Accurate well to seismic correlations of several producing sands and detailed analyses of reservoir characteristics have revealed hidden reserves in an aging field that was previously determined to be uneconomic. The combination of a recent 3D survey shot over Eugene Island Blocks 338 and 339, Gulf of Mexico, and new interactive workstation technology was instrumental in identifying swept and unswept portions of different oil reservoirs and allowed new infill wells to pinpoint key targets.

Seismic attributes were extracted along mapped horizons which showed lateral variations in reservoir properties, identifying depleted zones where the water front had passed through and areas it had missed. This observed seismic response is related to changes in water saturation associated with production and was verified by seismic modeling based on Biot-Gassman-Geertsman equations.

To apply these concepts, net pay maps for key reservoirs were constructed by calibrating detuned, composite amplitudes to pay thicknesses. The top and base of these net pay surfaces were displayed in geologic cross-sections to direct the paths of infill wells.

This proved to be a useful approach to plan conventional and horizontal well paths within the difficult internal stratigraphy of complex Pleistocene reservoirs having an associated structural complexity.

The result was a successful drilling program for Chevron and its operating partner Texaco. Chevron was able to participate in 11 out of 14 development wells after making a "turnaround" decision to keep what was once thought to be a marginal property.

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