Bitumoids in Cambrian deposits of the cis-Yenisei sub-basin: features of composition, distribution and diagnosis
E.A. Kostyreva1, A.E. Kontorovich1, I.S. Sotnich1
1Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences,
Novosibirsk, Russia
Keywords: autochthonous bituminous, allochthonous bituminous, residual autochthonous bitumoid, migration, biomarker hydrocarbons, bitumoid classification, Cambrian, Western Siberia
Abstract
The geological development history of the cis-Yenisei sedimentary sub-basin, the presence of several stratigraphic levels in the Cambrian section with organic-rich rocks, and the high level of catagenesis suggest intensive hydrocarbon generation processes in these deposits in the geological past. Migration processes in the Cambrian sediments caused a high variability of bitumoids (chloroform rock extacts), both in their content and in group and hydrocarbon composition, as evidenced by three kind of bitumoids (allochthonous, autochthonous, residual autochthonous), defined according to the Uspensky-Vassoevich regularity. In order to differentiate bitumoids more precisely, the article proposes a classification of bitumoids by group and hydrocarbon composition, distinguishing 7 classes. Allochthonous bitumoids (class VII ) have more hydrocarbonic composition and are the most migratory, and have been found to represent about 30% of the total amount of bitumoids, another 6% fall into the class of autochthonous-allochthonous (classes V, VI), the rest of the bitumoids are autochthonous and residual autochthonous, mainly of asphalt-resinous composition. Molecular analysis of the composition of bitumoids has generally shown the genetic unity of autochthonous and allochthonous bitumoids. For allochthonous bitumoids, however, there is a wider range of values for molecular indicators, confirming the influence of migration processes on their composition..
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