25th International Meeting on Organic Geochemistry IMOG 2011

P-298
Petroleum generation in siliceous deposits of Sakhalin Island
(Russia)
Nikolay Oblasov, Ivan Goncharov, Vadim Samoylenko, Svetlana Fadeeva
TomskNIPIneft, Tomsk, Russian Federation (corresponding author:oblasovnv@nipineft.tomsk.ru)
In the Far East of Russia, Sakhalin Island is the
center of hydrocarbon production, where there are
about 70 oil and gas fields within the territory itself, as
well as, in the offshore area. According to numerous
researches, the major source rocks in this region are
Neogene – paleogene siliceous deposits [1]. The
characteristic feature of Sakhalin siliceous rocks is
considered to be the rather early process origin of oil
and gas generation in comparison to the classical
scheme. It was supposed that the oil window zone is
within the limits of vitrinite reflectance changes from
0.4 to 0.8%, while oil formation begins at a depth of
1.5km or even deeper [1, 2, 3].
Rock-Eval and GC/MS research of siliceous rocks,
chloroform extracts of rocks and oils from wells drilled
in Sakhalin onshore and offshore areas was
conducted. According to the Rock-Eval results in the
sedimentary mantle cross-section, there are rocks
with high organic carbon content (up to 3.7%) and
high hydrogen index value (up to 571 mg HC/g TOC),
which correspond to kerogen type II. Most
investigated rocks with high generation potential are
related to Pilsk Formation depositions, which could be
the major source rock in Sakhalin. Besides the abovementioned
formation, high organic matter content can
be found in Matituksk, Majamrafsk, Vengerisk and
Kaskadian formation depositions. The territorial well
placement, containing siliceous rocks of rather high
generation potential, is in the north and north-east
Sakhalin offshore, where the major oil and gas
deposits have been discovered.
GC/MS research included 15 oil samples from 7 oil
fields in Sakhalin (Vostochnoe Ehkhabi, Zapadnoe
Sabo, Nel‘ma, Okruzhnoe, Pela-Lech, Shkhunnoe,
Udachnoe).All these oils are a single genetic group of
organic matter source, formed from marine
bioproducers with an insignificant amount of land
vegetation. Despite the biodegradation of most
studied oil samples, their biomarker composition
considerably matches the chloroform composition of
extracts from potential source rocks. Correlation of
some molecular parameter values of the thermal
maturity in rock and oil extracts (Fig. 1) showed that in
most investigated rock samples the organic matter
has not reached the thermal maturity level of existing
oils. The most near-maturity value for oils was
discovered in rock samples of Pilsk Formation, from
Vostochnyy Kaygan №2 well, the depth of which is
3.3-3.6km. The Rock-Eval value of Tmax parameter for
these samples ranges within 431-434 о С, which
proves that the rock organic matter is on set of oil
generation. It could be stated that the major oil
formation zone is located at a depth of more than
3.5km.
Fig.1. Relationship of molecular parameters of
thermal maturity for oil and extracts from silica rocks.
References
[1] Koblov E. G. et al (1997) Geology and
Development of oil and gas in Sakhalin and offshore.
Moscow: Nauchin Mir - 198 p.
[2] Bazhenova O.K. et al. (2000) Geology and
geochemistry of oil and gas, M,: MSU Publishing
House.- 384p..
[3] Punanova S. A. and Vinogradova T. L.
(2010) Geochemistry <strong>International</strong> 48, 1138-1147.
431