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<p>The long-term security of CO₂ geological storage critically depends on predicting the integrity of shale caprocks, which undergo chemical–physical–mechanical degradation upon exposure to supercritical CO₂ and brine. However, a quantitative understanding of the degradation kinetics and the multiscale coupling between chemical alteration and mechanical weakening remains limited, hindering reliable long-term predictions. This study reports a time-resolved (0–35 days) multiscale experimental and modeling investigation into chemical–physical–mechanical degradation of Chang 8 shale under representative storage conditions (15.7 MPa, 55.4 °C). Progressive dissolution of carbonate and feldspar minerals drove a linear increase in porosity from 2.786% to a peak of 3.692%. Concurrently, both microscale (hardness, elastic modulus) and macroscale (compressive strength, elastic modulus) mechanical properties exhibited significant exponential decay, with strength and stiffness reduced by up to 50%. Crucially, these degradations showed a strong correlation (<i>R</i><sup><i>2</i></sup> &gt; 0.92) with evolving porosity. Based on these findings, we developed a unified, porosity-dependent exponential decay model that quantitatively links dissolution-induced porosity changes to multiscale mechanical damage. This framework provides a robust mechanistic basis for predicting the kinetics of shale mechanical degradation, thereby greatly enhancing CO₂‑storage risk assessment and supporting environmental safety.</p>

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Shale Mechanical Degradation in Supercritical CO₂ and Brine Formations: A Multiscale Experimental and Modeling Study

  • 期刊论文

  • 发表日期：

    2025年7月8日

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  • Jun Huang,
  • Li Jiang,
  • Chanjuan Guo,
  • Jingning Ma

摘要

The long-term security of CO₂ geological storage critically depends on predicting the integrity of shale caprocks, which undergo chemical–physical–mechanical degradation upon exposure to supercritical CO₂ and brine. However, a quantitative understanding of the degradation kinetics and the multiscale coupling between chemical alteration and mechanical weakening remains limited, hindering reliable long-term predictions. This study reports a time-resolved (0–35 days) multiscale experimental and modeling investigation into chemical–physical–mechanical degradation of Chang 8 shale under representative storage conditions (15.7 MPa, 55.4 °C). Progressive dissolution of carbonate and feldspar minerals drove a linear increase in porosity from 2.786% to a peak of 3.692%. Concurrently, both microscale (hardness, elastic modulus) and macroscale (compressive strength, elastic modulus) mechanical properties exhibited significant exponential decay, with strength and stiffness reduced by up to 50%. Crucially, these degradations showed a strong correlation (R2 > 0.92) with evolving porosity. Based on these findings, we developed a unified, porosity-dependent exponential decay model that quantitatively links dissolution-induced porosity changes to multiscale mechanical damage. This framework provides a robust mechanistic basis for predicting the kinetics of shale mechanical degradation, thereby greatly enhancing CO₂‑storage risk assessment and supporting environmental safety.