【摘要】 虚拟偏移距(POM)偏移方法是基于Kirchhoff积分的叠前时间偏移方法,这种方法具有改善共反射点模糊成像的优势,较少依赖速度模型,具有良好的振幅保持能力,计算成本相对较低,且在横向速度变化不太剧烈的情况下能够取得较好的成像效果,是转换波叠前时间偏移的一种重要方法.因POM方法是通过将地震波旅行时的双平方根(DSR)方程转化为以虚拟偏移距为变量的单平方根双曲线方程,这种方法的虚拟震源与虚拟检波器并非并置在一起,其传播路径符合Snell定律,可抽取真正的共转换散射点(CCSP)道集,该道集不需要倾角时差校正(DMO),形成CCSP道集的过程就等于叠前时间偏移的过程.随着AVO技术的发展,振幅的保真性在偏移过程中越来越重要.本文详细分析了初始速度、虚拟偏移距和偏移孔径对共转换散射点(CCSP)道集的影响.通过转换波POM保幅成像模型试算,结果表明,利用虚拟偏移距进行叠前时间偏移时,选择合适的虚拟偏移距间隔和偏移孔径至关重要.更多还原

【Abstract】 POM(Pseudo Offset Migration) is a prestack time migration method which is based on Kirchhoff integral.It has the advantages of improving the sharpness of the imaging at common reflection points,and is independ with the velocity model.At the same time,it also has good amplitude preserving ability and relatively low computation expense.Futher more,it can obtain a good imaging under the condition that the lateral velocity has not a large variation.So it is an important method for Converted Wave Prestack time Migration.POM method converts the double square root(DSR) travel time equation of the seismic waves into a single square root hyperbolic equation whose variable is pseudo offset.Since POM doesn’ t put the pseudo shot and the pseudo receiver at the same point,the ray path of POM meets the Snell’ s Law.And then,the true common reflection point gathers can be extracted.The gathers does not need DMO correction.The process of forming CCSP gathers is equivalent to the prestack time migration process.With the development of the AVO technique,the AmplitudePreserving is more and more important in the process of migration.This paper analyzes the influence of the initial velocity,pseudo offset and migration aperture to the common conversion scatter point(CCSP) gathers.The modeling results of the converted wave POM amplitude-preserving prestack time migration imaging show that to select the appropriate pseudo offset interval and migration aperture is crucial in using pseudo offset to perform prestack time migration.更多还原