Investigation and application of high pressure water jet annularity slotting self pressure release mechanism

In order to overcome the difficulty of gas extraction in low permeability coal seams in deep mines,a technol-ogy of high pressure water jet annularity slotting self-pressure release is put forward. The gas flow pattern of normal boreholes and slotting boreholes is analyzed based on the gas flow theory. The differential equations of gas flow in the normal boreholes and slotting boreholes are established. The mechanism of improving coal seam gas extraction ability by the high-pressure water jet annularity slotting self-pressure release technology is obtained. The stress performance of the coal seam surrounding the borehole after the high pressure water jet slotting is modeled and analyzed by the FLAC3D software. The optimum slotting parameters are determined based on the coal seam pressure release and the distribution characteristics of the plastic zone. Through the field test of high pressure water jet annularity slotting self-pressure release technology,the BC-1 deformation inspecting instrument is used to measure the deformation amount of 0． 136% of the coal seam in the borehole,and the natural gas emission of the coal seam borehole is tested. The gas permeability coefficient of the coal seam increases 42 times,and the measured gas extraction rate is 3． 44-5． 32 timhigher than that of the ordinary borehole. Both the theoretical and field tests show that the high pressure water jet an-nularity slotting self-pressure technology can effectively improve the stress state of the coal seam,increase the gas per-meability of the coal seam and improve the gas extraction efficiency.es