Seismic data is usually acquired with a 3D geometry for exploration and exploitation purposes. This 3D geometry allows for the resolution of dipping, or oblique reflectors and eliminates the concern of sideswipe. 2D data is still being acquired and designed to be normal to the geological structures. However, some reflector may be oblique to the 2D line and may not be imaged correctly. These oblique reflectors can be imaged by varying the velocities during a poststack time migration, and then the best focusing velocities can used to estimate the angle of obliquity.
Should the same concept be applied to a prestack time migration? No.
Prestack time migration is very sensitive to the migration velocities which aids in defining accurate migration velocities. However, small perturbations in velocity can create significant artifacts. Therefore the prestack migration should be used to create one migrated section using the best velocities. Then this migrated section could be re-migrated to simulate poststack migrations with percent velocities, in an attempt to image oblique reflectors.
View full article as PDF (2.17 Mb)