Developing tracer management for long and sustainable use of the Upper Jurassic geothermal reservoir in South Germany

The carbonate Upper Jurassic aquifer (UJA) in the South German Molasse Basin (SGMB) is the most important exploration horizon for geothermal energy supply in Bavaria. The UJA shows a complex hydrogeology caused by a heterogeneous geology with karstic features and deep fault zones.

The great interest in the Upper Jurassic aquifer for geothermal energy supply led to an increasing construction of geothermal power plants in the greater Munich area. Today, there are 18 geothermal power plants in this area used for district heating and electricity generation.

To guarantee a long and sustainable use of the geothermal resource, understanding the dynamics within the reservoir is important. Tracer tests are a key tool for investigating groundwater flow paths, detecting potential thermal breakthroughs, and minimizing negative interactions between geothermal power plants.

In recent years, several tracer tests have been conducted, and the growing number of projects will lead to even more tracer testing in the coming years. Future tracer tests need to be carefully designed, as there is, up to now, only a limited number of traditional tracer substances available for use in a deep geothermal setting under high temperatures and pressures. Therefore, we developed tracer management for the UJA, including guidelines for different tracer tests, the suitability of different tracers for usage in a geothermal setting, and recommendations for individual locations.