MILEY, MONICA, Rice University, Houston,Texas;WALTER KESSINGER, Houston Advanced Research Center,The Woodlands,Texas

Abstract: Converted Modes in Subsalt Seismic Exploration

The goal of this work is to improve subsalt imaging through modeling and processing of converted shear waves from a Gulf of Mexico data set. These waves typically present obstacles to subsalt imaging and interpretation where they appear particularly strong. While converted modes obscure primary wave reflections and confuse identification of geologic horizons, they are also a potential source of information where illumination by primary waves is poor. In order to utilize this energy it is necessary to understand, characterize, and identify converted modes in data. Processing procedures must be tailored to account for the raypaths of these waves for imaging. Seismic modeling is used to study these events: to predict their strength, location, and understand their amplitude response. Models characterize conditions in which converted modes show promise for improving imaging and demonstrate whether these waves are sensitive to changes in rock properties. Models are also compared with subsalt data from Green Canyon to distinguish converted modes from primary events. Migration algorithms are adjusted for various shear wave raypaths through a salt body by selecting different velocity models. Additionally, the migration aperture is adjusted to discriminate for converted modes. Modeling and processing of converted modes for subsalt exploration has several potential benefits which include: improvements in base of salt imaging and interpretation, identification of artifacts, and possibly information about rock properties.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England