Inversion of SV-to-SV wave AVAZ data for fracture indicator: Synthetic example

Huaizhen Chen, Kristopher A. Innanen

Shear wave travel time analysis and reflection amplitude inversion can supply fracture estimation approaches established using P-wave azimuthal seismic data. Starting with rewriting SV-wave velocity as a function of normal and tangential fracture weaknesses in horizontal transversely isotropic (HTI) media, we present a new fracture indicator and express SV-wave velocities of two fractured layers across a reflection interface in terms of reflectivities of S-wave velocity and fracture indicator. Using the expressed SV-wave velocities, we derive SV-SV wave reflection coefficient based on a simplified version of Zoeppritz equations' solution, and we also present SV-SV wave anisotropic elastic impedance (EI) and its normalized form. Based on the derived reflection coefficient and anisotropic EI, we propose an inversion approach of employing SV-SV wave gathers to estimate unknown parameters involving S-wave velocity of background rock, density and fracture indicator, which is implemented as: 1) the least-squares inversion for anisotropic EI of different dominant incidence angles, and 2) the estimation of fracture indicator using the first- and second-order derivatives of anisotropic EI with respect to unknown parameters. We employ noise-free and noisy synthetic seismic gathers to illustrate the robustness and stability of the inversion approach, which reveals that the proposed approach may be reserved as a valuable tool for identifying fractures using SV-SV wave seismic gathers.