On the Accuracy of Ruger’s Approximations for PP Reflection Coefficients in HTI Media

We here investigate the accuracy of Ruger’s approximation for PP reflection coefficients within the context of seismic AVAZ analysis in HTI media; that is simple reservoir model with a single set of vertical fractures. An individual comparison of forward and inverse modelling results have been done for the interface between an isotropic and HTI medium. The comparison is performed for different contrast (small and large) and anisotropy by changing the fracture density. The elastic stiffness tensor of the fractured reservoir of HTI medium was calculated using a combination of T-matrix with Brown-Korringa relations. We have calculated the percentage error for the Ruger’s approximation(s) with respect to the exact formula for reflection coefficients. The inversion of this non-linear forward model with respect to fracture density and azimuthal fracture orientation was done in a Bayesian setting, which provide information about uncertainties as well as the most likely values. The maximum percentage error for large contrast and large anisotropy (fracture density = 0.2) may reach up to 70%. An application to the synthetic case of characterizing a fractured damage zone, where fracture density and orientation depend on distance from the fault core was also provided to elaborate the workflow.