Paul M. Harris¹, Jeff L. Warner²
(1) Chevron Petroleum Technology Company, Houston, TX
(2) Consultant

Abstract: Slope Deposits of the Tengiz Platform — Core and Log Data from a Key Well

Tengiz Field, located in western Kazakhstan, produces oil from a Carboniferous isolated platform carbonate. Tengiz-47 (T-47) is a flank well located off the southeast edge of the platform; it is an important well from the perspective of understanding the nature of deposition, diagenesis, reservoir quality, and log response in the flanks of the Tengiz platform.

Stratigraphy and Facies - The Bashkirian through Visean (Oksky) consists of two general rock types: (1) coarse-grained (rudstones and grainstones rich in boundstone intraclasts), and (2) finer-grained (grainstones, packstones, and wackestones). Both rock types represent debris that was shed down the slope from the platform margin. The Visean (Tula) is predominantly fine-grained slope packstones.

Diagenesis - T-47 penetrated a generally limestone stratigraphy; however: (1) dolomite-rich intervals with 50% to 70% dolomite occur in the basal Serpukhovian, and lower Visean (Tula) through top Devonian; and (2) a silica-rich interval is present in the Visean (Tula). Bitumen fills 10% to 15% of the potential porosity (defined as core measured porosity plus bitumen) in most samples; higher amounts occur in Bashkirian samples.

Reservoir Quality - The Bashkirian through Visean (Oksky) slope deposits have trace amounts of open porosity of three types: isolated vugs, pores between clasts, and microfractures. The Visean (Tula) packstones are varyingly silicified, and a few small, open vugs are the only visible porosity. Wireline logs indicate a porosity distribution that is generally consistent with the limited core data.

Logs - The Visean (Oksky) slope deposits appear on an FMI log as irregular layers that are rarely continuous across the image. Dips up to 30° are to the east, southeast, and south. Distal slope deposits of the Visean (Tula) are characterized by thin layers that are continuous across the image. Dips of 10° to 20° are to the east and southeast, with rare dips up to 50°.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana