【作者】 余传涛；

【导师】 刘鸿福；

【作者基本信息】 太原理工大学 ， 矿产普查与勘探， 2012， 博士

【摘要】 CSAMT法勘探采用人工建立的交变电场作为激发源会使地下极化介质产生激发极化效应,受此影响电流场作用范围内的大地电阻率应是一个与供电频率相关的复电阻率。然而在实际CSAMT的数据采集和处理过程中,认为大地电阻率与发射频率无关,这会给数据处理结果带来较大的误差,影响CSAMT法的探测精度。为此,本文以岩矿石的激发极化特性为基础,对稳定电流场以及交变电流场作用下的岩矿石的激发极化特性进行了研究,并基于岩矿石激发极化效应的Cole-Cole模型,讨论了岩矿石的复电阻率与Cole-Cole模型参数之间的关系；研究了复电阻率的虚分量、实分量、振幅及相位的频谱特性。结果表明：复电阻率振幅的频谱特性与实分量的频谱特性是相似的,即二者随频率的增大而减小,在频率较低时,二者均趋于直流电阻率值,而在频率较高时趋于无极化率时的初值；相位频谱特性与虚分量的频谱特性是相似的,即二者均随着充电率值的增大而增大,在频率较低和频率较高时相位与虚分量的数值皆趋于零,且在某个频率点处达到极值,而虚分量极值的大小只与时间指数有关(与时间指数成反比),相位的极值不仅与时间指数有关还与充电率和频率相关系数有关。在上述工作基础上,本文采用均匀半空间的Cole-Cole模型,研究了CSAMT电磁场各分量、视电阻率和相位与相关参数的关系,得到了充电率对正演结果的影响最大,频率相关系数次之,且时间指数影响最小的结论；研究了CSAMT电场Ex分量和磁场Hy分量在不同参数下随频率的变化特征,给出了①当固定模型的频率相关系数及时间指数参数而改变充电率参数时,电场Ex分量的实部和虚部的正演结果均为负值,其曲线的变化规律是相同的；②Ex分量的正演结果在低频段比较接近,而在高频段与充电率的大小是密切相关的,即充电率越大,正演结果值越小；③正演结果结果表明,磁场Hy的实部与参数的变化无关,不同参数下的虚部随频率变化,其规律是与电场Ex分量相似的。本文通过建立的三层电阻率模型,对极化层位于不同层位时的视电阻率、视相位、视电阻率比值和视相位比值的曲线特征进行了研究。结果表明：不同电阻率模型的视电阻率比值和视相位比值的异常反应最为直观,且二者曲线的形态相似,而前者曲线极值点所对应的频率略高,由此可知视电阻率比值和视相位比值异常只与极化层的深度和极化率大小有关,而与模型的电阻率无关。其次本文对4个经典2D模型进行了含激发极化效应的CSAMT2D正演模拟,得出视电阻率、视相位和视电阻率比值、视相位比值能更直观地反应异常的特性,且视电阻率出现异常时的频率比视相位出现异常时的频率高,视电阻率比值出现异常时的频率比视相位比值出现异常时的频率高。通过上述研究,本文提出了CSAMT与IP测深数据联合反演的方法,并用已知模型的正演结果数据进行验证,发现当介质存在激发极化特性时,联合反演比常规的CSAMT反演能更准确地反映异常体的位置和范围,由此表明联合反演方法具有一定应用前景。最后将该方法应用于浙江某铜多金属矿CSAMT及IP测深数据的反演,划分出了有利成矿带的位置、范围,推断了断层F5和F6的位置。通过布置K002号钻孔进行验证,与反演结果基本吻合,证明了该联合反演方法的有效性。更多还原

【Abstract】 In the exploration of controlled source audio-frequency magnetotellurics method (CSAMT),the artificial established alternative electric field, as the excitation source, will make hypogeal polarization medium produce induced polarization effect, owing to which the current earth resistivity in fact is a plural complex number to the line frequency. However, the earth resistivity is simply considered as a real number that is irrelated to the frequency while people collect and deal with the data in practice. Obviously, the change of real numbers to complex one will bring huge error to the data.In order to solve the problem, starting with the induced polarization characteristic (IPC) of rock ores, this thesis makes a thorough analysis on IPC in the field of stable electric current and alternating electric current in the first place. Then based on the Cole-Cole model of IPE, it explains the relationship between complex resistivity and the parameter of Cole-Cole model. Also, it expatiates the characteristic of real component, imaginary component, amplitude and phase for the complex resistivity. A conclusion can be drawed as follows: The frequency spectrum characteristic of complex resistivity amplitude is similar with that of real component. Both decrease with increasing frequency. They will tend towards direct current resistivity ρ0when frequency is low;(1-η)ρ0, when high. Likewise, the frequency spectrum characteristic of phase and that of imaginary component resemble with each other. Both increase with the increasing charging rate values. The numerical value of them will incline to zero when the frequency is both high and low, and an extreme will be obtained in a certain middle frequency. The extreme of imaginary component is only related to time constant, inversely proportional to time constant (τ). Nevertheless, the extreme of phase is related to charging rate (m), time constant (τ) and frequency exponent (c).The regulations of the impact of symmetrical semi-space Cole-Cole model parameter change on various component, apparent resistivity and apparent phase in CSAMT magnetic field imply some enlightenments as follows:Firstly, the data of the real part and imaginary part of direct gravimetric in electric field Ex are both negative numbers. The laws of curve are the same. Secondly, the value of the real part of magnetic field Hy maintained fixed. By contraries, the values of imaginary part vary with the change of frequency. Among the four parameters of Cole-Cole model, the impact of charging rate on forward result is the most intense one, then the frequency, the time constant ranks in the end.As for three layers of resistivity models, this thesis also probes deeply into the abnormal feature of specific value for the curve of apparent resistivity, apparent phase, and the ratio of them. In a conclusion, both apparent resistivity and apparent phase of different resistivity models present out of the way intuitionally. Moreover, the configurations of these two curves resemble with each other. And the frequency of apparent resistivity ratio extreme is a bit higher than that of apparent phase ratio. As is educed from the above passage, it is the depth of polarization layer and the scale of polarization ratio, that have something to do with the ratio of apparent resistivity and apparent phase, but have nothing to do with the resistivity models.This thesis also analyzes the CSAMT2D forward modeling of IPE for single low resistivity medium model, single high resistivity medium model, dual resistance medium one and fault’s. It is noticed that the consideration of IPE of medium makes the abnormity of forward modeling data more distinct than that showed without consideration of IPE. And likewise, apparent resistivity, apparent phase, and the ratio of them can intuitively reflect the characteristic of abnormity. The abnormity of apparent resistivity is more frequent than that of apparent phase. Similarly, the same thing happens on the ratio of apparent resistivity and apparent phase.A thought of joint inversion between CSAMT and induced polarization (IP) sounding has been put forward. It is discovered that whenever the medium is characterized by IPE, the data of joint inversion can fix the position and scope more exactly than those of CSAMT, which proves the superiority of joint inversion. The theory of joint inversion has been put into practice in the joint inversion of a Zhejiang cuprum polymetallic ore CSAMT and IP sounding. The position and scale of metallogenic belt have been marked off; the spots of fault of F5and F6have also been deduced. The experiment on ZK002drill hole discloses that Ⅰ、Ⅱ、Ⅲ、Ⅳ copper ore bodies are indigenous to crypto explosive breccia chimney and the F5and F6faults certainly exist. In a word, the joint inversion method is effectively feasible through the practical engineering.更多还原