The West Siberian petroleum basin (also known as the West Siberian hydrocarbon province or Western Siberian oil basin) is the largest hydrocarbon (petroleum and natural gas) basin in the world covering an area of about 2.2 million km2, and is also the largest oil and gas producing region in Russia.[1]
Geographically it corresponds to the West Siberian plain. From continental West Siberia, it extends into the Kara Sea as the East-Prinovozemelsky field.
Beneath lie remnants of the Siberian traps, thought to be responsible for the Great Dying 250 million years ago.[2] [3]
Gas was discovered in 1953 in Upper Jurassic sandstones and limestones, within the Berezov Field. Then in 1960, oil was discovered in the Upper Jurassic 400 km south, in the Trekhozer Field. A Neocomian oil discovery followed in 1961, in the Middle Ob Region, followed by several giant and large fields, including the Samotlor Field. Gas was discovered in Cenomanian sandstones in 1962 within the Taz Field. This was followed by several giant and large dry gas fields in the Aptian-Cenomanian Pokur Formation, including the Medvezhye Field and Urengoy Field, which commenced production in 1972 and 1978 respectively. Lower-Middle Jurassic discoveries were made in the Tyumen Formation in the 1970s, within the Krasnolenin Arch, including the Tallinn Field in 1976. The giant Rusanovskoye Field and Leningrad Field were discovered in the south Kara Sea in 1989-90.
Since the early 2010s Russia's state-owned energy company Gazprom has been developing Yamal project in the Yamal Peninsula area. As of 2020, Yamal produces over 20% of Russia's gas, which is expected to increase to 40% by 2030. The shortest pipeline routes from Yamal to the northern EU countries are the Yamal–Europe pipeline through Poland and Nord Stream 1 to Germany.[4] The proposed gas route from Western Siberia to China is known as Power of Siberia 2 pipeline.[5]
The basin occupies a swampy plain between the Ural Mountainsand the Yenisey River. On the north, the basin extends offshoreinto the southern Kara Sea. On the west, north, and east, thebasin is surrounded by the Ural, Yenisey Ridge, and Turukhan-Igarka foldbelts that experienced major deformations during theHercynian tectonic event and the Novaya Zemlya foldbelt thatwas deformed in early Cimmerian (Triassic) time. On the south,the folded Caledonian structures of the Central Kazakhstan andAltay-Sayan regions dip northward beneath the basin’s sedimentarycover.[6]
The basin is a relatively undeformed Mesozoic sagthat overlies the Hercynian accreted terrane and the Early Triassicrift system. The basement is composed of foldbelts that weredeformed in Late Carboniferous–Permian time during collisionof the Siberian and Kazakhstan continents with the Russian craton.The basement also includes several microcontinental blockswith a relatively undeformed Paleozoic sedimentary sequence.
The sedimentary succession of the basin is composed ofMiddle Triassic through Tertiary clastic rocks. The lower part ofthis succession is present only in the northern part of the basin;southward, progressively younger strata onlap the basement, sothat in the southern areas the basement is overlain by Toarcianand younger rocks. The important stage in tectono-stratigraphicdevelopment of the basin was formation of a deep-water sea inVolgian–early Berriasian time. The sea covered more than one million km2 in the central basin area. Highly organic-richsiliceous shales of the Bazhenov Formation were depositedduring this time in anoxic conditions on the sea bottom. Rocksof this formation have generated more than 80 percent of WestSiberian oil reserves and probably a substantial part of its gasreserves. The deep-water basin was filled by prograding clasticclinoforms during Neocomian time. The clastic material wastransported by a system of rivers dominantly from the easternprovenance. Sandstones within the Neocomian clinoforms containthe principal oil reservoirs. The thick continental Aptian–Cenomanian Pokur Formation above the Neocomian sequencecontains giant gas reserves in the northern part of the basin.
The Western Siberian oil basin is the largest oil and gas producing region in Russia. The oil extracted in this territory accounts 70% of the oil produced in the country.[1]
Three total petroleum systems are identified in the WestSiberian basin. Volumes of discovered hydrocarbons in thesesystems are 144 billion barrels of oil and more than 1,300trillion cubic feet of gas. The assessed mean undiscoveredresources are 55.2 billion barrels of oil, 642.9 trillion cubic feetof gas, and 20.5 billion barrels of natural gas liquids.
The largest known oil reserves are in the Bazhenov-Neocomian Total PetroleumSystem that includes Upper Jurassic and younger rocksof the central and southern parts of the basin. Oil reservoirs aremainly in Neocomian and Upper Jurassic clastic strata. Sourcerocks are organic-rich siliceous shales of the Bazhenov Formation.Most discovered reserves are in structural traps, but stratigraphictraps in the Neocomian clinoform sequence are productiveand are expected to contain much of the undiscoveredresources. Two assessment units are identified in this total petroleumsystem. The first assessment unit includes all conventionalreservoirs in the stratigraphic interval from the Upper Jurassic tothe Cenomanian. The second unit includes unconventional (orcontinuous), self-sourced, fractured reservoirs in the BazhenovFormation. This unit was not assessed quantitatively.
The Togur-Tyumen Total Petroleum System covers thesame geographic area as the Bazhenov-Neocomian system, butit includes older, Lower–Middle Jurassic strata and weatheredrocks at the top of the pre-Jurassic sequence. A Callovianregional shale seal of the Abalak and lower Vasyugan Formationsseparates the two systems. The Togur-Tyumen system isoil-prone; gas reserves are insignificant. The principal oilreserves are in sandstone reservoirs at the top and bottom of theLower–Middle Jurassic Tyumen Formation; comparativelysmall reserves are in pre-Jurassic carbonate and clastic rocks.The principal source rocks are lacustrine to marine shales of theToarcian Togur Bed. Traps are structural, stratigraphic, or acombination of the two. The total petroleum system was assessedas a single assessment unit. Most of the undiscoveredresources are expected in stratigraphic and combination traps.
The northern onshore and offshore parts of the basin areincluded in the Northern West Siberian Mesozoic CompositeTotal Petroleum System that encompasses the entire sedimentarycover. The system is strongly gas-prone; it contains giantgas reserves and comparatively small oil reserves. The majorpart of hydrocarbon reserves is dry gas in the upper Aptian–Cenomaniansandstones (Pokur Formation and equivalents). Smallerreserves of wet gas and some oil are in Jurassic and Neocomiansandstones. Source rocks for the dry gas in the Pokur Formationthat constitutes more than 80 percent of the hydrocarbonreserves are unknown. Wet Neocomian gas and oil were generatedfrom Jurassic source rocks, including the Bazhenov Formation.
Almost all discovered reserves are in structural traps;however, stratigraphic traps in the Neocomian interval probablycontain large undiscovered gas resources. The onshore and offshoreparts of the total petroleum system were assessed as separateunits because of different exploration maturity and differentinfrastructure requirements. The onshore area is substantiallyexplored, especially in the shallow Aptian–Cenomaniansequence, whereas only three exploratory wells have been drilledoffshore. Undiscovered gas potential of both assessment units isvery high.