Abstract The effect of silica on reservoir quality in chalk is subject to continuing debate. In particular, the stratigraphic variations in silica content within the chalk matrix have not been addressed sufficiently. In this study, a new approach is applied to constrain silica variability in reservoir chalk utilizing hand-held X-ray fluorescence (HH-XRF) on samples from four Maastrichtian–Danian cores from hydrocarbon-producing fields in the southern Danish Central Graben. The results indicate a significant lateral and stratigraphic variability in silica concentrations across the study area; data display a common stratigraphic signature in all wells, however, with maximum silica concentrations and minimum porosities occurring in the lower part of the Danian Ekofisk Formation. Correlation between HH-XRF quantified silica concentrations and biostratigraphic data indicates the synchronous onset of an at least semi-regional silica event during the mid-Danian, nannofossil zones NNTp2F–G to NNTp4A–D, whereas the upper boundary of the peak silica unit is poorly constrained. Generally, stratigraphic trends in silica concentrations appear to be negatively correlated with porosity trends. However, comparison between the HH-XRF quantified silica content and reservoir data (porosity, permeability, estimated pore radius and calculated specific surface area) shows poor correlation indicating that silica content within the Ekofisk reservoir is not the only factor controlling the reservoir quality. Unknown complex diagenetic interactions between calcite, silica and clay probably influence the reservoir properties by promoting calcite cementation in stratigraphically controlled zones, making the Ekofisk reservoir much less predictable than the underlying Maastrichtian Tor Formation.

中文翻译：

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丹麦中央地堑南部大年白垩岩地层控制硅化作用及其对储层性质的影响

摘要 二氧化硅对白垩岩储层质量的影响一直存在争议。特别是，白垩基质中二氧化硅含量的地层变化尚未得到充分解决。在这项研究中，采用一种新方法，利用手持 X 射线荧光 (HH-XRF) 对来自丹麦南部中央地堑产烃油田的四个 Maastrichtian-Danian 岩心的样品，限制储层白垩中二氧化硅的变异性。结果表明整个研究区域的二氧化硅浓度存在显着的横向和地层变异；然而，数据显示所有井都有一个共同的地层特征，最大的二氧化硅浓度和最小的孔隙率出现在 Danian Ekofisk 地层的下部。HH-XRF 量化二氧化硅浓度与生物地层数据之间的相关性表明，在大年中期，纳米化石区 NNTp2F-G 至 NNTp4A-D 期间至少半区域性二氧化硅事件同步发生，而峰值二氧化硅单元的上限为约束不力。一般来说，二氧化硅浓度的地层趋势似乎与孔隙度趋势呈负相关。然而，HH-XRF 量化的二氧化硅含量与储层数据（孔隙度、渗透率、估计的孔隙半径和计算的比表面积）之间的比较显示相关性较差，表明 Ekofisk 储层内的二氧化硅含量不是控制储层质量的唯一因素。方解石之间未知的复杂成岩相互作用，