Over 10 Years of Geological Investigations Within the HDR Soultz Project, France

Abstract

Several deep wells were drilled in the Rhine graben (Soultz, France) to evaluate the geothermal Hot Dry Rock potential of a deep fractured granite reservoir. Three main boreholes, which reached 2200, 3600 and 5100 m depth, intersected a crystalline basement overlain by 1400m of Cenozoic and Mesozoic sediments. Based on extensive geological database collected from 1987 to 1999, deep geology of the Soultz reservoir including hydrothermal alteration studies as well as an extensive fracture evaluation were characterised from core analysis, well-logging and borehole imagery interpretations. Conceptual models of hydrothermally altered and fractured zones are proposed. In order to build small-scale fracture distribution observed at Soultz from core data, simulation of 3D fracture network was done stochastically. At higher scale, several deterministic geometrical models were built by assuming fracture size in 3D. They showed that some potential connecting paths are outlined between the deep wells.