Optimization of multi-hole hydraulic cutting combined extraction parameters under superposition effect

In the process of hydraulic cutting in low permeability and high gas coal seams, there are problems such as unclear cutting disturbance range and unclear optimal hole spacing for cutting drilling. In order to solve the above problems, the 1908 working face of Gaoshan Coal Mine in Yuneng, Guizhou Province is taken as the research background. On the basis of establishing the fluid-solid coupling model of gas extraction in coal body with hydraulic cutting, with the help of COMSOL numerical simulation software, the effective extraction radius of hydraulic cutting borehole and the change of gas pressure around the borehole in the 1908 working face of Gaoshan Coal Mine are studied. Based on the simulation results, the effective extraction range and gas pressure change between holes are analyzed under the influence of the extraction superposition effect between holes when the hydraulic cutting drilling holes are arranged in multiple holes. Finally, the optimal hole spacing and extraction time are obtained. The results show the following points. ① The single hole extraction effect of hydraulic cutting drilling is significantly improved with the cutting depth. However, the effective extraction radius of the borehole increases slowly. In order to obtain the best cutting depth, the effective extraction radius of each borehole is fitted in a trinomial way. With the increase of hydraulic cutting depth, the range of effective extraction radius slows down after rapid increase and finally tends to be stable. The optimal cutting depth of Gaoshan Coal Mine is 1.5 m, and the effective extraction radius is 3.1 m. ② Under the same extraction time, the gas pressure in the coal body decreases with the shortening of the distance between two holes. It shows that the smaller the hole spacing is, the more serious the disturbance caused by hydraulic cutting between holes is, and the more significant the influence of the extraction superposition effect is. ③ On the premise of ensuring that the outburst elimination meets the standard, it is best to choose a hole spacing of 7 m for arranging hydraulic cutting drilling. ④ Originally, in the "square" hole arrangement, the maximum gas pressure at the point where the blind area may occur at the hole center is only 0.67 MPa, which is less than the critical value. The effective coverage area of the "square" hole arrangement is larger than that of the "triangle" hole arrangement, and the repeated area of drainage is reduced. This reduces the amount of drilling and improves the efficiency of gas control. ⑤ Through field test, it is concluded that in the 60 d extraction period, the hydraulic cutting drilling arrangement with a hole spacing of 7 m and a "square" hole arrangement can effectively improve the concentration and purity of gas extraction. It can also extend the period of high efficiency extraction. It can eliminate the blank zone of gas extraction in the coal body between boreholes to eliminate the outburst of the coal body in the area between boreholes.