Speaker(s): Guillaume Caumon

Location: Nancy.
 
Date: Thursday 2nd of April 4:00 pm.
 
Abstract:
 
Loop is a collaborative project dedicated to the development of an open source platform for modeling of highly deformed geological terrains and inversion. In this seminar, I will make a brief summary of the main advances shared by the 2020 Loop meeting participants in Western Australia. Themes include the overall project architecture, map and model validation, modeling, joint geophysical inversion.
Speaker(s): Corentin Gouache

Location: Nancy.

Date: Thursday 26th of March 2:00 pm.

Abstract:
 
Earthquakes occur everywhere and everytime. Moreover, large earthquakes that really impact our society are sparse events. That's why statistical analysis of seismicity attended to describe the large amount of small earthquakes in order to extrapolate to the large earthquakes through scaling laws. Thus, it has been found that independent seismicity uses to follow a Poissonian law whereas the dependant events follow a time-reversal law. However, these laws have been described in California or Japan, where seismicity is strong. Regarding the low amount of data in low seismicity areas like French mainland, the adequacy of these laws can be questioned. This seminar highlights the drawbacks brought by a classical model of seismic hazard estimation when applied on low seismic activity areas. A scheme is proposed to overcome these issues.
Speaker(s): Luc Scholtes

Location: Meeting room, ENSG Bat E, Nancy.
 
Date: Thursday 12th of March.

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.
Speaker(s): Zoé Renat

Location: Room G201, ENSG Bat G, Nancy.
 
Date: Thursday 27th of February, 1:00 pm
 
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.
Speaker(s): Khalifa Eldursi
 
Location: Meeting room, ENSG Bat E, Nancy.
 
Date: Wendnesday 19th of February, 1:00 pm
 
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.
Speaker(s): Yves Frantz

Location: Room G201, ENSG Bat G, Nancy.
 
Date: Thursday 13th of February, 1:00 pm
 
Abstract:
 
Bibliographic seminar presenting different karstic network skeleton simulation methods.
Speaker(s): DU KOU
 
Location: Meeting room, ENSG Bat E, Nancy.
 
Date: Thursday 06th of February, 1:00 pm
 
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.
Speaker(s): Capucine Legentil
 
Date: Thursday 23rd of January, 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).
Speaker(s): Farah Al Sahyouni

Date: Thursday 16th of January, 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.
 
Date: Friday 13th of December, 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.
Speaker(s): Assohoun Wilfried Ahoulou
 
Date: Thursday 28th of November, 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).

Speaker(s): Paul Baville

Date: Thursday 21st of November 2019

Location: room G201, ENSG, Nancy

Abstract:

My main Phd topic is the computer assisted well correlation and I will present you two correlation rules based on (1) facies interpretations and (2) time surface geometry applied on data set from the North Sea, provided by Equinor ASA.
1. Facies correlation. Wells are cored and these cores are interpreted in several facies categorized by their paleo-depth (from  distal to continental deposits). Wells are also categorized regarding their distality in the sedimentary basin and the main sediment transport direction in the basin. Knowing the well distality and the facies paleo-depth, it is possible to compute a correlation cost for each couple of markers (between two wells).
2. Time surface geometry. Dip meter data is acquired along well paths during their drilling. Using this 3D data, it is possible to generate a 2D curve (3D surface) between 2 markers (3+ markers) using bezier curves (surfaces). In this seminar I will focus on 2D curves and 3D triangles (correlation between 2 and 3 wells, respectively). Knowing the paleo-environment, the bezier curve or triangle is generated. The comparison of its geometry to the top and base reservoir surfaces leads to a validation or not of the correlation.

Speaker(s): Nicolas Clausolles

Date: Thursday 17th of October 2019

Location: room G201, ENSG, Nancy

Abstract:

Seismic imaging of salt environments is prone to large uncertainties due to the peculiar salt physical properties. A lot of studies have been focusing on the development of automatic interpretation methods during the last decades. These methods aim at determining the best possible predicate for the salt boundary, but do not allow for the characterizaion of the uncertainties underlying the generation of seismic images.
During my three years of PhD, I have been working on the development of a method for stochastically generating different structural interpretations of salt bodies from a given seismic image. During this seminary, I will present the method I have developed and early results on its application to the characterization and the sampling of the uncertainties underlying seismic images.

 


Speaker(s): Corentin Gouache

Date: Tuesday 08th of October 2019

Location: room G201, ENSG, Nancy

Abstract:

Les approches probabilistes du risque sismique sont sensibles à un paramètre-clé qu'est le catalogue de sismicité utilisé en entrée. Celui-ci conditionne aussi bien la spatialisation que la fréquence et la sévérité des évènements possibles modélisés. Dans le but de générer une multitude de séries de séismes indépendants pour la France (métropole et Antilles), une approche basée sur les temps de latence entre les évènements sismiques (Hainzl et al., 2006) est ici présentée. Celle-ci nous permet de calculer le pourcentage de séismes indépendants contenus dans un catalogue de sismicité. En multipliant ce pourcentage à la fréquence annuelle de l’ensemble des séismes par tranche de magnitude (Gutenberg-Richter, GR) il est possible de calculer une répartition temporelle des séismes indépendants en fonction de la magnitude. Cependant, les catalogues sismiques incorporent des incertitudes ou lacunes : faibles représentativité des faibles magnitudes dû à la résolution et à la géométrie du réseau de sismomètres, incertitudes sur les principaux paramètres des catalogues (localisation 3D et magnitude) dues aux modèles de vitesses utilisés ainsi qu’aux méthodes employées pour le calcul de la magnitude.

Afin de ne travailler que sur des catalogues exhaustifs en fréquence/magnitude des évènements selon différentes profondeurs historiques, une méthode d'optimisation basée sur la minimisation d'un résidu entre une loi GR théorique et une loi GR observée (Weimer et Wyss, 2000) est réalisée. Ainsi il est possible, à partir du catalogue initial, de ne garder que les informations validées selon des critères et servant à la génération stochastique de séismes.

Enfin, dans le but de propager les incertitudes sur les différents paramètres, et notamment la magnitude des séismes, une approche type Monte Carlo est utilisée. A partir du catalogue sismique de base, une infinité de catalogues initiaux peuvent être générés. Chacun de ces catalogues possède un nombre identique de séismes dont la magnitude est tirée dans une loi normale centrée sur la valeur initiale de la magnitude ± son incertitude.


Speaker(s): Modeste Irakarama

Date: Thursday 18th of July 2019

Location: room G201, ENSG, Nancy

Abstract:

Potential methods, such as gravity and magnetic, are extensively used for subsurface exploration of mineral and geothermal reservoirs. In the last five decades, a number of efficient schemes for forward modeling of potential methods have been proposed. In this seminar, I will present a basic review of these forward modeling methods. I will insist mainly on the numerical aspects of the methods. These methods rely on an efficient implementation of an integral solution to the Poisson equation. Because this integral solution does not require matrix inversion, and because the Poisson equation appears in a number of physical phenomena, I will conclude the talk by contemplating the possibility of solving physical problems on implicit subsurface structural models without matrix inversion. The physical problems of interest obviously include gravity and magnetic problems, which are the subject of this talk, but also other problems such as fluid flow in the subsurface.