Geochemical characteristics of oils from the lower Paleozoic deposits of the varandei-adzva structural zone of the Pechora syneclise

The hydrocarbon composition of oils from the Ordovician-Lower Devonian carbonate oil and gas complex in the northern part of the Timan-Pechora province has been studied. According to the composition of normal alkanes, the studied oils are confidently divided into two groups. The first group is characterized by the dominance of the C17 homologue among n-alkanes, which is characteristic of the organic matter of marine carbonates, and the second group is characterized by C17 and C19 predominance with a sharp decrease in the content of C20+ n-alkanes (which is a sign of a special OM of marine carbonates - algae G Prisca). Genetic indicators determined by the distribution of polycyclic biomarkers, for example, the ratio of αββ steranes of the composition С27:С28:С29, also indicate that oils of types I and II have a slightly different composition of the initial OM, but are characterized by close conditions of sedimentation of the initial OM, which occurred in shallow sea environments. The indicators of thermal maturity make it possible to attribute the studied oils to the peak of oil window. It is probable that the generation of oils occurred in rocks whose organic matter reached the catagenesis grade MK2. Data for polycyclic biomarkers give slightly lower maturity scores than those for aromatic (phenanthrenes and dibenzothiophenes) compounds.