Practical imaging of complex geological structures using seismic prestack depth migration

This thesis develops innovative procedures to address problems in imaging multi-channel reflection seismic data in regions of complex geology. Conventional common midpoint (CMP) based processing fails to produce adequate Earth images for complex geological structures with both vertical and lateral heterogeneities. Two powerful prestack depth migration techniques are developed through the integral and finite-difference solutions of the wave equation.; I first develop a new, robust, and accurate traveltime calculation method which is essentially a wavefront tracing procedure. This is implemented as a combination of a finite-difference solution of the eikonal equation, an excitation of Huygens' secondary sources, and an application of Fermat's principle. This method is very general and can be directly applied to compute first arrival traveltimes of incident plane waves. These traveltimes are extensively used by the Kirchhoff integral method to determine the integral surface, and also by the reverse-time migration to determine imaging conditions.; The prestack Kirchhoff integral migration of shot profiles which is developed using the WKBJ approximation to the Green's function is simply a summation of amplitudes of differential traces along an integral surface with amplitudes being modulated by certain geometrical functions. I demonstrate that this summation scheme along a general integral surface is the mathematically more rigorous extension of the summation scheme along diffraction surfaces and of the superposition scheme of aplanatic surfaces.; In contrast to the Kirchhoff method, reverse-time migration is based on a direct solution of the wave equation by approximating the differential terms of the wave equation with finite differences. It is theoretically more accurate than the Kirchhoff method since it attempts to solve the wave equation without a high frequency approximation. In addition to such attractions as implicit static corrections and coherent noise elimination based on velocity information, I find that there exist self-healing mechanisms of the wavefield due to constructive interference during the reverse-time propagation of the unaliased wavefield. The self-healing ability of waves thus provides the basis of migrating sparsely and irregularly sampled unaliased recordings relative to a fine finite-difference grid without prior interpolation of missing traces. This is particularly valuable in migrating unaliased shot records with a gridded velocity model as fine as common depth point (CDP) bins with no explicit trace interpolation.; Considering the nature of imaging in geologically complex areas, I view the geophysicists' goal of obtaining an accurate Earth image as an iterative interpretive imaging procedure. This procedure consists of an initial velocity model building followed by iterative prestack depth migration, geological interpretation and velocity analysis. I formulate a very general prestack depth migration velocity analysis method with illustrations of both simple and complex examples. (Abstract shortened by UMI.)...