Study on hydraulic fracturing-deep hole pre-splitting blasting composite permeability enhancement technology

In order to increase the permeability of low-permeability and high-gas coal seams and improve gas utilization rate and extraction efficiency, a hydraulic fracturing-deep hole presplitting blasting composite permeability enhancement technology was proposed.The mechanism of blasting cracking in hydraulic fracturing-deep-hole pre-split blasting was analyzed, and the crack stress intensity factor equation and the crack secondary radius equation under the action of detonation gas were established.The RFPA2D Flow simulation software was used to simulate the formation process and crack propagation law of coal and rock mass cracks around the hole wall after hydraulic fracturing.ANSYS/LS-DYNA finite element analysis simulation software was used to simulate the extent to which gas pre-cracks with different lengths affect the effect of gas drainage and permeability enhancement after deep-hole pre-crack blasting.At the same time, the on-site industrial test was carried out on No.8410 working face of Yangquan No.5 mine to verify the gas drainage and permeability enhancementeffect of the hydraulic fracturing-deep hole pre-cracking blasting composite permeability enhancement technology under the coal mine.The results show that the permeability of coal seam was significantly improved compared with the conventional deep-hole pre-splitting blasting after the hydraulic fracturing-deep-hole pre-split blasting composite technology.The initial gas emission of the cracked holes was 3.18 times of the ordinary blasting hole, the attenuation intensity of gas content was reduced by 77.3%.The effective influence radius of deep-hole pre-splitting blasting increases with the length of the pre-splitting in the blasting hole, and there was a linear relationship between the two.In this study, the effective radius of cracking after composite blasting could reach 6.98 m, which was consistent with the effective cracking radius of 6.763 m obtained from the numerical simulation results..At the same time, the results of numerical simulation and on-site industrial tests proved that the proposed hydraulic fracturing-deep hole pre-splitting blasting composite permeability enhancement technology could effectively increase the permeability of coal seam, improve the gas extraction efficiency, and provide references for other low permeability and high gas seam gas extraction and permeability enhancement technology.