Kenter, Jeroen A.M.¹, Paul (Mitch) Harris², Dennis Fischer³, L. James Weber⁴ 
(1) Vrije Universiteit, Amsterdam, Netherlands 
(2) ChevronTexaco Energy Technology Company, San Ramon, CA 
(3) TengizChevroil, Atyrau, Kazakhstan 
(4) ExxonMobil Exploraton Company, Houston, TX

ABSTRACT: Production from the Steep, Deep Flanks of an Isolated Carbonate Platform

Tengiz field in western Kazakhstan field produces oil from an isolated carbonate platform and its flanks. A broad Devonian platform exhibits accentuated vertical growth; backsteps of the platform margin occurred during the Tournaisian and Visean. The Serpukhovian is characterized by several kilometers of platform progradation, seaward of the Late Visean platform break and followed by drowning and termination of the platform in the early Bashkirian. Platform to basin relief during the Bashkirian approached 1.5 km. 
Late Visean and Serpukhovian slope facies form thick and aerially extensive reservoirs with distinctive seismic facies and production/performance characteristics. The upper slope typically consists of massive cement-rich boundstone, micrite-rich structureless boundstone and, in-place mosaic breccia. The middle slope (300-700 m) is layered with detrital boundstone breccia, crinoid dominated rudstone, and platform-top derived grainstone-packstone and argillaceous spiculitic lime mudstone. Finally, the latter 2 facies types and volcanic siltstone and sandstone progressively dominate the lower slope and basin, 700-1500 m. 
Fractures are generally restricted to the massive upper slope facies and can contribute significant non-matrix permeability. Fracture orientation indicates the dominant orientation of effective fractures is parallel to the margin. Flow and production in the platform are dominated by the stratigraphy in the sense that there are vertical permeability baffles that can be related to sequences and/or cycles. In contrast, flow and production in the flank are dominated by fractures that impart a tremendous amount of vertical connectivity. These contrasting characteristics are clearly shown by production logs (MDT pressure profiles) and the actual production data.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.