Kirchhoff波场延拓在OBC记录海水层基准面校正中的应用

Application of Kirchhoff integral wave field extrapolation to water layer datuming for OBC record

莺歌海盆地是南海西北部一个重要的含气盆地,大量含气带导致了常规地震资料中出现纵波地震反射模糊带,海底电缆(OBC)探测被作为揭示该区含气带特征的新方法。OBC探测能够提供更多的信息,然而由于它具有不同于海面拖缆观测方式:它的炮点和检波点不在一个基准面上,地震波沿不对称路径传播,不能直接采用常规地震数据处理方法处理,为此需要进行基准面校正将炮点和检波点校正到同一基准面上。常用的基准面校正方法包括静校正、Kirchhoff波场延拓法等,文章采用Kirchhoff波场延拓法对莺歌海盆地的OBC资料做基准面校正,并与静校正方法对比,结果表明,静校正方法对浅层速度分析造成的误差较大,超过10%;Kirchhoff波场延拓则保持了正确速度,并得到了目标基准面的正确波场。

The Yinggehai Basin is an important basin in the northwestern South China Sea where wealthy gas led to fuzzy reflection zones in the conventional P-wave seismic reflection record.Ocean bottom cable（OBC） survey was used as a new method to reveal the gas-bearing characteristics of the Yinggehai Basin.Multi-component OBC can provide more information than other existing methods.Different from the surface observation method,its shots and receivers are deployed several meters under the surface and on the sea-bottom,respectively;therefore,the wave ray-paths are highly asymmetric.As a result,conventional seismic data processing methods cannot be directly used to the OBC record.A primary preprocessing procedure is altitude datuming for the shots or receivers to make the shots and receivers in the same datum.The most-often used datuming methods include static correction and Kirchhoff wave field extrapolation.In this paper,Kirchhoff wave field extrapolation is used to compare with the static correction method for datuming of the OBC record collected from the Yinggehai Basin.The resultant velocity analysis and wave fields show that the static correction causes significant velocity deviation,more than 10 percent in the uppermost layer,whereas Kirchhoff wave field extrapolation maintains correct velocity for all layers,and obtain correct wave field to the target datum.