Optimization Method Of Angle-domain Gather Based On Reverse-time Migration

Reverse-time migration based on the two-way wave equation has attracted widespread attention because of its high imaging accuracy for complex structures.Reverse-time migration is very sensitive to speed.Compared with other migration methods,the same velocity error will bring greater deviation to the imaging result of the reverse-time migration.These imaging deviations caused by velocity errors will be reflected in the common imaging gathers,which generally show as the bending of the event.Angle-domain common imaging gather is currently recognized as the common imaging gather with the least artifacts.Stacking it after processing can improve the quality of reverse-time migration imaging.Therefore,this paper focuses on the optimization of angle-domain common imaging gather in reverse-time migration.Firstly,this paper discusses the forward simulation of seismic wave field by finite difference method,and deduces the finite difference scheme of wave equation.On this basis,the stability,dispersion and absorption attenuation of boundary reflection are discussed.Secondly,the theoretical method of reverse-time migration is studied.Aiming at the storage problem,the strategy that exchanges computing for storage is adopted,and the boundary absorption problem in wave field reconstruction is discussed in this paper.In terms of imaging,several imaging conditions commonly used in reverse time migration are introduced and the imaging effects are compared.In the aspect of denoising,the causes of low-frequency noise are analyzed,several denoising methods are briefly introduced,and finally Laplacian filter is used to suppress the low-frequency noise.In order to improve the imaging effect of reverse-time migration from the angle domain,this paper briefly discusses three types of angle-domain gather extraction methods,and finally uses the Poynting vector method to extract high-quality angle-domain gathers.On this basis,the effect of angle-domain imaging and the influence of velocity error on angle-domain gather is analyzed.Finally,for the effect of velocity error on imaging quality,this paper proposes a optimization method of angle-domain gather based on improved dynamic time warping algorithm.Aiming at the problems in traditional dynamic time warping,a improved dynamic time warping based on cross-correlation is proposed and applied to the optimization of angle-domain gathers.Tests show that this method can flatten the event of angle-domaingathers and has good robustness to waveform distortion.After processing,the event in the stacking profile is more focused than before.