Structural-velocity estimation -
imaging salt structures

Jos van Trier

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ABSTRACT

Depth migration is often needed for the correct imaging of salt structures. However, the velocity model necessary for the migration is hard to determine in salt regions, because of large lateral velocity variations and poor data quality. In previous reports I discussed a gradient optimization method to estimate a structural-velocity model in these regions. The method is based on the inversion of perturbations in prestack migrated events, where the events correspond to structural boundaries picked from the migrated image. The optimization does not require picking of prestack data; the data part of the gradient is determined from local semblance calculations. A preliminary analysis of a dataset recorded above a salt structure explores the difficulties in salt imaging, and illustrates the gradient calculation.