Experimental and Constitutive Investigation of the Thermo-Hydro-Mechanical Behavior of Shales: A Case Study of the Colorado Clay Shale
Date
2015-10-02
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Abstract
Shales play a significant role in the safe and economic design of steam injection oil recovery projects in Alberta, Canada, mainly as a result of their special thermo-hydro-mechanical properties. The present study aims at characterizing the thermo-mechanical strength and deformation characteristics of Colorado group shales in Alberta. As such, an extensive set of triaxial laboratory experiments is conducted in the present study, with the observed constitutive features subsequently formulated within the framework of the theory of plasticity.
A large variety of laboratory tests including triaxial compression and triaxial constant mean effective stress tests are performed on Colorado shale samples. Results of triaxial compression tests at various temperatures and pressures show that the tested shale initially decreased in volume and strain-hardened until reaching a peak deviatoric stress. Thereafter, strain-softening ensued to ultimately bring the deviatoric stress to a nearly constant value. Failure of all samples was brittle with the formation of a clearly defined shear plane that was shown to be smooth. The post-peak deformations of the sheared samples were characterized by a constant-rate dilation being governed by the orientation of the shear planes.
The experimental results also show that the Young's modulus of the tested shale reduced with temperature following a logarithmic relationship. The nonlinear peak and post-peak strength envelopes were described using a nonlinear temperature-dependent failure criterion which for mean stresses greater than 1 MPa, was suitably approximated by the Mohr-Coulomb failure criterion.
Based on the observed features in the lab experiments, new constitutive mechanisms were introduced into an advanced multi-yield-surface thermo-elastoplastic model. Of particular interest, the evolution of post-peak friction angle with degradation of interparticle bonding as a result of plastic strain development was modeled. A coupled thermodynamically admissible volumetric thermoelastic rule was proposed in order to describe the thermal variability of elastic properties. A generic thermoplastic formulation for describing the shrinkage of the yield limit at elevated temperatures was developed. Numerical simulations using the proposed mechanisms show the improved predictive capabilities of the reference model, not only in the case of the Colorado shale, but also for experimental observations on other clays/shales in the literature.
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Engineering--Civil
Citation
Mohamadighanatghestani, M. (2015). Experimental and Constitutive Investigation of the Thermo-Hydro-Mechanical Behavior of Shales: A Case Study of the Colorado Clay Shale (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/26050