海洋電磁一維正反演中英文摘要

1、-作者xxxx-日期xxxx海洋電磁一維正反演中英文摘要【精品文檔】海洋可控源電磁法一維正演與OCCAM反演研究作者簡介：劉方鏑，性別：男，1986年12月生，師從成都理工大學王緒本教授，2012年06月畢業(yè)于成都理工大學信號與信息處理專業(yè)，獲得工學碩士學位。摘 要1982年，Alan D.Chave和Charles S.Cox得到了頻率域中水平電偶源電磁場的解，至此海洋可控源電磁法一維的研究拉開了序幕。海洋可控源電磁法(Marine Controlled Source Electromagnetic)使用移動式水平導線源和海底電場接收機陣列。發(fā)射電極源盡量放置于深海處以減小來自水-空氣界面的

2、空氣波以及空間電磁噪聲的影響。發(fā)射源發(fā)送的低頻(十分之幾到幾十赫茲)電磁信號不僅向水中傳播而且向海底傳播。向海底傳播的電磁波進入海底，在那里與高阻層（可能含油氣）相互作用，產生響應電磁場，其中部分能量返回排列在海底的接收器。由于電磁波沿導電層傳播比沿高阻層傳播損耗更大，所以和缺乏高阻層的均質地層相比，油藏的出現(xiàn)會加強信號。地學家采用分析手段通過對比觀測資料和預測模型，或采用數(shù)學手段利用反演算法，能夠識別電阻率異常，并以此推斷地層結構信息。本文以現(xiàn)有的電磁場基本理論為基礎，分析研究了海洋可控源電磁法的基本理論與國內外最新發(fā)展狀況，主要完成了如下工作：(1)通過搜集和分析大量海洋大地電磁、海洋可控

3、源電磁等相關的技術資料，掌握了海洋可控源電磁法的基本原理，并介紹了海洋電磁法在國內外的研究現(xiàn)狀和發(fā)展趨勢，重點對頻率域海洋可控源電磁法做了研究。(2)介紹了電磁場與電磁波的基本理論，根據(jù)考夫曼推導水平層狀介質表面上電偶極子電磁場的思路，引入相關矢量位推導出了海洋可控源電磁法水平電偶極源在水平層狀介質時電磁場各分量解的表達式。(3)海洋可控源電磁法一維模型的正演研究。通過建立一系列常見模型，對其進行正演，驗證了海洋CSEM的可行性和有效性。通過模擬分析，研究了海洋CSEM磁場分量，電場分量對海底高阻層的響應情況，比較了上述分量對高阻層的敏感性。研究了發(fā)射源的幾何排列方式(Radial和Azimu

4、thal模式)與目標高阻層響應之間的關系，分析了發(fā)射源在徑向裝置和赤道裝置下對高阻體的敏感程度。通過模擬分析，討論了不同發(fā)射頻率下海洋CSEM的響應結果，對頻率的影響做了研究。對于海洋CSEM中影響結果重要因素之一的空氣波，本文通過設計恰當模型研究了空氣波對結果的影響與收發(fā)距、海水深度之間的關系，研究了海洋CSEM在淺海進行油氣探測的可行性。研究了海底高阻儲層的厚度對響應結果的影響，間接討論了程序對高阻薄層的分辨率。(4)海洋可控源電磁法一維OCCAM反演研究。本文在正演的基礎上，簡要概述了地球物理的相關反演算法，重點介紹了OCCAM反演的基本理論。 OCCAM反演不依賴初始模型，通過對模型進

5、行光滑約束，在擬合觀測數(shù)據(jù)的同時，使模型盡量光滑，并在可以擬合觀測數(shù)據(jù)的多個模型中，選擇最光滑模型作為反演結果，極大的改善了反演的多解性，是現(xiàn)在國外海洋CSEM一維反演的主流算法。本文在掌握了OCCAM反演基本原理的基礎上，將OCCAM算法應用到海洋CSEM反演中。通過建立模型，研究了不同發(fā)射頻率組合對OCCAM反演效果的影響。分析了不同海洋噪聲水平對反演結果的影響程度。討論并比較了在不同發(fā)射模式下的反演效果，得出相關結論對實際資料的反演提出了建設性建議。最后結合實際情況，通過建立復雜油藏模型并對初始模型加入限制性約束條件對其進行約束反演，極大的提高了反演精確度，達到了預期效果。關鍵詞：海洋電

6、磁法勘探； 油氣識別； OCCAM反演； 可控源【精品文檔】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