The Middle Ob’ Oils (West Siberia): the Geochemical Peculiarities and Genesis

The work generalizes the results of geochemical studies of Middle Ob’ oils (West Siberia) from Mesozoic deposits. Features of physicochemical and hydrocarbon (HC) composition showed the studied oils are mainly aquagene genesis. These oils are most likely to have be derived from mature organic matter of the Bazhenovo Formation. The differences observed in the studied oils can be explained by differences in biogeochemical facies of the Bazhenov Sea (the oxidation-reducing conditions of diagenesis, hydrodynamics and salt regime of the sea basin, the biota). On the other hand, the vertical migration of oil components from source-rock stratum J1-2 with mixed composition of OM can not be excluded. The strong contrast of light arenes distribution suggests the impact of the migration processes on the composition of most of the investigated oils. In the studied sampling, two samples have been revealed GC chromatograms of the saturated fraction of which are non-separated "naphthenic" hump that does not allow the identification of n alkanes and acyclic isoprenanes. There are biodegraded oils. But biodegradation has not affected the distribution of steranes and terpanes in these oils