Abstract

Supercritical CO₂ (Sc-CO₂), a supercritical solvent, can extract small organic molecules (fluid) from coal, changing pore structures to affect gases storage and migration in the coal matrix. Five undeformed coals before and after the second coalification jump were collected to simulate Sc-CO₂ extraction performed with supercritical extraction equipment. Pore structures of the samples before and after Sc-CO₂ extraction were characterized using mercury porosimetry. The results show that there are significant changes in pore size distribution of samples. ΔV_Ma and ΔV_Me of coal samples are positive, ΔV_Tr and ΔV_Mi are positive for most coals, and ΔV_Mi of higher coals are negative; the ΔS_Ma and ΔS_Me are positive with small values, the ΔS_Tr and ΔS_Mi are positive and negative before and after the second coalification jump; thus, the pore connectivity is improved. These results indicate that Sc-CO₂ extraction not only increases the numbers of micropores, but also enlarges the pore diameter size; these changes in the pore structure are influenced by the second coalification. The changes in the pore structure by Sc-CO₂ extraction provide more spaces for gas storage and may improve the pore throats for gas migration. View Full-Text