Velocity model building with wave equation migration: the importance of wide azimuth input, versatile tomography, and migration velocity analysis

摘要

Wave equation migration is suitable for imaging in complex structures. Ideally, its imaging capability should be matched bycorresponding velocity model building tools. However, the tool of choice for velocity model building, ray-based tomography,at first sight seems weakly compatible with wave equation migration. To overcome this contradiction we propose severalstrategies. The first is to convert the wave equation migration image gathers, typically indexed by subsurface offset, into aformat appropriate for tomography: local reflection angle or its tangent. In conjunction with this conversion, we employa datuming procedure to restrict the tomography to a localized domain where it is compatible with the wave equationmigration band-limited propagation. A second strategy, more expensive and not yet widely tested, is to replace ray-basedtomography with wave-equation-based migration velocity analysis, assuring complete compatibility with the imaging. Inall cases, we notice that having wide-azimuth data makes velocity model building easier, as any chosen subsurface azimuthcontains specular information.