Abstract

The Temir license area of western Kazakhstan lies at the eastern edge of the Precaspian salt basin, a prolific emerging basin of the former Soviet Union. The recent exploration phase resulted in the discovery of an oil field that shed a new light on postsalt (Triassic and Upper Permian) hydrocarbon plays.

Geologically, the area is dominated by salt tectonics. Typical salt-related structures are the site of potential hydrocarbon accumulations charged from presalt source rocks. These structures were evaluated using conventional data sources such as gravity, wells, and seismic lines. New information was gained from the combination of topography, seismic data, and satellite imagery: (1) the relationship between surface morphology and underlying structure, (2) comparison between faulting and seepage information, and (3) an understanding of salt withdrawal history.

The best reservoirs are Triassic and Tatarian continental sandstones. Older Kazanian sandstones, a mixed evaporite-clastics succession, show very poor reservoir parameters. The integration of well results (cores, wire-line logs), outcrop information, and seismic data indicates (1) seismic facies studies are not sufficient to discriminate between Tatarian (reservoir-rich) and Kazanian (reservoir-poor) sequences because both successions commonly exhibit comparable seismic characters; (2) evaluation of reservoir potential based on the analysis of stacking velocities can be erroneous, particularly in narrow salt withdrawal minibasins and on seismic lines close to salt structures; and (3) reservoir prediction in the Tatarian and Kazanian successions can be estimated based on the analysis of prestack depth migration (PSDM) velocity models on conventional two-dimensional seismic lines. For example, fast PSDM velocity value ranges derived from the model correspond mostly to Kazanian mixed clastics-evaporite sequences that have poor reservoirs. Slower velocities, however, indicate sections that have better quality reservoirs. Thus, we recommend using PSDM velocity analysis coupled with core calibrations to predict reservoir potential and quantify porosity values in complex salt-related prospects such as salt overhangs and salt flank traps.

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