Geothermal heat flow (GHF) is essential for evaluating the thermal states and energy balances of the lithosphere, playing a crucial role in geophysics and geothermal energy research. In this study, we initiate our analysis by exploring lateral variations in unknown thermal parameters across Germany. We apply a Bayesian Markov Chain Monte Carlo approach, using established data on surface heat flow, surface temperatures, and the temperatures and thicknesses at the lithosphere-asthenosphere boundary. Our investigation focuses on assessing the lateral variations in crustal and lithospheric mantle thermal conductivities, crustal heat production, and mantle heat flow.

To address the limitations posed by the sparse and uneven distribution of direct borehole data, which consists of only 595 heat flow points, our study integrates a broad spectrum of geophysical and geological datasets. These include gravity, magnetics, seismic data, topography, proximity to faults, and volcanoes, and compositional data within a machine-learning framework. This comprehensive approach not only surpasses traditional Curie depth estimations in accuracy but also robustly tackles the issue of data scarcity.

We employ quantile regression forests to clustering to integrate the datasets in a geothermal heat flow model. This probabilistic, multi-geophysical inversion method leads to a detailed quantification of uncertainties, offering a refined understanding of Germany’s geothermal potential.

Extracting heat from medium-deep hydrothermal reservoirs for municipal heat supply requires adequate reservoir characteristics, suitable extraction techniques, a sufficiently high heat demand and appropriate heat supply infrastructure. Furthermore, the acceptance of local stakeholders and consumers, as well as financial feasibility are crucial factors for the successful implementation of geothermal heat projects.

In the North German Basin (NDB) in particular, there are several deep geothermal projects that have been planned over the years but have never been completed, mostly due to the high exploration and financial risks at the beginning of the project. Some municipalities have already taken the initiative to restart projects.

The aim of this work is to provide technical support for local stakeholders to enable them to initiate and successfully implement hydrothermal projects.

In a first step, the authors identify aborted geothermal projects in NDB located in geologically well explored regions. Based on related feasibility studies, literature reviews and expert interviews, common constraints and challenges are discussed from geological, technical, social and economic perspectives.

Secondly, a number of selected projects are analysed in more detail. Alternative operating scenarios are developed and the positive impact of new technological developments such as high capacity heat pumps is examined.

Finally, the results will be generalised in order to derive recommendations for interested local stakeholders.

The work is part of the Warm-Up project, funded by the Federal Ministry for Economic Affairs and Climate Action (BMWK).

Geothermie spielt eine entscheidende Rolle für eine klimaneutrale Wärmeversorgung, jedoch sind bisher nur wenige Tiefengeothermie-Projekte in Niedersachsen umgesetzt worden. Das Norddeutsche Becken (NDB) beherbergt potenziell vielversprechende mitteltiefe geothermische Reservoire, insbesondere in den Kalkareniten der Reitbrooker Schichten des oberen Maastrichts. Diese wurden durch zahlreiche Bohrungen der Kohlenwasserstoff-Industrie erkundet und gelegentlich für die Abwasserentsorgung genutzt, was auf eine gute Gesteinsdurchlässigkeit hinweist. Spezifische Untersuchungen zu ihrer geothermischen Eignung fehlen jedoch bisher.

Bohrlochdaten und 3D-Seismik wurden analysiert, um das Reservoir zu kartieren und charakterisieren. Dabei wurden die Bohrungen über zwei mergelige Bereiche korreliert, welche die Arenite in obere und untere Bereiche unterteilen. Es wurde festgestellt, dass sich die Arenite der Reitbrooker Schichten lateral von Nord nach Süd zunehmend mit glaukonitreichem silikatischem Sand vermischen. Die aus Plug-Messungen von Kernproben gemessene Porosität und Permeabilität, kombiniert mit den berechneten Porositäten aus Sonic- und Density-Logs, lassen darauf schließen, dass tendenziell bei stratigraphisch höheren Arenite bessere Reservoirparameter zu erwarten sind. Die Verbreitung und Erhaltung der Arenite unterhalb des Paläozäns stehen im Zusammenhang mit der tektonischen Entwicklung, insbesondere der Inversion des Niedersächsischen Beckens. Große Mächtigkeitsschwankungen im Verbreitungsgebiet werden durch Halokinese verursacht, wobei besonders mächtige Ablagerungen in den Randsenken auftreten, während sie teilweise auf den Salzstöcken fehlen.

Das Zusammenspiel von Tektonik, Halokinese und Sedimentationsdynamik führt zu einem heterogenen Reservoir, das dennoch gut vorhergesagt werden kann. Zur Bewertung des geothermischen Potenzials, zur Kartierung und zur Entwicklung von Erschließungsstrategien sollen noch numerische Simulationen durchgeführt werden.

The geothermal heat anomaly in northern Bavaria was first discovered in the late 1970s and has recently been more precisely localized. An elevated temperature of 57 °C estimated at a depth of 1000 m is estimated to be higher than that based on the normal geothermal gradient. The geothermal gradient is approximately 4.5 °C/100 m with a heat flow density of 110 - 130 mW/m². The location and extent of the geothermal anomaly are constrained by the limited number of deep wells, which has left the cause of the positive heat anomaly in the region enigmatic. In this study, we use geophysical methods and modeling to locate the granitic intrusion in the subsurface as a possible source of the observed high geothermal anomaly.

An important feature of the northern Bavarian subsurface is the presence of granitic intrusions covered by early Carboniferous turbidites and Permian graben and half-graben structures (Rotliegend sandstone), similar to those exposed setting in the western Bohemian Massif. By integrating the geological and geophysical data and modeling, we define the location and geometry of a granitic intrusion and estimate the depth to basement. Our 2D forward models predict the structural and stratigraphic setting satisfying observed geological and geophysical data. Our integrated methodology describes the granitic intrusion, the sedimentary cover, and the regional structural patterns relevant to ongoing deep geothermal exploration. This study contributes to subsurface characterization (e.g. potential reservoir and buried fault zones) and reduces risks associated with exploration and potential future development.

The Bavarian part of the North Alpine Foreland Basin (NAFB) is highly relevant for geothermal exploration, especially amid recent play developments, highlighting the importance of an integrative geological and geophysical approach. Our work focuses on establishing a robust seismostratigraphic framework for the Bavarian NAFB using an unprecedented dataset consisting of digitised (vintage) seismic and well log data.

Based on this unique data set, we interpreted and correlated well logs and identified important seismic reflectors across the NAFB using seismic-to-well ties and synthetic seismograms, refining seismostratigraphic concepts from previous models such as GeoMol [GeoMol Team – Project Report (2015)]. Our study incorporates considerations of different depositional facies, focusing on the continuous traceability of major reflectors throughout the basin. We identified five major Tertiary reflectors that can be consistently tracked across various lithological and facial boundaries and follow major basin-wide unconformities. Especially the main reflectors identified within the complex Egerian successions and their ability to be traced across different lithostratigraphic units (i.e. Lower Freshwater/Brackish/Marine Molasse), serve as an example of how the reflectors are partially independent from stratigraphic boundaries and their varying facies distributions. Instead, the presence of major seismic reflectors in the NAFB is rather determined by basin-wide unconformities, whose distinctive seismic signatures serve as a basis for consistent identification across the basin.

Our work provides a fundamental step towards an integrated seismostratigraphic framework for the Bavarian NAFB, aiming for a coherent approach of seismic interpretation in industry, academia and authorities, thus promoting standardized methodologies for future (geothermal) well development.

The fit for 55 package, which outlines policy measures to deliver the EU Green Deal, calls for a greater than 40 % target for renewable energy sources by 2030 in the Renewable Energy Directive (RED). It also calls for an increased primary (39 %) and final (36 %) energy savings to be achieved by the Energy Efficiency Directive (EED). Accelerating the penetration of cost-effective and energy efficient renewable heating and cooling (RES HC) technologies will be key to the successful achievement of these targets.

Geothermal heat pumps are the most cost-effective and efficient source of renewable heating and cooling on the market. They can meet the heating and cooling needs in residential and non-residential buildings of all sizes with varied energy profiles. Furthermore, they can be applied as individual applications at building scale, or through renewable district heating and cooling systems.

One big challenge at the moment and for future years is decarbonising heating and cooling grids for new builds and in particular for existing buildings. geoENERGIE Konzept presents projects in different stages of development of their wide portfolio. Hereby lies the focus on district heating and cooling grids for new as well as existing buildings, hybrid systems with other renewable sources and underground thermal energy storage.