Wells are now (as of 1986) being drilled in the Dnieper-Donets depression to depths greater than 5000 m. The Kotelev-Berezov tectonic zone located in the northern part of the central graben is particularly favorable for such deep plays.
Commercial gas-condensate pools have now been discovered in upper Serpukhovian and upper Visean sediments in the 4500 to 5850 m depth interval. The lower Visean-Tournaisian, which occurs at depths greater than 6000 m, is considered to be favorable.
Kotelev-Berezov zone is an elongate high, within which are several anticlines.
The upper Serpukhovian sediments (micro-fauna horizons V-VIII) are in the 4500-4850 m depth interval and consist of alternating sandstones, siltstones, argillites, and rare beds of clayey limestone and coal. Total thickness of sandstones is 50-95 m. Pay zone B-16a is comparatively persistent and is up to 18-22 m thick.
Petrographic studies of the upper Serpukhovian and upper Visean pay zones in wells 50 and 47 of Berezov area show differences in reservoir properties. Sandstones in well 47 on the flanks of the structure have low porosity and permeability, whereas those from well 50 at the crest of the structure have good reservoir properties. The poor properties on the flanks are due to conforming contacts of the mineral grains, and the good properties at the crest are due to dissolving carbonate cement and partial corrosion of quartz grains.
Authigenic minerals are found in de-cemented sandstones of well 50 - ankerite, sphalerite, kaolin minerals, barite, pyrite, leucoxine, and solid carbonaceous matter. Sandstones of the identical section in well 47 do not contain sphalerite and barite, and ankerite and clay minerlas are insignificant.
Testing of sandstones of the lower part of Horizon B-16a in well 50 in the 5460-5492 m interval yielded a commercial flow of gas and condensate at 2080 thousand cubic meters per day through a 20 mm choke, and the upper part gave 1545 thousand cubic meters per day from the 5427-5446 m interval.
Faulting has contributed to the reservoir properties of these sandstones.
Taken from Krivosheya and others, 1986; digested in
Petroleum Geology,Vol. 23, No. 7/8.
Copyright 2003 James Clarke. You are encouraged to print
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