The upper Famennian salt complex of Pripyat downwarp consists of halite and clay-halite sub-complexes. Organic buildups and anhydrite banks occur widely in the halite sub-complex in the north structural zone of the downwarp, where oil pools are associated with them in the Poles, Davydov, Zapadno-Tishkov, and Zapadno-Dubrov fields.
In those parts of Pripyat downwarp that have been studied the most the Lebedyan Horizon consists of six rhythm-member, at the base of which are limestones, anhydrites, dolomites, and marls, and in the upper part is halite. Thickness of the basal and halite members ranges from tens to a few hundred meters, and correlations are good.
The basal bed of the first rhythm-member rests directly on deep-water upper Yeletsa clayey-bituminous limestones. Thickness of this bed ranges from 100 m and more at the crests of paleo-highs to complete absence on the flanks of some structures. This bed is composed of anhydrite and forms an anhydrite arch 2-3 km wide, which extends for tens of kilometers along the Rechitsa-Vishan zone of highs. At the crest of the arch are thick (up to 50 m) stromatoporoid bioherms.
The basal beds of the next two rhythm-members have been studied in Ostashkovich field. The lower part of the second rhythm consists of dolomite that is in varying degree clayey, and clay content increases from crest to flanks. Thickness of this basal bed is 15-30 m. The third basal bed is limestone and dolomite at the crest and clayey anhydrite and halite on the flanks. Thickness is 10-15 m. Neither of these beds are good reservoirs.
The basal bed of the fourth rhythm-member is known as the "extensive marker", and it contains commercial oil pools in the eastern part of the downwarp in Zapadno-Tishkov and Zapadno- Dubrov fields. This bed consists of three parts: the lower and upper parts are carbonate, and the middle is anhydrite and halite. The lower part has good reservoir properties.
The basal beds of the other three rhythm-members are largely clayey limestone, marl, anhydrite, and halite pelites. No organic buildups have been found there.
The anhydrite banks and organic buildups are the most widely distributed where the basal beds are thickest (first and fourth rhythm-members) in the north structural zone. During Lebedyan time this area was high, and during periods of extensive transgression conditions were favorable for growth of blue-green algae, which was the main reef maker. Since maximum water depth for blue-green algae does not exceed 60 m, the depth of salt deposition was even less.
As for the central structural zone, depth of the basin during Lebedyan time was greater than 60 m, and conditions were not favorable for formation of anhydrite banks and organic buildups. In the south structural zone the intra-salt beds are sandstone and sandy-clayey limestone due to proximity of the Ukranian Shield, which was a source of clastic material.
These Late Devonian Famennian organic buildups have good porosity and permeability and are exploration targets.
Taken from Moskvich and Konishchev, 1986; digested in
Petroleum Geology, Vol. 23, No. 7/8, one map and one cross
section. Copyright 2003, James Clarke. You are encouraged
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