Image Guided Full Waveform Inversion (IGFWI) Modelling of Shallow Channel Features in the Moray Firth

We present a successful case study of Full Waveform Inversion (FWI) used to resolve velocity heterogeneity due to complex channel systems in the shallow section. These velocity variations produce imaging distortions – pull ups in deeper reflections – that tomography methods cannot handle due to their short spatial wavelength. Therefore, a multiscale FWI approach is used to accurately update the rapid variations in velocity.

The initial model for FWI uses the time interval velocity converted to depth interval velocity, smoothed, calibrated to wells and updated with one iteration of tomography update. A modeled far-field signature is used as the initial source wavelet. Acquisition footprint is addressed by KxKy footprint removal applied on the raw gradient of each iteration. Image Guided smoothing using structural tensors is effective in minimizing leakage of velocities across geological boundaries created by shallow channels and faults.