Upper Cretaceous–Danian chalk forms a range of complex diagenetic fabrics despite its commonly white and monotonous appearance in outcrop and core. This reflects the interaction between processes linked to composition, depositional facies, texture, sedimentation rates, bioturbation, mineralogy, burial and hydrocarbon charging history. Such fabrics have a substantial impact on reservoir quality, either maintaining or reducing porosity and permeability through diagenetic processes. The potential influence of silica, a key component in the chalk, on the diagenesis of the chalk matrix is still poorly understood and forms the topic of this study. A new approach integrating qualitative methods such as micro-computed tomography (μCT) and scanning electron microscopy (SEM) with methods like X-ray diffraction (XRD) analyses supplemented with contact angle measurements, is used to characterise chalk fabrics and investigate the impact of silica on wettability. The study is focusing on a relatively narrow stratigraphic interval, the Danian Ekofisk Formation reservoir in a single well from the Danish North Sea, the Sif-1X, to avoid uncertainties associated with regional variations in burial history, depositional environment, age and hydrocarbon charging history. The Ekofisk chalk in Sif-1X is characterised by two fabrics distinguished based on variations in calcite microcrystal texture, silica content, silicification types and clay content. They are interpreted to represent two different diagenetic pathways. The Ekofisk Fabric I is silica-poor and has the highest porosity and permeability. It is interpreted to reflect a dual-step diagenetic pathway of initial mechanical compaction, during early burial, followed by later, limited pore-filling cementation associated with pressure dissolution. The Ekofisk Fabric II occurs in intervals with more than 5% silica and displays overall inferior reservoir quality compared to the Ekofisk Fabric I. It is interpreted to be the result of local calcite dissolution and cementation related to release of silica-rich fluids during the stabilisation of metastable opal phases into α-quartz, and the progressive stabilisation of silica ultimately led to pervasive silicification of the fine-grained chalk and cementation of the calcite microcrystals. We demonstrate, based on multi-scale data integration, that silica not only affects the chalk and other fine-grained carbonates through pervasive silicification but potentially also has a significant control on the carbonate system, leading to changes in the calcite microcrystal textures. This adds to the complexity of the porosity and permeability evolution in silica-rich chalk and other mixed silica-carbonate systems.

尽管在露头和岩心中通常为白色和单调的外观，但上白垩统-达年白垩形成了一系列复杂的成岩构造。这反映了与组成，沉积相，质地，沉积速率，生物扰动，矿物学，埋藏和碳氢化合物充注历史有关的过程之间的相互作用。这样的织物通过成岩过程维持或降低孔隙度和渗透率，对储层质量有实质性影响。二氧化硅（白垩中的关键成分）对白垩基质的成岩作用的潜在影响仍然知之甚少，因此成为本研究的主题。结合定性方法（如微计算机断层扫描（μCT）和扫描电子显微镜（SEM））和X射线衍射（XRD）分析方法以及接触角测量方法，该新方法用于表征粉笔织物并研究白垩织物的影响。二氧化硅对润湿性的影响。该研究的重点是相对狭窄的地层间隔，即丹麦北海Sif-1X单井中的Danian Ekofisk储层，以避免与埋藏历史，沉积环境，年龄和碳氢化合物充填历史的区域变化相关的不确定性。 。Sif-1X中的Ekofisk粉笔的特征在于两种织物，它们分别基于方解石微晶织构，二氧化硅含量，硅化类型和粘土含量的变化而有所区别。它们被解释为代表两种不同的成岩途径。Ekofisk织物I贫硅，具有最高的孔隙率和渗透性。它被解释为反映了在早期埋藏过程中初始机械压实的双步骤成岩途径，随后是与压力溶解相关的后期有限的充填胶结作用。与Ekofisk Fabric I相比，Ekofisk Fabric II的间隔时间超过5％的二氧化硅，并且储层总体质量较差。这被认为是局部方解石溶解和固结的结果，与稳定过程中富含二氧化硅的流体的释放有关将亚稳蛋白石相转变为α-石英，而二氧化硅的逐步稳定最终导致了细粒白垩的普遍硅化和方解石微晶的胶结。基于多尺度数据集成，我们证明了二氧化硅不仅会通过普遍的硅化作用影响白垩和其他细粒碳酸盐，而且还可能会对碳酸盐体系产生重大控制，从而导致方解石微晶织构的变化。这增加了富含二氧化硅的白垩和其他混合的二氧化硅-碳酸盐体系中孔隙度和渗透率演变的复杂性。