Clay Mineralogy: A Signature of Granitic Geothermal Reservoirs of the Central Upper Rhine Graben
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In this paper, a model of the fracture zones at the interface between the overlying sedimentary rocks and the granitic basement is proposed, where the present day permeability distribution is controlled by the fault and fracture network, which consists of sealed zones and unsealed zones.Abstract:
Clay minerals are the signature of hydrothermal alterations related to fluid circulation in volcanic and crystalline rocks. In the French part of the Upper Rhine Graben, in the deep-seated granites, illitic minerals (illite and I/S mixed layers (ml)) are typical products of the structurally-controlled argillic alteration in the Paleozoic granitic basement. In the new Illkirch geothermal well, GIL-1, drill-cuttings were studied with various petrographic methods to determine the characteristics of illite in paleo- and present-permeable zones, and to compare the alteration mineralogy with that of geothermal Soultz-sous-Forets and Rittershoffen sites. Alteration petrography, crystal structure as well as the chemical composition of the illitic minerals and the altered bulk rocks were performed all along the well. This complete characterization, combined with geophysical logs and structural results, highlighted that the illitic minerals at Illkirch, Soultz-sous-Forets, and Rittershoffen are composed of illite and illite-rich illite-smectite mixed layers (I/S ml) (<10% smectite). Two mineralogical assemblages were distinguished: chlorite + illite resulting from the propylitic alteration after the emplacement of the granitic basement under temperatures higher than 350 °C, and illite + I/S ml + carbonates + quartz resulting from the argillic alteration due to fluid circulation in the fractures at temperatures between 130 and 160 °C. Fracture zones are characterized by the occurrence of illitic minerals (illite and I/S ml), and specifically, by higher quantities of I/S ml in present-day permeable zones than in paleo-permeable zones. A conceptual model of the fracture zones at the interface between the overlying sedimentary rocks and the granitic basement is proposed. The present-day permeability distribution is controlled by the fault and fracture network, which consists of sealed zones and unsealed zones. Fluid convection in the URG implies paleo and present fluids circulating in both fractured sedimentary and crystalline reservoirs. Such circulations develop illitic minerals that could be considered as exploration guides for future geothermal sites in the URG. At Illkirch, the repartition of the present-permeable fracture zones (KFZs) in the GIL-1 well indicates that the moderately argillically altered granite distally situated from the Eschau fault is more permeable than the intensely argillically altered granite close to the Eschau fault.read more
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Fluid-Rock Interactions in a Paleo-Geothermal Reservoir (Noble Hills Granite, California, USA). Part 1: Granite Pervasive Alteration Processes away from Fracture Zones
Johanne Klee,Sébastien Potel,Béatrice Ledésert,Ronan L. Hébert,Arezki Chabani,Pascal Barrier,Ghislain Trullenque +6 more
TL;DR: In this paper, the authors characterized the pervasive alteration processes affecting this granite, away from the influence of the faults, in terms of mineralogical, petrophysical and chemical changes.
Journal ArticleDOI
Fluid-Rock Interactions in a Paleo-Geothermal Reservoir (Noble Hills Granite, California, USA). Part 2: The Influence of Fracturing on Granite Alteration Processes and Fluid Circulation at Low to Moderate Regional Strain
Johanne Klee,Arezki Chabani,Béatrice Ledésert,Sébastien Potel,Ronan L. Hébert,Ghislain Trullenque +5 more
TL;DR: In this article, a series of petrographic, petrophysical, and geochemical investigations, combined with a fracture distribution analysis, were carried out on samples collected across fracture zones.
Journal ArticleDOI
Clay Minerals in the Deep Reservoir of the Cerro Pabellón Geothermal System (Northern Chile)
Jeanne Vidal,Patricia Patrier,Daniel Beaufort,Santiago Nicolás Maza,Germain Rivera,Gianni Volpi,Diego Morata +6 more
TL;DR: In this article , the fine-grained clay fraction was analyzed using X-ray diffraction to observe the mineral distribution and variations of crystal structure of the clays in the geothermal reservoir of Cerro Pabellón.
Journal ArticleDOI
Origin of Fe-rich clay minerals in Early Devonian volcanic rocks of the Northern Minusa basin, Eastern Siberia
Maxim Rudmin,Adrián López-Quirós,Santanu Banerjee,Alexey Ruban,M.V. Shaldybin,Pragya Singh,Aigerim Dauletova +6 more
TL;DR: The formation of clay minerals in volcanic successions follows various evolutionary trends, the understanding of which is crucial for estimating the age of volcanism and the prospecting clay deposits as mentioned in this paper .
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