海洋电磁一维正反演中英文摘要

1、-作者xxxx-日期xxxx海洋电磁一维正反演中英文摘要【精品文档】海洋可控源电磁法一维正演与OCCAM反演研究作者简介：刘方镝，性别：男，1986年12月生，师从成都理工大学王绪本教授，2012年06月毕业于成都理工大学信号与信息处理专业，获得工学硕士学位。摘 要1982年，Alan D.Chave和Charles S.Cox得到了频率域中水平电偶源电磁场的解，至此海洋可控源电磁法一维的研究拉开了序幕。海洋可控源电磁法(Marine Controlled Source Electromagnetic)使用移动式水平导线源和海底电场接收机阵列。发射电极源尽量放置于深海处以减小来自水-空气界面的

2、空气波以及空间电磁噪声的影响。发射源发送的低频(十分之几到几十赫兹)电磁信号不仅向水中传播而且向海底传播。向海底传播的电磁波进入海底，在那里与高阻层（可能含油气）相互作用，产生响应电磁场，其中部分能量返回排列在海底的接收器。由于电磁波沿导电层传播比沿高阻层传播损耗更大，所以和缺乏高阻层的均质地层相比，油藏的出现会加强信号。地学家采用分析手段通过对比观测资料和预测模型，或采用数学手段利用反演算法，能够识别电阻率异常，并以此推断地层结构信息。本文以现有的电磁场基本理论为基础，分析研究了海洋可控源电磁法的基本理论与国内外最新发展状况，主要完成了如下工作：(1)通过搜集和分析大量海洋大地电磁、海洋可控

3、源电磁等相关的技术资料，掌握了海洋可控源电磁法的基本原理，并介绍了海洋电磁法在国内外的研究现状和发展趋势，重点对频率域海洋可控源电磁法做了研究。(2)介绍了电磁场与电磁波的基本理论，根据考夫曼推导水平层状介质表面上电偶极子电磁场的思路，引入相关矢量位推导出了海洋可控源电磁法水平电偶极源在水平层状介质时电磁场各分量解的表达式。(3)海洋可控源电磁法一维模型的正演研究。通过建立一系列常见模型，对其进行正演，验证了海洋CSEM的可行性和有效性。通过模拟分析，研究了海洋CSEM磁场分量，电场分量对海底高阻层的响应情况，比较了上述分量对高阻层的敏感性。研究了发射源的几何排列方式(Radial和Azimu

4、thal模式)与目标高阻层响应之间的关系，分析了发射源在径向装置和赤道装置下对高阻体的敏感程度。通过模拟分析，讨论了不同发射频率下海洋CSEM的响应结果，对频率的影响做了研究。对于海洋CSEM中影响结果重要因素之一的空气波，本文通过设计恰当模型研究了空气波对结果的影响与收发距、海水深度之间的关系，研究了海洋CSEM在浅海进行油气探测的可行性。研究了海底高阻储层的厚度对响应结果的影响，间接讨论了程序对高阻薄层的分辨率。(4)海洋可控源电磁法一维OCCAM反演研究。本文在正演的基础上，简要概述了地球物理的相关反演算法，重点介绍了OCCAM反演的基本理论。 OCCAM反演不依赖初始模型，通过对模型进

5、行光滑约束，在拟合观测数据的同时，使模型尽量光滑，并在可以拟合观测数据的多个模型中，选择最光滑模型作为反演结果，极大的改善了反演的多解性，是现在国外海洋CSEM一维反演的主流算法。本文在掌握了OCCAM反演基本原理的基础上，将OCCAM算法应用到海洋CSEM反演中。通过建立模型，研究了不同发射频率组合对OCCAM反演效果的影响。分析了不同海洋噪声水平对反演结果的影响程度。讨论并比较了在不同发射模式下的反演效果，得出相关结论对实际资料的反演提出了建设性建议。最后结合实际情况，通过建立复杂油藏模型并对初始模型加入限制性约束条件对其进行约束反演，极大的提高了反演精确度，达到了预期效果。关键词：海洋电

6、磁法勘探； 油气识别； OCCAM反演； 可控源【精品文档】1-D Marine Controlled Source Electromagnetic Methods Forward Modeling And OCCAM Inversion ResearchIntroduction of the author: Liu fangdi, male, was born in December, 1986 whose tutor was Professor Wang xuben. He graduated from Chengdu University of Technology in Signal

7、and Information Processing major and was granted the Master Degree in June, 2012.AbstractIn the year of 1982, Chave and Cox got the solutions of the electric dipole source in frequency domain and the controlled source electromagnetic methods has been studied. Marine controlled source electromagnetic

8、(CSEM)surveying has been in commercial use for predrill reservoir appraisal and hydrocarbon exploration for 10 years. In this dissertation, we examine the sensitivity of the CSEM method to such layers with forward and Occams inversion modeling in one dimension. A deep-towed transmitter close to the

9、seafloor injects a current of several hundred amps into the seawater from an electric dipole, creating magnetic and electric fields that propagate diffusively into the seafloor. The electromagnetic waves generated from the source propagate into the seafloor and interact with the high resistance laye

10、r in there.Electric dipole receivers record the seafloor electric fields at various ranges from the transmitter. Because the electromagnetic waves spread along the conductive layer would get greater attenuation than spread along the high resistance layer, compared with the structure which lack of hi

11、gh resistance layer, the emergence of the reservoir will strengthen the receive signal. So comparing the observed data and the prediction model or inversion using the CSEM data, the geophysicists can recognize the resistivity anomalies and speculate the geological informations.Based on existing grou

12、nd electromagnetic method, the main research work and achievements are as follows:(1) In the beginning of this dissertation，we studied the basic principle of marine CSEM through collecting and analyzing a large number of informations about marine MT and marine CSEM.The history and the research statu

13、s of marine CSEM sounding is reviewed, and we lookforward to the future.(2) According to Maxwell's equations and the basic theory of electromagnetic fields, especially the ideal from Nabighian's method of deriving formula of electric dipole, we deduced the expressions for the electromagnetic

14、 induction fields produced by horizontal current source in the conducting ocean overlying a one-dimensional earth.(3) Research on Marine CSEM 1D modeling. First, we verified the feasibility and effectiveness of the CSEM by using a series of common models.Through the simulation analysis, the electric

15、 and the magnetic field components are used to compare the sensitivity to the high resistance layer. The geometry of generator and receiver is studied, and the result shows that radial dipole geometr are more sensitive to the presence of the thin resistive layer than the azimuthal fields. The differ

16、ent transmit frequency will effect the response results.The air wave is one of the most important factors in CSEM, in the dissertation this would be discussed. In addition, we also discussed the sea depth and the offset distance which would effect the response results. And a conclusion will be given

17、 that CSEM methods is not completel T-equivalent, particularly at higher frequencies.(4) Research on Marine CSEM 1D Occams inversion. Based on the 1D forward modeling, this dissertation gives a brief summarizes of the geophysics inversion methods and focus on the theory of Occams inversion. The mode

18、l studies here use Occams inversion method which solves the regularized problem by searching for the smoothest model that fits the data. The utility of this method is that it generally produces smooth peaks in the model that correspond to features that are well constrained by the data, whereas featu

19、res not constrained by the data will be smoothed over or entirely absent in the model.A brief reviewe of the Occams inversion approach is given in this paper. In this dissertation Synthetic data studies indicate that jointly inverting frequencies of 0.1 and 1.0 Hz offers better resolution than inverting either frequency alone. An inline horizontal electric dipole is