A first and detailed study of the geochemistry and mineralogy characterizing the North Sea reservoir and non-reservoir chalk is provided in this work. The study is based on 185 cores from exploration and development wells in the North Sea. The cores related to reservoir development have different flooding status – unflooded or waterflooded at various temperatures – and are directly sampled from the Ekofisk field. Optical petrography shows a micritic carbonate matrix, with grains represented by various microfossils such as foraminifers and sponge spicules. Scanning electron microscopy (SEM) reveals post-depositional calcite precipitation and cementation. Dolomite is found only in the reservoir samples, but it is discussed as a diagenetic feature, unrelated to the hydrocarbon content or EOR exposure. The non-carbonate minerals observed with BSE-SEM and XRD include mostly quartz but also smectite, illite, kaolinite, mica, and pyrite. The abundance of clastic input varies, and there is a clear decrease in porosity stratigraphically downwards, with stronger cementation and higher compaction. δ¹³C reflects primary trends for Upper Cretaceous stages while δ¹⁸O in all samples is lower than the secular global isotopic values for this period. However, the δ¹⁸O values are not sufficiently low to imply a strong diagenetic overprint, but rather suggest the influence of a secondary fluid. This fluid cannot be a hydrocarbon-rich one, nor EOR fluids, as non-reservoir samples, as well as flooded and unflooded reservoir samples show very similar stable isotope values.

这项工作提供了对北海储层和非储层白垩特征地球化学和矿物学的首次详细研究。该研究基于北海勘探和开发井中的185个岩心。与油藏开发有关的岩心具有不同的淹没状态（在不同温度下未注水或注水），并直接从Ekofisk油田取样。光学岩相学显示出微碳酸盐碳酸盐基质，其晶粒由有孔虫和海绵针等各种微化石代表。扫描电子显微镜（SEM）显示沉积后方解石沉淀和胶结。白云岩仅在储层样品中发现，但被认为是成岩特征，与碳氢化合物含量或EOR暴露无关。用BSE-SEM和XRD观察到的非碳酸盐矿物主要包括石英，但也包括蒙脱石，伊利石，高岭石，云母和黄铁矿。碎屑输入量丰富，地层向下孔隙度明显降低，胶结作用更强，压实度更高。δ¹³ Ç反映初级趋势上白垩级而δ ¹⁸ o所有样品中是比此期间世俗全球同位素值低。然而，δ ^18个O值不是足够低，以暗示强成岩套印，而是提供一个二次流体的影响。该流体既不能是富含烃的流体，也不能是EOR流体，因为非储层样品以及注水和未注水储层样品都显示出非常相似的稳定同位素值。