Having long been restricted to volcanic regions, geothermal power generation is now also being developed in non-magmatic areas, such as sedimentary basins, where deep geothermal resources are being exploited for electricity, industrial heat and also cogeneration (power+heat). The development of deep geothermal energy in France, and Europe as a whole, will rely largely on these deep resources in the sedimentary and basement environments spread widely over the continent. It will, however, be both challenging and costly to characterize and confirm the resources of these systems; being generally hidden with few clear surface manifestations, these deep geological environments are, at present, poorly known. Even though oil & gas exploration has been carried out in some areas, like the Rhine Graben, the petroleum targets are shallower than the deep geothermal reservoirs. We require better knowledge of the deep geology so as to decrease the risk of drilling deep formations. This lack of data is at present a major scientific obstacle for developing the deep geothermal resource, particularly in terms of using Enhanced Geothermal Systems (EGS). We need new data and a new conceptual model to understand the long-term evolution of the reservoir, and also new exploration techniques for deep geothermal systems. In order to help overcome the lack of data required for developing deep geothermal resources in a sedimentary basin context, the CANTARE-Alsace project aims to characterize the transition zone between the sedimentary cover and the basement. The objective of this project is not only to determine the geothermal potential of this transition zone and so optimize the target of a geothermal operation, but also to provide data and exploration guidelines for future industrial projects. The project is based on four approaches that will enable an overall characterization of the transition zone between the sedimentary cover and the basement: - Structural analysis to characterize the basin’s fracture network pattern and the evolution of its large fault zone in relation to the different tectonic phases and their chronology. These data will be interpreted in terms of geological history related to fluid paleocirculations. - Water/rock interaction analysis involving a detailed petrographic study combined with a geochemical and isotopic study along with fluid-inclusion microthermometry and original methods of dating to identify and characterize (temperature, chemistry, origin) the different generations of fluids, and to advance our understanding of the fluid paleocirculations. - Petrophysical investigation to map the evolution of the permeability, elastic wave velocities and electrical conductivity throughout the transition zone by performing experiments on samples under in-situ conditions. The rheology of the rocks will be studied in order to gain insight on the future evolution of the reservoir. - Geophysical surveying to acquire new acoustic logs and resistivity data with which to develop numerical modelling and inversion for better imaging below the sedimentary cap and with a special focus on anisotropy. The CANTARE-Alsace project, incorporating the skills of two public research organisms (BRGM and 2 laboratories of Strasbourg University, IPGS and LHyGeS) and one private company (ES-G), will provide new knowledge for developing deep geothermal energy in Alsace but also other areas of Metropolitan France having similar suitable geological conditions.