25th International Meeting on Organic Geochemistry IMOG 2011

P-309
Comparative characteristics of molecular composition of
basement oils in various regions
Yury Savinykh 1 , Vu Van Hai 1
1 Institute of Petroleum Chemistry, Siberian Division of the Russian Academy of Sciences, Tomsk, Russian
Federation, 2 Nanional Research Tomsk Politechnic University, Tomsk, Russian Federation (corresponding
author:yu-sav2007@yandex.ru)
The present stage of development oil-gas
exploration geology is characterized by the greater
orientation on discovering non-traditional objects.
Such objects are natural reservoirs formed by
fractured crystal rocks. The major part of hydrocarbon
(HC) accumulations in such reservoirs is in buried
ledges of the basement represented by fractured
metasomatic igneous rock, quartzites, granites,
dolomites. The question of genesis of these oils
remains debatable till now. Among variety of
publications two ideas of HC genesis in fractured
basement can be emphasized:
-Oil-gas generating systems are located above the
basement or on slopes of ledges;
-Basement is considered as an independent oil-gas
generating object, in structure of which various types
oil-gas generating systems functioning under
influence of deep factors are developed, in form of
spontaneous, periodically shown deep ascending HC
streams.
Correlation of molecular structure of oils from
sediments and the crystal basement of Southern -
Tatar arch (STA) has shown both their syngenesis
and sharp distinction. And, in the latter case similarity
of molecular parameters of bitumen from
metamorphic rock of STA basement with the oil from
fractured basement of the White Tiger field (on the
shelf of Southern Vietnam) is marked. For fractured
reservoirs of Western Siberia two models of oil and
gas formation have been offered: additional, actually
Paleozoic not found out yet the source of
hydrocarbons and above laying sediments [1].
Correlation of oils from the basement and
sediments of Lower Oligocene of White Tiger field has
shown similarity of their molecular parameters,
however, a greater degree of maturity of basement
oil.
In this connection, it is interesting to compare the
molecular structure of oils from the basements of two
different regions of the planet. For the analysis, the oil
from fractured rock of Palaeozoic era of Western
Siberia (WS): Maloichskoe (WS-ML), Archinskoe
(WS-Ar), Urmanskoe (WS-Urm) oilfields, oil from
weathering crust: Ostaninskoe oilfield (WS-Ost) and
the oil from Basement fractured granitoids of White
Tiger oilfield (WT) have been chosen.
Oils of WS and WT oilfields have similar physical
and chemical properties. They are light, highly waxy,
low in sulphur, with low content of asphaltenes and
naphthenes. They have Pr/Phy index, which is typical
of reducing-low oxidizing conditions of sedimentation
(1,1-2,1).
Source of initial material.
As a whole, in С27-C28-С29 (m/z=217) steranes С27
(41-58 %) prevails as compared with C28 and С29
steranes (except for oil from WS-Ar). It indicates that
these oils were formed in open marine and delta
source zones.
In all oils Oleanane is present: a compound
generated by angiosperms. Oleanane Index is useful
to distinguish lacustrine-algal oils from terrigenous
fluvial-deltaic oils in South-East Asia. This biomarker
is present only in oils generated from Late Cretaceous
deposits or younger age. Its presence in Palaeozoic
oils of Western Siberia has no explanation.
Parameters of maturity.
The maturity of the investigated samples oils is
evaluated by the following basic geochemical
parameters: Ts / (Ts+Tm), MPI-1. White Tiger field
oils have a higher degree of maturity due to higher
temperature (140-150 O С) in a formation as compared
with Western Siberia oils (80-90 0С).
As a whole, comparison of a wide set of biomarkers
in the oils of WT and WS fractured reservoirs show a
uniform distribution pattern of steranes, hopanes, the
saturated and aromatic hydrocarbons. These
parameters are similar or identical: that can confirm
the idea of belonging of these oils to a common
genetic family. This is possible, when an additional
deep oil-generating source has the same mechanism
and generates oil of similar composition.
[1] Goncharov I.V., et al. (2003) Genetic types of oils
from Tomsk region [abs], In Proceeding of 15 th
Int.<strong>Meeting</strong> Oil and Gas Chemistry, Tomsk, Russia,
p.10.
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