Paper Summary

It is well understood that accurate salt interpretation is critical to subsalt imaging. When reflections from the saltsediment boundaries are not discernible, it takes many iterations to test various scenarios based on the geologic consistency of reflectors underneath the salt. Multiple iterations with wave equation migration are extremely time consuming and its computational cost is unacceptably high. We have developed a new methodology by incorporating demigration, fast beam migration, and polygon-based salt model update. We first demigrate a prestack depthmigrated image to a subsurface datum, which provides well-focused reflections at their unmigrated locations on a regular grid. Next, we pick inline and crossline ray parameters by dip scan. We then carry out fast beam migration to test different salt boundaries to evaluate the geologic consistency of reflections under the salt. This methodology enables us to interactively test many scenarios to generate the final model much faster than iterations using other migration techniques. Application to a 3-D field data set from the Gulf of Mexico demonstrates the effectiveness our methodology