PRESTACK DEPTH MIGRATION OF AN ALBERTA FOOTHILLS DATA SET - THE HUSKYEXPERIENCE

We produce depth images for an Alberta Foothills line by iteratively u sing a number of migration and velocity analysis techniques. In imagin g steeply dipping layers of a foothills data set, it is apparent that thrust belt geology can violate the conventional assumptions of elevat ion datum corrections and common midpoint (CMP) stacking. To circumven t these problems, we use migration from topography in which we perform prestack depth migration on the data using correct source and receive r elevations. Migration from topography produces enhanced images of st eep shallow reflectors when compared to conventional processing. In ad dition to migration from topography, we couple prestack depth migratio n with the continuous adjustment of velocity depth models. A number of criteria are used in doing this. These criteria require that our velo city estimates produce a focused image and that migrated depths in com mon image gathers be independent of source-receiver offset. Velocity m odels are estimated by a series of iterative and interpretive steps in volving prestack migration velocity analysis and structural interpreta tion. Overlays of velocity models on depth migrations should generally show consistency between velocity boundaries and reflection depths. O ur preferred seismic depth section has been produced by using prestack reverse-time depth migration coupled with careful geological interpre tation.