摘要
地震偏移对计算效率、波散特征、成像角度和适应速度变化等方面的矛盾性要求促进了波场外推算法的研究和应用。本文基于不同算法及其特点,提出二次波场外推和共时移矩阵偏移方法,其在保持良好偏移特性的条件下能够显著提高效率。在波场外推方面,先采用大深度步长Fourier有限差分法进行波场延拓,以节省计算并保持波场在高角度的频散特征和纵横向变速,从而在每个大步长深度上得到一个基本归位的完全波场;然后在每个大步长深度内采用正常深度步长有限差分法进行二次偏移,从而在反射波基本归位的基础上实现波场在两个大深度步长之间的平稳成像。在波场成像方面,引入共时移矩阵代替三角函数的计算,在保持相同精度的条件下,用少量的内存换取25%￣45%的计算量。
The contradiction requirements of seismic migration for the computation efficiency, divergence feature, imaging angle and suitable velocity distribution promote the research and application of the wavefield extrapolation algorithm. Based on the different algorithms and their characteristics, an implementation of migration by second wavefield extrapolation and common time-shift matrix is presented with improved efficiency under the same imaging performance. On side of the wavefield extrapolation, a Fourier finite difference extrapolation with long stride in depth is adopted to downward continution, in this way, the computation is saved and the divergence feature and the velocity changing behavior in lateral and vertical at high imaging angle is kept. As a result, a full wavefield in its right position at each depth of long stride is acquired. Asecondary migration is made by normal depth step finite difference method within each stride, and the wavefield is repositioned based on last wavefield between two depths. On side of wavefield imaging, the calculation of trigonometrical function, is taken to get 25%-45% reduction of the computation at the cost of a little EMS memory under the same precision.
出处
《油气地球物理》
2006年第3期9-12,共4页
Petroleum Geophysics
关键词
二次偏移
深度步长
共时移矩阵
连续相移
second migration, depth step length,common time-shift matrix and continuous phase shift
