PhD Position at Université de Lorraine (France) on the THM modeling of faults (rock mechanics, geological engineering)
Dear all,
We are looking for a PhD student to work on a project focusing on the "Thermo-Hydro-Mechanical modeling of fault-valve behavior using a DEM approach". The position is open at the Université de Lorraine / Laboratoire GeoRessources (Nancy, France), in collaboration with the Laboratoire Magmas et Volcans (Clermont-Ferrand, France). The Phd is expected to start on October 2024.
Every person interested can contact me directly at luc.scholtes@uca.fr for further details.
Please see the full announcement below:
Objectives and work summary: The complex evolution of fault permeability and strength during and after fault reactivation calls for a better description of the physical processes at stake. The current state-of-the-art in fault reactivation modeling proposes to describe macroscopically these weakening and strengthening mechanisms through phenomenological laws such as the widely used rate-and-state law. However, if these formulations have proven successful in reproducing some observed fault behaviors (e.g. Cappa and Rutqvist, 2011), they are based on empirically determined parameters and a part of the physics remain badly described (e.g., temperature effects, strain localization, permeability evolution associated to healing and sealing effects).
In this PhD thesis, we propose to relate the macroscopic response of both the gouge and damage zone of a fault to the micromechanical phenomena at work during its reactivation following the work initiated by Nguyen et al. (2021) and Zhang et al. (2021). For that purpose, we will utilize a discrete element model (DEM) coupled with a pore-scale finite volume (PFV) scheme implemented in the YADE DEM software (e.g., Mostafa et al., 2023). In a first step, we will simulate the steady state and transient behaviors of a sheared granular gouge under the effect of mechanical and hydraulic loadings (Figure 1), focusing more specifically on permeability evolution during the earthquake cycle simulated through the stick-slip dynamics of the modeled gouge. Then, we will examine the role of temperature on the overall behavior by considering either (or both!) the influence of thermal pressurization and shear heating. A similar investigation will be conducted for the damage zone. For that purpose, a discrete fracture network (DFN) will be generated and the hydraulic and mechanical responses induced by fluid overpressures will be simulated using a DEM model, either YADE DEM, or the 3DEC commercial software. In a second step, we will pursue the goal of upscaling the micromechanical properties of the simulated media (the gouge and the damage zone) to determine the effective properties of faults, taking advantage from direct numerical simulations. Indeed, rather simple constitutive models are classically implemented to work at basin scale whereas behavior laws play a key-role in the HM response of faults to valving processes. Compressive and direct shear tests will be performed numerically under different confinement pressures and at different damage states to estimate both elastic and strength properties of faults. In a similar way, effective thermal conductivity and permeability will be derived respectively from heat conduction tests and fluid injection tests. A damage-dependent hydraulic aperture will be also derived and related to the fault permeability. Finally, these THM properties will be assigned to a simplified fracture model using the discrete element-based commercial software 3DEC for validation purpose. Advanced behavior laws will be studied in 3DEC, derived from upscaling and compared with pore-scale DEM simulations.
Student profile: The candidate must be a highly-motivated and self-directed person with a recent university master’s degree (or equivalent) in computational mechanics, reservoir engineering, applied mathematics, civil engineering, or other relevant fields. He or she may demonstrate fundamental knowledge of solid and fluid mechanics principles governing the behaviour of porous and fractured media and motivation for work at the interface between disciplines. An experience in developing numerical methods, particularly DFN/DEM would be an asset, as well as knowledge of C++ and/or Python programming languages. Also, the candidate will need to be fluent in English.
Funding: The proposed PhD is funded as a part of the ANR research project EARTH-BEAT. This project, in collaboration with Orano Mining, BRGM, LJAD, Mines ParisTech, LMV and GeoRessources has the objective of boosting our understanding of mineral and geothermal resources and the development of predictive tools for potential assessment of these energy sources. This PhD is funded for 3 years, starting on October, 1st 2024 (gross salary, including social security: ~ 2 192 €/month). Location: This full-time position will be shared between GeoRessources (Univ. Lorraine) and LMV laboratories (Univ. Clermont Auvergne). This joint PhD will be located in both institutions (Clermont-Ferrand/Nancy: 1.5 year each).
How to apply: Applicants should send via email a Curriculum Vitae, copy of the master thesis and the names and email addresses of two references to: Fabrice Golfier (PR, fabrice.golfier@univ-lorraine.fr) Luc Scholtes (MCF, luc.scholtes@uca.fr)