Study on the influence of perforation on vndirectional hydraulic fracturing from the roof

To solve the problems that gas outburst accidents are prone to occur in the mining process of broken and soft outburst coal seam, and the existing research on the directional roof hydraulic fracturing of broken soft outburst coal seam lacks the analysis of roof bedding and perforation design, this paper uses the method of combining experiment with particle flow code (PFC), investigates the influence of perforation on the directional hydraulic fracturing of roof, and defines the optimal perforation layout scheme under the joint action of bedding and perforation. The results reveal that hydraulic fracture propagation is significantly influenced by the bedding angle and in situ stress conditions of the rock mass. During roof fracturing, once fractures propagate to the coal-rock interface, they induce the formation of a complex fracture network within the coal seam, effectively enhancing its permeability. PFC has accuracy and engineering adaptability in hydraulic fracturing numerical simulation. Under the conditions of different bedding angles, the directional hydraulic fracturing perforation should be arranged in different ways, a vertical perforation configuration is recommended for bedding angles of 0°–15°, while for angles of 30°–60°, perforations should be oriented perpendicular to the bedding direction. At 45°–60°, perforations should avoid alignment with the bedding plane and instead adopt a large-angle orientation. Under the parameter combination of “three perforations-optimized angle-suitable bedding,” the effect of directional hydraulic fracturing of bedding rock broken soft coal seam roof is the best. This perforation scheme offers an effective strategy for gas control in outburst-prone soft coal seams.