Complete anisotropic analysis of three component seismic data related to the marine environment and comparison to nine component land seismic data
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To facilitate the transfer of knowledge from one arena to another, a comparison between nine component, controlled polarization shear-wave land seismic data and three component mode converted seismic shear-wave data was made. The continuing movement of petroleum exploration into the offshore arena and the increasing number of aging offshore oil fields may necessitate the use of shear wave data for full characterization of reservoir properties for finding, characterizing, and prolonging the life of the oil fields through the description of anisotropy as an analog for rock properties. Operationally limited to the use of compressional seismic sources in the marine environment, mode-converted shear-wave data recorded by three component seismic receivers must be exploited to arrive at full characterization of anisotropy. Effective media theory, seismic modeling, and post stack analysis including four component matrix rotations and numerous other tools developed on land were adapted and used offshore. A full understanding of anisotropy, shear wave birefringence and polarization was required to evaluate the similarities and differences between direct shear vi waves and mode converted shear waves. The investigation of seismic anisotropy related to shear waves began with the Cymric Oil field in California, progressed out into shallow waters of the Gulf of Mexico to the Teal South Oil Field, and finished in the Williston Basin, Saskatchewan, Canada. It has been revealed that not only can lessons be learned from the historical practice of nine component seismic analysis on land and applied to the marine environment, but that also the reverse is true. The use of full azimuth, full offset data and prestack analysis was developed and has served to extend present day anisotropic analysis beyond its current limitation of 1D application. Pre-stack converted shear-wave layer stripping analysis techniques developed include extraction of a azimuthal and offset variant time-shifts for birefringence correction, as well as the analysis of azimuthal and offset variance in amplitudes and reflected polarization. A numerical comparison between controlled source polarization, direct shear-waves and uncontrolled source polarization, mode converted waves, led to a correction for apparent polarization effects on the direct shear-waves and a correction for incomplete acquisition geometry for mode-converted waves.