Exploration-relevant sandstones of the Bückeberg Group in Lower Saxony 1: 500 000 — Porosity from Well Measurements (WMS Service)

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.本概略图展示了布克贝格群（Bückeberg Group，包含下克拉伊德阶、上贝里阿斯阶（Unterkraide, Ober-Berriasium））在下萨克森盆地（Lower Saxony Basin）的分布范围，重点呈现了与勘探相关的砂岩及其物性特征。 区域上连续分布、厚度不小于5米的砂岩被认定为勘探相关砂岩。此类地层单元具备作为地热可利用含水层（geothermally usable aquifers）的潜力，但该潜力需针对具体点位逐一验证。本次制图中将布克贝格群划分为“上部”“中部”与“下部”的分级方式，属于非正式相对划分。 贝里阿斯阶的勘探相关砂岩主要分布于下萨克森盆地东部（富瑟组（Fuhse formation）顶部砂岩、巴林豪森亚组（Barsinghausen subformation）砂岩以及戴瑟-富瑟组（Deister and Fuhse formation）砂岩），偶尔见于奥斯纳布吕克地区（厄塞德组（Oesede formation）砂岩）。此类砂岩通常赋存于黏土岩、粉砂岩（siltstone）与局部低阶煤沉积的互层序列中。伊斯特贝格组（Isterberg formation）的黏土岩、粉砂岩、黏土胶结岩、粉屑灰岩及局部低阶砂岩被一并归为该类。 制图过程中未纳入岩性的孔隙度、渗透率与导水系数数据，但在具备相关实测资料时，会将其作为钻井相关参数予以标注。本次制图单元的边界划分依据现有公开文献，以及德国采矿、能源与地质州立办公室（State Office for Mining, Energy and Geology，LBEG）所藏精选地球科学数据的评估与解译结果。 本制图的基础资料包括：《德国西北部下白垩统古地理图集》（Schott，1969），该图集展示了下萨克森盆地下部白垩系的分布范围与岩性特征；《德国西北部及德国北海区域构造图集》（Baldschuhn等，2001）；以及《下萨克森州地质图1:50000》（GK50）。Schott（1969）绘制的“韦尔登群（Wealden）”分布边界（大致对应布克贝格群），以及因盆地反转作用遭受剥蚀的区域，均被纳入本次制图，并依据最新资料对部分边界进行了修正。本次图件所展示的盐构造源自《德国北部盐构造图1:500000》（BGR，2008）。 依据LBEG油气钻井数据库提供的信息，在布克贝格群的分布边界内遴选了具备完整制图所需数据的深井。本次制图单元的边界划分基于对层位录井、地球物理测井（geophysical well measurements）及岩心资料（drill core material）中地层学与岩相学信息的评估与解译。两个制图单元间的大型渐变过渡带以斜向面表示。两套砂岩单元的叠置关系以垂直刮面形式呈现。 分布范围中缺乏深部钻井资料或资料不足的区域，在本分布图中标记为“岩性认识不足或未制图区域”。盐丘侧翼与盐丘边界区域未开展进一步调查，因此未考虑该区域内厚度、岩相及岩石物性的局部变化。 本次使用的钻井均被列为参考点位。深部钻井的评估数据以数值分级形式展示。地层厚度与总厚度基于层位录井的评估结果。砂岩厚度数据源自测井分析与层位录井，指的是评估钻井中厚度最大的砂岩地层。 砂岩的孔隙度与渗透率数据源自油气数据库中的岩心分析资料，若有测井数据则一并纳入。岩心分析得到的孔隙度为有效孔隙度（%），测井得到的孔隙度为总孔隙度（%）。渗透率分级以毫达西（mD）与平方米（m²）为单位标注。砂岩的导水系数由其厚度与渗透率计算得出，依据计算基准分别以达西米（Dm）与立方米（m³）为单位，通过不同符号在图中展示。