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A group of vibration trucks during a seismic measurement.
Measurement campaign in the Ore Mountains begins in August

Schematic depiction of a seismic measurement
© juwi

Investigation of crystalline rock layers for geothermal energy

In Germany, most geothermal plants are currently located in the Bavarian Prealps and in the Upper Rhine Graben. These predominately use the natural heat from the sedimentary aquifers in these basins. However, the larger geological heat deposits are found in crystalline rock layers. Together with its partners, the Leibniz Institute for Applied Geophysics (LIAG) has therefore started a 12-week geophysical measurement campaign in a 100-km² area within the Erzgebirge mountains. This is intended to determine whether geothermal energy generation is possible there.

In a 100-km² area near Schneeberg in the Ore Mountains, the crystalline rock is being investigated with two different seismic measurement processes: three heavy vibration trucks create vibrations, whose spread is recorded by several thousand geophones. Small explosions are also being carried out at 24 sites around the central measurement area and monitored with measurement instruments. Based on the measurement values, the aim is to develop a detailed 3D model of the subsurface down to a depth of 6 km. Until now the geological composition of the region has been known through the century-long mining and drillings to a depth of around 2 km. “Making crystalline areas usable for deep geothermal energy would be a major step forward for this future-oriented energy, and seismics possibly provides the only key for accessing deep crystalline,” says Project Manager Dr Rüdiger Schulz from LIAG. The researchers will be presenting the course and goals of their work at an information event that is being held on 24 July in the Schneeberg Culture Centre.
In Germany, crystalline rock layers can be found amongst others in low mountain ranges, such as in the Black Forest, Bavarian Forest and Spessart. This rock has been formed by high temperatures and pressures as well as tectonic events during earlier geological ages, i.e. the underground is complex and inhomogeneous. The main aim of the measurements is to determine faults where fissures and cracks occur, and where hot deep waters possibly rise upwards. At such points there is a greater likelihood of finding comparatively high temperatures. In crystalline rock layers, such data evaluations represent uncharted scientific territory. Dr Hartwig von Hartmann is responsible for evaluating data at LIAG: “In determining structures in crystalline basement we are at the frontline of research, in terms of both the data processing and the interpretation.” The experience gained from the project will be exemplary for the aforementioned low mountain ranges. Internationally, such investigations in crystalline rock layers have already been conducted as part of geothermal projects in the USA, Japan and Italy.

The GeotIS geothermal information system

GeotIS systematically prepares geological and geophysical data so that they are available for planning geothermal projects. By providing online access to the data it is hoped that this will improve geothermal energy’s prospects for success. Until now, the existing data has predominantly focused on regions that are geothermally tapped using hydrothermal plants. However, there is considerably less data available for petrothermal plants, which would use the heat in crystalline rock layers. Investigations such as those in the Ore Mountains will help to integrate data about the geological structures of such areas into GeotIS and thus gradually close existing gaps.

Project partners and further information

In addition to LIAG, the TU Bergakademie Freiberg and the Institute for Geophysics and Geoinformatics at Hamburg University are also involved in the project. The German Federal Ministry of the Environment is funding the work as part of energy research. There is also close cooperation with the Saxony State Office for the Environment, Agriculture and Geology.
A short publication from LIAG (in German) provides more information about the measurement campaign in the Erzgebirge mountains. The "Forschungsjahrbuch Erneuerbare Energien” publication presents the project in more detail under the project number 0325363A (in German). In 2011, the Saxony State Office for the Environment, Agriculture and Geology published a study on deep geothermal energy in Saxony (“Tiefengeothermie Sachsen”). The BINE-Projektinfo brochure “Tracking deep geothermal energy” presents the GeotIS information system.



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