TTI介质qP波逆时偏移中伪横波噪声压制方法

摘要

在对地下复杂构造介质,特别是盐丘侧翼及岩下区域进行成像时,相对于传统的各向同性逆时偏移和VTI逆时偏移,具有倾斜对称轴的TTI逆时偏移成像效果最优.不仅反射同相轴更加的连续,而且能量得到了更好的聚焦.传统的各向异性介质全弹性波RTM的计算量大且计算效率低.由于目前仍以纵波勘探为主,因此TTI逆时偏移qP波波动方程的选取显得尤为重要.为了提高计算效率,采用将沿着对称轴方向的横波速度设为零的方法,简化得到qP波波动方程.然而,这样会引入一种严重影响成像效果的低速度、低振幅的qSV波人为干扰.本文建立了qP波方程的完全匹配层控制方程,而后借助于辅助波场采用一种高效的压制伪横波噪声传播的方法,通过模型测试验证了该方法的有效性.%Abstract In the process of imaging subsurface complex structure media,in particular with salt flank and the area bellow it,compared to the method of traditional isotropic reverse-time migration and VTI reverse-time migration,TTI reverse-time migration can produce the best image,not only the continiuity of reflection is much better,but also the energy can be focused more intensely.The traditional anisotropic full elastic wave reverse-time migration clearly is more computer resources demanding and inefficient.Because the information of qP-wave is still playing the leading role in seismic exploration at present,the methods of choosing qP-wave equations in TTI reverse-time migration become pretty important.For improving the calculating efficient,the anisotropic elasto-dynamic equations of motions are often simplified to acoustic equations which only allow qP-wave propagate by seting the velocity of SV-wave equal to zero along the symmetry axis orientation.However,it can bring a low-speed and low-amplitude qSV-artifacts which will destroy the results of reverse-time migration greatly.Firstly,We build the PML controlling equations of qP wave equations.After that,combined with the auxiliary wavefield,in this paper we introduce a cost-effective method which suppresses pseudo SV-wave artifacts perfectly.Numerical examples are included to show the validity of the algorithm.