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

Wenyong Pan and Kris Innanen

ABSTRACT

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 α and S-wave velocity β ) and attenuation models (P-wave quality factor Q α and S-wave quality factor Q β ). To mitigate strong velocity-attenuation tradeoffs, a two-stage approach is adopted. In stage-I, α and β 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 α and Q β 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 α and Q β 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 α and β 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 α (~20) and Q β (~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.

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