In the last decade, much of 3D seismic signal processing has been replaced by the single imaging process called prestack depth migration. Rapid advances in resolution and illumination have changed the way we explore, delineate, and monitor reservoirs. We now see more attention turning to the velocity models that make such depth imaging possible. For this supplement to the September-October 2008 issue of GEOPHYSICS, we invited summaries of existing practices, descriptions of new approaches, and case studies that illustrate the practical aspects of building and updating velocity models.
Velocities are implicit in every imaging or moveout-sensitive processing step. Velocities still consume the most hours of human labor and interpretation during seismic processing. We cannot simply delegate the geologic implications of a velocity model to a later interpretive step. We need velocities for a seismic image, an image for interpretation, and interpretation velocities.