Accuracy of 2.5D Seismic FDTD Modeling in the Presence of Small Scale Borehole Structures

The frequency dependence of the reflection coefficients can be an important interpretational tool in detecting and analyzing seismic anisotropy. We perform such analysis on experimental data containing multi-azimuth reflections from a simple water-plexiglas interface, where the underburden is designed to represent an HTI medium. We show that the frequency dependency of the AVO response of the data at pre-, near-, and post-critical offsets reveals clearly some of the anisotropy features of the HTI model including the azimuthal variation. Using the theory of effective reflection coefficients extended to HTI media, we can explain some of these observations, especially the offset dependency and the azimuthal variation for the post critical offset case. However, attenuation, among other physical phenomena present in the experiment, rendered the effective reflection coefficient theory useless in predicting the small frequency dependency and azimuthal variation at pre- and near-critical offsets.