21.02.2017: Under what conditions does the underground serve as a supplier for geothermal energy? Within the EU funded project IMAGE „Integrated Methods for Advanced Geothermal Exploration“, the PhD student Jessica Freymark investigates the characteristics of the Upper Rhine Graben and its potential as a supplier for geothermal energy. Together with colleagues from the GFZ, the RWTH Aachen, the TU Darmstadt, and the Hessian Agency for Nature Conservation, Environment and Geology, she now has published her results in Tectonophysics.

The Upper Rhine Graben is part of the European Rift System. This tectonically active zone extends as a linear across Central Europe. Alongside this rift zone the continental crust is stretched (less than one millimeter per year) and filled by a thick package of sediments.

Naturally occurring radioactive elements stick within the Earth’s crust, like potassium and uranium. The radioactive decay of these elements produces radiogenic heat in the deep underground. In addition, a continuous supply of heat comes from the Earth´s interior. Like a blanket, the thick sediment layers prevent the heat from the deep crust to rise towards the Earth’s surface and thus store it in the underground. This is why the sediments are key to the energy potential of the subsurface. The heat can be used for geothermal energy production from deep drilling sites that can reach down to four thousand meters.

A 3D model allows to look into the underground

Information on temperature distribution and thermal conductivity of the rocks in the subsurface layers are key to evaluate the geothermal energy potential. In order to assess the temperature distribution, the team around Jessica Freymark, GFZ section Basin Modelling, in cooperation with the TU Darmstadt and the Hessian and Baden-Württemberg Geological Surveys, generated a 3D model of temperatures and structures of important geological features of the Upper Rhine Graben and the underlying Earth’s crust. With their approach the scientists integrated for the first time diverse information on geological structures and physical properties of rocks into a large-scale model of the region.

The new model provides information on temperatures and processes of heat transport in the underground of the whole region, beyond single wells. This way the scientists were able to identify three promising areas with an enhanced geothermal gradient: the Upper Rhine Graben and adjacent areas of Baden-Württemberg and Northeastern France. The investigations of the team therewith provide a basis for future geothermal energy production in the whole area. (ak)

>>More information on the project

Original study: Freymark, J., Sippel, J., Scheck-Wenderoth, M., Bär, K., Stiller, M., Fritsche, J.-H., Kracht, M., 2017. The deep thermal field of the Upper Rhine Graben. Tectonophysics 694, 114-129. DOI: 10.1016/j.tecto.2016.11.013