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<p>The combined effects of temperature and bedding structure complicate the evolution of mechanical anisotropy and failure mechanisms in sedimentary geothermal reservoirs, posing challenges to deep geothermal exploitation and wellbore stability. In this study, a discrete-element model of bedded sandstone was established to investigate damage evolution, crack distribution, and strength anisotropy under thermo-mechanical conditions at different initial temperatures (20, 200, 400, and 600&#xa0;°C) and bedding inclinations (0°, 30°, 45°, 60°, and 90°). An empirical strength model incorporating both temperature and bedding inclination was further developed. The results show that differences in thermal sensitivity between the bedding zone and matrix minerals lead to a staged spatial redistribution of thermally induced microcracks. Below 400&#xa0;°C, cracks are mainly concentrated in the bedding zone and preferentially develop along bedding. Above 400&#xa0;°C, intergranular and transgranular cracks develop extensively in the matrix, and the crack distribution becomes diffuse with weakened directionality. Under uniaxial loading, thermal damage promotes matrix crack propagation and weakens bedding control over failure. At the critical instability stage, the crack concentration zone shifts from the bedding zone to the matrix, and the influence of bedding inclination on crack propagation decreases. As a result, the strength anisotropy of bedded sandstone first increases and then decreases with increasing thermal treatment temperature. These findings provide mechanistic insight into the anisotropic mechanical behavior and failure mechanisms of sedimentary geothermal reservoirs under high-temperature conditions.</p>

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Thermally induced cracking and the evolution of mechanical anisotropy in bedded sandstone under high-temperature conditions: a microscale perspective

  • 期刊论文

  • 发表日期：

    2026年7月6日

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  • Cao Liu,
  • Peng Jia,
  • Yiran Zhao,
  • Dunxiu Zhang

摘要

The combined effects of temperature and bedding structure complicate the evolution of mechanical anisotropy and failure mechanisms in sedimentary geothermal reservoirs, posing challenges to deep geothermal exploitation and wellbore stability. In this study, a discrete-element model of bedded sandstone was established to investigate damage evolution, crack distribution, and strength anisotropy under thermo-mechanical conditions at different initial temperatures (20, 200, 400, and 600 °C) and bedding inclinations (0°, 30°, 45°, 60°, and 90°). An empirical strength model incorporating both temperature and bedding inclination was further developed. The results show that differences in thermal sensitivity between the bedding zone and matrix minerals lead to a staged spatial redistribution of thermally induced microcracks. Below 400 °C, cracks are mainly concentrated in the bedding zone and preferentially develop along bedding. Above 400 °C, intergranular and transgranular cracks develop extensively in the matrix, and the crack distribution becomes diffuse with weakened directionality. Under uniaxial loading, thermal damage promotes matrix crack propagation and weakens bedding control over failure. At the critical instability stage, the crack concentration zone shifts from the bedding zone to the matrix, and the influence of bedding inclination on crack propagation decreases. As a result, the strength anisotropy of bedded sandstone first increases and then decreases with increasing thermal treatment temperature. These findings provide mechanistic insight into the anisotropic mechanical behavior and failure mechanisms of sedimentary geothermal reservoirs under high-temperature conditions.