Traveltime Inversion of Walkaway VSP Data for a Model with Dipping TI Layers

Walkaway vertical seismic profiling (VSP) data potentially provides the most reliable anisotropy estimates. In many cases, a 1D model is not quite adequate for real data. If walkaway first break function is not symmetrical with respect to the well, then we need a velocity model with dipping/curvilinear boundaries. In this paper, I present a traveltime inversion approach for transverse isotropy (TI) parameter estimation that takes into account lateral velocity changes in the overburden. I describe these changes with dipping boundaries above the shallowest receiver. Dipping boundaries, interval velocities and anisotropic TI parameters in the overburden are included, together with simultaneous estimations of anisotropic parameters within the receiver array depth interval. Tests on model data show reliable anisotropy estimates. This approach was applied to multi-azimuthal walkaway data.