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Vuataz, François

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Vuataz, François
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https://libra.unine.ch/handle/123456789/152

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  • Publication
    Accès libre
    Carbogaseous spring waters, coldwater geysers and dry CO2 exhalations in the tectonic window of the Lower Engadine Valley, Switzerland
    (Springer (Birkhäuser), 2006-08-14)
    Bissig, Pius
    ;
    Nico Goldscheider
    ;
    Mayoraz, Joëlle
    ;
    Surbeck, Heinz
    ;
    Vuataz, François 
    In the region of Scuol-Tarasp in the Lower Engadine Valley in the Eastern Swiss Alps, there are a variety of phenomena related to a geogenetic CO2 production, including carbogaseous mineral springs, previously active coldwater geysers and dry gas exhalations from the ground via mofettes. Previous isotopic studies revealed that the CO2 originates from the metamorphic decomposition of carbonate rocks in the crust. This paper presents an inventory of the springs, geysers and mofettes, and proposes a conceptual model on the regional gas and water circulation. Based on hydrochemical criteria, it was possible to identify six main groups of spring waters, three of which are carbogaseous mineral springs. Most of the carbogaseous springs and gas exhalations are bound to the Bündnerschiefer fractured aquifer. The different water types originate from mixing of groundwater and highly mineralised carbogaseous fluids from depth. Near-surface degassing of CO2 from the fluid phase creates the dry gas exhalations. CO2 and radon measurements in 178 soil boreholes suggest that the gas exhalations occur at a limited number of point-like anomalies, and there is no evidence for regionally important diffuse CO2 discharges from the ground.
  • Publication
    Accès libre
    Use of Cl/Br Ratio to Decipher the Origin of Dissolved Mineral Components in Deep Fluids from the Alps Range and Neighbouring Areas
    (2010)
    Sonney, Romain
    ;
    Vuataz, François 
    ;
    Cattin, Stéphane
    Cl/Br ratios were studied in deep groundwaters to decipher the origin of dissolved mineral components from the Alps and neighbouring areas. Cl/Br molar ratio represents a good marker to define if the salinity comes from seawater or residual brines (655 and lower) or from dissolution of halite or halite-rich gypsum, often present in the Triassic formations (upper than the seawater ratio). It can be an interesting tool for projects dealing with exploration and production of geothermal fluids. Results of this study showed the presence of trapped seawater in formations of the large basins from the Quaternary to the basement, resulting from infiltration during different marine intrusion periods. This method also showed the presence of brines in crystalline aquifers. Some of these waters discharge along subvertical faults and are diluted to various degrees by different types of meteoric waters. In some cases, this method raises new questions about the true geological origin of deep circulations.
  • Publication
    Accès libre
    L’énergie géothermique: Un grand potentiel et de nombreuses applications
    (2005)
    Vuataz, François 
    C’est en 1904 que la géothermie industrielle a démarré avec la production d’électricité en Toscane. A partir des années 1960, des centrales électriques géothermiques voient le jour dans 24 pays. L’utilisation directe de la chaleur souterraine, notamment pour le chauffage et pour le thermalisme, s’est développée dans 70 pays. En Suisse, les sondes géothermiques verticales pour le chauffage de villas familiales connaissent un fort engouement et les champs de sondes réalisés pour le chauffage et le refroidissement de bâtiments de grande taille se mettent en place avec succès. Dans un avenir proche, des centrales de production couplée d’électricité et de chaleur utiliseront des ressources de chaleur à grande profondeur.
  • Publication
    Accès libre
    Validation of Chemical and Isotopic Geothermometers from Low Temperature Deep Fluids of Northern Switzerland
    (2010)
    Sonney, Romain
    ;
    Vuataz, François 

    During more than 30 years, chemical and isotopic geothermometers have been extensively used to calculate and estimate the temperature of geothermal reservoirs in various geological, petrographical and thermal conditions. In this evaluation, chemical analyses of deep boreholes from the Molasse Basin and the Tabular Jura in Northern Switzerland were used to estimate reservoir temperatures with geothermometers, and results were compared to measured temperatures at depth. The presence of thermal waters in subhorizontal formations with a temperature range of 12-112°C, is associated with various geological and petrographical settings (sedimentary, crystalline rocks).

    Composition of geothermal fluids depends on various and sometimes competing processes, such as full or partial chemical equilibrium, mixing with shallow groundwater or trapped seawater, dissolution of evaporite, ionic exchange with clays, or residence time in the reservoir. These processes are constraining for the application of geothermometers. Moreover, some of them have a limited temperature range of application cannot be used in some petrologic environments. Thus, a range of possible reservoir temperatures is calculated depending on several assumptions and compared to measured temperature. Application of chemical and isotopic geothermometers, using several calibrations proposed in the literature, is discussed in this specific context.
  • Publication
    Accès libre
    Preliminary Modelling of the Permeability Reduction in the Injection Zone at Berlin Geothermal Field, El Salvador
    (2010)
    Portier, Sandrine
    ;
    Vuataz, François 
    ;
    Barrios Martinez, Antonina Luz
    ;
    Siddiqi, Gunter

    The exploitation of the Berlin geothermal field (El Salvador) started in February 1992 with two 5 MW electrical units. In December 1999, exploitation at a larger scale started with the operation of two turbo-generating condensation units of 27.5 MWe each. Since the beginning of exploitation until today, all the deep thermal fluids produced during the generation of electricity have been injected back to the reservoir. However, the well injectivities declined because of self-sealing processes of fracture thereby reducing permeability in the injection zones.

    Our study focuses on the factors that may have caused the observed loss of injectivity of reinjection wells, using numerical simulation of fluid flow with coupled chemical reaction modelling. Such a model helps quantitatively understand the complex interplay of thermal, hydraulic and chemical processes (THC) and to predict the impact of reinjection on reservoir properties. The first preliminary simulation was carried out with FRACHEM code. This paper presents simulation results that reproduce in some way the observed decrease of permeability in the injection zone with time.
  • Publication
    Accès libre
    The Database of Geothermal Fluids in Switzerland on Google Earth
    (2010)
    Sonney, Romain
    ;
    Vuataz, François 
    ;
    Cattin, Stéphane

    The database BDFGeotherm, containing physical, chemical and hydrogeological information on more than 200 deep fluids from 84 sites in Switzerland and some neighbouring regions, was first compiled on ACCESS code and was later modified to improve its availability and attractiveness by using Google Earth free software and the CREGE website (www.crege.ch/BDFGeotherm/). BDFGeotherm is a functional tool for various phases of a geothermal project such as exploration, production or fluid re-injection. This database allows gathering existing geothermal data, generally widely dispersed and often difficult to reach, towards a user’s friendly tool. Downloading the file “BDFGeotherm.kmz” from the CREGE website makes possible to visualize the 84 geothermal sites from Switzerland and neighbouring areas. Each one is represented with a pinpoint of different colour, for diverse temperature ranges.

    A large majority of sites is located in the northern part of the Jura Mountain and in the upper Rhone Valley. General information about water use, geology, flow rate, temperature and mineralization are given in a small window by clicking on the desired pinpoint. Moreover, two links to Internet addresses are available for each site in each window, allowing returning to the CREGE website or providing more details on each sampling point such as: geographical description, reservoir geology, hydraulics, hydrochemistry, isotopes and geothermal parameters. For a limited number of sites, photos and a geological log can be viewed and exported (Sonney et al., 2009).
  • Publication
    Accès libre
    Modelling Acid-Rock Interactions and Mineral Dissolution During RMA Stimulation Test Performed at the Soultz-sous-Forêts EGS Site, France
    (2010)
    Portier, Sandrine
    ;
    Vuataz, François 
    The Soultz EGS reservoir’s response to chemical stimulation is assessed by numerical simulation of coupled thermo-hydraulic-chemical processes. To assess chemical interactions between host rocks and a mixture of HCl and HF as well as its potential effects on the Soultz EGS reservoir, new modelling efforts using the FRACHEM code have been initiated. This paper presents the model calibration and results. Simulations consider realistic conditions with available data sets from the EGS system at Soultz. Results indicate that the predicted amount of fracture sealing minerals dissolved by injection of a mixture of acids (RMA) was consistent with the estimated amount from the test performed on GPK4 well at Soultz EGS site. Consequently reservoir porosity and permeability can be enhanced especially near the injection well by acidizing treatment.
  • Publication
    Accès libre
    Hydrology of a spring complex, studied by geochemical time-series data, Acquarossa, Switzerland
    (1990)
    Mazor, Emanuel
    ;
    Vuataz, François 
    A case study of three springs in Switzerland is used to demonstrate the value of geochemical time-series data as a powerful tool to study the dynamics of groundwater systems. Values of repeatedly measured parameters revealed intermixings of two water types : (a) a 29°C water, circulating to a depth of 1100 m and containing approximately 700 mg/l Ca, 2000 mg/l SO4, 700 mg/l HCO3, 20 mg/l of Na and Cl, 6 mg/l Fe, at least 47 mg/l SiO2, and with an isotopic composition of δD = − 73.0‰ and δ18 O = −10.9‰, and (b) a 12°C or colder water, shallow, and of a post-1953 age, containing 420 mg/l TDI or less, very low in Na and Cl (4 mg/l or less), isotopic values of δD = −71.0‰ and δ18 O = −10.5‰ and tritium as in recent (post-bomb) precipitation.
  • Publication
    Accès libre
    Properties of geothermal fluids in Switzerland: A new interactive database
    (2008)
    Sonney, Romain
    ;
    Vuataz, François 
    A database on geothermal fluids in Switzerland, called BDFGeotherm, has been compiled. It consists of nine related tables with fields describing the geographical, geological, hydrogeological and geothermal conditions of each sampling location. In all, 203 springs and boreholes from 82 geothermal sites in Switzerland and neighboring regions are listed in this new interactive Microsoft Access database. BDFGeotherm is a functional tool for various phases of a geothermal project such as exploration, production or fluid re-injection. Many types of queries can be run, using any fields from the database, and the results can be put into tables and printed or exported and saved in other files. In addition to describing the database structure, this paper also gives a summary of the reservoir formations, the geographical distribution of hydraulic parameters, the geochemical types of thermal waters and the potential geothermal resources associated with the sites.
  • Publication
    Accès libre
    Groundwater components in the alluvial aquifer of the alpine Rhone River valley, Bois de Finges area, Wallis Canton, Switzerland
    (2000)
    Schürch, Marc
    ;
    Vuataz, François 
    Origine, type et quantité de nombreux composants d'eau de l'aquifère alluvial dans la vallée supérieure du Rhône, Bois de Finges, Valais, Suisse, ainsi que leurs variations spatiales et temporelles ont été déterminés par différentes méthodes hydrochimiques. Les méthodes utilisées sont la modélisation hydrochimique, les isotopes stables, ainsi que l'échantillonnage en période de hautes eaux et de basses eaux pour étudier la distribution spatiale de la composition chimique, alors qu'un échantillonnage mensuel pendant trois ans sert à comprendre les processus de la variabilité saisonnière. Les paramètres physico-chimiques des eaux souterraines montrent des variations spatiales et saisonnières. La composition chimique de l'aquifère alluvial du Rhône indique un mélange entre une eau peu minéralisée venant du Rhône et une eau sulfatée s'écoulant du versant sud. La modification temporelle des paramètres chimiques des eaux souterraines et de la piézométrie reflètent les variations saisonnières des apports d'eau de la nappe souterraine. En période de hautes eaux durant l'été, seul le Rhône recharge l'aquifère alluvial., Source, type, and quantity of various components of groundwater, as well as their spatial and temporal variations were determined by different hydrochemical methods in the alluvial aquifer of the upper Rhone River valley, Bois de Finges, Wallis Canton, Switzerland. The methods used are hydrochemical modeling, stable-isotope analysis, and chemical analysis of surface water and groundwater. Sampling during high- and low-water periods determined the spatial distribution of the water chemistry, whereas monthly sampling over three years provided a basis for understanding seasonal variability. The physico-chemical parameters of the groundwater have spatial and seasonal variations. The groundwater chemical composition of the Rhone alluvial aquifer indicates a mixing of weakly mineralized Rhone River water and SO4-rich water entering from the south side of the valley. Temporal changes in groundwater chemistry and in groundwater levels reflect the seasonal variations of the different contributors to groundwater recharge. The Rhone River recharges the alluvial aquifer only during the summer high-water period., Se ha determinado el origen, tipo y cantidad de diversos elementos de las aguas subterráneas en el acuífero aluvial del valle superior del río Ródano (Bois de Finges, Cantón de Wallis, Suiza), así como sus variaciones espaciales y temporales, mediante métodos hidroquímicos. Entre las herramientas utilizadas, se incluye la modelación hidroquímica, el análisis de isótopos estables y el análisis químico de aguas superficiales y subterráneas. El muestreo en épocas de estiaje y lluvias sirvió para determinar la distribución espacial de la química del agua, mientras que la variabilidad estacional fue caracterizada por medio de muestreos mensuales durante un período de tres años. Los parámetros físicoquímicos de las aguas subterráneas muestran variaciones espaciales y estacionales. La composición química de las aguas subterráneas del acuífero aluvial del río Ródano indica que hay mezcla entre las aguas débilmente mineralizadas del río y las aguas cargadas en sulfato (SO4-2) que proceden de la parte meridional de valle. Los cambios temporales en la química de las aguas subterráneas y en los niveles piezométricos reflejan las variaciones estacionales de las diferentes contribuciones de la recarga. El río Ródano recarga al acuífero aluvial únicamente durante el período estival, cuando el caudal es elevado.