A new qP-wave approximation in tilted transversely isotropic media and its reverse time migration for areas with complex overburdens

Abstract

During seismic imaging in anisotropic media, undesired SV waves may be detected when conventional wave equations are used for wavefield simulation, which will contaminate the final seismic image. A pure qP-wave equation that is free of S-wave artifacts is desired, such that crosstalk introduced from the interference of different waves can be eliminated. We have developed a new fully decoupled P-wave equation in transversely isotropic media with titled symmetry axis that avoids unwanted energy during migration. The qP and qSV phase velocities for the new approximations are plotted and compared with the exact solution and some other approximations and indicate high accuracy for various anisotropic models (from low to high degrees of anisotropy). During wavefield simulation, the finite-difference and pseudospectral methods also are combined to accelerate the computation. Moreover, a hybrid perfectly matched layer (H-PML) that combines two different perfectly matched layers for second-order wave equations in the wavenumber domain also is proposed and applied to eliminate the artificial boundary reflections. Comparisons of different absorbing boundary layers also are illustrated to validate the wavenumber domain H-PML. Finally, the new proposed wave approximation together with the new absorbing layer is further incorporated in a new 3D anisotropic reverse time migration (RTM). We test the RTM on the 3D synthetic SEG Advanced Modeling Corporation data and offshore field data with a complicated overburden (salt and gas overburden) and obtain seismic images with high resolution. Benchmarks against commercial implementations also are demonstrated, which proves that the positioning of the reflectors is more reliable and accurate with the new algorithm.