Simulation study on effective influencing radius of submerged water jet forgas-drainage in low permeability coal seam

Water jet flushing is an effective gas drainage technology suitable for the soft and low permeability coal seams. The No.1075 drainage roadway in Liulong Coalmine is located at the same level as the No.1075 transportation roadway. In order to ensure the outburst control range of the lower ribs, it is inevitable that submerged jet conditions might be caused by the downward drilling holes.Based on the gas storage parameters of No. 7 coal seam and the target of extraction, the Darcy’s Law and the mass conservation law, as well as by considering the Klinkenberg Effect, the combination of theoretical calculation and COMSOL numerical simulation was used to establish the fluid-solid coupling model of gas drainage, and the influence of coal expansion on the effective influence radius under different extraction time was also discussed. The results show that the effective influence radius of borehole increases with the increase of drainage time and the increase of coal expansion. However, when the length of the extraction reaches the threshold, the increase in the effective radius of the reaming is significantly weakened as the gas flow is attenuated. Therefore, it is determined that the single-hole coal expansion is 1.03 t/m under the submerged jet condition of No.7 coal seam. The effective influencing radius is about 3 m and the borehole row spacing is 5 m×5 m. After the 3-month of pre-drainage cycle, it was tested to achieve a good effect of eliminating gas outburst, which alleviated the mining succession caused by the incomplete gas control.