A Case Study on the Fracturing Radius and Time Effects of CO2 Phase Transition Fracturing in Coal Seams

CO2 phase transition fracturing (CPTF) is considered to be a promising way to improve the recovery efficiency of coalbed methane in deep, tight coal seams. In addition, it is significant to the CO2-ECBM and CO2 storage in coal. To better understand the fracturing radius and time effects of CPTF, a field experimentation was conducted on the Ji-15 coal seam of Pingmei 8th Coal Mine. The results indicate that the fracturing radius and time effects are significantly related; with the increase in fracturing radius, the time for extraction rate to reach the peak value is shorter. The calculated value of effective fracturing radius is 7.56 m via the fitting relationship. According to the CO2 content in different extraction boreholes after fracturing, it can be concluded that the crack zone is 5 m. In addition, the extraction rate of methane firstly increases slowly for a while, and then reaches the peak. This work could provide theoretical directions for the arrangement of fracturing and extraction boreholes in CO2 fracturing works related to CO2-ECBM and gas pre-extraction in coal mining.