Reverse-time migration of optimized pure acoustic equation in anisotropic media by combining Poisson algorithm and wavefield decomposition imaging condition
XU Shigang1, BAO Qianzong1, REN Zhiming1, LIU Yang2
1. Department of Geophysics, School of Geological Engineering and Geomatics, Chang'an University, Xi'an, Shaanxi 710054, China; 2. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum (Beijing), Beijing 102249, China
Abstract:The traditional anisotropic reverse-time migration mainly adopts pseudo-acoustic wave equations (PWEs), which can easily lead to pseudo-shear wave interference on imaging profiles and numerical instability. Developing anisotropic pure acoustic wave equations (PAWEs) can solve the aforementioned problems. Therefore, this paper first reviews two commonly used PWEs in TTI media, and then an optimized pure acoustic wave dispersion relation based on least squares is obtained. On this basis, the high-accuracy PAWE is solved by the Poisson algorithm and finite-difference. In the conventional cross-correlation imaging condition, the full wavefield information is involved, which is prone to cause strong low-frequency noise. Given this issue and anisotropy, the isotropic imaging condition based on complex wavefield decomposition is further extended to anisotropic media. The wavefield can be decomposed to the different directional components, and the components with opposite propagation directions are selected for the final imaging. The basic theory and model examples verify that the combination of the optimized pure acoustic waves and the imaging condition for wavefield decomposition can effectively suppress pseudo-shear wave interference and low-frequency noise in anisotropic reverse-time migration, and high-quality imaging profiles can be produced.
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