A Comparison of Stratigraphic Architecture, Lithofacies, and Reservoir Quality in Adjacent Large and Small Isolated Carbonate Platforms: Tengiz and Korolev Fields, North Caspian Basin, Kazakhstan*
J.F. Collins1, K.L. Putney2, P.M. Harris2, A. Zhumagulova3, and D.J. Fischer3
Search and Discovery Article #20054 (2008)
Posted June 5, 2008
*Adapted from oral presentation at AAPG Annual Convention, Calgary, Alberta, June 19-22, 2005.
1 ExxonMobil Development Company, Houston, Texas
2 ChevronTexaco Energy Technology Company, San Ramon, California ([email protected])
3 TengizChevroil, Atyrau, Kazakhstan
Tengiz and Korolev are isolated platform complexes separated by less than 15 kilometers. They have similar thickness and stratigraphic age range, but Tengiz is large (100 km2) compared to Korolev (7 km2). Both platforms have similar sequence architecture and cycle thickness, suggesting that differential subsidence is only a minor factor governing platform evolution. Tengiz and Korolev thus provide an opportunity to examine the effect of areal extent on platform accretion, lithofacies, and reservoir properties.
Eight sequences are recognized from seismic and well data within the Tengiz and Korolev platforms: Devonian, Tournaisian, Visean D, Visean C, Visean B, Visean A, Serpukhovian, and Bashkirian. The Tournasian - Visean C sequences form the transgressive leg of a second-order supersequence that resulted in near-drowning of both platforms. The Visean B - Serpukhovian sequences comprise the regressive leg of the supersequence. At both platforms, this regressive phase is characterized by up to 2 kilometers of basinward progradation, primarily during the Serpukhovian. The Serpukhovian progradation is asymmetrical and irregular at both platforms, and the amount of progradation appears to have been controlled by the stacking geometries of the underlying aggradational Visean sequences.
The Visean A sequence demonstrates that the spatial distances over which platform facies variations occur appears to be independent of platform size. Visean A - Bashkirian reservoirs are dominated by interparticle porosity and matrix microporosity over much of the Tengiz platform. Vugs and solution-enlarged fractures become important only in the outer platform. At Korolev, these secondary pore types are more abundant throughout the platform in the same reservoir intervals, perhaps because of the comparatively greater number of fluid pore volumes that affected Korolev during later diagenesis.