Velocity as an Attribute: Continuous Velocity Estimation from 3D PreSDM CRP Gathers.

Here we present a technique for obtaining high-resolution velocity information from pre-stack time or depth migrated data. Essentially we employ techniques of continuous velocity estimation used for iterative model update (Jones, et al, 1997, 2000), but apply them in a different context. Rather that using the velocity estimator strictly for velocity model building (on a set of sparse lines), we apply the estimation techniques to the common reflection-point (CRP) gathers resulting from the final pre-stack migration for all CRPs in the 3D survey. This achieves two things: firstly it estimates a residual velocity correction for stacking the final CRP gathers to obtain an enhanced image (Jones, et al, 1998a), and secondly, it delivers a dense estimate of velocity for the entire 3D volume in a geologically coherent manner. It is this second feature which is the subject of this paper.