Extracting Polar Anisotropy Parameters from Seismic Data



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With Vp, Vs, and density well logs, we can do isotropic AVO forward modeling, using isotropic Zoeppritz equations or its approximations, and a wavelet extracted from the seismic data, to get synthetic seismic data. Compared with real seismic data, these synthetic data are scaled differently, and ignore many propagation effects. Conventionally, the seismic data are normalized to the isotropic synthetic data for comparison; this procedure suppresses the anisotropy information in the real data. In this study, I tested a new method, using log data of Vp, Vs, and density, together with seismic pre-stack Common Depth Point (CDP) gathers near the well site, to deduce anisotropy parameters from them. This dataset is from Colony Sand, Alberta, Canada. I calculated the normalization function, as in the conventional procedure, but then filtered it in frequency domain using a cut-off frequency to be determined empirically. The low-frequency part of the normalization function was used to eliminate the propagation factors in the real data, but not the reflection coefficients. After scaling, the difference between the real data, thus normalized, and the isotropic synthetic data are attributed to the anisotropic part of the reflection coefficients. The resulting distributions of and are compared to the gamma-ray log. There is a positive correlation between the anisotropy parameter and the gamma-ray log, which is an indication of the validity of the method.



Anisotropy, AVO