Summary

A new method is presented for extracting seismic polar anisotropy parameters, with the vertical resolution of the seismic wavelet, from prestack surface seismic data and vertical well logs. The method uses sonic

VP0, VS0

and

?

to construct an isotropic synthetic reflectivity gather, convolved with the (zero-phase) seismic wavelet, with no other propagation effects included. It uses a co-located surface CDP gather, in conjunction with this synthetic gather, to estimate the propagation effects. Then the arithmetric difference between the corrected seismic amplitudes and the isotropic synthetic amplitudes gives the jump in anisotropy parameters

d

and

e

at each major reflector in the logged interval. Integration of these differences, starting at a sandstone layer (with anisotropy assumed zero), yields a profile of the anisotropy itself. In a test case, this workflow yielded anisotropy parameters correlated with the gamma ray log. The anisotropic corrections were substantial.

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