BarentsKara

Petroleum Geology of the Barents and Kara Seas

Internet Geology News Letter, No. 14, October 11, 1999

Three structural stages are recognized in the sections of the Barents and Kara Seas. In the Barents Sea region the lowest is basement, which consists of rocks of various ages. The middle is represented by Paleozoic carbonate and clastic rocks of the platform cover; it is an offshore continuation of the Paleozoic rocks of the Timan-Pechora oil-gas province of northeastern European Russia. The upper stage consists of a clastic complex of the shelf basins, within which four sub-stages are recognized: Upper Permian - Triassic, Jurassic - Lower Cretaceous, Upper Cretaceous - Eocene, and Oligocene - Quaternary.

With rise of the Ural Mountains in mid-Permian time, deposition in the Barents Sea region shifted from largely carbonates to entirely clastics. Thickness of the Upper Permian - Triassic section is a few kilometers in the basins along the margins of the Barents Sea and on the Central Barents high, whereas in the more subsided regions it is 8-10 km thick. Of this, 5-7 km is Upper Permian. Thickness of the Triassic is 3-5 km in the North Barents depression and 5-6 km in the South Kara depression.

The Jurassic - Lower Cretaceous sub-stage is characterized by maximum transgression in the Arctic Ocean, reaching a peak late in the Jurassic when bituminous clays collected over broad areas of the shelf. Thickness of this part of the section is 2-3 km in the north of West Siberia, 1.5-2.5 km in the South Kara depression, and 500-600 m on the shelf of the Pechora platform. The upper part of the Jurassic - Lower Cretaceous section was eroded in some places during the neotectonic stage, and consequently original thickness must have been much greater.

The Upper Cretaceous - Eocene, and Oligocene - Quaternary clastics are present sporadically on the shelf of these Northern Seas.

The large volumes of sediments at depths greater than 4 km suggest that these regions may be gas-prone. Volume of the sedimentary pile in million cubic kilometers is 11 for the Pechora-Barents basin, 18 for the West Siberian basin, and 4 for the North Kara basin. Their areas in thousand sq km is 1600, 2900, and 720, respectively.

Commercial petroleum has now been found in the Paleozoic clastic-carbonate and Upper Permian - Mesozoic clastic complexes of the Barents Sea region. In the first of these are the large Prirazlon oil field and Severo-Gulyayev oil-gas-condensate field of the Pechora Sea. The large Murmansk and medium Severo-Kil'din gas fields occur in rocks of the Upper Permian - Triassic sub-stage in the south of the Barents Sea. The Jurassic - Lower Cretaceous sub-stage is particularly favorable for new discovery. Present there are the unique (super-giant) Shtokmanov and Ledov gas-condensate fields and the large Ludlov gas field.

Recent faulting had led to extensive redistribution of gas deposits of the study regions, particularly along the margins of the basins (Petroleum Geology, vol. 32, no. 2, p. 107-114, 1998).

Assessment of the Pechora, Barents, and Kara Seas recognizes 50 zones of oil-gas accumulation (plays) on the Russian offshore shelves with total hydrocarbon reseouces on the order of 190 billion barrels of oil equivalent (BBOE), of which 91 BBOE have already been discovered.

The Pechora shelf is assessed to contain 5.5 BBOE of hydrocarbons. Gas reserves of the Mesozoic of the Barents Sea are placed at 108 tcf. In the South Kara oil-gas region the largest of the 13 recognized zones (plays) are assessed to contain 32 BBOE (Petroleum Geology, vol. 34, no. 1, p. 47-52, 2000 - in press).