A VTI medium prestack migration method based on the De Wolf approximation

Abstract

Anisotropy of velocity is an inherent characteristic of subsurface rock layers, and neglecting its effects can lead to errors in imaging positioning. The present study assumes that subsurface anisotropy follows the VTI (vertically transversely isotropic) medium model and the De Wolf approximation is employed for wavefield computation to enhance imaging accuracy. Drawing on scattering theory, the medium parameters are divided into background parameters (background velocity and anisotropy) and disturbance parameters (velocity and anisotropy disturbances). The mathematical formulation of the De Wolf approximation integral equation in a VTI medium is derived, and a generalized screen approximation (VTI-GS) operator is developed for this medium. The VTI-GS operator is applied to prestack migration. An amplitude attenuation factor is introduced through algorithm implementation and programming to mitigate spatial aliasing and improve migration image accuracy. Error analysis and pulse response test demonstrate that the VTI-GS operator is well-suited for the VTI medium. Migration images for the concave model and the Hess model confirm that the VTI-GS operator yielded higher imaging accuracy than conventional isotropic imaging methods.