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Cavern storage 12.4.2017

Salt structures in northern Germany
© BGR

Using salt caverns throughout Germany

Which salt formations are suitable for storing hydrogen or compressed air? In the InSpEE-DS research project, scientists are developing criteria that enable locations to be assessed even if the exploration is still at an early stage. Compared with the previous InSpEE project, the researchers have now widened their investigations to cover all of Germany and also special salt formations.

Project status Compilation and analysis of geological data for shallow salt strata in Germany
Project duration October 2015 until March 2019

In collaboration with their project partners, scientists at KBB Underground Technologies are developing planning criteria for selecting sites and constructing storage caverns in salt domes. Such caverns could store renewable energy in the form of hydrogen or compressed air. Whereas the previous InSpEE project was limited to salt formations with considerable thickness in northern Germany, different salt structures throughout Germany are now being included. The researchers are developing requirements and criteria with which they can also evaluate shallower salt formations and multiple or double salt bodies. These will then also make it possible to make assessments when the site investigation is still at an early stage and there is only relatively limited knowledge about the structure of the salt formations.

Potential throughout Germany

Shallow salt layers just outside of Lower Saxony and Schleswig-Holstein offer considerable potential for the decentralised storage of renewable energy. Geological exploration results show that this is the case, for example, in North Rhine-Westphalia, Thuringia, Hesse, Saxony-Anhalt, Brandenburg and Baden-Württemberg. To estimate the storage possibilities, the scientists are preparing geological data. These include the distribution, depth and bedding conditions of the salt strata. The data analysis will be supplemented with mineralogical and geochemical surveys, the determination of geotechnically relevant rock parameters and extensive numerical modelling for interpreting the caverns.

Also potential in complex salt structures

About 100 of the roughly 700 salt structures in northern Germany are very complex. They occur in a limited area that extends across Schleswig-Holstein, Hamburg, the northern part of Lower Saxony and parts of the German North Sea sector. The structures described as double or multiple salt bodies do not consist solely of salt bodies from the Zechstein sequence. They also contain salt layers from the Rotliegend and, to a certain extent, Keuper sequences. Their composition and geomechanical properties differ from Zechstein salt bodies.

In comparison with salt bodies that consist only of Zechstein, little is known about the internal structure of multiple salt bodies, as these structures have not been used until now for mining. The researchers have therefore adopted a cautious approach for estimating the potential: they are only taking into account Rotliegend salt within double salt bodies. In addition, a whole series of the multiple salt structures are situated at a greater depth. These were not considered in accordance with the criteria of the previous InSpEE project. Since the double or multiple salt bodies lie near the coast, caverns close to existing and future onshore and offshore wind turbines could be solution-mined. The brine produced when excavating the caverns can also be disposed of comparatively easily. This is of particular importance when considering the potential of previously excluded structural areas.

However, there is still insufficient geological and geomechanical knowledge in order to assess the safety aspects in such cavern locations and produce economic feasibility studies based on them.

Optimising the criteria for southern Germany

The experience in constructing caverns in Germany relates primarily to large widths and good salt quality. In northern Germany, there are a large number of potentially suitable structures. Therefore until now there has been no need to optimise minimum widths or impose fewer requirements on the quality of the salt being solution-mined.

If these criteria were also maintained for southern Germany, it would hardly be possible to construct caverns there. However, salt formations with smaller widths are used for constructing caverns in other parts of Europe. The aim of the work packages is to enable informed estimations of the potential and to estimate the potential provided by salt formations with low widths that were previously not considered.

For this purpose, the researchers are gathering existing knowledge and generating new knowledge concerning the structure, rock mechanical behaviour and the regional environment for these salt formations. Using the example of a shallow salt formation, they are analysing its regional environment in detail and are translating it into a 3D model.

In order to infer the internal structure of the double and multiple salt bodies, researchers are using data from the regional geological survey agencies and private companies. They are evaluating seismic exploration and drilling data, drill cores and the information available from map series and structural descriptions about the shape and development of salt structures. Based on this data, for the first time 3D models of individual structures will then be developed which will significantly increase the informative quality when evaluating the potential of multiple salt structures for storing renewable energy.

Despite the partly theoretical nature of the project, the chances for the project's implementation will not be diminished. There is no criterion for aborting the project. However, the achievable level of detail and realism, and thus the achievable accuracy in estimating the potential, depend on the quality of the basic data.

Project structure

As part of the project "Salt information system: planning basics, selection criteria and estimation of the potential for constructing salt caverns for storing renewable energy (hydrogen and air) – double salt bodies and shallow salt strata", the following topics will be dealt with:

Sub-project: Salt and structural geology (BGR)

WP 1: Shallow salt formations: Compilation and evaluation of geological data concerning shallow salt strata in Germany

WP 2: Shallow salt formations: Investigation of the storage conditions and characteristics of shallow salt formations; material-structural characterisation of salt formations

WP 3: Double and multiple salt bodies: Material-structural characterisation of salt formations; investigation of the internal structure and geological 3D models

Sub-project: Rock-mechanical requirements (IGtH/IUB)

WP 4: Shallow salt formations: Rock-mechanical requirements

WP 5: Double and multiple salt bodies: Rock-mechanical requirements

Sub-Project: Evaluation criteria and estimation of potential (KBB UT)

WP 6: Shallow salt formations: Criteria and planning principles for estimating the potential

WP 7: Shallow salt formations: Determining the storage potential

WP 8: Double and multiple salt bodies: Precise determination of the storage potential

Supported by: The Federal Government on the basis of a decision by the German Bundestag

Dates

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Infobox

Previous project

Information on the previous project can be found here.

Research funding

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