The North Caucasus - Mangyshlak oil gas province extends over an area of about 600,000 sq km from the Black Sea on the west through the North Caucasus region, the Middle Caspian Sea, and into the Mangyshlak-Ustyurt region of Kazakstan. It is part of the Scythian and Turan platforms.
The Mangyshlak-Ustyurt region is in the western part of the Turan platform and is the area immediately east of the Middle Caspian Sea. The sedimentary cover there consists of two structural complexes: a Paleozoic-Triassic intermediate complex up to 11 km thick and a Jurassic-Quaternary typical platform complex up to 5 km thick. From north to south are three large east-west-trending structural features: North Ustyurt depression, Central Mangyshlak-Ustyurt zone of highs, and South Mangyshlak- Ustyurt zone of downwarps.
Present temperature fields and vitrinite paleo-reflectance indicate that massive hydrocarbon migration has taken place in the pre-Cretaceous rocks, reaching peaks between early and middle Miocene and again in post-Pliocene time. Migration was along newly activated faults. The equilibrium status of fluid systems was disturbed, leading to redistribution of formation waters and hydrocarbons, and consequently to redistribution of oil and gas pools. Indications of migration are the lack of correspondence between source beds and pools, the genetic similarity of all the oils from the Paleozoic to the Cretaceous, and gas anomalies in formation waters. Some indication of post-Pliocene formation of pools is the presence of gas caps on oil pools that are significantly undersaturated by gas.
At the present time the migration process has peaked out and stabilized except in the pre-Jurassic sedimentary rocks of the Zhetybay-Uzen tectonic step and Peschanomys-Rakushech domal uplift , located in the northwestern part of the South Mangyshlak-Ustyurt zone of downwarps. This stability is indicated by near normal formation pressures over most of the region.
Where formation pressure is more than 5-10 percent greater than the normal, it is supposed that fluids are in process of being redistributed. This is the situation in the above mentioned Zhetybay-Uzen tectonic step and Peschanomys-Rakushech domal highs. These overpressures are in fractured reservoirs. Taking into account that this fracturing is relatively late, the hydro- carbon pools in this part of the section are assumed to be in process of formation at the present time. Underpressure found in the Uzen field and Aginysh area is interpreted as being the result of dissipation of formation waters from the Cretaceous sediments.
Taken from Kraychik, 1987; digested in Petroleum Geology,
vol. 24, no. 3/4; one map and one graph of formation pressure.
Copyright 2001 James Clarke. You are encouraged to print out
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