低渗煤层淹没射流扩孔瓦斯抽采有效影响半径模拟研究

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

水射流扩孔是一种适用于松软低透煤层行之有效的瓦斯强化抽采技术。由于六龙煤矿1075抽放巷与被掩护掘进的1075工作面运输巷位于同一水平,为保证其下帮的消突控制范围,不可避免地出现下向钻孔布孔造成淹没射流条件。为考察淹没射流条件下的瓦斯抽采有效影响半径,根据7号煤层瓦斯赋存参数及抽采达标目标,并基于瓦斯流动理论、达西定律和质量守恒定律,在考虑克林伯格效应条件下,采用理论计算与COMSOL数值模拟相结合的方法建立瓦斯抽采流固耦合模型,探讨了不同抽采时长下扩煤量对有效影响半径的影响。结果表明:抽采有效影响半径随抽采时间增长和扩煤量的增加而逐渐增大,但当抽采时长增加到阈值时,随着瓦斯流量的衰减,扩孔有效影响半径的增长幅度明显减弱。由此确定了7号煤层在淹没射流条件下,单孔扩煤量1.03 t/m为宜,此时的扩孔有效影响半径为3.03 m,布孔间排距为5 m×5 m。3个月预抽后经检验达到了良好的消突效果,缓解了该矿因瓦斯治理不到位造成的采掘接替紧张。

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.