Cracking Mechanism and Numerical Simulation of Fractional Hydraulic Fracturing Cracks

Gas extraction is the fundamental way to control the gas disaster in coal mine.The segmented hydraulic fracturing technology can effectively solve the problem of stress concentration caused by conventional fracturing by implementing the measures of gas extraction hole and fracturing hole, and achieve the purpose of uniform pressure discharge of coal seam.This paper analyzes the expansion characteristics of small-scale hydraulic fracturing fracture and its penetration mechanism, It is concluded that the expansion of coal seam crack in hydraulic fracturing can be divided into preparation stage, crack generation stage and crack extension stage; The induced stress between the fractures can change the stress field of the formation, To create a stress superposition between the holes, Promote intra-seam steering of inter-hole cracks, When the gas extraction hole is arranged in coordination with the fracturing hole, Can connect the fracturing crack and the extraction hole fracture area, Form a whole pressure relief network; A numerical model of fractional hydraulic fracturing is developed, The extension law of fracturing crack and the change law of coal stress are simulated.The study shows that segmented fracturing can effectively solve the problem of stress concentration after conventional fracturing, to achieve the purpose of uniform pressure discharge of coal seam, but also can make the fracturing crack evenly expanded to both sides, so that the coal in the fracturing area is in a uniform pressure discharge state.