Abstract
Using the 1H NMR examination of a representative set of crude oils (86 samples, 54 oil fields and exploration areas) from the North Caucasus oil-and-gas basin, we obtained, for the first time, the structural-group composition of crude oils over the entire basin. Distribution density plots were presented for all the composition parameters measured. It was demonstrated that, because none of the parameters obeys normal distribution, non-parametric statistical analysis is needed for the data processing. In particular, medians and median confidence intervals (the latter being determined by signed-rank test), rather than means or root-mean-square deviations, should be relied upon. The North Caucasus oils were found to have a markedly lower content of aromatics (both monocyclic and bi-/polycyclic) than the crude oils from Western Siberia and Volga–Urals. Compared with the Eastern Siberia basin, the North Caucasus oils are distinguished by a slightly higher presence of bicyclic and polycyclic aromatics. At the same time, the North Caucasus oils exhibit the highest content of normal and monomethylated alkanes among the four basins under consideration. The North Caucasus oils were classified into three stratigraphic groups according to their oil composition. The first group consists of Triassic and Jurassic reservoirs. These crude oils have the lowest content of aromatics and the highest content of normal and monomethylated alkanes. The second group is the Cretaceous sediments, and the third group includes Paleogenic and Neogenic deposits. The content of aromatics increases consistently from the bottom to the top of the section.
Highlights
Using the 1H NMR examination of a representative set of crude oils (86 samples, 54 oil fields and exploration areas) from the North Caucasus oil-and-gas basin, we obtained, for the first time, the structural-group composition of crude oils over the entire basin
The present study continues a series of publications on the analysis of the composition of crude oils of major oil-and-gas basins (OGBs) in Russia and neighboring countries based on 1H and 13C NMR examination [1–7]
We examined 86 samples of crude oils from 54 fields and exploration areas (Table 1) that cover, in total, the entire basin area
Summary
Using the 1H NMR examination of a representative set of crude oils (86 samples, 54 oil fields and exploration areas) from the North Caucasus oil-and-gas basin, we obtained, for the first time, the structural-group composition of crude oils over the entire basin. The distributions of depths and temperatures for the tested oil samples (Fig. 1) are reasonably consistent with their frequency of occurrence in the OGB [12].
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