Dynamic evolution of rock mechanical properties of coal seam roofs under thermal loading: A case study of the Baikouquan area, Xinjiang, China

Authors

SUN Fangfang, Xinjiang Key Laboratory for Geodynamic Processes and Metallogenic Prognosis of the Central Asian Orogenic Belt, Xinjiang University, Urumqi 830047, ChinaFollow
LI Xin, Xinjiang Key Laboratory for Geodynamic Processes and Metallogenic Prognosis of the Central Asian Orogenic Belt, Xinjiang University, Urumqi 830047, China; Huairou Laboratory, Xinjiang Research Institute, Urumqi 830011, ChinaFollow
SANG Shuxun, Xinjiang Key Laboratory for Geodynamic Processes and Metallogenic Prognosis of the Central Asian Orogenic Belt, Xinjiang University, Urumqi 830047, China
QU Huailin, Xinjiang Oilfield Company, Karamay 834000, China
YANG Shuguang, Geological Research Institute, Xinjiang Uyghur Autonomous Region, Urumqi 830091, China
WEI Bo, Xinjiang Yaxin Coalbed Methane Investment and Development Group Co., Ltd., Urumqi 830009, China
WANG Ziqiang, Huairou Laboratory, Xinjiang Research Institute, Urumqi 830011, China
ZHANG Bin, Huairou Laboratory, Xinjiang Research Institute, Urumqi 830011, China
CHEN Yanpeng, Huairou Laboratory, Xinjiang Research Institute, Urumqi 830011, China
TIAN Wenling, Xinjiang Key Laboratory for Geodynamic Processes and Metallogenic Prognosis of the Central Asian Orogenic Belt, Xinjiang University, Urumqi 830047, China

Abstract

Objective Underground coal gasification (UCG) represents a key technology for the clean utilization of coal resources. However, during the UCG process, thermal damage to surrounding rocks under thermal effects directly affects the stability and engineering safety of gasification channels.Methods To address the thermal damage to surrounding rocks during UCG, this study investigated the silty mudstones and coarse-grained sandstones in the coal seam roof of the Xishanyao Formation, Baikouquan area, Xinjiang. Through high-temperature uniaxial compression experiments, combined with characterization methods like X-ray diffraction (XRD) and scanning electron microscopy (SEM), this study delved into the dynamic evolutionary patterns of rock mechanical properties and the macro-micro damage differentiation of both rock types under thermal effects. Moreover, this study quantified the critical threshold of thermal damage and analyzed the synergistic damage-inducing mechanisms.Results and Conclusions In terms of rock mechanical properties, the silty mudstones experienced thermal strengthening (25 ℃ to <400 ℃), thermal damage (400‒600 ℃), and thermal sintering (>600 ℃ to ≤800 ℃) stages, with peak stresses showing an increase of 36.24%, a decrease of 45.99%, and a surge of 75.20%, respectively. In contrast, the coarse-grained sandstones experienced the dehydration weakening (25 ℃ to <200 ℃), thermal expansion-induced compaction (200 ℃ to <400 ℃), and thermal damage (400‒800 ℃) stages, with peak stresses decreasing by 50.74%, 45.16%, and 52.78%, respectively. At 400‒600 ℃, the elastic moduli of the silty mudstones and coarse-grained sandstones significantly decreased to 58.87% and 69.42%, respectively, and their damage variables surged to 0.59 and 0.69, respectively. Concerning the controlling mechanisms in the three evolutionary stages, the silty mudstones were subjected to the synergistic effects of thermal evaporation and expansion, the synergistic destruction of thermal cracking and mineral phase transitions, and the sintering reaction process, sequentially. In contrast, for the coarse-grained sandstones, the controlling mechanisms in the three stages were dominated by thermal evaporation, thermal expansion, and thermal cracking - mineral phase transition in sequence. A temperature of 400℃ was identified as the initial threshold for the synergistic destruction by thermal cracking and mineral phase transitions (e.g., α–β phase transition of quartz, and kaolinite dehydroxylation) of both rock types. Beyond this threshold, damage to the transition zone of surrounding rocks accelerated. Therefore, in engineering practice, the temperatures of key roofs with sealing capacities in oxidation zones must be controlled below 400℃ to mitigate the rock instability risk. Overall, this study determines the thermal damage threshold and rock mechanical differentiation mechanisms of surrounding rocks under UCG-induced thermal effects in the Baikouquan area, providing key temperature-sensitive parameters and stability control criteria for the safe design of gasification channels.

Keywords

underground coal gasification (UCG), mechanical property under real-time high temperature, thermal damage threshold, dynamic response mechanism, surrounding rock stability, Baikouquan area, northwestern margin of the Junggar Basin

DOI

10.12363/issn.1001-1986.25.08.0621

Recommended Citation

SUN Fangfang, LI Xin, SANG Shuxun, et al. (2026) "Dynamic evolution of rock mechanical properties of coal seam roofs under thermal loading: A case study of the Baikouquan area, Xinjiang, China," Coal Geology & Exploration: Vol. 54: Iss. 3, Article 3.
DOI: 10.12363/issn.1001-1986.25.08.0621
Available at: https://cge.researchcommons.org/journal/vol54/iss3/3

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