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Discussion papers | Copyright
https://doi.org/10.5194/se-2018-83
© Author(s) 2018. This work is distributed under
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Research article 07 Sep 2018

Research article | 07 Sep 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Solid Earth (SE).

Seismic imaging of dyke swarms within the Sorgenfrei Tornquist Zone (Sweden) and implications for thermal energy storage

Alireza Malehmir1, Bo Bergman2,3, Benjamin Andersson4, Robert Sturk4, and Mattis Johansson2,3 Alireza Malehmir et al.
  • 1Dept. of Earth Sciences, Uppsala University, Sweden
  • 2Sweco Environment AB, Malmö, Sweden
  • 3WSP (presently), Malmö, Sweden
  • 4Skanska Sverige AB, Malmö, Sweden

Abstract. There is a large interest and demand for green-type energy storage in Sweden for both short- and long-terms (hours, days, weeks and seasons). While there are a number of approaches proposed (e.g., compressed air, geothermal and thermal), only a few have commercially been demonstrated through up-scaling projects. Among these, the thermal energy storage (TES) that stores energy (excess heat or cold) in fluids is particularly appealing. The excess energy then can be stored underground in excavated caverns and used for large district heating and cooling purposes. For an up-scaling underground thermal-energy-storage project within the Tornquist suture zone of Scania in southwest of Sweden three high-resolution, each approximately one kilometer long, 5m receiver and source spacing, seismic profiles were acquired. Geologically, the site sits within the southern margin of the Romeleåsen Fault Zone in the Sorgenfrei Tornquist Zone (STZ) where dolerite dyke swarms of Carboniferous-Permian age are observed striking in SE-NW direction for over 100s of kilometers both on land and in offshore seismic and magnetic data (from Scania to Midland Valley in the UK). These dykes, 5–20m thick, in the nearby quarries (within both Precambrian gneiss and quartzite) express themselves mostly sub-vertical. They can therefore act as a good water/fluid barrier, which can be an important geological factor for any thermal energy storage site. In the data acquisition, combined cabled- and wireless recorders were used to provide continuity on both sides of a major road running in the middle of the study area. Bedrock depressions are clearly depicted in the tomograms suggesting the possibility of weakness zones, highly fractured and/or weathered, in the bedrock and confirmed at several places by followed-up boreholes. Several steeply dipping (60–65°) reflections were imaged down to 400m depth and based on a series of arguments are judged to be from dolerite dykes. This includes their orientations, strong amplitudes, regular occurrences, and correlation with downhole logging data. In addition groundwater flow measurements within the unconsolidated sediments and in bedrock suggests steeply-dipping structures are the dominant factor in directing water towards SE-NW direction, which is consistent with the strike of the dyke swarm within the STZ. To provide further insight into the origin of the reflections even the historical crustal-scale offshore BABEL lines (A-AA-AB) were revisited. Clear multi-phase faults are observed as well as a Moho step across the Tornquist zone. Overall, we favour that the reflections are of dolerite origin and their dip component (i.e., not sub-vertical) may imply a Precambrian basement (and dykes) tilting, block rotation, towards NE as a result of the Romeleåsen reverse faulting. In terms of thermal storage, these dykes then may be encountered during the excavation of the site and can complicate underground water flow should they be used as a fluid barrier in case of a leakage.

Alireza Malehmir et al.
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Alireza Malehmir et al.
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Interest and demand for green-type energy usage and storage is growing worldwide. Among several, thermal energy storage that stores energy (excess heat or cold) in fluids is particularly appealing. For an up-scaling purpose, three seismic profiles were acquired within the Tornquist suture zone in southwest of Sweden and historical crustal-scale offshore BABEL lines revisited. A number of dykes have been imaged and implications for the storage and tectonic setting within the zone discussed.
Interest and demand for green-type energy usage and storage is growing worldwide. Among several,...
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