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 Saxon 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.本概览地图展示了下萨克森盆地内比克贝格组（Bückeberg Group，Unterkraide，Ober-Berriasium）的分布范围，重点呈现了勘探目标砂岩及其物性特征。区域连续分布、厚度不小于5米的砂岩被归类为勘探相关砂岩。据此可推定这类地层具备作为地热可利用含水层的潜力，但该潜力需逐点位实地验证。本次制图中对编录地层所采用的"上""中""下"比克贝格组划分，属于非正式且相对的划分方式。 贝里亚斯阶（Berriasium）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）底部砂岩、巴辛豪森亚组（Barsinghausen subformation）砂岩以及代斯特组与富瑟组砂岩），偶见于奥斯纳布吕克（Osnabrück）地区（厄瑟德组（Oesede formation）砂岩）。此类砂岩通常赋存于黏土岩、粉砂岩与局部低质煤系的互层序列中。伊斯特贝格组（Isterberg formation）的黏土岩、粉砂岩、胶凝黏土岩、粉砂质灰岩以及局部薄层砂岩均已纳入综合编录范畴。制图过程中未考虑岩性的孔隙度、渗透率与导水系数，但在有可用数据时，会将其作为钻井相关参数予以标注。 本次制图单元的划分依据现有文献，以及德国下萨克森州矿业、能源与地质国家局（State Office for Mining, Energy and Geology，LBEG）馆藏的精选地学数据的评估与解译成果。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），该图集描绘了下萨克森盆地内下白垩统下部白垩岩的分布与岩性特征；此外还涵盖《德国西北部及德国北海海域大地构造图集》（Baldschuhn等，2001）与《下萨克森州1:5万地质图》（GK50）。Schott（1969）所绘制的"韦尔登群（Wealden）"分布边界（其大致对应比克贝格组），以及经构造反转作用侵蚀的区域均已纳入本次制图范围，并依据最新资料对部分区域进行了调整。本次制图展示的盐构造数据源自《德国北部1:50万盐构造图》（BGR，2008）。 依据LBEG的油气钻井数据库提供的信息，本次制图在比克贝格组的分布边界范围内筛选了具备有效编录数据的深钻井。本次制图单元的划分依据地层编录目录、地球物理测井数据以及钻井岩芯资料中的地层与岩性信息的评估与解译结果。两个制图单元之间的大型过渡带或渐变区以倾斜面表示。两套砂岩单元的叠置关系以垂直刮擦面表示。分布地图中，无深钻井数据或深钻井数据不足的区域被标注为"岩性认知不足或未编录区域"。盐丘侧翼与盐丘边界区域未进行进一步勘探，因此未考虑这些区域内厚度、岩相及岩石特征的局部变化。 本次选用的钻井被列为参考点位。深钻井的评估数据以数值分级形式展示。钻井深度与总厚度依据地层编录目录的评估结果确定。砂岩厚度数据源自测井分析与地层编录目录，指的是所评估钻井中厚度最大的砂岩段。砂岩的孔隙度与渗透率数据基于油气数据库中的钻井岩芯资料计算得到，若有测井数据则一并纳入计算。钻井岩芯测得的孔隙度数据为有效孔隙度（%），而测井所得的孔隙度数据为总孔隙度（%）。渗透率分级以毫达西（mD）与平方米（m²）为单位标注。地图中采用不同符号区分各类数据源。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，通过不同符号进行展示。