Oil and Gas Potential of the Triassic in West Siberia?

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Permian-Triassic rocks are widely spread within the West Siberian basin, and they include volcanics, volcanoclastics, and clastics. Their thickness varies from tens of meters of 3000 m. Recently, three commercial oil pools have been discovered in Triassic effusive-sedimentary rocks. These discoveries, together with other geological and geochemical data, identify the Triassic complex as a major play. Oil-bearing intervals have been found in three different types of sequences; a fourth also may be prospective. The first type is represented by lacustrine-terrigenous sediments, which comprise oil-saturated sandstones interbedded with basalts (the Turin series). Oil influxes were obtained in the Yakhlinskaya and Triyurtin-skaya structures in the Shaim region. The second type is distinguished from the first by the presence of coal-bearing intervals in the upper part. Oil was produced in the Yerofeyev area of the Chelyabinsk garben. The third type differs from the other two by the presence of potassic rhyolites and dacites. Their age is not precisely dated, and supposedly they are of Permian age. The largest oil influxes have been obtained from fractured and eroded rocks of this type in the Rogozhnikovskaya and other places in the Krasnoleninsk region. Rhyodacites often underlie Turin basalts, but locally they occur in the uppermore » part of the series. Triassic and Permian-Trissic rocks of the three types are overlain by Jurassic and Cretaceous rocks with a large break. The fourth type of section is completely terrigenous (Tampei series). It is developed in the northern part of west Siberia. Here Triassic sediments are overlain by the Jurassic complex without a break. According to well-log data, productive horizons occur at Urengoy and Beregovaya (in the Urengoy region).« less