Velocity Resolution And Salt Boundary Placement In Subsalt Imaging

The interpretation of salt geometry is a critical aspect of velocity model building for 3D salt and subsalt<br>imaging. Here we investigate the effect of salt boundary placement error in the velocity model building<br>process. Using an example from deep water Gulf of Mexico, we first illustrate how velocity resolution<br>drops beneath salt . We then show how an error in salt boundary placement can produce significant<br>residual moveout in prestack migrated gathers. If this residual moveout is interpreted as arising from a<br>velocity anomaly in the sediment, a velocity update of the sediment will introduce error into the sediment<br>velocity model that in turn introduces false structure into the depth image. We show for this example that<br>the correct placement of salt both flattens gathers and eliminates the false depth structure. Techniques<br>for distinguishing between sediment errors and salt boundary placement errors are discussed.