28 January 2022

The research team of the joint project ZoKrateS makes the energy of hot rock layers accessible through hydraulic stimulation. It is a demonstrator project with the aim of opening up the Geretsried location in Bavaria for geothermal energy.

Geothermal energy has been successfully produced in the Munich region for many years. This is usually done with so-called hydrothermal, that is, natural thermal water reservoirs in the deep substratum. From these reservoirs, the hot water can easily flow to a well. However, in many cases the rock in the deep substratum is not very permeable, so that the hot thermal water cannot flow into the well. In such petrothermal reservoirs, the existing fissures, which are not very permeable to water, can be made permeable to thermal water through targeted stimulation. In the ZoKrateS project, the research team has now demonstrated for the first time at the Geretsried location south of Munich in an existing well that the method can be used to technically exploit the rock mass in the typical reservoir rock for geothermal energy.

Geretsried has hot rock of about 160 degrees Celsius at a depth of about 4.5 kilometres. However, the existing fissures are mostly closed. This means that the location is not suitable for hydrothermal geothermal energy. Yet the geological conditions show that it has clear potential for petrothermal use.

Hydraulic stimulation of the Geretsried well

A well was already drilled in 2017. The target was the hot water in the limestone layers of the Upper Jurassic strata, which lie at a depth of 4.4 to 4.8 kilometres at the Geretsried location. From July to October 2021, the project partners carried out hydraulic stimulation on a deep geothermal well in the limestone rocks of the Upper Jurassic strata for the first time in Germany. They did this by introducing special ceramic beads, known as proppants, deep into the existing fissure network in several zones. This allowed the research team to widen the natural flow pathways to the well and open them up for circulation of the thermal water. In order to plan and implement the ambitious project with extensive preliminary work, experts from science and industry worked together in an interdisciplinary manner.

The researchers are currently further evaluating the injection trials. Initial results indicate that the method was able to achieve a significant increase in rock permeability. The project team was able to inject and flush the proppants at very low pressures, so that they were only slightly above the water pressures prevailing in the reservoir. It was not necessary to exceed the acting rock load to transport the ceramic beads into the fissures to keep these open.

Potential for petrothermal utilisation

If the researchers are able to confirm the initial results, this would open up the possibility of petrothermal utilisation at the Geretsried location. In order to use the energy stored in the hot, dense rock, a large heat exchanger would be created between two wells by means of the tested method. To do this, water is pushed into the rock through a well. It flows through the interconnected fissures, which are opened by the proppants, to the second well and is heated in the process. The hot water can then be used in a power plant and subsequently cooled and returned to the first well. This would enable a closed circuit through which geothermal energy is generated.

With the hydraulic stimulation of the Geretsried well, the project team was able to demonstrate how the input of proppants as a basic technical prerequisite for future petrothermal utilisation can be successfully achieved. Furthermore, the research partnership gained important experience in using this technology so that it can be transferred to other locations in Germany in the future. The project represents an important milestone for geothermal energy in Germany. It is funded by the German Federal Ministry for Economic Affairs and Climate Action (BMWK). (av)


Prof. Dr. Tobias Backers
Ruhr Universität Bochum (RUB)
Arbeitsgruppe Ingenieurgeologie und Felsmechanik
Institut für Geologie, Mineralogie und Geophysik

+49 234 32 23881


Leibniz-Institut für Angewandte Geowissenschaften (LIAG)

Enex Geothermieprojekt Geretsried Nord

G.E.O.S. Ingenieurgesellschaft

Geothermie Neubrandenburg

Petrothermal geothermal energy

Petrothermal geothermal energy uses geothermal energy at depths of around three to six kilometres. It differs from hydrothermal geothermal energy in that no naturally existing steam or thermal water can be used to generate energy at these locations. In contrast, petrothermal geothermal energy draws on the natural heat provided by the hot, dry rock at this depth, which is why the methods used are known as "hot dry rock methods". For instance, water is pressed into fissures (separating surfaces in the rock). The water heats up in the rock, which has a temperature of around 200 degrees Celsius, and is then pumped back to the surface through a supply well. There, analogous to hydrothermal geothermal energy, it can be used via heat exchangers for heat supply and, by means of a turbine, also for electricity generation.

95 per cent of the geothermal reserves in Germany are suitable for hot dry rock utilisation. Hydrothermal geothermal energy accounts for only 5 per cent.

Among other things, EnArgus, the central information system for energy research funding, contains a database of all energy research projects - including this project.