高级检索

基于煤层钻孔卸压破坏的瓦斯涌出规律研究

Study on outburst patterns of coal mine gas based on pressure relief fracturing in coal seam boreholes

  • 摘要: 为了深入研究钻孔钻进过程中煤体松动破坏演化作用下的钻孔瓦斯涌出规律,基于弹性力学理论和黏聚力损伤原理,通过理论推导,建立了包含黏聚力软化参数的塑性区半径和破碎区半径解析表达式,进而构建了钻进扰动作用下塑性区渗流与破碎区及钻屑放散的钻孔瓦斯涌出动态数学模型。研究以晋城矿区里必煤矿3号煤层钻孔为工程背景,采用理论分析、数值模拟和现场试验相结合的综合研究方法,分析了钻孔钻进过程中塑性区及破碎区的随钻演化规律及其作用下的随钻瓦斯涌出规律。研究结果表明:钻孔围岩塑性区和破碎区体积随钻进距离呈显著线性增长趋势,其中塑性区体积扩展速率达到破碎区的5倍;钻孔扰动破坏主要集中于孔壁附近区域,由于塑性区内裂隙网络发育导致渗透率发生显著改变,孔壁瓦斯渗流量随钻进距离呈0.47倍线性增长规律,而未发生松动破坏的孔底渗流量则维持在较低水平;破碎区瓦斯放散量构成钻孔瓦斯涌出的主要来源,由于其时间衰减特性,当钻进距离由1 m增至8 m时,其占比从96%逐渐下降至90%,反映破碎区及钻屑瓦斯放散对钻孔瓦斯涌出贡献随钻弱化特性;现场工业试验数据与数值模拟结果高度吻合,二者得到的钻孔瓦斯涌出量−钻进距离关系均符合指数为0.46的指数函数,相对误差仅为11%。

     

    Abstract: To investigate the patterns of gas outburst from drill holes under the influence of coal mass loosening and fragmentation during drilling operations, this study is based on elasticity theory and cohesive strength damage principles. Through theoretical derivation, analytical expressions for the radius of the plastic zone and the radius of the fractured zone, incorporating cohesive strength softening parameters, were established. Subsequently, a dynamic mathematical model of gas outburst in drill holes under drilling disturbance was constructed, incorporating fluid flow in the plastic zone, gas release in the fractured zone, and drill cuttings dispersion. The study took the drilling holes in the No. 3 coal seam of the Libi Coal Mine in the Jincheng Mining Area as the engineering background. A comprehensive research method combining theoretical analysis, numerical simulation, and field experiments was adopted to analyze the evolution patterns of the plastic zone and fractured zone during drilling operations and the corresponding methane outburst patterns under their influence. The research results indicate: The volumes of the plastic zone and fractured zone in the borehole surrounding rock exhibit a significant linear growth trend with drilling distance, with the expansion rate of the plastic zone reaching five times that of the fractured zone; Drilling disturbance and damage are primarily concentrated in the vicinity of the borehole wall. Due to the development of a fracture network within the plastic zone, permeability undergoes significant changes. The methane seepage flow rate at the borehole wall exhibits a linear growth pattern of 0.47 times with drilling distance, while the seepage flow rate at the borehole bottom, which has undergone loosening and damage, remains at a relatively low level; Methane release from the fractured zone constitutes the primary source of methane outflow from the borehole. Due to its time-dependent decay characteristics, when the drilling distance increases from 1 m to 8 m, its proportion decreases gradually from 96% to 90%, reflecting the weakening contribution of methane release from the fractured zone and drill cuttings to borehole methane outflow with increasing drilling distance; Field industrial test data and numerical simulation results are highly consistent, with both yielding a borehole gas outflow-drilling distance relationship that conforms to an exponential function with an exponent of 0.46, and a relative error of only 11%.

     

/

返回文章
返回