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Stratigraphic Architecture, Lithofacies,
and Reservoir Quality: Tengiz and Korolev
Fields,
Harris, Paul (Mitch)1, Joel F. Collins2, Kevin L. Putney2,
Akmaral Zhumagulova3, Dennis J. Fischer3
(1) ChevronTexaco Energy Technology Company,
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.