Orthorhombic full-waveform inversion for wide-azimuth data imaging

The presence of orthorhombic anisotropy poses serious challenges in multi azimuth (MAZ) or wide azimuth (WAZ) data imaging. Orthorhombic anisotropy makes seismic velocity vary with azimuthal direction as well as polar direction. The polar direction dependency can cause well misties and higher order moveout. On the other hand, the azimuthal dependency can cause noticeable moveout fluctuation between different acquisition directions and hence prevent constructive summation of WAZ images, especially for the fault imaging. We have presented a ray-based tomographic inversion methodology for WAZ data model building in the presence of orthorhombic anisotropy in last year SEG (Zhou et al. 2015). However, in geologically complex areas, such as in the presence of complex faults or shallow gas clouds, the effectiveness of ray-based tomographic inversion is limited in providing high resolution velocity model, which is needed to optimize the final image of the complex structures. In this paper, we developed an orthorhombic full waveform inversion approach for building high resolution velocity model. We demonstrate that our method can effectively reconstruct high resolution orthorhombic model which not only fits with geology well but also significantly improves the focusing of the fault imaging with the WAZ OBC data. The combined effect of these improvements is a step-change in the final seismic image quality.