Central-difference time-lapse 4D seismic full-waveform inversion

Abstract

Repeated seismic surveys contain valuable information regarding time-lapse (4D) changes in the subsurface. Full-waveform inversion (FWI) of seismic data can provide high-resolution estimates of 4D change. We have adopted a new time-domain 2D acoustic time-lapse FWI method based on the central-difference scheme with higher order mathematical accuracy and reasonable computational cost. The method is rigorously tested on the SEG Advanced Modeling 4D time-lapse model and ocean-bottom-node data set. High-resolution 4D velocity estimates are obtained, which show strong (approximately 25%) velocity increases in a 75 m thick gas layer, as well as weaker (5%) changes due to geomechanical effects, the latter of which are poorly recovered by the conventional parallel 4D FWI method. We also perform the bootstrap 4D FWI method, and the result is contaminated by strong artifacts in the underburden, whereas the proposed central-difference method has fewer underburden artifacts allowing more reliable interpretations. In this realistic case study, acoustic FWI erroneously overfits some of the elastic scattered waves, and it cannot fit the strong elastic 4D coda waves well. The results show that the proposed central-difference 4D FWI method within the acoustic approximation may be a practical solution for time-lapse seismic velocity inversion.