Time-lapse 4D full-waveform inversion for ocean-bottom cable seismic data with seawater velocity changes

ABSTRACT Time-lapse 4D full-waveform inversion (FWI) is a valuable technology for high-resolution imaging of reservoir changes caused by hydrocarbon production and CO2 storage. However, it still faces challenges in dealing with nonrepeatability issues due to changes in seawater or near-surface velocity between baseline and monitor surveys. Despite recent advances, the ability of 4D FWI to address this problem has rarely been demonstrated. We investigate the effectiveness of current 4D FWI strategies, such as the parallel, double-difference, sequential, and common-model strategies (CMS), in resolving nonrepeatability issues for 4D ocean-bottom cable (OBC) seismic data. In addition, a three-stage 4D FWI strategy is developed for 4D OBC seismic data, involving the estimation of seawater velocities in the baseline and monitor models, obtaining a good common starting model, and a final convergence to obtain subsurface 4D changes. The synthetic data tests conducted with varying levels of seawater velocity changes indicate that among the investigated strategies, the CMS performs the best. However, the proposed three-stage strategy surpasses it, emphasizing the importance of accurately estimating seawater velocities for both baseline and monitor inversions in 4D FWI of OBC data.