CO 2 phase change induced fracturing and permeability enhancement technology in high gas and low-permeability coal seam mines

Abstract In the process of coal mining, high gas and low-permeability coal seam mines face problems such as low gas extraction efficiency and frequent ground pressure activities. In order to enhance the permeability and gas extraction efficiency of coal seams, a carbon dioxide phase change fracturing and permeability enhancement method is raised. By arranging drilling holes and setting blasting parameters, the coal seam is fractured employing shock waves and stress waves generated by the phase transition of liquid carbon dioxide. The experimental results show that the natural gas flow rate in the borehole significantly increases after blasting, with an average increase of nearly 15 times. The permeability coefficient also increases from 0.610–0.920 (10 −15 m 2 ) before blasting to 1.90–2.98 (10 −15 m 2 ), and the permeability coefficient of some measurement points even increases several times. In addition, the pore structure of coal seams has undergone significant changes, with a rise in the number of medium and large pores and an improvement in pore connectivity. These results indicate that carbon dioxide phase change induced fracturing and permeability improvement technique can effectively raise the permeability and gas extraction efficiency of coal seams. The research provides a new technological means for the secure and effective mining of high gas and low-permeability coal seam mines. By raising the permeability of coal seams and gas extraction efficiency, it can reduce the risk of mine gas accidents and ensure the safe production of coal mines.