A Decoupled Fracture- and Stress-Induced PP-wave Reflection Coefficient Approximation for Azimuthal Seismic Inversion in Stressed Horizontal Transversely Isotropic Media

Stress-induced seismic anisotropy is usually difficult to be separated or decoupled from intrinsic or fracture-induced anisotropy in the subsurface. To distinguish the effects of fracture and stress on azimuthal reflection amplitudes in an anisotropic medium, a feasible approximation for decoupled fracture- and stress-induced PP-wave reflection coefficient is presented used for azimuthal seismic inversion. Following nonlinear acoustoelastic theory, we first present the relationship between horizontal uniaxial stress and decoupled fracture- and stress-induced PP-wave reflection coefficient for an interface between two stressed horizontal transversely isotropic (HTI) media based on weak-contrast, weak-anisotropy and small-stress assumptions. Next, we present an inversion method of amplitude variations with angles of incidence and azimuth to estimate decoupled fracture- and stress-induced anisotropy using the seismic amplitude differences between different azimuths. Finally, both synthetic and real data sets are used to validate our proposed inversion method, and it can provide an alternative way to estimate the decoupled fracture- and stress-induced anisotropic parameters in stressed shale gas reservoir with HTI symmetry from azimuthal reflection amplitude data.