Elastic full-waveform inversion and parameterization analysis applied to walk-away vertical seismic profiling data for unconventional (heavy oil) reservoir char

Wenyong Pan, Kristopher A. H. Innanen, Yu Geng

Seismic full-waveform inversion (FWI) methods hold strong, though still largely un-tapped, potential to recover multiple subsurface elastic properties for hydrocarbon reser-voir characterization. Simultaneously updating multiple physical parameters introduces the problem of interparameter tradeoff, arising from the inherent ambiguities between dif-ferent physical parameters, which increases nonlinearity and uncertainty of multiparame-ter FWI. The coupling effects of different physical parameters are significantly influenced by model parameterization and acquisition arrangement. An appropriate choice of model parameterization is critical to successful field data applications of multiparameter FWI. The objective of this paper is to examine the performances of various model parameteri-zations in isotropic-elastic FWI with walk-away vertical seismic profile (W-VSP) dataset for unconventional Heavy oil reservoir characterization. Six model parameterizations are considered: velocity-density (, and '), modulus-density (, and ), Lam-density ( , ' and '''), impedance-density (IP, IS and ''), velocity-impedance-I (', ' and I'P), and velocity-impedance-II ('', '' and I'S). We begin analyzing the interparameter trade-off with scattering radiation patterns for each of these parameterizations, which is one common strategy for qualitative parameter resolution studies in isotropic-elastic FWI. In this paper, we discuss the advantages and limitations of the scattering radiation patterns for interparameter tradeoff analysis and recommend to evaluate the interparameter trade-offs using interparameter contamination kernels, which provide complete and quantitative measurements of the interparameter contaminations and can be constructed efficiently with the adjoint-state approach. Synthetic W-VSP isotropic-elastic FWI experiments verify our conclusions about interparameter tradeoffs for various model parameterizations. Density profiles are most strongly influenced by the interparameter contaminations; depending on model parameterization, the inverted density profile can be over-estimated, under-estimated or spatially distorted. The model parameterization, velocity-density, appears amongst the six cases to provide stable and informative density features not included in the starting model. Field data applications of multicomponent W-VSP isotropic-elastic FWI were also carried out with various model parameterizations. The target Heavy oil reservoir zone, characterized by low -to- ratios and low Poisson’s ratios, can be identified clearly with the inverted isotropic-elastic parameters.