Application of chemo-stratigraphic division of deepwater turbidite sandstone in oilfield in the North Sea, UK

Generally, deep-water turbidite sandstone oilfields are characterized by large well spacing, fast lateral reservoir variation, and irregular spatial distribution. Small-scale stratigraphic division and correlation often rely on high-resolution seismic data. When seismic data cannot meet the accuracy requirements, conventional stratigraphic correlation methods often prove ineffetive. Taking the BD oilfield in the North Sea of the UK as an example, core and rock fragment mineral assemlage were analized and geochemical elements indicative to ancient sources, ancient climate, and ancient sedimentary environment were screened. Following the idea of “Hierarchical Progression”, a macroscopic stratigraphic framework was established at first based on the deep-water turbidite mudstone background, then the internal sand bodies were finelly correlated within the macroscopic framework, from which an inorganic geochemical sedimentary sequence was established in the target area. Finanlly, the deep-water turbidite sandstone formation of the oilfield was finely divided in chemo-stratigraphy. Among nearly 50 mineral elements identified in the target area, three principal components (PC1, PC2, PC3) were selected through principal component analysis. PC1 reflects symbiotic mineral combination that matches mudstone, PC2 is a symbiotic mineral combination that matches sandstone, and PC3 indicates the degree of late diagenesis. Based on the analysis on the coexisting mineral elements in sandstone and mudstone, the key chemical element ratios of coexisting minerals (6 for sandstone and 5 for mudstone) were selected to distinguish between mudstone and sandstone units, thereby establishing a chemo-stratigraphy scheme as the identification and division standards applicable to the area, with which 6 sets of mudstone layers (CP0 to CP5) and 7 sets of sandstone layers (SP0 to SP6) in the target layers were recognized. The method provided a tool for fine stratigraphic correlation of small layers similar to the similar cases of oil fields.