针对横向速度变化模型的不同地震成像方法对比研究

Comparative Study of Different Seismic Imaging Methods for Lateral Velocity Variation Models

时间域偏移成像和深度域偏移成像是常用的地震成像手段,不同的成像方法对复杂模型适用性不同。为了研究不同成像方法对横向速度变化模型的成像能力优劣,首先建立包括横向速度缓慢变化的起伏层和横向速度剧烈变化的复杂模型,其次,利用有限差分方法进行声波正演模拟,然后分别采用Kirchhoff叠前时间直射线偏移、Kirchhoff叠前时间弯曲射线偏移、叠前共炮分步傅里叶深度偏移、叠前傅里叶有限差分深度偏移、叠前共炮集45°至90°有限差分偏移、叠前共炮相移加插值深度偏移方法完成对应的偏移成像处理。成像结果表明,前2种时间偏移成像方法对低倾角具有成像能力,但存在位移问题,角度越大,位移越严重;后4种深度偏移方法均能对倾角小于等于30°界面实现准确成像,当目标界面倾角等于45°时,除叠前共炮相移加插值深度偏移外,其他方法成像结果均出现同相轴保幅性差。综合考虑连续性和保幅性两方面因素,叠前共炮相移加插值深度偏移是本文成像能力最优的偏移方法。

Time domain migration imaging and depth domain migration imaging as commonly used seismic imaging methods have different applicability to complex models.In order to study the imaging capabilities of different imaging methods for lateral velocity change models,this paper firstly establishes a complex model that includes undulating layers with slow lateral velocity changes and severe lateral velocity changes.Secondly,finite difference method is used to conduct acoustic forward modeling,in couple with 6 methods to complete corresponding migration imaging processing,including Kirchhoff pre-stack time straight ray migration,Kirchhoff pre-stack time curved shot migration,pre-stack common shot fractional Fourier depth migration,pre-stack Fourier finite difference depth migration,pre-stack common shot set 45 to 90 degree finite difference migration and pre-stack common shot phase shift plus interpolation depth migration.The imaging results show that the first and the second time migration imaging methods have imaging capabilities for low dip angles,but there are displacement problems.The larger the angle,the greater the displacement.The third to sixth depth migration methods can achieve accurate imaging of interfaces with an inclination angle of less than or equal to 30°.However,when the inclination angle of the target interface points to 45°,the amplitude preservation of the third to fifth depth migration results turns poor.This paper achieves the best imaging effect by combining the two factors of continuity and amplitude preservation,pre-stack common shot phase shift plus interpolation depth migration is the migration method.