Numerical Study of Erosion and Dissolution Mechanisms in Rock Fractures: Application to Geothermal Engineering

**Numerical study of erosion and dissolution mechanisms in rock fractures: Application to geothermal engineering**:

- Réf **ABG-130192**
- Sujet de Thèse
- 10/04/2025
- Contrat doctoral
- INERIS
- Lieu de travail- VERNEUIL EN HALATTE - Les Hauts de France - France
- Intitulé du sujet- Numerical study of erosion and dissolution mechanisms in rock fractures: Application to geothermal engineering
- Champs scientifiques- Ecologie, environnement

**Description du sujet**:

- BACKGROUND AND MOTIVATIONS OF THE THESIS
- The main studies presented in the literature are based on different numerical approaches to analyse the influence of various parameters, in particular the intensity of the hydraulic gradient and the particle size of the particles circulating within the fractures of the medium, as well as the morphology and characteristics of the fracture. Several experimental studies have also been carried out, demonstrating the influence of similar parameters. Experimental results have highlighted several clogging and unclogging mechanisms depending on various parameters associated with the nature of the fracturing (roughness, tortuosity, network), the nature of the particles (size, gradation, concentration,...) and the fluid flow (hydraulic gradient, fluid viscosity,...). The various numerical modelling approaches presented in the literature take some of these parameters into account more or less directly.
- AIM OF THE RESEARCH
- The thesis will focus on one component of the THMC (thermo-hydro-mechanical and chemical) behaviour of a multi-fractured medium under hydraulic and thermal loading, representing the injection of fluids at a temperature different from that of the geological medium and corresponding to the context of geothermal production.
- The aim is to explore different modelling approaches (continuous and/or discrete) in order to highlight the main mechanisms governing the behaviour of the fractured rock mass at different spatial and time scales. The approach will be based firstly on a deterministic framework and then, if necessary, on a probabilistic one, to take account of uncertainties in fault geometry, density and spatial distribution, as well as on the effects of non-planarity discontinuity and fracture persistence.
- Several directions of research are already emerging and could be investigated, based on CFD-DEM (Computational Fluid Dynamics - Discrete Element Method) numerical simulations, continuing the work of Wang et al (2024). This involved the study of particle migration in a fracture by investigating the influence of various fracture characteristics and resulted in a formula for calculating particle velocity across the fracture.
- The study's perspectives include the influence of fracture tortuosity, the influence of relative particle-wall friction, fracture wall erosion due to attrition and/or impact of particles circulating in the medium, and the consequences for fluid flow.
- Moreover, in the more specific case of geothermal energy, dissolution phenomena can arise, in particular as a result of temperature changes in the fluids circulating in the fissures, as well as recrystallization phenomena resulting in solid deposits in the cracks. The effect of temperature change on the properties of the medium and on erosion will also be taken into account in the numerical simulation.
- Thesis chronology:

- Literature review
- Formalization of the problem for a medium containing a single fracture: one
- and two-dimensional problem
- Extension of the approach to a medium containing several fractures: 2D and 3D analyses
- Numerical modelling of coupled THMC boundary problems using discrete and continuous approaches and different computational software.
- COLLABORATION
- In previous research, we collaborated with Professor Yin's team at PolyU Hong Kong to complete the study of particle migration in a fracture, studying the influence of different fracture parameters on particle migration, and obtaining the expression of particle velocity through the fracture. The perspectives of the present thesis topic are a continuation of this collaboration undertaken several years ago.
- Regular working meetings will be organized between Ineris, Centrale Nantes and PolyU. Hong Kong Polytechnic University will be mainly involved in research related to numerical simulation techniques, while Centrale Nantes and Ineris will be responsible for the analysis of numerical results and theoretical development. The aim is to produce a comprehensive set of erosion simulation methods for geothermal engineering, as well as a theoretical framework for quantitatively assessing the degree of erosion during the geothermal exploitation of a site.
- POSITIONING AND CAREER PROSPECTS FOR THIS RESEARCH
- This research, with its fundamental and applied components, is part of a virtuous process for the environment: the use of decarbonized green energy.

**Nature du financement**:

- Contrat doctoral

**Précisions sur le financement**:
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