Characterization of Discontinuities in Potential Geothermal Reservoirs of Vieux Habitants Area (Guadeloupe, French West Indies)

Geotref program aims at developing geothermal resources in andesitic rocks of Basse Terre of Guadeloupe (French West Indies) at an about 2km depth. No drill-hole being available, a surface natural analogous system was found in a 2Ma old area of Basse Terre representing an exhumed 2km-deep portion of crust. In order to better know the morphology of deep reservoirs, an analysis of discontinuity networks was performed. The methods used in the field and in the lab are multiscale analysis of scan lines, mozaiks of pictures, fractal analysis, intensity and density of fracture measurement, analysis of schistosity. The main results are: the regional-scale fractures are recorded at the outcrop scale ; discontinuities that carried hydrothermal fluids are interconnected vertical fractures and horizontal schistosity with a similar filling of newly-formed hydrothermal clay minerals. All of these evidences indicate that fluid flow in such environments occurs not only thanks to vertical fractures as described at Bouillante, a few kilometers to the north, but also via horizontal discontinuities such as schistosity and likely lava flow or debris flow boundaries. Fluid flow occurs from millimetric to metric scale (and likely even more) in the three dimensions of space.