Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
From outcrops located in Provence (South-East France), we describe the distribution, the microstructures, and the petrophysical properties of deformation band networks related to both contractional and extensional tectonic events. In contraction, pervasively distributed networks of reverse-sense compactional shear bands are observed in all folded sand units of the foreland, whereas localized networks of clustered reverse-sense shear bands are only observed close to a large-scale thrust. In extensional setting, networks of clustered normal-sense shear bands are generally observed adjacent to map-scale faults (100 m–10 km scale), although some randomly distributed bands are also observed between these faults. Normal-sense cataclastic faults, i.e. zone of deformation bands containing a localized slip-surface, are also observed to be restricted to sand units, suggesting that faults initiated in the sands during extension, but not during contraction. Shear bands and faults show cataclastic microstructures with high-permeability reduction whereas compactional shear bands show crush microbreccia or protocataclastic microstructures with moderate permeability reduction. This basin-scale analysis underlines the major role of tectonic settings (thrust-fault versus normal-fault andersonian-stress regime) and the influence of inherited large-scale faults on the formation/localization of low-permeability shear bands. We also provide a geometrical analysis of the band network properties (spacing, thickness, shear/compaction ratio, degree of cataclasis, petrophysical properties) with respect to the median grain size, porosity and grain sorting of host sand. This analysis suggests that grain size, although less important than stress-state conditions and the presence of large-scale faults, has a non-negligible effect on band network geometry. No correlations are observed between the grain sorting, porosity and band network geometry.
ISSN: 0264-8172

hal-01116421
https://hal.archives-ouvertes.fr/hal-01116421
DOI : 10.1016/j.marpetgeo.2013.12.020

Éditeur(s) : HAL CCSD
Résumé : International audience
The purpose of our study is to model a geothermal reservoir. When geothermal reservoir are assumed to be composed of pure water, the transfer of mass and energy is classically described by two balance equations: mass balance equation and the energy balance equation. In addition to those equations, fluid velocity ist classically given by the Darcy law while thermodynamic properties, inferred from theoretical or empirical equations of state, are used to close the mathematical system. Once this system is closed, there exist different solutions. The first one is to solve for pressure and temperature with a variable switch to saturation in the two-phase region (e.g. TOUGH2). The second one is to solve for pressure and enthalpy to increase stability of phase transition between single and two-phase states (e.g. Hydrotherm). We adopted the second option and chose te use a splitting method to get rid of the complexity of coupling equations and a finite volume method for the spatial discretization. Selecting object-oriented languages, we developed a multi-language framework, combining Python, Fortran and a C++ implementation of IAPWS (from the freesteam project) including the supercritical equations, in porous media velocity is given by Darcy law and to close the system physical properties are determined by the IAPWS-IF97 thermodynamic formulation. We resolve the equations in pressure and enthalpy instead of pressure and temperature in order to increase stability and to handle easier the passage from a single-phase to a two-phase system. We solve the system by using a splitting method - to get rid of the complexity of coupling equations - and a finite volume method. We offer some freedom to users thanks to the implementation of several methods like explicit or implicit Euler, Runge-Kutta or BDF2 for time solvers or GMRES and BICGSTAB for the linear solver. We can handle several boundary conditions like no-flow - describing a boundary which can not exchange matter with the exterior - or like a mixed-therm condition - a Dirichlet condition to the pressure and a Dirichlet or an outflow condition to the temperature in order to describe a recharge or a discharge zone - ... We're developing a multi-language framework, combining Python, Fortran and the C++ implementation of IAPWS (from the freesteam project). All these languages are object-oriented. We've applied this simulation model to the dogger in Paris, France, to several one-dimensional systems and a two-dimensional one made by Coumou with the CSMP++ platform. The dogger is a reservoir exploited to produce heat by pumping water at 70 and reinjecting it in the reservoir at 40. In the one-dimensional systems we wanted to observe the process of heat transfer from a higher temperature boundary to a smaller one in a high-energy domain. The last simulation shows the natural convection of water in a fault. For every simulation we compared the solutions we found with an other code (TOUGH2 or CSMP++) and they agreed. The next step will be to model the geothermal plant in Guadeloupe, West Indies. It's the only place in France - and in the West Indies so far - producing electricity with the earth power. The temperature can reach up to 1000 and the pressure range is around a few hundreds MPa. In some surface zones we can see two-phase water at atmospheric pressure. In the 1980s Bouillante was a laboratory for France. Since 1995 Bouillante has given 30GWh electricity a year to the Guadeloupeans.
PROCEEDINGS, Thirty-Ninth Workshop on Geothermal Reservoir Engineering
Stanford, United States

Droits : info:eu-repo/semantics/OpenAccess
hal-00944133
https://hal-brgm.archives-ouvertes.fr/hal-00944133
https://hal-brgm.archives-ouvertes.fr/hal-00944133/document
https://hal-brgm.archives-ouvertes.fr/hal-00944133/file/Copol.pdf

Éditeur(s) : HAL CCSD
Résumé : In coastal carbonate aquifers submitted to a saline intrusion, water - rock interactions processes at the interface between freshwater and saltwater are a cause for heterogeneities development within the porous media. The dissolutions and precipitations induced by the mixing zone play a major role in the transport properties of the reservoir and so in the long term evolution of the saltwater intrusion. The characterization and the in situ observation of a current saline intrusion in the Llucmajor carbonate platform at the experimental site of Ses Sitjoles (South-Easth of Mallorca Island, Spain), allowed to study the temporal evolution of the saltwater intrusion and the biogeochemical processes active in the mixing zone. The influence of microstructure, characterized using X-Ray microtomography, on the petrophysical and flow properties was investigated in laboratory and flow-through experiments were also conducted to study the modifications of the microstructures when submitted to water - rock interactions processes. The mixing zone at the Ses Sitjoles site appears as quite thick and not very sensitive to climate and anthropic stress and is proved to be the locus of active microbiological activity. Laboratory studies highlight a strong control of the microporosity on transport processes and of pCO2 on water - rock interactions. The percolation experiments of slightly reactive waters reveal calcite dissolution together with a decrease in permeability due to a rearrangement of micro-grains within the microporous network.
Les processus d'interactions fluide-roche à l'interface eau douce-eau salée, dans les aquifères carbonatés côtiers soumis à une intrusion saline, sont une des causes du développement d'hétérogénéités dans la structure du milieu poreux. Les dissolutions et/ou précipitations engendrées par la présence de cette zone de mélange jouent un rôle déterminant pour les propriétés de transport du réservoir et donc l'évolution à long terme de l'intrusion d'eau salée. En prenant l'exemple de la plateforme carbonatée de Llucmajor au niveau du site expérimental de Ses Sitjoles (Sud-Est de Majorque, Espagne), un travail de caractérisation et d'observation in situ à moyen terme de l'intrusion saline actuelle de ce réservoir permet de décrire son évolution temporelle et les processus biogéochimiques actifs dans la zone de mélange. L'influence de la microstructure du milieu poreux, caractérisée par microtomographie RX, sur les propriétés pétrophysiques et hydrodynamiques est étudiée en laboratoire et des expériences de percolations d'eaux réactives (mélanges eau douce - eau salée et eau pure chargée en CO2) sont réalisées afin d'étudier les modifications de ces microstructures lorsqu'elles sont soumises à des interactions eau - roche. La zone de mélange eau douce - eau salée rencontrée au niveau du site de Ses Sitjoles est large et peu sensible aux contraintes extérieures (climatologiques et anthropiques) et constitue un lieu d'activité microbiologique particulièrement actif. En laboratoire, on observe un fort contrôle des phénomènes de transport par la microporosité et des processus d'interactions eau - roche par la pCO2. Dans le cas d'une percolation de fluides moyennement réactifs, les expériences mettent en évidence une dissolution de calcite accompagnée par une diminution de la perméabilité, liée à un réarrangement des micro-grains à l'intérieur du réseau microporeux.
https://tel.archives-ouvertes.fr/tel-00767152

tel-00767152
https://tel.archives-ouvertes.fr/tel-00767152
https://tel.archives-ouvertes.fr/tel-00767152/document
https://tel.archives-ouvertes.fr/tel-00767152/file/thesegaring.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Numerical programs for simulating flow and reactive transport in porous media are essential tools for predicting reservoir properties changes triggered by CO2 underground injection. At reservoir scale, meshed models in which equations are solved assuming that constant macroscopic properties can be defined in each cells, are widely used. However, the parameterization of the dissolution-precipitation problem and of the feedback effects of these processes on the flow field is still challenging. The problem arises from the mismatch between the scales at which averaged parameters are defined in the meshed model and the scale at which chemical reactions occur and modify the pore network geometry. In this paper we investigate the links between the dissolution mechanisms that control the porosity changes and the related changes of the reactive surface area and of the permeability. First, the reactive surface area is computed from X-ray microtomography data obtained before and after a set of dissolution experiments of pure calcite rock samples using distinctly different brine-CO2 mixtures characterizing homogeneous to heterogeneous dissolution regimes. The results are used to validate the power law empirical model relating the reactive surface area to porosity proposed by Luquot and Gauze (2009). Second, we investigate the spatial distribution of the effective hydraulic radius and of the tortuosity, two structural parameters that control permeability, in order to explain the different porosity-permeability relationships observed for heterogeneous and homogeneous dissolution regimes. It is shown that the increase of permeability is due to the decrease of the tortuosity for homogeneous dissolution, whereas it is due to the combination of tortuosity decrease and hydraulic radius increase for heterogeneous dissolution. For the intermediate dissolution regime, identified to be the optimal regime for increasing permeability with small changes in porosity, the increase of permeability results from a large increase in the mean effective hydraulic radius of the sample.
ISSN: 0169-7722

hal-00617671
https://hal.archives-ouvertes.fr/hal-00617671
DOI : 10.1016/j.jconhyd.2010.07.004