Structure of the low permeable naturally fractured geothermal reservoir at Soultz

Chrystel Dezayes (1) , Albert Genter (2) , Benoît Valley (3)

1 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)
2 GEIE Exploitation Minière de la Chaleur
3 ETH Zürich - Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology [Zürich]

The permeability of the granite geothermal reservoir of Soultz is primarily related to major fracture zones, which, in turn, are connected to dense networks of small-scale fractures. The small-scale fractures are nearly vertical and the major direction is about N0°E. This direction differs from that of the Rhine graben, which is about N20°E to N45E in northern Alsace. A total of 39 fracture zones, with a general strike of N160°E, have been identified in six wells between 1400 and 5000 m depth. These fracture zones are spatially concentrated in three clusters. The upper cluster at 1800-2000m TVD (True Vertical Depth) is highly permeable. At 3000-3400m TVD, the intermediate cluster in composed of a dense network developed in an altered matrix and forms the upper reservoir. In the lower part of the wells, the deeper cluster appears as a fractured reservoir developed within a low permeable matrix. Fracture zones represent a key element to take into account for modeling of geothermal reservoir life time submitted to various thermo-hydro-mechanical and chemical processes generated by hydraulic or chemical stimulations and hydraulic circulations

Keywords: Rhine Graben; Fractures; Fracture zones; Cores; Borehole images; Enhanced Geothermal System

Domains: Earth Sciences

Chrystel Dezayes, Albert Genter, Benoît Valley. Structure of the low permeable naturally fractured geothermal reservoir at Soultz. Comptes Rendus Géoscience, 2010, 343 (7-8), p. 517-530. ⟨10.1016/j.crte.2009.10.002⟩. ⟨hal-00492278⟩