Hydrogeological Exploration of an Alpine Marble Karst for Geothermal Utilisation

Abstract

Karst aquifers can affect advantageously the efficiency of geothermal systems due to its elevated permeabilities. However, karst aquifer properties require special exploration and exploitation. The marble karst aquifer of the Hochstegenformation was investigated to construct a middle deep borehole heat exchange storage at Finkenberg, Austria. Investigations of streams and springs all over the Tux valley led to an attribution of characteristic hydrochemical signatures to each tectonic unit in accordance to its lithology. Determining the surroundings of Finkenberg it became evident, that the geological catchment of the Hochstegenformation reaches there from 840 to 2650 m above sea level. Results of geological mapping and an exploration well showed that the tectonic situation is much more complex than described in the official geologic map. The Hochstegenformation can reach locally significant higher thicknesses than estimated before. In addition, the layer sequence is more unconformable as supposed. Karstified zones till 400 m depth could be detected within the boreholes. Groundwater flow velocities up to 14 m/d were measured. The drilling operations were accompanied by a conservation of evidences at neighbouring springs. Thereby collected data allow the calculation of the groundwater velocities. A total number of nine 400 m deep boreholes were drilled. The borehole heat exchange storage system has an heat production performance of about 1 GWh/a and 400 MWh/a storage performance. The successful conclusion of this project and gathered knowledge up to now led to the idea to explore the Hochstegenformation for extensive geothermal use. Exploration of a 1200 m deep well for hydrothermal use is in process now.