双平方根方程偏移反假频研究

Anti-aliasing of double square root equation migration

1.南方海洋科学与工程广东省实验室(湛江),广东湛江524088;
2.上海青凤致远地球物理地质勘探科技有限公司,上海200093;
3.中海石油(中国)有限公司湛江分公司,广东湛江524088;
4.中石化上海海洋油气分公司勘探开发研究院,上海200120

1. Southern Marine Science and Engineering Guangdong Laboratory (Zhanjiang),Zhanjiang 524088,China;
2. Shanghai QFZYGEO Inc.,Shanghai 200093,China;
3. Zhanjiang Branch,CNOOC,Zhangjing 524088,China;
4. Sinopec Institute of Shanghai Offshore Petroleum,Shanghai 200120,China

假频的存在给地震数据的去噪、偏移和反演带来了很大干扰。根据双平方根方程偏移公式及偏移成像假频理论,从输入的地震观测数据、偏移算子以及成像条件三个方面对基于双平方根方程的偏移方法假频来源进行了全面分析,得出该偏移方法不存在算子假频以及成像条件假频的结论,指出偏移距方向的数据假频才是该方法主要的假频来源。结合CMP数据时距曲线公式和空间假频基本公式,推导出双平方根方程偏移输入数据在偏移距方向的采样规则。分析当今主流地震数据采集观测系统后发现,该偏移方法的输入数据在偏移距方向很难满足采样条件,因此,双平方根方程偏移会面临较严重的数据空间假频影响。结合三角平滑滤波器,提出了一种压制偏移距方向数据假频的方法。利用模型数据对新的反假频方法处理结果和加密采样方法处理结果进行了对比,验证了新的反假频方法的正确性及其计算内存需求、计算量方面的优势。三维实际数据测试结果表明,新的方法能够压制假频噪声,改善成像效果。最后讨论了新方法的适应性和加密采样方法处理三维数据的局限性,认为将加密采样与本文方法结合,能够得到计算效率和成像效果均衡的结果。

Aliasing results in considerable interference in the denoising,migration,and inversion of seismic data.Based on the formula of double square root equation migration and imaging aliasing theory,a comprehensive analysis of the aliasing sources of the migration method is made from three aspects:input data,migration operators,and imaging conditions.It has been shown that there is no operator and imaging condition aliasing in this method.The input data aliasing in the offset direction is the main aliasing source that needs to be dealt with.Combined with the CMP data time-distance curve and the basic spatial aliasing formula,the input data sampling rules in the offset direction of double square root equation migration were derived.It is difficult to meet the sampling condition in offset directions using the input data of current acquisition geometry;therefore,the square root equation migration faces serious data aliasing.Based on the triangular smoothing filter,a method for suppressing data aliasing in offset direction is proposed.On the basis of theoretical data,the method is compared with the traditional dense sampling method,and the correctness,computational memory requirements,and advantages of the calculation amount are verified.The results of the 3D real data test show that the proposed method can suppress aliasing noise and improve imaging effect.Finally,the adaptability of the proposed method and the limitations of the dense sampling method in processing 3D data are discussed,and it is believed that the combination of dense sampling and the proposed method can achieve balanced calculation efficiency and imaging effect.

国家重点研发计划变革性技术关键科学问题重点专项(2018YFA0702503)和南方海洋科学与工程广东省实验室(湛江)资助项目(ZJW-2019-04)共同资助。

10.3969/j.issn.1000-1441.2023.01.007