Oil and gas in reef reservoirs in the former USSR

Productive reefs in the former USSR are known from the Lower Cambrian to the Upper Jurassic. They contain more than 31% of the oil and about 29% of the gas resources of the FSU occurring in carbonate reservoirs. Giant and supergiant fields such as Karachaganak, Tengiz, Zhanazhol, Shurtan etc. are associated with reefs. Reservoir architecture and variation of reservoir properties depends upon the shape and origin of the reefs. Zones of improved reservoir properties are located in the central parts of dome-like reefs or in circumferential or ring-shaped zones in the atoll-like reefs. In asymmetric reef systems the best reservoir intervals are shifted towards the bioherm zone and forereef slope.