Correlation of basic 1H and 13C NMR-measurable structural group parameters of crude oils of the Volga–Urals oil and gas basin

Abstract

Among 120 pairwise relations between 16 main ¹H and ¹³C NMR-measurable characteristics of the structural group composition of Volga–Urals crude oils, 10 most consistent relations (correlation coefficients |r_s| ≥ 0.9), 13 relations with |r_s| in the range of 0.8–0.9, and 33 pairs with loosely related or mutually independent members (|r_s| ≤ 0.3) have been revealed. Several relationships are parametric. The main parameter is C_ar. The overall picture of the relationships is complex; correlation coefficients with the absolute value above 0.7 are observed not only between the parameters characterizing the structure in the same group of entities (aromatic, n-alkyl): it has been found that C_ar correlates with the total content of n-alkyl structures (r_s =–0.76). Having definitely common features, oils from the Volga–Urals and Western Siberia oil and gas basins noticeably differ from one another. To explain the differences, it is necessary to launch an integrated study that is methodologically beyond the scope of contemporary petroleum geochemistry. The paper demonstrates the capabilities of correlation analysis for solving problems to which this method has not been yet applied in petroleum geochemistry: partial correlation coefficients as a means of identifying parametric relationships and Spearman correlation coefficients for nonnumeric values in determining differences in the composition between oils of different structures and from different territories or stratigraphic plays.