Speaker: Baptiste Rousset
Date: Wednesday 21st of February 2024, 1:15pm.
Abstract:
Like earthquakes, transient slow slip events participate in the release of accumulated strain at plate boundaries. They occur in various tectonic contexts including shallow creeping sections of strike slip faults, the brittle ductile transition of subduction zones in concurrence with tectonic tremors and the seismogenic part of subduction zones, sometimes associated with seismicity. In this talk, I will present the advantages and limits of geodesy techniques including GNSS, InSAR and tiltmeters, to characterize slow slip events in these various contexts through three case studies. The first one will be on the Izmit section of the north Anatolian Faults in Turkey, the second on the Mexico subduction zone and the third on the Sagami trough in Japan. I will finally present an ongoing project to measure the transient aseismic deformation associated with deep geothermal wells in Alsace.
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- Category: Seminar
Speaker: Simon Daout
Date: Thursday 21st of December 2023, 1:15pm.
Abstract:
In this presentation, I will present you the results obtained in a recent publication entitled: « Along-strike variations of strain partitioning within the Apennines determined from large-scale multi-temporal InSAR analysis, https://doi.org/10.1016/j.tecto.2023.230076 ». In this paper, we produced and analyzed a large set of GPS and InSAR measurements over the Apennines (Italy), where the origin of the long-wavelength topography and the driving mechanisms of the extension are debated. Our continuous mapping of the surface displacements across the range allows to understand how the different deformation scales (fault tectonic, landslides, surface processes, hydrological loading, mantle processes) are imbricated and how faults behave in relation to driving mechanisms at the boundaries of the system. Although, I hope this presentation can be relevant from the scientific point of view of various fields (seismology, geomorphology, geodynamic, remote sensing), here, I would like to particularly focus on numerical models and the development of inversion tools to derive the spatio-temporal evolution of seismic and aseismic slip on faults.
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- Category: Seminar
Speaker: Augustin Gouy
Date: Thursday 15th of February 2024, 1:15pm.
Abstract:
In karst aquifers, groundwater flow is highly influenced by the interconnected underground cavities and conduits that form the karst network. Modeling karst flows requires the use of spatially distributed approaches accounting for these networks. Their exploration is, however, often complex, and mapping them using indirect methods such as geophysical ones has proven challenging. To overcome these limitations, stochastically simulating discrete karst networks should account for the uncertainties on conduit position and geometry. Only a few existing methods can reproduce realistic and diverse karst morphologies. We present a public C++ code, KarstNSim, for simulating discrete karst networks, that incorporates field data to generate a range of possible karst network geometries. It relies on the computation of the shortest path between the inlets and outlets of the network with the use of an anisotropic cost function defined on an n-nearest neighbor graph conformal to geological and structural heterogeneities. This cost function represents the physico-chemical processes that govern speleogenesis – such as erosion and chemical weathering – providing simplified control over the geometry of the generated networks. Our approach reproduces the vadose-phreatic partition visible in the karst networks, by generating sub-vertical conduits in the unsaturated zone and sub-horizontal ones in the saturated part. It encompasses geological parameters such as inception surfaces, fractures, permeability, and solubility of layers, along with considering the hydrological context of recharge by assigning relative weights to the inlets. A demonstration of how to use the code will be provided, covering the process from defining inputs to displaying outputs on a geomodeling software.
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- Category: Seminar
Speaker: Yu Zhang
Date: Friday 26th of January 2024, 1:15pm.
Abstract:
Natural gas hydrate is regarded as a potential unconventional alternative clean energy with development prospects because of its huge reserves, high calorific value, and environmental protection. The Outline of China's Medium-and Long-Term Science and Technology Development Plan (2006-2020) clearly puts forward "breaking through the safe exploitation technology of natural gas hydrate"; China's 14th Five-Year Plan and the long-term goal outline for 2035 also put forward "trial production of natural gas hydrate in South China Sea and other areas". In the process of gas hydrate exploitation, the reservoir pores are in the state of gas hydrate solid-decomposed liquid-decomposed gas coexisting and filling, showing the characteristics of "high porosity, gas-water permeability and slightly low strength"; Macroscopic performance is reservoir compaction and wellbore collapse, and microscopic performance is pore structure and gas-water permeability evolution, which directly affects wellbore stability; The above problems are bottlenecks faced by efficient exploitation of natural gas hydrate
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- Category: Seminar
Speaker: Ahmad Marvi Mashhadi
Date: Thursday 30th of November 2023, 1:15pm.
Abstract:
At the present time, however, the geological storage of H2 remains very little studied despite of the specific behaviour of this gas. A key point in the development of such technology is to characterize and constrain the biological processes that could alter qualitatively and quantitatively the resource within the storage framework in porous reservoir rocks. As first electron donor for life and crucial energy source for subsurface microbial processes, indeed, H2 allows the autotrophic growth of microorganisms under oligotrophic conditions (i.e. limited supply of carbon) in deep environments. In the presence of an available terminal electron acceptor such as nitrate (NO3-), ferric iron (Fe3+), sulfate (SO42-) or carbon dioxide (CO2), H2 is susceptible to be consumed by microorganisms to gain energy. To date, unravelling the contribution of H2-consuming microbes in the biogeochemical cycle of hydrogen is of high importance in a number of subsurface industries including H2 gas storage in the energy transition context. Particularly, bacterial activity is susceptible to produce methane (CH4) or hydrogen sulfide (H2S) to the detriment of H2. The main objective of this work will be to evaluate the kinetics of H2 consumption by bacterial model strains and multi-bacterial consortia under geological storage conditions in terms of temperature, pressure, salt concentration and electron acceptor availability. Batch and flow-through experiment will be designed to reproduce these storage conditions.
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- Category: Seminar
Speaker: Guillaume Pirot
Date: Thursday 18th of January 2024, 1:15pm.
Abstract:
The mining industry faces various challenges to satisfy the increasing demand of minerals for clean energy transitions. One of them is to improve geological characterization at the stage of undercover exploration. This usually requires costly drilling operations. Can we reduce our exploration footprint and costs while reducing geological uncertainty by optimising our drilling location design? Here I propose two ways to look at this problem, based on data from the Hamersley basin, WA, Australia. One examines legacy drillholes in the area and investigate the impact of removing drillholes on the quality of geological models. The other one explores an iterative drilling optimisation approach to reduce modelled geological uncertainty, based on a synthetic case.
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- Category: Seminar
Speaker: Amandine Fratani
Date: Thursday 23rd of November 2023, 1:15pm.
Abstract:
During geological exploration, interpretation of faults can be ambiguous and uncertain because of disparate and often sparse observations such as fault traces on 2D seismic images or outcrops. The problem of associating partial fault observations was considered by Godefroy et al (2019), who decided to define a graph where each possible association of two fault observations (the graph nodes) are represented by an edge. The likelihood of this association was computed by using expert geological rules. However, fault observations are not pairwise independent, which limits the consideration of higher-order effects. For instance, the multiple-point association can be used to infer the evolution of the throw along the fault. In addition, the definition of rules in a multiple-point problem is also difficult because of the very large number of cases to consider. Here, we propose a machine learning approach to compute the likelihood of three-point fault data association. First, a computation of fault features (i.e. the length of the fault trace) from sections extracted from known 3D geological models is realized to create a data set of fault observations. The supervised machine learning problem is formulated as a classification problem to determine the probability that 3 fault observations belong to the same fault objects based on the feature vector. To prevent overfitting, we propose to mimic a partly interpreted case: we split the 3D domain in two disjoint sectors A and B, and use only data from sector A as training and data from sector B to test the method. However, the results are not conclusive, so an analysis of the features are proposed to choose the correct ones. At the same time, methods to deal with imbalanced dataset are explored.
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- Category: Seminar
Speaker: Franck Sfiligoi-Taillandier
Date: Thursday 11th of January 2024, 1:15pm.
Abstract:
Les modèles Agent (ou modèles multi-agents), issus du domaine de l’Intelligence Artificielle, sont particulièrement intéressants pour la modélisation et la simulation des systèmes sociaux et sociaux-techniques. Contrairement aux approches par apprentissage (Deep learning, Machine learning…), ils passent par une modélisation et une simulation explicite et naturelle des entités constitutives des systèmes et de leurs interactions, ce qui permet de faciliter la compréhension du système et de l’explorer. Ce côté intuitif et ouvert (par opposition aux boites noires), rend ces modèles particulièrement adaptés aux approches de modélisation et de simulation participatives. La modélisation participative est une approche dans laquelle les parties prenantes sont directement impliquées dans la construction du modèle. La simulation participative renvoie à une simulation interactive dans laquelle l’utilisateur peut modifier le cours de la simulation ; cette approche est beaucoup utilisée dans le cadre des jeux sérieux. Dans cette présentation, je reviendrai sur ces différents éléments en me basant sur des applications liées à la gestion des territoires, et en essayant de vous convaincre de l’intérêt de ces approches dans un dispositif d’aide à la décision ainsi que de leur valeur scientifique.
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- Category: Seminar