Distinct features of crude oils from Nyurol'ka Depression (Southeast of Western Siberia)

Aryl isoprenoids detected in Nyurol'ka Depression oils are unique biomarkers of photic zone anoxia (PZA) and they could be a key for the oil nature determination. In this study, the composition of the oils from four adjacent territories was investigated in order to characterize the PZA features within Nyurol'ka Depression. Samples were analyzed using the gas chromatography-mass spectrometry, the gas-liquid chromatography, and spectrophotometry. To characterize the PZA recorded in the Paleozoic oils from Nyurol'ka Depression they were compared with the Paleozoic oils from Volga-Uralskaya and Timano-Pechorskaya oil and gas provinces. Despite the fact that aryl isoprenoids were identified in the Paleozoic samples from the three studied territories, Nyurol'ka Depression oils demonstrate individual composition. The differences lie in the distribution of isoprenoid alkanes, allcylcyclohexarres, steranes, hopanes, aryl isoprenoids, triaromatic hydrocarbons, dibenzothiophenes and biphenyls relative abundance. The biomarker composition indicates a less stable PZA in the sedimentary basin in Nyurol'ka Depression, as well as a greater degree of thermal maturity. Jurassic oils from Nyurol'ka Depression were compared with the Jurassic oils from Koltogorskiy rift, which is an adjacent territory to the area under study. Unlike the oils from the Koltogorskiy rift, the Jurassic oils of Nyurol'ka Depression are characterized by the presence of aryl isoprenoids and absence of nickel porphyrins. The combination of aforementioned features could be caused by the presence of a PZA in Nyurol'ka Depression and its absence on the territory of Koltogorskiy rift. It is concluded that the presence of the PZA affected the biomarker composition and could be an indicator of one or similar sources for most of the Paleozoic and Jurassic oils in Nyurol'ka Depression.