New Thermal Property Data Base of the Swiss Molasse Basin Sediments: Integrating Wireline Logs, Cores and Cuttings

Authors: Werner Leu, Ladislaus Rybach, Ulrich Scharli , Thomas Megel & Beat Keller
Keywords: Swiss Molasse Basin, thermal conductivity, heat capacity, shallow geothermal resources
Conference: European Geothermal Conference Session: Shallow Resources and Sustainability
Year: 1999 Language: English
Geo Location:
Abstract: To improve the development of shallow geothermal resources and underground heat storage facilities, a new data base of thermal conductivity (A), heat capacity (cp) and bulk rock density (p) was compiled for Tertiary sediments of the Swiss Molasse Basin (uppermost 500 m). Laboratory measurements from boreholes and outcrops were used to calibrate empirical relationships between geophysical wireline logs and geothermal parameters. For five different lithologies in three Molasse groups (Lower Freshwater Molasse USM, Upper Marine Molasse OMM and Upper Freshwater Molasse OSM) linear relationships with specific coefficients could be derived. Thermal conductivity can be calculated as a direct function of sonic velocity, whereas heat capacity depends on bulk density. Application of these new empirical laws at locations with only wireline logs, allowed to increase the previously available data density by a factor three. The software tool SwEWS facilitates the evaluation of the data base for any location in the Swiss Molasse Basin. Based on the information of an input spread sheet (Swiss coordinates, elevation, bed thickness, lithology) the program extracts the appropriate thermal properties with error estimates. The thermal conductivity and the specific heat capacity for each bed, as well as the depth dependent temperature, can be exported or displayed graphically. The statistical evaluation of all data illustrates the regional variation of the petrophysical and geothermal parameters. For most data groups bulk rock density and thermal conductivity increase, whereas heat capacity decreases in the direction towards the Alpine front. Thermal conductivity shows a distinct increase with depth. This new data base allows more precise heat extractiodstorage model simulations for planned geothermal facilities.
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