Correlation between main structural group parameters of crude oils of the Volga–Urals oil and gas basin by 1H and 13C NMR data

Abstract

In Volga−Urals crude oils, an increase in the aromatics content is characterized by a rapid increase in the relative amount of polysubstituted aromatic rings and a generally lower proportion of bi- and polycyclic aromatics, unlike the case of Western Siberia oils. The difference between the oil and gas basins is most probably due to the special features of the source organic matter of the oils. The regional features of the Volga−Urals oils are a relatively weak relationship between the concentrations of mono- and bi- + polycyclic aromatics and a relatively close relation of Σn-Alk to typically uninformative parameter Hβ, which indicate a high uniformity of the composition of saturated cyclic compounds and moieties of hybrid naphthenoaromatic components. In addition, the assumption that (H/C)ar/(H/C)al = const does not hold for Volga−Urals oils. However, the relationships between the main parameters describing total aromaticity (primarily, Car, Har) and n-alkyl structures (primarily, Σn-Alk) are identical for oils from both the basins. The total number of relationships that can be universal for oils from different oil-and-gas basins is fifteen. To estimate Car from 1H NMR data for Volga−Urals crude oils, a linear dependence on the two variables Har and Hα should be used. The expressions obtained to relate the structural-group parameters have made it possible to reveal a number of oils that stands out among the others.