面向目标的叠前角度道集提取策略

Extraction scheme for object-oriented prestack angle gathers

（1.中国科学院地质与地球物理研究所，北京100029；2.中国石油大庆油田有限责任公司勘探开发研究院，黑龙江大庆163712）

Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

为解决三维叠前角度道集的生成和存储问题，在局部谐波分解思路的基础上，将二维情形下的角度道集生成技术推广到三维情形。方法的基本原理是：通过定义局部角度变换、波数和空间域滤波因子，给出入射波及散射波的角度域表达形式；利用上（下）行波的角度道集三角展开系数，结合相关成像条件，生成反射系数角度道集的三角展开系数体，并由指数映射，获得反射系数角度道集。在具体实现时，利用面向目标的大步长波场延拓，实现快速、准确，针对目标层的偏移成像，同时，在角度域计算谐波分解三角展开系数；采用炮域并行思路，将主节点和各节点的计算加以分解，以节省各节点中间环节的角度道集存储空间，各节点只计算三角展开系数，在主节点回收并生成系数数据体；然后，根据具体目标需求，输出相应的角度道集。由此，极大地减少了角度道集数据存储量，解决了计算效率及存储空间问题。利用中国东部某油田的三维地震资料对方法进行了测试，结果表明方法可行实用。

To solve the problems of the generation and storage for 3-D prestack angle gathers, based on the idea of local harmonic decomposition, the 2-D angle gathers generation technology was extended to 3D. The principles of this method are as follows. The expressions for incident wave and scattered wave in angle domain are presented through defining local angle transform and filtering factors in wave-number domain and spatial domain. Utilizing the trigonometric expansion coefficients of angle gathers for up- and down-going waves, together with relevant imaging conditions, the trigonometric expansion coefficients cube of reflectivity angle gathers is generated. Furthermore, with exponential mapping, reflectivity angle gathers are obtained. When coding the program, the research result of object-oriented large-step wavefield extrapolation is also resorted to realize the high efficient, accurate and target-aimed imaging. Meanwhile, the trigonometric expansion coefficients of harmonic decomposition are calculated in angle domain. The program adopts shot domain parallel scheme where the computation for host-node and that for servant-nodes are separated so as to free servant-nodes from saving angle gathers in middle procedures. Thus, the main duty for servant-nodes is to compute trigonometric expansion coefficients, while that for hostnode is to reclaim them and generate a coefficients cube. Then, according to specific demands for target profile or cube, corresponding angle gathers are formed. Thanks to the schemes above, rather less disk space is enough for generating angle gathers. So, the problems of computing efficiency and storage are solved. The result of test, with 3D seismic data from an oilfield in Eastern China, shows that this method is feasible and practical.