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Hydrocarbon accumulations in the Lower Pliocene Productive Series of Apsheron Peninsula have formed owing to subvertical hydrocarbon migration from the underlying Maykop and Diatom source formations. This concept has been substantiated by the recent studies based on the molecular-isotopic characteristics of organic matter, oil and gas. The most notable feature of the Apsheron oils is the stable predominance of paraffin-naphthene HCs in all oil fractions, and this is true for all the fields considered. Meanwhile two geological features had major influence on formation of the composition and properties of Lower Pliocene oils in Apsheron Peninsula. In structures unaffected by tectonic erosion more mobile light components of oils happened accumulated in upper stratigrafically younger horizons due to natural fractionation of hydrocarbons on their upward migration routes. In anticlinal folds with washed out crestal part physical and biochemical degradation has caused the loss of light hydrocarbons, first of all of methane fraction, and in this way weighting up of oils. From top to bottom, towards the basal PS suites the distillate fractions show reduction in the light ends (gasoline and naphtha), which is predictably accompanied by an increase in the amount of bottoms. Compositional variation in oil hydrocarbons laterally and through the section of the peninsula is graphically demonstrated on the basis of gasoline, ligroin, kerosene and diesel cuts of oil. In terms of elemental composition, the deeper the stratigraphic occurrence of the reservoir, the more the whole oil is enriched in sulphur- and nitrogen-containing polar compounds. Keywords: oil; hydrocarbon composition; Apsheron Peninsula; the Productive Series; Lower Pliocene.
Tagiyev et al. (Sun,) studied this question.