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University of Wyoming, Department of Geology and Geophysics, IER, Laramie, WY

Abstract: A Sonic Anomaly Study of the Sacramento Basin, California

The Sacramento basin, one of the primary gas reserves in California, is comprised of depositional units that are predominantly submarine in origin, with shelf, slope, deltaic and submarine canyon-fill facies represented. All of the units have endured a severe tectonic history, as the western coast of the North American continent has been subjected to subduction and to accretion events throughout the basin?s evolution. Lateral fluctuations due to depositional environments and the unrelenting tectonism have conjoined to increase the difficulty with which economical reserves can be found.

The primary goal of this study was to test an analysis method based on sonic anomalies that has met with success in Laramide basins in defining hydrocarbon horizons by identification of overpressured zones. Sonic logs were obtained and compiled into a digital database, which was then used for the analysis.

The anomalous sonic velocity horizons derived from the database defined three-dimensional surfaces which coincided well with the known producing horizons in the basin. This study reinforces the validity of the sonic anomaly method as an exploration tool and demonstrates its more broad application to basins developed under different tectonic and depositional regimes than the Laramide basins in which the method was originally applied.

AAPG Search and Discovery Article #90919©1999 AAPG Rocky Mountain Section Meeting, Bozeman, Montana