A Comparison of AVO Behavior after Prestack Time Migration, Prestack Depth Migration, and Prestack Imaging

James Allen, Carolyn Peddy, Anat Canning, Glen Denyer

In the presence of strong lateral velocity gradients or structural complexity, prestack depth migration may be required for AVO analysis in order to properly image the prospective reflectors. The use of prestack migration for AVO analysis presents a conceptual problem in that the migration process collapses seismic energy to the image point where source-receiver locations coincide. This of course removes the dependence of seismic information with angle of incidence. Therefore, prestack migration algorithms used for AVO analysis should be specially designed. Until this time, we have compared the AVO results of prestack time migration and prestack depth migration for data with a simple velocity structure and for data with a complex velocity structure to test the ability of restack depth migration to maintain relative amplitudes. We also tested a velocity-independent time-migration approach know as prestack imaging (PSI). The first example is data across a Gulf Coast bright spot that corresponds to a gas-producing sand. Dips in the small fault block containing the bright spot are about 6???. The reflection from the gas sand displays an increase in amplitude with offset. The AVO behavior of the prestack time migrated CMP gathers matches the Zoeppritz ray-trace AVO model derived from the well logs. The prestack depth migration we used is a Kirchhoff routine. A quantitative measure of amplitudes at varying offsets at the target reflection was compared for each gather covering the bright spot for the three processing techniques. The relative amplitudes of the p estack time and depth migrated gathers were similar. The PSI results were also qualitiatively similar, although the algorithm was not specifically designed for relative amplitude preservation. The second comparison was made for a seismic survey crossing a structurally complex zone in the Arkoma Basin of Oklahoma.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995