液态CO2−水蒸气循环冲击煤体增透及瓦斯抽采效果模拟

Coal permeability enhancement via cyclic percussion using low-temperature liquid CO2 and high-temperature water vapor and simulations of resultant gas drainage performance

    摘要
  • 摘要:
    目的 为解决液态CO2煤层增透技术应用时煤层内部孔隙水受冷凝结为冰阻塞瓦斯运移通道这一问题，提出液态CO2−高温水蒸气冷热循环冲击煤体增透技术。
    方法 利用低场核磁共振仪、煤岩渗透率自动测试仪、接触角测试仪和三维CT扫描仪分析液态CO2−高温水蒸气冷热循环冲击煤体渗透率演化规律。
    结果和结论 结果表明：(1)液态CO2−高温水蒸气冷热循环冲击煤体T2曲线面积随冷热循环冲击次数增加而增加。(2)煤体渗透率增量与液态CO2−高温水蒸气冷热循环冲击次数指数相关，循环冲击次数增加，煤体渗透性和润湿性均增强。(3)液态CO2−高温水蒸气冷热循环冲击次数达到12次时，渗流孔体积比例增加23.57%，渗透率增加0.009 3×10−3 μm2，接触角减小39.45°。(4)煤体渗透性与渗流孔体积比例、接触角相关，渗流孔体积比例与煤体渗透率正相关，接触角与煤体渗透率指数相关。基于实验研究结果，利用COMSOL软件数值模拟低温液态CO2−高温水蒸气冷热循环冲击煤层工程现场应用。依据试验结果确定恢复到室温25 ℃时的有效作用半径为0.7198 m，以此数据模拟矿井煤层瓦斯抽采，结果显示煤层温度与瓦斯抽采效率成正比。试验及模拟结果揭示了液态CO2−高温水蒸气冷热循环冲击煤体增透技术的现场钻孔布置及瓦斯抽采运移规律，为该技术下一步现场应用提供参考。

     

    Abstract:
    Objective In the application of the coal seam permeability enhancement technique based on liquid CO2, pore water in coal seams freezes due to low temperatures, blocking pathways for gas migration. Hence, this study developed a technique for coal permeability enhancement through cyclic percussion using low-temperature liquid CO2 and high-temperature water vapor (also referred to as the cyclic cold and hot percussion).
    Methods This study delved into the permeability evolutionary patterns of coals under cyclic cold and hot percussion using a low-field nuclear magnetic resonance (NMR) spectrometer, an automatic coal permeability tester, a contact angle tester, and 3D CT scanner.
    Results and Conclusions  Key findings are as follows: (1) The area of the NMR T2 curves of coals subjected to cyclic cold and hot percussion increased with the number of the cold and hot percussion cycles. (2) The incremental coal permeability was exponentially related to the number of cold and hot percussion cycles. The coal permeability and wettability increased with this number. (3) After 12 cold and hot percussion cycles, the pore volume ratio of seepage increased by 23.57%, the permeability increased by 0.009 3×10−3μm2, and the contact angle decreased by 39.45°. (4) The coal permeability was correlated positively with the pore volume ratio of seepage and exponentially related to the contact angle. Based on the experimental results, this study conducted numerical simulations of the field engineering application of the cyclic cold and hot percussion of coal seams using the COMSOL software. The experimental results reveal an effective temperature influence radius of 0.7198 m as the coal seam temperature was restored to room temperature (25 ℃). This effective temperature influence radius was used to simulate gas drainage from coal seams in a coal mine, revealing that the coal seam temperature was directly proportional to the gas extraction efficiency. The experimental and simulation results reveal the on-site borehole arrangement, as well as gas drainage and transport patterns, in the application of the technique for coal permeability enhancement through cyclic cold and hot percussion, providing a reference for subsequent field application of this technique.

     

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