Deep geothermal resources of the North German Basin: The hydrothermal reservoirs of the Stuttgart Formation (Schilfsandstein, Upper Triassic)
The enormous geothermal resources of the North German Basin are bound to Palaeozoic petrothermal and Mesozoic hydrothermal reservoirs. Based on previous exploration campaigns, six Mesozoic reservoir complexes were identified among which the hydrothermal reservoirs of the Stuttgart Formation were underexplored so far. To evaluate the potential of these reservoirs, an interdisciplinary exploration strategy was applied to a large database of cores, wireline logs and seismic data. Repeated transgressions from Tethyan waters resulted in formation of inland seas covering large parts of the basin. Accordingly, the deposition of the Stuttgart Formation was primarily controlled by 3 rd - and 4 th -order T-R sequences; in particular the basinwards-directed progradation of the fluvio-deltaic Lower and Upper Schilfsandstein members are related to lowstands. Within both members, fine- to medium-grained sandstones of channel fills and levee/crevasse splay complexes form compound reservoirs representing the main target of geothermal exploration. For the Lower Schilfsandstein, this channel belt reservoir type is characterised by a median thickness of 23 m, median porosity of 22.7 % and median permeability of 443 mD. For the Upper Schilfsandstein, the channel belt reservoir type is characterised by a median thickness of 17 m, median porosity of 24 % and median permeability of 546 mD. The quality of these reservoirs is limited by the generally low compositional maturity of sandstones being lithic arkoses and feldspatic litharenites, the partly high content of detrital matrix within pores and substantial diagenetic cementation. The resulting high lateral variability of reservoir qualities contributes to considerable exploration risks. Despite this, reservoirs of high quality could be proven for individual localities where they may be considered an alternative option if the development of Upper Keuper or Middle Jurassic hydrothermal reservoirs fails.
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Document Type: Research Article
Publication date: September 1, 2018
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- Zeitschrift der Deutschen Gesellschaft für Geowissenschaften (ZDGG) is an international peer reviewed journal that accepts papers on research and applied topics in the Earth Sciences. It is published online and in print. One volume, consisting of four issues is published annually. The journal is continously published by the German Geological Society since its foundation in 1848. It was relaunched in 2005.
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