Speaker: Nathan Amrofel

Date: Thursday 15th of September 2022, 1:15 pm.

Abstract:
A full understanding of the migration behavior of corrosion gases in clay rock is of fundamental importance for the reliability of scenarios predicting the long-term evolution of geological repositories. Due to the low permeability of host clay rock, the produced gas will accumulate as a distinct phase until the pressure becomes large enough. The high pressure generated will desaturate the surrounding clay rock by displacement of pore water far along gas paths, but also by the diffusion of water vapor through the gas. In order to better understand the impact of key transport processes occurring in gas flow in clay material, a pore-scale numerical study taking into account the capillary-dominated two-phase flow, the diffusion of water vapor in the gas phase and specific features of nanoporous materials such as kelvin effect is proposed. The work has been carried out using the Smoothed Particle Hydrodynamics (SPH) method, a Lagrangian and meshless method which has emerged as an efficient and reliable tool for simulating complex fluid flows. A drying algorithm with Kelvin effect, which drives the thermodynamic equilibrium between the fluid phase and the gas phase at nanoscale, has been implemented in a two-phase flow SPH code, initially developed at IRSN.

Speaker: Narges Dashtbesh

Date: Thursday 23rd of June 2022, 1:15 pm.

Abstract:

Understanding and modelling contaminant transport is necessary to assess the lifetime of pollution sources and their severity and optimize the remediation strategies. The transfer of contaminants from the NAPL (Non-Aqueous Phase Liquid) phase to the aquifer is a multi-scale problem driven by mass transfer between both phases and is generally described by local non-equilibrium models. While the mass exchange coefficient, an important property in such models, play a key role in the fate of the pollution source, it is usually approximated by a constant value estimated from empirical correlations. However, it generally shows a transient behaviour and can evolve with NAPL phase composition and relative solubilities, which remains poorly studied. In this work, we upscale numerically this effective property from 2D pore-scale numerical simulations. We study the impact of different factors on the form and behaviour of the mass exchange coefficient in the presence of a multi-component NAPL source depending on whether the internal mass transfer is limiting. The potential implications of replacing this time-and-space-dependent mass transfer coefficient with a constant and unique value are discussed.

 

Speaker: Julien Herrero

Date: Thursday 16th of June 2022, 1:15 pm.

Abstract:

Evaluation of georesources involves to appropriately manage the level of detail needed in geomodels for subsurface porous flow and transport problems. The non-uniqueness of the problems considered in aquifer or reservoir modeling calls for using methods such as stochastic Bayesian inversion to appropriately estimate rock property parameters and quantify uncertainty. These approaches often consider a fixed number of model parameters. In geomodeling, however, some model components are discrete at the scale of concern (e.g., minerals, facies, fractures, layers), hence lead to unknown number of parameters in the inverse problem. To address this issue, we propose to use transdimensional Monte Carlo methods (also known as reversible jump Markov chain Monte Carlo) which are a way to solve the inverse problem with a suitable geological parameterization when the number of model parameters is an unknown. We consider as a first application example the 2D case of implicit layer interfaces defined by a level-set in a porous reservoir model. Using a Voronoi diagram parameterization, the number of discrete layers becomes an unknown parameter. Rather than randomly perturbing the petrophysical field of interest, we build the prior model by an averaging process of log data located inside layers. Hence, each layer is defined by thickness and interface depth information, and a constant petrophysical value. Through a history matching problem, a set of flow simulations is performed to generate production data used in the Markov chain as an acceptance criterion. These numerical simulations can only be solved on a model discretization conformal to discontinuities. To address this challenge, we capitalize on the local mesh updating strategy presented by Legentil et al. (2022). First results on a set of horizontal layers demonstrate that the algorithm is capable to capture the main geological discontinuities from a prior permeability model and flow data, suggesting that this transdimensional tool could be applied for more complex geometries such as anticlines or faulted reservoir models.

Speaker: Gloria Arienti

Date: Thursday 19th of May 2022, 1:15 pm.

Abstract:

Introduction to the geomodelling workflow that is being used to build the new 3D structural model of the Italian North-Western Alps. Input data are represented by structural surveys and detailed geological mapping, defining a truly 3D dataset that compensates for the absence of subsurface data thanks to important differences in elevation of 3-4 km, from valley floors to mountain summits. Our modelling workflow is based on a first step of conceptual modelling in vertical cross-sections, based on classical and sound structural concepts, followed by interpolation with implicit and explicit surface algorithms. In our area, geological complexity is given by several finite faults, internal to the model, that intersect each other as the result of multiple brittle deformation events. The basement units are also interested by polyphase ductile tectonics: isoclinal and cuspate-lobate folds, polyphasic folds, and other structures that produce great thickness variations of the lithological bodies.

Speaker: Luyu Wang

Date: Thursday 12th of May 2022, 1:15 pm.

Abstract:

In a geological repository, percolation of gas through clay rock may generate an expansion of the conductive pathways, which will lead to a localized displacement of water away from these paths. To this end, this work investigates the hydromechanical coupling during gas migration in saturated porous media. A mesoscopic model based on the multiple relaxation time Lattice Boltzmann Method (MRT-LBM) and the spring model is proposed, in which the interpolated bounce-back (IBB) boundary is applied to capture the exact displacement of the deformable pore walls with irregular shapes. We propose a numerical assessment of this non-conforming method, coupling IBB and LBM, by comparing with the reference solution obtained on the boundary-conforming grid. The impact of grid resolution on accuracy is discussed for single- and two-phase flow conditions.

Speaker: Guillaume Caumon

Date: Thursday 28th of April 2022, 1:15 pm.

Abstract:

This seminar will mainly consist of a review and explanation of some aspects of a recent paper by Miltenberger, Mukerji, Hariharan, Passalacqua & Nesvold (Mathematical Geoscience 2022), entitled: "A Graph-Theoretic Monte Carlo Framework for Comparing Delta Surface Dynamics and Subsurface Structure in Numerical Models and Physical Experiments".

Speaker: Xiaodong Zhang

Date: Thursday 21st of April 2022, 1:15 pm.

Abstract:

The prediction of fracture mechanisms in engineering materials and structure components is of great interest. The regularized damage modeling named as phase field approach has shown great efficiencies by approximating sharp crack surface with a diffusive variable to automatically study crack initiation and propagation without additional considerations of sharp crack discontinuities. This presentation proposes a phase field model for fracture in poroelastic media based on total energy minimization. We model the fluid flow by modifying Darcy's law considerig an additive part because of the crack and the fluid flow is controlled by the elastic energy and dissipation energy not the mass conservation balance as most papers. We use a staggered scheme and implement our approach in FEniCS.  Several benchmark examples are first realized for the assessment and validation of the proposed phase field model.

Speaker: Guillaume Modeste

Date: Thursday 14th of April 2022, 1:15 pm.

Abstract:

Malgré la forte émission de gaz à effet de serre liée à sa combustion, le charbon demeure une ressource stratégique. Produit lors du processus d'houillification, du méthane (ou gaz de charbon) est présent dans les couches de charbon, adsorbé à la surface des pores de la matrice charbonneuse. En diminuant la pression de fluide dans la couche de charbon par le pompage continu des eaux naturellement présentes, le méthane se désorbe puis est extrait. Comme toute activité souterraine, la question sur l'impact de l'extraction de gaz de charbon sur les déplacements de surface et la sismicité de la région se pose. La question est d'autant plus pertinente que la désorption induit des effets physico-mécaniques supplémentaires. La transposition des connaissances concernant les réservoirs conventionnels aux couches de charbon n'est donc pas triviale. En premier lieu, une cartographie des déplacements de surface sur la période 2014-2019 est réalisée par la technique d'interférométrie radar. La carte des résultats se révèle être le reflet des exploitations souterraines passées et présentes du bassin houiller lorrain. Le soulèvement dû à l'ennoyage des travaux miniers est par ailleurs nettement détecté. Ensuite, après une synthèse des propriétés géomécaniques des éléments géologiques et des contraintes régionales, un modèle géomécanique est élaboré pour étudier les déplacements de surface. En reproduisant la déformation volumique de la couche de charbon, la propagation de la perturbation à travers le recouvrement et ses répercussions en surface sont modélisées. La déformation induite par l'extraction est estimée à partir d'une loi empirique. Des déplacements cumulés de l'ordre de quelques centimètres peuvent être attendus. En dernier lieu, les travaux investiguent le potentiel impact de l'extraction sur la sismicité induite et la réactivation de failles. Toutefois, cette partie des travaux n'est que fraichement abordée et aucun résultat préliminaire n'est disponible. Ainsi, à travers cette étude, des informations sont apportées concernant l'état actuel des déplacements de surface dans le bassin houiller lorrain et des éléments de réponse concernant le potentiel impact de l'extraction de gaz de charbon sur les déplacements et la sismicité induite.

Speaker: Augustin Gouy

Date: Thursday 7th of April 2022, 1:15 pm.

Abstract:

Like most of the carbonate formations, the Barrois Limestones (South-east of the Paris Basin, France) are prone to karstification. At local scale, several penetrable conduits are known close to the main karst outlets, but little is known for smaller karst drainage systems. At the scale of the recharge area, tracer tests and many surface and subsurface karst features reveal a large extension of the karst drainage system governing flow and transport in the whole aquifer, but its exact geometry is also unknown. This lack of information is the main factor limiting the use of physically-based models of flow and transport for most karst aquifers. A method able to simulate possible karst network geometries accounting for uncertainties at different scales is thus required. While several methods have been proposed in the literature, none of them have been tested on a well-documented site like the Barrois Limestones. Indeed, this case study is characterized by a large amount of pluri-disciplinary data used to build a 3D comprehensive and integrative conceptual model of the whole karst aquifer, including stratigraphic and geological models, cave topographies and speleogenetic concepts, land markers of karsts, well logging and hydraulic tests, surface observations of fractures, geochemistry, tracer tests, etc. In this work, we aim at explicitly generating a set of possible geometries for the Barrois karstic network using a stochastic approach constrained by the pluridisciplinary information stored in the 3D conceptual model. After presenting the site, we propose a brief review of karstic networks simulation methods. Their applicability is discussed regarding the different scales at which we want to study the area, the corresponding data and the objectives of the associated flow simulation.