Elastic full-waveform inversion in attenuative and anisotropic media applied to walk-away vertical seismic profile data

Wenyong Pan, Kristopher A. Innanen

Viscoelastic full-waveform inversion (FWI) is applied to walk-away vertical seismic profile (W-VSP) data acquired at a producing heavy-oil field in Western Canada, for the determination of subsurface velocity models (P-wave velocity and S-wave velocity ) and attenuation models (P-wave quality factor Q and S-wave quality factor Q). To mitigate strong velocity-attenuation tradeoffs, a two-stage approach is adopted. In stage-I, and models are first inverted using a standard waveform-difference (WD) misfit function. Following this, in stage-II, different amplitude-based misfit functions are used to estimate the Q and Q models. Compared to the traditional WD misfit function, the amplitude based misfit functions show stronger sensitivity to attenuation anomalies and appear to be able to invert Q and Q models more reliably in the presence of velocity errors. Overall, the root-mean-square amplitude-ratio and spectral amplitude-ratio misfit functions outperform other misfit function choices. In the final outputs of our inversion experiments, significant drops in both and ratio (~1.6) and Poisson’s ratio (~0.23) are apparent within the Clearwater formation (depth ~0.45-0.5 km) of Mannville Group in Western Canada Sedimentary Basin. Strong Q (~20) and Q (~15) anomalies are also evident in this zone. These observations provide informative inferences to identify the target attenuative reservoir saturated with heavy-oil resources. In the final section of this report, anisotropic-elastic FWI in vertical transverse isotropic (VTI) media with different model parameterizations are applied to this W-VSP data.