海洋电磁勘探中空气波相互作用机制和水深影响分析  

Analysis of air wave interaction mechanism and effect of sea water depth on electromagnetic prospecting

作　　者：沈金松[1,2,3] 詹林森[1] 王鹏飞[1] 马超[1] 连福明[1] 

机构地区：[1]中国石油大学地球物理与信息工程学院,北京102249 [2]中国石油大学油气资源与探测国家重点实验室,北京102249 [3]中国石油大学中国石油集团公司物探重点实验室,北京102249

出　　处：《中国石油大学学报（自然科学版）》2011年第6期51-58,共8页Journal of China University of Petroleum(Edition of Natural Science)

基　　金：国家'973'重点基础研究发展计划项目(2007CB209607);中国石油天然气集团公司基础研究项目(07A10303)

摘　　要：基于一维层状介质的电磁位和电磁场分析,采用电磁场的模式分解理论建立空气、海水层和海底地层之间的电磁场相互作用关系。以假想无限水深模型和五层介质模型为基础,导出水平电偶极子(HED)的横电(TE)和横磁(TM)模式的电磁场数学关系,分析空气波占优的临界偏移距随水深和海底地层电导率的变化规律,指出前人定义的300 m水深作为浅水域和深水域分界深度的缺陷。以电磁响应理论为基础,讨论空气波与其他介质层相互作用强耦合特征,考察电磁响应水平分量与垂直分量受空气层相互作用影响的差异和横电与横磁模式受空气波影响的不同特征。结果表明:空气波是电磁波在空气层、海水层和海底地层的相互耦合作用下产生的散射波场,且在TM和TE两种模式上表现出较大差异;电场垂直分量只有TM模式的贡献,受空气波影响小,测量垂直电场分量将有利于减弱空气波的影响;要根据海底电导率、水深和偏移距的关系确定空气占优的临界偏移距,不能笼统定义深水和浅水的界限。Based on the analysis of electromagnetic （EM） potential and electromagnetic field of 1D layer model, the interac- tion relationships of EM fields among air, sea Water layer and undersea formation were established by using mode decomposition theory of EM field. Based on the presumed infinite sea water model and five-layer model, the EM field expressions of the TE and TM modes which were decomposed from the EM responses excited by the horizontal electric dipole （HED） source were derived. The variation laws of critical offsets with the under sea floor conductivity and sea water depth. It is pointed out that the conventional recognition of former researchers of the boundary depth of 300 m between the deep sea water and shallow water has drawbacks. Theoretical analysis shows that the air wave interaction with signals from other media is strongly cou- pled, and the ways that the horizontal and vertical electromagnetic components, also the TM mode and the TE mode are con- taminated by the air waves are very different. Numerical results show that the air wave is a kind of diffusive wave interacted among sea surface, sea water and undersea formation, and the effects of the air wave interaction on TM and TE modes present significant differences. And the vertical component E has only TM mode and is affected by the air wave on the least degree. Therefore, measurement of Ex component is of helpful in reducing the effects of the air wave. In practical use, it is necessary to define the critical offset by considering the relationship among under sea floor formation conductivity, sea water depth and the offset, and the conventional boundary concept between deep water and shallow water has drawbacks.

关 键 词：电磁勘探 电磁场 电磁波 电导率 空气波相互作用 模式分解 层状介质模型 

分 类 号：P631.4[天文地球—地质矿产勘探]