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<p>In-situ explosive methane fracturing creates fracture networks within reservoirs, providing efficient migration channels for the effective extraction of shale gas. However, combustion and explosions induce impact and thermal damage to the wellbore, while in-situ ground stress drives shale creep; these coupled effects ultimately result in the collapse of wellbore casings. In this study, step-loading creep experiments were conducted to evaluate the effects of impact strength and temperature on the creep characteristics of shale. The results indicate that higher impact strength accelerates the creep rate of shale samples: the decelerated and steady-state creep rates increase by an average of 61.2% and 138.2%, respectively. In contrast, as temperature rises, the shale creep rate exhibits a "first decrease then increase" trend, with critical transition temperatures at 100&#xa0;°C and 200&#xa0;°C. Based on these findings, a creep model for damaged shale was established to derive a three-dimensional constitutive equation. The model and parameters were imported into FLAC<sup>3D</sup> software and simulation was performed to analyze the effect of creep formation on the wellbore casing equivalent stress after shock–high temperature effects, with results indicating that as the casing equivalent stress increases and the safety factor of the casing decreases over time, reducing the long-term service life of the wellbore. The elastic modulus of the cement sheath significantly affects the equivalent stress in the casing, and damage to the cement sheath poses a substantial risk to the long-term stability of the wellbore. These findings provide critical theoretical insights for evaluating wellbore stability and optimizing designs under efficient shale gas extraction conditions.</p>

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Shale Creep Characteristics After Dynamic Load Impact and Effect of High Temperature on Long-Term Stability of Wellbore

  • 期刊论文

  • 发表日期：

    2025年11月25日

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  • Hu Qu,
  • Chun Liu,
  • Yuyang Chen,
  • Genyuan Tan,
  • Jianqing Liu,
  • Qiaojun Chen

摘要

In-situ explosive methane fracturing creates fracture networks within reservoirs, providing efficient migration channels for the effective extraction of shale gas. However, combustion and explosions induce impact and thermal damage to the wellbore, while in-situ ground stress drives shale creep; these coupled effects ultimately result in the collapse of wellbore casings. In this study, step-loading creep experiments were conducted to evaluate the effects of impact strength and temperature on the creep characteristics of shale. The results indicate that higher impact strength accelerates the creep rate of shale samples: the decelerated and steady-state creep rates increase by an average of 61.2% and 138.2%, respectively. In contrast, as temperature rises, the shale creep rate exhibits a "first decrease then increase" trend, with critical transition temperatures at 100 °C and 200 °C. Based on these findings, a creep model for damaged shale was established to derive a three-dimensional constitutive equation. The model and parameters were imported into FLAC3D software and simulation was performed to analyze the effect of creep formation on the wellbore casing equivalent stress after shock–high temperature effects, with results indicating that as the casing equivalent stress increases and the safety factor of the casing decreases over time, reducing the long-term service life of the wellbore. The elastic modulus of the cement sheath significantly affects the equivalent stress in the casing, and damage to the cement sheath poses a substantial risk to the long-term stability of the wellbore. These findings provide critical theoretical insights for evaluating wellbore stability and optimizing designs under efficient shale gas extraction conditions.