Speaker: Kou Du

Date: Thursday 18th of February 2021, 1:20 pm.

Abstract:

The aim of this presentation is to extend recent works devoted to the study of the effect of 3D pores of concave shape embedded in isotropic matrix to the case of transversely isotropic (TI) matrix. In the first part, we'll present a brief review of numerical calculation of compliance contribution tensors (which have been introduced in this seminar last year). Then, the approximate relations for the compliance contribution tensor of pores of two reference shapes, supersphere, and axisymmetrical superspheroid, are developed on the basis of 3D Finite Element Modelling, and known exact solutions for the limiting cases of spherical pores and circular crack. In the last part application to effective elastic coefficients of transversely isotropic materials in the frame of homogenization theory is presented to illustrate the impact of concavity parameter on overall properties.

Speaker: Guillaume Caumon

Date: Thursday 11th of February 2021, 1:20 pm.

Abstract:

In this seminar, I will present some work recently done in collaboration with Equinor on the use of magnetostratigraphic data to better constrain the ages of formations in the Central Graben. For this, we used individual correlation to 5 wells to the geomagnetic polarity time scale (GPTS) using the Cupydon code (Lallier et al, EPSL 2013). As the recorded series are relatively short, we also started to use magnetic chrons to constrain log-based multi-well correlation. The ultimate goal is to use these correlation results to create a composite magnetostratigraphic series that could be matched to the GPTS. Significant uncertainty yet exists about the results, as no external dating constraints are available. I will suggest some avenues for improving the methods and discuss some sources of uncertainty in the process.

 

Speaker: Ahmad Mostafa

Date: Thursday 4th of February 2021, 1:20 pm.

Abstract:

Coal beds are dual permeability systems characterized by a porous matrix enclosed within sets of orthogonal fractures known as cleats. Production of coalbed methane (CBM) consists of desorbing methane from the low permeable coal matrix to the high permeable cleat system. Unlike in conventional reservoir exploitation, sorption mechanisms cause shrinkage and swelling of the matrix which increase the complexity of the phenomena at stake, leading to complex reservoir behaviors in terms of production. A 3D discrete element method (DEM) coupled to a pore scale finite volume method (PFVM) is used here to better understand the different mechanisms at stake. The model, implemented in the open-source software Yade Open DEM (Smilauer et al., 2015), is an offspring of the hydro-mechanical model proposed by Catalano et al. (2014). The coal matrix is treated as an assembly of bonded particles interacting one with another through elastic-brittle contact laws. The pore space is discretized into tetrahedra, generated from a regular triangulation of the particle assembly. Both Knudsen and surface diffusion, as well as sorption processes, are modeled considering the coal matrix as a microporous material. The method is hydro-mechanically coupled in the sense that changes in pore pressure produce hydrostatic forces that deform the solid skeleton, while deformation of the pore space induces pore pressure changes that promote interporal flow. In addition, sorption induced deformations are taken into account by considering an additional pressure term related to the concentration of gas within the medium (the so-called solvation pressure). In this work, we first present the model and its constitutive equations. We assess its capabilities by comparing its predictions to well established solutions describing diffusive flow in porous media as well as to classic poroelasticity concepts. In particular, we focus on the influence of sorption induced deformations on the Biot coefficient estimation. Finally, we compare the model predictions to swelling test data from the literature to illustrate its consistency.

Speaker: Enrico Scarpa

Date: Thursday 28th of January 2021, 1:20 pm.

Abstract:

Nowadays, karst aquifers are strategic groundwater resources for the provision of drinking water all around the world. One-fourth of the population worldwide drinks water stored in karst aquifers, which are extremely vulnerable to various pollution sources. However, due to the complexity of karstification patterns and geometries, it is not easy to simulate groundwater flow in karstic aquifers. Over the last years, different techniques have been proposed to model karstic conduit networks (e.g., MODFLOW-CFP, GROUNDWATER). Those techniques include methods based on purely statistical approaches, object-based methods, genetic algorithms that mimic the physico-chemical processes that bring to conduit formation. Consequently, new possibilities have been introduced to evaluate the impact of karstic network architectures on groundwater flow accurately.
This work focuses on modeling the karst network stochastically using a geostatistical technique known as Multiple-Point Statistics (MPS) to characterize the karst architecture in the Dogger aquifer at the hydrogeological experimental site (HES) of Poitiers, France. In particular, here we apply the Direct Sampling (DS), an MPS simulation method, with the recent implementations proposed from the literature. Field data include core description, hydrogeological tests, and seismic surveys. A critical review of the available data set suggests the occurrence of cave patterns and several, well-identified, karst layers. The first step consists of reviewing all the (available data) collected in the last ten years and then studying the correlation between the geological, geophysical, and hydrogeological information. In the second step, DS simulations are performed to obtain several equiprobable realizations. These different DS outcomes can be compared and can estimate a global 3D karstic framework architecture of the Dogger aquifer. The resulting representation of the geological heterogeneity can support flow modeling at the HES and explore the impact of the karstic framework on the dynamic flow. 

Speaker: Fabrice Gbewade

Date: Thursday 21st of January 2021, 1:20 pm.

Abstract:

Prévoir l’endommagement hydraulique dans les systèmes géologiques constitue un challenge majeur dans l’ingénierie de subsurface. Ces processus très couplés hydro-mécaniquement (HM) qui naissent à différentes échelles, de l’échelle de la fissure (centimètre) à celle de la fracture ou de la faille (mètre ou décimètre), constituent des problèmes majeurs en géo-ingénierie qui ne sont pas encore complètement compris. L’objectif principal de ce projet est donc d’améliorer notre compréhension des processus HM qui prennent place en subsurface pour une meilleure évaluation des risques associés et de proposer des méthodes non intrusives permettant d’améliorer l’évaluation de ces processus. La présentation portera sur une synthèse bibliographique des essais de fracturations hydrauliques avec écoute acoustiques présents  dans la littérature en fonction de paramètres hydromécaniques.

Speaker: Capucine Legentil, Paul Baville & Zoé Renat

Date: Thursday 14th of January 2021, 1:20 pm.

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 et 3ème année (Capucine Legentil, Zoé Renat et Paul Baville).

Speaker: Xiaodong Zhang

Date: Thursday 7th of January 2021, 1:20 pm.

Abstract:

It is about a diffusive crack modeling based on the introduction of a phase field. A thermodynamically consistent framework has been primarily studied aiming at developing phase field models for elastics solids by considering the hydromechanical coupling.

Speaker: Fabrice Taty

Date: Thursday 17th of December 2020, 1:20 pm.

Abstract:

Le but de cet article était donc d’utiliser la théorie des graphes pour mieux comprendre les incertitudes liées à l’interprétation structurale. En effet, compte tenu des observations limitées et de la qualité médiocre des images sismiques, définir une architecture structurale est cependant fastidieux et est sujet à des incertitudes. Le formalisme de graphe nous permettra de trouver les associations possibles entre les différentes preuves de failles spatialement tout en utilisant des règles géologiques numériques dans le but de contraindre ces associations.

Speaker: Francois Bonneau

Date: Thursday 3rd of December, 1:20 pm and Thursday 10th of December, 1:20 pm.

Abstract:

Fracture networks (FN) are systems of complex mechanical discontinuities that dramatically impact the physical behavior of rocks. Their statistical characterization is an important first step of stochastic modeling. It is, however, a big challenge because field data are sparse and incomplete. Field observations present several biases due to sampling (censoring, truncation, orientation). The present paper concentrates on the statistical analysis of outcrops, which often may be considered as planar sections through three-dimensional FN. For the corresponding planar FN there exist well-elaborated statistical methods that yield first-order characteristics such as fracture density or fracture length distributions. Using ideas from stochastic geometry, in particular the theory of fiber processes and marked point processes, we develop second-order characteristics called pair correlation function and mark correlation function, which describe the variability of planar FN and their inner spatial correlations. Surprisingly, one of these characteristics is closely related to characteristics used in statistics of fractals applied to FN. We demonstrate the application of our ideas by field outcrops already published in the literature.