Deep geothermal energy (DGE) may play an important role for future energy production considering its base load capacity and ubiquitous availability. Funded by the EU Interreg North-West Europe (NWE) Programme, DGE-ROLLOUT promotes the DGE potential of Lower Carboniferous carbonate rocks following a multi-disciplinary geoscientific approach.

With the Geological Survey of North Rhine-Westphalia as lead partner, project partners include the national geological surveys of Belgium, France and the Netherlands, as well as industry partners (DMT GmbH & Co. KG; Energie Beheer Nederland B.V.; RWE Power AG) and research institutions (Fraunhofer Institution for Energy Infrastructures and Geothermal Systems; Technical University Darmstadt; Flemish Institute for Technological Research). Furthermore, DGE-ROLLOUT collaborates with ten sub- and associated partners, including the national geological surveys of Great Britain and Ireland and the European Geothermal Energy Council.

DGE-ROLLOUT comprises three administrative, one investment and three implementation work packages (WP T1-T3): T1 provides a reconciled knowledge baseline for the DGE market development in NWE, including a transnationally harmonised depth and thickness map of the Lower Carboniferous. T2 fills information gaps through the acquisition of 2D seismic surveys, drillings, reprocessing vintage seismic data, and developing 3D subsurface models. T3 increases the efficiency of existing geothermal systems, implementing new or improved production techniques regarding reservoir behaviour, cascading systems and thermal energy storage.

After five years of excellent collaboration, DGE-ROLLOUT comes to an end in October 2023. We are keen on presenting our final results, including two webtools comprising the results of WPs T1-T2. DGE-ROLLOUT collaborations will continue through annual network meetings.

The Bavarian Molasse Basin, is one of Europe’s most successful hydrothermal energy plays. The geological potential of hydrothermal usage of the prolific Upper Jurassic carbonate reservoir also suggests that a significant development of the geothermal output is very feasible, in particular for heating purposes. In order to master this development, challenges associated with exploration, drilling and production have to be further mitigated: For example, around 20% of all deep geothermal exploration wells yielded reduced or insufficient flow rates, at least 25% of all deep geothermal projects experienced severe drilling problems in at least one well and, although not a critical risk in the Bavarian Molasse Basin, few geothermal sites have also been associated with minor microseisimicity. These challenges are mostly related to the complex nature of the exploited Upper Jurassic carbonate reservoir and the foreland basin setting of the Bavarian Molasse Basin, suggesting that an improved regional understanding of the geological and geomechanical evolution and present-day state is necessary. Over the past years, we analysed and integrated geophysical and drilling data of more than 300 deep wells (hydrocarbon and deep geothermal) from the Bavarian Molasse Basin to gain a better understanding of sediment distribution and compaction (basin analysis) as well as the distribution and magnitudes of subsurface stresses and pore pressure (geomechanics). In this contribution we will provide an update and synopsis of these results and discuss possible implications for challenges associated with future geothermal drilling, exploration and production in the Bavarian Molasse Basin.

Geothermal brines in the Upper Rhine Graben (Germany) are highly saline and contain a significant load of dissolved gases, leading to operational challenges in the surface facilities. The decreasing pressure during production of the brine and the thermal transfer from the geothermal fluid to a secondary fluid used to produce electricity results in scaling and corrosion issues, reducing the efficiency of the geothermal energy system.

A thorough characterization of the brine and understanding of the chemical processes are essential to prevent scaling and corrosion and thus to increase the efficiency of the heat transfer and secure a long-term and sustainable extraction of lithium from the geothermal fluid, which is the aim of the Zero Carbon Lithium^TM Project from the Vulcan Energy Group. To avoid degassing and the resulting scaling and corrosion issues, an effective system of pressure control in combination with chemical treatments is used in the Insheim geothermal power plant in Rhineland Palatinate (Germany).

In frame of the European H2020 project GEOPRO (Grant Agreement 851816), Vulcan contributes to a better understanding of the gas behavior in the brine of the Insheim geothermal power plant to prevent degassing related issues by using a joint field and modelling approach. In the presented Insheim case study the operational influence of slight variations in the composition and of minor elements in the geothermal fluid are investigated and the origin of the dissolved gases in the geothermal fluids of the Upper Rhine Graben are studied using the composition of the gases and their isotopic signature.

Fault zones in granites and granodiorites exhibit distinct structural, geochemical, and petrological features that have significant implications for hydraulic heterogeneities. These features arise due to the brittle deformation and fluid-rock interactions within fault zones. The interconnected fractures and fault planes provide preferential pathways for fluid flow, enhancing the permeability contrast compared to the surrounding rock matrix. Additionally, the presence of hydrothermally altered or weathered minerals can modify locally the permeability, resulting in heterogeneous fluid flow patterns.

The aim of this contribution is to integrate refined mineralogical analysis through, XRD, EMP, and ICPMS, along with structural analysis from borehole logs, to characterize the heterogeneities present in faulted granodiorites and granites in two locations in the crystalline Odenwald.

The first location, e.g. the SKEWS demo-site (Projektträger Jülich, 03EE4030A), is a heat-storage demonstrator targeting granitic and granodioritic units, in which the upper section is affected by a fault. The second location is the Otzberg Fault Zone at the Eastern Border of the Tromm Granite, which is a major large-size structural element, which can serve as an analog for structures targeted in deep geothermal reservoirs, and thus is a potential site for the realization of GeoLaB.

These geological features influence fluid flow pathways, storage capacity, and fluid-rock interactions within the fault zones, ultimately affecting the development and distribution of hydraulic heterogeneities. Such understanding is vital for subsurface resource exploration and management, from deep geothermal EGS to heat-storage potential subsurface assessments in regions characterized by granitic and granodioritic rocks, in Germany or Europe-wide

The decision for the site of the GeoLaB (geoscientific underground laboratory) infrastructure considers many aspects. One of the geoscientific aspects comprise the mineralogical-petrological, petrophysical and geomechanical properties which will be investigated in the exploration stage of the project. Potential targets comprise on the one hand the Tromm ridge and the Otzberg fault zone in the Odenwald and the Omerskopf area and Glashütte fault zone in the Black Forest on the other hand.

In a recent field campaign more than 50 samples, comprising fresh, altered, and cataclastic rocks as well as fault gouge material, from the Odenwald and the Black Forest were probed. This first set of samples will be investigated for quantitative mineral composition and clay mineralogical composition, mineral chemistry, the presence of micro-fractures and alteration patterns in the thin sections via element mapping.

The investigation of micro-structures at microscale will be linked to the structural geology at macroscale. Furthermore, the same analytical approach will be applied to core samples from exploration drilling as soon as they will be available.

These first results will be combined with structural geological field data, geophysical and geomechanical experiments to generate a scientific database for the GeoLaB site selection and future scientific work. In the future the samples will undergo a complex thermo-hydraulical-mechanical and chemical investigation routine established in pre-runner projects.