The belt of shallow water directly adjacent to a shore line of a marine basin is designated as a "transition zone". It has long been inaccessible for marine geophysical surveys and onshore study. As a consequence the correlation of offshore and onshore information depended to a great extent on remote sensing methods, largely magnetic surveys. For this reason these transition zones have remained a blank spot on many maps of oil-gas potential.
Many onshore oil-gas areas located close to marine basins extend offshore. Such shallow-water zones are prime targets because extrapolation from the onshore is not that much of a problem. Even small fileds may be economic. The transition zones include coastal marshes, embayments, banks, river deltas, shallow- water reefs, broad tidal zones, littoral zones, and shallow-water coastal sectors, where water depth is generally less than 10-15 m. Typical of all of these are conditions that are not favorable for seismic surveying.
Some provinces, regions, and fields extend into transition zones. Such fields as Kharasavey in Yamal and Medyn in the Pechora Lowland are divided by the shore line into almost equal parts. The zone of the Russian Shelf with shallow water depths of 0-20 m extends over an area of 570,000 sq km, and the Arctic Shelf is assessed to contain up to 25 percent of the total Arctic offshore resources.
In the west of the Arctic Shelf are two large oil-gas provinces, the transition zones of which have high potential. One of these is the broad shallow-water area adjacent to the Pechora Lowland and Kolguyev Island. Traps there are small and pay zones have a wide stratigraphic range. Density of predicted resources of individual sectors of this transition zone is commensurate with maximum values of resources of well studied onshore structures. The shallow-water zone of the Mezen depression in the south of the Barents Sea may also offer good targets.
Another broad favorable belt of shallow water is in the Kara Sea. This is a direct continuation of the West Siberian province. A whole series of large fields extend offshore from Yamal and Gyda Peninsulas. In spite of relatively simple and well studied geology, geophysical investigation of these transition zones is difficult.
Favorable shallow-water zones are known also in the eastern
Arctic Sea, but they have received little study. The Ust'-Khatanga
and Ust'-Lena shallow-water areas are the most favorable. The latter
is located on a continuation of the Mid-Atlantic Ridge and conditions
are similar to those of California. The entire Yano-Indigirka Lowland
along with a broad belt of shallow water is favorable; however, its
development is decades away. Taken from Verba and others, 2000;
digested in Petroleum Geology, vol. 35, no. 3, one map, in preparation.
Copyright 2001 James Clarke. Earlier News Letters are available at
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