Geochemistry of Oils and Condensates from the Tambey Group of Fields (Yamal Peninsula, West Siberia)

For geochemical typification of oils and condensates from the fields of the Tambey group (the Yamal Peninsula) and determination of their assumed sources, the data on the organic geochemistry of the major oil-gas-source rock masses were generalized and compared with the results of geochemical interpretation of the analytical data on the composition of the studied naphthides. In accordance with the genetic hydrocarbon indicators (concentration ratios based on the composition of n-alkanes, acyclic isoprenanes, steranes, terpanes) and with the isotopic composition of carbon, three genetic types of naphtides are distinguished in the considered collection. The mixed genotype predominates, one sample corresponds to the aquagene genotype, and several samples correspond mainly to the terragenic genotype. Maturity indices with respect to the composition of steranes, terpanes and arenes provide evidence of the formation of the analysed samples under the conditions of the main oil generation zone. Relying on gas-liquid chromatographic data (the naphthenic hump, the absence of n-alkanes or their lower content compared to acyclic isoprenanes), condensates from the Albian-Cenomanian and, partially, from the Aptian deposits underwent microbial oxidation of the moderate and initial stages, respectively. The features of the physicochemical properties indicate the condensation type of most of the studied samples. This is consistent with the localization of the deposits in the zone of predominant gas-condensate accumulation.