Iterative Pre-Stack Depth Migration With Velocity Analysis

Abstract

Migration image critically depends on the chosen velocity model. In principle, correct velocities are needed to obtained a correct migration image; however, such a priori knowledge of accurate velocity distributions are not always possible. In this case, a reliable velocity analysis technique is definitely needed to avoid improper data interpretation. Post-migration common-depth gather provides an excellent domain for controlling migration velocity. Examining the migrated data collected at the same depth point form different shot records, it may be understood if the initial velocities were correct and how best to approach a correct migration image. By incorporating the migrated common-depth gather with the pre-stack layer-stripping reverse-time migration technique, an iterative pre-stack depth migration scheme has been successfully developed with velocity analysis. The proposed algorithm analyzes migrated data iteratively until the accurate velocities are achieved. Once the correct velocity is obtained, the bottom of the migration layer may also be determined. This method allows the user some quantitative control over the final migration image. In this paper, the authors illustrate the success of the iterative velocity analysis method by using synthetic data. Field data applications are discussed elsewhere.

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