• 标题：An enhanced coalbed methane recovery technique based on CO2 phase transition jet coal-breaking behavior
• 关键词：Low-permeability coal seam,CO2 phase transition jet,Coal rock breaking,Enhanced coalbed methane recovery
• 作者：Xin Bai, Dongming Zhang, Sheng Zeng, Shuwen Zhang, Dengke Wang, Fulin Wang

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In recent years, CO2 phase transition jet (CPTJ) coal-breaking technology has been reported to increase coal seam permeability. However, the structural evolution effffect of coal subjected to CPTJ technology is unclear, which restricts widespread CPTJ technology application. In this study, a laboratory experimental system and fifield technical equipment were developed, and coal-breaking experiments under difffferent CPTJ pressure conditions were conducted. We investigated pore structure changes by combining scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) to better understand the coal pore structure evolution characteristics under difffferent CPTJ pressures. Furthermore, an enhanced coalbed methane (ECBM) recovery experiment using CPTJ coal-breaking technology was conducted with the self-developed technical equipment. The results show that notable damage occurs in the coal body inflfluenced by CPTJ, and the damage area increases with increasing jet pressure. The SEM results revealed that more pores and cracks are produced due to liquid CO2 CPTJ, and the porosity and crack size increase with increasing jet pressure. MIP analysis indicates that the pore structure of the breaking coal samples mainly includes macropores, and coal sample macroporosity increases signifificantly with increasing jet pressure. The fifield ECBM experiment showed that CPTJ technology can reduce the coalbed methane (CBM) drainage decay coeffiffifficient and increase the CBM extraction pure flflow rate and recovery effiffifficiency 8.3–10.4 and 20.4 times, respectively.