Diagenesis and Controls on Reservoir Quality of Lower Triassic Sandstones (Buntsandstein) from a Marginal Basin Facies

Abstract

Summary With regard to climate change and the search for potential lithologies for geothermal applications and simultaneous metal extraction, the red bed deposits of the Buntsandstein from the southern margin of the Central European Basin (SW Germany) have gained in importance in geoscientific research. Here we combine petrophysical (i.e., porosity and permeability) and petrographical (point counting) data of aeolian and fluvial sandstones from the Lower, Middle, and Upper Buntsandstein in order to better understand their diagenetic history and the distribution of reservoir quality over different scales. Permeabilities vary from 0.001 to 515 mD over six orders of magnitude and porosities range from 7.9 to 21.5%. Large grain sizes typical for aeolian deposits are the major control on reservoir quality, whereas authigenic phases such as illite and syntaxial quartz overgrowths exert a local influence on reservoir quality. Moreover, extensive illite coatings on detrital quartz grains efficiently prevented syntaxial quartz growth. The lack of illite grain coatings, enabled quartz to develop syntaxial overgrowths. The comparison with other studies shows that the Buntsandstein is a heterogeneous reservoir system over small and large scales and within the same stratigraphic levels.