Nonlinear Three-term AVO Inversion Based on Exact Zoeppritz Equations

Abstract

Obtaining interlayer weak reflection information that helps identify properties and accurate density information from complex and elusive reservoirs is particularly important for reservoir characterization and detection. However, conventional AVO inversion method is strongly influenced by the accuracy of the approximate Zoeppritz equations, which suppresses weak reflections coming from the commonly used prior distribution. In this abstract, we address these problems by using exact Zoeppritz equations. First, the inverse problem was constructed and the modified Cauchy distribution was introduced as the prior information by utilizing Bayes’ theorem. We then combined the idea of generalized linear inversion with Iterative Reweighed Least-Squares (IRLS) Algorithm to solve the problem. From the Zoeppritz equations, the complicated objective function was used for inversing the P- and S-wave velocities and density. The idea of GLI is used to solve the objective function, from which a nonlinear solution of the model parameters’ perturbations can be calculated. The IRLS Algorithm was applied to solve the nonlinear expression to obtain an updated iterative formula of the model parameters. Both synthetic and field data examples show that the new method can not only directly inverse P- and S-wave velocity and density, but also provides accurate estimation results, particularly for density.