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Terrestrial heat flow in basin modelling: New findings for the North German Basin

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Fuchs,  Sven
6.2 Geothermal Energy Systems, 6.0 Geotechnologies, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

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Förster,  A.
6.2 Geothermal Energy Systems, 6.0 Geotechnologies, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

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Zitation

Fuchs, S., Förster, A. (2018): Terrestrial heat flow in basin modelling: New findings for the North German Basin - Book of Abstracts, GeoBonn 2018 (Bonn, Germany 2018).


Zitierlink: https://gfzpublic.gfz-potsdam.de/pubman/item/item_3518901
Zusammenfassung
Knowledge of the subsurface temperature field is paramount in the exploration of resources, such as hydrocarbons and geothermal energy. The terrestrial heat flow representing the conductive thermal field is a crucial parameter in such a characterization. It is determined from measured borehole temperature (temperature gradient) and rock thermal conductivity (TC). In situations of no drill core availability, TC needs to be determined indirectly. We have developed a well-log based approach to arrive with TC predictions for clastic rocks, carbonates and evaporites. The prediction equation describe interrelations between standard well-log data (bulk density, natural gamma-ray, sonic interval transit time, hydrogen index, photoelectric factor, and petrophysical descriptors determined from these) and rock thermal properties as derived from a ‘synthetic data set’ of global nature. Thus TC predictions can be made of good quality requiring no knowledge of the rock mineral composition or details of lithotypes in borehole. The application of such a well-log based approach to data of the GeneSys borehole at Hannover resulted in a complete TC profile to 3800 m depth, which was validated by TC laboratory data. Using the TC profile and measured temperature log data, heat-flow density was calculated along an entire borehole section. With this approach a reduction of heat flow of up to 25 mW m² was observed in the upper kilometer of the borehole. The general alignment between interval temperature gradients and lithology (and hence TC) allows to exclude fluid-driven heat transport responsible for this reduction. Given this fact, the observation is as a clear evidence for the paleo-climate impact on the subsurface temperature by last glacial periods. The finding calls for critical evaluation of former heat-flow data in terms of depth realm of determination before they are used in basin modeling. The undisturbed surface heat flow at the Hannover site of about 85 mW m² is within the range of new values (68–91 mW m²) for the eastern part of the NGB, determined at depths not afflicted by paleoclimate. The new values, being much higher than those previously reported for the basin, will alter temperature predictions from basin modeling. Thus, a thorough underpinning of the data for the NGB by further studies is warranted.