Image-guided wavefield tomography for VTI media

Abstract

Transversely isotropic (TI) models have become essential in generating accurate depth images from seismic data. Here, we develop image-domain tomography (IDT) for building acoustic VTI (TI with a vertical symmetry axis) models from P-wave reflection data. Based on a separable dispersion relation, the modeling operator extrapolates only P-wavefields without the shear-wave artifacts. The inversion algorithm includes leastsquares reverse-time migration (LSRTM), which improves the quality of the extended images and accuracy of parameter estimation. Whereas the zero-dip NMO velocity (V nmo) and anellipticity parameter η are updated by focusing energy in space-lag LSRTM gathers, the Thomsen parameter δ is constrained by image-guided interpolation between two or more boreholes. We also apply image-guided smoothing to the IDT gradients of V nmo and η to steer the inversion towards geologically plausible models. To mitigate the trade-off between V nmo and η, we adopt a multistage approach that gradually relaxes the constraints on the spatial η-variation. The robustness of the algorithm is demonstrated on the elastic VTI Marmousi-II model. We also present preliminary inversion results for a line from a 3D data set acquired in the Gulf of Mexico.

Structure-guided 3D anisotropic tomography - a case study

“…A classical approach to stabilization is regularization (Costa et al, 2008). More recently, in order to estimate geologically conformable models, inclusion of structural information to better conditioning geophysical inversion have been and continue being developed (Clapp et al, 2004;Ma et al, 2012;Shank et al, 2017;Li et al, 2018;Zhou et al, 2016;Guo et al, 2017). Our implementation used the structural smoothing equation (Hale, 2009) to enforce a conformable geological model,…”