Research and application of anti-reflection technology of liquid CO2 coal seam

In order to increase the permeability of coal seam, improve the utilization rate of gas and strengthen the effect of gas extraction, the anti-reflection technology of liquid CO2 gas explosion in low permeability coal seam was put forward. Based on the relevant basic data of coal mine gas and the mechanism of liquid CO2 blasting cracking and anti-reflection, the principle, process and energy conversion of liquid CO2 blasting were explained and the TNT equivalent conversion of liquid CO2 gas explosion energy release was analyzed. According to the change of CO2 pressure curve in the splitter during the monitoring of blasting, the change of liquid CO2 pressure in the splitter in four different stages during blasting was analyzed. The coal and rock gas explosion damage model was established by ANSYS/LS-DYNA simulation software. The evolution process of single hole and double hole liquid CO2 blasting was simulated. The effect of liquid CO2 blasting was compared and analyzed from the Mises stress cloud map and the coal rock damage cloud map. The LS-DYNA finite element analysis and simulation software was used to simulate the damage propagation law of coal rock under different arrangement of the crack generator. According to the numerical simulation results, industrial tests of CO2 phase change blasting were carried out to comprehensively evaluate the anti-reflection effect of liquid CO2 gas explosion cracking and anti-reflection. The results show that the radius of single hole blasting measured by the relative pressure index method is 2.5 m, which is close to the numerical simulation results. After the CO2 phase change blasting, the permeability coefficient of coal seam is increased by more than 50 times higher than that before the enhancement.The gas extraction concentration was increased by 73.7% compared with that before anti-reflection improvement.The extraction flow rate is 5.1 times that of the normal drainage hole. Numerical simulation and field underground industrial test show that liquid CO2 blasting can increase the desorption rate of coal adsorbed gas, promote the development of fractures in coal body, achieve the purpose of increasing the permeability of coal seam, and improve the gas extraction effect of coal seam obviously. The research results can provide a theoretical basis for the actual construction of liquid CO2 gas explosion technology and provide a solution to the problem of gas extraction in low permeability coal seams in China.