Tiefe Geothermie ist für die Wärmewende in Deutschland eine Schlüsseltechnologie. In Hochpotenzialgebieten wie dem Oberrheingraben, dem Molassebecken und dem Norddeutschen Becken stellt Tiefe Geothermie oftmals heute schon die wirtschaftlichste Wärmegewinnungsmethode für kommunale Wärmenetze dar, die zudem auch mit Abstand den niedrigsten CO₂-Ausstoß aller erneuerbaren Energien aufweist. Die Wirtschaftlichkeit ist dabei aber vom lokalen Wärmebedarf und der Größe des bestehenden Fernwärmenetzes und der Bereitschaft der kommunalen Wärmeversorger dieses zeitnah auszubauen und die damit einhergehenden Kosten stemmen zu können, abhängig.

Die Gewinnung von Lithium aus den geförderten Thermalsolen des Oberrheingrabens oder Norddeutschen Beckens stellt dabei einen signifikanten weiteren Einnahmestrom aus der Geothermieanlage dar und kann über entsprechende Abnahmeverträge zur Reduzierung der Wärmegestehungskosten verrechnet werden. Anhand von spezifischen Beispielen kann dargestellt werden, wie hierdurch unerwünschte Steigerungen des Endkundenpreises für die Wärme minimiert und somit ein Anschluss and das Wärmenetz attraktiver gestaltet werden können. Die Gewinnung des Lithiums wiederum erfolgt durch die parallele Wärme- und ggf. Stromgewinnung bilanziell CO₂-frei und in Europa und stärkt damit die europäische Unabhängigkeit für kritische Rohstoffe.

Göttingen is located at the eastern margin of the of N-S trending Leinetal Graben, which developed within ~ 1500 m of Permian-Mesozoic cover rocks. Potential geothermal horizons for heat extraction and/or storage in medium-depth geothermal systems include Zechstein salt and dolomite layers, Middle Buntsandstein strata, and karstified Muschelkalk carbonates. Strategies for the geothermal exploitation of the meta-sedimentary rocks of the Variscan fold-and-thrust belt, which are expected to underlie the sedimentary cover, have been developed based on analogue studies in the Harz Mountains.

A multi-target approach is proposed for Göttingen, integrating both shallow and medium-deep geothermal systems, in coordination with existing surface heating and cooling infrastructure. Feasibility studies to date have relied primarily on detailed geological surface maps and two intersecting seismic lines, approximately 10 and 11 km in length, recorded in 2015. These seismic profiles supplement the very limited well data available for the sedimentary cover. The geological interpretation of the seismic data remains highly uncertain, however, because of the scarcity of well data, significant lithological thickness variations within the graben, and intense faulting and halokinesis in its central part. A scientific exploration well is essential as the next step to reduce exploration risk, particularly in terms of economic feasibility. Simultaneously, only optimally designed transformation strategies for energy supply and surface infrastructure will enable the successful implementation of multiple geothermal systems.

Fluvial geothermal reservoirs are often characterized by complex and heterogeneous reservoir geometries and sandstone-body connectivities. One particular example is the Rhaetian Distributive Fluvial System (RDFS), whose channel belt reservoirs represent key targets of medium-deep geothermal energy exploration. By combining a data- and a model-based approach, we recreate for the first time the depositional environment of Rhaetian Lower Exter Formation in the Darss area, located in Northeast Germany. In this region, high sandstone thicknesses can be found in distributary channel belt reservoirs, which consist of different morphological elements of meandering fluvial channels. The lateral and vertical distribution of channel vs. overbank facies is realistically modeled by the process-based and stochastic simulation software FLUMY™, creating a heterogeneous 3D reservoir model of the study area. Additionally, existing well data is integrated in the user-defined multi-sequence scenario to hard condition the simulation. Further, we propose a multistage workflow, featuring the pre-processing, the hard conditioned simulation and finally the post-processing. The detailed facies-classification of the wells and the consequently developed 3D reservoir model allows for a better in-depth understanding of channel belt reservoirs of the RFDS concerning lateral distribution of sand-prone facies and sandstone-body connectivity.

Upper Jurassic Carbonates (“Malm”) are the most widely used hydrothermal reservoir in Germany. Located in the North Alpine Foreland Basin, reservoir temperature gradients vary with values below 24 K/km and up to 43 K/km. The lowest values are present within a large negative anomaly around the city of Wasserburg in eastern Bavaria – so far, a largely underexplored region.

The diagenetic history of the reservoir is complex, with indications of syn-sedimentary emergence, Cretaceous burial, subsequent local exhumation, and rapid burial during the alpine orogeny (Tertiary) to depth of up to 5.000 m. Widespread dolomitization occurred in several phases. Fluid inclusions of authigenic carbonates revealed temperatures far exceeding today’s values.

Until now, a correlation between permeability and reservoir pressure, approximately related to depth, was used to predict flow rates of geothermal projects. However, this was not viable for the region of the large negative temperature anomaly. Here, the correlation of permeability with reservoir temperature yields a significantly better fit. The trend deduced can also be used in adjoining areas, although the difference to the pressure correlation is less obvious here.

The relation of reservoir permeability to present-day temperatures indicates the formation of authigenic minerals during much higher palaeo-temperatures did not affect the reservoir properties significantly. Therefore, the current temperature field is likely to have been stable since a long time. Due to the new correlation, a higher reservoir permeability than previously can be predicted for the currently underexplored region, where higher flowrates may compensate for the relatively low temperatures.

Germany's aquifers hold significant potential for geothermal applications at both shallow and greater depths. For the North German Basin, siliciclastic aquifers in the Lower Jurassic (Hettangian-Pliensbachian) and Upper Triassic (Rhaetian) formations are promising targets for deeper ATES systems. However, high-temperature ATES applications at greater depths remain rare, primarily due to high investment costs, operational uncertainties, and associated risks.

This study investigates fluid-mineral interactions in an anoxic siliciclastic aquifer (carbonate content <1 wt.%) of Hettangian age in Berlin, representative of the North German Basin. Numerical modelling was conducted, using the geochemical code PHREEQC, to study the impact of gas pressure and temperature on fluid-mineral equilibria. Specifically, the effects of groundwater temperature at constant partial gas pressures were analysed. Furthermore, the tendency for mineral precipitation/dissolution was evaluated under varying partial pressures of carbon dioxide and oxygen at selected temperatures (5°C–120°C), simulating the effects of carbon dioxide degassing and oxygen intrusion on the reservoir.

Using site specific mineralogical and geochemical composition, contour plots were generated to visualize precipitation and dissolution trends as functions of temperature and carbon dioxide or oxygen concentrations in the studied system. Results indicate (1) negligible pressure-dependent changes in the stability of iron (hydr-)oxide and carbonate mineral phases; (2) calcite precipitation at elevated temperatures due to changes in species activity and the temperature-dependent solubility constant of calcite, (3) Correcting hydrochemical field data is essential to match thermodynamic equilibrium conditions in the aquifer and significantly affects modelling results, especially with regard to iron speciation and iron mineral phase stability.

The 500 m deep, fully cored and logged GeoLaB1 exploration borehole was drilled in Q1/2025 into the Tromm ridge in the south-eastern Odenwald. The up to 578 m a.s.l. high Tromm ridge is a N-S-trending, morphologically distinct feature and the explored potential target for the first geothermal research underground laboratory in Germany. The granitic-monzonitic rocks are intensively faulted and fractured exhibiting predominant argillitic, minor propyllitic, alteration. Hydrotesting revealed transmissivityies and permeabilityies values common for crystalline rocks. Fault planes commonly outline normal faulting displacements, but also minor reverse faulting can be documented. At c. 410 m below surface deformation style and petrophysical properties and fracture density change significantly with the occurrence of subhorizontally foliated, partly mylonitic to ultramylonitic, granitic-granodioritic and metasedimentary rocks below the Tromm granites. We interpret these findings as a major tectonic contact between the Tromm pluton and the underlying metamorphic rocks. Regional structural data, a concave upward seismic reflector, and gravimetric data suggest a continuation of subhorizontal, possibly antiformal, metamorphic rocks of the Böllstein antiform (and/or the “Zwischenzone”) below the granites of the Tromm ridge. Further structural, geochemical, geochronological, and geophysical work will have to constrain this hypothesis.