Petrophysical properties of volcanic rocks and impacts of hydrothermal alteration in the Guadeloupe Archipelago (West Indies)

International audience13 The GEOTREF project aims at developing high enthalpy geothermal energy in fractured reservoirs. It 14 focuses on active volcanic islands and especially on the Basse-Terre Island (Guadeloupe archipelago). As part 15 of this project we measured several petrophysical properties to better understand how fluids flow in the 16 hydrothermal system, provide a set of parameters to modelers and build dataset for the future interpretation of 17 well logs. The thermo-physical rock properties: bulk and grain density, porosity, permeability, compressional 18 wave velocity, thermal conductivity and diffusivity and finally specific heat capacity of outcropping volcanic 19 rocks from Guadeloupe archipelago (Lesser Antilles) were measured and a dataset was built. According to 20 field observation, samples were gathered into three lithological classes and then separated by degree of 21 alteration thanks to macroscopic aspect and optical microscopy. Geochemical data were obtained, and 22 magnetic minerals identified combining AMS and variation of magnetic susceptibility with temperature. 23 Investigated lithotypes are lava flows, debris flows and pyroclastics gathering ash, pumice and scoria 24 deposits. For lavas and debris flows, three degrees of alteration were defined: fresh, slightly to moderately 25 altered and highly hydrothermalized. Only fresh pyroclastics were studied because the altered state was not 26 outcropping. 27 Samples are typically of andesite composition and belong to tholeiitic and calc-alkaline series. Porosity of 28 lavas consists in high density cooling joints and vesicles of different shapes whereas pores in debris flows and 29 pyroclastics are located both between and into particles. Median porosities and permeabilities are clearly 3