State Key Laboratory Cultivation Base for Gas Geology and Gas Control, Henan Polytechnic University, Jiaozuo, China.
School of Safety Science and Engineering, Henan Polytechnic University, Jiaozuo, Henan, China.
PLoS One. 2020 May 21;15(5):e0232182. doi: 10.1371/journal.pone.0232182. eCollection 2020.
To understand the effects of thermal shock on microcrack propagation and permeability in coal, thermal shock tests were conducted on coal specimens by using a constant temperature drying oven (105 °C) and a SLX program controlled cryogenic tank. The growth and propagation of microcracks were measured with computer tomography (CT) scanning and scanning electron microscope (SEM) tests. Results showed that thermal shocks improved the permeability of coal significantly. Notably, the permeability of coal after thermal shocks increased from 211.31% to 368.99% and was positively correlated with temperature difference. CT scanning images revealed that thermal shocks increased the crack number, crack volume and crack width as well as smoothened and widened the gas flow paths, thereby enhancing coal permeability. Moreover, SEM images showed that heating-cooling shocks created more new microcracks, forming more complex crack propagation paths and better connectivity among microcracks in coal compared to cooling shocks. We proposed a crack propagation criterion for coal to explain the mechanism of crack failure and propagation during thermal shocks. Our experiment results and theoretical analysis indicate that the heating-cooling shock is more effective in damaging and breaking coal than the cooling shock. Thus, it can be used as an alternative approach to enhance coal permeability in the production of coalbed methane (CBM).
为了理解热冲击对煤体微裂纹扩展和渗透性的影响，使用恒温干燥箱（105°C）和 SLX 程控低温槽对煤样进行了热冲击试验。通过计算机断层扫描（CT）和扫描电子显微镜（SEM）测试测量了微裂纹的生长和扩展。结果表明，热冲击显著提高了煤的渗透性。值得注意的是，热冲击后煤的渗透率从 211.31%增加到 368.99%，与温差呈正相关。CT 扫描图像显示，热冲击增加了裂纹数量、裂纹体积和裂纹宽度，并使气流路径更加平滑和变宽，从而提高了煤的渗透性。此外，SEM 图像显示，与冷却冲击相比，加热-冷却冲击在煤中产生了更多的新微裂纹，形成了更复杂的裂纹扩展路径和微裂纹之间更好的连通性。我们提出了一个煤的裂纹扩展准则来解释热冲击过程中裂纹失效和扩展的机制。我们的实验结果和理论分析表明，与冷却冲击相比，加热-冷却冲击更有效地破坏和破碎煤体。因此，它可以作为一种替代方法，用于提高煤层气（CBM）生产中的煤体渗透性。
