Exploration drilling on the Barents Shelf has disclosed a spatial- genetic association of large gas deposits with the Shtokmanov-Lunin mega-saddle. The presently known pools are on the south flank of the Barents-Kara belt of highs but with small but different distances from the crest region. At the same time in a whole series of anticlines located at considerable distance from the Barents-Kara belt of highs the Jurassic resevoirs are water-flooded or exhibit weak gas flows. This circumstance indicates a key role of the ancient positive structure in formation of the large zones of regional gas accumulation on the Barents Shelf. Some aspects of this control are unclear; however, most of them have now been confirmed.
Structural and facies reconstructions of the Jurassic Period are a basis for proposing that formation of the reservoirs and seals during this time was controlled by positive paleo-structure. In Middle Jurassic time and in part in the Late Jurassic individual high regions of the Barents-Kara belt of highs were subjected to erosion, products of which were transported into the surrounding depressions in the marine basin. Evidence of this are clinoforms that show up on the seismic sections. Judging from the dimensions and direction of inclination of these clinoforms, the most abundant detritus was derived from the Fersman high, which lies in the western part of the belt. These erosion products were deposited on the paleo- flanks of the highs to form highly poropus sandy reservoirs, sealed by transgressive Jurassic clays.
Conditions favorable for generation of hydrocarbons obtained for a long time in the basins next to the Barents-Kara belt of highs. They were the most favorable in the thick, largely clay units of the Triassic of the rift depressions with their high heat flow. The organic matter of these Triassic sediments penetrated by wells in the south part of the shelf is only humic or mixed type. However, indications of marine clays have been noted in the north of the Late Permian- Triassic mega-downwarp both by seismic data and geological observations in Franz Josef Land. This indicates presence there of sapropelic organic matter and therefore the possible presence of oil pools on the north flank of the Barents-Kara belt of highs.
Within the Barents-Kara belt of highs the Shtokmanov-Lunin mega-saddle is particularly favorable of hydrocarbon accumulation. It has been a region of petroleum accumulation from neighboring depressions, and it contains thick Jurassic and Cretaceous sediments that carry good reservoirs and seals. Structures have been preserved in spite of extensive structural changes.
Structures of the Shtokmanov-Lunin mega-saddle type are expected to be present extensively in association with the Barents-Kara belt of highs and should be prime targets for oil-gas exploration.
Taken from Gramberg, Suprumenko, and Shipel'kevich, 2001.
Digested in Petroleum Geology, vol. 36, no. 1, 2002, in preparation;
three paleo-structural maps, two cross sections, and one seismic
section.
Copyright 2001 James Clarke. You are encouraged to print out
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