(1. Research Institute of Petroleum Exploration and Development，PetroChina，Beijing 100083，China；2. CNPC Key Laboratory of Coal-rock Gas，Langfang，Hebei 065007，China；3. National Energy Shale Gas R&D(Experiment) Center，Langfang，Hebei 065007，China；4. School of Energy Resources，China University of Geosciences(Beijing)，Beijing 100083，
China；5. School of Mechanics and Optoelectronic Physics，Anhui University of Science and Technology，Huainan，
Anhui 232001，China；6. Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines，
Northeastern University，Shenyang，Liaoning 110819，China)
Abstract：To investigate the thermal deformation and failure mechanisms of surrounding rock in medium-deep gasification cavities，the influence of high temperature and thermal stress on the thermal damage of the rock is identified on the basis of the testing of rock samples in the profile of the spontaneous combustion coal seam and the analysis of numerical simulation，the mechanical model of the gasification cavity roof was established based on the structural characteristics of medium-deep UCG cavities. Based on the results of multi-physical field coupling numerical simulation of the surrounding rock，the stress-deformation patterns of the surrounding rock is proposed. Finally，the thermal deformation damage process of surrounding rock is systematically described from three dimensions(rock，roof and surrounding rock). The research results show that：(1) temperature affects the microstructure and permeability of rock，when the temperature is 25 ℃–400 ℃，the percentage of micropores in muddy siltstone increases，when the temperature is 400 ℃–1 000 ℃，the percentage of micropores decreases，the percentage of mesopores increases and macropores begin to appear，when the temperature is more than 1 200 ℃，the percentage of macropores is the largest，and 600 ℃ is the threshold for the increase of permeability. The difference in thermal expansion coefficients of mineral components positively contributes to the tensile thermal stress. Under the joint action of rock thermal physicochemical reaction and thermal stress，the rock thermal damage shows the change rule of slow growth，rapid development and tends to be stable. In the stage of slow growth and stabilization phase，the thermophysical-chemical reaction is dominant，and in the stage of rapid development，the thermophysical-chemical reaction and thermal stress play a joint role. (2) Compared with the assumption of the beam model，the thin plate model of the gasification cavity roof is more consistent with the characteristics of the gasification cavity of medium-deep coal. After the roof meets the instability condition，the roof will have the destructive process of small-scale collapse of solid support model，large-scale collapse of simply support model, and the arch structure tends to be stabilized in sequence. (3) The surrounding rock in the gasification cavity shows a stress deformation pattern of“three deformation characteristic zones and five stress characteristic zones”，and the multi-field coupling effect leads to the increase of the scope of the“butterfly-shaped”shear plastic zone. The tensile damage mainly occurs around the gasification cavity，the top and bottom of the cavity are deformed downward and upward respectively，and the vertical stress of the surrounding rock on both sides of the gasification cavity increases by 30 %. The development height of the shear plastic zone in the overlying rock of the gasification cavity is generally 2–5 times of the coal thickness，and it should be ensured that the water barrier in the upper part of the coal seam meets the thickness requirement when selecting the site. The research results are of theoretical significance for the safe site selection of underground gasification of medium-deep coal.
[1] 邹才能，陈艳鹏，孔令峰，等. 煤炭地下气化及对中国天然气发展的战略意义[J]. 石油勘探与开发，2019，46(2)：195–204.(ZOU Caineng，CHEN Yanpeng，KONG Lingfeng，et al. Underground coal gasification and its strategic significance to the development of natural gas industry in China[J]. Petroleum Exploration and Development，2019，46(2)：195–204.(in Chinese))
[2] PERKINS G. Underground coal gasification-Part I：Field demonstrations and process performance[J]. Progress in Energy and Combustion Science，2018，67：158–187.
[3] BLINDERMAN M S，KLIMENKO A Y. Underground coal gasification and combustion[M]. Duxford：Woodhead Publishing，2018：125–151.
[4] OTTO C，KEMPKA T. Thermo-mechanical simulations of rock behavior in underground coal gasification show negligible impact of temperature-dependent parameters on permeability Changes[J]. Energies，2015，8(6)：5 800–5 827.
[5] NAJAFI M，JALALI S M E，KHALOKAKAIE R. Thermal-mechanical-numerical analysis of stress distribution in the vicinity of underground coal gasification(UCG) panels[J]. International Journal of Coal Geology，2014，134/135：1–16.
[6] KASANI H A，CHALATURNYK R J. Coupled reservoir and geomechanical simulation for a deep underground coal gasification project[J]. Journal of Natural Gas Science and Engineering，2017，37：487–501.
[7] SHENG Y，BENDEREV A，BUKOLSKA D，et al. Interdisciplinary studies on the technical and economic feasibility of deep underground coal gasification with CO2 storage in bulgaria[J]. Mitigation and Adaptation Strategies for Global Change，2016，21(4)：595–627.
[8] ELAHI S M，NASSIR M，CHEN Z. Effect of various coal constitutive models on coupled thermo-mechanical modeling of underground coal gasification[J]. Journal of Petroleum Science and Engineering，2017，154：469–478.
[9] 陆银龙，王连国，唐芙蓉，等. 煤炭地下气化过程中温度–应力耦合作用下燃空区覆岩裂隙演化规律[J]. 煤炭学报，2012，37(8)： 1 292–1 298.(LU Yinlong，WANG Lianguo，TANG Furong，et al. Fracture evolution of overlying strata over combustion cavity under thermal-mechanical interaction during underground coal gasification[J]. Journal of China Coal Society，2012，37(8)：1 292–1 298.(in Chinese))
[10] 辛 林，程卫民，王 刚，等. 煤炭地下气化多层热弹性基础梁模型及其应用[J]. 岩石力学与工程学报，2016，35(6)：1 233–1 244. (XIN Lin，CHENG Weimin，WANG Gang，et al. Multi-layer thermoelastic foundation beam model of UCG and its application[J]. Chinese Journal of Rock Mechanics and Engineering，2016，35(6)：1 233–1 244.(in Chinese))
[11] 黄温钢，王作棠，夏元平，等. 煤炭地下气化热–力耦合作用下条带开采数值模拟研究[J]. 煤炭科学技术，2022，50(8)：16–23. (HUANG Wengang，WANG Zuotang，XIA Yuanping，et al. Numerical simulation of strip mining under thermal-mechanical coupling of underground coal gasification[J]. Coal Science and Technology，2022，50(8)：16–23.(in Chinese))
[12] 刘洪涛. 富氧CO2煤炭地下气化过程试验与模拟研究[博士学位论文][D]. 武汉：华中科技大学，2019.(LIU Hongtao.Experimental and numerical simulation study of CO2-Oxy underground coal gasification process[Ph. D. Thesis][D]. Wuhan：Huazhong University of Science and Technology，2019.(in Chinese))
[13] 席建奋. 煤炭地下气化过程特征场演化规律研究[博士学位论文][D]. 北京：中国矿业大学(北京)，2016.(XI Jianfen. Study on the evolution law of characteristic fields in the context of underground coal gasification[Ph. D. Thesis][D]. Beijing：China University of Mining and Technology(Beijing)，2016.(in Chinese))
[14] 张华磊，赵鲲鹏，王连国，等. 煤炭地下气化燃空区覆岩移动规律研究[J]. 安全与环境学报，2016，16(6)：89–92.(ZHANG Hualei，ZHAO Kunpeng，WANG Lianguo，et al. On the migrating regularity of the overlying strata in the combustible space area in the underground coal gasification[J]. Journal of Safety and Environment，2016，16(6)：89–92.(in Chinese))
[15] 刘建明. 煤炭地下气化燃空区扩展及顶板稳定性研究[硕士学位论文][D]. 徐州：中国矿业大学，2014.(LIU Jianming. Study on the combustion cavity growth and stability of the roof during underground coal gasification[M. S. Thesis][D]. Xuzhou：China University of Mining and Technology，2014.(in Chinese))
[16] 董志浩. 煤炭地下气化覆岩高温损伤与评估研究[硕士学位论文][D]. 徐州：中国矿业大学，2020.(DONG Zhihao. Study on thermal damage and evaluation of overburden rock in underground coal gasification[M. S. Thesis][D]. Xuzhou：China University of Mining and Technology，2020.(in Chinese))
[17] 戴永浩. 非饱和板岩细观试验与本构模型研究[博士学位论文][D]. 武汉：中国科学院武汉岩土力学研究所，2006.(DAI Yonghao. CT testing analysis and constitutive model study of unsaturated slates[Ph. D. Thesis][D]. Wuhan：Wuhan Institute of Rock and Soil Mechanics，Chinese Academy of Sciences，2006.(in Chinese))
[18] NAJAFI M，JALALI S M E，KALOKAKAIE R，et al. Prediction of cavity growth rate during underground coal gasification using multiple regression analysis[J]. International Journal of Coal Science and Technology，2015，2(4)：318–324.
[19] DAGGUPATI S，MANDAPATI R N，MAHAJANI S M，et al. Laboratory studies on combustion cavity growth in lignite coal blocks in the context of underground coal gasification[J]. Energy，2010，35(6)：2 374–2 386.
[20] PRABU V，JAYANYTI S. Simulation of cavity formation in underground coal gasification using bore hole combustion experiments[J]. Energy，2011，36(10)：5 854–5 864.
[21] 徐芝纶. 弹性力学简明教程[M]. 北京：高等教育出版社，2002：249–253.(XU Zhirong. A concise course in elastic mechanics[M]. Beijing：Higher Education Press，2002：249–253.(in Chinese))
[22] 刘潇鹏. 煤炭地下气化高温烧变围岩移动破坏机制研究[博士学位论文][D]. 徐州：中国矿业大学，2019.(LIU Xiaopeng. Study on high temperature burnt surrounding rock movement and failure mechanism in UCG[Ph. D. Thesis][D]. Xuzhou：China University of Mining and Technology，2019.(in Chinese))
[23] 潘显涛. 考虑温度修正项的薄板壳结构优化设计[硕士学位论文][D]. 大连：大连理工大学.(PAN Xiantao. The optimization of thin thermal plate and shell structures considering temperature correction[M. S. Thesis][D]. Dalian：Dalian University of Technology，2018.(in Chinese))
[24] 李维特，黄保海，毕仲波. 热应力理论分析及应用[M]. 北京：中国电力出版社，2004：66–73.(LI Weite，HUANG Baohai，BI Zhongbo. Thermal stress theory analysis and application[M]. Beijing：China Electric Power Press，2004：66–73.(in Chinese))
[25] 王作棠，钱鸣高. 顶初次来压步距的计算预测法[J]. 中国矿业大学学报，1989，18(2)：9–18.(WANG Zuotang，QIAN Minggao. The calculating method of the first weighting span of main roof[J]. Journal of China University of Mining and Technology，1989，18(2)：9–18.(in Chinese))
[26] 东 振，任 博，陈艳鹏，等. 中深层煤炭地下气化的气化腔安全宽度计算方法[J]. 煤炭科学技术，2024，52(2)：183–193.(DONG Zhen，REN Bo，CHEN Yanpeng，et al. Calculation method of safe width of gasification cavity for medium-deep underground coal gasification[J]. Coal Science and Technology，2024，52(2)：183–193.(in Chinese))
2025, Vol. 44 
