逆时偏移随机噪声影响分析  

Analysis of effect of random noise 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6期2618-2627,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)和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,一般采用互相关成像条件.首先将源波场沿时间进行正传,然后将接收波场沿时间进行反传,最后将所有时刻可能相遇的源波场和接收波场相乘叠加,从而得到最终的偏移成像结果.源波场正传和接收波场反传都是采用同一个波动方程,这里采用波动方程一阶应力-速度形式,数值计算方法采用交错网格有限差分方法.采用振幅补偿拉普拉斯滤波方法压制逆时偏移成像中的低频噪声.采用三次样条插值方法解决逆时偏移成像中的波形不光滑问题.在源波场进行正传时,需要给定震源子波作为初值条件.而在接收波场进行反传时,需要将地震记录作为边界条件.一般地震记录都会存在各种噪声,这些噪声随着接收波场逆传被带到最终地震偏移成像结果中.地震记录噪声类型非常多,一些属于规则的线性和非线性干扰,可以通过一些特定的方法进行压制;还有一些属于不规则的干扰,随机噪声就是其中一种最常见的类型.通常在偏移成像前对地震记录进行去噪处理,在一定程度上可以压制噪声,但去噪常常会破坏有效信号的特征.如果不去噪的话,对偏移成像结果到底有多大的影响呢?为了简便,本文基于不同信噪比地震记录,分析了不同程度随机噪声对逆时偏移成像结果的影响,并和单程波波动方程偏移成像进行了对比分析.本文研究结果对逆时偏移成像技术在实践中的应用具有一定的参考价值.Reverse time migration, as an advanced seismic migration imaging method, usually adopts cross-correlation imaging conditions. Firstly, the source wavefield is propagating forward along time, and then the receiver wavefield is propagating backward along time. Finally, the source wavefield and the receiver wavefield that may meet at all times are multiplied and superimposed, so as to obtain the final migration imaging result. In the implementing process of forward propagation of the source wavefield and backward propagation of the receiver wavefield, the same wave equation and first-order stress-velocity form are adopted. The numerical calculation method adopts the staggered-grid finite difference method. The amplitude-compensated Laplacian filtering method is used to suppress the low-frequency noise in reverse time migration. Cubic spline interpolation method is used to solve the problem of unsmooth waveform in reverse time migration. When the source wavefield is propagating forward, the source wavelet should be given as the initial value condition. However, seismic records should be used as the boundary conditions when the receiver wavefield is propagating backward. In general, there are various noises in seismic records, and these noises are carried to the final seismic migration imaging results through the propagation of the receiver wavefield. There are many types of seismic noise, some of which belong to regular linear and nonlinear interferences, and can be suppressed by some specific methods. Others are irregular interferences, of which random noise is the most common type. The noise can be suppressed to some extent by denoising seismic records before migration imaging, but denoising often destroys the characteristics of the effective signals. If no denoising, how much impacts will it have on the migration imaging results? For simplicity, using seismic records with different signal-to-noise ratios, the effects of different degrees of random noise on reverse time migration imaging are analyzed, and compared

关 键 词：逆时偏移 互相关成像条件 振幅补偿拉普拉斯滤波 波形校正 单程波波动方程偏移 随机噪声 

分 类 号：P631[天文地球—地质矿产勘探]