Efficient algorithms for mode decoupling of elastic wavefield in transversely isotropic media with a vertical symmetry axis

For the elastic wave mode decoupling in anisotropic media, conventional approaches with divergence and curl operations lead significant errors.The accurate mode decomposition algorithm, however, is prohibitively expensive because the polarization projection operators are model- and direction-dependent.Based on previous work, we focus on developing efficient algorithms for mode decoupling in heterogeneous medium with vertically transverse isotropy (VTI).First, for the pseudo-divergence or pseudo-curl operators constructed by the deviation of propagation and polarization direction of the dominant energy, we improve the accuracy of qP/qS separation by taking into account the variations of the deviation angle with the propagation direction.This improvement is very important when different wave modes overlap in the same spatial zone at the same time.Then, for the accurate but prohibitively expensive algorithm of mode decoupling through polarization projection, based on the existing low-rank approximation of the projection operator, we achieve a balance between the accuracy and computational cost using the strategies of model partitioning and graph processing unit (GPU) acceleration.The example on the SEG Hess VTI model demonstrates the features and validities of the improved pseudo-divergence/pseudo-rotation algorithm and the GPU-based low-rank approximate polarization projection algorithm. © 2019, Editorial Department OIL GEOPHYSICAL PROSPECTING. All right reserved.