Full wavefield least-squares reverse time migration

Abstract

Waveform inversion based on least-squares reverse time migration (LSRTM) usually involves Born modeling, which models the primary-only data. As a result, the inversion process handles only primaries and corresponding multiple elimination preprocessing of the input data is required prior to imaging and inversion. Otherwise, multiples left in the input data are mapped as false reflectors, also known as crosstalk, in the final image. At the same time, the developed full-wavefield migration (FWM) methodology can handle internal multiples in an inversion-based imaging process. However, because it is based on the framework of the one-way wave equation, it cannot image dips close to and beyond 90°. Therefore, we have aimed at upgrading the LSRTM framework by bringing in the functionality of FWM to handle internal multiples. We inject the secondary source term, as used in the original formulation of FWM, to define a wavefield relationship that allows modeling multiple scattering via reflectivity. The secondary source term is based on the estimated reflectivity and can be injected into the pressure component when simulating the two-way wave equation using finite-difference modeling. We use this modified forward model for estimating the reflectivity model in an FWM-type manner and validate the method on synthetic and field data containing visible internal multiples.