The super-giant Tengiz field of western Kazakhstan produces oil from an isolated Devonian and Carboniferous carbonate platform that extends over 160 km2. Seismic and well data clearly show two principle regions within the buildup—platform and flank—that directly relate to reservoir quality and production characteristics.

The supersequence stratigraphic framework was developed through an integrated interpretation of seismic, core, log and biostratigraphic data. An initial broad Late Devonian platform was followed by punctuated backsteps during the Tournaisian and Viséan. The Serpukhovian is characterized by several kilometers of platform progradation. Drowning in the Early Bashkirian halted carbonate platform growth. Paleotopographic relief from the top of the Bashkirian platform to the basin floor approaches 1,500 meters.

On the platform, hydrocarbons are produced from Upper Viséan through Bashkirian grainstones and mud-lean packstones. Multiple porosity types are recognized, but matrix permeability is controlled primarily by intergranular porosity. Within the flanks, in-place, upper slope, microbial boundstone and transported lower-slope boundstone debris form thick and areally extensive mappable reservoirs. Late Viséan and Serpukhovian reservoirs have distinctive seismic facies and production/ performance characteristics. Fractures contribute to non-matrix permeability in these boundstones.

The coarse stratigraphic architecture was used to further subdivide the platform portion of the reservoir for better reservoir characterization and reservoir modeling. The temporal and spatial variability in reservoir quality of the platform, as shown by cross sections and maps, is directly related to stratigraphy. The reservoir is also partitioned based on geographic position along a platform-to-basin profile. Time-slice mapping of synchronous depositional facies provides the basis for predicting reservoir distribution and continuity.

Acknowledgments

This study was very much a team effort. The ExxonMobil “Tengiz team” is acknowledged for its hard work and many discussions of all aspects of Tengiz geology. Kevin Putney created porosity and isopach

Unnumbered Figure. Location map of the super-giant Tengiz field of western Kazakhstan which produces oil from an isolated Devonian and Carboniferous carbonate platform.

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maps for the various reservoir layers, Steve Bachtel interpreted seismic cross sections and maps, and Tom Kane analyzed well production data. Ray Garber and Phil Bassant (ChevronTexaco) provided core descriptions, which were instrumental in our work. We warmly thank Jeroen Kenter (Vrije Universiteit, Amsterdam), Paul Brenckle (Consultant) and Tom Heidrick (TengizChevroil) for the many stimulating technical discussions in the core warehouse facility at Tengiz. Jeroen’s knowledge of modern and ancient carbonate slope settings and Paul Brenckle’s biostratigraphic data were invaluable to our studies.

Also, we recognize the significant contributions of the following people from ExxonMobil (I. Mitchell, S. Perkins, L. Vaughn, B. Evans, P. Allred and J. Grillot) and TengizChevroil (D. Fisher, A. Azizi, P. Bateman, C. Brown, N. Dzhamikeshev, E. Furlin, J. Hohenberger, K. Nahm, O. Petrova, B. Robertson, L. Rowe and A. Tyshkanbaeva). We thank TengizChevroil and its shareholder companies (ChevronTexaco, ExxonMobil, Kazmunaigaz and BPLukArco) for support of our studies and permission to publish this paper.

Unnumbered Figure. Carbonate geological model for Tengiz field.

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