煤炭地下气化是目前温度最高（超过1200 ℃）的化石能源非常规开发方式，中深层（本文指埋深800～1500 m）煤炭地下气化在提高气化压力、降低地质安全风险方面优势明显，科学预测气化腔安全宽度对保障气化稳定运行十分重要，由于目前基于可控注入点后退（CRIP）工艺的气化腔安全宽度计算方法尚未建立，为保证现场试验顺利实施，需要开展针对性研究。气化腔顶板“裸露”在气化腔后会受到高温影响，通过数值模拟方法研究了压应力约束条件下岩石内部热应力产生位置以及颗粒、基质热膨胀系数差异对热应力大小的影响规律，结合高温处理后的岩石电镜扫描结果，查明了高温下岩石热损伤机理。根据CRIP气化工艺造腔特点，建立了考虑高温影响的气化腔顶板薄板模型，结合“关键层”理论提出了气化腔安全宽度计算方法。研究表明：岩石热损伤是岩石物理化学反应与热应力互相促进、共同作用的结果，高温下岩石发生不规则变形，岩石热损伤引起的微观结构变化是导致岩石力学性质、物理性质变化的根本原因。岩石的最大拉张热应力出现在颗粒界面或热膨胀系数较小的颗粒中，颗粒与基质热膨胀系数比值在[0.01～1）时，最大拉张热应力随颗粒热膨胀系数减小而快速增加。泥岩加热到200 ℃时开始出现微裂隙；加热到400 ℃时裂隙发育更加明显，主要是沿颗粒边缘破裂；加热到600～800 ℃时，裂隙数量增多、尺寸变大；加热到1000 ℃时，除出现较大裂隙外，还产生了大量孔隙；1200 ℃时裂隙连通性明显增加，气孔发育较大。由于高温的影响，薄板模型的步距准数不再是定值，需要根据气化腔顶板热破坏范围与顶板硬岩层的空间位置关系确定具体数值。气化腔安全宽度受温度影响，在研究算例中，砂岩顶板在35、1000 ℃时安全宽度计算结果分别为34.3 m和14.1 m，相差达58.9%，泥岩顶板在35、1000 ℃时安全宽度计算结果分别为16.7 m和15.9 m，相差4.8%。最后从降低顶板垮落风险、有利于气化控制角度，提出了煤层纵向靶区位置的确定方法，当煤层厚度超过气化腔安全宽度一半时，建议将水平井纵向靶区设计在距离煤顶不超过气化腔安全宽度一半的位置。

Underground coal gasification is currently the highest temperature (over 1200 °C) unconventional fossil energy development method. Medium-deep (specifically 800～1500 m) underground coal gasification has obvious advantages in improving gasification pressure and reducing geological safety risks. Scientific prediction of safe width of gasification cavity is important for ensuring stable operation of gasification. Since the calculation method of safe width of gasification cavity based on controlled injection point retreat (CRIP) process has not been established, targeted research is needed to ensure the smooth implementation of field tests. Once the top of the gasification cavity is “exposed” behind the gasification cavity, it will be affected by high temperature. The position of thermal stress generation inside the rock and the influence law of the difference of thermal expansion coefficient between particles and matrix on the thermal stress size are studied by numerical simulation method under the constraint condition of compressive stress. Combined with the scanning electron microscope results of rock after high temperature treatment, the thermal damage mechanism of rock under high temperature is clarified. Based on the CRIP gasification process, a thin plate model of the gasification cavity roof that takes into account the high temperature effect is established, and a method for calculating the safe width of the gasification cavity is proposed based on the “key layer” theory. The study reveals that rock thermal damage is caused by the interaction and synergy of rock physicochemical reactions and thermal stress, and that rock undergoes irregular deformation at high temperatures. The changes in rock microstructure due to thermal damage are the fundamental cause of the changes in rock mechanical and physical properties. The maximum tensile thermal stress in rock occurs at the grain boundary or in grains with a smaller thermal expansion coefficient. When the ratio of the thermal expansion coefficient of the grain to that of the matrix is in the range of [0.01−1), the maximum tensile thermal stress increases rapidly as the thermal expansion coefficient of the grain decreases. Mudstone develops microcracks when heated to 200 °C; the cracks become more evident when heated to 400 °C, mainly occurring along the grain boundaries; the cracks increase in number and size when heated to 600−800 °C; large cracks and numerous pores form when heated to 1000 °C; the cracks become more interconnected and the pores enlarge at 1200 °C. The high temperature effect causes the step constant of the thin plate model to vary, and its value depends on the spatial relationship between the extent of thermal damage on the gasification cavity roof and the location of the hard rock layer. The temperature also affects the safe width of gasification cavity. In the example, the safe widths of sandstone roof at 35 °C and 1000 °C are 34.3 m and 14.1 m respectively, with a 58.9% difference, while the safe widths of mudstone roof at 35 °C and 1000 °C are 16.7 m and 15.9 m respectively, with a 4.8% difference. Lastly, to reduce the risk of roof collapse and improve gasification control, a method for determining the longitudinal target area of coal seam is proposed. When the coal seam thickness is more than half of the gasification cavity safe width, it is suggested to design the longitudinal target area of horizontal well within half of the gasification cavity safe width from the coal top.