WO2021042952A1 - 一种接地导线源瞬变电磁响应中ip信息的提取方法 - Google Patents

一种接地导线源瞬变电磁响应中ip信息的提取方法 Download PDF

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WO2021042952A1
WO2021042952A1 PCT/CN2020/108532 CN2020108532W WO2021042952A1 WO 2021042952 A1 WO2021042952 A1 WO 2021042952A1 CN 2020108532 W CN2020108532 W CN 2020108532W WO 2021042952 A1 WO2021042952 A1 WO 2021042952A1
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field
response
polarization
effect
transient electromagnetic
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PCT/CN2020/108532
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French (fr)
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周楠楠
雷康信
薜国强
陈稳
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中国科学院地质与地球物理研究所
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Priority to US17/375,255 priority Critical patent/US20210341638A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
    • G01V3/083—Controlled source electromagnetic [CSEM] surveying
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/12—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with electromagnetic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
    • G01V3/083—Controlled source electromagnetic [CSEM] surveying
    • G01V2003/086—Processing

Definitions

  • the invention belongs to the technical field of transient electromagnetic methods, and relates to a method for extracting IP information in the transient electromagnetic response of a grounded wire source.
  • transient electromagnetic method plays an important role in the exploration of metal minerals and geothermal resources.
  • the measured transient electromagnetic data contains the influence of the induced polarization effect. In severe cases, distortion and sign reversal will occur. It is particularly important to accurately analyze the influence law of the ip effect and accurately invert the transient electromagnetic data containing the ip effect.
  • Transient electromagnetics can be divided into loop sources (magnetic sources) and grounded wire sources (electrical sources) according to the form of field sources.
  • the analysis of the transient electromagnetic IP effect of the loop source can be traced back to 1980. After recognizing the change law of the response brought by ip, how to eliminate the impact of the Ip effect and further realize the inversion of transient electromagnetic data including the ip effect has become the first problem to be solved. There are relatively few researches on the IP effect in the grounded wire source transient electromagnetics.
  • IP information from the data of transient electromagnetic observation of the grounded wire source use the early transient response to invert the resistivity, and then forward to obtain the transient electromagnetic response within the observation time range, and remove the electromagnetic response from the observed data to obtain IP response, further inversion to obtain IP information, compared with the previous IP inversion based on DC data to obtain higher accuracy.
  • the observation of the horizontal electric field component is a major advantage of this method because of the horizontal electric field.
  • the component has strong resolving power for both high impedance and good guidance targets.
  • the difference in the detection ability of different electromagnetic components is closely related to the difference in the polarization type. Then, the influence of the IP effect on different components will also differ due to the different polarization types.
  • the purpose of the present invention is to provide a method for extracting IP information in the transient electromagnetic response of a grounded wire source.
  • a method for extracting IP information from the transient electromagnetic response of a grounding wire source including the following steps:
  • IP information such as the polarization rate, frequency correlation coefficient and time constant.
  • the grounded wire source transient electromagnetic method mainly observes the horizontal electric field and the vertical magnetic field, and the expression on the uniform layered earth surface is:
  • r is the distance from the source to the observation point, R and R'are the distances from the two ground electrodes to the observation point respectively;
  • 2L is the length of the emission source, J 1 ( ⁇ r) and J 0 ( ⁇ r) are the first order and Zero-order Bessel function of the first kind,
  • ⁇ represents a variable related to the wave number;
  • the intrinsic admittance of free space Means surface admittance
  • the intrinsic impedance of free space Represents the surface impedance (the surface impedance and admittance are obtained through the bottom layer recursion),
  • ⁇ represents the angular frequency, i represents a complex number,
  • ⁇ 0 represents the dielectric coefficient of the underground uniform half-space, and ⁇ 0 represents the permeability of the underground uniform half-space.
  • the response of the layered earth surface observation is only the TE polarization field, and the horizontal electric field includes both the TM generated by the ground term
  • the polarization field also includes the TE polarization field excited by the ground term and the wire source.
  • the (dispersion) complex resistivity of the Cole-Cole model can be expressed as:
  • ⁇ (i ⁇ ) is the dispersion resistivity including the induced polarization effect
  • ⁇ 0 is the zero-frequency resistivity
  • m is the charging rate or polarizability of the medium.
  • the charging rate affects the intensity of the spectrum, but does not affect the shape of the spectrum. , It is mainly affected by the content of metal minerals, the degree of mineral density and the degree of infiltration.
  • ⁇ is the time constant, which mainly affects the phase of the extreme value of the spectrum. Under certain conditions, it is most affected by the degree of densification, the depth of the ore body, and the scale.
  • c is the frequency correlation coefficient, which determines the visibility of the spectrum characteristics, which is mainly affected by the buried depth of the ore body; the forward model of the galvanic transient electromagnetic method with the induced polarization effect will be carried out, and the frequency domain electromagnetic method of the same device will be solved first Forward modeling, and use the complex resistivity of the Cole-Cole model to replace the DC resistivity of the formation in the frequency domain, and then use the sinusoidal transformation to obtain the transient electromagnetic response of the galvanic source with IP information.
  • ⁇ 0 10 -4 ⁇ 10 5 ⁇ m
  • m 0 ⁇ 0.98
  • ⁇ 10 -3 ⁇ 10 5 s
  • c 0.1 ⁇ 0.6.
  • the second layer is a polarized layer
  • the length of the emission source is 1000 meters, and the emission current is 10A.
  • the present invention has the following beneficial effects:
  • the present invention calculates the influence of the polarizer IP effect on the two types of fields through theoretical simulation, and the TM field is much more affected by the IP effect than the TE. Further analysis of the commonly used horizontal electric field and vertical magnetic field in the actual measurement are affected by the IP effect of the polarizer: under the same background model, the horizontal electric field containing TE and TM fields is affected by the IP effect much more than the vertical magnetic field containing only the TE field. For the two-line source transient electromagnetic dominated by the TM field, the influence of the IP effect is more obvious.
  • Figure 1 is a schematic diagram of the observation mode of transient electromagnetic of the grounding wire source
  • Figure 2 shows the response changes of different TE and TM fields affected by the IP effect (low-resistance polarization layer), where (a) is TM and (b) is TE;
  • Figure 3 shows the response changes of different TE and TM fields affected by the IP effect (high-resistance polarization layer), where (a) is TM and (b) is TE;
  • Figure 4 shows the changes in TE and TM fields caused by IP effects when the polarization parameters are different, (a_b) m parameters cause changes in TE and TM fields; (c, d) c parameters cause changes in TE and TM fields; (e, f) ⁇ parameters cause changes in TE and TM fields.
  • Figure 5 shows the traditional grounding wire source transient electromagnetic field affected by the polarization layer IP effect, (a) the vertical magnetic field response comparison affected by the IP effect; (b) the horizontal electric field response comparison affected by the IP effect
  • Figure 6 is the layout of the survey line
  • Figure 7 is a multi-channel diagram of the transient electromagnetic response of the grounding conductor source, where a) is Hz, b) is Ex,
  • Figure 8 is the observed vertical magnetic field and horizontal electric field, where a) is Hz and b) is Ex;
  • Figure 10 shows the drilling results.
  • the grounded wire source transient electromagnetic method mainly observes the horizontal electric field and the vertical magnetic field.
  • the expression on the uniform layered earth surface is:
  • r is the distance from the source to the observation point, R and R'are the distances from the two ground electrodes to the observation point respectively;
  • 2L is the length of the emission source, J 1 ( ⁇ r) and J 0 ( ⁇ r) are the first order and Zero-order Bessel function of the first kind,
  • ⁇ represents a variable related to the wave number;
  • the intrinsic admittance of free space Means surface admittance
  • the intrinsic impedance of free space Represents the surface impedance (the surface impedance and admittance are obtained through the bottom layer recursion),
  • ⁇ represents the angular frequency, i represents a complex number,
  • ⁇ 0 represents the dielectric coefficient of the underground uniform half-space, and ⁇ 0 represents the permeability of the underground uniform half-space.
  • the response of the layered earth surface observation is only the TE polarization field, and the horizontal electric field includes both the TM generated by the ground term
  • the polarization field also includes the TE polarization field excited by the ground term and the wire source.
  • the (dispersion) complex resistivity of the Cole-Cole model can be expressed as:
  • ⁇ (i ⁇ ) is the dispersion resistivity including the induced polarization effect
  • ⁇ 0 is the zero-frequency resistivity
  • m is the charging rate or polarizability of the medium.
  • the charging rate affects the intensity of the spectrum, but does not affect the shape of the spectrum. , It is mainly affected by the content of metal minerals, the degree of mineral density and the degree of infiltration.
  • ⁇ is the time constant, which mainly affects the phase of the extreme value of the spectrum. Under certain conditions, it is most affected by the degree of densification, the depth of the ore body, and the scale.
  • c is the frequency correlation coefficient, which determines the visibility of the frequency spectrum, and is mainly affected by the buried depth of the ore body.
  • the forward modeling of the galvanic dual source transient electromagnetic method with induced polarization effect is carried out, and the forward modeling of the frequency domain electromagnetic method is first solved for the same device, and the complex resistivity of the Cole-Cole model is used in the frequency domain to replace the DC resistance of the formation Then, the sine transform is used to obtain the transient electromagnetic response of the galvanic source with IP information.
  • the second layer is the polarized layer
  • the length of the emission source is 1000 meters, and the emission current is 10A. Take the measuring point (500, 1000) as an example to analyze the influence of different types of fields on the IP effect.
  • Figure 2 shows the response comparison before and after the TE and TM-type fields are affected by the polarization layer.
  • the TE field is almost unaffected by the IP effect of the polarized layer, and the TM field is greatly affected by the IP effect of the polarized layer.
  • the high-resistance polarized layer has the same effect. The deviation of the two curves of No appears later, and the negative response phenomenon appears later under the influence of the high-resistance polarization layer.
  • the TE field is very weakly affected by the IP effect. Changing the time constant and frequency correlation coefficient will not change the TE field. Even the change in the polarization rate will have a very significant impact. Small ( Figure 4b, d, f). Unlike the case of the TE field, the TM field is more sensitive to the polarization rate, time constant, and frequency domain correlation coefficient, and changes in parameters bring about greater changes in the field. The larger the parameter, the earlier the anti-sign phenomenon appears, and the greater the signal strength caused by the distortion.
  • Formula (1)(2) is used to calculate the vertical magnetic field and horizontal electric field of the traditional grounding wire source when the polarization layer exists and does not exist, and the electromagnetic field is affected by the IP effect of the polarization layer when the TE and TM fields of the layered earth have different proportions. The change.
  • the vertical magnetic field of the pure TE field is slightly affected by the ip polarization effect, and the response curves almost completely overlap;
  • the horizontal electric field of the grounding wire source is affected by the ip effect, and the response curve starts to separate at 1E-2s, and at 1E The sign reversal began to appear around -1s.
  • the horizontal electric field is easier to observe the influence of the ip effect.
  • the outcropping strata in the area are mainly the Lower Carboniferous Nanmingshui Formation (C 1 n), followed by the Middle Devonian Yunduhala Formation (D 2 y), and the Lower Tertiary Paleocene-Eocene Honglishan Formation. (E 1-2 h) and the fourth system brand new system (Q 4 ).
  • the upper part of the Nanmingshui Formation is the surrounding rock of the main ore-bearing rock mass in the area.
  • the resistivity ( ⁇ s) of massive copper-nickel ore and tertiary system are both low.
  • the ⁇ s of the surface quaternary system is generally higher.
  • the resistivity of other lithologies varies greatly with alteration, metal sulfide content, and carbon content.
  • the ⁇ s of fresh rock bodies and surrounding rocks are relatively high, while the ⁇ s of mineralized rock bodies and charcoal and pyrite-bearing tuff are relatively low.
  • the polarization of ore bodies, mineralized rock bodies, and carbonaceous surrounding rocks is relatively low.
  • the polarizability of massive ore bodies and surrounding rocks rich in graphite and pyrite is the highest.
  • the near-surface strata, surrounding rocks and rock masses that do not contain carbon and pyrite have very low polarizabilities.
  • the copper-nickel ore body in the mining area has the characteristics of strong magnetism, high density, high polarizability, and low resistivity, which can cause comprehensive geophysical anomalies of "three highs and one low”.
  • the properties of high polarization and low resistance provide us with extremely favorable conditions for the study of transient electromagnetic fields affected by the IP effect of the polarizer.
  • a survey line perpendicular to the extension direction of the vein is arranged.
  • AB represents the emission source.
  • the C at the midpoint position is the opposite polarity to A and B.
  • the pole is introduced into the emission source.
  • the transmission and reception distance of the survey line L103 is 1000 meters, and the fundamental frequency is observed: the vertical magnetic field is mainly at 8.3 Hz, and the electric field observation at the fundamental frequency of 1 Hz is carried out.
  • Transmitting current: 10A, transmitting line length: 1.5Km, receiving electrode distance 40m, effective receiving area of the magnetic bar is 40000m 2 .
  • the vertical magnetic field of the line source shows a monotonous decreasing change law as a whole.
  • the early data shows a change of first increase and then decrease (Figure 7a), which is related to the relative position of the measurement point and the emission source (the planar distribution law of the response) )related.
  • the horizontal electric field of the line source shows an obvious reverse sign in the range of No. 400-1200 measuring points ( Figure 7b).
  • the horizontal electric field is obviously affected by the IP effect, and the horizontal electric field can better distinguish the IP effect.
  • the observed vertical magnetic field has no obvious distortion or anti-sign phenomenon, while the corresponding horizontal electric field has an obvious anti-sign phenomenon.
  • the reverse sign of the horizontal electric field of the single-line source occurs at 6.74ms, and the reverse sign of the horizontal electric field of the double-line source occurs at 0.848ms, and the reverse sign occurs at an earlier moment.
  • the inverse sign of the observation response corresponds to the underground carbonaceous tuff, as shown in Figure 9.
  • the extracted resistivity and polarizability information is verified by drilling, as shown in Figure 10.

Abstract

一种接地导线源瞬变电磁响应中IP信息的提取方法，包括以下步骤：1)利用受IP效应影响较小的垂直磁场反演获取地下电阻率信息；2)基于获得的地下电性结构正演得到未受IP效应影响的电场响应；3)在观测的响应中去除IP效应的影响，得到纯IP响应；4)对获得的IP响应进行反演，获得极化率、频率相关系数和时间常数的IP信息。

Description

一种接地导线源瞬变电磁响应中IP信息的提取方法 技术领域
本发明属于瞬变电磁法技术领域，涉及一种接地导线源瞬变电磁响应中IP信息的提取方法。
背景技术
瞬变电磁法作为地球物理的重要分支，在金属矿产、地热资源勘查中起到重要作用。但地下存在极化体时，实测的瞬变电磁数据中包含激电效应的影响，严重时会出现畸变和符号反转现象。准确分析ip效应的影响规律和精确反演含ip效应的瞬变电磁数据变得尤为重要。
瞬变电磁按照场源形式可以分为回线源(磁性源)和接地导线源(电性源)两种。对于回线源瞬变电磁IP效应的分析可以追溯到1980年。在认清ip带来的响应的变化规律后，如何消除Ip效应的影响，并进一步实现包含ip效应的瞬变电磁数据的反演成为首要解决的问题。接地导线源瞬变电磁中的IP效应问题的研究相对较少。从接地导线源瞬变电磁观测的数据中得到IP信息，利用早期瞬变响应来反演电阻率，然后正演获得观测时间范围内的瞬变电磁响应，从观测的数据中去掉电磁响应，得到IP响应，进一步反演获得IP信息，相较于以往基于直流数据的IP反演获得更高的精度。然而，与回线源瞬变电磁方法观测垂直磁场或时间导数不同，接地导线源瞬变电磁除观测垂直磁场或其时间导数外，水平电场分量的观测是该方法的一大优势，因为水平电场分量对高阻和良导目标都具有较强的分辨能力。不同电磁分量探测能力的不同与其极化类型不同有密切的关联。那么，不同分量受IP效应的影响也会因极化类型的不同而产生差别。
为了更加清晰的认知不同分量受IP效应影响的更本质的原因，首先从层状大地表面的接地导线源瞬变电磁响应中分别提取TE和TM极化场，然后通过正演模拟分析，分析不同类型极化场受IP效应的影响规律，之后，给出不同分量受IP效应的影响特征，为从观测的瞬变电磁数据中提取IP信息提供新的方法。
发明内容
本发明的目的在于提供一种接地导线源瞬变电磁响应中IP信息的提取方法。
其具体技术方案为：
一种接地导线源瞬变电磁响应中IP信息的提取方法，包括以下步骤：
1)利用受IP效应影响较小的垂直磁场反演获取地下电阻率信息；
2)基于获得的地下电性结构正演得到未受IP效应影响的电场响应；
3)在观测的响应中去除IP效应的影响，得到纯IP响应；
4)对获得的IP响应进行反演，获得极化率、频率相关系数和时间常数等IP信息。
进一步，接地导线源瞬变电磁法主要观测水平电场和垂直磁场，在均匀层状大地表面的表达式为:
Figure PCTCN2020108532-appb-000001
Figure PCTCN2020108532-appb-000002
其中，r是源到观测点的距离，R and R'分别是两个接地电极到观测点的距离；2L是发射源的长度，J 1(λr)和J 0(λr)分别为一阶和零阶第一类贝塞尔函数，λ表示与波数相关的变量；
Figure PCTCN2020108532-appb-000003
表示电场分量入射平面时电磁波的反射系数，
Figure PCTCN2020108532-appb-000004
表示垂直磁场入射平面时电磁波的反射系数，
Figure PCTCN2020108532-appb-000005
自由空间的本征导纳，
Figure PCTCN2020108532-appb-000006
表示地表导纳，
Figure PCTCN2020108532-appb-000007
自由 空间的本征阻抗，
Figure PCTCN2020108532-appb-000008
表示地表阻抗(地表阻抗和导纳通过最底层递推得到)，
Figure PCTCN2020108532-appb-000009
Figure PCTCN2020108532-appb-000010
ω表示角频率，i表示复数，ε 0表示地下均匀半空间的介电系数，μ 0表示地下均匀半空间的磁导率。
Figure PCTCN2020108532-appb-000011
以r TE、r TM作为TE极化场和TM极化场的判断依据，对于垂直磁场，层状大地表面观测的响应中只有TE极化场，而水平电场中既包括由接地项产生的TM极化场，也包含接地项和导线源激发的TE极化场。为了分析不同极化类型受IP效应的影响，这里，以水平电场为例，分别提取出其中包含的TE和TM场表达式。
Figure PCTCN2020108532-appb-000012
Figure PCTCN2020108532-appb-000013
对于极化层，电阻率转换为复电阻率，采用Cole-cole模型，Cole-Cole模型是研究IP效应中最经典、最常用的极化模型，已被广泛证明可以有效反映极化大地的IP特性。Cole-Cole模型的(频散)复电阻率可表示为：
Figure PCTCN2020108532-appb-000014
式中，ρ(iω)为包含激电效应的频散电阻率，ρ 0为零频电阻率,m为介质的充电率或极化率，充电率影响频谱的强度，但不影响频谱的形态，它主要受金属矿物含量、矿物致密程度和浸染程度的影响。τ为时间常数，主要影响频谱极值的相位，在一定的条件下，受致密程度、矿体埋深及规模影响最大。c为频率相关系数，决定频谱特征的显现度，主要受矿体埋深的影响；将对含激电效应的电偶源瞬变电磁法正演，采取先求解相同装置的频率域电磁 法的正演，并在频率域中用Cole-Cole模型的复电阻率代替地层的直流电阻率，然后采用正弦变换得到带有激电信息的电偶源瞬变电磁响应。
利用公式(3)和(4)分别计算接地导线源瞬变电磁中TE场和TM场，不含极化层的地电模型为
H:ρ 1＝100Ω·m,h 1＝500m；ρ 2＝10Ω·m,h 2＝20m；ρ 3＝200Ω·m。
再进一步，上述参数的取值范围一般为：ρ 0＝10 -4～10 5Ω·m，m＝0～0.98，τ＝10 -3～10 5s，c＝0.1～0.6。
再进一步，对于含极化层的地电模型，第二层为极化层，设定的极化参数为m＝0.1，τ＝1s，c＝0.3。发射源长度为1000米，发射电流10A。
与现有技术相比，本发明的有益效果：
本发明通过理论模拟计算极化体IP效应对两种类型场的影响，TM场受IP效应的影响远远大于TE受到的影响。进一步分析实测中常用的水平电场和垂直磁场受极化体IP效应的影响：相同背景模型下，包含TE和TM场的水平电场受IP效应的影响要远大于只包含TE场的垂直磁场，对于TM场占主导的双线源瞬变电磁而言，IP效应的影响更加明显。这些结论在新疆喀拉通克铜镍矿集区的实测中得到验证。为进一步提取瞬变电磁响应中提取IP信息提供新的思路。
附图说明
图1是接地导线源瞬变电磁的观测模式示意图；
图2是IP效应影响的不同TE、TM场的响应变化(低阻极化层)，其中，(a)为TM，(b)为TE；
图3是IP效应影响的不同TE、TM场的响应变化(高阻极化层)，其中，(a)为TM，(b)为TE；
图4是不同极化参数时，IP效应引起TE、TM场的变化，(a_b)m参数引起TE、TM场的变化；(c,d)c参数引起TE、TM场的变化；(e,f)τ参数引起TE、TM场的变化。
图5是传统接地导线源瞬变电磁场受极化层IP效应的影响，(a)受IP效应影响垂直磁场响应对比；(b)受IP效应影响水平电场响应对比
图6是测线布置图；
图7是接地导线源瞬变电磁响应多测道图，其中，a)为Hz，b)为Ex，
图8是观测的垂直磁场和水平电场，其中，a)为Hz，b)为Ex；
图9是反演结果；
图10是钻孔结果。
具体实施方式
下面结合实施例对本发明的技术方案作进一步详细地说明。
接地导线源瞬变电磁法主要观测水平电场和垂直磁场，在均匀层状大地表面的表达式为:
Figure PCTCN2020108532-appb-000015
Figure PCTCN2020108532-appb-000016
其中，r是源到观测点的距离，R and R'分别是两个接地电极到观测点的距离；2L是发射源的长度，J 1(λr)和J 0(λr)分别为一阶和零阶第一类贝塞尔函数，λ表示与波数相关的变量；
Figure PCTCN2020108532-appb-000017
表示电场分量入射平面时电磁波的反射系数，
Figure PCTCN2020108532-appb-000018
表示垂直磁场入射平面时电磁波的反射系数，
Figure PCTCN2020108532-appb-000019
自由空间的本征导纳，
Figure PCTCN2020108532-appb-000020
表示地表导纳，
Figure PCTCN2020108532-appb-000021
自 由空间的本征阻抗，
Figure PCTCN2020108532-appb-000022
表示地表阻抗(地表阻抗和导纳通过最底层递推得到)，
Figure PCTCN2020108532-appb-000023
Figure PCTCN2020108532-appb-000024
ω表示角频率，i表示复数，ε 0表示地下均匀半空间的介电系数，μ 0表示地下均匀半空间的磁导率。
Figure PCTCN2020108532-appb-000025
以r TE、r TM作为TE极化场和TM极化场的判断依据，对于垂直磁场，层状大地表面观测的响应中只有TE极化场，而水平电场中既包括由接地项产生的TM极化场，也包含接地项和导线源激发的TE极化场。为了分析不同极化类型受IP效应的影响，这里，以水平电场为例，分别提取出其中包含的TE和TM场表达式。
Figure PCTCN2020108532-appb-000026
Figure PCTCN2020108532-appb-000027
对于极化层，电阻率转换为复电阻率，采用Cole-cole模型，Cole-Cole模型是研究IP效应中最经典、最常用的极化模型，已被广泛证明可以有效反映极化大地的IP特性。Cole-Cole模型的(频散)复电阻率可表示为：
Figure PCTCN2020108532-appb-000028
式中，ρ(iω)为包含激电效应的频散电阻率，ρ 0为零频电阻率,m为介质的充电率或极化率，充电率影响频谱的强度，但不影响频谱的形态，它主要受金属矿物含量、矿物致密程度和浸染程度的影响。τ为时间常数，主要影响频谱极值的相位，在一定的条件下，受致密程度、矿体埋深及规模影响最大。c为频率相关系数，决定频谱特征的显现度，主要受矿体埋深的影响。上述参数的取值范围一般为：ρ 0＝10 -4～10 5Ω·m，m＝0～0.98，τ＝10 -3～10 5s， c＝0.1～0.6。将对含激电效应的电偶源瞬变电磁法正演，采取先求解相同装置的频率域电磁法的正演，并在频率域中用Cole-Cole模型的复电阻率代替地层的直流电阻率，然后采用正弦变换得到带有激电信息的电偶源瞬变电磁响应。
利用公式(3)和(4)分别计算接地导线源瞬变电磁中TE场和TM场，不含极化层的地电模型为
H:ρ 1＝100Ω·m,h 1＝500m；ρ 2＝10Ω·m,h 2＝20m；ρ 3＝200Ω·m
对于含极化层的地电模型，第二层为极化层，设定的极化参数为m＝0.1，τ＝1s，c＝0.3。发射源长度为1000米，发射电流10A，以测点(500，1000)为例，分析不同类型场受到IP效应的影响情况。
图2给出TE、TM型场受极化层影响前后的响应对比。
通过对比发现，TE场受极化层IP效应的影响较小，响应之间的差别极化可以忽略(图2a)，而对应的TM场受极化层IP效应的影响较大，响应曲线在1E-2s后出现明显的差别，特别是反号现象的出现，TM场相较于TE场受到IP效应的影响更大。
为了更好的分析极化层电阻率对不同类型场的影响，改变极化层的电阻率，
K:ρ 1＝100Ω·m,h 1＝500m；ρ 2＝1000Ω·m,h 2＝20m；ρ 3＝200Ω·m。
与低阻极化层类似，TE场几乎不受到极化层IP效应的影响，TM场受到极化层IP效应的影响较大，相较于低阻极化层，高阻极化层存在与否的两条曲线出现偏离的时间更晚，高阻极化层影响下响应负值现象出现的更晚。
为了更好的分析极化层各参量对响应的影响，分别计算不同m＝0.05，0.2，0.5，τ＝0.001，0.1，10s，c＝0.1，0.25，0.6。
和前面图2、图3的结果一致，TE场受IP效应的影响很微弱，改变时间常数和频率相关系数，TE场不会产生变化，即使是极化率的变化，带来的影响也很小(图4b,d,f)。与TE 场的情况不同，TM场对极化率、时间常数和频域相关系数都比较敏感，参数的变化带来场的较大变化。参数越大，反号现象出现的越早，畸变带来的信号强度也越大。
采用公式(1)(2)计算极化层存在和不存在时的传统接地导线源垂直磁场和水平电场，分析层状大地TE、TM场占比不同情况时电磁场受极化层IP效应的影响的变化。
如图5所示，纯TE场的垂直磁场受ip极化效应的影响很小，响应曲线几乎完全重合；接地导线源水平电场受ip效应的影响，响应曲线在1E-2s开始分离，在1E-1s附近开始出现符号的反转。水平电场更容易观测到ip效应的影响。
为了更好的分析不同极化场受极化层IP效应的影响，选择具有典型极化层的新疆某铜镍矿集区开展数据采集和分析(图6)。
区内出露地层主要为下石炭统南明水组(C 1n)，其次有中泥盆统蕴都哈拉组(D 2y)、下第三系古新—始新统红砾山组(E 1-2h)以及第四系全新统(Q 4)。其中南明水组上段是区内主要含矿岩体的围岩。块状铜镍矿石和第三系的电阻率(ρs)都较低。表层第四系的ρs一般比较高。其它岩性的电阻率随蚀变情况、金属硫化物含量、炭质含量等的不同有较大变化。一般新鲜岩体和围岩的ρs较高，而矿化岩体和含炭、含黄铁矿的沉凝灰岩的ρs则相对偏低，矿体、矿化岩体、炭质围岩的极化率都较高，其中块状富矿体及富含石墨和黄铁矿的围岩的极化率最高。近地表的地层、不含炭和黄铁矿的围岩及岩体的极化率都很低。矿区铜镍矿体具有强磁性、高密度、高极化率、低电阻率的特征，可引起“三高一低”的综合物探异常。高极化、低电阻的性质为我们研究瞬变电磁场受极化体IP效应影响提供了极为有利的条件。
如图6所示，在测区的东南，布置垂直于矿脉延伸方向的测线，AB代表发射源，当采用双线源发射时，中点位置的C作为与A、B极性相反的一极引入到发射源中。测线L103的收发距为1000米，观测基频：垂直磁场以8.3Hz为主，进行1Hz基频的电场观测。发射电流：10A，发射线长度：1.5Km，接收电极距40m，磁棒的有效接收面积40000m 2。
线源垂直磁场整体上呈现单调递减的变化规律，在1800-2200测点，早期数据出现先增后减的变化(图7a)，这与测点和发射源的相对位置(响应的平面分布规律)有关。线源的水平电场在400-1200号测点范围出现明显的反号现象(图7b)，水平电场受IP效应的影响明显，水平电场对IP效应有更好的分辨。
观测的垂直磁场没有出现明显的畸变或反号现象，而对应的水平电场出现明显的反号现象。单线源水平电场反号发生在6.74ms，而双线源水平电场的反号现象发生在0.848ms，在更早的时刻发生反号现象。观测响应的反号现象对应地下的炭质沉凝灰岩，如图9所示。提取的电阻率和极化率信息得到钻孔验证，如图10所示。
以上所述，仅为本发明较佳的具体实施方式，本发明的保护范围不限于此，任何熟悉本技术领域的技术人员在本发明披露的技术范围内，可显而易见地得到的技术方案的简单变化或等效替换均落入本发明的保护范围内。

Claims (4)

  1. 一种接地导线源瞬变电磁响应中IP信息的提取方法，其特征在于，包括以下步骤：
    1)利用受IP效应影响较小的垂直磁场反演获取地下电阻率信息；
    2)基于获得的地下电性结构正演得到未受IP效应影响的电场响应；
    3)在观测的响应中去除IP效应的影响，得到纯IP响应；
    4)对获得的IP响应进行反演，获得极化率、频率相关系数和时间常数的IP信息。
  2. 根据权利要求1所述的接地导线源瞬变电磁响应中IP信息的提取方法，其特征在于，接地导线源瞬变电磁法主要观测水平电场和垂直磁场，在均匀层状大地表面的表达式为:
    Figure PCTCN2020108532-appb-100001
    Figure PCTCN2020108532-appb-100002
    其中，r是源到观测点的距离，R and R'分别是两个接地电极到观测点的距离；2L是发射源的长度，J 1(λr)和J 0(λr)分别为一阶和零阶第一类贝塞尔函数，λ表示与波数相关的变量；
    Figure PCTCN2020108532-appb-100003
    表示电场分量入射平面时电磁波的反射系数，
    Figure PCTCN2020108532-appb-100004
    表示垂直磁场入射平面时电磁波的反射系数，
    Figure PCTCN2020108532-appb-100005
    自由空间的本征导纳，
    Figure PCTCN2020108532-appb-100006
    表示地表导纳，
    Figure PCTCN2020108532-appb-100007
    自由空间的本征阻抗，
    Figure PCTCN2020108532-appb-100008
    表示地表阻抗(地表阻抗和导纳通过最底层递推得到)，
    Figure PCTCN2020108532-appb-100009
    Figure PCTCN2020108532-appb-100010
    ω表示角频率，i表示复数，ε 0表示地下均匀半空间的介电系数，μ 0表示地下均匀半空间的磁导率；
    Figure PCTCN2020108532-appb-100011
    Figure PCTCN2020108532-appb-100012
    以r TE、r TM作为TE极化场和TM极化场的判断依据，对于垂直磁场，层状大地表面观测的响应中只有TE极化场，而水平电场中既包括由接地项产生的TM极化场，也包含接地项和导线源激发的TE极化场；为了分析不同极化类型受IP效应的影响，这里，以水平电场为例，分别提取出其中包含的TE和TM场表达式；
    Figure PCTCN2020108532-appb-100013
    Figure PCTCN2020108532-appb-100014
    对于极化层，电阻率转换为复电阻率，采用Cole-cole模型；Cole-Cole模型的复电阻率表示为：
    Figure PCTCN2020108532-appb-100015
    式中，ρ(iω)为包含激电效应的频散电阻率，ρ 0为零频电阻率,m为介质的充电率或极化率，充电率影响频谱的强度，但不影响频谱的形态，它主要受金属矿物含量、矿物致密程度和浸染程度的影响；τ为时间常数，主要影响频谱极值的相位，在一定的条件下，受致密程度、矿体埋深及规模影响最大；c为频率相关系数，决定频谱特征的显现度，主要受矿体埋深的影响；将对含激电效应的电偶源瞬变电磁法正演，采取先求解相同装置的频率域电磁法的正演，并在频率域中用Cole-Cole模型的复电阻率代替地层的直流电阻率，然后采用正弦变换得到带有激电信息的电偶源瞬变电磁响应；
    利用公式(3)和(4)分别计算接地导线源瞬变电磁中TE场和TM场，不含极化层的地电模型为
    H:ρ 1＝100Ω·m,h 1＝500m；ρ 2＝10Ω·m,h 2＝20m；ρ 3＝200Ω·m。
  3. 根据权利要求2所述的接地导线源瞬变电磁响应中IP信息的提取方法，其特征在于，上述参数的取值范围为：ρ 0＝10 -4～10 5Ω·m，m＝0～0.98，τ＝10 -3～10 5s，c＝0.1～0.6。
  4. 根据权利要求2所述的接地导线源瞬变电磁响应中IP信息的提取方法，其特征在于，对于含极化层的地电模型，第二层为极化层，设定的极化参数为m＝0.1，τ＝1s，c＝0.3；发射源长度为1000米，发射电流10A。
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