Database of petrophysical properties of the Mid-German Crystalline Rise

Abstract

Abstract. Petrophysical properties are a key element for reservoir characterization but also for interpreting the results of various geophysical exploration methods or geophysical well logs. Furthermore, petrophysical properties are commonly used to populate numerical models and are often critically governing the model results. Despite the common need for detailed petrophysical properties, data are still very scarce and often not available for the area of interest. Furthermore, both the online research for published property measurements or compilations, as well as dedicated measurement campaigns of the selected properties, which require comprehensive laboratory equipment, can be very time-consuming and costly. To date, most published research results are often focused on a limited selection of parameters only, and hence researching various petrophysical properties, needed to account for the thermal–hydraulic–mechanical behaviour of selected rock types or reservoir settings, can be very laborious. Since for deep geothermal energy in central Europe, the majority of the geothermal potential or resource is assigned to the crystalline basement, a comprehensive database of petrophysical properties comprising rock densities, porosity, rock matrix permeability, thermal properties (thermal conductivity and diffusivity, specific heat capacity) as well as rock mechanical properties as compressional and shear wave velocities, unconfined compressive strength, Young's modulus, Poisson's ratio, tensile strength and triaxial shear strength was compiled from measurements conducted at the HydroThermikum lab facilities of the Technical University of Darmstadt. Analysed samples were mostly derived from abandoned or active quarries and natural or artificial outcrops such as road cuts, riverbanks or steep hillslopes. Furthermore, samples of the cored deep wells Worms 3 (samples from 2175–2195 m), Stockstadt 33R (samples from 2245–2267 m), Weiterstadt 1 (samples from 2502–2504 m), Tiefbohrung Groß-Umstadt/Heubach, B/89–B02 and the cored shallow wells (Forschungsbohrung Messel GA 1 and 2) as well as GWM17 Zwingenberg, GWM1A Zwingenberg, Langenthal BK2/05, EWS267/1 Heubach, and archive samples of the Institut für Steinkonservierung e.V. in Mainz originating from a comprehensive large-scale sampling campaign in 2007 were investigated. The database (Weinert et al., 2020b; https://doi.org/10.25534/tudatalib-278) aims to provide easily accessible petrophysical properties of the Mid-German Crystalline Rise, measured on 224 locations in Bavaria, Hessen, Rhineland-Palatinate and Thuringia and comprising 26 951 single data points. Each data point is addressed with the respective metadata such as the sample identifier, sampling location, petrography and, if applicable, stratigraphy and sampling depth (in the case of well samples).

Comment on se-2021-118

“…Base measurements were taken three times per day at a fixed station to record the instrument drift. A complete Bouguer anomaly was calculated for all gravity measurements by applying the standard correction density of 2.67 kg m -³, which corresponds approximately to the mean rock density of the Tromm Granite (Weinert et al 2021), as also confirmed by the Nettleton method. Particular focus was on the topographic correction, which along some profiles reaches up to 2 mGal due to the steep terrain.…”

“…The continuous model was converted into a discrete cuboid voxel model with a cell size of 50 x 50 x 50 m. Further decreasing the cell size potentially resolves more details but exponentially increases the computational time of the inversion. As starting value for the rock density, a mean density of the Tromm Granite of 2.67 ± 0.05 g m -³ was defined (Weinert et al, 2021).…”

“…In all areas with greater distance to deep boreholes with image-log data, the fracture network properties are therefore poorly constrained. To gain new insights and especially a better spatial and multiscalar understanding of the fracture network characteristics, the exposed crystalline rocks at the graben shoulders can be used as an outcrop analogue for the URG basement (Dezayes et al, 2021;Weinert et al, 2021). The presented study focuses on the Tromm Granite in the southern Odenwald (Fig.…”

Rock alteration at the post-Variscan nonconformity: implications for Carboniferous–Permian surface weathering versus burial diagenesis and paleoclimate evaluation

“…This hints at a chemical overprint of the gabbroic diorite by the overlying basaltic andesite, whereas the Ca in the lower part appears to be primary. The spike in τ Ca at a depth of 23.5 m can also be explained by porosity data (Weinert et al, 2021), which can be considered as a measure of fracture density and grain disaggregation in igneous rocks. The porosity decreases sharply from 24 % at a depth of 21.5 m to 3 % at 23.6 m (Fig.…”

“…360 and 320 Ma during the Carboniferous (Powell and Conaghan, 1973;Schulmann et al, 2014). Due to a southward-directed subduction of the oceanic lithosphere below the Armorica microplate, the socalled Mid-German Crystalline Zone (MGCZ) was formed as a magmatic arc at the northern margin of Armorica during the Early Carboniferous; as a highland, this region continuously weathered and eroded until thermal subsidence began to dominate in central Europe (von Seckendorff et al, 2004a;Willner et al, 1991;Zeh and Brätz, 2004;Zeh and Gerdes, 2010). As a consequence, the post-Variscan nonconformity was formed, which represents a diachronous time gap of multiple tens to hundreds of millions years in central Europe (Henk, 1995;Kroner et al, 2007;von Seckendorff et al, 2004b;Zeh and Brätz, 2004).…”