非规则测区三维地震偏移的边界吸收层法

AN ABSORBING-LAYER METHOD OF 3-D SEISMIC MIGRATION IN AN IRREGULAR ACQUISITION GEOMETRY

对不规则测区的地震资料直接进行三维偏移不仅可减少计算量 ,而且可提高偏移剖面的质量 .本文在单程波方程中增加了一项简单的阻尼因子 ,其作用如同在实际不规则测区的外部有一个薄吸收层 .因为波穿越这个薄层时 ,波场值迅速衰减 ,所以偏移时把吸收层外边界处的波场值取为零所产生的反射非常微弱 .又因为不规则测区零边界条件偏移程序极易编制 ,所以就可以实现对不规则测区的地震资料直接进行三维偏移 .通过对实际地震资料的处理 。

D seismic migration for an irregular acquistion geometry usually needs zero trace padding to form a regular geometry. The benefit of zero padding is easy to do 3 D migration,but it will reduce the computative efficiency and migrated quality. In this paper we use an additional absorbing thin layer surrounding the irregular geometry instead of zero padding. It has greatly decreases computative cost and improves the migrated seismic data quality. In order to form an absorbing layer, a damping factor is added to one way wave equation. Since the wave field attenuates quickly when the wave penetrates this thin layer,the reflection is very small when the wave field at the outer boundary of the absorbing layer is taken as zero,Since the migration program with the zero boundary condition is easy to be implemented,3 D migration of seismic data for a irregular acquisition geometry can be done directly. The effectivity of this method is illustrated by processing the practical data.