Caractérisations structurale et pétrophysique d'un système géothermique en contexte volcanique d'arc de subduction : exemple de l’archipel de Guadeloupe

Abstract : The Vieux-Habitants area gathers indicators allowing to suppose a high-temperature hydrothermal system. The interpretation of geophysical data acquired for the exploration of this system requires the analysis of analogues. Several hydrothermal paleo-systems were studied in order to propose a conceptual model of a geothermal system for the Vieux-Habitants area. Studies of these analogues are based on a multi-scale study of the brittle deformation and a petrophysical characterization of the different volcanic rocks. The organization of fractures indicates the occurrence of a characteristic scale for each level of observation. Volcano-sedimentary units are far less deformed compared to highly fractured lavas. The brittle deformation in volcano-sedimentary deposits is highly localized in fractured corridors. Some fault intersections control major fluid flow at the kilometer scale. Moreover, the most hydrothermalized rocks are localized in the vicinity of these intersections. Volcanic rocks are divided according to their mechanism of formation (lava, debris flow…) and their degree of alteration. They exhibit strong heterogeneities of petrophysical properties. Fresh rocks are separated in two distinct groups, on one side lavas and on the other side debris flows and pyroclastic deposits. Hydrothermal alteration produces mineralogical replacements involving a complete reorganization of both the matrix skeleton and the pore network. It is marked by a removal of magnetic signal, an increase of porosity and permeability in lavas and a decrease of these properties in debris flows and pyroclastic deposits. Therefore, hydrothermalized rocks form a group with intermediate reservoir properties between the two groups of fresh rocks. The reservoir model combines both structural components and lithological heterogeneities that allow an efficient fluid transfer, whereas the matrix properties of primary and secondary origins will rather control the fluid and heat storage properties.
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Vivien Navelot. Caractérisations structurale et pétrophysique d'un système géothermique en contexte volcanique d'arc de subduction : exemple de l’archipel de Guadeloupe. Sciences de la Terre. Université de Lorraine, 2018. Français. ⟨NNT : 2018LORR0339⟩. ⟨tel-02324899⟩

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