Image-guided WEMVA for azimuthal anisotropy

Azimuthal anisotropy is common in layered basins with strong folding and fracturing effects. Traditional processing on individual azimuths usually yields images with inconsistent depths. In this paper, we propose to use an image obtained from one azimuth to constrain the image-space velocity analysis on other azimuths. This method directly tackles the differences in anisotropic parameters among different azimuths. By keeping the vertical velocity constant across the azimuths, we separate the kinematic effects due to the anisotropic parameters from those due to the velocity error. We test the imageguided migration velocity analysis algorithm on a 2-D example with flat reflectors and a homogeneous orthorhombic subsurface. We compare the residual images and the first η gradient obtained by our image-guided method with the differential semblance method under three different conditions: accurate velocity, fast velocity and slow velocity. Our results show that despite the velocity error, the image-guided migration velocity analysis algorithm provides consistent η gradients, whereas the gradients given by differential semblance optimization may be misled by the velocity error.