本文關(guān)鍵詞： 可控源電磁法 三維正演 三維反演 反演理論 MPI 并行計(jì)算　出處：《中國(guó)地質(zhì)大學(xué)》2015年博士論文　論文類型：學(xué)位論文

【摘要】：頻率域可控源電磁法(controlled-source electromagnetic methods, CSEM)通過觀測(cè)人工場(chǎng)源在地層、空氣和海水等介質(zhì)中激發(fā)的電磁場(chǎng)來獲取介質(zhì)的電性分布,長(zhǎng)期以來一直是金屬礦勘探中最重要的地球物理方法,并在最近十多年逐漸成為海洋油氣勘探中一種不可或缺的地球物理技術(shù)。為了通過CSEM觀測(cè)數(shù)據(jù)盡可能真實(shí)地還原出介質(zhì)的電性結(jié)構(gòu)以提升勘探效果,實(shí)施三維勘探并對(duì)數(shù)據(jù)進(jìn)行三維模擬是必需的。反演是電磁資料的處理解釋中極其關(guān)鍵的一步,目前可控源電磁法已經(jīng)從最初的一維地電結(jié)構(gòu)假設(shè)步入到二維甚至三維反演階段。本文的主要目標(biāo)是發(fā)展出一套高效、準(zhǔn)確且既適用于陸地勘探又適用于海洋勘探的頻率域CSEM三維正演與反演模擬工具。正演模擬是反演模擬的核心。電磁法的三維數(shù)值模擬是一個(gè)對(duì)數(shù)值算法和計(jì)算機(jī)硬件要求都非常高的問題。對(duì)常用的微分類方法如有限單元法和有限差分法而言,求解最后所得的大型線性系統(tǒng)方程是至關(guān)重要的一步,直接影響到正演算法的實(shí)用性。如何高效、穩(wěn)定且準(zhǔn)確地解線性方程長(zhǎng)期以來一直是被探討的問題。本文實(shí)現(xiàn)了基于線性系統(tǒng)直接求解技術(shù)的頻率域可控源電磁(CSEM)三維正演。使用交錯(cuò)網(wǎng)格有限體積法(FV)來離散化關(guān)于二次電場(chǎng)的Helmholtz方程；使用直接解法取代傳統(tǒng)的迭代解法來求解離散線性系統(tǒng),即對(duì)系統(tǒng)矩陣進(jìn)行完全LU分解,具體通過調(diào)用大規(guī)模并行矩陣直接求解器(MUMPS)來實(shí)現(xiàn)�；诶碚撃Ｐ妥隽艘幌盗袛�(shù)值實(shí)驗(yàn),證明了直接解法的高精度和穩(wěn)定性,并考察了其內(nèi)存需求、計(jì)算時(shí)間和并行可伸縮性等主要計(jì)算性能,檢驗(yàn)了所開發(fā)的算法快速模擬多場(chǎng)源CSEM問題的能力以及對(duì)常規(guī)海洋和陸地CSEM模擬的有效性。在使用電偶極發(fā)射源的可控源電磁法(CSEM)勘探中,發(fā)射源的方位、長(zhǎng)度、形狀等對(duì)觀測(cè)數(shù)據(jù)有重要的影響,然而現(xiàn)有的大部分三維數(shù)值模擬方法沒有全面地將這些因素考慮進(jìn)來,很多都只能應(yīng)對(duì)非常簡(jiǎn)單的場(chǎng)源形態(tài),例如單一方位的點(diǎn)電偶極子,這有可能顯著降低模擬結(jié)果的準(zhǔn)確性。本文的三維正演算法能夠模擬形態(tài)相對(duì)復(fù)雜的場(chǎng)源,包括任意方位的有限長(zhǎng)直導(dǎo)線和彎曲導(dǎo)線發(fā)射源。由于了使用一次場(chǎng)／二次場(chǎng)方法,只要在計(jì)算一次場(chǎng)時(shí)考慮復(fù)雜的場(chǎng)源形態(tài)便可以實(shí)現(xiàn)同樣場(chǎng)源的三維正演。通過與一維理論模型的解析解對(duì)比驗(yàn)證了三維程序的準(zhǔn)確性,并針對(duì)三維理論模型進(jìn)行了一系列正演測(cè)試,初步考察了場(chǎng)源形態(tài)對(duì)三維正演結(jié)果的影響。闡述了當(dāng)前電磁反演中主流的線搜索類方法的優(yōu)化計(jì)算思路,對(duì)這一類反演方法中的最核心的數(shù)值計(jì)算問題——靈敏度矩陣的計(jì)算問題作了詳細(xì)的討論。基于面向?qū)ο蟮摹澳K化電磁反演系統(tǒng)”ModEM框架,實(shí)現(xiàn)了并行化的頻率域CSEM的三維反演。通過理論模型的反演試驗(yàn),驗(yàn)證了三維反演程序的有效性。
[Abstract]:The frequency domain controlled source electromagnetic method (CSEMEM) has been the most important geophysical method in metal ore exploration for a long time, by observing the electromagnetic fields excited by artificial field sources in strata, air and sea water, etc. In the last decade or so, it has gradually become an indispensable geophysical technique in offshore oil and gas exploration. In order to restore the electrical structure of the medium as truthfully as possible through the CSEM observation data, It is necessary to carry out 3D exploration and 3D simulation of data. Inversion is an extremely critical step in the processing and interpretation of electromagnetic data. At present, the controllable source electromagnetic method has moved from the initial assumption of one dimensional geoelectric structure to the stage of two-dimensional or even three-dimensional inversion. The main goal of this paper is to develop a set of high efficiency. The frequency domain CSEM 3-D forward modeling and inversion simulation tool, which is accurate and suitable for both land exploration and ocean exploration, is the core of inversion simulation. The electromagnetic three-dimensional numerical simulation is a logarithmic algorithm and calculation. For the commonly used micro-classification methods such as finite element method and finite difference method, Solving the final equations of large linear systems is a very important step, which directly affects the practicability of forward algorithm. The stable and accurate solution of linear equations has been discussed for a long time. In this paper, three dimensional forward modeling of frequency domain controllable source electromagnetic (CSEMM) based on direct solution technique of linear systems is realized. Discretization of the Helmholtz equation for the quadratic electric field; The direct solution is used instead of the traditional iterative method to solve the discrete linear system, that is, the complete LU decomposition of the system matrix. A series of numerical experiments based on the theoretical model are carried out to prove the high accuracy and stability of the direct solution, and the memory requirement of the direct solution is investigated. Main computing performance, such as computing time and parallel scalability, The ability of the developed algorithm to quickly simulate the multi-field source CSEM problem and the effectiveness of the conventional oceanic and terrestrial CSEM simulation are tested. The azimuth and length of the emission source in the electromagnetic-controlled source exploration of the electric dipole emitter are tested. However, most of the existing 3D numerical simulation methods do not fully take these factors into account, and many can only deal with very simple field source shapes, such as single azimuth spot electric dipoles. This may significantly reduce the accuracy of the simulation results. The 3-D forward algorithm in this paper can simulate relatively complex field sources, including finite length straight conductors and curved wire emitters with arbitrary azimuth. The three-dimensional forward modeling of the same field source can be realized by considering the complex field source shape when calculating a single field. The accuracy of the three-dimensional program is verified by comparing the analytical solution with the one-dimensional theoretical model. A series of forward modeling tests are carried out for the 3D theoretical model, and the influence of field source morphology on the 3D forward modeling results is preliminarily investigated. The optimal calculation ideas of the current mainstream line search methods in electromagnetic inversion are expounded. In this paper, the calculation of sensitivity matrix, which is the most important numerical computation problem in this kind of inversion method, is discussed in detail. Based on the object-oriented ModEM framework of "modularized electromagnetic inversion system", The parallel 3D inversion of CSEM in frequency domain is realized, and the validity of the 3D inversion program is verified by the inversion experiment of the theoretical model.
【學(xué)位授予單位】：中國(guó)地質(zhì)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：P631.325

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