Investigations of Near-Field Thermal-Hydrologic-Mechanical-Chemical Models for Radioactive Waste Disposal in Clay/Shale Rock (original) (raw)
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Physics and Chemistry of The Earth, 2004
Terri (Suisse) : données et interprétation -La migration de gaz dans les roches argileuses est un sujet d'intérêt dans le cadre de différents types d'exploitation du sous-sol : que ce soit par exemple dans le domaine du stockage de gaz naturel, de la séquestration du CO 2 , comme éponte imperméable d'un aquifère, ou dans le domaine du stockage de déchets. Une analyse quantitative de la migration de gaz dans ces milieux à très faible perméabilité nécessite l'estimation des propriétés physiques de l'écoulement. Au laboratoire souterrain du Mont Terri (Suisse), dans les argiles à Opalinus, une roche sédimentaire jurassique, une série de tests hydrauliques et d'injection de gaz a été conduite en forages d'expérimentation. Leur but était en particulier de déterminer les propriétés de transfert des gaz dans cette roche. Cet article présente les résultats d'une campagne de tests (sollicitations de type essai hydraulique classique et test d'injection de gaz et récupération de pression de longue durée), conduite dans la roche « intacte », c'est-à-dire non perturbée mécaniquement par le creusement des galeries. Il présente une interprétation détaillée des tests reposant sur l'ajustement des données expérimentales au moyen d'un logiciel de simulation numérique biphasique (eau/gaz) de l'écoulement en milieu poreux (TOUGH2/iTOUGH2). Par analyse séquentielle, il a été possible d'obtenir un set de paramètres hydrauliques mono-et diphasiques cohérent sur l'ensemble de l'expérimentation. L'utilisation d'informations additionnelles et indépendantes sur les caractéristiques pétrophysiques de la roche (porosité et pression capillaire) a permis de mieux contraindre le problème inverse à l'étude. Bien qu'il soit difficile sur la base des différents modèles et ajustements réalisés, d'obtenir une solution unique en terme de courbe de pression capillaire et de perméabilité relative, les résultats indiquent qu'une paramétrisation classique de type Van Genuchten -Mualem serait valide. Enfin, des simulations prospectives sont présentées qui montrent que l'amélioration de la performance des essais en termes de détermination des paramètres biphasiques nécessiterait une augmentation notable de la durée de l'essai (> 1 an).
E3S Web of Conferences, 2016
The French national radioactive waste management agency (Andra) research program is dedicated to preparing the construction and operation of a deep geological disposal facility for high-level and intermediate-level long-lived radioactive waste (HL, IL-LLW) in the Callovo-Oxfordian claystone (COx). The characterization of the COx thermo-hydro-mechanical (THM) behavior, at different scales of interest, must gradually give relevant data for design and safety calculations. The effects of saturation and desaturation of COx claystone are studied in laboratory conditions (sample scale) and in situ (drift scale), in order to improve knowledge on ventilation effect at gallery wall as galleries will remains open during operational phase (more than 100 years for some specific galleries) in the repository. The Saturation Damaged Zone (SDZ) experiment is outlined and its results are discussed. This experimentation aims to change the relative humidity in an isolated portion of a gallery in order to follow the HM behavior of the surrounding rock mass. Drying and wetting cycles could induce in certain cases cracks and swelling and modify the hydromechanical behavior of the claystone around the gallery (Young modulus, strength, creep…). The long term behavior of the COx claystone at the vicinity of gallery is then studied by performing climatic, hydraulic, geological and geomechanical measurements. Results of the in situ experiment are discussed with respect to the identified process on samples. The discussion given on this paper intends to highlights the inputs from 7 years of an in situ experiment to better understand the unsaturated behavior of the COx claystone.
Active porosity in swelling shales: insight from the Callovo-Oxfordian claystone
Géotechnique Letters, 2018
In swelling shales, significant clay–water interactions take place along the faces of the smectite minerals contained in the clay fraction, giving rise to the distinction between free water and adsorbed water. Further insight was recently gained by means of microstructure investigations, showing that the hydration mechanisms of pure or compacted smectites also explain the hydration and swelling behaviour of the Callovo-Oxfordian claystone, a possible host rock for deep radioactive waste disposal in France. In this rock, the proportion of water molecules adsorbed in intra-platelet pores was estimated to be around 25% of the total porosity, with 75% of the porosity containing free water. On the basis of these findings, the data of high-precision poroelastic measurements conducted in an isotropic compression cell showed that the porosity to account for a proper calculation of Skempton's B coefficient is not the total porosity, but the 75% proportion of the porosity corresponding to...
Journal of Rock Mechanics and Geotechnical Engineering, 2018
The Canadian Nuclear Safety Commission (CNSC), Canada's nuclear regulator, conducts regulatory research in order to develop independent knowledge on safety aspects related to the deep geological disposal of radioactive wastes. In Canada, the Cobourg limestone of the Michigan Basin is currently considered as a potential host formation for geological disposal. The understanding of the hydromechanical behavior of such a host rock is one of the essential requirements for the assessment of its performance as a barrier against radionuclide migration. The excavation of galleries and shafts of a deep geological repository (DGR) can induce damage to the surrounding rock. The excavation damaged zone (EDZ) has higher permeability and reduced strength compared to the undisturbed rock and those factors must be considered in the design and safety assessment of the DGR. The extent and characteristics of the EDZ depend on the size of the opening, the rock type and its properties, and the in situ stresses, among other factors. In addition, the extent and characteristics of the EDZ can change with time due to rock strength degradation, evolution of fractures within the EDZ, and the redistribution of pore pressure around the excavation. In this research project initiated by the CNSC, the authors conducted experimental and theoretical research in order to assess the hydro-mechanical behavior of the Cobourg limestone under undamaged and damaged conditions, both in the short and long terms. The short-term behavior was investigated by a program of triaxial tests with the measurement of permeability evolution on specimens of Cobourg limestone. The authors formulate a coupled hydro-mechanical model to simulate the stress-strain response and evolution of the permeability during those triaxial tests. Using creep and relaxation data from a similar limestone, the model was extended to include its long-term strength degradation. The model successfully simulated both the short-and long-term hydro-mechanical behavior of the limestone during those tests. This provides confidence that the main physical processes have been adequately understood and formulated.
Applied Geochemistry, 2006
Disposal of nuclear waste in deep geological formations is expected to induce thermal fluxes for hundreds of years with maximum temperature reaching about 100-150°C in the nearfield argillaceous environment. The long-term behavior of clays subjected to such thermal gradients needs to be perfectly understood in safety assessment considerations. In this respect, a Toarcian argillaceous unit thermally disturbed by the intrusion of a 1.1-m wide basaltic dike at the Perthus pass (Herault, France), was studied in detail as a natural analogue. The thermal imprint induced by the dike was evaluated by a mineralogical, chemical and K-Ar study of the <2 lm clay fraction of shale samples collected at increasing distance from the basalt. The data suggest that the mineral composition of the shales was not significantly disturbed when the temperature was below 100-150°C. Closer to the dike at 150-300°C, changes such as progressive dissolution of chlorite and kaolinite, increased content of the mixed layers illite-smectite with more illite layers, complete decalcification and subsequent increased content of quartz, were found.