coal was collected from a ScCO(2)-rich reservoir to examine the effect of second exposure to ScCO(2) on pore morphology. Mercury intrusion porosimetry (MIP) after data correction using the Tait equation (TE) and low-pressure N(2) gas adsorption (LPN(2)GA) were employed. The decrease of coal matrix compressibility and increase of pore volume compressibility indicate that sub-bituminous coal becomes more resistant to microfracture closure and pore shrinkage after ScCO(2) treatment. Both the thermodynamics fractal model after MIP data correction and Frenkel–Halsey–Hill (FHH) model, which are strongly scale-dependent and meaningful from a geometric viewpoint, reveal a downward trend of the irregularity and heterogeneity of pore structures for sub-bituminous coal. The effects of hydrocarbon mobilization and inorganic matter dissolution by ScCO(2) play an important role in pore size distribution (PSD), pore volume (PV), and pore shape (PS) alterations, whereas these changes are quite small for bituminous coal. The above observed alterations of sub-bituminous coal are all positive, such as closed pore reopening, pore volume enlargement, pore roughness decline, pore connectivity enhancement, and gas desorption improvement, which makes sub-bituminous coal a desired option for CO(2)-ECBM recovery.