gebo-G2

In the frame of this project electric and electromagnetic prospection methods are investigated concerning their ability to image geological fault zones in depths of interest for geothermal applications. For large-scale geologic structures with depths up to a few km, e.g. fault systems, resistivity can become a valuable key parameter, because low resistivity is an indication for the presence of conductive minerals and/or brines within fractures and hydrothermal fluids

Numerical and practical investigations are carried out with emphasis on the comparison of the possibilities and limitations of the methods used. Electric and electromagnetic methods are jointly operated at selected fault systems and interpreted alongside with seismic data. Initially, well-known shallow fault zones are considered. At a later stage of the project the exploration will be extended to deeper structures. The evaluation of a suitable field survey design and interpretation for a joint operation of these methods is envisaged.

Two field surveys were already carried out at the project area Leinetal Graben. As a result it was possible to image a typical fault zone in Lower Saxony using DC resistivity and Transient Electromagnetic measurements, combined with structural information from seismic surveys.

In the ongoing project the application of very large-scale DC and of the Magnetotelluric method is envisaged for obtaining greater investigation depths. A concept for a suitable field survey design will be evaluated, supported by modelling studies especially adapted to the specific geological features in Northern Germany. Overall aim is the application of a joint strategy for the investigation of fault zones by electric/electromagnetic measurements.

The principle survey design of the two methods used and the assumed geological conditions are shown as well as a preliminary result from the field surveys. The DC resistivity surveys were performed by help of a high current source which delivers up to 40 A, the used terraTEM instrument was complemented by a strong transmitter, delivering up to 50 A.

 

First result of the large-scale DC resistivity (section) and the large scale TEM survey (layered models). The investigation depth reaches about 600 – 800 m. The assumed fault zone can be mapped well, additional seismic structural information (black lines) was added to the interpretation. The 2d interpretation of the DC resistivity shows the fault structure, while layers with low resistivity determined by the TEM fit to the seismic structure.

In the ongoing project the application of very large-scale DC and of the Magnetotelluric method is envisaged for obtaining greater investigation depths. A concept for a suitable field survey design will be evaluated, supported by modelling studies especially adapted to the specific geological features in Northern Germany. Overall aim is the application of a joint strategy for the investigation of fault zones by electric/electromagnetic measurements.

Status 2011

 

The results of project G2 were published after the termination of the gebo project:

Schaumann, G., Grinat, M. & Günther, T. (2015): Detection of Fault Zones Using Electric and Electromagnetic Methods, in: "Final Report of Geothermal Energy and High-Performance Drilling Collaborative Research Program (gebo) Niedersachsen". Schriftenreihe des Energie-Forschungszentrums Niedersachsen, Band 30, ISBN 978-3-7369-9080-7, Cuvillier Verlag Göttingen.

Team

Project lead

Michael Grinat
+49 511 643-3493

Dr. Thomas Günther
+49 511 643-3494

Funding

Products & Publications