A Multi-Physics Elasto-Visco-Plastic Constitutive Framework for Geomechanics

Sari Mustafa1, Poulet Thomas1, Alevizos Sotiris2 and Veveakis Manolis3

1CSIRO, Mineral Resources, WA, Australia, 2National Technical University of Athens, Athens, Greece, 3Civil and Environmental Engineering, Duke University, Durham, USA

Understanding and improving the performance as well as the productivity of reservoirs at extreme conditions (high pressure and high temperature is big challenge in Geomechanics. This is particularly important for the operation of unconventional shale gas reservoirs, but also applies to other areas like geothermal or deep conventional formations. Other applications include environmental remediation around nuclear waste disposal sites, as well as deep underground storage of energy resources. In order to meet such a formidable challenge, constitutive modelling is required that can span the temperature and pressure range of the Earth’s upper crust, and offer possibilities for long-term forward modelling at such extreme conditions. The main requirement is to formulate a plasticity theory which helps describe and even predict long-term behavior, at conditions where materials are frequently well beyond their initial yield, in environments where rocks may experience extreme temperatures, pressures, as well as internal transformations. To model such multi-physical processes, we suggested a multi-physics elasto-visco-plastic constitutive framework including the effect of interface processes, whereby the hardening law of plasticity is a function of the global and internal state variables of the problem (temperature, pressure, density, chemical potentials). The evolution of the laws of the state variables are therefore obtained from the governing laws of physics for mass and energy balance. We included the effect of interface processes at the grain contacts and surface, through an energy upscaling of the internal enthalpy of the system. The framework was validated against a suite of multi-physical tests in different materials, showing good agreement for a realistic range of material parameters. The analysis also showed that simulation results contain enough information to constrain the parameter space for the definition of the mechanical enthalpy, providing insights to develop further the underlying theoretical model and emphasizing the complementarity of data-driven and physics-based approaches.


Biography

Mustafa obtained his PhD in Geomechanics at, UNSW, to develope a new multiphysics framework for Geomaterials characterization with multiphysics feedback, through theoretical, numerical and experimental approaches. In 2019 he started with CSIRO in Mineral recourses department. In this role he is developing a novel non-destructive rock characterisation methodology.

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