First Steps in the Development of a New Geothermal Field in the Northern Part of the Upper Rhine Graben, Germany

Abstract

The northern part of the Upper Rhine Graben (URG) is the geothermal province with the highest geothermal gradients in Germany. The geological setting of the URG is well known by hydrocarbon exploration. Over the last 50 years, the most productive oil and gas fields were developed in the central part of the graben around the cities of Landau and Karlsruhe and in the northern part around Stockstadt and Worms. The whole graben was and still is tectonically active. Exploration wells show geothermal gradients up to 7.7°C/100 m. The first geothermal power plant was built in Landau and started production in 2008 using ORC power generation. A second plant in Bruchsal will start operating in 2010.
The geological setting of the northern part of the URG is very different compared to the mid and southern part. The Mesozoic and early Paleogene is represented by a hiatus, therefore the sediments of a Permo-Carboniferous foreland-basin with a thickness up to 4000 m is underlying the Eocene. This setting demands a new exploration and development strategy. Because of this situation geothermal development has been slow compared to the central and southern part.
Exploration wells in the northern part show a geothermal gradient up to 5.6°C/100 m. To reach reservoir temperatures above 150°C a drilling depth of 2500 to 3000 m is necessary. The exploration concept depends on the reservoir rocks and the tectonic setting in this part of the graben. The first results of a reconnaissance study are based on seismic exploration data of the oil and gas industry acquired between 1974 and 1985 and outcrop analogue studies of the Saar-Nahe Basin. The Nahe Group of the Lower Rotliegend especially seems to contain a high prospective reservoir. However, high amplitude reflectors in the Paleogene anticipate an interpretation of the reservoir in old seismic data. Therefore, various attractive fault-zones were identified. Hence, new 2D-seismic data will be acquired.