GEOCHEMISTRY OF OILS FROM THE NORTHERN TIMAN-PECHORA BASIN, RUSSIA
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A geochemical study of 36 oils from the northern Timan-Pechora Basin indicates four oil types. Two types of sulfur-rich oils (range 1.4-2.5% sulfur) can be identified on the basis of both gross and molecular properties. These oils are found primarily in the Toravey, South Toravey and Roman Trebs fields. They are also present in the offshore Prirazlom field, thereby extending the geographic range of sulfur-rich oils into the Pechora Sea. Another oil type exhibits a distinctive odd predominance of n-alkanes in the range n-C11 through n-C19 and a diminished abundance of n-alkanes greater than C19. These oils, which occur primarily in the A. Titov and Labogan fields, show striking similarities to Ordovician-sourced oils from other Paleozoic basins throughout the world. Their biomarker and isotopic compositions, for example, bear a strong resemblance to oils generated from the Ordovician Viola Limestone of the Anadarko Basin. The fourth oil type occurs in the northwestern portion of the basin in the Khylchuyu field. Some mixing between the various types is evident. Light oils and condensates of the Peschano-ozyor, Shtokman, Rusanov and Vasilkovo fields cannot be readily assigned to any of these four types. The Upper Devonian Domanik Formation is generally thought to be the major oil source in the Timan-Pechora Basin. However, geochemical characteristics of Timan-Pechora oils analyzed do not closely resemble those of other Upper Devonian-source oils, such as those generated from the Duvernay Formation of Western Canada. These differences might reflect variations in the organic matter preserved in the two basins during the late Devonian or may indicate that the Upper Devonian is not an important hydrocarbon source in the northern Timan-Pechora region. The results suggest that the Timan-Pechora oils analyzed are generated from Paleozoic carbonate or calcareous shale source rocks, at least one of which appears to be of Ordovician age. 1995.
