基于热损伤效应的煤层覆岩渗透性演变机制研究

The evolution mechanism of rock permeability with thermal damage is the key technology for underground coal gasification. It is also a hot topic for deep engineering and rock mechanics. Up to now, although the thermal damage characteristics of rock have been studied deeply, the mechanism and critical threshold of high temperature on rock permeability need to be further strengthened. This project intends to use the micro-nano CT scanning and three-dimensional reconstruction technology to build a refined three-dimensional model of rock structure which is considering the effect of thermal damage, and reveal the physical essence of the variation of permeability from the evolution of the three-dimensional structure (especially the development of cracks and pores). Through the microscopic test methods (such as TG / DSC, XRD, XRD, SEM, mercury intrusion and Raman spectroscopy), the microcosmic mechanism of rock thermal damage can be revealed from microstructure, thermodynamics and mineralogy; Based on the permeability test under servo-control condition (which is considering the thermal damage path and confining pressure) and the three-dimensional structural scanning and microscopic characteristics test, the evolution model of rock permeability, which reflects the characteristics of thermal damage, could be established by the servo penetration test of the typical rocks of overlying strata of coal seam (different genesis, mineral composition and structural characteristics), the evolution mechanism of rock permeability with thermal damage could be revealed and the critical temperature threshold for significant changes in permeability will be clarified.

岩石渗透性随热损伤的演变机制是煤炭地下气化急需突破的关键技术，也是深部工程和岩石力学亟待开展的热点。目前对岩石热损伤特征已有了较深入研究，但高温作用对岩石渗透性的影响机制和临界阈值研究仍有待加强。本课题拟利用微纳米CT扫描和三维重构技术，构建考虑热损伤的岩石三维结构精细化模型，从三维结构（尤其是孔裂隙）演变上揭示渗透性变化的物理本质；采用TG/DSC、XRD、XRF、SEM、压汞和拉曼光谱等微观测试方法，从微观结构、热动力学及矿物岩石学等角度阐明热损伤作用下岩石渗透性变化的微观机理；通过考虑热损伤路径和围压的煤层覆岩典型岩石（不同成因、矿物组分、结构特征等）的伺服渗透试验，结合三维结构扫描及微观特性测试，建立反映热损伤特征的岩石渗透性演变模型，揭示岩石渗透性随热损伤的演变机制，识别渗透性发生显著变化的临界温度阈值。

煤炭地下气化是煤炭改革方向的新型采煤工艺，其可以将煤原位转化为可燃气体，变传统采煤为化学采煤，具有安全性高、投资少、效益高、污染少等优点，目前已备受世界关注。煤炭地下气化过程中会产生大量的热，致使围岩遭受不同程度的热损伤作用，从而引起其渗透性发生变化，带来潜在危害和地下环境污染问题。因此，本项目开展的基于热损伤效应的煤层覆岩渗透性演变机制研究不仅具有重要的理论意义，也对相关工程具有深远的应用价值。. 本次研究以砂岩、灰岩和花岗岩为研究对象，首先对其进行不同程度的热损伤作用，然后进行渗透性、波速、电阻率、热导率、强度、应变等物理力学性质测试，得到了高温作用后岩石性能的演变特征，重点分析了渗透率的变化规律；基于扫描电镜、X射线衍射、差热-失重分析、CT扫描等微观测试探究了岩石热损伤及渗透性演变的成因机理；结合微-宏观试验结果，获取了岩石结构损伤在宏观参量上的响应特征。研究结果表明：随着经历温度的升高，砂岩、灰岩和花岗岩的渗透率均逐渐增大，并分别于500℃、400℃和300℃后增大速率明显加快；波速、热导率、单轴抗压强度、弹性模量均逐渐减小；300-500℃是岩石热损伤和性能演变的一个临界温度阈值。岩石微观结构在较低温度时的变化主要由物理反应造成，在较高温度时主要由矿物分解、热应力、熔融作用等物理化学反应共同控制。