SpannEnD 2.0

Geomechanical-numerical modeling to characterize the crustal stress state for the disposal of high-level nuclear waste in Germany

The aim of the project is to provide geomechanical-numerical models and tools for the robust prediction of the recent crustal stress state in Germany.

Facts about the project

Project manager: Dr. Steffen Ahlers PhD project: Victoria Kuznetsova +++ Duration: 01.04.2022 – 31.03.2026 +++ Project funding: Bundesgesellschaft für Endlagerung (BGE), Peine +++

Offizielle Website zum SpannEnd 2.0 Projekt

Knowledge of the tectonic stress state is a key factor in site selection. In the first work package, the project aims to further develop and provide the geomechanical-numerical stress model for Germany (Ahlers et al., 2022). This stress model for Germany can be used, among other things, for sub-area and large-scale regional comparisons, but also provides necessary boundary conditions for more detailed regional and local models. Corresponding submodeling techniques for the consistent linking of the different model scales will be further developed in a second work package. In the third work package, the various measurement methods for determining stress magnitudes will be evaluated and generally applicable recommendations for optimizing exploration programs with regard to the parameterization and calibration of geomechanical-numerical models will be developed. Overall, the four-year R&D project will thus provide all the basic principles and modeling tools required for a robust prediction of the in situ stress state in Germany.

In the course of the SpannEnD project (www.spannend-projekt.de/en), a 3D stress model was created for Germany for the first time, taking into account published structural models and geomechanical data, and calibrated to measured data records on stress magnitudes and orientations. Based on a new geological 3D model of Germany (Ahlers & Henk 2025) a new geomechanical model has been created whose publication is in preparation. Due to the improved geological model, twice as many units – in comparison to the former model – are resolved in the new geomechanical model. In addition, a five-time higher vertical resolution is used and the number of stress magnitude data records used for calibration could be tripled. The video shows an example of the predicted stresses of the maximum horizontal stress (SHmax) from the uppermost 5 km in the central part of the geomechanical model.

Results of the SpannEnD 2 model

The local refinement of the geomechanical-numerical models for stress prediction is examined using a sub-area model as an example. The study area is located between the federal states of Bavaria and Baden-Württemberg and covers an area of 120 km2 (8 km x 15 km). The basis for the model is the reconstruction of the subsidence and uplift history using the current subsurface structure. The 3-D model takes into account 19 events and comprises 17 stratigraphic units from the crystalline basement to the Quaternary. The boundary conditions represent the development of the surface temperature and the basal heat flow as well as the changes in the supra-regional stress field over time. The model is calibrated using temperature and vitrinite data as well as information on the orientation and magnitude of the recent stress field. Based on the previous results, a larger geomechanical model with an area of 200 km x 80 km will be created and these two models will be linked with the multi-scale approach of submodeling.

Sketch of a multi-scale approach combining large scale models (1000 km) with local scale models (1s to 10s km).
Sketch of a multi-scale approach combining large scale models (1000 km) with local scale models (1s to 10s km).

The prediction of field sizes in the geosciences usually faces the problem that they are controlled by long-wavelength processes such as plate tectonics, but at the same time high resolution is required for practical application at the site scale. In order to consistently model field quantities across different scales, a multi-scale approach (Fig. 2) will be further developed. This approach has already been successfully implemented in 3D kinematic models, i.e., for displacements (e.g., Hergert et al., 2011). In contrast, the transfer of 3D stresses across spatial scales has not yet been extensively studied. A first test for the use of the multi-scale approach for 3D stress models is shown by Ziegler et al. (2016).

For the search of a desposit, the requirements for exploration programs – for geomechanical data and in situ stress measurements – are significantly different from those of the hydrocarbon industry. In particular, the target horizon is generally shallower – at 300-1500 m below ground surface – and the host rocks have significantly different geomechanical properties than those of hydrocarbon reservoirs. In addition, besides the target horizon, i.e. the host rock, the strata in the overburden and underburden must also be geomechanically assessed, since those play an important role for geotechnical issues in repository construction, but also in modeling long-term safety, e.g. with respect to erosion or loads due to glaciation cycles. Likewise, the demands on the accuracy of model results are higher, so that the choice and planning of measurement programs in boreholes or their optimal localization in terms of parameterization and calibration of geomechanical models represent special challenges. Another central and controversially discussed question in the literature is the influence of disturbances on the components of the stress tensor (Yale, 2003), which has been investigated by Reiter et al. (2024).

Picture Gallery

3D models that are implemented in the new geological model (grey area). Details are described in Ahlers & Henk (2025).

View of the new geomechanical model of Germany

Sinking history of the model.

3D view of the model.

Conference Contributions

  • Ahlers, S., Henk, A., Reiter, K., Hergert, T., Röckel, L., Morawietz, S., Heidbach, O., Ziegler, M., and Müller, B.: SpannEnD 2.0 – Improved present-day stress prediction of Germany by a new 3D geomechanical-numerical model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, https://doi.org/10.5194/egusphere-egu25-15638, 2025.
  • Louison, L., Ziegler, M., Reiter, K., Heidbach, O., Desroches, J., Giger, S., and Cotton, F.: Minimum amount of stress magnitude data for reliable geomechanical modelling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, https://doi.org/10.5194/egusphere-egu25-6868, 2025.
  • Reiter, K., Heidbach, O., Henk, A., Degen, D., and Achour, R.: Impact of resolution and finite element type in geomechanical-numerical modelling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, https://doi.org/10.5194/egusphere-egu25-9583, 2025.
  • Velaga, L. S. A. R., Heidbach, O., Ziegler, M., Reiter, K., and Henk, A.: The Role of Faults in Shaping Present-Day Stress Fields: Implications for 3D Subsurface Models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, https://doi.org/10.5194/egusphere-egu25-10251, 2025.
  • Ziegler, M., Reiter, K., Heidbach, O., Seithel, R., Rajabi, M., Niederhuber, T., Röckel, L., Müller, B., and Kohl, T.: Faults in geomechanical models – Necessary, nice, or nonsense?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, https://doi.org/10.5194/egusphere-egu25-8308, 2025.
  • Ahlers, S., Röckel, L., Reiter, K., Hergert, T., Henk, A., Morawietz, S., Heidbach, O., Ziegler, M., Müller, B., and Kuznetsova, V.: Prediction of the recent crustal stress state of Germany – The SpannEnD project, Tectonic Stress: from the lithosphere to the wellbore, London, United Kingdom, 21–22 May 2024, 2024.
  • Ahlers, S., Reiter, K., Henk, A., Hergert, T., Röckel, L., Morawietz, S., Ziegler, M., Heidbach, O., Müller, B., and Kuznetsova, V.: SpannEnD 2.0 – The crustal stress field of Germany: results of a refined geomechanical–numerical model, GeoSaxonia 2024, Dresden, Germany, 23-26. Sep 2024, 2024.
  • Ahlers, S., Reiter, K., Henk, A., Hergert, T., Röckel, L., Morawietz, S., Heidbach, O., Ziegler, M., Müller, B., and Kuznetsova, V.: The recent crustal stress state of Germany – results of a new geomechanical–numerical model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, https://doi.org/10.5194/egusphere-egu24-16586, 2024.
  • Kuznetsova, V., Henk, A., and Ahlers, S.: Geomechanical modeling of a potential site for nuclear waste repository in Germany – The SpannEnD project, GeoSaxonia 2024, Dresden, Germany, 23-26. Sep 2024, https://doi.org/10.48380/63me-w860, 2024.

Publications

  • Ahlers, S. and Henk, A.: 3D Geological Model for Germany and Adjacent Areas, Earth Syst. Sci. Data, 2025, submitted.
  • Ziegler, M. O., Seithel, R., Niederhuber, T., Heidbach, O., Kohl, T., Müller, B., Rajabi, M., Reiter, K., and Röckel, L.: Stress state at faults: the influence of rock stiffness contrast, stress orientation, and ratio, Solid Earth, 15, 1047–1063, https://doi.org/10.5194/se-15-1047-2024, 2024.
  • Reiter, K., Heidbach, O., and Ziegler, M. O.: Impact of faults on the remote stress state, Solid Earth, 15, 305–327, https://doi.org/10.5194/se-15-305-2024, 2024.

Status Quo & Outlook

The project is in its final year. Initial results are currently being prepared for publication.

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