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<p>Sealing integrity at the casing–cement sheath interface (CCSI) is essential to maintaining overall well integrity. Excessive mechanical load may cause structural damage, such as micro-cracks at the CCSI. Given the disparity in material properties existing on either side of the interface, the results of conventional numerical calculation methods based on the continuity assumption have a singularity at the interface. Peridynamics (PD), with its nonlocal formulation, overcomes this limitation by describing the mechanical response through spatial integral equations, thereby naturally accommodating discontinuities. In this study, a PD-based model for the CCSI is developed to investigate its damage evolution under varying internal and external pressures. Simultaneously, the damage law of CCSI caused by cement’s elastic modulus and casing’s wall thickness is explored. The analysis reveals that the interface experiences initial damage as the internal pressure within the casing exceeds a critical value of 70MPa. As the internal pressure within the casing rises, the extent of damage at CCSI becomes increasingly apparent. When both the internal and external pressures simultaneously increase, the damage at the CCSI propagates outwards, resulting in cracks. When the cement elastic modulus exceeds 10GPa, the maximum damage value observed at the CCSI exceeds 0.5, indicating severe degradation. There is almost no damage at the CCSI when the casing wall thickness exceeds 20 mm. These findings hold immense significance for mitigating the damage of CCSI and ensuring long-term wellbore integrity.</p>

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Study of the Damage Mechanisms at Casing–Cement Sheath Interface Based on Peridynamics

  • 期刊论文

  • 发表日期：

    2025年10月17日

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  • Fei Li,
  • Yongsheng Liu,
  • Jianxin Xia,
  • Shangyu Yang,
  • Lihong Han

摘要

Sealing integrity at the casing–cement sheath interface (CCSI) is essential to maintaining overall well integrity. Excessive mechanical load may cause structural damage, such as micro-cracks at the CCSI. Given the disparity in material properties existing on either side of the interface, the results of conventional numerical calculation methods based on the continuity assumption have a singularity at the interface. Peridynamics (PD), with its nonlocal formulation, overcomes this limitation by describing the mechanical response through spatial integral equations, thereby naturally accommodating discontinuities. In this study, a PD-based model for the CCSI is developed to investigate its damage evolution under varying internal and external pressures. Simultaneously, the damage law of CCSI caused by cement’s elastic modulus and casing’s wall thickness is explored. The analysis reveals that the interface experiences initial damage as the internal pressure within the casing exceeds a critical value of 70MPa. As the internal pressure within the casing rises, the extent of damage at CCSI becomes increasingly apparent. When both the internal and external pressures simultaneously increase, the damage at the CCSI propagates outwards, resulting in cracks. When the cement elastic modulus exceeds 10GPa, the maximum damage value observed at the CCSI exceeds 0.5, indicating severe degradation. There is almost no damage at the CCSI when the casing wall thickness exceeds 20 mm. These findings hold immense significance for mitigating the damage of CCSI and ensuring long-term wellbore integrity.