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  • Publication
    Accès libre
    Multidisciplinary approach to understand the localization of geothermal anomalies in the Upper Rhine Graben from regional to local scale
    (2012)
    Baillieux, Paul
    ;
    Schill, Eva 
    This thesis is devoted to understanding the localization of geothermal anomalies in extensional tectonic settings away from active volcanic areas. In this context, the European Cenozoic Rift System (ECRIS) hosts some of the major geothermal anomalies in Europe. Its central segment, the Upper Rhine Graben (URG), stretching over 300km between Basel Switzerland) and Frankfurt (Germany), reveals several surface heat flow anomalies in the order of up to > 150 mW m-2 (compared to an average of 60 mW m-2 in Europe) and temperatures up to 120°C at 1km depth, when usually a mean temperature gradient of 30°C km-1 is observed.
    In the Upper Rhine Graben, geothermal activity has mainly been attributed to free hydrothermal convection at graben scale, as well as free convection along the major faults in the area of Landau and at the European Enhanced Geothermal System (EGS) test-site Soultz.
    These local phenomena emphasize that temperature is not homogeneously distributed in the URG and neither are geothermal anomalies. Different geological facts were solicited to explain the localization of geothermal anomalies in the URG. The geothermal anomaly at Soultz has been on the one hand attributed to recent compressive shear strain occurring parallel to the central segment of the graben, allowing hydrothermal circulation to occur along favorably oriented fracture zones in the basement and in the high porosity sandstone aquifer above it. On the other hand it has been correlated to the lithological nature of the basement and its inherited orientations.
    In this thesis, 3D geological modeling, boreholes temperatures distribution, gravity, magnetics, slip and dilation tendencies analysis, neotectonic activity and geodynamic modeling have been used to investigate geological patterns associated with the localization of geothermal anomalies at graben-wide scale (the URG) and pluri-kilometric scale (in the area of the EGS Soultz).
    The comparison of geophysical data with the temperature distribution at graben scale has shown that zones of temperature highs can be related to the occurrence of low density basement that can be attributed to crystalline ridges offering an optimal radiogenic heat production and heat conductivity but also to porosity changes associated with faulting and hydrothermal circulation. In particular, zones of magnetic highs and gravity lows are related to additional temperatures in the order 10-20°C at 2000m true-vertical depth (TVD) at a graben wide scale (temperature 100-110 °C compared to a mean 90°C with minimum value of 75°C).
    Additionally, the occurrence of compression shear and uplift regime, with low Quaternary sedimentation, in the central segment of the URG appears to be linked to the major geothermal anomalies (120 to > 140 °C at 2000 m TVD) in the area of Soultz, Landau and Speyer. This may be explained by a change in tectonic regime from the Early Miocene to up to Present, and is in favor of the interpretation of the central segment of the URG being a restraining band separating two-pull apart basin in a sinistral strike-slip regime. Surprisingly, a relative low seismicity is observed in this area, which to an uncertain extent, maybe linked to the occurrence of naturally circulating fluids.
    More locally in Soultz area, a new 3D geological model has been elaborated on the basis of a high density set of 2D seismic profiles and deep boreholes to understand the links between structural and lithological patterns and the temperature distribution. A mean temperature anomaly of 40 °C at top basement has been linked to a light and magnetic granodioritic pluton offering a rather high radiogenic heat production. Moreover, hydrothermal circulation has been found to occur along N-S directed major faults with a West dipping signature in the western side of horst structures, and is held responsible for temperature anomalies above 60 °C, and this correlates with magnetotelluric observations and fracture orientations in Soultz boreholes. The majority of faults are favorably oriented in the current stress field to be reactivated and undergo dilation at depth and thus allow hydrothermal convection, but no clear relationship between these phenomena has been observed in the slip and dilation tendency analyses, and this can possibly be explained by asymmetric deformation patterns in the area, or by the sealing of the other faults due to intense mineralization. Another possible explanation is the fluid circulation characterized by an upward flow of hot water with a meteoric signature as a result of fluid inclusions analyses, and this deep circulation is interpreted to be coming from the Vosges mountain basement to the West, and this correlates with gravity residuals analyses.
    Finally, the geodynamic modeling of the graben opening showed that simple models can explain the patterns of deformation observed along the deep seismic profiles perpendicular to the graben. In particular, the observed graben asymmetric geometry is reproduced and asymmetric localized faulting is observed on the side opposite to the master fault accommodating the majority of vertical deformation.
  • Publication
    Accès libre
    Multidisciplinary approach of geothermal prospection in the Argentera Massif (South-Western Alps)
    (2012)
    Guglielmetti, Luca
    ;
    Schill, Eva 

    Cette thèse vise à développer un nouveau concept multidisciplinaire pour caractériser l'état géologique et structural du sous-sol pertinent à l'exploitation géothermique des réservoirs locaux dans l'environnement alpin. Dans le passé, la plupart des informations de ce type de réservoirs a été acquit grâce à l'analyse géochimique des fluides thermiques, qui peuvent fournir une indication de la zone d'infiltration, la voie de circulation, et la température du réservoir. Dans cette étude, en outre, de nouvelles données chimiques des fluides, trois aspects principaux ont été inclus:
     L'observation détaillée des réseaux de fractures à la surface en proximité des sources thermales.
     Acquisition de données gravimétriques et magnétotelluriques pour recueillir des informations sur la densité et la distribution de résistivité dans le sous-sol, qui peut être indicatif pour la fracturation existant et la présence du fluide géothermique en profondeur.
     Modélisation géologique en 3D pour intégrer les observations structurales, géochimiques et les données géophysiques pour contraindre les structures géologiques qui peuvent être impliqués dans la circulation du fluide thermique.

    L'intégration de ces méthodes à permis une meilleure compréhension des conditions géologiques liés à des anomalies thermiques du sous-sol dans des systèmes hydrothermales en milieu Alpin. Deux sites géothermiques ont été choisis pour tester ce concept: Bagni di Vinadio et Valdieri dans le Massif de l’Argentera (AM). Les résultats de cette approche ont été finalement utilisée pour déduire le potentiel géothermique dans ces deux domaines.
    Les observations géologiques ont révélé différentes systèmes de fractures. Les sources thermales dans les deux sites sont situés le long d'une direction NE-SO dont les fractures ont un faible pendage vers le SE, qui est directement reliée aux principaux systèmes de failles décrochâtes orientées NW-SE. Les eaux thermales ascendant le long les failles principaux mais c’est les systèmes de failles qui se croisent, qui contrôlent soit la sortie des fluides thermales a la surface soit le mélange entre les eaux thermales et les plus froides et superficiels.
    Les études géochimiques ont souligné les différences de composition chimique des eaux thermales aux deux sites d'étude. La principale différence est la teneur en chlorure qui est beaucoup plus élevée dans l'eau thermale à Vinadio, où les sources atteindent une température de 70° C. En revanche, le type d'eau Na-SO4 révèle à Valdieri est typique des eaux profondes circulant dans les massifs cristallins. Le rapport Cl/Br donnent des informations de l'origine de la salinité à Vinadio: une interaction de l'eau thermale de Vinadio avec les formations évaporitiques, qui entourent le AM et qui peut être aussi pincé dans les principales structures du massif, est possible. Les temperatures du reservoir ont été estimés à 130 ° C à Vinadio et 100 ° C à Valdieri.
    Les méthodes gravimétriques et magnétotelluriques ont été utilisées pour enquêter sur les informations du sous-sol et on donnè des important informations sur les variations de la densité et de distribution de la résistivité électrique en profondeur. Le résultat principal était l'identification des régions à faible densité dans la région des sources thermales, qui peuvent être liés à une réduction de la densité par la fracturation. La modélisation geologique tridimensionnelle a été employée, en particulier, pour contraindre les structures geologiques et leur paramètres physiques en profondeur à partir des observations à la surface. Les deux modèles ont ensuite été combinées aux observations géophysiques et finalement modifiée et validée pour correspondre aux résultats géophysiques au moyen de la modélisation directe e de l'inversion. De cette façon, l'emplacement , le volume et la porositè des zones de rétention des eaux thermales a été estimée.
    Enfin, plusieurs méthodes d'estimation de du potentile geothermique ont été comparés. Le potentiel géothermique est estimée à l'ordre de ~300kWEL et de chaleur pour environ 250 habitants à la condition d’utiliser une approche en cascade.,
    This thesis aims at developing a new multi-disciplinary concept to characterize geological and structural subsurface condition relevant to geothermal exploitation of local reservoirs in Alpine environment. In the past, most of the information of such type of reservoirs was gained through geochemical analysis of thermal fluids, which may provide indication for the infiltration area, the circulation path, and the reservoir temperature. In this study, additionally to new fluid chemical data, three main aspects were included:
     Detailed observation of fracture networks at the surface close to the thermal springs.
     Acquisition of new gravity and magnetotelluric data to gather information about the density and resistivity distribution in the subsurface, which may be indicative for existing fracturation and the occurrence of deep geothermal fluid circulation.
     3D geological models to integrate the structural and geochemical observations and geophysical data for constraining geological structures that may be involved in the thermal fluid circulation.

    The integration of these methods allowed a better understanding of the physical conditions related to thermal anomalies in the deep subsurface of Alpine systems. Two geothermal sites have been chosen to test this concept: Bagni di Vinadio and Valdieri in the Italian Argentera Massif (AM). The findings of this comprehensive approach have been finally used to infer the geothermal productivity of the local reservoirs in these two areas.
    The geological observations revealed different sets fractures. Thermal springs at both sites are located along an NE-SW oriented low-angle set of fractures dipping towards SE that is directly connected to the main steep fault systems oriented NW-SE. The vertical upflow of the thermal fluids seems to be related to the intersecting fault systems.
    Geochemical investigations point out the differences in terms of chemical composition of thermal waters at the two study areas. The main difference is the anomalous high chloride content in thermal water at Vinadio, where springs reach a temperature of 70°C. In contrast, the Na-SO4 water type at Valdieri reveals typical water circulating in crystalline massifs. The Cl/Br molar ratio reveals the origin of the salinity at Vinadio: a possible interaction of the thermal water of Vinadio with the evaporitic formations which surround the AM and that can be pinched within the main structures of the massif. Reservoir temperatures were estimated to 130°C at Vinadio and 100°C at Valdieri.
    Gravity and magnetotelluric methods were employed to investigate the subsurface and provided important information on density and electrical resistivity distribution at depth. The main result was the identification of low density regions in the area of the thermal springs, which can be related to a reduction of density by fracturation. Three dimensional geological modelling was employed, in particular, to infer the structural setting at depth from the observations at the surface. The two models were then combined to geophysical observations and finally modified to match the geophysical results by means of forward modelling and inversion processing. In this way, the location, the volume and the porosity of the reservoir zones of the thermal springs was estimated.
    Finally, several methods of estimating the productivity of these deep reservoirs were compared. The geothermal potential is estimated to be in the order of ~300kWEL and heat for about 250 habitants under the condition to install a cascade approach.
  • Publication
    Métadonnées seulement
    Oroclinal bending and regional significant clockwise rotations of the Himalayan arc - constraints from secondary pyrrhotite remanences
    (2004)
    Schill, Eva 
    ;
    Appel, E
    ;
    Crouzet, C
    ;
    Gautam, P
    ;
    Wehland, F
    ;
    Staiger, M
    ;
    Sussmann, A
    ;
    Weil, A
  • Publication
    Accès libre
    Review: Thermal water resources in carbonate rock aquifers
    Goldscheider, Nicola
    ;
    Mádl-Szőnyi, Judit
    ;
    Erőss, Anita
    ;
    Schill, Eva 
    Cet aperçu présente les connaissances actuelles sur les ressources en eau thermale des aquifères carbonatés, expose les processus géochimiques créant la porosité des réservoirs ainsi que les diverses modes d’utilisation de ces ressources, tels établissements thermaux, énergie géothermique, séquestration du CO2). Les aquifères carbonatés constituent probablement les réservoirs d’eau thermale les plus importantes hors zones volcaniques. Plusieurs processus regroupés sous le terme spéléogénèse contribuent à la formation de la porosité: remobilisation de la calcite, corrosion induite par flux de drainance, dissolution par acides terrigènes d’origine profonde. Des eaux thermales et minérales karstiques alimentent des stations thermales dans le monde entier, tels les fameux bains de Budapest, Hongrie. Des installations géothermiques utilisent ces ressources pour la production d’électricité, le chauffage urbain et autres usages, avec faibles émissions de CO2) et occupation du sol restreinte, e.g. la plus grande installation géothermique d’Allemagne, à Unterhaching près Munich. Faille régionale et champs de fractures sont souvent les zones les plus productives, mais quelques fois difficiles à localiser en raison de l’incertitude relativement forte de la recherche. Des dispositifs géothermiques sur roches carbonatées profondes pourraient aussi être utilisés pour la séquestration du CO2) (le gaz dissolvant le carbonate et augmentant de ce fait la porosité du réservoir). L’utilisation de dispositifs géothermiques à cette fin devrait être d’avantage explorée., The current knowledge on thermal water resources in carbonate rock aquifers is presented in this review, which also discusses geochemical processes that create reservoir porosity and different types of utilisations of these resources such as thermal baths, geothermal energy and carbon dioxide (CO2) sequestration. Carbonate aquifers probably constitute the most important thermal water resources outside of volcanic areas. Several processes contribute to the creation of porosity, summarised under the term hypogenic (or hypogene) speleogenesis, including retrograde calcite solubility, mixing corrosion induced by cross-formational flow, and dissolution by geogenic acids from deep sources. Thermal and mineral waters from karst aquifers supply spas all over the world such as the famous bath in Budapest, Hungary. Geothermal installations use these resources for electricity production, district heating or other purposes, with low CO2) emissions and land consumption, e.g. Germany’s largest geothermal power plant at Unterhaching near Munich. Regional fault and fracture zones are often the most productive zones, but are sometimes difficult to locate, resulting in a relatively high exploration uncertainty. Geothermal installations in deep carbonate rocks could also be used for CO2) sequestration (carbonate dissolution would partly neutralise this gas and increase reservoir porosity). The use of geothermal installations to this end should be further investigated.