Elastic Full Waveform Inversion of VSP Data
from a Complex Anticline in Northern Iraq
IMAGE (SEG) 2021 (Oral)
We demonstrate an application of isotropic elastic Full-Waveform Inversion (FWI) to a field data set of Vertical Seismic Profiles (VSP) from a structurally complex narrow anticline in Northern Iraq. A practical elastic FWI workflow is developed to invert offset VSP seismic data. Synthetic tests indicate that this approach can give accurate wave speed updates for the target anticlinal structure. We use inverted wave speed models to perform elastic migration of the data. We propose an alternative way to implement the Least-Squares Reverse Time Migration (LSRTM) without the need of the Born modeling, which means it can handle the multiple reflections. Both RTM and LSRTM results show that the shear wave speed (Vs) image has a higher resolution than the compressional speed (Vp) image for the target structure, owing to the presence of interpretable P-to-S converted waves. The elastic LSRTM has improved the amplitude balancing and image resolution and mitigated some migration artifacts compared to elastic RTM. The results of the field test show that elastic FWI produces elastic models from which we obtain clear Vs images of the thrust fault of interest which is consistent with the elastic LSRTM image of surface seismic data.