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  本文選題：可控源電磁法　切入點：各向異性　出處：《吉林大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：可控源電磁法是一種在地球物理勘探中常用的人工源低頻電磁勘探方法。通過電偶極源或長直導(dǎo)線源發(fā)射電磁波并接收電磁總場響應(yīng),進(jìn)而獲得地表或海洋環(huán)境下的電性信息。在過去,出于緩解反演多解性和節(jié)約計算成本的考慮,大多數(shù)國內(nèi)外三維可控源電磁法正反演均通過假設(shè)地下介質(zhì)的電各向同性來實現(xiàn)模擬計算。然而近年來的研究表示,在很多情況下,地下沉積層和晶粒排列方式會表現(xiàn)出很強(qiáng)的電各向異性。此時如果依舊采用傳統(tǒng)的各向同性正反演方法,反演結(jié)果會非常容易受到觀測響應(yīng)中原本包含的各向異性信息的影響,并在原異常周圍產(chǎn)生不準(zhǔn)確甚至錯誤的各向同性異常體。針對這個問題,本文的研究主要集中在開發(fā)出高效、穩(wěn)定的三維各向異性可控源正反演算法,并可同時適用于陸地勘探和海洋勘探。在正演方面,為了計算復(fù)雜三維電性介質(zhì)的電磁響應(yīng),本文首先將不同頻率的電磁波分解為發(fā)射源直接產(chǎn)生的一次場(背景場)與異常體感應(yīng)產(chǎn)生的二次場,其中一次場可以利用一維全空間頻率域?qū)訝罱橘|(zhì)偶極源格林函數(shù)進(jìn)行計算;二次場則是在麥克斯韋方程組和邊界條件的基礎(chǔ)上推導(dǎo)出有限差分離散正演方程組后,再將主軸各向異性電導(dǎo)率通過電流密度項引入方程組中,最后采用交錯網(wǎng)格有限差分法對推導(dǎo)出的離散二次電場的偏微分方程組進(jìn)行求解。在有限差分各向異性正演的基礎(chǔ)上,本文提出了一個三維頻率域可控源主軸各向異性反演算法,并將其應(yīng)用于理論模型算例中,得到了較好的反演效果。采用主軸各向異性的原因主要是主軸各向異性電阻率中存在較少的獨立電導(dǎo)率分量,這可以緩解反演的多解性并更容易得到可靠的反演結(jié)果;另一方面,主軸各向異性模型也適合對典型地質(zhì)情況分別進(jìn)行三個主軸方向的理論分析。在模型試算中,本文重點測試了將不同各向異性異常體嵌入各向同性大地介質(zhì)中的反演效果,以及兩種不同收發(fā)裝置對反演的影響,驗證了算法的有效性和穩(wěn)定性。
[Abstract]:The controllable source electromagnetic method is a commonly used artificial source low frequency electromagnetic exploration method in geophysical exploration. The electromagnetic wave is emitted by the electric dipole source or the long straight wire source and the total electromagnetic field response is received. And then get electrical information on the surface or in the marine environment. In the past, for the sake of mitigation, inversion, multiplicity, and cost savings, Most of the three dimensional controlled source electromagnetic forward inversion at home and abroad is simulated by assuming the electro isotropy of underground media. However, recent studies have shown that, in many cases, If the conventional isotropic forward and inverse method is still used, the inversion results will be easily affected by the anisotropic information originally contained in the observed response. In order to solve this problem, this paper focuses on the development of an efficient and stable 3-D anisotropic controllable source forward and inversion algorithm. And it can be applied to both land and ocean exploration. In the forward modeling, in order to calculate the electromagnetic response of complex three-dimensional electric medium, In this paper, the electromagnetic waves with different frequencies are first decomposed into the primary field (background field) generated directly by the emitter and the quadratic field induced by the anomalous body. The first order field can be calculated by using the Green's function of dipole source in layered media in one-dimensional full space frequency domain, and the quadratic field is derived from the finite difference discrete forward equations on the basis of Maxwell's equations and boundary conditions. Then the anisotropic conductivity of spindle is introduced into the equations by the current density term. Finally, the partial differential equations of discrete secondary electric field are solved by staggered grid finite difference method. On the basis of forward modeling of finite difference anisotropy, In this paper, a 3-D anisotropic inversion algorithm of controllable source spindle in frequency domain is proposed and applied to a theoretical model. The main reason of adopting spindle anisotropy is that there are less independent conductivity components in the resistivity of spindle anisotropy, which can alleviate the multi-solution of inversion and obtain reliable inversion results more easily. On the other hand, the principal axis anisotropy model is also suitable for the theoretical analysis of three principal axis directions for typical geological conditions. The inversion effect of embedding different anisotropic anomalous bodies into isotropic geodetic media and the influence of two different transceiver devices on the inversion are mainly tested in this paper. The validity and stability of the algorithm are verified.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：P631.325

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本文編號：1635732