True-amplitude CRS-based Kirchhoff time migration for AVO/AVA analysis

The achievable image quality and the reliability of amplitudes in Kirchhoff migration strongly depend on the selection of the migration aperture. Too small an aperture leads to meaningless amplitudes and/or the loss of steep events. On the other hand, too large apertures tend to cause operator aliasing and include unnecessary noise and contributions from unwanted events. Our aim is to use minimum apertures based on the results of the Common-Reflection-Surface stack method in Kirchhoff prestack time migration to obtain optimized input for AVO/AVA analyses. The basic idea is demonstrated for a synthetic data set where we consider a common sequence of gas/oil/water contacts beneath a dome-like structure. We discuss the determination and extrapolation of stationary points and projected Fresnel zones based on CRS wavefield attributes, as well as a simple and efficient way to set up a migration velocity model. The results show a significant reduction of amplitude dispersion in common-image gathers as well as in the resulting AVA crossplots.