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

摘要

Defining the correct velocity is critical for proper subsaltimaging.Asubsalt velocity perturbation scan based on waveequation migration is an effective way to update subsalt velocityand has become a standard industry practice. A factorlimiting its use is that the cost of generating migration scansremains comparatively high. With the even more expensivereverse-time-migration RTM tool progressively becominga routine, the extension of this subsalt-velocity-perturbationscanapproach to RTM becomes impractical. We propose anew methodology for updating subsalt velocity using anRTM-based scan composed of multiple migrated images.Rather than perturbing the velocity, each image is producedby a variable time-imaging condition. The zero-time imagingcondition generates the normal RTMoutput, and the positiveand negative nonzero-time delayed imaging time, or DITimaging condition generates a scan of images called a DITscan. The generation of the RTM-based DIT scan requiresonly a single RTM pass. Synthetic and field data examplesconfirm the effectiveness of this new approach and suggestthe DIT scan approach could serve as an efficient alternativeor even a replacement to the standard subsalt migration scanapproach forRTM.