Distribution Patterns of the Main Structural-Group Parameters of Crude Oils from the Dnieper–Donets Basin Based on 1H NMR Data

Abstract

This study employs ¹H NMR spectroscopy to investigate a representative set of crude oils and gas condensates from the Dnieper–Donets oil-and-gas basin (OGB). For the first time, at least the structural-group composition of crude oils is comprehensively characterized over the entire basin, with specific focus on the distribution of hydrogen across various aromatic structures, including monoaromatic rings, isolated double bonds, and aliphatic groups. Distribution density plots were generated for all measured compositional parameters. The results reveal polymodal distributions with significant deviations from normality, underscoring the need for nonparametric statistical methods—an approach rarely applied in petroleum geochemistry. Accordingly, medians and their confidence intervals are recommended over means and standard deviations. A comparative analysis with previously explored major basins shows that the Dnieper–Donets oils are compositionally closest to those of the West Siberian OGB. However, they exhibit strong statistical similarity to the Timan–Pechora OGB in terms of hydrogen content in aromatic fragments. In contrast, marked differences are observed when compared to oils from East Siberia and North Caucasus (on one side) and from the Volga–Urals region (on the other). Notably, the Dnieper–Donets OGB contains oil deposits rich in radiogenic unsaturated hydrocarbons, with the highest detected concentration corresponding to a radiation dose of approximately 6 MGy. Furthermore, certain deposits within the basin display an anomalous composition characterized by exceptionally high aromatic content, with ¹H NMR spectra revealing elevated concentrations of components that are typically found only in trace amounts in crude oils.