TUCKER, JAMES W. and HALLIN, JAMES S.
CGG Geoscience, Houston, TX

Abstract: Detailed Correlations of Marginal Marine Reservoir and Seal Units in the Upper Cretaceous Winters Formation Sandstones, Sacramento Basin, California, USA

True 3D impedance inversion of modern 3D seismic data integrated with well log and other data have allowed improved correlation of reservoir and potential seal units in the Winters Sandstone Solano County, California. A gas play was established in this area in 1992, targeting the near-offshore Winters sandstones. The production results from correlated sandstones suggested discontinuous reservoirs within a defined stratigraphic package. A 1995 3D seismic survey over this area suggested subtle seismic amplitude variations in the reservoir interval, but the reservoir and gas pay intervals were much thinner than the seismic data wavelength at the objective depth. Well log correlations seemed variable, but confined to a narrow stratigraphic range. No dipmeter logs are available.

The seismic data were inverted to determine if subwavelength information could be derived. The resulting 3D impedance volume indicated inclined layers with similar impedances within a stratigraphic interval of relatively constant thickness. Comparison of the impedance layers with the time-scaled well logs allowed revised correlations of the sandstone reservoir units, as well as the difficult-to-correlate shaly interval immediately above. This interpretation is consistent with the presumed environment of deposition, but more detailed than either the seismic or well log interpretation alone allows. The strength of this approach is that it uses existing well log and seismic data, combined in a new way.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas