--> ABSTRACT: Tengiz Oil Field, Kazakstan: A Carbonate Platform and Supergiant Field, by William R. Wood and Raymond A. Garber; #91019 (1996)

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Tengiz Oil Field, Kazakstan: A Carbonate Platform and Supergiant Field

William R. Wood and Raymond A. Garber

The Tengiz oil field was discovered in 1979 on the northeastern shore of the Caspian Sea in western Kazakstan. The Carboniferous and Devonian age carbonate reservoir is more than 2000 m thick, 270 km2 in areal extent and buried to a depth of 4000 m (13,120 ft). The oil column exceeds 1450 m in length and is highly overpressured.

The Tengiz reservoir resembles a modern day constructional-type carbonate platform in size, shape and lithofacies. The top of the platform is relatively flat, except for structural highs along the northern, eastern and southern platform margins that developed during post-depositional down-faulting of the platform interior. The platform edge is a depositional escarpment along which subsequent faulting has occurred. Debris-slope conglomerates, shed off the platform during growth, surround the platform escarpment.

Bashkirian age oolitic, crinoidal, algal grainstones comprise the upper 100 m of the platform and overlie 350 m of Serpukhovian and Okskian age brachiopodal, crinoidal, algal packstones. Lithofacies are areally widespread and show little variation in composition and statigraphic thickness across the entire platform. Depositional cycle thicknesses are less than 5 meters for the Bashkirian grainstones and up to 30 meters for the Serpukhovian/Oksky packstones. Lagoonal and reefal lithofacies have not been identified in core to date.

Porosity is highly variable and includes interparticle, moldic, channel, vuggy and fracture pore types. Solid bitumen is present in much of the pore space. Secondary porosity formed both before and after bitumen precipitation. Production logs and core data reveal that zones with secondary porosity provide fluid entry into the wellbore.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California