Full Wavefield Migration to Image Salt-flanks Using Turning Waves in Walkaway VSP Data

Abstract

Imaging of steeply-dipping or overturned salt-flanks is still a challenge for conventional migration techniques applied to surface seismic data. In the past, walkaway Vertical Seismic Profiling (VSP) data has proven to add value in mapping or imaging the steep salt-boundaries. In this paper, we discuss an extension of the Full Wavefield Migration (FWM) scheme to image salt-flanks using the turning waves in VSP data. FWM is an inversion-based imaging algorithm, that utilizes all the multiples (surface and internal multiples) in the observed unblended or blended VSP data to explain the subsurface reflectivity. The extended FWM uses both vertical and horizontal wavefield extrapolation in the imaging scheme and, therefore, is able to image complex and steep-dip structures. In this paper, we briefly discuss the forward modelling and inversion scheme, followed by some numerical examples to illustrate the imaging of steep structures. These examples involve both unblended and blended VSP experiments, and also illustrate the effect of complex overburden in the imaging of salt-flanks.