Speaker: Jeremie Giraud
Date: Thursday 15th of May 2025, 11:00 am.
Abstract:
We present and apply a pseudo trans-dimensional inversion method for 3D geometrical gravity inversion, in which the number of rock units, their geometry, and their density can vary during sampling. The method builds on a multiple level set framework and uses a birth-death process to insert or remove rock units from an existing model. Interface geometries are perturbed using random fields, and densities are sampled from distributions informed by prior geological knowledge. Sampling is performed using a non-reversible Metropolis-Hastings algorithm designed to efficiently explore complex model spaces while ensuring a parsimonious solution.
- Details
- Category: Seminar
Speaker: Bastien Morin
Date: Thursday 27th of February 2025, 1:15pm.
Abstract:
Les réservoirs miniers, formés par l’ennoyage des travaux après l’arrêt de l’exploitation du charbon, sont le siège de processus géochimiques complexes. Dans la mine de lignite de Gardanne, la roche exploitée se mêle à des formations calcaires, entraînant des interactions eau-roche spécifiques qui influencent les équilibres géochimiques. Les concentrations en fer, issues du drainage minier neutre, y posent d’importants défis environnementaux. Cette présentation décrit la campagne de terrain menée au puits Gérard à Mimet fin octobre 2024 dans le cadre de mes travaux de thèse. Au cours de cette campagne, des mesures physico-chimiques détaillées ont été réalisées, accompagnées de prélèvements d’eau à différentes profondeurs, suivis d’analyses chimiques, isotopiques et microbiologiques.
- Details
- Category: Seminar
Speaker: Yifan Xu
Date: Thursday 13th of February 2025, 1:15pm.
Abstract:
Variational gradient damage modeling, known nowadays as the variational phase field method, has been widely utilized in recent decades thanks to their efficiency in describing the transition from damage to fracture and predicting fracture nucleation and growth. In this work, we aim at proposing a phase field based Cohesive Zone Model (CZM) to simultaneously investigate the full coupling between gradient damage, poroelasticity and fluid flow phenomena in saturated porous media, as well as to well describe the damage zone that develops near the tip of quasi-brittle fractures. To this end, we mainly rely on the recent works of Zhang et al., 2024 (J. Mech. Phys. Solids, 187, 105614) and Wu, 2017 (J. Mech. Phys. Solids, 103, 72-99) in order to incorporate the cohesive zone effect in the corresponding incremental variational formulation of this fully coupled system. The proposed incremental variational approach consists in the minimization of a three-field incremental energy functional, which depends on the displacement and damage fields of the skeleton phase of the porous media as well as the pore fluid pressure. For numerical implementation, we adopt a semi-staggered optimization algorithm by making use of FEniCS platform and apply it to simulations of the KGD fracture problem and hydraulic fracturing problems involving multiple cracks for which corresponding analytical solution and/or numerical results are available. Taking advantage of this framework, this is finally applied to assess the feasibility and stability of an industrial radioactive waste repository in the Callovo-Oxfordian (COx) claystone formation, where the host rock presents significant cohesive characteristics. The numerical results are compared with the in-situ observations. Reliable predictions such as the extension of the excavation-induced damaged zone (EDZ) as well as pore pressure distribution are provided.
- Details
- Category: Seminar
Speaker: Loïs Letellier
Date: Thursday 10th of April 2025, 1:15pm.
Abstract:
Well log interpretation is a time consuming task, which, moreover, depends on the interpreter's experience, as there exists different admissible interpretations for a same input log. To account for the uncertainty of the interpretation, we propose to use a signal processing technique, the Continuous Wavelet Transform (CWT), that gives information on the signal considering both depth and scale parameters. The result of this transform is then processed to extract some features of the signal (i.e. the local extrema of the signal at different scales), and propose different geological scenarios. We then compare the different solutions with experts' interpretations.
These different scenarios are destined to be included in a correlation process, in order to study correlations with a multi-scale approach, which allows to explore the range of possibilities, while reducing the computational cost using a hierarchical process.
- Details
- Category: Seminar
Speaker: Léo Letellier
Date: Thursday 06th of February 2025, 1:15pm.
Abstract:
To Rust or not to Rust, that is the question in today's choice of programming languages. While hunting for bugs and security vulnerabilities is a principal concern in software development, memory safety is found to be involved in a majority of such cases (70% of all vulnerabilities reported by a Microsoft engineer in 2019). Multiple tools and enhancements are proposed to mitigate this risk. The Rust programming language was developed to answer this problem in a more controlled way, providing systematic memory safety while preserving performance. It is particularly fit for usage in CLI (Command Line Interface), networking, and embedded devices. It also targets WebAssembly, making code web-ready with minimal changes. Considering these features, multiple agencies such as the NSA emphasize the need to use memory-safe languages such as Rust. Rust was also determined to be the most admired language for multiple years in a row by the developer survey of Stackoverflow (83% in 2024), and is ranked 14 in the January 2025 Tiobe index.
- Details
- Category: Seminar
Speaker: Mike Heap
Date: Thursday 27th of March 2025, 1:15pm.
Abstract:
Hydrothermal alteration describes a process that progressively, and additively, modifies the chemical, physical, mechanical, and transport properties of rock by fluid-rock interactions. At active volcanoes, mixtures of magmatic and meteoric fluids circulate within the rocks forming the volcano and, as a result, hydrothermal alteration can be pervasive. Because the properties of volcanic rocks and rock-masses, such as their strength or their permeability, play a role in dictating the hazard potential of a volcano, then it follows that hydrothermal alteration can progressively modify the hazard potential of a volcano. However, not only does subsurface hydrothermal alteration proceed largely imperceptibly, leading to unpredictable hydrothermal explosions and mass wasting events, but we also do not fully understand the timescales required for hydrothermal alteration, nor its influence of rock properties. As a result, and despite its potential importance, hydrothermal alteration is not routinely monitored at active volcanoes, and often does not feature in routine volcanic hazard assessments. In this seminar, I will outline recent, multidisciplinary advancements in our understanding of hydrothermal alteration, and its influence on volcanic hazards.
- Details
- Category: Seminar