Prestack time-migration velocity analysis using remigration trajectories

Abstract

We have developed a prestack time-migration tool for local improvement of the seismic migration-velocity model. The method is based on remigration trajectories that describe the position of an image point in the image domain for different source-receiver offsets as a function of the migration velocity. It determines kinematic migration parameters using local-slope information of migrated seismic reflection events. These parameters, in turn, are used to locally correct the velocity model. The main advantage of this technique is that it allows us to carry out a moveout correction not just at a fixed point in a zero-offset (poststack) time-migrated gather, but varying through all offsets of a common-image gather, taking into account the reflection-point displacement in the midpoint direction. In other words, it provides for time-migration velocity analysis from prestack data. We have tested the feasibility of the method on synthetic data from four simple models and the Sigsbee2B data. Our tests determined that the proposed tool increases the velocity-model resolution and provides a plausible time-migrated image. The quality of the initial model is not critical. The procedure is quite efficient. Significant effort was spent on manual event picking.