各向异性介质中可控源音频大地电磁三维数值模拟

发布时间：2018-03-08 02:09

本文选题：各向异性　切入点：CSAMT　出处：《吉林大学》2017年硕士论文　论文类型：学位论文

【摘要】：可控源音频地电磁测法(CSAMT)是利用人工源发出各种频段的电磁波信号,通过在远区接收信号,得到观测区域的视电阻率的频率域测深法。该方法具有较高的分辨率,信噪比高,而且观测时间短,因此越来越多地被应用在野外勘探中,特别是近年来在地热勘探方面的应用越来越广泛。随着可控源音频大地电磁法的快速发展,三维CSAMT正反演理论正成为新的探讨的热点。目前关于可控源音频大地电磁法三维正演的研究大多是基于各向同性介质的,但是由于地下沉积和岩石成分的影响,实际地下介质特别复杂,表现出电各向异性,基于各项同性的理想情况很难真实地反映地下构造,所以各向异性可控源音频大地电磁法的研究更有实际意义。此外,在实际勘探中,采用人工源作为场源有利也有弊,与MT相比造成了一些额外的效应,包括各种场源效应和静态效应等,这些效应的存在使得卡尼亚视电阻率受到影响,不利于地下构造的分析。研究分析各向异性和场源效应对CSAMT实际应用的影响,对可控源三维正反演有着重要意义。本文主要研究了各向异性介质中可控源三维数值模拟的有限差分算法,并应用模拟了可控源电磁法中常见的场源效应和静态效应问题。介绍了CSAMT法出现场源效应和静态效应的特殊情况,然后介绍了各向异性介质中电导率的处理问题,随后根据前人在可控源电磁法三维正演和各向异性频率域电磁正演的研究,以麦克斯韦方程组为起点,独立地逐步推导了CSAMT包括人工源的控制方程,加入边界条件,基于交错采样有限差分法进行网格剖分,结合各向异性介质的不同方向电阻率不同的特性,构建了各向异性介质中CSAMT的正演方程组。首先使用Krylov方法预处理得到的大型稀疏矩阵,而后使用QMR算法进行求解,求解过程中加入散度校正方法,加快了方程求解的速度,同时使求解精度得到了保证。利用FORTRAN语言完成了各向异性介质中可控源电磁法三维正演模拟程序,随后利用层状模型对程序进行了验证。基于该三维正演程序分别模拟了各向异性介质中的场源效应、静态效应,通过设置不同各向异性强度,以及改变异常体的高阻和低阻性质,得到各种情况下的视电阻率相位曲线,以及XY平面图和拟断面图,并将得到的数据与均匀大地各向同性下的数据进行对比,分析了各向异性与场源效应和静态效应之间的相互关系。
[Abstract]:The controllable source audio ground electromagnetic method (CSAMT) is a frequency-domain sounding method for obtaining the apparent resistivity of the observed region by using artificial sources to send out electromagnetic wave signals in various frequency bands. The method has high resolution and high signal-to-noise ratio (SNR). And the observation time is short, so it is more and more widely used in field exploration, especially in geothermal exploration in recent years. With the rapid development of controllable source audio magnetotelluric method, The theory of 3D CSAMT forward and inverse modeling is becoming a new research hotspot. At present, most of the researches on the 3D forward modeling of controlled source audio magnetotelluric method are based on isotropic media, but due to the influence of underground deposition and rock composition, The actual underground media is very complicated and shows electrical anisotropy. It is difficult to reflect the underground structure in the ideal condition of each homogeneity, so the study of the anisotropic controllable source audio magnetotelluric method is more practical. In addition, the study of the anisotropic controllable source audio magnetotelluric method is more practical. In actual exploration, using artificial source as field source has both advantages and disadvantages. Compared with MT, some additional effects are caused, including various field source effects and static effects, which make Kania apparent resistivity affected. It is not conducive to the analysis of underground structures. The effects of anisotropy and field source effects on the practical application of CSAMT are studied. In this paper, the finite difference algorithm for 3D numerical simulation of controllable sources in anisotropic media is studied. The problems of field source effect and static effect in controlled source electromagnetic method are simulated. The special case of field source effect and static effect by CSAMT method is introduced, and the treatment of conductivity in anisotropic medium is introduced. Then, based on the previous studies on the three-dimensional forward modeling of controllable source electromagnetic method and anisotropic frequency domain electromagnetic forward modeling, and taking Maxwell's equations as the starting point, the governing equations of CSAMT, including artificial sources, are derived step by step independently, and boundary conditions are added. Based on the staggered sampling finite difference method, the meshing method is used to combine the different resistivity characteristics of anisotropic media in different directions. In this paper, the forward equations of CSAMT in anisotropic medium are constructed. The large sparse matrix obtained by Krylov method is preprocessed first, and then solved by QMR algorithm. The divergence correction method is added in the process of solving the equation, which accelerates the speed of solving the equation. At the same time, the accuracy of the solution is guaranteed. The 3-D forward modeling program of controllable source electromagnetic method in anisotropic medium is completed by using FORTRAN language. Then the program is verified by using layered model. Based on the 3D forward program, the field source effect and static effect in anisotropic medium are simulated, and different anisotropic strength is set up. The phase curves of apparent resistivity, XY plane diagram and pseudo-sectional diagram are obtained by changing the properties of high and low resistivity of anomalous bodies, and the obtained data are compared with those of isotropic homogeneous earth. The relationship between anisotropy, field source effect and static effect is analyzed.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P631.325

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