Variation in Oil Composition in the West Siberian Basin

Malvin Bjorøy¹, Peter Barry Hall², Ian Ferriday², and Alla Nemchenko-Rovenskaya^3
1Geolab Nor AS, 7437 Trondheim, Norway
²Geolab Nor AS, Trondheim, Norway
³V.I. Vernadskiy Institute Organic Geochemistry GEOKHI RAS, Moscow, Russia

Over three-hundred and fifty oils from the West Siberian Basin have been analysed. The oils come from the Pri-Ural, Frolov, Mid-Ob, Nadym-Pur, Pur-Taz, Yamal-Gydan and Vasyugan and Kamysov regions.
Most routine organic geochemical techniques were employed in the study, including whole oil GC, deasphaltening, MPLC and GC and GC-MS (SIR and MRM) of saturated and aromatic hydrocarbons. Stable carbon isotope analysis was also performed on all fractions. In addition, GC-IRMS was performed on oils from Yamal-Gydan and Frolov.
The oils can be divided up into several different families. The dominant family, typical for oils from marine anoxic source rocks, are sourced by the Bazhenov Fm.. This family can be divided into subgroups due to source facies variations. There is a small group of oils comprising a separate family of non marine origin. These are most probably sourced by non-marine Lower-Middle Jurassic algal-rich deposits (Tyumen Fm.).
Another large group of oils show intermediate characteristics, but most show characteristics typical of marine depositional environments. These are found mainly in the northern part of Nadym-Pur and in Yamal-Gydan. They have different origins, including, more terrestrial (nearshore marine?) Bazhenov Fm. and marine/nearshore marine source rocks of the Tyumen Fm. In addition, some oils might be co-sourced from both source rock types.
The main differentiating characteristics of the oils are obtained from biomarkers and carbon isotope compositions.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece