Speaker(s): {Radu Stoica}

Date: Thursday 11^th of April 2019

Location: room G201, ENSG, Nancy

Abstract:

Spatial data are sets of observations made of elements having two components. The first component gives the coordinates where the observation took place. The second component, represented usually by a multi-dimensional real vector, represents the measures associated at the corresponding location. Digital images, environmental data in epidemiology or catalogues of celestial bodies in astronomy are some typical examples of spatial data.
The spatial character of the data induces a strong morphological component to the possible answers that may be given to questions arising from the data analysis. This explains why the question almost always arising is what is the pattern hidden in the data ?
The main assumption of our work is that the pattern we are looking for is made of random objects that interact.
Marked point processes are a probabilistic tool able to model random configurations of interacting objects. The main difficulty with these models is that they do not always exhibit a precise analytical form for their normalising constants. Hence sampling from such a probability density requires adapted MCMC simulation. Within this framework, statistical inference can be done,using methods such as the simulated annealing algorithm, the Monte Carlo maximum likelihood, permutation tests and bootstrap methods.
The aim of this talk is to introduce marked point processes and to illustrate their applications with examples and data sets coming from : cosmology, image analysis and environmental sciences.

Speaker(s): {Jean-Marc Montel}

Date: Thursday 26^th of March 2019

Location: room G201, ENSG, Nancy

Abstract:

La statistique des semis de point (point processing) est un outil de statistique spatiale qui permet de caractériser la distribution des points sur une surface ou dans un espace. Il n'a jusqu'ici que très peu été utilisé en géosciences. Au cours de mon séminaire, je reviendrai sur les bases des semis de point puis j'expliquerai la démarche que je développe qui combine l'élaboration d'outils, le développement de simulations et la recherche d'objets géologiques pertinents. Je terminerai en montrant quelques exemples d'application.

Speaker(s): Philippe Renard

Date: Tuesday 12^th of March 2019

Location: amphitheater H, ENSG, Nancy

Abstract:

Groundwater resources are heavily used on earth for drinking water supply and agriculture. They are endangered by overexploitation and contamination. To manage and protect them, it is often important to model aquifers with an apropriate level of details, and most often the main difficulty is to represent geological heterogeneity. How to represent the geological heterogeneity in groundwater models and is it worth to do it are the main questions that will be discussed in this presentation with a pair of practical examples in fluvio-glacial systems.

Speaker(s): {mattia martinelli}

Date: Thursday 7^th of March 2019

Location: room G201, ENSG, Nancy

Abstract:

Outcrop analogues have an important role in hydrocarbon exploration and reservoir characterization, because they can help filling the gap between seismic and borehole scale. In this seminary, I will present the results from our project in the Gozo Island (Maltese Archipelago). Here, a Late Oligocene-Early Messinian carbonatic sequence, composed by different types of carbonates, was affected by two main extensional tectonic : i) NW-SE extension during the Aquitanian ii) N-S extension from the Middle Miocene onward. These tectonic events instigated the formation of a complex fracture network, that was investigated using 3D Digital Outcrop Models (DOM) based on photogrammetric drone surveys, and extracted from key outcrops in different units. It allowed us to quantitatively characterize fracture parameters within different mechanic/stratigraphic facies. All this information were used to reconstruct the fracture pattern variability at the scale of the whole island. The next step of this work will be to realize a DFN model using the obtained fracture parameters.

Speaker(s): Pierre Anquez

Date: Tuesday 21^st of February 2019

Location: room G201, ENSG, Nancy

Abstract:

In this work in collaboration with the MouvGS team of the CEREMA (Sophia-Antipolis), we study site effects in the lower Var valley near Nice. We propose to simulate plane wave propagation in a SW-NE cross-section using Discontinuous Galerkin FE solver. To do so, we need a triangular mesh of the cross-section. Due to tangential contacts and thin layers, the quality of the mesh is poor : some triangles are very flat leading us to decrease time discretization for the simulations. As a consequence, the computation time of simulations severely increases. A 6-second wave propagation simulation on this model takes us more than 18 days ! This is completely impractical.
In this seminar, I will show strategies of model simplifications, using manual and automatic methods, with the aim of decreasing the computation time. We propose different models and we make a comparison of simulations results using these models.

Speaker(s): Paul Baville

Date: Tuesday 14^th of February 2019

Location: room G201, ENSG, Nancy

Abstract:

Depuis près de 10 ans, une intense activité autour des corrélations automatiques de puits s'est mise en place. Ainsi, 2 thèses ont été menées par Florent Lallier (Corrélation de puits stochastique en 2012) et Jonathan Edwards (Gestion des incertitudes dans la corrélation stratigraphique de puits en 2017) au sein de l'équipe et un nouveau projet WeCo a vu le jour depuis environ 1 an. C'est à mon tour désormais et je voudrais vous présenter les différents outils utilisés et développés au labo que je vais utiliser pendant ma thèse.
Je vais d'abord faire un bref résumé de ce qu'on peut interpréter à partir de données de carottes et de logs pour obtenir des marqueurs sur chaque puits. Ensuite je vais vous présenter l’outil Dynamic Time Warping DWT et comment il est utilisé dans le processus de corrélation de puits. Et pour finir je vais vous parler de ce que je compte faire au début de ma thèse.

Speaker(s): Guillaume Caumon

Date: Tuesday 31^rst of January 2019

Location: room G201, ENSG, Nancy

Abstract:

Le but de ce séminaire est de partager avec vous quelques aspects très intéressants des thèses auxquelles j'ai eu la chance de participer depuis Décembre: Résolution du problème inverse (Christoph Jäggli, Neuchâtel), Modélisation de surfaces complexes (Joseph Baudrillard, Grenoble), Cartes Généralisées (Valentin Gauthier, Poitiers). Je ne parlerai donc pas de l'état adjoint continu (Hamid Badri, Strasbourg), car il nous a déjà été présenté l'an dernier par Fred Delay et Philippe Ackerer.

Speaker(s): Yves Frantz

Date: Tuesday 15^th of January 2019

Location: room G201, ENSG, Nancy

Abstract:

Despite intensive explorations by speleologists, karstic systems remain only partially described as many conduits are not accessible to humans. Paleokarsts are buried karstic systems with a significant reservoir potential but they are not easily identifiable on seismic images, which leads to a huge uncertainty on the corresponding underground flow simulations. Stochastic simulations of karstic networks allow to better assess that uncertainty but only if the simulated networks are comparable to those observed in the field. One way to ensure some realism is to reproduce the topologies and geometries of explored networks, as proposed in various recent works.  
The height and width of the conduits are directly measured by speleologists. The general width-height ratio of different networks was already studied, but no generic study seems to have be done on their spatial repartition. It leads to a lack of constraints when simulating conduit dimensions (sections or volumes) during modeling, which is, however, a crucial parameter for further flow simulations.
During this seminar, I will present the results obtained during the analysis of a set of different explored karstic systems. Our goal was to check if there are typical distributions of height, width and section of conduits within the networks. Based on the obtained results, I will also present a method to stochastically simulate the average radius and width-heigth ratio of karstic conduits.

Speaker(s): Mustapha Zakari

Date: Friday 21^st of December 2018

Location: room G201, ENSG, Nancy

Abstract:

Fluid flow modelling is usually based on "averaging strategies" which allow to reduce the number of unknowns in order to obtain accurate and efficient models. Classic fluid models like Navier-Stokes ones consider fluid particles which are usually large group of molecules and model their behavior using macroscopic quantities like densities, averaged velocities and so on. At a larger scale, porous media flow models use macroscopic cells containing "fluid and solid" information like porosity and permeability. Finally at the reservoir modelling scale, blocks of these macroscopic cells are used and upscaling procedures applied to produce large scale efficient models. This presentation will briefly introduce each of these "Upscaling" strategies. In order to check the validity of unstructured mesh Upscaling strategies, a single phase Control Volume Finite Element Method reservoir model will be presented. This model based on unstructured mesh calculations is then compared to a similar TPFA (Two Point Fluid Approximation) model to check its higher accuracy.