Joint AVO Inversion of PP and PS waves using Exact Zoeppritz Equation

摘要

Most of the current pre-stack AVO inversion mathods are based on various approximations of the equation, which have accuracy limited to seismic data with weak contrasts of parameters and limited angles. For reservoirs with strong contrast interfaces (salt domes, heavy oil fields, basalts, etc) and long offset ranges, the conventional AVO inversion based on approximations isn't suitable. For the aim of stabilizing and improving the inversion results, we can incorporate PS data. This paper makes effort to explore nonlinear joint least-squares inversion using both PP and PS reflection data. By rewriting the exact Zoeppritz equations as the function of four independent parameters, we invert the density ratio and three velocity ratios. Inversions using P-P data alone are compared to those using P-P and P-S data jointly. Our tests indicate that PP inversion can only stably invert P-velocity and density ratio, and two S-velocity ratios can't be inverted accurately. Moreover, the reflection angles needed reaches up to 65° to obtain sufficiently accurate P-velocity and density ratio by using PP seismic data alone. However, all four ratios converge to their true model values successfully if we use PP and PS data jointly and the reflection angles needed to achieve the same accuracy reduce to 35°. Considering the heavy burdens introduced by wide angle acquisition and processing, this joint inversion is of great potential for practical applications, compared with wide angle PP inversion and conventional Generalized Linear Inversion.