25th International Meeting on Organic Geochemistry IMOG 2011

P-117
Lithology, organic geochemistry, paleo-geography, oil bearing
capacity and petroleum-generating potential of the Bazhenovo
Formation in West Siberia
Alexey Kontorovich, Valentina Danilova, Albina Zamiraylova, Yuriy Zanin, Elena
Kostyreva, Vasiliy Melenevskiy, Valeriy Moskvin, Vika Eder
Trofimuk Institute of Petroleum Geolodgy and Geophysics SB RAS, Novosibirsk, Russian Federation
(corresponding author:DanilovaVP@ipgg.nsc.ru)
In the course of a detailed study of lithology
and organic geochemistry of the Bazhenov Formation
there was obtained new factual material at IPGG
RAS, which allows to improve and develop existing
ideas about the conditions of origination of the
Bazhenov Formation, and assumptions on its
petroleum potential.
There present two main types of rocks in its
section. First, with low content of clay minerals -
carbon-clayey-carbonate-siliceous and siliceous
rocks, characterized by abnormally high (10-25% and
more) concentrations of TOC and authigenic biogenic
silica. N.B. Vassoevich called these rocks
‗bazhenovites‘. The second type is of high clayey
content - mudstone and siliceous mudstone
containing 5-7, rarely up to 10% TOC. Both the
amount of bazhenovites in the section and the
concentration of TOC in them increase from the
periphery to the central, deepest part of the basin.
Bazhenovites and mudstones differ in terms
of indications of salinity, oxidation-reduction (redox)
sedimentation conditions, and in volumes of eolian silt
inclusions, as well as textural characteristics.
Bazhenovites and mudstones also differ in
the specific features of OM. Residual oil and gas
generating potential of the OM of bazhenovites
amount to 350-450 mgHC / g TOC, averaging at 236
mgHC / g TOC in mudstones - 122 mgHC / g TOC.
OM characterized by such diversity in volume and
composition when entering the main zone of oil
generation (oil window) prove to have been the
source of various bitumens. In mudstones their
content varies from 0.06 to 0.77%, making on the
average 0.26%. The bazhenovites are uniquely
enriched in bitumoids (chloroform extractable
bitumens) (their content account for 0.33 – 2.73%,
averaging at 1.30%). By their physico-chemical
parameters and biomarker characteristics, the
bitumoids of the types of rocks under consideration
are not identical, although they all belong to the
marine genotype.
Bitumoids (chloroform extractable bitumens)
of mudstones, compared with those of bazhenovites,
are characterized by low (0.5-1%) sulfur content, by
the dominance of saturated structures in the mass of
hydrocarbons, and by increased ratios n- С 27/ C17 (>
2) and Pr / Ph (> 1). Ethylcholestanes slightly
predominate among steranes. Concentrations of C21,
C23 and C29 appear to be leading in the mass of
tricyclanes. Tetracyclanes are represented, mainly, by
tetracycline C24.
Bitumoids, chloroform extractable bitumens,
of the bazhenovites are known to be richer in sulfur
(3-5 %) and vanadyl porphyrins (2-3 %). Given that
the ratios of n-С27/С17 are not high (from 0.1 to 0.4) и
Pr/Ph (< 1), the CPI approximates 1. Steranes С27,
С28, С29 are present in approximately equal
concentrations Tricyclanes predominate among
terpanes, cheilanthanes С23-С25 concentrations
prevailing in their mass. The tricyclane index value is
2(С19+С20)/(С23-26), on average