Prediction of Thermal Properties for Mesozoic Rocks of Southern Germany

Abstract

In general, the variation for thermal rock properties is too large to constrain thermal characteristics at a specific site. To improve this situation, this project will provide statistically relevant data of thermal and hydraulic properties for the subsurface of Germany. In a first stage, a large number of mesozoic rock samples from the South-West German Molasse basin was studied: About 280 core samples were tested by thermal and petrophysical core scanning yielding high resolution information on thermal conductivity, density, porosity and sonic velocity of the rocks in dry and saturated condition. In addition, 100 core plugs were taken for measurements of specific heat capacity and hydraulic permeability and for XRD and XRF analyses. Thus, thermal properties could be related to the petrophysical characteristics and to the mineralogical and chemical rock composition. The geometric mixing law was confirmed as a fast and robust estimator for thermal conductivity, especially for limestones and dolomites regardless of their stratigraphic age and genetic origin. In a more sophisticated approach, the data were further used to compare and to calibrate theoretical models for thermal conductivity prediction. Rock type specific parameters were determined describing the relations between rock matrix, porosity, rock morphology, and the effective thermal conductivity. This grouping by rock type and rock generation allows an enhanced prediction of thermal properties of the mesozoic strata of German sedimentary basins.