Abstract Thermal damage mechanisms and the characteristics of performance deterioration of a repository host rock is critical for evaluating the potential of an underground coal gasification project. Previously, many studies have primarily focused on the microstructural evolution of various rock types after high-temperature treatment only. However, relatively little is known regarding the coupled thermo-hydro-mechanical (THM) behavior of rock, which is frequently encountered in geo-engineering underground regions with high-temperatures. In this study, using a self-developed universal tester with the ability of THM coupling of high temperature and high pressure, permeability evolution in sandstone under real-time high temperature (20–700 °C) and triaxial stress (hydrostatic pressure = 25 MPa) were observed. The microphysical parameters of these specimens subjected to the THM environment were then measured, and the corresponding morphological evolution processes were also assessed using scanning electron microscopy (SEM) and micro-computed tomography (MCT). Further, for the purpose of contrast, we have also determined the microphysical parameters for the sandstone after heat treatment only. The results show that the evolution of the microscopic structures within the sandstone under the coupled THM condition is vastly different from those subjected to heat treatment only. The experimental results in this study can provide theoretical guidance for the stability of surrounding rock of a combustion cavity during in-situ coal gasification.

中文翻译：

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实时高温作用下热-水-力耦合环境下砂岩渗透率和微观孔隙结构演化及其弱化机制

摘要 储库围岩的热损伤机制和性能劣化特征对于评价煤炭地下气化项目的潜力至关重要。此前，许多研究主要集中在仅经过高温处理后各种岩石类型的显微结构演化。然而，人们对岩石的热-水-机械耦合 (THM) 行为知之甚少，这在高温地质工程地下区域中经常遇到。本研究采用自主研发的具有高温高压THM耦合能力的万能测试仪，实时高温（20-700℃）和三轴应力（静水压力=25 MPa）砂岩渗透率演化) 被观察到。然后测量这些样品在 THM 环境下的微物理参数，并使用扫描电子显微镜 (SEM) 和显微计算机断层扫描 (MCT) 评估相应的形态演变过程。此外，为了对比，我们还确定了仅热处理后砂岩的微物理参数。结果表明，耦合THM条件下砂岩内微观结构的演变与仅经过热处理的情况有很大不同。本研究的实验结果可为原位煤气化过程中燃烧腔围岩的稳定性提供理论指导。并且还使用扫描电子显微镜（SEM）和显微计算机断层扫描（MCT）评估了相应的形态演变过程。此外，为了对比，我们还确定了仅热处理后砂岩的微物理参数。结果表明，耦合THM条件下砂岩内微观结构的演变与仅经过热处理的情况有很大不同。本研究的实验结果可为原位煤气化过程中燃烧腔围岩的稳定性提供理论指导。并且还使用扫描电子显微镜（SEM）和显微计算机断层扫描（MCT）评估了相应的形态演变过程。此外，为了对比，我们还确定了仅热处理后砂岩的微物理参数。结果表明，耦合THM条件下砂岩内微观结构的演变与仅经过热处理的情况有很大不同。本研究的实验结果可为原位煤气化过程中燃烧腔围岩的稳定性提供理论指导。我们还确定了仅经过热处理的砂岩的微物理参数。结果表明，耦合THM条件下砂岩内微观结构的演变与仅经过热处理的情况有很大不同。本研究的实验结果可为原位煤气化过程中燃烧腔围岩的稳定性提供理论指导。我们还确定了仅经过热处理的砂岩的微物理参数。结果表明，耦合THM条件下砂岩内微观结构的演变与仅经过热处理的情况有很大不同。本研究的实验结果可为原位煤气化过程中燃烧腔围岩的稳定性提供理论指导。