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Analysis of Conventional and Converted-Mode Reflections at Putah Sink, California, Using Three-Component Data

Clint W. Frasier, Don F. Winterstein

In 1980, Chevron recorded a three-component seismic line, with P and SH vibrators, over the Putah Sink gas field near Davis, California. The purpose of this line was to record the total vector motion of conventional P and SH reflections and converted P-SV waves.

As seen in earlier Conoco data, the P section shows the well-known gas bright spots at producing well locations, and the SH section shows none. Shot profiles of P source data displayed strong converted P-SV events on the expected radial horizontal component. Quite unexpectedly, the SH source profiles showed low amplitude but clear SV-P converted waves on the V component. These were produced by SH splitting into components, one of which arrived at the interfaces with significant SV energy. At reflection, these SV components were converted to P waves, which arrived at the receivers in a clean time window ahead of the primary SH events.

The two converted wave types were stacked by common reflection point (CRP) instead of common midpoint (CMP) to correct for the asymmetry of reflection ray paths. CRP stacking improved P-SV and SV-P event resolution and laterally aligned structural features with their counterparts on the conventional P and SH sections.

AAPG Search and Discovery Article #91035©1988 AAPG-SEPM-SEG Pacific Sections and SPWLA Annual Convention, Santa Barbara, California, 17-19 April 1988.