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Wavefield-reconstructed least-squares reverse time migration with dynamic constraint factor

Ding Yi, Li Zhenchun, Zhang Kai, Lin Yuzhao

Acta Geophysica

2023

Vol. 71, no. 2

671--680

Least-squares reverse time migration is a high-precision migration method, the objective function of this method appears as a strong nonlinear function which is likely to plunge into local minimization, and the whole migration process requires massive calculation. Wavefield reconstruction is an optimized inversion theory proposed in recent years, and has achieved good results in full waveform inversion. In this method, the objective function introduces the wave equation as its penalty term to expand the search space of the solution and weaken the influence of the local minimization. In this paper, the idea of wavefield-reconstructed inversion is introduced into the least-squares reverse time migration. The scattering wavefield reconstruction algorithm under Born approximation is used to constrain the migration process, and the dynamic constraint factor in time–space domain is introduced to suppress the high-order scattering artifacts and improve the signal-to-noise ratio of the migration results. Generally, the method can ensure the accuracy of the update gradient. The experimental results show that this method can effectively suppress the artifacts caused by high-order scattering wave when there are large-scale high-velocity anomalies in the velocity field. In addition, the method has also achieved good results in the test of field datasets.

Elastic full waveform inversion in VTI media using logging data constraints and gradient precondition

Xu Yipeng, Zhang Kai, Li Zhenchun, He Zilin, Gao Jinfeng, Zhao Xianyang

Acta Geophysica

2022

Vol. 70, no 4

1665--1676

Elastic full waveform inversion (EFWI) in VTI media using velocity model-based parameterization (PARM-VTIEFWI) can improve the sensitivity of anisotropic parameters, but there are still the problems of gradient’s interference and Nonunique. Research has shown that logging data can constrain the Non-unique of FWI. Therefore, in this paper, we use the logging data as a constraint to limit the Non-unique of the PARM-VTIEFWI. We derive the objective function and gradient equation for the PARM-VTIEFWI based on the constraint of logging information. In addition, to reduce the interference between the gradients of parameters in VTI media, we incorporate a pseudo-Hessian matrix to precondition the gradients and derive a gradient preconditioning formula based on the pseudo-Hessian matrix in this paper. In summary, we propose a new PARM-VTIEFWI method based on logging information constraint and gradient precondition, which reduces the interference between the parameter gradients and constrains the Non-unique of the inversion. The correctness and validity of the method were demonstrated by examples.