Dip correction for coherence-based time migration velocity analysis

Abstract

Migration velocity analysis (MVA) is a seismic processing step that aims to translate residual moveout in an image gather after migration with an erroneous velocity model into velocity updates. An analysis of the position of a reflection event in an image gather after migration with an incorrect velocity allows us to extend the original coherence-based MVA approach to dipping reflectors. The extended MVA technique includes the reflector dip which is treated as an additional search parameter that is to be detected together with the velocity updating factor. Both parameters are searched for simultaneously by the application of two-parameter search techniques. The search consists of determining trial curves as a function of the search parameters and stacking the migrated data along these curves. The highest coherence determines the best-fitting curve and thus the optimal parameter pair. A numerical example demonstrates that the additional search parameter improves the quality of the velocity updates, thus requiring less iterations in the MVA.