--> Abstract: The Giant Yurubchen-Tokhomo Zone of Oil and Gas Accumulation in the Riphean of the Siberian Platform, by A. E. Kontorovich, A. N. Izosimova, I. D. Timoshina, A. A. Kontorovich, V. G. Sibgatullin, and A. S. Yefimov; #90942 (1997).

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Abstract: The Giant Yurubchen-Tokhomo Zone of Oil and Gas Accumulation in the Riphean of the Siberian Platform

KONTOROVICH, A.E., A.N. IZOSIMOVA, I.D. TIMOSHINA, A.A. KONTOROVlCH, V.G. SIBGATULLIN, A.S. YEFIMOV

Exploration for the Precambrian oil and gas is performed in many countries of the world (Russia, China, Oman, Australia, Brazil, etc.). The most significant discoveries are made in Russia, in the Siberian Platform. The Yurubchen-Tokhomo zone of oil and gas accumulation is the largest among them.

The Yurubchen-Tokhomo zone of oil and gas accumulation occurs in the near-dome part of the Kamovsk arch in the Baykit anteclise. The Riphean section in the zone is represented by alternating clay-dolomite and dolomite members. The age of deposits in the zone is from 1000 to 1400 Ma. The zone occupies an area of about 16,000 km2 and is faulted into several blocks. The Riphean and Vendian deposits are oil- and gas-bearing in the zone. The main Riphean pool of the horizon P1 is confined to the Riphean outcropping deposits of different age. Reservoir type is cavernous-fractured in the pool. The height of oil base is about 40 m; that of gas cap is about 90 m.

Oil source rocks are rather thick carbonaceous deposits of the Madra Formation with TOC concentrations to 2.5%. Kerogen is of polymerlipid nature and is enriched in 12C carbon isotope (d13C= -33 to -34o/oo). The pool resulted from vertical migration of hydrocarbons during two stages, initially as an oil pool (Ordovician - Silurian) and then as oil-gas pool (late in Permian-early in Triassic). One cannot exclude also lateral migration of hydrocarbons from the continental margin of the Siberian craton (Yenisey Ridge) where several carbonaceous units have formed.

Oils of the Yurubchen-Tokhomo zone are light, contain few waxes and n-alkanes. The latter are dominated by C17-C18 hydrocarbons, Pr/Ph ratio is less than 1. Ethylcholestane concentrations are dominant among steranes. The oil is similar in composition to the Vendian oils from the Nepa-Botuoba anteclise and Oman.

There are prospects for new discoveries.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria