Determining P-wave Azimuthal Anisotropy from Walkaround VSP with Offset-dependent Slowness Corrections

P-wave local slowness data from a walkaround VSP can provide a measure of azimuthal velocity anisotropy to characterize fractured rocks or stress fields around a well. When the acquisition is constrained to have irregular shot points, shot-offset-dependent corrections are required. For unconventional plays, a correction for background polar anisotropy might also be necessary to effectively extract the azimuthal anisotropy around the well. This study introduces a modified total slowness and a two-step correction technique to remove the background VTI and minimize the residual offset bias in the walkaround VSP. Field data tests demonstrate that this new technique can provide a quick and quantitative measure for the orientation and magnitude of fracture- or stress-induced azimuthal anisotropy.