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Abstract: Implications of Seismic Interpretation on Reservoir Architecture at Tengiz Field, Kazakhstan

Rex A. Hanson, Malik Musagaliev, Spencer S. Quam

Vintage 1982-89 2-D and 3-D seismic paper sections over the Tengiz Field were scanned and loaded to an interpretation workstation as a tight (500 meter) 2-D orthogonal grid. Tops from 80 wells were converted to time and tied to the seismic lines using recently recorded velocity surveys in workover wells. These velocity surveys showed little velocity variation across the carbonate platform, which allowed a simple velocity space to be developed for depth conversion.

Previous mapping shows the field to be a large, unfaulted, dome-like carbonate platform/flank where platform facies grade smoothly into detrital flank facies, and facies thicknesses are thinned by erosion from platform to flank. The new mapping shows onlapping clinoform geometries for the flank sediments and at least four periods of faulting.

Earliest faulting appears to be rifting of the Devonian Clastic section, which provided a subtly elevated horst block upon which later Devonian and Carboniferous carbonate platforms grew. Steep, syndepositional, small-offset faults that lose throw with depth occur within the carbonate platforms, and were probably caused by differential compaction of platform sediments. Later slump faults, probably of Bashkirian age, developed within the detrital material on the flanks and sole out with depth. There is evidence that at least part of these fault planes may actually be onlap surfaces of detrital sediments against the steep platform walls. The youngest faulting is due to movements of the Kungurian salt layer which immediately overlies the carbonate reservoir. These faults detach within th salt layer without penetrating the reservoir facies.

New features brought forth from the seismic interpretation include: possible reservoir compartmentalization due to flank faulting and facies onlap, possible enhanced permeability near fractures on the platform, and potential for drilling hazards very near to fault planes. Many of these features have since been corroborated by careful review of drilling and production histories.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France