Geologic Framework for the Tengiz and Korolev Fields,
Kazakhstan—Carboniferous Isolated Carbonate Platforms

The supergiant Tengiz field exhibits depositional features typically observed in isolated carbonate platforms but rare for the Carboniferous: extensive inner and outer platform deposits, a raised rim feature, steep platform margins, and thick flank deposits. Many of the same platform and slope features observed in Tengiz are inferred from much less well data for Korolev.

The Tengiz and Korolev platforms formed during the Carboniferous on the Primorskian Arch, one of several structural highs in the southeast portion of the Caspian Basin in western Kazakhstan. The platform edges are abrupt, showing a relatively rapid change from the platform top (platform, shoal, or platform margin) to slope environment. Platform deposition includes cycles shoaling upward from open marine packstones to shoal grainstones. A reef (microbial boundstone with scattered megafossils) is localized to a very narrow belt along the platform margin. Boundstones give way downslope to breccias and finally argillaceous lime mudstone beds. A variety of open porosity types are present; karst zones are best developed in the rim and fractures characterize both the rim and flanks.

A hierarchy of cycles, sequences, and composite sequences is developed by integrating core and well logs with newly acquired 3D seismic data. The stratigraphic framework, although not finalized, explains many aspects of the reservoir quality. The buildup (actual thickening) of the platforms was seemingly initiated in the Devonian and accentuated greatly during Visean time. The areal extent of both platforms generally diminished during the Carboniferous as evidenced by backstepping of the younger margins.