Anisotropy estimation for a simulated fractured medium using AVAZ inversion: A physical modeling study

Abstract

We present a linear prestack amplitude inversion of PP data, collected through physical modeling, for the Thomsen anisotropy parameters (ε, δ , and γ) of a simulated fractured medium. 3D physically-modeled PP data were acquired along several azimuths over a phenolic layer using the Physical Seismic Modeling Facility at the University of Calgary. The PP amplitudes picked from the reflection off the top of the fractured layer for several azimuths were used as input for the inversion. A linearized PP reflection coefficient approximation for an HTI (horizontal transverse isotropy) medium was used to facilitate the least-squares AVAZ inversion. Some constraints on the vertical velocities and density were also incorporated in the inversion process. The results for all three anisotropy parameters from AVAZ inversion compared very favourably to those obtained previously by a traveltime inversion. This result makes it possible to compute the shear-wave splitting parameter, γ, (historically determined from shearwave data) directly related to fracture density from a quantitative analysis of the PP data.