低透煤层瓦斯超前排放钻孔布置方式优化研究

Optimization of over-emission drilling arrangement for low-permeability coal seams

目的为有效解决低透气性煤层瓦斯突出问题,有效消除阵列布孔方式带来的瓦斯排放盲区以及对角圆相切布孔方式造成的钻孔数量增加、重复排放等问题。方法通过理论分析,在超前排放钻孔有效排放半径一定的情况下提出阵列菱形法优化超前排放孔的布置方式(R为有效排放半径,煤层走向排放孔的间距为√3R),其钻孔数量约为对角圆相切法的3/4,重复排放面积减少至11%,减少了对角圆相切布孔方式的重复排放面积,减少了钻孔的数量。结果运用COMSOL Multiphysics对阵列菱形法布孔方式进行数值模拟运算,结果表明,阵列菱形法布孔方式排放20 d后,钻孔有效排放半径内整体瓦斯压力低于0.5 MPa,排放100 d后瓦斯压力低于0.30 MPa,卸压效果优于对角圆相切布孔方式的。将阵列法和对角圆相切法两种布孔方式排放100 d时钻孔周围的瓦斯压力分布情况与阵列菱形法布孔方式排放20 d时的分布情况交叉对比,发现阵列菱形法布孔方式卸压速率更快,卸压范围更广。结论提出阵列菱形法设计钻孔布孔方式,并运用COMSOL Multiphysics对3种钻孔布孔方式的卸压情况进行数值模拟运算,对比发现,阵列菱形法钻孔布孔方式比阵列法和对角圆相切法布孔方式更具优势,且在相同时间内卸压速率更快、卸压范围更广,对低透煤层预防瓦斯突出具有重要的意义。

Objective In order to effectively solve the problem of gas protrusion in low permeability coal seam,the blind area of gas discharge brought by array hole arrangement method and the problems of increasing the number of boreholes and duplicate discharge caused by diagonal circle tangential hole arrangement method are effectively eliminated.Methods Through theoretical analysis,the array rhombus method is proposed to optimize the arrangement of over-emission holes under the condition that the effective radius of over-emission holes is certain(R is the effective emission radius,and the spacing of coal seam heading emission holes is √3R),and the number of holes is about 3/4 of that of diagonal circular tangent method,and the duplicated emission area is reduced to 11%,which reduces the duplicated emission area of diagonal circular tangent method and the number of holes.Results The results show that the overall gas pressure within the effective discharge radius of the borehole is less than 0.5 MPa after 20 d of discharge by the array diamond method and less than 0.3 MPa,after 100 d of discharge by the array diamond method,which is better than the diagonal circular tangent method in terms of pressure relief.Cross comparison of the gas pressure distribution around the borehole at 100 d of discharge by array method and diagonal circle tangent method with the gas pressure distribution around the borehole at 20 d of discharge by array rhombus method shows that the pressure relief rate of array rhombus method is faster and the pressure relief range is wider.Conclusion Put forward the array rhombus method design drilling holes,and use the COMSOL Multiphysics for three drilling pressure discharge numerical simulation operation,by comparing found the array diamond drilling way compared with array and diagonal circular method more advantages,and in the same time pressure discharge rate faster,wider range,for low permeability coal seam prevention gas outburst is of great significance.