Speaker(s): Yves Frantz

Date: Tuesday 15th 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 21st 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.

Speaker(s): Corentin Gouache

Date: Thursday 13th of December 2018

Location: room G201, ENSG, Nancy

Abstract:

During this seminar I will deal with seismic catalogues exhaustiveness. The goal is to find from which minimal threshold magnitude (cut magnitude) all the happened earthquakes have been recorded. This study is regionalized for the purpose of finding suspected different seismic behaviors according to geodynamical context. To do that, I will present you the catalogue that I use. Then I will show you different methods used to find the cut magnitudes of each catalogue (one per region). Finally I will discuss results coherency by applying scale laws on these supposed exhaustive catalogues.

Speaker(s): Nicolas Mastio

Date: Thursday 29th of November 2018

Location: room G201, ENSG, Nancy

Abstract:

Time-lapse seismic has become a useful tool for reservoir monitoring and well stability assessment. Geophysicists have developed numerous methods to retrieve time-lapse attributes for the reservoir and for the overburden. However, these methods do not consider the physical differences between these two area during the inversion process. From a theoretical perspective, the elastic properties depend on the stress state. Consequently, this induces an anisotropy in the time-lapse velocity change which can have various origins: reservoir compaction, rocks damaging, etc.

Edgar and Mastio (2017) expose a reflection travel time tomography adapted to retrieve the time-lapse velocity change. An extension of this method which considers velocity change general anisotropy is presented and applied to a real case.

Speaker(s): Pauline Collon

Date: Friday 23rd of November 2018

Location: room G201, ENSG, Nancy

Abstract:

During this seminary, I present an overview of all the works related to the karstic systems thematic that have been carried out over the last ten years at RING. I emphasize especially two complementary aspects I worked on: the stochastic simulation of karstic systems and the statistical analysis of existing karstic networks.

Speaker(s): Modeste Irakarama

Date: Thursday 15th of November 2018

Location: room G201, ENSG, Nancy

Abstract:

I introduce a new method for implicit structural modeling. The method is based on a finite element discretization of recently proposed regularization operators for implicit modeling. A finite element implicit modeling scheme offers some geometrical flexibility as it is readily implemented on structured, unstructured, and mixed-element grids. While implicit modeling on unstructured grids is not new, the method proposed here is, to my very limited knowledge, the first implementation based on finite elements. The finite element method is routinely used to solve boundary value problems. However, because boundary conditions are usually unknown in implicit structural modeling, the traditional finite element method requires minor adjustments in order to be suitable for implicit modeling.

Speaker(s): Corentin Gouache

Date: Friday 12th of October 2018

Location: room G201, ENSG, Nancy

Abstract:

Ce séminaire sera l'occasion de faire découvrir aux 3A 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.

 

Speaker(s): Guillaume Caumon

Date: Friday 5th of October 2018

Location: room G201, ENSG, Nancy

Abstract:

Geologists and geophysicists often approach the study of the Earth using different and complementary perspectives. To simplify, geologists like to define and study objects and make hypotheses about their origin, whereas geophysicists often see the earth as a large, mostly unknown multivariate parameter field controlling complex physical processes. This chapter discusses some strategies to combine both approaches. In particular, I review some practical and theoretical frameworks associating petrophysical heterogeneities to the geometry and the history of geological objects. These frameworks open interesting perspectives to define prior parameter space in geophysical inverse problems, which can be consequential in under-constrained cases.

This seminar is associated with the eponymous book chapter published in the 2018 IAMG Handbook of Mathematical Geosciences (available for download here).

Speaker(s): Paul Cupillard

Date: Friday 14th of September 2018

Location: room G201, ENSG, Nancy

Abstract:

We present a general concept for evolutionary, collaborative, multiscale inversion of geophysical data, specifically applied to the construction of a first-generation Collaborative Seismic Earth Model. This is intended to address the limited resources of individual researchers and the often limited use of previously accumulated knowledge. Model evolution rests on a Bayesian updating scheme, simplified into a deterministic method that honors today’s computational restrictions. The scheme is able to harness distributed human and computing power. It furthermore handles conflicting updates, as well as variable parameterizations of different model refinements or different inversion techniques. The first-generation Collaborative Seismic Earth Model comprises 12 refinements from full seismic waveform inversion, ranging from regional crustal- to continental-scale models. A global full-waveform inversion ensures that regional refinements translate into whole-Earth structure.