The physicochemical characteristics and hydrocarbon composition of crude oils of the Timan–Pechora petroliferous basin

The total hydrocarbon composition and average structural-group characteristics of typical Paleozoic crude oils of the Timan–Pechora petroliferous basin are described. The hydrocarbon (HC) types of crudes are compared, which were conventionally determined from the composition of their gasoline fractions, by mass-spectrometric analysis of the HC composition of crudes, and by structural-group analysis of crudes, based on radiospectrometric data. The analyses have shown the presence of 30 structural types of HCs with up to 43 carbon atoms. The whole series of members up to C43 are specific only for HCs with no more than three rings in the molecule. It has been established that the carbonate strata in the basin under investigation, independently of the depth of their occurrence and the age of the host deposits, generate and accumulate heavy high-resin high-sulfur oils rich in alicyclic structures and assigned by HC composition to the naphthene–methane or even naphthene type. Terrigenous reservoirs here abound in crudes of methane–naphthene type. The contents of sulfur and resinous substances and the fraction of carbon atoms in alicyclic HC structures decrease as the depth of occurrence of the host deposits grows, thus reflecting the known gradual process of “methanization” of petroleum composition.