Physical simulation experiment on influence of borehole spacing along the seam on effect of gas drainage

Based on the self-developed multi-field coupling testing system for coalbed methane exploitation, a series of physical simulation experiments of gas drainage under different spacing distances between boreholes was conducted to investigate the evolution of gas pressure and gas flow rate during drainage process. The results show that the gas pressure at different measuring points in the coal seam drops faster with the decrease of the distance from the drainage pipe. With the influence of the drainage superimposed effect, the gas pressure drop rate of areas between the drainage pipes is greater than that of the outside under the same distance condition, and the pressure difference rapidly reaches the peak value after the start of drainage, and then drops. The closer to the drainage pipe or with the increase in the borehole spacing, the less the effect of the superimposed effect is. There exists a power function relationship between pressure gradient and instantaneous flow rate on the section of the coal seam perpendicular to the borehole. With the increasing amounts or decreasing spacing of boreholes, the gas pressure of the same position drops faster, the instantaneous flow rate decreases, the cumulative flow rate increases, and the value of coal seam permeability coefficient "a" increases, indicates that the gas drainage efficiency is higher. It can provide theoretical basis for reasonable arrangement of boreholes.