In order to solve the coalbed methane extraction problems characterized by low permeability of coal seam,small extraction vol-ume and low extraction rate,for the 3-1 coal seam of Hongqinghe Coal Mine,the fine view parameters of the model were considered to match the macroscopic properties of coal samples by trial-and-error method,a flow-solid coupling model of hydraulic fracturing of coal rock based on particle discrete element program was established,the particle bonding model and smooth joint model were used to simu-late the structural characteristics of coal and rock,and the influence of prefabricated transverse grooves in strips,triangles,and squares on the difficulty of coal and rock cracking and the morphology of crack propagation was studied.The simulation results show that:the prefabricated transverse grooves can drive the fracture initiation and expansion along the grooves,and under the conditions of controlling the same water pressure and the surrounding pressure ratio of 1.0,the number of fractures in the coal and rock is the lowest but the av-erage fracture length is the longest in the strip grooves,and the number of fractures in the coal and rock is the highest but the average fracture length is the shortest in the square grooves;under the comprehensive comparison,the square transverse grooves are easier to form a complex seam network and increase the effective transformation volume of the coal seam than the strip grooves and triangular grooves,and all three transverse grooves can reduce the fracture initiation difficulty of the coal and rock,and the more the tip angle of the transverse grooves,the less the fracture initiation difficulty;the damage form in the part of the coal and rock hydraulic fracturing near to the transverse groove hole is mainly tension damage,and the fracture is relatively straight and does not show bifurcation,and the part farther from the transverse groove hole starts to show shear damage.
coal and rockdiscrete elementprefabricated transverse groovehydraulic fracturingfracture initiationfracture extension
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