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Strain-Rate Dependent Pre-Failure, Failure and Post-Failure Behavior of Shale: Experiments and Modeling
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, Sixth EAGE Shale Workshop, Apr 2019, Volume 2019, p.1 - 5
Abstract
Summary
The strain rate dependent mechanical behavior of shale was extensively characterized using triaxial compression tests carried out at different axal strain rates. Based on the experimental results, a constitutive model for shale under different rates of loading was proposed. The model is based on a combination of viscoelasticity and damage mechanics and is formulated to predict the brittle behavior of shales from the pre-peak stage, peak and post peak strain softening regimes. Shear failure and strain softening are attributed to damage due to the growth of fractures in the shale, and de-bonding and decohesion mechanisms responsible for the fracture evolution. Damage is described by a scalar variable D and is assumed to commence when the stress-strain behavior deviates from linear elasticity. It was found that damage evolution during shearing in shale can be adequately represented probabilistically using a Weibull probability distribution function based on the axial strain level. An empirical axial strain rate dependent Young's modulus, together with the damage evolution law, completes the viscoelastic damage model. The model is shown to adequately represent the complete stress-strain response of shale at different axial strain rates and to predict the axial strain rate dependent shear strength of shale.
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