Map migration and 3D modelling in a complex velocity medium

Abstract

Many structures cannot be adequately migrated by two-dimensional methods unless the orientation of seismic lines is such that every line is effectively a dip line. This is rarely the case, and on steep sided structures such as salt domes or pinnacle reefs, severe misties will probably exist after two-dimensional migration, making mapping impossible. One solution is to shoot a 3D survey, but this is expensive and the migration algorithm will have to be chosen carefully if dips significantly greater than 50 or 60 degrees are involved. A quicker and cheaper approach is to migrate a time map. However, several questions must be answered before assessing the validity of the results. In particular, how sensitive is the migration to the input velocity model and how detrimental to the final result is the omission of multi-valued points, such as bow-ties?