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The Bazhenov Formation or Bazhenov Shale is a stratum in the West Siberian basin formed from sediment deposited in a deep-water sea in Tithonian–early Berriasian time. The sea covered more than one million square kilometers in the central basin area. Highly organic-rich siliceous shales were deposited during this time in anoxic conditions on the sea bottom. The sea was connected to the world's oceans and contains trace minerals derived from dissolved minerals and organic materials similar to sapropel sediments in the Black Sea.
In addition to being a prolific deep water marine source rock (it has been called the world's largest oil source rock) the formation is believed to contain substantial reserves of tight oil. An estimate by Wood Mackenzie of the Bazhenov Formation puts oil in place at 2 trillion barrels. In 2013, the Russian oil company Rosneft estimated recoverable reserves of 22 billion barrels for the formation. The Russian government agency Rosnedra estimated in 2012 that the Bazhenov contained 180 to 360 billion barrels of recoverable reserves. According to U.S. Energy Information Administration estimates published in June 2013:
For the total Bazhenov shale prospective area in the West Siberian Basin, we estimate a risked shale oil in-place of 1,243 billion barrels, with 74.6 billion barrels as the risked, technically recoverable shale oil resource.... In addition, for this prospective area, we estimate a risked shale gas in-place of 1,920 Tcf, with 285 Tcf as the risked, technically recoverable shale gas resource...
