地面垂直钻孔预抽特厚煤层瓦斯数值试验与应用

Numerical test and application of gas pre-drainage in an extra-thick seam by using ground vertical boreholes

为解决塔山煤矿高强度开采条件下瓦斯低含量、高涌出的问题,同时为了弥补大型物理实验和现场试验成本高、操作难的缺点,根据该矿8101工作面所属区域煤层的地质和瓦斯赋存条件,确定了数值试验方案,对地面垂直钻孔预抽特厚煤层瓦斯的效果进行优化分析。基于煤岩(体)的孔隙特征,构建了含瓦斯煤岩(体)破裂过程气-固耦合和渗透率-损伤耦合数学本构模型。采用RFPA^(2D)瓦斯分析版软件建立地面钻孔抽放瓦斯的数值计算模型,设置有关简化条件、边界条件和物性参数,通过数值试验得出:地面垂直钻孔的终孔位置布置在煤层底部比较合理;在综合考虑地面垂直钻孔投入成本和瓦斯抽采效果的基础上,确定地面垂直钻孔间距为50～60 m比较合理。同时,由8101工作面地面垂直钻孔抽采煤层瓦斯的实际应用效果分析可知,当地面垂直钻孔的终孔位置布置在煤层底部,且钻孔间距布置为50m时,能够实现良好的瓦斯抽放效果,这也从一定程度上进一步验证了数值试验的合理性和可行性。

This study is to solve the problems of the low content and high gush of gas under high-intensity mining conditions in Tashan coal mine, and to make up the disadvantages of high cost and difficult operation of large-scale physical experiments and field tests. According to the geological and gas occurrence conditions of regional coal seam which covers 8101 working face in Tashan coal mine, numerical testing schemes were designed to optimise and analyse the gas pre-drainage effect in the extremely thick seam by using ground vertical boreholes. Based on the pore characteristics of coal-rock(body), we developed mathematical constitutive models of gas-solid coupling and permeability-damage coupling in the gas-bearing coal-rock(body) rupture process. A numerical model of gas drainage was established by using RFPA2D-Gasflow software, and the relevant physical parameters, simplified initial conditions and boundary conditions were established. The following results can be achieved through the above numerical tests. First, the reasonable borehole bottom location of ground vertical boreholes is at the bottom of coal seam. Then, on the basis of considering the drilling cost and the drainage effect, the reasonable borehole spacing between adjacent ground vertical boreholes is from 50 to 60 m. Meanwhile, the actual application effect of gas extraction by using ground vertical boreholes in 8101 working face demonstrates a good gas drainage effect when the borehole bottom location is at the bottom of coal seam and the borehole spacing is 50 m. To a certain extent, the rationality and feasibility of numerical tests are further verified.