Abstract: Geology and Petroleum Potential of the Lower Jurassic Alluvial-Lacustrine Deposits of the West Siberian Basin

KONTOROVICH, A.E., V.P. DANILOVA, O.G. ZHERO, I.A. IVANOV, V.I. ILYINA, V.I. MOSKVIN, M.A. LEVCHUK, O.O. ABROSIMOVA, YEGOROVA, L.I., V.A. KONTOROVICH, V.P. MANGAZEYEV

In the southern and central West Siberia the lower Jurassic deposits are represented mainly by continental sediments. They fill in the depressional zones. Reservoirs are sand-silt horizons, seals are mainly argillite members. The most persistent of them is the Togur Formation (beginning of Early Toarcian) accumulating in vast lake reservoirs, intermittently connected with each other and with boreal sea.

The Togur Formation is the main oil-generative stratum. Its rocks contain up to 3% mainly aquagenic organic matter (type II, partly type III), there are high concentrations of n-alkanes (maximum C21-C24) in extractable bitumens, Pr/Ph ratio is greater than 1, steranes are dominated by C29 ethylcholestane. Organic matter maturity corresponds to the main zone of oil generation (Ro=0.7-0.9).

The giant Talinskoye oil field has been discovered in the Lower Jurassic, deposits in the west of the basin. Pools are confined to extended traps of shoestring type. Sediments accumulated in a canyon-like trench surrounded by mountains composed of granites and quartz-bearing metamorphic rocks and are represented by alluvial fans and channel lag and bar deposits. Prospective zones of similar structure (Novonadezhdinskaya, Severomezhovskaya) have been distinguished in the southeast of the basin on the slopes of the Aleksandrovsk megaswell and Mezhovka arch. There is a possibility to find lithologic traps in the lake delta and beach deposits.

Geochemical peculiarities of oils and correlation "oil source rocks-oil" In the southern and central West Siberia the lower Jurassic deposits are represented mainly by continental sediments. They fill in the depressional zones. Reservoirs are sand-silt horizons, seals are mainly argillite members. The most persistent of them is the Togur Formation (beginning of Early Toarcian) accumulating in vast lake reservoirs, intermittently connected with each other and with boreal sea.

The Togur Formation is the main oil-generative stratum. Its rocks contain up to 3% mainly aquagenic organic matter (type II, partly type III), there are high concentrations of n-alkanes (maximum C21-C24) in extractable bitumens, Pr/Ph ratio is greater than 1, steranes are dominated by C29 ethylcholestane. Organic matter maturity corresponds to the main zone of oil generation (Ro=0.7-0.9).

The giant Talinskoye oil field has been discovered in the Lower Jurassic, deposits in the west of the basin. Pools are confined to extended traps of shoestring type. Sediments accumulated in a canyon-like trench surrounded by mountains composed of granites and quartz-bearing metamorphic rocks and are represented by alluvial fans and channel lag and bar deposits. Prospective zones of similar structure (Novonadezhdinskaya, Severomezhovskaya) have been distinguished in the southeast of the basin on the slopes of the Aleksandrovsk megaswell and Mezhovka arch. There is a possibility to find lithologic traps in the lake delta and beach deposits.

Geochemical peculiarities of oils and correlation "oil source rocks-oil" confirm that the Lower Jurassic oils and partly Middle Jurassic oils were sourced from the Togur Formation.

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