Summary
Common-offset vector (COV) binning provides single-fold data sets that can be migrated with surface offset and azimuth preserved. The latter allows post-migration processing such as Radon demultiple or azimuthal residual moveout flattening to enhance the quality of the final stacked image. Single fold coverage enables each COV volume to produce a clean image with limited migration-operator artefacts, and with the potential to preserve the AVO character. However, in the COV domain, this works only for surveys with sources and receivers on the same acquisition datum and with a single-mode arrival having symmetric ray paths in a flat earth (such as P-waves). Irregular subsurface illumination for dual-datum acquisition or mode-converted PS-wave data causes artefacts in migration of COV binned data, including acquisition footprints. Here we describe a technique to reduce these artefacts. The method bins recorded data into gathers corresponding to each offset vector tile (OVT) and computes time and velocity-model dependent weighting and muting functions for each OVT gather in such a way that uniform illumination is obtained at all levels beneath a reference level.
Introduction
The concept of common-offset vector binning was introduced almost simultaneously by Vermeer (1998 and 2002) and Cary (1999) as an alternative to cross-spread binning for 3D wide-azimuth surveys. Conventional cross-spread processing assumes that reflection points and common mid-points (CMPs) share the same lateral location. However, ocean-bottom data and mode-converted PS-waves violate this assumption. Recently, Stewart and Gaiser (2011), Bale et al. (2013) and Gaiser (2014) have revisited COV processing problems of PS-waves, and demonstrated corrections for illumination area distortion.
In this paper we address problems with COV illumination for PP- and PS-waves of various geometries. The aim is to improve the reflection point distribution within a COV image. As opposed to Stewart and Gaiser (2011) and Bale et al. (2013) we describe time-dependent corrections of offset-vector tile gathers that can be applied for orthogonal cross-spread PS-wave land data and for PP- or PS-wave marine data of dual-datum ocean-bottom geometries.
