Conference Agenda

The deep subsurface of Berlin hosts several potentially exploitable geothermal reservoir horizons, including the Sinemurian, Hettangian, Schilfsandstein, Schaumkalk, and Middle Buntsandstein aquifers. These reservoirs differ significantly in depth, temperature, hydraulic properties, and geological architecture, requiring distinct geothermal development concepts and technologies. Geothermal development in Berlin therefore requires an integrated assessment of multiple stacked reservoir systems rather than a single-reservoir approach. However, the geological data base remains limited and is largely derived from a small number of seismic surveys acquired between the 1960s and 1980s, a few deep wells, and data from the former gas storage facility in Spandau. Consequently, substantial uncertainties persist regarding reservoir geometry, facies distribution, structural controls, and reservoir quality.

To address these challenges, a coordinated reservoir management strategy has been developed that considers the subsurface as an integrated three-dimensional resource system. In 2025, the State of Berlin acquired exploration rights for geothermal energy, brine, and lithium across approximately two-thirds of the city area. Mechanisms are currently being established to enable the coordinated allocation of exploration and utilization rights while safeguarding long-term development options across reservoir horizons and operators.

A comprehensive exploration program is underway to improve the geological understanding of Berlin’s subsurface. Following a pilot 2D seismic survey completed in 2025, a city-wide 3D seismic campaign is planned for 2027. In parallel, a large-scale research project and several state-funded exploration wells will be carried out between 2026 and 2030. These activities aim to reduce the exploration risk and provide the foundation for a comprehensive and sustainable development of Berlin’s geothermal resources.

As part of the drilling and exploration programme, the Geological Survey of North Rhine-Westphalia conducted a pilot seismic survey between Steinfurt and Rheine with a profile length of approximately 12 kilometres in 2025. The aim was to evaluate different vibroseis technologies for exploring potential geothermal reservoirs in the northern Münsterland region, and determine optimised measurement parameters for future seismic exploration. The investigation focused on Upper Cretaceous carbonates and potential Triassic and Permian aquifers. High-resolution images were generated of potential geothermal reservoirs as well as the fault inventory down to depths of approximately 3.5 km.

The survey line run along a former railway line, offering the ideal setting for comparing different source concepts in identical geological conditions due to its straight geometry, the near-continuous acquisition, and low ambient seismic noise.

A key feature of the pilot survey was the first-time use of two innovative vibroseis technologies in North Rhine-Westphalia. In addition to the conventional use of hydraulic AHV-IV vibrators from DMT, the fully electric Storm and Hurricane eVibes from Faraday Geophysics were tested. Furthermore, the pilot line featured the world’s first field deployment of Herrenknecht’s UrbanVibroTruck (UVT), a vibroseis technology currently still under development for use in infrastructure-sensitive and urban areas.

The recorded seismic data were processed using modern methods, including pre-stack time and depth migration. For the reference dataset acquired with the AHV-IV vibrators, extensive omission tests were conducted to investigate the influence of reduced shot and receiver point densities on the quality of the seismic imaging of the subsurface.

The state government of North Rhine-Westphalia (NRW) aims to accelerate the use of medium and deep geothermal energy in NRW. Therefore, the Geological Survey of NRW (GD NRW) was appointed to lead the 5-year “Explorations- und Bohrprogramm NRW” within the state geological survey.

In addition to processing and digitising legacy data (boreholes, well logs, reports, seismic data), the acquisition and interpretation of approx. 1,000 kilometres of 2D-seismic data, and the creation of geological and geothermal models of the subsurface, potential hydrothermal reservoirs in NRW are now being investigated through scientific drilling. The main focus is on Cretaceous and Palaeozoic carbonate rocks, as well as Tertiary sand, which can be used as ATES.

In Krefeld, a 1,000-metre-deep scientific borehole has confirmed NRW’s first geothermal reservoir: the Carboniferous Kohlenkalk. Earlier 2D-seismic surveys confirmed the presence of the Kohlenkalk at this location. The formation’s thickness, previously estimated at approx. 250 metres, was later corrected to 500 metres. Geophysical measurements along the entire section and the analysis of 500 metres of drill cores revealed notable karst formation, particularly in the lower section of the Kohlenkalk. A short-term pumping test confirmed a high inflow of deep water. Regional municipal utility companies are already incorporating these findings in their own projects.

A borehole in Cologne is being drilled to investigate the next reservoir - the Devonian Massenkalk – with the same approach. Furthermore, two boreholes up to 2,000 metres in depth are planned, which can be reused by municipal utility companies if they yield sufficient energy.

Through the exploration initiative "Masterplan Geothermie NRW" of the state government, deep geothermal energy is becoming increasingly important in NRW. In the "Geothermie Minden" permit field of Energieservice Westfalen Weser GmbH – the first and so far only deep geothermal energy project in OWL – the preliminary hydrothermal potential below the city of Minden is being investigated as part of a feasibility study.

Minden lies at the transition between the North German Basin and the Inverted Lower Saxony Basin. The city with over 80,000 inhabitants, a large canal port and energy-intensive industrial areas has a high demand for heat and process heat.

The overburden consists of Mesozoic clastic and evaporitic rocks. Only a few kilometres to the south, thermal water with a temperature of approx. 36 °C has been extracted from Triassic layers up to 1,000 m deep for balneological purposes in Bad Oeynhausen for around 100 years.

Based on these regional conditions and other drilling data, a temperature of around 130 °C is expected in the Minden Syncline at a depth of about 4 km. This opens up an economically attractive scenario for hydrothermal heat generation. Doublet drilling is planned to pump the thermal water and to feed the district heating network.

Availability of deep boreholes and seismic data is limited in OWL. To further improve the conceptual structural model and reduce geological uncertainties, a 3D seismic survey is planned for 2027. A continuous risk assessment, taking into account ecological, social, economic and technical aspects, forms a central basis.

Decades of hydrocarbon exploration in the North German Basin have yielded an extensive archive of subsurface borehole data, offering a comprehensive database for geothermal resource assessment. Within the BMWK-funded research project "Warm-Up", the Aalenian (Middle Jurassic) sandstones, historically referred to as Dogger-β, are being assessed as potential geothermal reservoirs in the northern part of the Gifhorn Trough, located east of Hanover, Lower Saxony.

This study demonstrates how legacy hydrocarbon borehole data, accumulated since the mid-1950s during oil and gas exploration, can be re-evaluated for geothermal purposes. The dataset comprises stratigraphic -, wireline logs, and routine core analyses (RCA) from 14 wells. Seven cores were reevaluated and 19 new core plug measurements were performed to complement and verify existing petrophysical data.

The core study reveals that the Aalenian sandstones were deposited in a predominantly river-dominated delta system with moderate wave influence. Recognised facies include pro-delta mudstones and siltstones, delta-front heterolithics, distal and proximal mouth bars, distributary channels, chute channels, and tidally influenced channel fills. Reservoir quality is primarily controlled by grain size and facies: proximal mouth bars and distributary channels yield the highest porosities and permeabilities, while delta-front heterolithics represent poor reservoir intervals. Carbonate cementation locally degrades reservoir quality, whereas open fractures, documented in one well, the Wesendorf-Süd 12 well, may significantly enhance hydraulic conductivity.

Petrophysical log analysis of all 14 wells confirms an overall high-quality, but heterogeneous reservoir system. Averaged across all sub-units, the Aalenian sandstones yields a mean net thickness of approximately 16 m, a net-to-gross ratio of ~0.69, an effective porosity of ~22%, and a mean calculated permeability of ~275 mD. The Upper Reservoir is the most continuous and best-developed unit, with net-to-gross values approaching 1.0 in the Hankensbüttel area, effective porosities averaging ~24%, and permeabilities locally exceeding 350–400 mD. Core measurements from fine- to medium-grained sandstones reach permeabilities in the Darcy range, confirming excellent hydraulic properties suitable for geothermal utilisation.

Our work demonstrates a transferable workflow for geothermal reservoir characterisation based entirely on legacy oil and gas data, enabling risk reduction and productivity prediction in areas with limited new data. The results will be made publicly available and are intended to stimulate further geothermal exploration in this area.

In the North German Basin, Eocene, Oligocene and Miocene sands and sandstones have got potential for medium-deep geothermal heat, although mainly Mesozoic and Palaeozoic reservoirs have been explored prior to a discovery of Eocene sandstones with better properties than expected in 2022 in Hamburg [1].

Only 20 kilometres away, the Stadtwerke Norderstedt, a municipal water and energy supplier, is planning to drill a medium-deep exploration well doublet to test Miocene sands for thermal water production and injection. In case of discovery, the thermal output will be increased by large-scale heat pumps and supplied to a district heating network. GeoDienste GmbH delivered the geological expertise and feasibility study [2] for the project.

The Miocene was deposited in transitional marine and non-marine environments [3]. Two unconsolidated sand intervals are embedded between clay-rich strata. In deep depressions related to salt migration, such as below the city of Norderstedt, these formations are buried below a few hundreds of meters of middle to late Miocene clay-rich strata and Quaternary deposits. Primary target is the lower of the two reservoirs, which is, according to the prognosis, composed of unconsolidated sands of about 300 m thickness with best permeability in the medium to coarse grained shallower section. Water temperature of 23-28°C is expected. The target area was delimited to protect drinking water production from the same reservoir.

Tertiary sands are widely preserved in Northern Germany and possible targets for medium-deep hydrothermal heat exploration.

[1] Kombrink 2022 GEOExPro [2] GeoDienste 2024 unpubl. study [3] Vinken 1988 Geol.Jb A100