基于Poynting矢量行波分离的最小二乘逆时偏移  

Least-squares reverse time migration with wavefield decomposition based on the Poynting vector

作　　者：王晓毅 张江杰[1,2] 许宏桥 田宝卿 WANG XiaoYi;ZHANG JiangJie;XU HongQiao;TIAN BaoQing(Key Laboratory of Petroleum Resource Research,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;Innovation Academy for Earth Science,Chinese Academy of Sciences,Beijing 100029,China;University of Chinese Academy of Sciences,Beijing 100049,China;Key Laboratory of Shale Gas and Geoengineering,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China)

机构地区：[1]中国科学院地质与地球物理研究所,中国科学院油气资源研究重点实验室,北京100029 [2]中国科学院地球科学研究院,北京100029 [3]中国科学院大学,北京100049 [4]中国科学院地质与地球物理研究所,中国科学院页岩气与地质工程重点实验室,北京100029

出　　处：《地球物理学报》2021年第2期645-655,共11页Chinese Journal of Geophysics

基　　金：国家自然科学基金(41604120);国家科技重大专项(2017ZX05008-007)资助.

摘　　要：因为在逆时偏移中基于双程波动方程构建震源波场和检波器波场,所以在波场延拓过程中地震波遇到波阻抗界面时,背向发育的反射波会与正常传播的波场互相关产生较强振幅的低频噪声.这一特点使得以逆时偏移为基础的最小二乘偏移方法在梯度计算时同样存在着低频噪声的干扰,从而导致反演收敛的速度减慢.考虑到计算量和存储成本的因素,本文借助Poynting矢量良好的方向指示性实现波场的上下行波分离,并在早期迭代的梯度计算中只保留震源波场和检波器波场沿不同垂直方向传播的组分之间的互相关,有效避免了成像噪声的干扰,提高了算法收敛的速率.数值算例验证了方案的有效性.Because the source wavefield and receiver wavefield are constructed based on the two-way wave equation in the reverse time migration,the reflection waves developed in the back direction can cross-correlate with the normally propagating waves and generate low-frequency noises with high amplitude when the seismic waves meet the impedance interface during the wavefield extrapolation.This feature makes the least-squares migration based on reverse time migration is also disturbed by low-frequency noise during gradient calculation,which leads to slower inversion convergence.Considering the calculation amount and storage cost,we utilize the Poynting vector that represents the wave propagation direction to achieve wavefield decomposition.Then only retaining the cross-correlation between the parts of the source wavefield and the receiver wavefield in different vertical directions in the gradient calculation of the early iteration can suppress the imaging noise and improve the rate of algorithm convergence.Numerical examples verify the effectiveness of this scheme.

关 键 词：Poynting矢量 行波分离 梯度算子 最小二乘逆时偏移 

分 类 号：P631[天文地球—地质矿产勘探]