Processing, correlating, and interpreting converted shear waves from borehole data in southern Alberta

Borehole measurements coupled with phase information from Zoeppritz equation modeling has assisted in accurate correlation between a VSP converted S-wave section and both the surface and VSP P-wave sections from southern Alberta. For the most part, both the character and polarities of the sections agree; however, there are some differences. Some reflections are stronger and more distinct on the S-wave section than on the P-wave section. Spectral analysis of the time-domain upgoing P-wave and S-wave energy shows that the frequency content of the S-waves is comparable to the P-waves. Thus, the slower velocity S-waves have a shorter wavelength and provide better vertical resolution of some interfaces. Other upgoing S-wave modes can interfere with the P-SV mode and contribute to the differences between the P- and S-wave sections.The match between P-wave and S-wave velocities (V (sub P) and V (sub S) ), determined from VSP traveltime inversion and the full-waveform sonic log, is best in the Paleozoic carbonate section; there is some discrepancy in Cretaceous sandstone intervals. A basal salt unit in the Paleozoic Beaverhill Lake formation has a VSP-determined V (sub P) /V (sub S) ratio of 1.97, suggesting that salt can be distinguished from carbonates using both P-wave and S-wave velocity information in this region.