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Effects of indentation parameters on microscale creep behavior of ScCO2-exposed shale under hydrochemical conditions
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DOI：10.1016/j.jrmge.2026.06.014.png)
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Abstract
En 中文
Understanding the micromechanical and creep behavior of shale under supercritical CO2 injection is essential for evaluating long-term reservoir integrity in carbon capture and storage (CCS). However, the microscale creep behavior of shale under different peak loads and holding times after exposure to natural-moisture, deionized-water-saturated, and brine-saturated conditions remains insufficiently understood. In this study, nanoindentation tests with varying peak loads and holding times were conducted to investigate the influence of fluid chemistry on the time-dependent microscale deformation of shale. Mineralogical composition and microstructural changes were characterized using X-ray diffraction, nuclear magnetic resonance, scanning electron microscopy, and automated mineral analysis with a TESCAN integrated mineral analyzer. Higher loads and longer holding times intensified particle sliding and pore rearrangement, resulting in greater creep depth and permanent deformation. This effect tended to plateau in deionized water but became more pronounced in brine because of sustained microslip. Deionized water produced the greatest reductions in indentation modulus and hardness but limited long-term creep, whereas brine maintained moderate stiffness and promoted greater creep displacement through ionic lubrication. A nanoscale creep constitutive model was developed by combining logarithmic and Newtonian components with load- and time-dependent parameters. The model accurately captured transient and steady-state creep responses in hard and soft phases and reproduced elastic recovery during creep, indicating that steady-state creep was reached after approximately 10 s. Parameter analysis showed that transient creep was primarily load-dependent, whereas steady-state creep was more sensitive to fluid chemistry. These findings support long-term stability assessments in CCS applications.
Keywords:
CO2 geological storage
Shale creep
Nanoindentation
Constitutive creep modeling
Water chemistry
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