Wave-equation based pre-stack processing for two-dimensional seismic data

Conventional seismic processing produces a good image of the subsurface only for geological structures that can be characterized by flat layers or layers with small dips and constant velocities. Standard seismic techniques like statics, velocity analysis, and CMP stacking are based on the assumptions that recording apertures are small, moveout is hyperbolic, reflections are precritical and there are no lateral velocity variations present within a CMP. Data from areas with complex tectonics may contain strong lateral velocity variations, steep dips and/or wide recording apertures. Standard seismic data processing fails to produce an acceptable image in these cases, as these data do not satisfy many of the assumptions built into the system. Wave-equation based, prestack migration is recognized as a better way to process such data, but in most cases, preliminary processing such as elevation and statics correction are still applied through the CMP processing.; The goal of this dissertation is to design, implement and apply a simple, but complete, wave-equation based processing system with fewer assumptions and fewer processing steps than conventional processing. A complete, wave-equation based, prestack processing system using reverse-time migration was developed for 2-D seismic data. This system has only two main components; Velocity Analysis and Prestack Depth Migration. Velocities are estimated by tomographic imaging of prestack traveltimes including both reflection and refractions. This has the effect of increasing the effective aperture of the observations, and hence of better constraining the velocity estimation. The estimated velocity distribution becomes the basis of implicit statics corrections in prestack migration. The estimated velocities are interval velocities. Reflection tomography and prestack migration are used iteratively to get the best focussed image.; Field data from the Andean orogenic belt in South America, provided by Mobil Oil Company, with extreme topography were successfully processed using the prestack system with no a priori geological or geophysical information.; The prestack system developed here contains a highly streamlined processing philosophy that takes full advantage of the properties of the wave equation and so naturally integrates and collapses most of the steps in standard processing.; This system was tested on an iPSC860 machine as it is ideally suited to parallel processing; each common-source gather may be processed independently. Finally, the prestack approach presented here is well-poised to take advantage of future developments in full-wavefield inversion as well as anisotropic processing.