GeoLaB (Geothermal Laboratory in the Crystalline Basement) is envisioned as a pioneering underground research laboratory (URL) designed to enable interdisciplinary, in-situ experimentation within fractured crystalline rock. Developed to bridge the scale gap between laboratory studies and field-scale geothermal applications, GeoLaB is strategically located within the thermally anomalous and tectonically active Upper Rhine Graben.

The scientific focus of GeoLaB encompasses coupled thermo-hydro-mechanical-chemical (THMC) processes, reservoir stimulation, induced seismicity, and the validation of digital simulation models for Enhanced Geothermal Systems (EGS).

Since its inception, the project has made significant progress. Over the past year, two deep exploration boreholes (GLB-1 and GLB-2) were successfully drilled, a 2D seismic survey was conducted, and additional geophysical investigations were carried out. These efforts have yielded critical geological, structural, and hydrothermal data, helping to refine the site model and assess the suitability of the Odenwald region as the GeoLaB location.

GeoLaB is coordinated by the Karlsruhe Institute of Technology (KIT), in collaboration with the Helmholtz Centres GFZ and UFZ, and TU Darmstadt. The project follows a milestone-based development strategy and employs the Integrated Project Delivery (IPD) model to manage technical complexity, legal frameworks, and interdisciplinary collaboration.

By integrating advanced field technologies, participatory governance, and a digital twin approach, GeoLaB aims to become a cornerstone of European geothermal innovation and a global reference for the safe, sustainable, and socially accepted development of deep geothermal energy.

The up to 578 m a.s.l. high Tromm ridge is a N-S-trending, morphologically distinct feature and is currently explored as target for the first geothermal research underground laboratory in Germany. 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 granitic to quartz-monzonitic magmatic arc rocks are intensively faulted and fractured exhibiting predominant argillitic, minor propyllitic, alteration. Drilled fault planes outline predominant normal faulting and minor reverse faulting kinematics, while strike-slip faulting was rarely observed. 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 orthogneisses and metasedimentary rocks below the Tromm granites. We interpret these findings as a major mylonitic-cataclastic tectonic contact between the Tromm pluton and the metamorphic rocks. Regional structural data, a concave upward seismic reflector, and first gravimetric data suggest a continuation of subhorizontal, possibly antiformal, metamorphic rocks of the Böllstein antiform (and/or the “Zwischenzone”) beneath the Tromm granites of the Tromm ridge. Ongoing structural, geochemical, geochronological, and geophysical work will refine and constrain our current concept. Our findings provide the opportunity to develop a geothermal research infrastructure enabling experiments to be carried out in both granitic and metamorphic rocks.

The GeoLaB (Geothermal Laboratory in the Crystalline Basement) project (a Helmholtz initiative) aims to realize an underground geothermal research laboratory in crystalline rocks (i.e., granite-granodiorite). Considerable efforts were and are currently implemented exploring the area of the Tromm, Odenwald Germany. The occurrence of fractured and permeable granites makes the region very promising for the realization of the underground laboratory.

The exploration encompasses an ample range of activities which deliver reliable inputs to complete a site decision and to proceed with the laboratory construction.

One seismic campaign, potential geophysics and two exploration wells (GeoLaB-1 and GeoLaB-2) were completed along with logs and tests on the cores. A second seismic campaign is planned for September 2025.

A broad and comprehensive investigation program (with destructive and non-destructive measurements targeting, among others, geochemical, mineralogical, and micro-structural analyses, flow-cell experiments as well as geomechanical investigations on the cores) will be implemented.

Once the Tromm site will be confirmed as a location to build the GeoLaB underground laboratory, we will be closer to the realization of a unique research platform to investigate the use of crystalline rocks for geothermal purposes thus representing a remarkable contribution for renewable energy exploitation.

Deep geothermal energy is potentially one of the key options for ensuring a sustainable energy supply. However, there are still unresolved research questions regarding the processes that occur at several hundred meters depth. For this reason, the research project GeoLab was initiated, which plans to establish an underground research laboratory in the granitic Tromm Pluton in the Odenwald region. Extensive exploration activities, as well as later a construction phase, are required for this purpose. These activities could potentially impact the surrounding water resources, which are used by local communities in the valley areas for their local water supply.

It is therefore of great importance to document the hydrogeological boundary conditions of the area and to implement a hydrogeological monitoring program. This must be done with great transparency to build trust within the local population for the GeoLab project, the associated scientific work, and the responsible institutions.

In the region around the Tromm Pluton, especially in the valley of the Weschnitz river, extensive hydrogeological and hydrochemical investigations have been, and are being, conducted to determine the water balances of the potentially affected catchment areas. This serves to document the baseline conditions in the study area, which can be used as a reference for later investigations during the construction phase and during the operation of the underground laboratory. Central to this are studies that aim to generate knowledge about the interaction between near-surface aquifers, the interbedded weathered layer, and the underlying bedrock. In this context, geophysical, hydrochemical, and isotope methods are employed.

The GeoLaB infrastructure will be the first underground research laboratory (URL) for investigating the sustainable und safe use of deep geothermal energy in Germany. To support researchers from multiple research centres in Germany, a digital infrastructure has established for a digital twin of the laboratory. A 3D visualisation of the surrounding area has been modelled, containing geographical, hydrological, geological, and administrative data. On the surface, this gives an overview of settlements, protection areas, land use and much more. In addition, the subsurface includes detailed information on geological layers and existing boreholes. First seismic, geophysical and hydrological campaigns have been conducted in the area and test drillings performed. A large amount of these data from these campaigns have been added into the visualisation framework along with the layout of a potential tunnel system. This system serves to support the planning stage of the project and provide information for knowledge transfer activities for stakeholders and the public. The visualisation is interactive and users can explore the integrated datasets. Supplemental information such as websites, videos, or documents can be linked to specific structures to provide additional information. Already set up data loggers and sensors are being shown and measured data can be accessed by simply clicking the respective 3D representation. As a first spin-off of the digital GeoLaB, the GeoDT project was just launched to develop a Digital Twin prototype for the potential in-situ laboratory site in the Odenwald. GeoDT is a project by the BMFTR (see more information https://www.ufz.de/index.php?en=52045).