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CGG Geoscience, Houston, TX

Abstract: Improved Correlations Within Reservoir and Seal Intervals by Use of Stratigraphically Layered Seismic Inversion Techniques for Upper Cretaceous Sandstones, Sacremento Basin, California, USA

A gas play was established in marginal marine sandstones of the Upper Cretaceous Winters Formation in Solano Co. CA during 1992. The discontinuous sands are stratigraphically trapped along the west-dipping basin paleoshelf. The entire reservoir and seal interval has very minor thickness changes, initially suggesting relatively uniform subparallel correlations within the major stratigraphic packages. However, production results suggested complex correlations and pinchouts are present. No dipmeter logs were run for paleocurrent or primary dip calculation.

A 1995 3D seismic dataset suggested subtle amplitude variations within the reservoir interval, confined to a one half-cycle seismic trough. The seismic data were inverted, and the resulting 3D impedence volume indicated at least three inclined 8-10 ms thick layers of similar impedences at the reservoir interval, within a stratigraphic interval of relatively uniform thickness. Comparison of the impedence layers with the well logs improved internal correlations within the reservoir sandstone interval and the relatively characterless shaly seal units immediately above. This interpretation is consistant with the interpreted environment of deposition, but more detailed than either the seismic or well log interpretation alone allows. The particular strength of this approach is that existing seismic and well log data are used, but combined in a new way.

AAPG Search and Discovery Article #90918©1999 AAPG Southwest Section Meeting, Abilene, Texas