Multidisciplinary exploratory study of a geothermal resource in the active volcanic arc of Basse-Terre (Guadeloupe, Lesser Antilles)

Abstract

International audience ; The GEOTREF project (high enthalpy geothermal energy in fractured reservoirs), supported by the French government program, "Investissements d'avenir" develops a sustainable geothermal resource in the Vieux Habitants area, 8-km south of the currently exploited Bouillante geothermal field. The Basse Terre Island is a recent volcanic arc (< 3 Myr) belonging to the Lesser Antilles subduction zone. It is composed of arc typical calc-alkaline volcanic rocks. Outcrops of the studied area consist either of andesitic lava flows, volcanic sedimentary facies or dikes. Field studies allow to propose a structural framework and highlight three major directions N000˚ E, N050˚ E and N090˚ E, which are consistent with the regional tectonic trends of the arc. Petrographical and petrophysical studies displayed that the major part of outcropping facies in the Vieux-Habitants area are not altered. Andesitic lava flows have poor reservoir properties with porosity and permeability lower than 5 % and 10-15m2 respectively. These results are in contrast with measurements performed in volcano-sedimentary rocks, which have heterogeneous petrophysical properties ranging from 15 to 50 % for porosity and from 10-15to 10-9m2 for permeability. Such surface data would probably change and decrease when depth increases. As there is a lack of underground data under the Vieux-Habitants area (wireline, drill core), exhumated rocks outcropping in the northern part of Basse-Terre Island (Basal Complex) have been studied. Such rocks have been identified in the Basal Complex (2.5 - 3 Myr) located in the northern part of the Basse-Terre Island. Previous works have demonstrated a 1000 m/Myr erosional rate, which corresponds at least to a 2 - 3 km exhumation. The petrography study of the Basal Complex reveals sub-greenschist type mineralogical transformations (chlorite, white mica, quartz.) changing the andesitic protolith in a meta-andesite. This metamorphism forms cleavage plans thanks to a pressure-solution mechanism. ...