逆时偏移速度误差影响分析  

Analysis of effect of velocity error on reverse time migration

作　　者：杨仁虎[1,2] YANG RenHu(China Institute of Disaster Prevention,Sanhe 065201,China;Hebei Key Laboratory of Earthquake Dynamics,Sanhe 065201,China)

机构地区：[1]防灾科技学院,三河065201 [2]河北省地震动力学重点实验室,三河065201

出　　处：《地球物理学进展》2021年第4期1630-1639,共10页Progress in Geophysics

基　　金：河北省地震动力学重点实验室开放基金(FZ202101);河北省地震局地震科技星火计划项目(DZ20200827053)联合资助。

摘　　要：逆时偏移作为一种先进的地震偏移成像方法,其成像结果的好坏取决于很多因素,其中最关键的是速度.速度越准确,成像效果就越好.但在实践当中,速度往往是未知的,只能通过速度反演等各种手段来估计近似速度.由此导致逆时偏移成像结果存在误差,从而降低后续地震解释的精度.那么速度误差对逆时偏移成像的影响到底有多大呢?实际当中一般估计出来的近似速度可能在模型每一个地方都不同,很难直接进行逆时偏移速度误差系统分析.为了简化,本文采用等效速度误差——速度模型整体平均误差,进行逆时偏移成像分析.逆时偏移成像采用互相关成像条件,低频噪声压制采用振幅补偿拉普拉斯滤波方法,源波场正推和接收波场逆推采用波动方程一阶应力-速度形式及交错网格有限差分方法.首先对比分析不同速度误差对逆时偏移成像结果的影响,并和单程波波动方程偏移进行对比分析;然后分析速度误差对逆时偏移和单程波波动方程偏移成像位置的影响;最后基于偏移速度分析方法估计得到的近似速度模型,进行逆时偏移和单程波波动方程偏移成像试验.结果表明:在不同速度误差情况下,逆时偏移成像在同相轴连续性和能量聚焦等方面要好于单程波波动方程偏移;速度误差对逆时偏移和单程波波动方程偏移成像位置的影响程度相当.本文研究成果对逆时偏移在实践中的应用具有一定的参考价值.As an advanced seismic migration imaging method, the imaging results of Reverse Time Migration(RTM) depends on many factors, among which the most critical factor is the velocity. The more accurate the velocity, the better the image. But in practice, the velocity is often unknown, and can only be estimated by various methods such as velocity inversion. This results in errors in RTM imaging, which reduces the accuracy of subsequent seismic interpretation. So how much impact does velocity error have on RTM imaging? In practice, the approximate estimated velocity may be different in every part of the model, so it is difficult to directly analyze the velocity error of RTM systematically. For simplification, the equivalent velocity error—the overall average error of the velocity model is adopted to carry out RTM imaging analysis. During the process of RTM, the cross-correlation imaging condition is used, the amplitude-compensated Laplacian filtering method is used for the low-frequency noise suppression, and the first-order stress-velocity form of wave equation and the staggered-grid finite difference method are used for the forward modeling of source wavefield and the backward modeling of receiver wavefield. Firstly, the effects of different velocity errors on RTM imaging results are analyzed, and the results are compared with one-way Wave Migration(WEM). Then the influences of velocity error on the imaging position of RTM and WEM are analyzed. Finally, based on the approximate velocity model estimated by the migration velocity analysis method, the imaging experiments of RTM and WEM are carried out. The results show that RTM is better than WEM in terms of continuity of in-phase axis and energy focus under different velocity errors. The effect of velocity error on the imaging location of RTM and WEM is similar. The research results of this paper have a certain reference value for the application of RTM in practice.

关 键 词：逆时偏移 单程波波动方程偏移 等效速度误差 

分 类 号：P631[天文地球—地质矿产勘探]