Speaker(s): Luc Scholtes
Date: Thursday 12th March 2020 - 1:00 pm
Location: Meeting room, ENSG Bat E, Nancy.
Abstract:
Predicting the strength of shale rocks is a basic but nonetheless critical requirement when designing CO2 or nuclear wastes storages. Even though geologic structures need to be considered above the meter scale when evaluating the strength of such systems, the intact rock behavior has to be thoroughly characterized before any further analysis. A particular feature of shale rocks is that they present highly nonlinear failure envelopes. Interestingly, despite this unanimously observed behavior, the linear Mohr-Coulomb criterion is still widely used in engineering practice (see for instance the petroleum or reservoir geomechanics taught in university courses). Of course, non-linear strength criteria exist and should thus be considered more systematically when dealing with shale rocks (see for instance the criterion proposed by Singh). Nonetheless, as practical as they are for assessing the integrity of geologic materials, these formulations (empirical for the most of them) do not explain the underlying mechanisms involved in the failure processes. As a matter of fact, shale rocks present anisotropic structures, characterized by laminations, parallel layering or bedding features. These fabric properties induce a strong anisotropic behavior which directly controls the strength of shale rocks. It is thus crucial to consider such characteristics to better understand the associated failure mechanisms. In this work, we describe the dependency of Tournemire shale strength on the orientation of the loading relative to the bedding over a large range of confining pressures (from 2 to 80 MPa) based on a comprehensive series of experimental tests. Then, we assess the relevance of two practical empirical failure criteria to describe Tournemire shale strength. Finally, we simulate the triaxial tests performed on Tournemire shale using a specifically developed anisotropic discrete element model to get further insights into the mechanisms controlling its strength.
- Details
- Category: Seminar
Speaker(s): Zoé Renat
Date: Thursday 27th February 2020 - 1:00 pm
Location: Room G201, ENSG Bat G, Nancy.
Abstract:
Microseismic events are earthquakes of weak intensity and are difficult to locate with traditional methods. In the presentation, I will present some methods based on backward propagation of seismic recordings: time reversal method & reverse time modeling.
- Details
- Category: Seminar
Speaker(s): Khalifa Eldursi
Date: Wendnesday 19th February 2020 - 1:00 pm
Location: Meeting room, ENSG Bat E, Nancy.
Abstract:
Canada’s uranium production, currently ranked second worldwide and accounting for 17% of the world’s total, is entirely from the Athabasca Basin in northern Saskatchewan. The unconformity-related uranium deposits associated with this basin are among the highest-grade and largest uranium deposits in the world. Many of these deposits were discovered based on an empirical model that uranium mineralization took place near faults crosscutting the sub-Athabasca unconformity, where uranium-bearing oxidizing fluids met and reacted with reducing agents (i.e., graphite and hydrocarbons derived from, as well as ferrous iron-rich lithologies) and precipitated uranium ores. However, after more than 40 years of intensive exploration, this model is facing more and more challenges, and a better understanding of the factors controlling mineralization is needed.
- Details
- Category: Seminar
Speaker(s): Yves Frantz
Date: Thursday 13th February 2020 - 1:00 pm
Location: Room G201, ENSG Bat G, Nancy.
Abstract:
Bibliographic seminar presenting different karstic network skeleton simulation methods.
- Details
- Category: Seminar
Speaker(s): DU KOU
Date: Thursday 06th February 2020 - 1:00 pm
Location: Meeting room, ENSG Bat E, Nancy.
Abstract:
One of the most important subjects in mechanics of materials is to describe the macroscopic behaviours by considering the evolution of the complex microstructures and matrix anisotropy. It is especially for the porous composite geomaterials relating to the propagation of the micro-cracks and the growth of the micro-voids, which enormously affect their damage process. In our work, we are firstly interested in the microporoelastic modelling in order to estimate the effective properties of the studied geomaterials by taking into account the microstructure and matrix anisotropy. It is actually important for the derivation of micromechanical damage models that will be next realized in order to carry out the phase field modeling in the second part of this thesis.
- Details
- Category: Seminar
Speaker(s): Capucine Legentil
Date: Thursday 23rd January 2020 - 1:00 pm
Location: Room G201, ENSG Bat G, Nancy
Abstract:
Ce séminaire sera l'occasion de faire découvrir aux 3As l'IAMG (International Association for Mathematical Geosciences) et son Student Chapter. L'IAMG est l'association scientifique la plus proche des thématiques de recherche de l'équipe, et possède un Student Chapter à Nancy, qui est géré par les doctorants de l'équipe.
Le bureau de cette année est composé des doctorants de 1ère et 2ème année (Capucine Legentil, Zoé Renat et Paul Baville).
- Details
- Category: Seminar
Speaker(s): Farah Al Sahyouni
Date: Thursday 16th January 2020 - 1:00 pm
Location: Meeting room, ENSG Bat E, Nancy
Abstract:
Storage in salt caverns is currently the most efficient method for large scale storage of hydrogen. The reservoir capacity, but mainly its sealing integrity (k <2 * 10-21 m2, in undisturbed areas) are the main reasons. However, if the deviatoric stress crosses the dilatancy boundary, it resolves the deformations in the pore structure and increases the permeability. Thus, the risk of leakage increases. Our goal is to study the change of the hydraulic and mechanical properties according to the damage. Several experimental techniques were used to characterize the changes in the properties of the samples before and after the mechanical tests, on cylindrical salt cores respecting the REV. The evolution of permeability as a function of the stresses is imposed by the modifications of the rheological behavior of the salt. It follows a percolation curve and the breakthrough point is at the dilatancy boundary. The hardening stage allows a reduction of the permeability.
- Details
- Category: Seminar
Speaker(s): Melchior Schuh-senlis
Date: Friday 13th December 2019 - 1:00 pm
Location: Room G201, ENSG Bat G, Nancy
Abstract:
As the need for natural ressources arises with human growth, we need more and more to characterize the Earth's subsurface. Geometric models of underground structures, in 2D and 3D, help to do just that. However, their validity can be questionned, as it is not always clear if they assess well the deformation history of the modeled area. Structural restoration has arisen as one method to verify this validity, by unfolding and unfaulting structures. It was first introduced with geometrical assumptions like a geometrical flattening and a conservation of layer length. Later on, in order to add more physical meaning to the restoration process, geomechanical restoration was introduced, computing the internal deformation of the model with the elastic properties of the rock layers. While this helped improve the quality of the restoration, many issues remain, such as the still mainly geometrical ways of dealing with faults and boundary conditions, or the incapacity to deal with salt layers.
This seminar will introduce my PhD work, that aims at introducing a new geomechanical restoration scheme using creeping flow equations to model the deformation of the subsurface through time, at basin scale.
- Details
- Category: Seminar
Speaker(s): Assohoun Wilfried Ahoulou
Date: Thursday 28th November 2019 - 1:00 pm
Location: Meeting room, ENSG Bat E, Nancy
Abstract:
Depuis la fin des années 1990, marquées par des travaux expérimentaux menés par (Daccord, 1987) ou (Hoefner et Fogler, 1988), de nombreuses études expérimentales et numériques ont été réalisées afin de comprendre le mécanisme de dissolution en milieu poreux. Ces études trouvent leurs applications dans l’ingénierie pétrolière et minière, la séquestration de CO2, les systèmes karstiques, les problématiques environnementales … En effet, lorsqu'un fluide acide est injecté dans une roche carbonatée, il dissout généralement la matrice poreuse et crée des canaux d’écoulements préférentiels appelés wormholes. Ces régimes de dissolutions sont au nombre de 5 (compact, conique, dominant, ramifié et uniforme) et dépendent des paramètres opératoires tels que le débit d’injection, la concentration de l’acide, la porosité/perméabilité du milieu ...
L'objectif général de ma thèse consiste à analyser les effets du contraste de masse volumique sur ces régimes de dissolution. Pour cela, une étude expérimentale bidimensionnelle est faite à l’aide d’une cellule de type Hele-Shaw orientée verticalement et horizontalement à l’intérieure de laquelle un massif constitué de mélange sel-plâtre est dissous. Les dissolutions obtenues sont analysées qualitativement et quantitativement à l'aide d'outil de traitement d'image (ImageJ).
- Details
- Category: Seminar