Pilot area activities – #2 Geological and geophysical surveys in Linköping, Sweden

Mikael Erlstroem, 20 November 2019

Field measurements for a High Temperature Energy Storage site (H-BTES)

Many feasibility studies, including investigations of the geological conditions, are presently performed for a large-scale energy storage in Linköping. The planned storage will consist of up to 1400 boreholes each around 300 m deep with an individual spacing of five meters that will enable to store 100 GMh heat in summer for heating in winter.

The investigations included drilling of three 240 – 300 m deep test boreholes. Thermal response tests and geophysical wire-line logging collect data inside these boreholes. Bedrock mapping and magnetic and electromagnetic (VLF) geophysical surveys were applied on the ground surface. Thermal conductivity scanning was performed on rock samples.

This multidisciplinary approach resulted in a detailed picture of the underground composition and the thermal properties of the rocks. Further studies aim towards a 3D bedrock and fracture model as well as an evaluation of the hydraulic conditions.

For more information, please contact:
Mikael Erlström, State geologist, Geological Survey of Sweden

 Left: Performed geophysical survey lines and location of rock samples. Right: Preliminary interpretation of main rock types and conductive fracture zones from the geophysical survey data. Inserted photo: Example of field measurements with a portable magnetometer.
Results from measurements of the thermal conductivity on rock samples from the pilot area. The granite has a significantly higher thermal conductivity (average 3.23 W/mK) in comparison to the basic rock types (average 2.56 W/mK).
Left: Composite logs from two of the test wells with different rock types (Blue curves – Distorp Åkern, Red curves – Distorp Hagen). Primarily there are more basic rocks in the Distorp Åkern well whereas gray and red fine-grained granite dominates the Distorp Hagen well. The natural gamma ray levels reflect this with higher values related to higher amount of feldspars in the granites. The high amount of feldspar is also responsible for a higher thermal conductivity seen in the Differential Thermal Response (DTRT curves). Right: Logging operation with an Acoustic Televiewer giving a picture of the fracture zones in the well.

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