Multisource reverse time migration in anisotropic media

Wenyong Pan, Kristopher A. Innanen, Gary F. Margrave

Reverse Time Migration (RTM), a two-way wave equation method for accurate imaging, has attracted geophysicists' attention for many years for its great power in imaging the complex structures with dip angles. While seismic anisotropy in dipping shales can result in imaging and positioning problems for underlying structures. Isotropic RTM also suffers from seismic anisotropy. In this research, the pseudo-spectral method is used to solve the P-wave equation in Titled Transversely Isotropic (TTI) media for anisotropic RTM. Furthermore, RTM suffers from extensively computational cost for traditional shot by shot method, which limits its practical application considerably. The plane-wave source migration with densely distributed sources has been introduced in seismic imaging to reduce the computational cost. This strategy forms supergathers by summing densely distributed individual shots and can improve the efficiency of RTM considerably. While in practical application, the sources are always sparsely arranged. In this condition, the crosstalk artifacts which arise from the undesired interactions between unrelated shot and receiver wavefields will become very obvious. The phase encoding technique is introduced to shift or disperse these crossterms by slant stacking over sufficient number of ray parameters. In this research, we applied the phase encoded anisotropic RTM on Hess VTI (Vertical Transversely Isotropic) model. We also analyzed the influence of the number of encoded sources to the phase encoded images. And the imaging results for different phase encoding methods are also compared and discussed.