Joint PP and PS anisotropic AVO inversion using exact Zoeppritz equations

摘要

Various approximations of the Zoeppritz equations, based on the assumptions of weak contrast boundary and small incident angle, are widely used in conventional AVO inversion. These approximations not only limit the scope of application, but also reduce the result accuracy. In addition, with the situation that the reservoir structure becomes more and more complex, isotropic medium cannot accurately describe the subsurface of the earth. Therefore, we develop a joint PP and PS (using more available seismic information) anisotropic AVO inversion method using the exact Zoeppritz equations. We introduce the Riiger approximations to describe the anisotropic feature. During the implementation of least-squares inversion, we conduct the Marquardt method to ensure the stability of our inversion. In addition, we use the analytical solution to calculate the gradients of the reflection coefficients with respect to rock properties, which can speed up the inversion process. Finally, we use a synthetic seismic test to verify our method. The outputs are the elastic parameters (P- and S-wave velocities, density) and Thomsen parameters (ε and δ). The inversion results indicate that our new method is more accurate than conventional method for anisotropic medium.