MDBT estimation ratio for transformation organic matter ratio in Bazhenov Formation of Western Siberia (Tomsk Oblast, Russia)

Abstract

The Bazhenov Formation is the main source rock in the West Siberian Basin, because of high organic-rich Bazhenov black shales, with a total organic carbon (TOC) content of 10-15wt.% generally. Based on Rock-Eval pyrolysis data, the initial generative potential for a significant part of West Siberian Bazhenov Formation organic matter (OM) is from 10 to 60% expended. Most West Siberian oils are in the Bazhenov Formation due to very high oil potential (initial hydrogen index = 710mgHC/gTOC) and widespread regional distribution). Vitrinite reflectance (Ro) does not correctly indicate the transformation ratio (TR) of the OM in Bazhenov black shales. However, GC-MS analysis of extracts indicated a good correlation between some molecular maturity and Rock-Eval maturity parameters. Molecular maturity parameters based on naphthalenes and phenanthrenes are not applicable for Bazhenov Formation OM. While the parameters based on 4-methyldibenzothiophene and 1- methyldibenzothiophene ratio (4MDBT/1MDBT) is applicable in estimating the hydrocarbon potential of Bazhenov Formation black shales and, consequently, provides more reliable information about marine OM TR than does Ro. The 4MDBT/1MDBT ratio is more consistent and precise than pyrolysis data. Therefore, it is more applicable in the case of scarcity of core samples throughout the whole formation.