Numerical simulation of effective drainage radius and optimization of hole spacing under the influence of stack effect

In view of the problems such as blindness and uncertainty existing in the hole spacing for pre-drainage of coal seam gas, a mathematical model of solid-liquid coupling for coal seam gas drainage was established based on the principle of solid-liquid coupling, and then the effective drainage radius of drilling in pre-drainage of coal seam gas was studied by numerical simulation with the help of FLUENT numerical simulation software. Based on the numerical simulation of multiple holes, the layout parameters of pre-drainage hole of coal seam gas in 4207 working face in Jianxin Coal Mine were optimized. The results show that the effective extraction radius increases in logarithmic form with the increase of extraction time; the mutual disturbance between holes can produce stack effect when drilling with multiple holes, the denser the spacing between holes, the more significant the decrease of gas pressure between boreholes; in the pre-drainage period of 90 d, the effective radius of single hole extraction is 2.02 m, and the spacing of multiple holes extraction is between 2.86 m to 4.50 m. Based on the thickness of coal seam, the equilateral triangle hole layout scheme is put forward. The gas parameters are up to standard and the hole layout scheme is effective in field application.