Improvement of local anisotropy estimation from VSP data through experimental design

We investigate a linear inversion scheme to determine the local anisotropy around a well using multi-azimuthal walkaway VSP data. The input data consist of the vertical components of the slowness vector and the polarization vector of direct and reflected P-wave measurements. The inversion assumes that weak anisotropy can be modelled by first-order perturbations around an isotropic reference medium. This inversion scheme is not restricted to symmetrical classes of anisotropy and the well local orientation. Based on numerical simulations, we show that the inversion is sensitive to the number and orientation of the acquired azimuths. Using conservative assumptions regarding the noise level, phase velocity can be well estimated for a limited angular opening around the well local orientation. (paper)