AVA and 3D VSP

While walkaways have been used to measure AVO for a long time and elastic properties have been recovered by inversion under an assumption of lateral invariance, the recovery of elastic properties away from the well is problematic due to the limited angular illumination provided by the typical multi-offset VSP geometry. Previous work on using walkaway VSPs for pre-stack elastic inversion made use of a 2D assumption and wavefield extrapolation to mimic a surface seismic geometry, but such approaches break down in 3D. In this paper the problem of AVA parameter estimation in multi-offset VSP imaging is studied using linear inverse theory and an algorithm that honours the true 3D VSP geometry is described that recovers information from AVA in pre-stack 3D VSP migrated images.