Prestack depth imaging of multi-azimuth seismic data in the presence of orthorhombic anisotropy

Abstract

The presence of orthorhombic anisotropy can severely affect the imaging of multi- and wide-azimuth data which is rapidly developing with the benefit of better illumination, better imaging, and better multiple elimination. Analysis of multi-azimuth (MAZ) data often reveals noticeable fluctuations in moveout between different acquisition directions, preventing constructive summation of MAZ images. Vertical transverse isotropy (VTI) effects can also co-exist causing well misties and higher order moveout. We have developed an approach for imaging in the presence of orthorhombic anisotropy. In this paper, we first describe our approach, including a newly developed orthorhombic imaging method and a newly developed practical method for orthorhombic anisotropy model building. We then demonstrate with both synthetic and real data from offshore Australia that our approach can successfully take into account the coexisting HTI/VTI effects, reduce the structural discrepancies between seismic images built for different azimuths, thereby producing constructive summation of MAZ datasets and resolving well misties to match with geology. The combined effect of these improvements is a step-change in the final seismic image quality.