Abstract
Aiming at the problem of coal and gas outburst prevention and control in serious outburst dangerous coal seam under complex geological conditions in Qidong Coal Mine, the water jet drilling and expanding integrated device was used to implement the measures that expand holes and increase permeability by high-pressure water at a 912 working face. The experimental results show that when the pump pressure is between 13 MPa and 15 MPa, the particle size of pulverized coal can be effectively reduced and the discharge of pulverized coal can be increased. The coal output of a single hole is 0.8~2.3 t/m, with an average of 1.1 m/t. The unreamed conventional borehole has a single-hole initial gas drainage rate of 50.74 m3/d and a single-hole cumulative gas drainage rate of 736.12 m3 within 30 days. The initial single-hole gas drainage volume of the reaming borehole is 178.74 m3/d, and the cumulative single-hole gas drainage volume in 30 days is 2227.57 m3. After reaming, the initial gas drainage scalar of a single hole increases 3.52 times of the original unreamed conventional drilling and the average cumulative gas drainage scalar of a single hole reaches 3.03 times of the original unreamed conventional drilling. This technology and equipment have a good promotion and application value in gas treatment of soft, low-permeable coal seams.
Highlights
As is known to all, coal and gas outburst is the result of a comprehensive action of in situ stress, gas, and physical and mechanical properties of coal [1, 2]
The field test shows that the reaming process can effectively reduce the particle size of expanded pulverized coal, improve the discharge of pulverized coal, reduce the stress concentration of coal and rock mass around the mining space, and greatly increase the permeability of the coal seam, which can provide a certain reference for mines with similar conditions
In order to investigate the effect of high-pressure water jet drilling and expansion integration on pressure relief and permeability enhancement of coal seam 9, eight verification holes were constructed in the no. 3 drilling field two months after the test
Summary
As is known to all, coal and gas outburst is the result of a comprehensive action of in situ stress, gas, and physical and mechanical properties of coal [1, 2]. Zhang et al [25] determined the impact of key parameters on slotting depth; these key parameters include the nozzle diameter, jet pressure, speed, and slotting time They established and verified the waterjet groove depth calculation model based on the grooving experiments under different working conditions. Jun et al [26] took Shihuatian Coal Mine which is located in Guizhou province, China, as an example; a high-pressure water jet is used to open holes in the coal seam to relieve the gas pressure inside the coal seam and increase the permeability of the coal seam, thereby improving the efficiency of gas drainage and eliminating outburst risk. By using the integrated device of water jet drilling and expanding, the high-pressure water is used to expand the hole to strengthen the pressure relief and effectively increase the permeability of the coal seam. The field test shows that the reaming process can effectively reduce the particle size of expanded pulverized coal, improve the discharge of pulverized coal, reduce the stress concentration of coal and rock mass around the mining space, and greatly increase the permeability of the coal seam, which can provide a certain reference for mines with similar conditions
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