Subsalt velocity update and composite imaging using reverse-time-migration based delayed-imaging-time scan

摘要

Defining the correct velocity is critical for proper subsalt imaging.Asubsalt velocity perturbation scan based on wave equation migration is an effective way to update subsalt velocity and has become a standard industry practice. A factor limiting its use is that the cost of generating migration scans remains comparatively high. With the even more expensive reverse-time-migration RTM tool progressively becoming a routine, the extension of this subsalt-velocity-perturbationscan approach to RTM becomes impractical. We propose a new methodology for updating subsalt velocity using an RTM-based scan composed of multiple migrated images. Rather than perturbing the velocity, each image is produced by a variable time-imaging condition. The zero-time imaging condition generates the normal RTMoutput, and the positive and negative nonzero-time delayed imaging time, or DIT imaging condition generates a scan of images called a DIT scan. The generation of the RTM-based DIT scan requires only a single RTM pass. Synthetic and field data examples confirm the effectiveness of this new approach and suggest the DIT scan approach could serve as an efficient alternative or even a replacement to the standard subsalt migration scan approach forRTM.