Effect of supercritical CO2 extraction on pore characteristics of coal and its mechanism

Abundant pore space in coal is not only the place for accumulation of coalbed methane (CBM), but also tunnel gas migration. In this study, five sets samples before and after second coalification were selected from eastern margin Ordos Basin to simulate supercritical CO 2 (Sc-CO ) extraction equipment. The evolutions structure porosity tested by mercury intrusion porosimetry nuclear magnetic resonance spectroscopy compare changes due Sc-CO extraction, explain related mechanism. results show that: (1) Pore volume, specific surface area, connectivity characteristics changed significantly increment volume area presented a law increase–decrease–increase with increase rank, turning point was near coalification. (2) change trend increasing again coalification, which supports results. (3) observed through pore-increasing expanding effects. Before effects co-existed micropores, pore-expanding effect mainly existed transitional pores above. (4) variation model established. conclusions offer important theoretical significance -enhanced CBM (CO -ECBM) mechanism -ECBM engineering.