Mechanism of crack-oriented of hydraulic fracture and its technique in mine

Abstract

Drainage is inefficient of coal seam treated by hydraulic fracture due to disordered propagation of fracture. Therefore, we propose a novel approach of fracture-oriented via slotting a slitting in coal seam by high pressure water jet. Firstly, boreholes-oriented are drilled around the borehole of hydraulic fracture. Then we slot the coal seam via high pressure water jet. Finally, we carry out hydraulic fracture in the borehole. Shear destruction area which is formed under geostress is located on crack tip. And crack propagates along horizontal direction because the major principal stress direction is horizontal. Besides, we develop the technique of crack-oriented and apply it in typical low permeability coal seam. The results show that the technique is efficient. The diameter of hydraulic fracture is larger than 25 m, the concentration of gas drainage is 68% on average, and the gas flow is 0.037 m3/min. The concentration and flow of gas increase 2.12 times and 11.26 times respectively comparing to those of traditional technique.