Ultrasound‐Assisted Supercritical CO 2 Modification of Coal Pore Structure: Experimental Study and Permeability Enhancement

ABSTRACT The infiltration and flow expansion in coal seams have long remained a critical challenge in coal mining. This study introduces an innovative method employing ultrasound‐assisted supercritical CO 2 (ScCO 2 ) for coal modification, utilizing custom‐designed experimental apparatus. By synergistically combining the chemical dissolution capacity of ScCO 2 with ultrasonic cavitation and mechanical vibration, the technique enables multiscale active intervention within the coal matrix—from macroscopic fractures to nanopores. This technology effectively addresses the efficiency constraints of conventional single‐phase supercritical fluid methods. Experimental results revealed a substantial improvement in coal pore structure after ultrasound‐assisted ScCO 2 treatment, with the total pore volume and porosity reaching 0.2166 mL/g and 23.93%, respectively, and the macropore volume accounting for 93.35% of the total pore volume. In addition, the pore fractal dimension and structural complexity decreased. Permeability tests showed a strong positive correlation between treatment duration and enhancement, with increases of 733.33%, 872.92%, and 1157.29% observed after 4, 7, and 10 days, respectively. These findings provide a promising pathway toward more efficient coalbed methane extraction.