Youssouf Abdallah

Comportement thermo-hydro-mécanique et évolution de la microstructure des roches sédimentaires sous fortes contraintes et hautes températures : application à la géothermie

Advisors: Jean Sulem (NAVIER), Siavash Ghabezloo (NAVIER), Ioannis Stefanou (NAVIER), Sébastien Brisard (NAVIER), Michel Bornert (NAVIER)

Brief summary:

The objective of the thesis is to explore the thermo-hydro-mechanical behavior of a carbonate rock within a large range of stresses and temperatures for applications to geothermal reservoirs. Special attention is devoted to the mechanisms of deformation and the evolution of the microstructure in zones of localized deformation (microcracking, grain crushing, pore collapse). Multi-scale modeling within the framework of higher order continuum theories will be developed in order to provide a framework for robust computations of post-localization regime.

Triaxial tests with controlled temperature and stress paths in a high pressure cell (confinement up to 150 MPa, temperature up to 200 °C) will be associated to permeability measurements and with detailed observations of zones of localized deformation and damage using SEM and Xray tomography. The large range of confining pressures and temperatures permits to explore the transition from the brittle regime to the cataclastic flow regime and identify the microprocesses associated to the various modes of deformation banding (shear bands, compaction bands) and the consequences in terms of permeability changes. The validity of the effective pressure principle will also be checked over a large range of stresses for carbonate rocks.

The results of the thesis will provide tools for modeling of the evolution of a reservoir under significant changes of temperature and stress as it is the case for deep geothermal systems.

Figure1: High pressure triaxial cell

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