Improving pre-salt targets using wave-equation velocity analysis

Abstract

Despite continuous improvements in model-building technologies, imaging below salt remains challenging. Reflection full-waveform inversion (RFWI) is effective at providing low-wavenumber velocity updates beyond the penetration depth of diving waves, however it is still susceptible to amplitude mismatch between input and modeled data. It also suffers from limitations imposed by narrow-azimuth (NAZ) seismic acquisition. To reduce the adverse impact of amplitude differences between input and modeled data, we present here a stack-power waveequation migration velocity analysis (WEMVA) method. Differently than RFWI, this method uses an objective function defined in the image domain. Therefore, it depends more on the kinematic part of the propagated wavefields, resulting in a more reliable inversion scheme. We also introduce a regularization term that reduces the footprints created in the velocity updates by NAZ seismic data. We demonstrate the effectiveness of this method by using synthetic and field data with NAZ acquisition geometries. Finally, we discuss some of its limitations, and suggest ideas for further improvements.