Speaker: Marius Rapenne

Date: Thursday 20th of April 2023, 1:15pm.

Abstract:

Seismic wave simulation are often performed within limited region spanning from tens of meters, for civil engineerings applications, to hundreads of kilometers, for seismic hazard mitigation. In order to properly model the wavefield, accurate boundary conditions on the domains limits are needed. However, designing the boundary condition in a geological settings is very difficult as they rely on geological information outside from the domain of interest that are typically unknown. As such, a classical idea is to prevent any reflection of the wave at the boundaries. There is a variety of such boundary condition in the literrature. The object of this seminar will be to present one of these method: the Perfectly Matching Layer (PML).

Speaker: Pauline Collon

Date: Thursday 13th of April 2023, 1:15pm.

Abstract:

Ce séminaire aura pour objet de vous présenter l'ANR DECACLIM acceptée en décembre 2022 et dans lequel je suis impliquée comme co-porteuse d'un WP. DECACLIM [DEcorated CAves under CLIMate changes : Redefining an effective conservation strategy] a pour objectif de lutter contre la dégradation des grottes ornées face au changement climatique. Le projet de recherche rassemble 8 laboratoires et est porté par Bruno Lartiges du GET.

Speaker: Pierre Thore

Date: Thursday 6th of April 2023, 1:15pm.

Abstract:

Full field dynamic simulations are extremely cost expensive especially in the context of multi-realizations or during inverse problems. Many alternative approaches (proxies) have been proposed generally based on Fast-Marching but have shown strong short comings. Here we propose to use classic flow simulator with a pseudo grid composed of cells at each node of a graph and only connected through graph edges. In this approach the pre-processor of the simulator is by-passed and transmissibilities are pre-computed and provided to the flow simulator. This is still an ongoing work and results are still unsatisfactory showing discrepancies with full field simulations. The second aspect of the presentation deals with graph calculation by using skeletonization of properties (Computers & Geosciences, 2013). This technique can be applied either to geophysical measurements such as 4D or 3D inversion results or to reservoir grid properties. In the former case connectivity paths are based on data and do not depend on model.

Speaker: Ever Coarita

Date: Thursday 30th of March 2023, 1:15pm.

Abstract:

Les travaux portent sur l'analyse des cavités salines dans le contexte du stockage souterrain de l'hydrogène et de la transition vers les énergies renouvelables. Le sel gemme présente de bonnes caractéristiques hydromécaniques pour le stockage du gaz dans les cavités salines. Cependant, en raison de la demande, par exemple pour le chauffage en hiver, les cavités sont soumises au soutirage ou à l'injection de gaz. Ces opérations peuvent endommager la roche saline et, par conséquent, provoquer des fuites de gaz à travers la paroi de la caverne. L’exposé présentera les résultats de la modélisation hydromécanique des cavités salines soumises à des cycles d'exploitation saisonniers et journaliers, ainsi que les travaux de modélisation en cours.

Speaker: Bérénice Vallier

Date: Monday 27th of March 2023, 2pm.

Abstract:

Many numerical models studying the natural hydro-thermal circulation and the impact of industrial exploitations have been developed over the past decades. However, numerical methods which integrates several multi-physical and multi-scale measurements are under-represented. In the first part of the research, a natural large-scale hydro-thermal circulation is studied using a simplified thermo-hydro-mechanical model. Key rock physics properties are inverted from observed temperature and stress-depth profiles. On the other hand, this model with a complex coupling does not incorporate the details of the fluid flow along the major faults. The study provides new insights on the extension of the hydro-thermal convection cells through depth and on the up-scaling of rock physics properties from laboratory scale to field scale. In the second part, the anthropogenic impact on a natural large-scale system is analyzed. The aim of the study is to simulate far-field pore pressure disturbances from fluid injection in fractured porous medium. Studying the diffusion of pressure disturbances will allow to understand the evolution of the effective stress and to quantify the triggered seismicity. A large-scale homogeneous porous medium as a fault structure is represented. The pressure disturbances’ distribution is investigated under different states: (i) controlled injection; (ii) injection/production system. The numerical pressure perturbations are in good agreement with the analytical results. To improve the current models, further work employing more realistic scenarios of fluid injection conditions are currently under investigation.

Speaker: Paul Marchal

Date: Thursday 23rd of March 2023, 1:15pm.

Abstract:

When modelling hydrothermal deposits, it is critical to consider the interrelationship between fluid flows, tectonic structures, such as faults, and the initial petrophysical characteristics of the rocks. This is essential to improve current modelling processes, which are mainly based on classical deterministic interpolation methods, by incorporating geological knowledge within the modelling approach. This allows a better understanding of orebodies genetic processes and thus help the planning of exploration campaigns, as characterizing altered zone geometry is often a proxy for targeting ore zones in several types of deposits. It also improves the mineral resources of deposits evaluation for mining purposes. The key idea is to translate the hypothetical genetic link between faults, stratigraphic contacts, and fluid sources on the one hand, and the geometry & shape of altered rocks halos on the other, into the modelling approach. We choose to extend the skeleton-based approach, developed by [Henrion et al., 2010] who models karst conduits as an implicit distance function to a structural skeleton, which is perturbed by a data-constrained disturbance field, to incorporate and assess uncertainties. Moreover, based on the work of [Rongier et al., 2014], we wants to incorporate anisotropic behaviour of rocks by customizing this implicit distance field using petrophysical data, such as permeability. Then, given the sparse nature of drillholes datasets, we suggest that generating unknown structural elements between data is essential to better assess uncertainties related to halos’ shapes. This works develops these methodologies to model genetically–related concentric alteration & mineralization halos related to hydrothermal processes such as Unconformity-related uranium deposits of the Athabasca.

Speaker: Boris Kratz

Date: Thursday 16th of March 2023, 1:15pm.

Abstract:

Les métropoles sont confrontées à une saturation de leurs axes de mobilité, ce qui a entraîné la mise en place de nouveaux grands projets d'infrastructures tels que la construction de tunnels. Cependant, la construction de tunnels comporte des risques, notamment les déplacements surfaciques causés par les travaux d'excavation. Pour évaluer ces risques et protéger les bâtiments situés à la surface, il est nécessaire de prédire et surveiller l'ampleur des tassements. Pour cela, différentes méthodes de prédiction ont été développées, allant des méthodes empiriques et analytiques aux méthodes numériques. Les modèles 3D par éléments finis (EF), avec des lois de comportements mécaniques des sols réalistes, sont considérés comme étant les plus prédictifs, mais sont complexes et coûteux en temps de calcul. Un méta-modèle, ou modèle de substitution, peut fournir une approximation suffisamment précise d'un modèle (EF), avec l'avantage d'être beaucoup moins coûteux en temps de calcul. Cette présentation vise à expliquer les étapes nécessaires pour développer un tel méta-modèle pour le problème de l'excavation par un tunnelier. En particulier, nous discuterons de la précision des méta-modèles en fonction du nombre de simulations effectuées pour la construction du méta-modèle.

Speaker: Augustin Gouy

Date: Thursday 9th of March 2023, 1:15pm.

Abstract:

Karst systems, which are often present in carbonate rocks, are characterized by a complex ensemble of underground drains which strongly control the water flow in the massif. It is therefore necessary to take into account the karst network to model the hydrogeological functioning of karstified rocks. Information on the position and the geometry of those caves is however often scarce, indirect and imprecise. A discrete karst network simulation approach is proposed, capable of representing the diversity of possible models for a given dataset, while exploiting those data to reduce the ensemble distribution. This method solves a shortest path algorithm between sinks and springs –respectively the inlets and outlets of the network- with the use of an anisotropic cost function defined in the whole domain. The cost represents in a simplified way the physico-chemical processes of karstification, while facilitating control of the geometry and topology of the generated networks. Examples derived from a real case study show how the position, density, connectivity rules and hierarchy of the network’s inlets and outlets can be used to create realistic karst networks under various underlying hypotheses.

 

Speaker: Paul Cupillard

Date: Thursday 2nd of March 2023, 1:15pm.

Abstract:

Tectonic processes and the industrial exploitation of the subsurface induce brittle deformations in the earth crust, leading to fractures at all scales. Geological observations have evidenced that a power law is appropriate to describe the density of a fracture set as a function of the fracture size. Nevertheless, for either theoretical or computational reasons, studies on seismic wave propagation in fractured media have been restricted to a short range of fracture sizes so far. In particular, effective medium theories all rely on an Elementary Representative Volume (ERV) consisting of a host matrix in which cracks are included. Assuming the ERV small with respect to the wavelength, then it is in a quasi-static regime of stress so that techniques from micromechanics can be used to compute an equivalent medium. In the frame of a 18-month post-doc, Anaïs Ibourichène started working on the application of the non-periodic homogenization method to fractured media to go beyond the ERV setting and explore the effect of a wide distribution of crack sizes on seismic wave propagation. I here present the preliminary results obtained by Anaïs in 2D. First, the effective properties computed using the homogenization in the case of Eshelby problems are compared to analytical solutions provided by various effective medium theories. Then, the homogenization is applied to a synthetic mass rock which contains different fracture sets, each set being characterized by a length l (up to λmin/4) and a density d ∼ l−3. Finally, some short-term and long-term perspectives of this work are discussed.