Some remarks on nonlinear amplitude versus scattering angle‐azimuth inversion in anisotropic media

Abstract

A feasibility study for inverting reflection coefficients for a single‐interface model consisting of a shale overlying a fractured sand is presented. To characterize the medium contact from amplitude versus scattering angles (AVA) behavior associated with the reflection from a particular interface, in view of the anisotropy, wide‐angle scattering data are required. However, wide‐angle scattering turns the inverse problem into an essentially nonlinear one. The inverse problem is hence analyzed with a global optimization procedure—a genetic algorithm with constraints. The key to making a genetic algorithm work for our AVA inverse problem appears to be a proper parameterization of the direct scattering problem and introducing a parameter hierarchy. These reduce the complexity of the misfit function occurring in the optimization procedure and let this function become convex over a relatively large range of medium parameter values. We illustrate how well our approach performs with a single‐interface example representing a shale/fractured‐sandstone contact. In this example, we assume the overburden, i.e., the shale, to be known; we allow the data to be contaminated with noise.