Experimental study on axial fracture cutting and fracturing of abrasive jet in boreholes within hard rock roofs

In order to improve the pre-splitting pressure relief effect of hard roofs,a new technology for cutting and fracturing and anti-flushing of the frosted jet axis in boreholes was developed. After the drilling borehole is completed,the drill pipe is operated to advance or retreat uniformly in the borehole. At the same time,the frosted jet system is used to perform directional cutting on the borehole wall to form a certain depth of axial cracks in the borehole wall. Hydraulic fracturing is then performed after the packer is sealed. Under the action of high-pressure water,the artificial fractures are propagated in a preset direction,so as to achieve the purpose of accurate cutting and relief. The on-site slit test shows that under the conditions of a jet pressure of 50 MPa and a slit speed of 0.1 m/min,the radius of the slit in the hole can reach 300-500 mm. The fracturing test after slitting shows that the prefabricated fractures have excellent guiding effect,and the fracture propagation direction is mainly along the depth of the prefabricated fractures. The test pump pressure is 40 MPa,the fracturing time is 20 min,and the fracture propagation distance can reach more than 22 m. This technology is expected to improve the controllability of the fracture direction of hydraulic fracturing,make the fracture expand along the best cutting direction,and improve the pressure relief effect.