Mechanism study on effect of CO2 phase transition fracturing on methane adsorption in coal

Liquid CO2 phase transition fracturing（LCPTF） technology is a novel water-free fracturing technique that can enhance coalbed methane recovery. To study the changes in coal adsorption characteristics before and after CO2 phase transition fracturing, the No. 3 coal seam from the Yuwu coal mine was selected for experimentation. High-pressure mercury intrusion, low-temperature liquid nitrogen adsorption experiments, and CH4 isothermal adsorption tests were conducted to analyze the impact of liquid CO2 phase transition fracturing on coal adsorption. The results showed that after liquid CO2 phase transition fracturing, the pore volume and specific surface area of adsorption pores in coal decreased; the specific surface area of seepage pores decreased while the pore volume of seepage pores increased. The liquid CO2 phase transition fracturing technique could influence the change in the Langmuir adsorption constant of coal by altering the pore structure. After liquid CO2 phase transition fracturing, the Langmuir adsorption constant “a” value decreased and the “b” value increased, indicating that the fracturing process reduced the coal’s adsorption capacity and enhanced the desorption rate. This study provides theoretical guidance for the improvement and optimization of liquid CO2 phase transition fracturing technology for field applications.