Geological Criteria for Site Selection

What is GeoLaB?

With the decision on geological suitability, the exploration phase has been completed. The results show that the subsurface in the Odenwald offers favorable conditions for geothermal research. The detailed planning of the rock laboratory and its approval phase will now begin.

The laboratory is planned to be built in the so-called crystalline basement. These basement rocks are the oldest and form the foundation for all overlying rock layers. They are made up of many small crystals (for example, the granite found in the Odenwald consists of feldspar, quartz, and mica). Over millions of years, additional rocks—so-called sedimentary rocks—have been deposited on top of this basement. The crystalline basement can be used for geothermal heat production at depths of about 2 to more than 5 kilometers.

On both sides of the Upper Rhine Graben, rock layers have been uplifted over thousands of years, forming today’s Black Forest, Vosges, and Odenwald. In some areas, sedimentary layers have been eroded. As a result, crystalline rock is widely exposed at the surface here and is therefore more accessible for research than in other parts of Germany. Unlike rocks in the deep subsurface, experiments in a rock laboratory can be carried out under controlled conditions and observed over space and time. While not all physical conditions in a rock lab match those of the deep geothermal rocks, important insights can still be transferred. One key difference is temperature: due to the shallower depth, it would be significantly lower in a rock lab than in deep geothermal formations.

The area around the Tromm is suitable for a rock laboratory. Here, the rock shows strong similarities to the crystalline basement found at depths suitable for geothermal use. The Tromm granite forms a relatively uniform rock body and is bounded to the east by the so-called Otzberg fault zone — the juxtaposition of these zones is especially interesting for geothermal research.