VSP的双程无反射波动方程逆时偏移

VSP reverse-time migration using two-way nonreflection wave equation

VSP 资料通常为共炮点道集,因所含数据量较少,采用常规偏移方法,难以获得良好的偏移结果。而用双程无反射波动方程作逆时偏移,可以剔除内部界面反射波和层间多次波,同时使用 Clayton 的吸收边界条件,还可以消除VSP 中的边界反射波。可见采用这种逆时偏移方法能够较好地改善偏移效果。其成像条件仍由 Claerbout 成像原理推广,求解镜像方程得到,此法是一种适用性很强的波动方程偏移方法,既适用叠前 VSP 记录,又适用常规多偏移距的炮点道集,还可用于 VSP 和地面资料的联合偏移,并能适应各种速度的变化。此法用于实际 VSP 资料处理时,要预先切除初至波,剪接边道或设置边道阻尼,并要作空间插值补道、频率滤波等项处理,否则将影响 VSP 偏移剖面的质量。

VSP data are usually recorded in common-shot gather and contain less informations.It is difficult,therefore,for us to obtain good mig- ration result by using conventional migration methods.Both inner in- terface reflections and interformational multiples can be removed by reverse-time migration with the use of two-way nonreflection wave equation;besides,boundary reflection in VSP can be eliminated using Clayton's absorption boundary condition.It is proved that reverse-time migration is able to improve migration quality.The imaging condi- tion is still obtained by generalizing Claerbout's imaging principle and solving eikonal equation.This is a very practical wave equation migration method.This method is applicable to prestack VSP data, conventional multiple-offset shot gather and the simultaneous migra- tion of VSP data and surface seismic data.Besides,it is adaptable to various velocity variations. Before applying the method to VSP data processing,we should fi- nish the following processing work:muting the first arrivals,tailing the boundary traces(or putting a damping on boundary traces),inter- polating traces,frequency filtering etc.;otherwise we'll fail to make good VSP migration.