坚硬顶板孔内磨砂射流轴向切缝及压裂试验研究

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

为了提高坚硬顶板的预裂卸压效果,开发了孔内磨砂射流轴线切顶压裂防冲新技术,即施工完顶板钻孔后,在预设位置操作钻杆匀速前进/后退,同时,采用磨砂射流系统对钻孔孔壁进行定向切割,使孔壁形成一定深度的轴线裂缝,再采用封隔器封孔后压裂,在高压水的作用下,人造裂缝沿着预设方向定向扩展,从而达到精准切顶卸压的目的。现场切缝试验表明,在射流压力为50 MPa,切缝速度为0.1 m/min的条件下,孔内切缝半径可达300~500 mm。通过切缝后压裂试验表明,预制裂缝具有较好的导向作用,裂缝扩展主要沿着预制裂缝深度方向,试验泵压为40 MPa,压裂时间为20 min,裂缝扩展距离可达22 m以上。该技术可提高水力压裂裂缝方向的可控性,使裂缝沿着最佳切顶方向扩展,从而提高卸压效果。

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.