The Role of Structural Changes for Geothermal Projects in the Area of Basel

Abstract

A refined structural model of the area of the two geothermal sites of Basel and Riehen has been developed. In particular, gravity data have been analyzed for the structural setting in the crystalline basement and for zones of high fracturation in the investigation area. The thermally relevant Permo-Carboniferous graben structures could be relocated. As a consequence of this, the geothermal wells of Basel and Riehen appear now to occur in a supposed hydraulically favorable situation at the rim of the trough structure. The comparison of temperature and hydraulic conditions with further major heat flux anomalies in Switzerland reveal similar conditions for an enhanced thermal gradient of about 40 °C km-1. The hydraulic field, however, seems to be mainly influence by Rhenian and re-activated Hercynian structures. This is shown by the permeability and tracer test analysis at Riehen, as well as the indication of high porosity along these types of structures. A compilation of the structures in the areas of major positive heat flux anomalies in Switzerland shows that not only the Permo-Carboniferous troughs, but also the Hercynian structures are present in these areas.