Study and Application of Antireflection Technology for Ultra-high Pressure Hydraulic Slitting of Long Bedding Borehole

In view of the problem that occur in the bedding borehole of hard coal seam in low permeability,such as the range of extraction radius is small and the extraction effect is poor,this paper studied the technique of ultra-high pressure hydraulic slitting of long bedding borehole in the working surface,the mechanism of coal breaking by water jet was studied by stress wave effect,the principle of pressure relief and antireflection of ultra-high pressure hydraulic slitting was analyzed.A complete set of ultra-high pressure hydraulic slitting equipment with working pressure up to 100 MPa was developed.The integrated drilling and slotting technology that not out of drill pipe and remote operation function under the super high pressure condition were realized,the parameters of ultra-high pressure hydraulic slitting were investigated,and the technology of ultra-high pressure slitting was developed.The results of field test show that the average amount of coal produced by single cutting hole is 0.32 t,the equivalent slit radius is from 1.51 m to 2.08 m.The gas extraction concentration in borehole after slitting increased by 1.44 times and the net gas extraction flow increased by 3 times,the effective extraction radius is 3.6 times of the contrast borehole.The construction time of borehole is shortened by about 30%,and the standard time of extraction is shortened by about 40%.The application shows that the permeability of coal seam can be improved obviously by the application of antireflection technology for ultra-high pressure hydraulic slitting,which achieves the purpose of rapid pressure relief and antireflection.