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Three Dimensional Tensor Controlled Source Electromagnetic Modeling Based The Vector Finite Element Method

Posted on:2016-04-25Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y C HuFull Text:PDF
GTID:1220330467493957Subject:Earth Exploration and Information Technology
Abstract/Summary:PDF Full Text Request
Due to the use of artificial source emits, controlled source audio-frequencymagnetotellurics(CSAMT) has many characters such ashigher anti-jamming abilityand higher SNR,it has been widely used in deep prospecting, groundwater exploration,and other fields. However, scalar CSAMT measurement always be used in thepractical application.It always be made2D inversion interpretation, even1D inversioninterpretation in the processing and interpretation of data, never theless, someerrorswill be resulted for the complexof3D geoelectric structure using scalarobservation data. Therefore, tensor CSAMT measurement should be used in thepractical application.First of all, based on the previous results, the six components of magnetic fieldand electric fieldwhich produce by the X and Y directions the finite length wire arecalculated by using Green function in the layered medium, and are verified on the halfspace. It can be seen very high precision from the error curve. The forward modelingof1D tensor CSAMT is achieved, and impedance tensor, resistivity, and impedancephaseof the many geoelectric section on the half-space, two-layers, and three-layersmodel are shown, that are compared with1D scalar CSAMT.Considering the rockresistivity changed with the frequency, the Cole-Cole model is also added to1Dtensor CSAMT, and in this paper, it was studied the effect of four parameters in theCole-Cole model on the impedance tensor, resistivity, and impedance phase of the1Dtensor CSAMT.Secondly, the3D tensor CSAMT forward modeling is achieved by using vectorfinite element method. The total magnetic field will be respectively solved that isdivided into the background field and the scattered field (secondary field).Background field is calculated with analytic solution, and the scattered field(secondary field) is calculated by using vector finite element method. In this paper,the boundary value problem of3D CSAMT is derived from Maxwell equations.According to generalized variational principle, we solve the minimum of function aland then we get the forward linear algebraic equations. By solving the equations, weget each side of the field. In the simulation, we used a rectangular mesh, which issimple interpolation function component, fast calculation speed. Moreover, theuncontinuity of the electric field normal direct is satisfied by using vector finiteelement method, therefore it will not do scatter correction. In three-dimensional tensorCSAMT simulation, the calculation formula of impedance tensor is suitable for1D,2D, and3D. In order to verify the correctness of the3D algorithm, theelectromagnetic field and the impedance tensoris calculated in three layered mediamodel, and from the statistical results in the error of the numerical solution andanalytical solution, it shows that the calculation accuracy of the high frequencyelectromagnetic field calculation is below1.5%, the calculation accuracy of the lowfrequency electromagnetic field calculation is below5%, and the calculation accuracyof the impedance tensor is below3%, so three-dimensional CSAMT tensorcalculation is correct andrelatively high precision by usingvector finite elementmethod. After that, in the model of3D abnormal body example which contain3Dresistive body or low resistivity body, impedance tensor model, resistivity andimpedance phase of the forward response are shown separately, and theircharacteristics areanalyzed. At last, the resistivity and phaseresponse of3D tensorCSAMT in the2D model and3D model were comparison, and the calculationaccuracy and efficiency of three-dimensional finite element method and finitedifference methodare analyzed.Finally, The Cole-Cole model is also added to3D tensor CSAMT forward, and3D tensor CSAMT with IP effect is achieved. The effect of the four parameters in theCole-Cole model on the3D tensor CSAMT was discussed, and the results show thatInfluence of polarization effect of tensor is relatively large, therefore, it should beconsidered in the IP effect in the CSAMT actual data processing.
Keywords/Search Tags:VFEM, CSAMT, Impedance tensor, Model, Cole-Cole
PDF Full Text Request
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