Extension of forward modeling phase-screen code to for AVO analysis in isotropic and anisotropic media

Abstract

The computationally efficient phase-screen forward modeling technique is extended to allow investigation of non-normal ray paths. The code is developed to accommodate all diffracted and converted phases up to critical angle, building on a geometrical construction method. The new approach relies upon pre-scanning the model space to assess the complexity of each screen. The propagating wavefields are then divided as a function of horizontal wavenumber, and each subset is transformed to the spatial domain separately, carrying with it angular information. This allows both accurate 3-D phase corrections and Zoeppritz reflection and transmission coefficients to be applied. The phase-screen code is further developed to handle simple anisotropic media. During phasescreen modeling, propagation is undertaken in the wavenumber domain where exact expressions for anisotropic phase velocities are available. Travel-times and amplitude effects from a range of anisotropic shales are computed and compared with previous literature.