Abstract

This work provides explorationists with simple procedures to perform depth conversion more accurately than can be achieved with simple vertical layer cake depth conversion. The use of image rays, which are inadequate in structurally complex areas, is avoided. Migrated time interpretations are still used and are 'demigrated' using the Kirchhoff time migration equations. This backs out the effect of the time migration prior to a ray depth migration and enables the lateral shifts between the time migrated image and a depth migrated image to be quantified. These shifts can be separated into a mismigration component and a refraction component. The relative size of the components define whether time or depth migration is required and may be used to justify a remigration of the seismic image. Furthermore, the tedious layer by layer approach to ray depth migration may be avoided by using the velocity depth model from the vertical layer cake depth conversion of the time-migrated data for ray depth migration of the unmigrated data for all horizons in a single step. A satisfactory result is usually achieved without the need to iterate. These methods are illustrated with both a synthetic example and a real 3-D data set from the Norwegian North Sea.

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