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Paper Number: 49
Mozhegova, S.V. and Dakhnova, M.V.
1All
Russia Research Geological Oil Institute, 36, Shosse Entuziastov,
Moscow, 105118, Russia; mozhegova@vnigni.ru
In oil and gas regions of Russia the formations of “shale” with high
bitumen content are represented mainly by the Kuonamsk and (its
analogue) Inikansk suite (Lower-Middle Cambrian deposits of the Siberian
Platform), Domanik suite (Middle-Upper Frasnian-Tournaisian of the East
European platform), Bazhenov suite and (its analogue) Lower Tutleimsk
sub-suite (Upper Jurassic-Neocomian of the West Siberian Platform) and
Kumsk and Khadumsk suites (Eocene and Oligocene-Miocene in the
Pre-Caucasus foredeep).
These suites are known as both important oil source and oil reservoir
series. The distribution of oil in such deposits has similar nature.
Hydrocarbon (HC) accumulations in these suites are believed to associate
with laterally persistent widely distributed reservoirs.
Because of the specific structure of such strata it is not always
possible to identify and delineate the existing oil-saturated reservoirs
based on the traditional methods only. This problem can be successfully
solved by integrating organic geochemistry methods into the methodology
applied.
These methods permit to study specific features of distribution of
various forms of organic matter (OM), including oil, in these
strata.
The Rock-Eval method is most effective for identification of
oil-saturated intervals in sections of such suites. It permits to
confidently identify oil intervals based on high values of peak
S1 relative the TOC (Total Organic Carbon) background.
Study of the Bazhenov and Domanik deposits shows that in zones where
OM maturity attains the "oil window" peak the oil-saturated intervals
are identified in the form of single small-thickness layers
predominantly made of relatively organic-lean non-clay rocks.
In zones of OM late maturity the presence of mobile oil is noted
almost all over the suite section. Besides, free high-molecular oil
components are present in these rocks. This is indicated by reduced
values of peak S2 obtained by repeated Rock-Eval analysis of
the extracted rocks.
For suites drilled with sufficient core recovery it is possible to
evaluate thickness of the identified oil-saturated intervals.
One of the reservoir geochemistry methods based on results of GC
analysis and comparison of oils and bitumen [1] can be used to identify
productive intervals and to determine the extent of vertical and lateral
oil reservoirs continuity.
These geochemical studies permits to obtain more accurate data on
thickness and lateral distribution of the oil-saturated bodies and
amount of oil contained therein, which results in obtaining more
accurate (compared to currently used) parameters needed for assessment
of resources (calculation of reserves) of HC in oil-shale
formations.
References:
[1] Kaufman R.L. et al. (1987) In Proc. of the Sixteenth Annual
Convention of the Indonesian Petroleum Association: Indonesian Petroleum
Association, Jakarta, 247-268
