Abstract

We use seismic modeling of shot records to simulate the effects of acoustic-wave propagation, P/SV-wave conversion, intrabed multiple reflections, anelastic attenuation, and transverse isotropy in materials representative of a shallow Gulf of Mexico environment. The study focuses on the estimates of three kinematic properties: vertical traveltime, velocity used for depth conversion, and depth to the reflector. The primary tool used for the measurement is velocity spectral analysis along hyperbolic traveltime-distance curves.Analyses of numerous modeling experiments in the Gulf of Mexico environment lead to the following conclusions: First, the kinematic properties are affected mainly by anelastic attenuation, vertical velocity heterogeneity, and velocity anisotropy. The effects of P/SV-wave mode conversion and intrabed multiples are of secondary significance. Second, anelastic attenuation coupled with heterogeneity contribute up to 3 percent in depth error, mainly in the form of apparent time delays. Transverse isotropy is likely to add up to an additional 2 percent, for a total of 5 percent depth error. Since the depth error magnitude agrees closely with published field observations, we conclude, therefore, that attenuation, heterogeneity, and transverse isotropy account for most of the errors in depth estimation in horizontally layered media.

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