Angle-Domain Common-Image Gathers for Imaging of Multiples Using Poynting Vectors

Abstract

As a complementary to imaging of primaries, multiples can be used for imaging and produce additional angular illumination. These additional illumination angles can improve imaging resolution. There are several methods to calculate angle gathers from imaging of primaries, among which the directional vector methods are matured and have been implemented in practice. For conventional directional vector algorithms using common-shot reverse time migration, usually only one angle with the main contribution to each imaging point is collected, which is referred to as one-shot, one-position, and one-angle mapping strategy. This strategy is appropriate for imaging of primaries. However, the principle fails in imaging of multiples, where more than one angle exists at an imaging point even using a shot gather. Therefore, conventional directional vector approaches cannot separate different imaging angles produced by imaging of multiples. In this paper, we introduce the Poynting vector method to calculate angle gathers for imaging of multiples. Based on the one-shot, one-position, and one-angle mapping strategy, we search for the peak of modulus of Poynting vectors in a time window to differentiate imaging angles at an imaging point. The ray-path diagrams and angle-gather imaging conditions are used to demonstrate the improved angular illumination from imaging of multiples. Then, the arrival-time equation is derived mathematically to demonstrate wavefield arrival-time differences for different imaging angles from imaging of multiples. Based on the arrival-time differences, a Poynting vector algorithm is proposed to compute more than one angle at one subsurface location for imaging of multiples. Data examples are used to validate our approach.