逆断层区域采动煤体渗透率模型构建及应用

    Construction and application of coal permeability model in reverse fault area

    • 摘要: 逆断层区域构造应力与地应力叠加,挤压应力形成的力学特点导致瓦斯积聚,煤体渗透率发生改变,采掘期间容易引起瓦斯涌出异常,甚至发生煤与瓦斯突出事故。为了掌握逆断层区域采动煤体渗透率演化规律,首先开展了逆断层区域采动煤体渗透率测试试验,通过应力加卸载方式模拟逆断层影响下采动煤体应力变化,得出:在峰前阶段,煤体压缩、裂隙闭合,煤体渗透率降低;峰后阶段,煤体应力达到峰值,原有裂隙扩展连通,同时产生新裂隙并出现损伤,煤体渗透率增加并达到最大值;第1组加载方案模拟工作面前方煤体应力集中系数逐渐增大条件下,M1、M2和M3煤样的渗透率分别提高了22.1%、28.0%和36.7%,第2组加载方案模拟模拟工作面前方煤体应力集中系数先增大后减小条件下,M4、M5和M6煤样的渗透率分别提高了23.6%、37.2%和20.8%。然后结合煤体渗透率试验结果,建立了逆断层影响下采动煤体渗透率表征模型,推导出煤体峰前和峰后阶段渗透率计算表达式,用瓦斯吸附/解吸造成煤体体积应变的函数来表示吸附/解吸对煤体裂隙体积的影响,从而更加准确的表征逆断层影响下采动煤体渗透率。最后将渗透率模型导入COSMOL软件,结合新春煤矿1503工作面F4逆断层现场情况进行模拟计算,得出随着与逆断层距离减小,煤体应力集中系数增大的情况下,煤体瓦斯压力和渗透率峰值均逐渐增大,容易造成瓦斯涌出异常,需要加强瓦斯浓度监测。

       

      Abstract: The superposition of tectonic stress and geostress in the reverse fault area, and the mechanical characteristics formed by compressive stress lead to gas accumulation, change of coal permeability, and easy to cause abnormal gas emission during mining, even coal and gas outburst accidents. In order to master the evolution law of the permeability of coal bodies mined in the reverse fault area, firstly, the permeability test of coal bodies mined in the reverse fault area was carried out, and the stress change of coal bodies mined under the influence of reverse faults was simulated by stress loading and unloading. It was concluded that in the pre peak stage, the coal body compressed, the cracks closed, and the permeability of coal bodies decreased; in the post peak stage, the coal stress reaches the peak, the original fractures expand and connect, while new fractures are generated and damaged, and the coal permeability increases to the maximum. The first loading scheme simulates that the permeability of coal samples M1, M2 and M3 increases by 22.1%, 28.0% and 36.7% respectively when the stress concentration factor of coal in front of the workingface increases gradually; the second loading scheme simulates that the permeability of coal samples M4, M5 and M6 increases by 23.6%, 37.2% and 20.8% respectively when the stress concentration factor of coal in front of the working face increases first and then decreases. Then, combined with the permeability test results of coal, a characterization model of coal permeability under the influence of reverse fault is established, and the calculation expressions of coal permeability at the pre peak and post peak stages are derived. The function of coal volume strain caused by gas adsorption/desorption is used to express the impact of adsorption/desorption on coal fracture volume, so as to more accurately characterize the coal permeability under the influence of reverse fault. Finally, the permeability model is imported into COSMOL software, and combined with the on-site situation of F4 reverse fault in 1503 working face of Xinchun Coal Mine, the simulation calculation is carried out. It is concluded that with the decrease of the distance from the reverse fault and the increase of the stress concentration coefficient of the coal, the gas pressure and the peak permeability of the coal are gradually increasing, which is easy to cause abnormal gas emission, and the gas concentration monitoring needs to be strengthened.

       

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