Abstract

The processing of seismic data in areas of complex geological structures has always been most demanding on conventional processing techniques. Many of the algorithms used are based on simple geologic models and therefore impose limitations in the resolution of the image. This paper compares two recent developments in seismic processing used to image data: dip moveout (DMO) and prestack migration. Either process approximately solves the problem of multivalued moveout due to dip dependence and raypath effects due to depth-dependent interval velocities.

DMO corrects for the dip dependence of moveout and inherently applies a migration correction. This is only a partial prestack migration shift and the data after stack requires a post-stack migration. Depending on the changes in interval velocity with depth, the DMO operator used is based either on a time-invariant or time-variant DMO algorithm. To some extent the velocity variation dictates the choice of migration method used for the post-stack migration.

Prestack migration is implemented as an extension of post stack migration by using the data organized in common offset planes. For economic reasons, data recorded with high fold will usually be decimated before migration. Once the migration is completed, the data is reorganized into the common depth point (CDP) domain. The velocity analysis for stack will use this migrated data. A commitment to a velocity field for migration is usually delayed to the latest stage possible but with prestack migration this step must be taken before stack.