Practical elastic full-waveform inversion in the Gulf of Mexico

Abstract Elastic full-waveform inversion (EFWI) improves velocity model building accuracy through its utilization of a more accurate representation of wave propagation in the subsurface. Such accuracy is desirable in areas with high-impedance contrasts (e.g., at interfaces separating salt bodies from the surrounding sediments), where acoustic wave propagation is inadequate to describe and model the full wavefield. On the other hand, elastic modeling and inversion incur extra geophysical and computational challenges with the introduction of the shear wave and the corresponding velocity model. Although low-frequency hydrophone data show sensitivity to S-wave velocity variations, joint inversion for P- and S-wave velocity models can be especially challenging in complicated subsalt settings commonly encountered in the Gulf of Mexico (GoM). To simplify this problem, we assume prior knowledge of the P-wave velocity to S-wave velocity ratio in the inversion and perform a P-wave-only velocity update. We use synthetic and field data examples from the GoM to justify our approach and demonstrate the effectiveness of the proposed EFWI workflow. Results show that in such geologic settings, EFWI can readily replace AFWI for low- to high-frequency velocity model building, as well as for computing FWI-derived reflectivity images.