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<p>Nanoindentation provides an alternative approach for characterizing shale creep. However, standardized loading protocols are still lacking, making the reported properties sensitive to peak load and material heterogeneity. In this study, we investigate the creep behavior of Yanchang shale (Ordos Basin, China) using nanoindentation combined with viscoelastic constitutive modeling. The results show that the mechanical properties of Yanchang shale are strongly load-dependent, and a peak load interval of 300–400&#xa0;mN provides the most representative (approximately homogeneous) estimates for this shale. With increasing indentation load, the creep strain rate sensitivity (<i>m</i>) first decreases and then increases. Overall, <i>m</i> ranges from 0.061 to 0.122, indicating that the creep is likely governed by dislocation/defect-related mechanisms. Four creep models were compared against experimental creep curves, and the four-element Burgers model is identified as the preferred option because it achieves good accuracy with relatively low computational cost and fewer parameters. These nanoindentation-derived creep parameters and the corresponding constitutive models form the microscopic foundation for field-scale geomechanical assessments.</p>

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Characterizing creep behavior of shale by nanoindentation and constitutive modeling: application to the Chang 7 Member of Triassic Yanchang Formation, China

  • 期刊论文

  • 发表日期：

    2026年3月19日

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  • Tao Zeng,
  • Yuan Fang,
  • Xiang Zhao,
  • Yongtang Yu,
  • Yalin Nan

摘要

Nanoindentation provides an alternative approach for characterizing shale creep. However, standardized loading protocols are still lacking, making the reported properties sensitive to peak load and material heterogeneity. In this study, we investigate the creep behavior of Yanchang shale (Ordos Basin, China) using nanoindentation combined with viscoelastic constitutive modeling. The results show that the mechanical properties of Yanchang shale are strongly load-dependent, and a peak load interval of 300–400 mN provides the most representative (approximately homogeneous) estimates for this shale. With increasing indentation load, the creep strain rate sensitivity (m) first decreases and then increases. Overall, m ranges from 0.061 to 0.122, indicating that the creep is likely governed by dislocation/defect-related mechanisms. Four creep models were compared against experimental creep curves, and the four-element Burgers model is identified as the preferred option because it achieves good accuracy with relatively low computational cost and fewer parameters. These nanoindentation-derived creep parameters and the corresponding constitutive models form the microscopic foundation for field-scale geomechanical assessments.