Geothermal Cascade Use at Geinberg, Austria

Abstract

Situated in the Upper Austrian Molasse Basin Geinberg was one of the 6rst geothermal projects in Austria. Based on the well "Geinberg 1" hot water &om the Malm aquifer was used since early 1980 for geothermal purposes. Legal aspects and growing demand for thermal water showed the necessity of a second well, to complete a geothermal doublet. This new well "Geinberg Thermal 2" was planned as a deviated well situated in the vicinity of the existing old well "Geinberg 1" with a distance between the withdrawal and reinjection in the carbonate deep-groundwater aquifer of some 1,600 m. The drilling started as a vertical drilling to a depth of 600 m. Using a top drive device deviational drilling was brought to the total depth of 3,155 m MD (2,225 m TVD) in 52 days. Quartemary, Tertiary and Upper Cretaceous sequences were penetrated before entering the thermal reservoir in the carbonate rocks of Malmian age at 2,910 drilling meters. A h acid stimulation and testing the regular geothermal production started at 22" of December with a h e overflow of app. 20 Vs. The outflow temperature is in the order of 100 O C. The established geothermal cascade enables the use of a temperature interval of a maximum of 70 "C, which equals a thermal output of app. 5.8 MW. The reinjection temperature reaches a minimum of 30 'C thus allowing the reinjection without pressure. As backup heating is needed the return temperature of 30 "C is independent of the outside temperature. Geinberg is the first geothermal plant -in Austria to perform cascade use. Further thermal use including heat pumps are intended.