PhD opportunities

Inferring permeability enhancement during fault slip reactivation in the laboratory

Thesis proposal

Area of expertiseGeoscience and Geoengineering
Doctoral SchoolGéosciences, Ressources Naturelles et Environnement
SupervisorM. Pierre DUBLANCHET
Co-supervisorM. Hervé CHAURIS
Research unitCentre de Géosciences
ContactDUBLANCHET Pierre
Starting dateOctober 1st 2022
KeywordsFluid induced fault reactivation, fault permeability, hydromechanical modeling, Bayesian inversion, deterministic inversion, laboratory experiment
AbstractEarthquakes induced in the framework of geothermal exploitation are generally interpreted as the reactivation of rapid slip on preexisting critical fractures, caused by thermo-poro-elastic stress changes. These earthquake sequences are nowadays largely uncontrolled essentially because the physics controlling fault slip reactivation is poorly understood. Recent experiments and models have shown that the mode of slip reactivation is highly sensitive to the way fluids diffuse into the faults, which is primarily controlled by the fault permeability. To achieve a better understanding and control on fluid induced fracture reactivation, it is therefore important to better constrain how fault permeability depends on strain and stress variations.

The objective of this PhD project is to infer fault permeability evolution during injection experiments performed on saw-cut centimetric scale rock sample loaded in a tri-axial loading cell. Experiments were performed by F.X. Passelègue and collaborators from EPFL and GéoAzur rock-mechanics laboratories. The resulting slip, strain and pore pressure measurements will be confronted to the predictions of different thermo-hydro-mechanical fault models in order to constrain the permeability changes. For that, we will use both deterministic and bayesian inversion approaches, already developed in the geophysical group.

This project will not only provide a better understanding of what controls fault slip reactivation, but will also allow to better quantify the permeability enhancement associated with damage and seismicity in reservoirs.

The permeability laws derived from the analysis of laboratory experiments will be also confronted to the development of natural fluid driven earthquake swarms in the Corinth rift. The earthquake migration could be seen as an indicator of fault diffusivity, that has been shown to evolve during these swarms, in particular due to aseismic slip. This allow to estimate how far permeability evolution at the laboratory scale could be applied to the kilometric scale of natural fault systems.
Profile-Background in rock/solid mechanics or geophysics or scientific computing
-Programming skills
-A first experience in inverse problem analysis, experimental or computational rock mechanics will be an advantage

How to apply
Candidates must contact the director(s) of the thesis proposal or the contact person specified. The latter will then hold auditions and select the most suitable candidate for their project.
Content of the application :
-a CV
-a letter of motivation
-transcript of marks of Master 2 (or equivalent)
-summary of the Master 2 report (or equivalent)
-Letter of recommendation from the Master 2 internship supervisor (or equivalent)
FundingConcours pour un contrat doctoral