应用黏弹性波动方程模拟地震低频阴影  

Low-frequency shadow numerical simulation with visco-elastic wave equation

作　　者：兰锋[1] 李明[1] 李艳东[1] 田瀚[1] 

机构地区：[1]中国石油勘探开发研究院,北京100083

出　　处：《石油地球物理勘探》2015年第1期84-90,16,共7页Oil Geophysical Prospecting

摘　　要：以地震频谱分解为基础的低频阴影提取技术是一项有效的烃类检测方法,但是对于低频阴影的产生机理一直缺少明确的解释。本文通过建立含流体饱和介质的等效地质模型,采用黏弹性波动方程进行正演模拟,对得到的合成地震记录进行频谱分解,探讨低频阴影现象的产生机制。在低频(如15Hz)瞬时频谱剖面中,含油气储层下方表现为强能量团;当频率增加到55Hz以上时,含油气储层下方的能量则比低频瞬时剖面中对应位置的能量要弱得多,这就是典型的低频阴影现象。对低频阴影形成条件的分析结果表明,对于具有低Q值(QP小于90,QS小于70)且达到一定厚度(厚度大于半个地震波长)的储层,低频阴影现象明显,出现在储层下方最先存在波阻抗差异的地层界面处。Based on the instantaneous spectral analysis(ISA)method,low-frequency shadows(LFSs)have been used as an effective hydrocarbon indicator.But the cause of these shadows is unclear.We try here to find out the cause with numerical simulation method. With equivalent fluid-saturated media models,we perform the forward modeling by visco-elastic wave equation based on the KelvinVoigt model.Then we obtain corresponding ISA sections of different seismograms using time frequency continuous wavelet transform(TFCWT).On low-frequency(e.g.15Hz)ISA sections,the spectral energy of the area under oil-bearing reservoirs is much stronger than that of the same area on high-frequency ISA sections(e.g.>55Hz).Our study reveals that LFS is more apparent if reservoir is thicker(>λ/2)and quality factors are lower(QP<90and QS<70).It is concluded that LFSs will appear around the first interface with impedance difference under reservoirs.

关 键 词：低频阴影 地震波衰减 黏弹波动方程 频谱分解 

分 类 号：P631[天文地球—地质矿产勘探]