Exploration-relevant sandstones of the Bückeberg Group in Lower Saxony 1: 500 000 — Porosity from core data

The overview map shows the spread of the Bückeberg Group (Unterkraide, Ober-Berriasium) in the Lower Saxony Basin and presents in particular exploration-relevant sandstones and their properties. Regionally contiguous sandstones with a thickness of at least five metres are referred to as exploration relevant. For these units, a potential as geothermally usable aquifers can be presumed, which, however, must be demonstrated on a site-by-case basis. The subdivision used here into the “upper”, “medium” and “lower” Bückeberg group for the mapped units is to be considered informal and relative. Exploration-relevant sandstones of the Berriasium are mainly found in the eastern part of the Lower Saxony Basin (head sandstone of the Fuhse formation, sandstones of the Barsinghausen subformation and sandstones of the Deister and Fuhse formation) and occasionally in the Osnabrück area (sandstones of the Oesede formation). The sandstones are usually embedded in an alternating sequence of claystone, siltstone and locally low-power coal deposits. Clay stones, siltstones, clay gelstones, shilt limestones and locally low-powered sandstones of the Isterberg formation are summarised. Porosity, permeability and transmissibility of lithologies have not been taken into account during mapping, but are indicated as drilling-related parameters where available. The demarcation of the mapping units is based on existing literature and the evaluation and interpretation of selected geoscientific data available at the State Office for Mining, Energy and Geology (LBEG). The basis is the Paleogeographic Atlas of the Lower Cretaceous of Northwest Germany (Schott; 1969), in which the distribution and lithology of the lower chalks in the Lower Saxony Basin are depicted, as well as the Geotectonic Atlas of Northwest Germany and the German North Sea sector (Baldschuhn et al. 2001) and the Geological Map of Lower Saxony 1: 50 000 (GK50). The distribution limit of the “Wealden” mapped by Schott (1969) (equivalent largely to the Bückeberg group) as well as the areas eroded by the pelvic inversion were incorporated into the present map and in some cases modified according to more recent information. The salt structures shown are from the map of the salt structures of northern Germany 1: 500 000 (BGR 2008). Deep drilling with appropriate data for mapping was selected within the Bückeberg Group’s diffusion boundary based on the information provided by the hydrocarbon drilling database of the LBEG. The demarcation of the mapped units is based on the assessment and interpretation of stratigraphic and lithological information from stratigraphic and lithological information from layer directories, geophysical well measurements and drill core material. Large-scale gearing or transition areas between two carting units are represented as slanted surfaces. The superposition of two sandstone units is depicted as a vertically scraped surface. Areas where there is no or insufficient information from deep drilling are identified in the distribution map as “areas with insufficient knowledge of lithology or not mapped”. The areas of the saltstock flanks and saltstock edges have not been investigated further. Local changes in thickness, lithofazies and rock characteristics in these areas are therefore not taken into account. The holes used are listed as reference points. The evaluated data from the deep boreholes are displayed as value classes. The depth and overall power is based on the evaluation of the strata registers. Information on the thickness of the sandstones comes from the analysis of borehole measurements as well as from the layer registers and refers to the most powerful sandstone layer of an evaluated hole. Porosity and permeability of the sandstones were calculated from the information from the hydrocarbon database from drill core data and, if available, from well measurements. The data of porosities from drill core data are to be understood as effective porosities (%) and from well measurements as total porosity (%). The permeability classes are given in Millidarcy (mD) and square meters (m²). In the maps, the different data bases are marked by symbols. The transmissibility of the sandstones results from their thickness and permeability and is shown in different symbols in the units Darcymeter (Dm) and cubic meters (m³) according to the calculation basis.