PETROV, ALEXANDER, and PETZOUKHA, YU., Institute of Geology and Exploitation of Fossil Fuels, Moscow, Russia

ABSTRACT: Biomarkers and Geochemical Classification of Oils in Some Basins of the Commonwealth of Independent States

Contemporary geochemical classification schemes of crude oils are based on the use of the composition and quantitative ratios of individual hydrocarbons, mainly biomarkers.

This paper discusses biomarkers, whose composition is closely related to the basic parameters (factors) of crude oil formation such as type of original organic matter; degree of catagenesis of the organic matter, kerogen, and crudes; degree of biodegradation of the oil; facies conditions of diagenesis; and geological age of the original organic matter.

The identification by mass fragmentography (= chromatography) of a large number of biomarkers has enabled the geochemical classification of the crude oils of a series of basins in the Commonwealth of Independent States. Some of the biomarkers thus determined are n-alkanes, isoprenanes, C21-C30 steranes of either regular or rearranged types of structure, tricyclic and pentacyclic terpanes, cheilantanes, hopanes, 25, 28, 30- trisnorhopanes, 28, 30- and 25, 30-bisnorhopanes, g - lupane, g-cerane, and others.

The geochemical conditions of petroleum formation and the geochemical classification are discussed in light of the following typical basins and stratigraphical complexes: western Siberia (Paleozoic-Jurassic-Cretaceous); eastern Siberia (Precambrian-Cambrian-Permian-Triassic-Jurassic), and Timano-Pechora (Silurian-Devonian-Carboniferous-Permian-Triassic) and near Caspian (Devonian-Carboniferous-Permian-Jurassic). In the four basins, some 200 crudes were studied, in each of which about 20 different correlation ratios of the most important biomarkers were determined. This work has resulted in the elucidation of the effect of the main factors of petroleum formation on the geochemistry and features of petroleum generation in the basins and stratigraphic complexes under study.

The study of the composition of biomarkers has enabled the determination of the geological and geochemical conditions of petroleum formation, the correlation of composition with the geological age, chemical type of the original organic matter, the determination of the severity of the oxidizing conditions, the degree of microbiological activity in diagenesis, and also has provided information on the lithology of parent rocks and on other geochemical parameters of petroleum formation.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.