钻孔不同变形失稳时抽采负压分布规律研究

Research on negative pressure distribution laws of drainage borehole with different deformation and instability

  • 摘要: 针对钻孔内瓦斯流动变质量流的特点及钻孔变形情况,建立了综合考虑钻孔负压动态变化的瓦斯抽采固-流耦合模型,并以新安煤矿为例,采用多物理场耦合软件Comsol Multiphysics对钻孔不同变形失稳时抽采负压分布进行了数值模拟研究。结果表明:① 完整孔孔口、孔底附近煤层瓦斯分布基本相同,抽采负压损失较小。② 钻孔塌孔时,仅塌孔段附近煤层瓦斯分布与完整孔稍有不同,总负压损失比完整孔大,但与孔口负压相比仍较小。③ 钻孔堵孔时,孔口、孔底周围煤层瓦斯分布差异巨大,钻孔有效抽采长度缩短,堵孔段附近煤层出现抽采空白带;完整段抽采压力变化相对较小且仍为负压,堵孔段抽采压力变成正值,且越靠近钻孔底部越接近附近煤层瓦斯压力。现场测试结果表明完整孔抽采负压损失较小,且随抽采时间的延长而变小,与数值模拟结果一致。

     

    Abstract: A solid-flow coupling model of gas drainage was established which synthetically considered dynamic variation of negative pressure of drainage borehole according to variation mass flow characteristic of gas flowing in the borehole and its deformation situation. Taking Xi'an Coal Mine as an example, distribution of negative pressure of drainage borehole with different deformation and instability were numerically simulated by use of multi physical fields coupling software Comsol Multiphysics. The simulation results show that: ① Coal-seam gas distribution near hole collar and hole bottom of complete borehole is almost the same. Negative pressure loss is little. ② When borehole is collapsed, coal-seam gas distribution around collapsed section is only slightly different from that in the complete borehole. The total negative pressure loss is larger than that in the complete borehole, but still lower than that at hole collar. ③ When borehole is blocked, the difference of coal-seam gas pressure between hole collar and hole bottom is significant, effective drainage length of borehole reduces, and blank tape will appear in coal-seam near the blocked section. Drainage pressure in the complete section varies little and is still negative pressure, while that in the blocked section becomes positive. What's more, the drainage pressure in the blocked section is close to coal-seam gas pressure gradually with approach to hole bottom. The field test results show that the negative pressure loss of complete borehole is small and decreases with prolongation of drainage time, which is consistent with numerical simulation results.

     

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