3D orthorhombic elastic full waveform inversion in the reflection domain from hydrophone data

摘要

We formulate the theory of 3D orthorhombic full-waveform inversion using adjoint state techniques for recovery of shear and p-wave elastic stiffness coefficients from acquired pressure data. In formulating the adjoint of forward Born scattering, we use a novel transformation of wavefields that allows us to use the same high performance elastic propagation kernel for the adjoint that we use for forward elastic modeling. We further derive inversion equations suitable for recovery of p-wave and shear velocities in fixed inhomogeneous density media with fixed inhomogeneous anisotropic coefficients, through the use of a chain rule formulation. We demonstrate that for a simple model with a strong Class 2 AVO signature involving phase reversal, a sequence of short-offset p-wave elastic stiffness recovery (equivalently velocity or impedance) folllowed by long offset shear elastic stiffness recovery produces a significant uplift in data fitting when compared to simple acoustic inversion for p-wave velocity. We also demonstrate effective recovery in 2D using similar techniques, for a more complex model with thin sands exhibiting strong AVO behavior.