Potsdam the provincial capital of the German state Brandenburg started with an ambitious program to reduce its climate impact about 10 years ago. The program includes the substitution of fossil energy sources for district heating by renewable energy. The investigation of the geothermal potential of the urban area forms an important component of this strategy.

Several deep saline aquifers in the closer surrounding of Potsdam show a potential for a geothermal utilization. They are used for different purposes like natural gas storage (Buntsandstein), underground heat storage (Jurassic), balneology (Rhaetian) or injection of process water (Muschelkalk, Jurassic). The exploration campaign started with 2D seismic measurements which were focused on the investigation of the Mesozoic succession up to a depth of about 2,500 m bgl. Based on the seismic results a drill site was determined where a vertical borehole was drilled into a depth of 2,157 m bgl. The exploration well encountered the succession down to the Muschelkalk formation with partly surprising results. The investigation of the encountered aquifers favoured the further exploitation of the Middle Jurassic Aalenian sandstone as a geothermal reservoir. Accordingly, the second well was deviated to reach this horizon in a deeper situated part of the structure.

Hydraulic tests of the aquifer show promising results with respect to a future use in a local heating system of the surrounding residential buildings. The overrun could be feed into the nearby district heating network. Besides, the results will be used for the development of further locations for a geothermal utilization.

Low enthalpy geothermal systems are well established in north-eastern Germany. The first German hydrothermal doublet started heat production in Waren/Müritz in 1984. Since then other sites in Mecklenburg-Western Pomerania and Brandenburg were explored and realized. Very recently the geothermal heating plant of Schwerin-Lankow has officially started operations and will substitute about 20 percent of fossil energy use in this town.

In most of these projects deep saline aquifers of Mesozoic age were used, which formed in the eastern part of the North German Basin. The well suited reservoir sandstones were often deposited in fluvial and deltaic systems within up to 15 km wide distributary channel belts. The porosity and permeability of channel facies sandstones reach very high values up to 30 % and >6 Darcy, respectively.

On basis of integrated sedimentological-palaeontological investigation and facies analyses using cores and wire logs of numerous deep wells, 15 different stratigraphic channel systems could be detected and mapped (www.sandsteinfazies.de). The results can be used together with temperature distribution data for a first site evaluation. Estimations of productivity and temperature have to be combined with numbers of potential users and existing or planned heat distribution infrastructure in larger communities.

The Geological Survey and ministries of Mecklenburg-Western Pomerania will encourage politicians and decision makers to think about geothermal energy use in their field of responsibility but also support investors to claim for financial support to realize renewable energy projects. This includes open access to available geological and geophysical data according to the Geological Data Act (GeolDG).

The North German Basin yields enormous resources of heat in place bound to the Palaeozoic–Mesozoic succession and to fault systems. Early exploration campaigns have identified highly permeable Mesozoic sandstones at depth of <2,300 m with temperatures of <100°C. Despite the fundamental knowledge established by these campaigns, the development of hydrothermal reservoirs remained limited due to considerable pre-drilling risks resulting from uncertainties in reservoir predictions at individual localities.

To minimise risks associated to subsurface uncertainties, an interdisciplinary work flow integrating sedimentological, geophysical, and petrophysical methods was designed to re-evaluate the six Mesozoic reservoir complexes of the North German Basin. Within the projects Sandsteinfazies, GeoPoNDD and mesoTherm this work flow was applied to an extensive database of cores and wireline logs leading to high-resolution maps depicting facies, thickness and quality of individual hydrothermal reservoirs. These maps enable reliable predictions of key parameters, i.e. net-thickness and permeability, on regional to local scales and, thus, make a significant contribution to the reduction of subsurface uncertainties. The potential of these subsurface reservoir maps to increase the utilisation of geothermal energy is demonstrated on the example of the reservoir development at Schwerin, a previously underexplored locality. There, reservoir predictions enabled targeting a highly productive sandstone at 1,250 m depth. The operation combines a conventional doublet system with industrial heat pumps to supply 7 MW_th to the local heating grid. The lessons learned from Schwerin demonstrate significant opportunities in medium-deep reservoirs enabling a sustained increase of developments for heat supply in North Germany.

This study focusses on Lower Cretaceous sandstone units of Valanginian and Berriasian age in Lower Saxony. The understanding of the distribution and the hydraulic properties of these aquifers is essential to identify suitable areas for geothermal applications. Relevant aquifer units were defined in this study by a significant regional distribution, a thickness of more than 5 m and suitable hydraulic properties.

Three sandstone units can be mapped for the Valanginian stage: The Bentheim Sandstone, the Dichotomiten Sandstone and the so called Hauptsandstein. For the Berriasian stage, the most important sandstone units are the so-called Kopf-Sandstein (Fuhse Formation) and the sandstones of the Basinghausen Subformation. All of these sandstones are located in depths between several hundreds of meters up to 1500 m with a resulting temperature between 30°C to around 50°C.

Aquifers of Valanginian age have the best transmissivities and could be a target for geothermal application. Sandstone units of Berriasian age barely meet the minimum requirements for geothermal use on a regional scale. Nevertheless, suitable aquifer conditions may be developed locally.

All maps of the Lower Cretaceous sandstones can be found at the NIBIS mapserver and the data compilation is free to download. A base map with the relevant sandstone units and all analyzed data points such as well logs, cores and outcrops are available for each geological unit. Parameters for geothermal applications (e.g. depths of the formation, total thickness, sandstone thickness, porosity, permeability and transmissivity) are available as individual layers.

The Mesozoic succession of the North German Basin (NGB) yields enormous resources of heat in place bound to Mesozoic sandstone reservoirs located at depths of up to 2.500 m. Compared to highly-permeable sandstone reservoirs, which are exploited for heat production since the 1980s, carbonate reservoirs are underexplored so far. This study evaluates the potential of Mesozoic carbonates on the example of the Rüdersdorf Formation (“Schaumkalk”) in the subsurface of Berlin/Brandenburg.

The data are based on an extensive bed-by-bed outcrop study in the Rüdersdorf open-pit mine to the East of Berlin, and examination of well cores from Berlin-Spandau and Potsdam. The vertical succession exposed in outcrop and well cores shows gradual transitions from marly limestone background facies (“Wellenkalk”) to thick cross-bedded oolitic grain- to packstone reservoir facies (“Schaumkalk”). Based on analyses of carbonate microfacies and reservoir properties, oolitic reservoir facies exhibit high secondary porosities but low permeabilities. The late-diagenetic dissolution of oolites contributed to oomoldic porosity volumes of up to 27,4 % resulting in the typical foamy texture. But due to matrix-supported grain fabrics, the pore connectivity remained low as emphasized by the permeability range of 0.004–7.7 mD. The potential of the reservoir facies is further limited as fluid circulation along open fractures and faults did obviously not contribute to an enhanced matrix permeability. Accounting for this and the limited lateral extent of thick oomoldic reservoir facies, proven in regional well-to-well correlations, the opportunities for reservoir developments in the Rüdersdorf Formation seem to be very limited.