How informative are single well tracing experiments? : an assessment using Bayesian evidential learning

ATHEN

Muons tomography applied to geosciences and volcanology

Imaging the inner part of large geological targets is an important issue in geosciences with various applications. Dif- ferent approaches already exist (e.g. gravimetry, electrical tomography) that give access to a wide range of informations but with identified limitations or drawbacks (e.g. intrinsic ambiguity of the inverse problem, time consuming deployment of sensors over large distances). Here we present an alternative and complementary tomography method based on the measurement of the cosmic muons flux attenuation through the geological structures. We detail the basics of this muon tomography with a special emphasis on the photo-active detectors.Comment: Invited talk at the 6th conference on New Developments In Photodetection (NDIP'11), Lyon-France, July 4-8, 2011; Nuclear Instruments and Methods in Physics Research Section A, 201

Anisotropy of electrical conductivity of the Excavation Damaged Zone in the Mont Terri Underground Rock Laboratory

International audienceElectrical resistivity measurements were performed to characterize the anisotropy of electrical resistivity of the excavation damaged zone (EDZ) at the end-face of a gallery in the Opalinus clay of the Mont Terri Underground Rock Laboratory (URL). The data were acquired with a combination of square arrays in 18 zones on the gallery's face and in two series of four boreholes perpendicular to the face. Each data set is independently inverted using simulated annealing to recover the resistivity tensor. Both the stability and the non-uniqueness of the inverse problem are discussed with synthetic examples. The inversion of the data shows that the face is split in two domains separated by a tectonic fracture, with different resistivity values but with a common orientation. The direction of the maximum resistivity is found perpendicular to the bedding plane, and the direction of minimum resistivity is contained in the face's plane. These results show that the geo-electrical structure of the EDZ is controlled by a combination of effects due to tectonics, stratigraphy, and recent fracturing produced by the excavation of the gallery

Mise au point d'une méthode de tomographie utilisant les muons d'origine cosmique : Applications au laboratoire souterrain du Mont Terri et au volcan de la Soufrière de Guadeloupe

Les muons sont produits suite aux interactions de particules cosmiques avec l'atmosphère. La faible probabilité d'interaction des muons avec la matière leur permet d'atteindre la croûte terrestre et d'en traverser les premiers kilomètres. L'étude de l'atténuation du flux de muons permet alors d'obtenir une mesure directe de l'opacité de la roche. Cette opacité correspond à la masse volumique du milieu, intégrée le long du trajet parcouru à travers la roche. Il est donc possible de réaliser une tomographie d'objets géologiques. Un modèle de flux de muons souterrain est construit ici à partir de modèles de flux estimés en surface et d'un modèle d'atténuation à travers la roche. Il est nécessaire d'évaluer le temps minimal d'acquisition de données pour réaliser une tomographie. Une équation de faisabilité de la méthode est établie, elle dépend de l'objet étudié ainsi que de la capacité de détection du capteur utilisé. Des télescopes à muons ont été construits et conditionnés pour supporter une installation sur le terrain. Nous avons développé la modélisation de leur capacité de détection et de leur résolution angulaire et également mis au point une méthode de calibration permettant de corriger le signal d'une éventuelle distorsion. Le développement de cette nouvelle méthode de tomographie géophysique est ensuite illustrée de deux exemples d'applications. Les mesures réalisées dans le laboratoire souterrain du Mont Terri nous ont permis de bénéficier de conditions d'acquisition stables pour perfectionner la construction des télescopes et valider les différents modèles. Un second détecteur a ensuite été installé sur les flancs de la Soufrière de Guadeloupe

Design and operation of a field telescope for cosmic ray geophysical tomography

International audienceThe cosmic ray muon tomography gives an access to the density structure of geological targets. In the present article we describe a muon telescope adapted to harsh environmental conditions. In particular the design optimizes the total weight and power consumption to ease the deployment and increase the autonomy of the detector. The muon telescopes consist of at least two scintillator detection matrices readout by photosensors via optical fibres. Two photosensor options have been studied. The baseline option foresees one multianode photomultiplier (MAPM) per matrix. A second option using one multipixel photon counter (MPPC) per bar is under development. The readout electronics and data acquisition system developed for both options are detailed. We present a first data set acquired in open-sky conditions compared with the muon flux detected across geological objects

Assessment of short-term aquifer thermal energy storage for demand-side management perspectives : experimental and numerical developments

In the context of demand-side management and geothermal energy production, our proposal is to store thermal energy in shallow alluvial aquifers at shorter frequencies than classical seasonal aquifer thermal energy storage. We first conducted a one-week experiment in a shallow alluvial aquifer, which is characterized by a slow ambient groundwater flow, to assess its potential for thermal energy storage and recovery. This experiment has shown that up to 90% of the stored thermal energy can be recovered and would therefore suggest that aquifer thermal energy storage could be considered for demand-side management applications. We then conceptualized, developed, and calibrated a deterministic 3D groundwater flow and heat transport numerical model representing our study site, and we simulated 77 different scenarios to further assess this potential. This has allowed us to demonstrate that low-temperature aquifer thermal energy storage (temperature differences of −4 K for precooling and 3, 6, and 11 K for preheating) is efficient with energy recovery rates ranging from 78 to 87%, in a single aquifer thermal energy storage cycle. High-temperature aquifer thermal energy storage (temperature differences between 35 and 65 K) presents lower energy recovery rates, from 53 to 71%, with all other parameters remaining equals. Energy recovery rates decrease with increasing storage duration and this decrease is faster for higher temperatures. Retrieving directly useful heat (without upgrading with a groundwater heat pump) using only a single storage and recovery cycle appears to be complicated. Nevertheless, there is room for aquifer thermal energy storage optimization in space and time with regard to improving both the energy recovery rates and the recovered absolute temperatures