Abstract: Geologic Model for Tengiz Field, Kazakstan

Chuck Rubins, Jerry Anthony, Koubental Suyesinov, Malik Musagaliev

Tengiz Field in Kazakstan, located on the southeastern margin of the Pre-Caspian basin, is a giant oil field which produces high quality crude oil from Carboniferous-age limestones. Current production is from -3917 m to -5197 m subsea. The deepest wells in the reservoir (to -5429 m subsea) have not penetrated an oil-water contact. Extensive processing of Soviet-era well logs and interpretation of limited seismic data and core material have led to a consistent geologic model of a build-up analogous to modern carbonate banks such as the Bahamas. Seismic and biostratigraphic data and log correlations define a flat central platform surrounded by flanks with a slope of 10 to 15 degrees. Permian shales and a thick salt layer serve as a seal for the high pressure, hydrogen sulph de-rich oil. Faults intersect the platform and flanks and, combined with stratigraphic complexity, compartmentalize the production. Porosity and permeability in the reservoir derive from primary features and a complex sequence of secondary sources, including karst, dissolution and probably fractures. Bitumen occludes some pore space in the reservoir which complicates the interpretation of effective porosity. Porosity generally decreases with depth in the reservoir and this factor will control the currently unknown limits of deep production.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela