地震波逆时偏移中不同域共成像点道集偏移噪声分析

地震波逆时成像方法通常输出2种共成像点道集：一种是共成像点偏移距道集，另一种是共成像点角度道集。开展了针对地震波逆时偏移的2种共成像点道集波场特征及其差异的数值实验。以倾斜界面模型和复杂的Marmousi模型为例，合成了2种共成像点道集，其中角度道集是在逆时延拓过程中采用波印廷矢量制作的。计算结果表明，在速度模型准确的情况下，2种共成像点道集均可拉平，其中偏移噪声在偏移距道集上的分布规律较差，不利于后续的精细处理，而在角度道集上的偏移噪声主要集中在90°附近的高角度区域．对小角度范围内的地震道进行叠加时，逆时成像剖面的信噪比和地层的刻画能力均可得到有效提高，同时低频噪声能量与界面的反射系数存在正相关性。

Seismic wave reverse-time migration noise analysis within different common imaging point gathers

There are two kinds of common imaging point gathers of the seismic imaging methods, one is the common imaging point offset gather, and the other is common imaging point angle gather. We carried out numerical experiments on the wave field characteristics and difference of two kinds of common imaging point gathers with relation of seismic wave reverse-time migration method. Taking tilted interface model and complex Marmousi model as examples, we composed two kinds of common imaging point gathers, of which the angle gather was made up by using Poynting vector during the reverse-time migration process. The computational results show that both the two kinds of common imaging point gathers are flat with correct velocity model. The noise distribution in the offset gather is not fixed, therefore, so it is not suitable for refining processing afterward, while the migration noise of the angte gather is almost focused on higher angle gather area, and with the branch angle stack processing, the low angle stacking section has the better S/N and the formation information is improved greatly. What＇ s more, the low frequency noise energy is positive proportional to the reflection coefficient of the interface.