Sredne-Nazymsky field: features of gasoline cut hydrocarbon composition and oil genesis

The authors discuss studies of molecular composition of oil contained in structurally complicated low-permeable reservoir rocks constituting the Jurassic and pre-Jurassic accumulations in the Sredne-Nazymsky field; the field is situated within the West Siberian Frolovsky Petroleum Region. The hydrocarbon source of accumulations in pre-Jurassic and Middle Jurassic deposits is still debatable. At the same time, monitoring of the Upper Jurassic high-carbon formation development is a topical and sophisticated problem. The Rock-Eval pyrolysis was used to determine the possible source rocks, the Organic Matter type and generation potential in the studied interval. Molecular composition of biomarker hydrocarbons obtained from the gas-liquid chromatography and chromatography-mass spectrometry data were used in genetic typification of oil from the Jurassic and pre-Jurassic accumulations and in oil-rock chemocorrelation. In addition, data on the isotopic signature of carbon in crude oils, bitumoids, kerogen of Upper Jurassic rocks, and trace element and vanadyl porphyrin content in oils of different reservoirs in the field under consideration were used. Particular attention was paid to the study of hydrocarbons in gasoline cut of oils. Informative molecular parameters (С6-С7, ratios in hydrocarbon composition) were determined that makes it possible to identify oils from Upper Jurassic, Middle Jurassic (ЮК2-7 reservoirs) deposits and pre-Jurassic sequence (PZ reservoir). The authors propose to use these parameters in determination of oil belonging to the objects/accumulations under consideration and in monitoring of the Sredne-Nazymsky field development