A multi-offset Vertical Seismic Profiling (VSP) experiment for anisotropy analysis and imaging

A multi-offset Vertical Seismic Profiting (VSP) experiment;was carried out in the Rocky Mountain Foothills of Southern Alberta, Canada. The purpose of this survey was to determine I;whether the dipping shale strata in the stu dy area exhibit seismic velocity anisotropy, and to obtain an estimate of t he error in the imaged location of the target underneath these shales if an isotrophy is not taken into account during seismic data processing. Travelt ime inversion of the first arrival data from the multi-offset VSP has revea led that the shales exhibit velocity ansiotrophy of about 10%. For a target depth of about 3,000 m and moderate dips of 30 degrees to 50 degrees in th e anisotropic overburden, this may lead to a lateral shift in the imaged lo cation of the target of up to 300 m in the up-dip direction of overlying be dding. The anisotropic parameters derived from this study will also be used in the anisotropic prestack depth migration of the VSP and surface seismic data.