摘要
共炮记录叠前偏移对输入的速度非常敏感，要求偏移中所使用的延拓公式能较为精确地适应速度的纵横向变化。因此，本文在推导共炮记录偏移公式时，特别把相位移加有限差分混合法引入，使整个延拓过程既适应速度的纵、横向变化，同时也能够得到陡倾地层的精确归位，从而较好地实现共炮记录叠前偏移。正因为共炮记录叠前偏移对偏移速度非常敏感，故本文提出的方法又可用作速度分析。任何形式的叠前偏移都需大量机时，特别是对于迭代的叠前偏移速度分析，计算量更大，为此，本文针对混合法共炮记录偏移的特点，从两个方面讨论提高计算效率的方法。首先针对在频率、波数域中运算的相移法，引入F－K滤波，在波场延拓中，仅就有关的频率、波数进行运算，大大地减少了计算次数．同时又通过滤波提高了偏移的精度；然后针对整个混合法在频率域中的运算，讨论了减少频率循环次数来提高计算效率的方法；最后，作为一个特例，把共炮记录叠前偏移稍作简化，得到精确、高效的叠后混合偏移方法。总之，本文提出的基于共炮记录的算法不仅成为较为精确的、高效实用的波动方程叠前偏移方法，而且还可作为一种强有力的手段，用于偏移速度的分析之中。数值试算结果表明，本文提出的各种方法达到了预期目的。
Prestack migration of common shot records is very sensitive to the velocity input, and demands a kind of continuation formula which can adapt to both vertical and lateral velocity variations. In order to meet the demand we introduce the phase-shift plus finite-difference hybrid method in the paper when we deduce the shot records migration formula. Because of the prestack migration of shot records belng very sensitive to migration velocity, the method proposed in the paper can also be used for velocity analysis. It is well-known that any types of prestack migration need a large amount of cornputation time especially for the iterative prestack migration velocity analysis. For this reason, we have a discussion on how to irnprove the computation efficiency in the following two aspects in view of the characteristics of the hybrid method. First,considering the phase-shift algorithm calculated in F-K domain, we present the F-K filtering. In wavefield continuation the calculations are conducted on1y for the frequencies and the wavenumbers concerned, which reduces the computation arnount greatly and in the mean time improves the migration accuracy by filtering. Second, considering the whole hybrid method in frequency domain, we discuss how to cut down the frequency circulation numbers to improve the computation efficiency. Finally we simplify the prestack migration of shot records and obtain an accurate and efficient poststack hybrid migration method. In a word, the algorithm based on the shot records is not only an accurate and efficient wave-equation prestack migration method but also can be used as a powerful tool for migration velocity analysis. The numerical calculation results show that the expected objective has been attained.
出处
《石油物探》
EI
CSCD
北大核心
1998年第4期48-54,84,共8页
Geophysical Prospecting For Petroleum
基金
油气 年科研基金
关键词
共炮记录
叠前深度偏移
声波方程
地震勘探
shot records, wave equation, prestack depth migration, hybrid continuation method, F-K filtering
