Effects of Liquid CO₂ Phase Transition Fracturing on Methane Desorption of Coal

Abstract

In this study, liquid CO2 phase transition fracturing treatment (LCPTF) and CH4 adsorption–desorption experiments were carried out on coal to explore the effects of LCPTF on the methane desorption capacity in coal. The results show that the LCPTF treatment caused about 35% reduction of desorption, indicating the transformed effect of coalbed methane (CBM) from the adsorbed state to the free state during the LCPTF process. Also, the enhanced effect of LCPTF on the effective desorption range and capacity was revealed. This effect can further enhance CBM production by prolonging the steady gas production period and delaying the arrival of the depletion stage of CBM production. This study provides an access to understanding the mechanism of LCPTF for enhancing CBM recovery from the perspective of the dynamic desorption process. The five-index method on the effect evaluation of the LCPTF technique for enhancing the CBM recoverability was proposed. The expected results are conducive to improving the evaluation system and optimizing the field application of the LCPTF technique.