摘要
远年来,波动方程偏移技术已经有了很大的发展。随着勘探工作的复杂化,要求有更完善的偏移技术。针对横向变速层的地质模型,有限差分法较其它方法有独到的优点,差分网格可以灵活地区划变速空间,而在每个网格之内只要求速度恒定。但是,传统的有限差分方法也有它的局限性,15°有限差分在降阶时忽略了波场对深度的二次导数,45°有限差分在降阶时忽略了波场对深度的三次导数,它们均没有实现全波动方程偏移。鉴于这种情况,本文提出一种新的方法——共轭偏移法,通过把一个全波动方程差解成两个低阶微分方程,一次共轭迭代,基本实现了全波动方程偏移。通过理论模型的试算和实际资料的处理,证明了共轭思想是成功的。
Abstract
The technique of wave equation migration has made a considerable progress in recent years. Owing to the conditions of exploration are becoming more and more complicated, there are naturally the needs of more sophisticated technique for doing migration. For the geological model with lateral variation in velocity, the finiie difference method has its unique merits than the others. As long as the velocity in each of the grids is constant, the difference grid may thus be used flexibly to differentiate the space with variable velocity. But the conventional finite difference method has its limitations: the quadratic derivatives of wave field with respect to depths are neglected in reducing the order of 15° finite difference and the cubic derivatives are neglected in 45° finite difference. All of them are not in essence the full wave equation migration. Considering of this, we suggest a new technique-the technique of conjugate migration. By differentiating a full wave equation into two differential equations of lower order and through only one conjugate iteration, the full wave equation migration could taus be implemented. It has been proved by trial and error modelling and field data processing that the idea of conjugate migration is right and proper.
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