Geothermal Fluid and Reservoir Properties in the Upper Rhine Graben, Europe

Hydraulic and hydrochemical data from several hundred deep wells in three different geothermal reservoirs of the Upper Rhine Graben area in France and Germany have been compiled, examined, validated, and analyzed with the aim to characterize the fluids and reservoir properties for supporting geothermal projects. The hydraulic conductivity of the examined geothermal reservoir formations are quite different and reflect the diverse flow structures of the fractured and the karstified rocks. The hydraulic conductivity decreases very little with depth, probably because the Upper Rhine Graben is a young tectonically active structure. The chemical composition of the waters at shallow depth (500 - 800 m) results from intensive chemical interaction with the rocks. The total of dissolved solids increases with depth and thermal waters in the three different aquifer formations all grade into NaCl-rich saline fluids independent of the dominant reservoir rock.