Depth migration from irregular surfaces with depth extrapolation methods

This note presents a technique that allows extrapolation in depth, through a grid, where shot and receivers are located on a nonflat surface. The proposed technique does not require any datuming or elevation static corrections before applying the migration. The technique can be applied to prestack depth migration algorithms, with no limitations on surface irregularity, complexity of the subsurface structure, or velocity function. After application of static corrections from the earth's surface to a smoothed surface ("floating datum'), the technique can be applied to poststack depth migration (Ellis and Kitchenside, 1989). The method is described with the simple phase-shift algorithm, followed by examples of prestack depth migration. -from Author