垂直地震剖面的KIRCHHOFF积分偏移

Kirchhoff integral migration of VSP data

把垂直地震剖面(VSP)资料转换到偏移距—深度域,可以通过 VSP CDP叠加来实现,也可用偏移技术来达到。但是,由于 VSP 为共炮点道集,所含数据量较少,所以用常规偏移方法很难获得良好的偏移效果。本文把传统的 Kirchhoff 积分算法推广到变速的叠前 VSP 资料偏移。要把Kirchhoff 积分算法用于 VSP 资料,其关键在于确定 Kirchhoff 轨迹,这相当于确定以源点和接收点为焦点的一等时轨迹。此轨迹与常规地面地震资料所用的常速 Kirchhoff 积分偏移形成的椭圆轨迹不同。本文采用射线方程来确定这种变速 Kirchhoff 轨迹。这种偏移方法的具体实现步骤和一般叠前偏移方法是一样的,主要包括成像时间的确定、近似的 Kirchhoff 积分记录波场外推和求和成像处理等内容。

The conversion of VSP data into offset-depth domain can be achie- ved by either VSP CDP stacking or migration techniques.But conven- tional seismic migration techniques can hardly bring desirable VSP mi- gration result because VSP data usually appear as common-shotpoint gather and contain less data volume. Kirchhoff integral algorithm is extendedly applied to variant-velo- city prestack migration of VSP data.The key to applying Kirchhoff integral algorithm to VSP data lies in determining Kirchhoff locus, which is equivalent to determining an isochronous locus whose foci are at the source point and the receiving point.This locus is different from the elliptic locus formed in constant-velocity Kirchhoff integral migration of conventional surface seismic data.The variant-velocity Kirchhoff locus is determined using the ray equation. This migration method includes the same steps as usual prestack migration methods.The main steps are the determination of imaging time,record wavefield extrapolation using an approximate Kirchhoff algorithm,summation for imaging,etc.