Stratigraphic Architecture, Lithofacies, and Reservoir Quality: Tengiz and Korolev Fields, Caspian Basin, Kazakhstan

Harris, Paul (Mitch)¹, Joel F. Collins², Kevin L. Putney², Akmaral Zhumagulova³, Dennis J. Fischer³ (1) ChevronTexaco Energy Technology Company, San Ramon, CA (2) ExxonMobil Development Company, Houston, TX (3) TengizChevroil, Atyrau, Kazakhstan

Tengiz and Korolev are isolated carbonate platform reservoirs separated by less than 15 kilometers in the southeastern portion of the PriCaspian basin. They have similar thickness and stratigraphic age range, but Tengiz is large (100 km2) compared to Korolev (7 km2).

Eight sequences are recognized within the Tengiz and Korolev platforms from seismic and well data: Devonian, Tournaisian, Visean D, Visean C, Visean B, Visean A, Serpukhovian, and Bashkirian. The Tournasian through Visean C sequences form the transgressive portion of a second-order supersequence that culminated in near-drowning of both platforms. The Visean B through Serpukhovian sequences comprise the regressive part of the superse­quence. This regressive phase is characterized by up to 2 kilometers of basinward progra­dation during the Serpukhovian; the progradation is asymmetrical and irregular at both plat­forms.

Reservoirs in the Visean A through Bashkirian sequences are dominated by interparticle porosity and matrix microporosity in grain-rich facies over much of the Tengiz platform, whereas vugs and solution-enlarged fractures produce drilling circulation losses in micro­bial boundstone slope facies surrounding the platform. Lost circulation greatly enhances well productivity and reservoir connectivity in this facies even though it is commonly asso­ciated with scattered, relatively thin high permeability zones. At Korolev, secondary pore­types and lost circulation zones are present in the both the platform and slope facies in the same reservoir intervals, resulting in increased connectivity throughout the field.