Study on Key Controlling Factors of Fracture Propagation by Shaped Charge Blasting in Coal Seams

Gas drainage is the fundamental approach to controlling gas disasters in coal mines. For single low‐permeability coal seams, it should be supplemented by coal seam permeability enhancement technologies to improve gas drainage efficiency. This paper conducted a numerical simulations study on the key controlling factors affecting the fracturing effect of shaped charge blasting in coal seams, specifically focusing on the energy‐gathering direction, in‐situ stress, and borehole distance. Field tests were also carried out to evaluate the effectiveness of permeability enhancement. The results show that the energy‐gathering direction significantly influences the distribution of the maximum fracture radius of the coal, and the maximum fracture radius in the energy‐gathering direction is always larger than that in the non‐energy‐gathering direction. In‐situ stress has a significant impact on the development of coal fractures. Under bidirectional symmetric in‐situ stress conditions, the maximum fracture radius in both the energy‐gathering and non‐energy‐gathering directions decreases as the in‐situ stress increases. Under bidirectional asymmetric in‐situ stress, the maximum fracture radius in the energy‐gathering direction is negatively correlated with the lateral pressure coefficient, while the maximum fracture radius in the non‐energy‐gathering direction is positively correlated with it. The restraining effect of in‐situ stress on fracture development is much greater than its promoting effect. In the non‐energy‐gathering direction, the maximum fracture radius initially increases and then decreases with increasing borehole distance, eventually stabilizing. The field tests show that shaped charge blasting can significantly improve the gas drainage efficiency in low‐permeability coal seams. After implementing shaped charge blasting, the gas concentration and CH 4 flow rate increased 4.1 times and 8.8 times, respectively. The research results are of positive significance for deeply understanding the mechanism and technical practice of fracture propagation in shaped charge blasting in coal seams.