High enthalpy hydro-geothermal reservoirs: insights from basalt petrophysical properties.

• Main Author: Violay, Marie
• Other Authors: Géosciences Montpellier, Université des Antilles et de la Guyane (UAG)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Université Montpellier II - Sciences et Techniques du Languedoc, Philippe Pezard([e-mail])
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2010
• Subjects: High enthalpy geothermal energy; mid oceanic ridge; hydrothermal circulation; petrophysical properties; basalts; géothermie haute enthalpie; circulation hydrothermale; propriétés physiques; ride medio océanique; basalte; Islande; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Iceland
• Online Access: https://tel.archives-ouvertes.fr/tel-00591798; https://tel.archives-ouvertes.fr/tel-00591798/document; https://tel.archives-ouvertes.fr/tel-00591798/file/THESE_MV_pro.pdf

Geothermal energy is considered as a green and infinite energy source at human scale. Currently, the yield of geothermal power plants is limited to temperatures of the operating fluid which 350 °C. From tectonic and volcanic activity at mid-ocean ridges, Iceland is a location where supercritical fluid extraction (T> 375 °C) can considered for the near future. Exploiting such fluids could theoretically multiply by a factor of ten the electrical power delivered by geothermal wells. Can such fluids circulate at the base of brittle oceanic crust? This work investigates the petrophysical properties of basalts in order to constrain geophysical observations in Iceland and predict the behavior of very high temperature geo-hydrothermal reservoirs. The first approach consisted in studying the physical properties of rocks that have hosted deep hydrothermal circulations at oceanic ridges. The study of these rocks at ODP Site 1256 shows that the porosity measured both in the field and in the lab is associated with amphibolite facies alteration minerals (T> 500 ° C). The second approach was to recreate in the laboratory the conditions of pressure, temperature and pore fluid pressure of high temperature to supercritical hydrothermal systems to predict the mechanical and electrical properties of basalts under these conditions. The mechanical results indicate that the brittle/ductile transition occurs at a temperature of about 550° C, where a strong permeability decrease is expected. The implementation and calibration of a new cell for measuring electrical conductivity at high temperature provide the first results for the interpretation of geophysical data. When applied to basaltic crustal conditions in Iceland, these results indicate that hydrothermal fluids could circulate, at least temporarily, in a supercritical state up to 5 km depth. La géothermie est considérée comme une source d'énergie propre et inépuisable à échelle humaine. Actuellement, le rendement des centrales géothermiques est limité à l'exploitation de ...