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<p>Sandstone-shale interbeds are typical layered composite rock masses found in unconventional oil and gas reservoirs, and their mechanical behavior plays a crucial role in hydraulic fracture initiation and propagation. This study investigates the damage evolution mechanisms of 60° bedding-layered sandstone-shale interbeds under uniaxial compression conditions. Experiments were conducted using three cyclic loading paths: constant amplitude, incremental, and stepwise. The results demonstrate path-dependent damage accumulation: constant-amplitude loading leads to fatigue damage and distributed fracture networks, incremental loading causes progressive stiffness degradation with concentrated fractures, and stepwise loading induces brittle failure with complex fracture systems. Energy analysis shows that step-like load fluctuations significantly enhance plastic deformation energy dissipation, accounting for up to 44% of total dissipation. Based on these observations, a memory-effect damage model was developed, with calibrated memory decay coefficients (λ) of 0.05, 0.20, and 0.15 for constant-amplitude, incremental, and step loading, respectively. These findings provide experimental evidence for understanding the fundamental failure mechanisms in complex geological environments and offer a novel framework for optimizing fracturing designs by incorporating path-dependent damage effects.</p>

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Study on mechanical response and damage models of sandstone-shale interbedding under different cyclic loading modes

  • 期刊论文

  • 发表日期：

    2026年7月11日

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  • Yu Suo,
  • Wenjing Yang,
  • Xuanwen Kong,
  • Xiaoguang Wang,
  • Lingzhi Zhou,
  • Guangchao Zhang,
  • Zhejun Pan,
  • Bin Huang

摘要

Sandstone-shale interbeds are typical layered composite rock masses found in unconventional oil and gas reservoirs, and their mechanical behavior plays a crucial role in hydraulic fracture initiation and propagation. This study investigates the damage evolution mechanisms of 60° bedding-layered sandstone-shale interbeds under uniaxial compression conditions. Experiments were conducted using three cyclic loading paths: constant amplitude, incremental, and stepwise. The results demonstrate path-dependent damage accumulation: constant-amplitude loading leads to fatigue damage and distributed fracture networks, incremental loading causes progressive stiffness degradation with concentrated fractures, and stepwise loading induces brittle failure with complex fracture systems. Energy analysis shows that step-like load fluctuations significantly enhance plastic deformation energy dissipation, accounting for up to 44% of total dissipation. Based on these observations, a memory-effect damage model was developed, with calibrated memory decay coefficients (λ) of 0.05, 0.20, and 0.15 for constant-amplitude, incremental, and step loading, respectively. These findings provide experimental evidence for understanding the fundamental failure mechanisms in complex geological environments and offer a novel framework for optimizing fracturing designs by incorporating path-dependent damage effects.