25th International Meeting on Organic Geochemistry IMOG 2011

P-305
Geochemical indices of hydrocarbon systems of early
generation
Svetlana Punanova, Tatyana Vinogradova
Institute of Oil and Gas Problems, Russian Academy of Sciences, Moscow, Russian Federation
(corresponding author:punanova@mail.ru)
This study analyzed and categorized geochemical
composition of early catagenetic hydrocarbon (HC)
accumulations of petroliferous basins of Russia,
Azerbaidzhan, Turkmenistan, Belorussia, Japan,
China, Australia, Indonesia, USA, Canada, Israel and
Guatemala. Oils from these basins were grouped by
lithofacial conditions of their source OM: marine (deep
and shallow water) and continental (lacustrine, coal-
bearing and subcoal alluvial-paludal) [1].
The following indices were used in the study: contents
of n-alkanes, isoprenoids, arenes, odd-even CPI,
biomarkers (steranes, hopanes, mono and tri-
aromatic steranes); ratios of some of the biomarker
indices and also trace elements (TE) and
metalloporphyrin complexes (MPC). We utilized
classification of chemical composition of oils [2]. The
presence of moretanes and low ratios of HC
biomarkers in fluids of all facies, such as 20S/20
(S+R) – by C29 (less than 55%); 22S/22 (S+R) – by
H31 (48% - 58%); 22S/22 (S+R) by M32 (~35%)
demonstrates early-generation stage of oil generation.
Compared to mature fluids, immature accumulations
of chemical types A-2, A a -1, A b -1 and A c -1 have
elevated values of P/n-C17 (up to 9.7) and Ph/n-C18
(up to 5.2).
Oils generated by OM of marine deep water facies
have low ratios of P/Ph (up to 1.7), prevalence of
steranes C27 (cholestanes) and wide range of
hopanes H27-H35. Oils of terrigenous-siliceous facies
have monomodal distribution of n-alkanes in C15-C19
domain, prevalence of P over Ph, tricyclanes over
tetracyclanes, trisnorhopane Tm over Ts, steranes
over hopanes, presence of oleanane and 28,30bisnorhopane.
Oils of terrigenous-carbonate and
carbonate facies have bimodal distribution of nalkanes,
prevalence of even n-alkanes in C22-C28
domain, Ph over P, tetracyclanes over tricyclanes,
trisnorhopane Ts over Tm, hopanes over steranes,
presence of gammacerane.
Oils generated by OM of shallow water facies have
equal contents of steranes C28 and C29, low quantities
of light steranes C21-C22, sterane C30 and oleanane,
as well as some hopanes H27-H33.
Oils of marine genesis have low contents of V+Ni (6.9
ppm), MPC (52 ppm) and V/Ni < 1 (0.6). However,
oils generated by OM of the Monterey Formation
(California) have higher concentrations of these
elements V+Ni (348 ppm), MPC (300 ppm) and V/Ni >
1. Oils of the Monterey Formation were generated in
strongly reducing conditions of diagenesis during the
longlasting and stable subsidence of the
sedimentation basin. The OM of the source rocks (an
analogue of the Domanik Formation in the Eastern
European Platform) shows a higher grade of
catagenesis.
Oils generated by OM of continental lacustrine facies
have the increased content of tricyclic HC C20-C29,
wide presence of light steranes C21-C22, steranes C30,
dinosteranes and gammacerane. Oils of lacustrine
salty facies are distinguished by prevalence of even
n-alkanes over odd n-alkanes, Ph over P, abundance
of alicyclic isoprenoids, and wide range of hopanes
H27-H35. Oils and condensates generated by OM of
continental coal-bearing and subcoal alluvial-paludal
facies have high concentrations of P, with P/Ph up to
13.8. Wide presence of bisnorlupanes and oleanane
is found in West Canada, while 25,30-bisnorhopane,
25,28,30-trisnorhopane and 25-norhopane are found
in West Siberia. Oils of these facies have significantly
lower contents of TE and MPC. Contents of Ni in
these oils is usually higher than V (V/Ni = 0.1-0.7).
Similar ratio is characteristic of MPC (Vp/Nip < 1).
Due to the prevalence of Ni over V these oils are
combined into a group of Ni-bearing oils.
The established specific indices of early-generation
oils and condensates are recommended to be used in
geochemical correlation of oils and in predicting of
both HC and TE compositions of oils generated by
OM of different lithofacial types.
References
[1] Vinogradova, T., Punanova, S. Hydrocarbon
Systems of Early Generation, Geokhimiya, No. 1,
103–108 (2009)
[2] Petrov, Al. Oils of the Early Generation
Stages, Geol. Nefti Gaza, No. 10, 50–53 (1988)
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