We have reformulated the law governing the refraction of rays at a planar interface separating two anisotropic media in terms of slowness surfaces. Equations connecting ray directions and phase‐slowness angles are derived using geometrical properties of the gradient operator in slowness space. A numerical example shows that, even in weakly anisotropic media, the ray trajectory governed by the anisotropic Snell’s law is significantly different from that obtained using the isotropic form. This could have important implications for such considerations as imaging (e.g., migration) and lithology analysis (e.g., amplitude variation with offset). Expressions are shown specifically for compressional (qP) waves but they can easily be extended to SH waves by equating the anisotropic parameters (i.e., ε = δ ⇒ γ) and to qSV and converted waves by similar means. The analytic expressions presented are more complicated than the standard form of Snell’s law. To facilitate practical application, we include our Mathematica code.

A three-component 3D vertical seismic profile (VSP) was acquired over the Blackfoot oil field in Alberta, Canada. The VSP survey was recorded simultaneously with a surface seismic program. The objectives of the VSP were to develop recording logistics, data handling, and processing procedures and to determine if the 3D VSP volumes could image the glauconitic sand reservoir of the Blackfoot field.Dynamite shots from the surface seismic survey, which fell within a 2200-m offset from the recording well, were used in the VSP analysis. The shots were recorded by a string of three-component borehole receivers that was moved seven times, resulting in a receiver depth range of 400 to 910 m. The borehole data were processed using basic VSP processing techniques that included hodogram analysis, wavefield separation using median filters, and VSP deconvolution. The final P-P and P-S image volumes were obtained by VSP common-depth point and VSP common-conversion point stacking the upgoing wavefields followed by f -x y deconvolution. The P-P and P-S images from the VSP correlate well with those from the surface seismic survey. Time slices from the VSP also indicate the trend of the sand channel of the Blackfoot field.

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A simultaneous surface and borehole 3C-3D survey was acquired over the Blackfoot field in southern Alberta. Along with the land surface 3C-3D seismic program covering about 15 sq. km., 3-C VSP measurements were made over depths from 400 to 910m. In this paper, we outline the acquisition and processing considerations involved with the Blackfoot 3C-3D VSP experiment. Final P-wave and converted-wave images from the 3-D VSP tie reasonably well with those from the surface survey. A method was also developed for rapid VSPCDP mapping and results are shown for the VSP data.

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