The effect of leakage characteristics of liquid CO2 phase transition on fracturing coal seam: Applications for enhancing coalbed methane recovery

Liquid carbon dioxide phase-transition blasting (LCO2-PB) is a promising alternative method for enhanced coalbed methane (ECBM) extraction and prevention of coal and gas outbursts. During the process of the LCO2-PB fracturing the coal seam, the improper application of fracturing model will reduce the efficiency of gas drainage and cause gas disasters. To clearly understand the ECBM modes of LCO2-PB fracturing coal seam process, this paper employed experiments to investigate the effect of leakage characteristics of the LCO2-PB on fracture models of coal cubes, including release pressure (Pr), filling level (V), release diameter (Dr) and blasting hole diameter (Db). We propose the combination I and II of the LCO2-PB leakage parameters and applied two methods to the in-situ tests. The results revealed that the gas flow of the boreholes of the LCO2-PB with the combination I is 0.368 m3/min, which is 2.07 times that of the combination II (0.178) in the soft coal seam. Besides, the average methane flow of the boreholes with combination II is 0.796 m3/min, which is 1.78 times the combination I (0.448) in the hard coal seam. The adjustment of leakage parameters of the LCO2-PB technology can be helpful for ECBM and reduce the risk of coal and gas outbursts in the soft and hard coal bed.