Preprints
https://doi.org/10.5194/egusphere-2024-257
https://doi.org/10.5194/egusphere-2024-257
26 Feb 2024
 | 26 Feb 2024
Status: this preprint is open for discussion.

Combining crosshole and reflection borehole-GPR for imaging controlled freezing in shallow aquifers

Peter Jung, Götz Hornbruch, Andreas Dahmke, Peter Dietrich, and Ulrike Werban

Abstract. During test operation of a geological latent heat storage system as a potential option in the context of heat supply for heating and cooling demands a part of a shallow quaternary glacial aquifer at the “TestUM” test site is frozen. To evaluate the current thermal state in the subsurface the dimension of the frozen volume has to be known. With the target being too deep for high resolution imaging from the surface, the use of borehole Ground-Penetrating-Radar (GPR) is assessed. For imaging and monitoring of a vertical freeze-thaw boundary, crosshole zero-offset and reflection measurements are applied. The freezing can be imaged in ZOP, but determination of ice body size is ambiguous, because of lacking velocity information in the frozen sediment. Reflection measurements are able to image the position of the freezing boundary with an accuracy determined through repeated measurements of ±0.1 m, relying on the velocity information from ZOP. We found, that the complementary use of ZOP and reflection measurements make for a fast and simple method, to image freezing in geological latent heat storage systems. Problematic is the presence of superimposed reflections from other observation wells and low signal-to-noise ratio. The use in multiple observation wells allows for an estimation of ice body size. A velocity model derived from zero-offset profiles (ZOP) enabled to extrapolate geological information from direct-push based logging and sediment cores to a 3D-subsurface model.

Peter Jung, Götz Hornbruch, Andreas Dahmke, Peter Dietrich, and Ulrike Werban

Status: open (until 22 Apr 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on egusphere-2024-257', Giacomo Medici, 29 Feb 2024 reply
  • RC1: 'Comment on egusphere-2024-257', Anonymous Referee #1, 11 Mar 2024 reply
Peter Jung, Götz Hornbruch, Andreas Dahmke, Peter Dietrich, and Ulrike Werban
Peter Jung, Götz Hornbruch, Andreas Dahmke, Peter Dietrich, and Ulrike Werban

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Short summary
We demonstrate the feasibility of imaging vertical freezing boundaries using borehole-GPR in an experimental geological latent heat storage, where a part of a shallow quaternary aquifer is frozen. To get insight on the current thermal state in the subsurface the dimension of the frozen volume is assessed. We show, that a combination of crosshole and reflection measurements enables to image the ice body with high accuracy in the, for GPR, challenging environment of saturated sediments.