The TUNB project, conducted from 2014 to 2021, marks an important step in the geological 3D modelling of the North German Basin. Through the collaboration of the State Geological Surveys of the participating federal states and the Federal Institute for Geosciences and Natural Resources, a comprehensive 3D model was created, comprising 13 geological horizons and important structural elements such as faults and salt structures. The model finds application, for example, as a basis for further investigations and planning in the subsurface, ranging from CO2 storage to the final disposal of radioactive materials.

The follow-up project, 'TUNB Velo 2.0,' extends this work by evolving the geological 3D structural model towards a parameterized volume model, with 'seismic velocity' as the key parameter. This enhancement allows the precise conversion of seismic data from the time domain to the depth domain, thereby correcting the apparent geometry of geological structures distorted by velocity variations. This allows for a more realistic spatial representation of the geological subsurface and paves the way for the creation of more accurate and detailed future 3D geological models in this region.

TUNB Velo 2.0 marks a significant step forward in the geological exploration of the North German Basin and is a vital tool for enhancing the precision and resolution of future geological 3D models. In our presentation, we will introduce the project and its history, summarize ongoing work, discuss key challenges, and highlight the expected benefits for future projects.

A harmonized regional 3D depth model of the subsurface for the North German Basin from Cenozoic to the base of Zechstein was developed from 2014 to 2020 in the framework of the TUNB project. In a next step, this model will be parametrized with a focus on seismic velocities (and optionally other parameters).

The seismic database in the former Eastern and Western parts of Germany differs due to different historical conditions (e.g. concepts of exploration and interpretation, availability of seismic equipment and computing power).

In the eastern part of the North German Basin (Federal States of Mecklenburg-Western Pomerania, Brandenburg, Saxony-Anhalt) most of the velocity data were acquired in 2D-seismic surveys from the 1960s to the 1980s that focused on deep Permian reservoirs. Strata and structure of the Mesozoic were also documented, but were usually not an exploration target. Besides processing velocities and in a minor extent sonic logs comprehensive data from check-shots and vertical seismic profiles were documented for several hundreds of wells. Based on these heterogeneous data, interpretations concepts and velocity models were developed from the 1960s to the 1980s on local scales for detailed seismic surveys and on regional scales for Northeastern Germany.

The main goal of the ongoing project is to develop workflows to revitalize the historical data with modern methods and possibilities of 3D modelling to derive cross-country-wide harmonized and seamless 3D-velocity fields. These velocity models allow large-scale depth-time- and time-depth-conversions of geological 3D models and support upcoming seismic processing and reprocessing campaigns.

The TUNB model provides a 3D model for the North German Basin consisting of 13 lithostratigraphic units from Zechstein to Tertiary and numerous salt domes and fault systems. The aim of the project TUNB Velo 2.0 is to assign reasonable seismic velocities to the lithostratigraphic units. The resulting velocity model enables to convert information on a regional scale from time to depth domain and vice versa. Therefore, a 3D volume model is created from the 3D structural model and then parameterised with seismic velocities.

For Schleswig Holstein and Lower Saxony, Jaritz (1991) published a regional velocity study within the Tectonic Atlas (GTA) project that serves as the database for velocity modelling. The authors derived the velocities mainly from Vertical Seismic Profiling measurements as well as considerations of the regional geology. Their model covers 11 layers from Zechstein to Tertiary. For every sediment layer, maps display its surface velocity. The velocities can be calculated in depth using the surface velocities, an individual gradient for every layer and the dedicated depth.

Both Federal States use Aspen SKUA for region-wise velocity modelling. Close to the border, we harmonized the velocities to enable the creation of a consistent, trans-border model.

In this talk, we will provide insights in the processing of the database, the modelling methods in Aspen SKUA and show the resulting velocity distribution.

References:

Jaritz W., Best G., Hildebrand G., Jürgens U. (1991) Regionale Analyse der seismischen Geschwindigkeiten in Nordwestdeutschland. Geol Jahrb 45:23–57

Reliable geological models of the North Sea are essential for a robust assessment of subsurface potentials in this vital European economic region. While commercial and scientific surveys have effectively explored the upper 2 to 4 km, there is currently no well data reaching the base of the locally more than 10 km deep rift structures such as the Central and Horn Graben. This leads to considerable uncertainties in the regional seismic velocity model and thus in the depth-conversion of reflection seismic profiles. Our objective is to reduce these uncertainties in the German North Sea by integrating the abundant gravity data, offering additional constraints on both the geometry and petrophysical properties of deep basins. We present the results of 2D gravity forward modelling, which combines existing regional and global crustal models with the most recent structural model of the Paleozoic to Cenozoic sedimentary sequences. Density information is thereby derived from well logs, seismic tomography studies, and further literature implications. The calculated free-air gravity anomalies are then compared with the measured gravity field to assess the quality of the used crustal and sedimentary models. The insights gained will subsequently inform a more intricate inverse 3D modeling, resulting in a quantitative description of the geological uncertainties.

The new Dresden - Prague railway line is a Saxon vision. Since 2014, the Geological Survey of Saxony has been developing the geological 3D model on the basis of archive data and geophysical investigations.

In cooperation with the TU Bergakademie Freiberg (TU BAF) and the Czech geological survey, a cross-border model was built that illustrates the complex geological structures in the underground of the route corridor. As part of an INTERREG project, the model was presented to the public in a walk-through 3D room at the TU BAF.

When the planning task was assigned to Deutsche Bahn, the geological 3D model proved its worth as a basis for the first steps of exploration planning, regional planning and preliminary planning in combination with GIS.

The model will be updated as knowledge is gained during the explorations.

It is a real pilot project for successful cooperation between authorities, research institutions and the railway companies in using graphic datamangement and 3D-modeling.