PP-Wave Reflection Coefficient Equation for HTI Media Incorporating Squirt Flow Effect and Frequency-Dependent Azimuthal AVO Inversion for Anisotropic Fluid Indicator

In hydrocarbon exploration and development, fluid indicators that can directly identify reservoir hydrocarbons from seismic data are of great significance for seismic interpretation in fracture-induced horizontal transversely isotropic (HTI) reservoirs. In this article, based on the unified elastic wave theory of the medium, a new anisotropic fluid indicator is constructed, incorporating a squirt flow effect between the cracks of rocks. The novel anisotropic fluid indicator can better reflect the influence of pore fluid within the rock on wave propagation. Compared with conventional elastic parameters, the newly established anisotropic fluid indicator is more sensitive to oil/gas. Subsequently, by combining the perturbation of the elastic stiffness component in fluid-saturated fractured porous media and the inverse scattering function, an anisotropic PP-wave reflection coefficient is derived in terms of an anisotropic fluid indicator incorporating squirt flow effect and fracture weaknesses. The comparison of Ruger's equation and the new reflection coefficient equation confirms the validity of our equation for parameter estimation. Our reflection coefficient equation is used to establish further an anisotropic frequency-dependent azimuthal amplitude variation with offset (AVO) inversion method to estimate the anisotropic fluid indicator and fracture weaknesses. The feasibility of the inversion method is verified by the field data application in eastern China, which demonstrates that the anisotropic fluid indicator with the squirt flow effect is certainly sensitive to the gas-bearing fractured reservoirs and can provide a more effective method for fluid identification in gas-fractured reservoirs.