Decoupled TTI P-wave Poststack RTM and Demigration Using Pseusdo-spectral Operators

The pure P-wave equation for tilted transverse isotropic reverse-time migration is free of shear-wave artifacts unlike the widely used coupled TTI equations. A new hybrid pseudo spectral and finite-difference algorithm has recently been developed to solve the TTI pure P-wave equation for prestack RTM. This algorithm applies part of the wave propagation in the wave number domain and part in the space domain and is inherently parallel improving its computational efficiency. Here we extend this hybrid algorithm to 3D post-stack de-migration. De-migration of stacked images is the reverse process of migration and generates un-migrated seismograms compatible to seismic data with zero offset. We have tested the proposed de-migration on both field and synthetic seismic data and we have also used the proposed demigration to establish a workflow to validate or build anisotropic models. After de-migration is performed with the models used in the previous migration, we select a series of anisotropic models to re-migrate the seismograms generated by the de-migration. The new models may be derived from seismic-well ties, perturbation of anisotropic parameters, perturbation of locations of interpreted horizons. By investigating a series of re-migrated images, an experienced interpreter can identify which model is the most geologically plausible.