Application of Chemical Elements for Stratigraphic Division of Deepwater Turbidite Sandstone Oilfield in the North Sea, UK

Generally deep-water turbidite sandstone shows the characteristics of less well, fast lateral change and irregular spatial distribution, and its stratigraphic division and comparison often rely on high-resolution seismic data. When seismic cannot meet the accuracy requirements, conventional stratigraphic correlation methods often have poor results. This article takes the BD oilfield in the North Sea of the UK as an example, and through core and rock fragment mineral analysis, geochemical elements that are sensitive to sedimentary control factors such as ancient sources, ancient climate, and ancient sedimentary environment are selected. Following the idea of "hierarchical progression", a macroscopic stratigraphic framework is first established based on the deep-water turbidite mudstone background, then fine comparison of internal sand bodies is done following the above macroscopic framework. Finally, an inorganic geochemical sedimentary sequence is established in the target area. And the deep-water turbidite sandstone formation is finely divided. Research shows that based on the analysis of nearly 50 identified mineral elements in the target area, three principal components (PC1, PC2, PC3) are selected through principal component analysis; PC1 is a symbiotic mineral combination that matches mudstone; PC2 is a symbiotic mineral combination that matches sandstone; PC3 indicates the degree of late diagenesis; Based on the analysis of coexisting mineral elements in sandstone and mudstone, the key element ratios of distinguishable coexisting minerals in mudstone and sandstone (6 types identified in sandstone and 5 types identified in mudstone) are selected to define the identification of mudstone and sandstone units in different stages of the target layer, thereby establishing a chemical stratigraphy stratigraphic identification and division standard applicable to the area. Based on the geochemical stratigraphic characteristics of coexisting mineral elements, the target layers in this area are divided into 6 sets of mudstone layers (CP0 to CP5) and 7 sets of sandstone layers (SP0 to SP6). This type of method can provide a basis for fine comparison of small layers similar to oil fields.