Kolguyev Island, Barents Sea

Internet Geology News Letter No. 16, October 25, 1999

Kolguyev Island in the southeast of the Barents Sea measures 80 by 80 km. It is of particular interest for regional exploration. Seismic surveys were made on the island from 1983 to 1990. As of 1995 more than 50 wells had been drilled. The fields that have been discovered are at depths of 1700-2000 m and occur in Lower Triassic rocks.
In Peschanoozer field in the eastern part of the island the Lower Triassic secton is host to gas, gas-condensate, and oil pools. The first impression is that there is no regularity to the occurrence of the pools. Restoration of the ancient relief, however, discloses that the pay zones are sandstones of ancient river systems that existed during the Early Triassic. Beginning with a basal sandstone there are eight sedimentational rhythms. As a rhythm is understood the sediment that accumulated from the time a river was introduced into an area until its final disappearance. Due to meandering of a river, a rhythm is not a continuous sand body but rather a group of individual strata separated by clay seams.
The oils of Peschanoozer field are intermediate between ordinary oils and gas condensate. They may be oils of gas-condensate origin. A heavy isotopic composition of the carbon of the methane in the northern part of the Timan-Pechora province indicates generation at depths greater than 7 km in the thermal gas window. This suggests that the main flow of gas in the Timan-Pechora province including that of Kolguyev Island was introduced from the Barents Sea region on the north, where the sedimentary section is thicker and deeper. It is proposed that high-temperature gas flowed from the Barents Sea region to pass through oil pools in Permian and/or Carboniferous carbonates dissolving oil from them. This oil-gas-condensate system migrated along the basal member of rhythm A and then migrated vertically into the overlying reservoirs where it underwent phase differentiation (Petroleum Geology, vol. 32, no. 2 p. 151-156, 1998).
The Paleozoic section has now been drilled extensively on Kolgulev Island. Six litho-stratigraphic complexes are recognized: 1) Ordovician transgressive clastics; 2) Lower Devonian clastics and carbonates; 3) Upper Devonian clastics and some carbonate in the Famennian; 4) Lower Carboniferous - dark gray to black, organic-rich clastics and carbonates in the Tournaisian, carbonates and black shale in the Visean, and light anhydrite and carbonate in the Serpukhovian; 5) Middle Carboniferous-Sakmarian largely carbonates including reefs; and 6) Artinskian-Tatarian largely clastic from the rising Urals.
The Lower and Middle Paleozoic section of Kolguyev Island is typical of a young platform. Then the Upper Carboniferous-Sakmarian section exhibits a different facies zonality. A chain of reefs convex to the north extends across the island. To the south was a lagoon in which anhydrite-bearing sediments collected. It is proposed that deep-water sediments collected to the north of this reef belt (Petroleum Geology, vol 32, no. 2, p. 157-166, 1999)

Copyright 1999 James Clarke. You are encouraged to print out this News Letter and to forward it to others. Kolguyev