Joint PP- and PS-wave amplitude variation with angle inversion for thin interbeds

Since transmission losses, internal multiples, and mode conversions are not considered, conventional inversion methods based on the Zoeppritz equations and related approximations have limited capability in high-resolution inversion of thin interbeds. Reflectivity methods, which account for these wave propagation effects, are more suitable for inverting thin interbeds; however, most related studies approximate thin interbeds as several isotropic thin beds, which are inadequate for complex thin interbeds containing thin vertical transverse isotropy (VTI) beds. In this study, thin VTI beds with the characteristics of short-term cycles are regarded as the fundamental compositional units of thin interbeds. We propose a joint PP- and PS-wave amplitude variation with angle inversion method for thin interbeds containing thin VTI beds. The method uses second-order approximations to the Kennett equations for thin interbeds containing thin VTI beds as the forward operator. The inversion objective function is established using the Levenberg–Marquardt algorithm, incorporating sparse constraints to improve the stability and resolution of the five-parameter inversion. Inversion results from model tests and field data demonstrate that the proposed method more accurately extracts elastic parameters and anisotropic information from thin interbeds compared to conventional methods based on the exact Zoeppritz equations, effectively improving inversion accuracy and offering a technical advancement for fine prestack inversion of complex thinly interbedded reservoirs.