Speaker: Imadeddine Laouici
Date: Thursday 12th of June 2025, 1:15pm.
Abstract:
Building structural models of geological entities is generally addressed as an interpolation problem that requires human experts to interpret input data and use knowledge (Wellmann and Caumon, 2018). Although experts can effectively interpret, their interpretations can be subjective and occasionally prone to error (Bond, 2015). This is largely due to under-sampling of data, requiring experts to make choices in the selection and preparation of these data and knowledge (Bond et al., 2012), and selection and configuration of modeling algorithms (Caumon et al., 2009). Modeling algorithms also do not reflect the complex expert interpretation process, as they incorporate only a portion of the knowledge typically held by experts and have limited ability to directly interact with experts during the interpretation process itself. This makes it challenging to build geologically complex models and systematically identify and address inconsistencies in a model. A crucial step toward resolving these issues is the formalization of the interpretation process and the explicit use of formalized knowledge. In this work we develop and prototype such a formalization. A prototype algorithm and tool (Figure 1) are presented and applied to simple folding structures, and the results are favorably compared to existing approaches. This comparison highlights the potential of the proposed approach to reduce the need for expert involvement and increase the range of knowledge utilized.
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- 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.
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- Category: Seminar
Speaker: Jeremie Giraud
Date: Thursday 15th of May 2025, 11am.
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.
The method is applied to gravity data from the prospective Boulia region (Queensland, Australia) to image rocks beneath sedimentary cover. In this field case, an implicit geological model—constructed from the interpretation of 2D seismic lines, borehole data, and geological rules—is used to define prior geological constraints on the inversion. To aid interpretation, a workflow combining dimensionality reduction and clustering is applied to the ensemble of sampled models, allowing identification of families of geologically plausible solutions. Preliminary results suggest that up to two dense rock units, not initially identified by the geological model, may be needed to explain the observed data. Overall, our analysis of results suggests the ability of the method to infer the presence of previously unrecognized geological features, such as buried intrusions or facies variations, and indicates its potential as a tool to support exploration.
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- 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.
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- 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.
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- 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.
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- Category: Seminar