Frequency-selecting exploration method based on natural electromagnetic method phase observation

Abstract

The invention relates to the technical field of natural electromagnetic method exploration, in particular to a frequency selection exploration method based on natural electromagnetic method phase observation. Horizontal electric field components of a to-be-detected area are detected through a natural electric field frequency selection method, a potential curve graph is obtained through the horizontal electric field components under multiple different detection frequencies, and when a good conductor exists underground, an abnormal potential point appears at a first detection point in the potential curve graph due to a static effect, and the potential point is detected. Specifically, potentials of a plurality of detection frequencies are reduced at the same time at abnormal potential points; according to the scheme, the abnormal potential point caused by the static effect is utilized to judge whether the good conductor exists underground or not, and then the abnormal potential point is subjected to dipolar profile multi-frequency detection so as to further determine the horizontal position of the good conductor underground. Therefore, the interference signal caused by the static effect is reasonably utilized to explore the underground good conductor.

Description

Technical Field

[0001] The invention relates to the technical field of natural electromagnetic exploration, and in particular to a frequency-selective exploration method based on natural electromagnetic phase observation. Background Art

[0002] The natural electric field frequency selection method (TEFSM), also referred to as the frequency selection method (FSM), belongs to the category of natural electromagnetic address detection methods, just like the magnetotelluric method (MT) and the audio magnetotelluric method (AMT); they are all methods that use natural electromagnetic fields to study the electrical structure of the ground, and their basic theories follow the propagation theory of natural electromagnetic waves. In essence, the frequency selection method is a further extension and development of the audio frequency earth electric field method (TEF) and the audio frequency earth current method (AET).

[0003] When using the natural electric field frequency selection method for geological exploration, when there are lateral electrically inhomogeneous bodies (geological anomalies) on the surface or near the surface, the earth's current density near the surface or near the surface will increase or decrease, that is, there will be obvious current distortion in the surface electric field component; specifically, the apparent resistivity curve will shift upward or downward, but the shape of the apparent resistivity curve and the phase curve will not change. This is the static effect.

[0004] Because there are always inhomogeneous electrical bodies near the surface, static effects are inevitable when using magnetotelluric methods for geological exploration. Because static effects are a kind of interference signal in traditional magnetotelluric measurements, in order to improve the measurement accuracy, common methods such as spatial filtering must be used to correct static effects in the processing of magnetotelluric data. However, interference signals are relative to effective signals. If they can be effectively utilized, interference signals will also become effective signals. Therefore, there is an urgent need for a natural electric field frequency selection scheme that can utilize static effects to carry out the exploration of underground good conductors (such as groundwater sources). Summary of the invention

[0005] The main purpose of the present invention is to provide a frequency selection exploration method based on natural electromagnetic phase observation, aiming to solve the problem that a natural electric field frequency selection scheme that can utilize static effects is urgently needed to carry out the exploration of underground good conductors.

[0006] The technical solution proposed by the present invention is:

[0007] A frequency-selective exploration method based on natural electromagnetic phase observation is applied to a frequency-selective exploration system based on natural electromagnetic phase observation; the system includes a detection host and detection electrodes communicatively connected to the detection host; the number of detection electrodes is 2; the method includes:

[0008] Determine a region to be tested and a plurality of first detection points within the region to be tested, wherein the plurality of first detection points are equally spaced and arranged in a straight line within the region to be tested, and the detection electrodes are used to be embedded in the first detection points for detection;

[0009] Acquire, by a detection host, a horizontal electric field component along a first measurement line direction obtained by the detection electrode at a plurality of different detection frequencies, wherein a common direction of a plurality of the first detection points is the first measurement line direction;

[0010] The potential curve diagrams at different detection frequencies are obtained by detecting the host based on the horizontal electric field component along the first measuring line direction;

[0011] Determining whether there is an abnormal potential point in the first detection point based on the potential curve diagram;

[0012] If it exists, a dipole profile multi-frequency detection is carried out on the abnormal potential point to determine the horizontal position of the underground good conductor.

[0013] Preferably, the acquiring, by the detection host, the horizontal electric field component along the first measuring line direction obtained by the detection electrode at a plurality of different detection frequencies comprises:

[0014] Let the harmonic factor be e -iωt , to obtain the frequency domain electromagnetic field equations:

[0015]

[0016] Where, E is the electric field strength in the detection area, H is the magnetic field strength in the detection area; J s represents the field source term, μ0 is the magnetic permeability in vacuum, i is the imaginary unit, and satisfies: i 2 =-1, t is the time variable, ω is the circular frequency, σ is the conductivity of the medium;

[0017] Ignore the displacement current to find the curl on both sides of formula (1), and substitute formula (2) to obtain the second-order vector Helmholtz equation satisfied by the electric field in the medium:

[0018]

[0019] Let the field source term be 0 and apply the first-type boundary condition on the boundary to obtain formula (5), where the first-type boundary condition is as shown in formula (4):

[0020]

[0021] nE=nE0, (5)

[0022] Where n is the external normal vector of the boundary mesh and E0 is the electric field response of the one-dimensional medium on the boundary.

[0023] Preferably, the field source term is set to 0, and the first type of boundary condition is applied on the boundary to obtain formula (5), which then includes:

[0024] An unstructured tetrahedral grid is used to discretize the underground good conductors in the test area, where the six edges of the underground good conductors satisfy the following formula:

[0025]

[0026] In the formula, E k is the tangential electric field value defined on the kth edge of the underground good conductor, N k is the vector shape function on the kth edge of the underground good conductor;

[0027] Assume that the kth edge of the underground good conductor is connected by nodes i→j, then:

[0028]

[0029] Where λ is the barycentric coordinate of the node; shape function N k The curl of is expressed accordingly as:

[0030]

[0031] Based on formula (8), the discrete form of the first boundary condition is constructed to obtain an N DoF ×N DoF The complex system matrix A is symmetrical but not self-adjoint, and the linear equation (9) constructed by the complex system matrix A is solved to obtain the distribution of the electric field on the edge, where the linear equation (9) is:

[0032] Ax=b(9)

[0033] Where N DoF Represents the number of all edges of good underground conductors.

[0034] Preferably, the discrete form of the first boundary condition is constructed based on formula (8) to obtain an N DoF ×N DoF The complex system matrix A is symmetric but not self-adjoint. The linear equation (9) constructed by the complex system matrix A is solved to obtain the distribution of the electric field on the edge, which is then followed by:

[0035] Assume that the conductivity distribution of the background of the area to be measured is σ0(r), and there are multiple underground good conductors distributed near the surface of the area to be measured. The conductivity of the mth underground good conductor is determined as σ m (r),σ m The difference between (r) and σ0(r) is δσ m (r) = σm (r)-σ0(r), to obtain the integral equation solution of the electric field E(r) at any position r inside or outside the mth underground good conductor:

[0036]

[0037] Where μ is the magnetic permeability of the underground medium in the test area, r is the spatial position of any point in the underground good conductor, V m is the volume of the mth underground good conductor; E(r′) is the electric field vector at r′, g(r,r′) is the scalar full-space Green’s function; E 0 (r) is the normal field or regional field; e1(r) is the inductive distorted electric field generated by a good conductor near the surface and underground. G (r) is the current-type distorted electric field generated by a good conductor in the local underground near the surface;

[0038] Using the Born approximation, replace E(r′) in the integral of formula (10) and formula (11) with the normal electric field E 0 (r) to obtain the observed electric field E(r) and E 0 The relationship between (r):

[0039] E(r)=|I+G(r)(IG(r) -1 )|E 0 (r)=c(r)E 0 (r)(12)

[0040] Where G(r) is the Green's vector tensor function; the distortion tensor c(r) is simplified to a second-order real tensor that is independent of frequency;

[0041] The observed electric field E(r) is taken as the horizontal electric field component along the direction of the first survey line.

[0042] Preferably, the step of obtaining potential curves at different detection frequencies based on the horizontal electric field component along the first measuring line direction by the detection host includes:

[0043] The horizontal electric field component along the first measuring line direction is used as the ordinate of the potential curve graph, and the positions of the first detection points distributed along the first measuring line direction are used as the ordinate of the potential curve graph to obtain potential curve graphs under multiple different detection frequencies, wherein the number of detection frequencies corresponding to the potential curve graph is 3.

[0044] Preferably, judging whether there is an abnormal potential point in the first detection point based on the potential curve diagram includes:

[0045] Determine whether there is a first detection point that meets the preset conditions in the potential curve graph;

[0046] If so, it is determined that there is an abnormal potential point in the first detection point, and the first detection point that meets the preset conditions is marked as an abnormal potential point, wherein the preset conditions are: at each detection frequency, the horizontal electric field component collected by the abnormal potential point is greater than the horizontal electric field component collected by the first adjacent detection point before the abnormal potential point, and the horizontal electric field component collected by the abnormal potential point is greater than the horizontal electric field component collected by the first adjacent detection point after the abnormal potential point.

[0047] Preferably, the method of performing a dipole profile multi-frequency detection on the abnormal potential point to determine the horizontal position of the underground good conductor includes:

[0048] Determine a plurality of second detection points in the area to be tested, wherein the plurality of second detection points are equally spaced and arranged in a straight line in the area to be tested, the distance between two adjacent second detection points is a second point distance, and the second point distance is smaller than the first point distance, the abnormal potential point is one of the second detection points, and the abnormal potential point is located in the middle of the plurality of second detection points;

[0049] The detection electrodes are sequentially embedded in each second detection point, so as to obtain the horizontal electric field components along the second measurement line direction obtained by each detection electrode at multiple different detection frequencies through the detection host, wherein the direction in which multiple second detection points are located together is the second measurement line direction, the distance between the two detection electrodes when embedded in the second detection points for detection is the second pole distance, and the second pole distance is consistent with the first pole distance, and the number of detection frequencies corresponding to the two detection electrodes when embedded in the second detection points for detection is greater than the number of detection frequencies corresponding to the potential curve graph;

[0050] A pseudo-section diagram of a dipole profile is obtained based on the horizontal electric field component along the second survey line direction;

[0051] Determine the horizontal position of underground good conductors based on the pseudo-section diagram of the dipole profile.

[0052] Preferably, obtaining the dipole profile pseudo-section diagram based on the horizontal electric field component along the second survey line direction comprises:

[0053] The horizontal electric field component along the second survey line direction is used as the section line of the dipole profile pseudo-section diagram, the apparent depth is used as the ordinate of the dipole profile pseudo-section diagram, and the positions of the second detection points distributed along the second survey line direction are used as the upper abscissa of the dipole profile pseudo-section diagram to obtain the dipole profile pseudo-section diagram, wherein the ordinate apparent depth of the dipole profile pseudo-section diagram is obtained by inverting the skin depth formula of the electromagnetic wave and the empirical coefficient.

[0054] Preferably, the determining the horizontal position of the underground good conductor based on the pseudo-section diagram of the dipole profile includes:

[0055] The horizontal position corresponding to the maximum value of the horizontal electric field component in the pseudo-section diagram of the dipole section is marked as a suspected position point;

[0056] Determine whether the horizontal distance between the suspected position point and the abnormal position point is less than a preset value;

[0057] If so, the suspected position point is taken as the horizontal position of the underground good conductor.

[0058] Preferably, when there is a high-voltage cable near the area to be measured, the first measuring line direction is set to be parallel to the extension direction of the high-voltage cable.

[0059] Through the above technical solution, the following beneficial effects can be achieved:

[0060] The frequency selection exploration method based on natural electromagnetic phase observation proposed in the present invention can detect underground good conductors simply and quickly; the horizontal electric field component of the area to be tested is detected by the natural electric field frequency selection method, and then the potential curve is obtained by the horizontal electric field components at multiple different detection frequencies. When there is a good conductor (such as a water source) underground, the static effect will cause an abnormal potential point to appear at the first detection point in the potential curve, specifically, the situation where the potential of multiple detection frequencies decreases at the abnormal potential point at the same time. The idea of ​​the traditional solution is to remove the interference signal caused by the static effect, but it is difficult to achieve the purpose of finding the underground near-surface good conductor we want; while the present solution uses the abnormal potential point caused by the static effect to determine whether there is a good conductor underground, and then performs a dipole profile multi-frequency detection on the abnormal potential point to further determine the horizontal position of the underground good conductor, thereby achieving the reasonable use of the interference signal caused by the static effect to carry out the exploration of underground good conductors. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0062] Figure 1 A flowchart of the steps of the first embodiment of a frequency-selective exploration method based on natural electromagnetic phase observation proposed by the present invention;

[0063] Figure 2 A potential curve diagram obtained after the natural electric field selective frequency exploration method is carried out at the A site in the ninth embodiment of the frequency selective exploration method based on natural electromagnetic method phase observation proposed by the present invention;

[0064] Figure 3A pseudo-section diagram of a dipole profile obtained after a dipole profile multi-frequency detection is performed at site A in the ninth embodiment of a frequency-selective exploration method based on natural electromagnetic phase observation proposed by the present invention;

[0065] Figure 4 A potential curve diagram obtained after the natural electric field selective frequency exploration method is carried out at the B site in the ninth embodiment of the frequency selective exploration method based on natural electromagnetic method phase observation proposed by the present invention;

[0066] Figure 5 A pseudo-section diagram of a dipole profile obtained after a dipole profile multi-frequency detection is performed at site B in the ninth embodiment of a frequency-selective exploration method based on natural electromagnetic phase observation proposed by the present invention;

[0067] Figure 6 A horizontal electric field curve corresponding to the plate-like body current distortion model in the fourth embodiment of a frequency-selective exploration method based on natural electromagnetic phase observation proposed by the present invention;

[0068] Figure 7 It is a horizontal electric field pseudo-section diagram corresponding to the plate-like body current distortion model in the fourth embodiment of the frequency-selective exploration method based on natural electromagnetic phase observation proposed by the present invention;

[0069] Figure 8 A horizontal electric field curve corresponding to the spherical anomaly model in the fourth embodiment of a frequency-selective exploration method based on natural electromagnetic phase observation proposed by the present invention;

[0070] Fig. 9 It is a horizontal electric field pseudo-section diagram corresponding to the spherical anomaly model in the fourth embodiment of the frequency-selective exploration method based on natural electromagnetic phase observation proposed by the present invention;

[0071] Fig.10 A horizontal electric field curve corresponding to a spherical anomaly model affected by plate-like current distortion in the fourth embodiment of a frequency-selective exploration method based on natural electromagnetic phase observation proposed by the present invention;

[0072] Fig.11 This is a horizontal electric field pseudo-section diagram corresponding to the spherical anomaly model affected by plate-like current distortion in the fourth embodiment of the frequency-selective exploration method based on natural electromagnetic phase observation proposed by the present invention. DETAILED DESCRIPTION

[0073] It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0074] The present invention proposes a frequency-selective exploration method based on natural electromagnetic phase observation.

[0075] As attached Figure 1As shown, in a first embodiment of a frequency selective exploration method based on natural electromagnetic phase observation proposed by the present invention, the frequency selective exploration method based on natural electromagnetic phase observation is applied to a frequency selective exploration system based on natural electromagnetic phase observation; the system includes a detection host, and detection electrodes communicatively connected to the detection host; the number of detection electrodes is 2; this embodiment includes the following steps:

[0076] Step S110: determine the area to be tested and multiple first detection points within the area to be tested, wherein the multiple first detection points are equally spaced and arranged in a straight line within the area to be tested, the detection electrode is used to embed the first detection points for detection, and the distance between two adjacent first detection points is the first point distance.

[0077] Step S120: Acquire, by the detection host, the horizontal electric field component along the first survey line direction obtained by the detection electrode at multiple different detection frequencies, wherein the direction in which multiple first detection points are located together is the first survey line direction, and the distance between the two detection electrodes when embedded in the first detection point for detection is the first electrode distance.

[0078] Specifically, in this embodiment, the first point distance is 5 meters, and the first electrode distance is 10 meters; the detection electrode adopts the natural electric field frequency selection method (FSM) for detection; when there is a high-voltage cable near the area to be measured, the first measuring line direction is set to be parallel to the extension direction of the high-voltage cable.

[0079] Step S130: obtaining potential curves at different detection frequencies based on the horizontal electric field component along the first measuring line direction by the detection host.

[0080] Specifically, different detection frequencies can reflect geological conditions at different underground depths, so a potential curve diagram can be obtained by obtaining horizontal electric field components from detection electrodes at multiple different detection frequencies.

[0081] Step S140: judging whether there is an abnormal potential point in the first detection point based on the potential curve diagram.

[0082] Specifically, if the potential of multiple detection frequencies on the potential curve graph drops simultaneously at a certain horizontal position point, the corresponding horizontal position point is the abnormal potential point, and there is a high probability that there is a good underground conductor (such as a water source) below the abnormal potential point, but further confirmation is still needed.

[0083] Step S150: If it exists, perform a dipole profile multi-frequency detection on the abnormal potential point to determine the horizontal position of the underground good conductor.

[0084] Specifically, by performing a dipole profile multi-frequency detection on the abnormal potential point, the horizontal position of the underground good conductor can be further determined, and the horizontal position of the underground good conductor can be obtained more accurately.

[0085] The frequency selection exploration method based on natural electromagnetic phase observation proposed in the present invention can detect underground good conductors simply and quickly; the horizontal electric field component of the area to be tested is detected by the natural electric field frequency selection method, and then the potential curve is obtained by the horizontal electric field components at multiple different detection frequencies. When there is a good conductor (such as a water source) underground, the static effect will cause an abnormal potential point to appear at the first detection point in the potential curve, specifically, the situation where the potential of multiple detection frequencies decreases at the abnormal potential point at the same time. The idea of ​​the traditional solution is to remove the interference signal caused by the static effect, but it is difficult to achieve the purpose of finding the underground near-surface good conductor we want; while the present solution uses the abnormal potential point caused by the static effect to determine whether there is a good conductor underground, and then performs a dipole profile multi-frequency detection on the abnormal potential point to further determine the horizontal position of the underground good conductor, thereby achieving the reasonable use of the interference signal caused by the static effect to carry out the exploration of underground good conductors.

[0086] In addition, in the traditional MT (magnetotelluric method) or AMT (audio-frequency magnetotelluric method), when the underground good conductor is close to the surface or the terrain is seriously undulating, the static effect type current distortion causes the apparent resistivity curve to appear steep strips in the pseudo-section diagram, so the current distortion is often eliminated as interference. However, in this scheme, the exploration depth of the natural electric field frequency selection method is relatively shallow. For example, the detection depth in groundwater exploration is mostly less than 300m. We can use this electric field distortion to find shallow surface local anomalies. In addition, the application of the natural electric field frequency selection method is mostly in areas with more human interference such as towns. How to effectively avoid human interference (such as high-voltage power lines) or effectively utilize the interference source is also a problem worthy of attention and consideration in the practical application of the natural electric field frequency selection method. In this embodiment, the direction of the first survey line is set to be parallel to the extension direction of the high-voltage cable; as long as the survey line direction is parallel to the high-voltage transmission line, the natural electric field frequency selection method can still obtain a good application effect in groundwater exploration.

[0087] In a second embodiment of a frequency selective exploration method based on natural electromagnetic phase observation proposed by the present invention, based on the first embodiment, step S120 includes the following steps:

[0088] Step S210: Let the harmonic transformation factor be e -iωt , to obtain the frequency domain electromagnetic field equations:

[0089]

[0090] Where, E is the electric field strength in the detection area (detected by the detection electrode), H is the magnetic field strength in the detection area; J s represents the field source term, μ0 is the magnetic permeability in vacuum, i is the imaginary unit, and satisfies: i 2 =-1, t is the time variable, ω is the circular frequency, and σ is the conductivity of the medium.

[0091] Specifically, any electromagnetic problem satisfies Maxwell's equations, so the above-mentioned frequency domain electromagnetic field equations are obtained.

[0092] Step S220: Ignore the displacement current to obtain the curl on both sides of formula (1), and substitute formula (2) into the formula to obtain the second-order vector Helmholtz equation satisfied by the electric field in the medium:

[0093]

[0094] Specifically, in the practical application of frequency domain electromagnetic method, the observation frequency is generally less than 104 Hz, so the displacement current can be ignored.

[0095] Step S230: Since FSM belongs to the natural electromagnetic method, the field source term can be set to 0, and the first type of boundary condition is applied on the boundary to obtain formula (5), where the first type of boundary condition is shown in formula (4):

[0096]

[0097] nE=nE0, (5)

[0098] Where n is the external normal vector of the boundary grid and E0 is the electric field response of the one-dimensional medium on the boundary, which is obtained by analytical method.

[0099] In a third embodiment of a frequency selective exploration method based on natural electromagnetic phase observation proposed by the present invention, based on the second embodiment, step S230 further includes the following steps:

[0100] Step S310: discretize the underground good conductors in the test area using an unstructured tetrahedral grid, wherein the six edges of the underground good conductors satisfy the following formula:

[0101]

[0102] In the formula, E k is the tangential electric field value defined on the kth edge of the underground good conductor, N k is the vector shape function on the kth edge of the underground good conductor. In this embodiment, the lowest order shape function is used for simplicity.

[0103] Step S320: Assume that the kth edge of the underground good conductor is formed by connecting nodes i→j, then:

[0104]

[0105] Where λ is the barycentric coordinate of the node; shape function N k The curl of is expressed accordingly as:

[0106]

[0107] Step S330: construct a discrete form of the first boundary condition based on formula (8) to obtain an N DoF ×N DoF The complex system matrix A is symmetrical but not self-adjoint, and the linear equation (9) constructed by the complex system matrix A is solved to obtain the distribution of the electric field on the edge, where the linear equation (9) is:

[0108] Ax=b(9)

[0109] Where N DoF Represents the number of all edges of good underground conductors.

[0110] Specifically, since the electric field calculations at different frequencies are independent of each other, the MKL Pardiso parallel direct solver is used in this embodiment to perform the solution to improve the calculation efficiency.

[0111] In a fourth embodiment of a frequency selective exploration method based on natural electromagnetic phase observation proposed by the present invention, based on the third embodiment, step S330 further includes the following steps:

[0112] Step S410: Assume that the conductivity distribution of the background of the area to be measured is σ0(r), and there are multiple underground good conductors distributed near the surface of the area to be measured, and determine the conductivity of the mth underground good conductor as σ m (r), σ m The difference between (r) and σ0(r) is δσ m (r) = σ m (r)-σ0(r), to obtain the integral equation solution of the electric field E(r) at any position r inside or outside the mth underground good conductor:

[0113]

[0114] Where μ is the magnetic permeability of the underground medium in the test area, r is the spatial position of any point in the underground good conductor, V m is the volume of the mth underground good conductor; E(r′) is the electric field vector at r′, g(r,r′) is the scalar full-space Green’s function; the integral is performed on the area occupied by all underground good conductors near the surface; E 0(r) is the normal field or regional field, that is, the electric field generated by the regional structure we are concerned with; e1(r) is the inductive distortion electric field generated by a good conductor near the surface and underground. G (r) is the current-type distorted electric field generated by the local underground good conductor near the surface. The intensity of these two distorted fields depends on the volume and shape of the underground good conductor near the surface and the difference in electrical properties between it and the surrounding rock.

[0115] Specifically, when there are small-scale local electrical inhomogeneities near the surface of the ground, the electric field observed by the frequency domain electromagnetic method will be distorted, which is called current distortion. The cause of current distortion is that the induced current flows in the horizontal direction. When there are shallow local inhomogeneities, the uniformity of the horizontal current density in the medium will be changed, thereby causing the current density to be densely or sparsely distributed around the shallow local inhomogeneities, resulting in an increase or decrease in the electric field component observed on the surface. Current distortion is an unavoidable physical phenomenon in frequency domain electromagnetic observations, which will cause deviations or errors in the interpretation of electromagnetic data results.

[0116] From the perspective of three-dimensional geological conditions, current-type distortion is caused by the superposition of the scattered field generated by the charge accumulation on the electrical interface of small-scale inhomogeneities near the surface and the normal field vector generated by the regional results.

[0117] Step S420: Using the Born approximation, replace E(r′) in the integral of formula (10) and formula (11) with the normal electric field E 0 (r) to obtain the observed electric field E(r) and E 0 The relationship between (r):

[0118] E(r)=|I+G(r)(IG(r) -1 )|E 0 (r)=c(r)E 0 (r)(12)

[0119] Where G(r) is the Green's vector tensor function; for the detection frequency bands of conventional MT, AMT and FSM methods, the inductive distortion can be ignored, and the distortion tensor c(r) is simplified to a second-order real tensor that is independent of frequency.

[0120] Step S430: taking the observed electric field E(r) as the horizontal electric field component along the first survey line direction.

[0121] This embodiment improves the specific solution of how to obtain the horizontal electric field component along the first measuring line direction based on the detection electrodes at multiple different detection frequencies.

[0122] Based on the above embodiments, the natural electric field frequency selection method can be used to explore the area to be tested. The simulation demonstration process of the exploration can be exemplified as follows:

[0123] Three simpler three-dimensional anomaly models are constructed, namely, the plate-like current distortion model, the spherical anomaly model, and the spherical anomaly model affected by the plate-like current distortion, to analyze the variation law of the horizontal electric field component along the survey line.

[0124] The simulation range of the model domain is -4-4km in the x, y, and z directions. The size of the study area is 400m 400m 200m. The grid is encrypted in the study area to ensure the accuracy of the forward calculation results. The thickness of the air layer is 4km, the total number of grid divisions is 1063926, and the number of edges is 1245326.

[0125] The survey line is laid out along the y-axis direction, with a range of -100-100m, where the point spacing within the range of -20-20m is 0.5m and outside the range is 1m. The calculation frequency is 61 frequencies of f=10.^(1:0.05:4). The developed algorithm is used for solution.

[0126] 1. Plate current distortion model:

[0127] The plate-like body is a horizontal, upright, locally good-conducting plate-like body in a uniform half-space with a given resistivity of ρ0 = 1000Ω·m. The resistivity of the plate-like body is ρ1 = 0.1Ω·m, and the top surface burial depth H is 6m. The length l of the plate-like body is 5m, the thickness d is 2m, and the height h is 4m; the angle α between the strike of the plate-like body and the y-axis is 30°. The projection point of the center of the plate-like body on the surface corresponds to the origin O of the coordinate system, and it is assumed that the survey line is on the y-axis.

[0128] The simulation results are attached. Figure 6 and attached Figure 7 As shown (attached Figure 6 The horizontal electric field curve corresponding to the plate current distortion model is shown in the figure below. Figure 7 is the horizontal electric field pseudo-section diagram corresponding to the plate-shaped current distortion model), Figure 6 The vertical axis is the horizontal electric field component |E y |, the horizontal axis is the horizontal position; the calculation result |E y |It is the result of vector superposition under the combined action of TE polarization and TM polarization.

[0129] Figure 6 The horizontal electric field component of the ground surface along the survey line |E y The profile curve only plots the simulation calculation results of 6 frequencies (i.e. 101.1Hz, 101.4Hz, 101.6Hz, 101.85Hz, 102Hz and 102.25Hz).

[0130] Depend on Figure 7 It can be seen that |E of different frequenciesy | curve has a relatively low potential anomaly just above the plate-like body, and the size of the relative anomaly increases with the increase of frequency; at the same time, |E y The profile curve of | rises upward as the frequency increases, that is, the background value increases as the frequency increases. This is because the overall signal is enhanced when the frequency is high and the exploration depth is shallow.

[0131] Figure 7 |E plotted for the calculation results using 61 frequencies y | pseudo-section diagram. The ordinate axis is the logarithm of the frequency f. According to the skin characteristics of plane electromagnetic waves (i.e., low-frequency penetration depth is large, high-frequency penetration depth is small), the ordinate is equivalent to the apparent depth coordinate, that is, the detection depth gradually increases from top to bottom, and the abscissa is the horizontal position. Figure 7 It can be seen that as the frequency f decreases, the deep signal weakens and the skin depth of the electromagnetic wave gradually increases; at the horizontal position corresponding to the low-resistance anomaly, |E y |The contour lines have obvious "hanging noodles" phenomenon from high frequency to low frequency, which is the current distortion effect in three-dimensional conditions, that is, the static effect of natural electromagnetic method. Static displacement is a special case of current type distortion effect, which only causes the translation of impedance amplitude and apparent resistivity, but current type distortion generally affects both impedance amplitude and phase.

[0132] 2. Spherical abnormal body model:

[0133] The sphere model is a low-resistance sphere in a uniform half-space with a given resistivity of ρ0 = 1000Ω·m, a resistivity of ρ2 = 1Ω·m, and a top burial depth of H0 of 50m. The radius r0 of the sphere is 25m, and the projection point of the center of the sphere on the surface corresponds to the origin O of the coordinate system. It is assumed that the survey line is consistent with the y-axis.

[0134] |E of the sphere model y For the forward modeling results, please see the attached Figure 8 (Attached Figure 8 is the horizontal electric field curve corresponding to the spherical anomaly model); it can be seen that the sphere has a significant impact on the electric field signal. Figure 6 Compared with the front panel model, the response influence range is wider and the curve is flatter. This is because the burial depth and resistivity value of the sphere are larger than those of the front panel model, and the abnormal electromagnetic induction field generated by it has a greater impact on the surface |E y |The impact is weakened.

[0135] It can be seen that the closer the electrically inhomogeneous body is to the surface, the greater the impact on the surface electric field component, and the greater the impact on the MT detection results. Similarly, there is also a relatively low potential anomaly above the low-resistance sphere, but the anomaly is not Figure 6 As obvious as in Figure 8 There is no obvious "hanging noodles" phenomenon.

[0136] Attached Fig. 9 is the horizontal electric field pseudo-section corresponding to the spherical anomaly model, Fig. 9 Middle|E y | The changing rules of curves and pseudo-sections are generally similar to Figure 7 The similarity indicates that in anisotropic media, even if there is no electrical inhomogeneity in the shallow layer, a curve shape very similar to the current type distortion will appear, and the two are difficult to distinguish. In MT, the phase tensor analysis method can be used to distinguish them.

[0137] 3. Spherical anomaly model affected by plate-shaped current distortion:

[0138] This model is a combination of a plate model and a sphere model; the size, burial depth and electrical parameters of the anomaly are exactly the same as those of the previous two models. y |As Fig.10 As shown (attached Fig.10 (Figure 2 is the horizontal electric field curve corresponding to the spherical anomaly model affected by the plate-like current distortion).

[0139] Depend on Fig.10 From the simulation results, we can see that the changing characteristics of the profile curve are Figure 6 and Figure 8 The superposition of Fig.10 and Figure 6 The difference between the two can determine the existence of deep low-resistance anomalies; Fig.11 (Attached Fig.11 The horizontal electric field pseudo-section diagram corresponding to the spherical anomaly model affected by the plate-like current distortion is similar to the previous Figure 7 It is difficult to judge the existence of deep low-resistance spheres by comparison.

[0140] It can be seen that |E y The current distortion caused by the shallow low-resistance plate-like body in the pseudo-section diagram of | masks the response characteristics of the electric field component of the deep sphere, which will bring difficulties to the inversion analysis in practical applications. To this end, we further plot the electric field component |E along the survey line y The phase φ pseudo-section diagram of | can clearly show the superposition characteristics of the anomaly. Although the current distortion of the shallow plate body has an impact on the spherical anomaly body, the impact is relatively large compared to |E y |The pseudo-section image has obviously weakened, and we can determine the existence of deep spherical anomalies through phase changes.

[0141] In this solution, the detection host can calculate the phase information of the measured electric field component to determine the geological anomaly at depth.

[0142] The forward simulation results of the three geoelectric models mentioned above show that in three-dimensional conditions, local anomalies near the surface will cause the electric field component |E y |It will also cause obvious distortion anomalies above the anomaly. Therefore, the direction of the survey line will not affect the application of the frequency selection method.

[0143] In a fifth embodiment of a frequency selective exploration method based on natural electromagnetic phase observation proposed by the present invention, based on the fourth embodiment, step S130 includes the following steps:

[0144] Step S510: Using the horizontal electric field component along the first survey line direction as the ordinate of the potential curve graph, and using the positions of each first detection point distributed along the first survey line direction as the ordinate of the potential curve graph, so as to obtain potential curve graphs under multiple different detection frequencies, wherein the number of detection frequencies corresponding to the potential curve graph is 3.

[0145] In a sixth embodiment of a frequency selective exploration method based on natural electromagnetic phase observation proposed by the present invention, based on the fifth embodiment, step S140 includes the following steps:

[0146] Step S610: Determine whether there is a first detection point in the potential curve graph that meets a preset condition.

[0147] If so, execute step S620: determine whether there is an abnormal potential point in the first detection point, and mark the first detection point that meets the preset conditions as an abnormal potential point, wherein the preset conditions are: at each detection frequency, the horizontal electric field component collected by the abnormal potential point is greater than the horizontal electric field component collected by the first adjacent detection point before the abnormal potential point, and the horizontal electric field component collected by the abnormal potential point is greater than the horizontal electric field component collected by the first adjacent detection point after the abnormal potential point.

[0148] Specifically, this embodiment provides a specific solution for determining whether there is an abnormal potential point in the first detection point; Figure 2 The potential curve shown in Figure 2 The ordinate in is the potential value ΔV; Figure 2 The abscissa in is the horizontal position x in the direction of the first survey line.

[0149] In a seventh embodiment of a frequency selective exploration method based on natural electromagnetic phase observation proposed by the present invention, based on the sixth embodiment, step S150 includes the following steps:

[0150] Step S710: Determine multiple second detection points in the area to be tested, wherein the multiple second detection points are equidistant and arranged in a straight line in the area to be tested, the distance between two adjacent first detection points is a first point distance, the distance between two adjacent second detection points is a second point distance, and the second point distance is smaller than the first point distance, the abnormal potential point is one of the second detection points, and the abnormal potential point is located in the middle of the multiple second detection points.

[0151] Step S720: The detection electrodes are respectively embedded in each second detection point in sequence, so as to obtain the horizontal electric field components along the second survey line direction obtained by each detection electrode at multiple different detection frequencies through the detection host, wherein the direction in which multiple second detection points are located together is the second survey line direction, the distance between the two detection electrodes when embedded in the first detection point for detection is the first pole distance, the distance between the two detection electrodes when embedded in the second detection point for detection is the second pole distance, and the second pole distance is consistent with the first pole distance, and the number of detection frequencies corresponding to the two detection electrodes when embedded in the second detection point for detection is greater than the number of detection frequencies corresponding to the potential curve graph.

[0152] Step S730: obtaining a pseudo-sectional view of the dipole profile based on the horizontal electric field component along the second measuring line direction.

[0153] Step S740: Determine the horizontal position of the underground good conductor based on the pseudo-section diagram of the diode profile.

[0154] In the eighth embodiment of the frequency selective exploration method based on natural electromagnetic phase observation proposed by the present invention, based on the seventh embodiment, step S730 includes the following steps:

[0155] Step S810: Use the horizontal electric field component along the second survey line direction as the section line of the dipole profile pseudo-section diagram, use the apparent depth as the ordinate of the dipole profile pseudo-section diagram, and use the positions of each second detection point distributed along the second survey line direction as the upper abscissa of the dipole profile pseudo-section diagram to obtain the dipole profile pseudo-section diagram, wherein the ordinate apparent depth of the dipole profile pseudo-section diagram is obtained by inverting the skin depth formula of the electromagnetic wave and the empirical coefficient.

[0156] Specifically, as attached Figure 3 As shown, Figure 3 The vertical coordinate in is the apparent depth h s , Figure 3 The upper horizontal axis in the second survey line direction is the horizontal position x; the profile areas of different colors represent different potential values ​​ΔV; this embodiment provides a specific solution for obtaining a pseudo-section diagram of a dipole profile based on the horizontal electric field component along the second survey line direction; the above-mentioned skin depth formula and empirical coefficient of electromagnetic waves are common knowledge and will not be repeated here.

[0157] In a ninth embodiment of a frequency selective exploration method based on natural electromagnetic phase observation proposed by the present invention, based on the eighth embodiment, step S740 includes the following steps:

[0158] Step S910: Mark the horizontal position corresponding to the maximum value of the horizontal electric field component in the pseudo-section image of the diode cross section as a suspected position point.

[0159] Step S920: Determine whether the horizontal distance between the suspected location point and the abnormal location point is less than a preset value (eg, 2 meters).

[0160] If yes, execute step S930: taking the suspected position point as the horizontal position of the underground good conductor.

[0161] Specifically, this embodiment provides a specific solution for determining the horizontal position of an underground good conductor based on a pseudo-section diagram of a dipole profile.

[0162] Specifically, the FSM is applied to sites A and B for groundwater exploration as follows, using examples to illustrate that the FSM can use the distortion characteristics of earth currents to perform groundwater exploration; at the same time, it also illustrates the effectiveness of the FSM in a strong electromagnetic interference environment such as a high-voltage transmission line.

[0163] Site A and Site B are both located in mountainous areas with dense vegetation and limited working space, so it is difficult to carry out work using conventional geophysical methods. At the same time, the commonly used electromagnetic method is greatly interfered by the presence of high-voltage transmission lines near Site A and Site B. Therefore, the scheme proposed by the present invention is used to carry out groundwater source exploration work in these two places.

[0164] The detection process of site A is as follows:

[0165] The exposed lithology at the working point of site A is Carboniferous limestone. There is a high-voltage cable about 10m above the right side of the first survey line corresponding to site A, and the height of the high-voltage cable is about 6m from the ground; drinking water needs to be found for a private villa, and the exploration range can only be within the land acquisition range of the villa. Therefore, the influence of the high-voltage cable cannot be avoided, so the direction of the first survey line is set to be parallel to the high-voltage cable.

[0166] Figure 2 The potential curve of the natural electric field frequency selection method (the number of detection frequencies is 3, namely 25Hz, 67Hz and 170Hz) for site A is shown in the figure. Figure 2 The frequency value corresponding to each curve is the observed frequency. The first pole distance is 10m, the first point distance is 5m, and the detection host model is TC150 frequency selector. Figure 2It can be seen that the curve change trends of the three different frequencies are generally synchronized, but the detection results of 25Hz are generally greater than those of 67Hz, which is not completely the same as the theoretical forward modeling results (that is, the profile curve rises as the frequency increases); this may be due to the influence of human factors, the surrounding environment has an interference signal of about 25Hz, and this signal also becomes the field source of FSM. In addition, there are obvious relatively low potential anomalies at 15m and 55m in the direction of the first survey line. That is, 15m and 55m in the direction of the first survey line are both determined as abnormal potential points.

[0167] Subsequently, it is necessary to conduct subsequent dipole profile multi-frequency detection on the two abnormal potential points of 15m and 55m to determine the horizontal position of the underground good conductor; at the actual detection site, considering the actual situation on site and the requirements of Party A, in this embodiment, the dipole profile multi-frequency detection of FSM is further carried out at 15m:

[0168] The number of the second detection points here is 9 (respectively 5m, 7m, 9m, 11m, 13m, 15m (this point is an abnormal potential point), 17m, 19m and 21m in the direction of the second survey line, then the second point distance is 2m, and the second pole distance is 10m), that is, 33 frequencies within 20-5000Hz are observed at each second detection point (that is, the number of detection frequencies corresponding to the two detection electrodes when embedded in the second detection point for detection is 33); and a pseudo-section diagram of the dipole profile is drawn; Figure 3 That is, the pseudo-section diagram of the dipole profile near 15m (abnormal potential point) in the direction of the second survey line; it can be observed that the maximum value of the horizontal electric field component of the pseudo-section diagram of the dipole profile reaches 22.316mV (at 13m). That is, the suspected location point is 13m in the direction of the second survey line; because the distance between 13 meters and the above-mentioned abnormal potential point (15m) is less than the preset value, it is determined that the suspected location point is directly above the underground good conductor (water source); when the drilling operation is started and the drilling depth is 100m, the water volume reaches about 100t / d; the final well depth is 150m, the water output is greater than 300t / d, and the main water output depth is about 120m, which proves that there is indeed a water source below the suspected location point, confirming the accuracy of the detection work.

[0169] The detection process of site B is as follows:

[0170] The strata in the working area of ​​the detection area corresponding to site B are roughly divided into four layers: ① Quaternary sub-clay (Q4), with a thickness of about 18m; ② Sanjia Chong section of the Anyuan Formation of the Upper Triassic (T3a2), mainly composed of sandy shale, siltstone, fine-medium quartz sandstone, locally intercalated with thin coal seams of 0.1-0.3m, and the thickness of this layer is generally 90-120m; ③ Zijia Chong section of the Anyuan Formation of the Upper Triassic (T3a1), mainly composed of siliceous conglomerate, locally composed of sandy conglomerate intercalated with sandy shale and coal lines, about 5-10m thick; ④ Huanglong Group of the Middle Carboniferous (C2hn), thick-layered dolomite intercalated with a small amount of thick-layered limestone.

[0171] According to the terrain, landforms and building facilities at site B, a total of 5 first survey lines of different lengths (L1, L2, L3, L4 and L5) were selected, and the detection host model was TC300 frequency selector. After detecting the 5 first survey lines, the first survey line of L2 was finally selected to generate the potential curve; during this detection process, the first pole distance was 10m and the first point distance was 5m. There were 3 detection frequencies (25Hz, 67Hz and 170Hz respectively), and the potential curves of the 3 detection frequencies are shown in the attached figure. Figure 4 As shown; attached Figure 4 The curves in the figure rise as the frequency increases, and the variation patterns along the survey line are roughly the same; only the 25Hz curve shows a relatively low value locally at 15m and 25m along the survey line, which may be caused by interference.

[0172] Attached Figure 4 The most obvious feature is that all three curves show very obvious low potential anomalies at 40m of the first survey line, so 40m in the direction of the first survey line is determined as the abnormal potential point; further, a subsequent dipole profile multi-frequency detection is carried out near 40m to determine the horizontal position of the underground good conductor; the number of the second detection points here is 11 (respectively 35m, 36m, 37m, 38m, 39m, 40m (this point is the abnormal potential point), 41m, 42m, 43m, 44m and 45m in the direction of the second survey line); the second pole distance is 10m, and the second point distance is 1m; the detection frequency is 40 frequencies within 10-5000Hz, and a pseudo-section diagram of the dipole profile is drawn after detection, as shown in the attached figure. Figure 5 Observe the attached Figure 5 It can be seen that the maximum value of the horizontal electric field component of the bipolar profile pseudo-section reaches 243.874mV (at 39.5m). That is, the suspected location point is 39.5m in the direction of the second survey line; because the distance between 39.5m and the above abnormal potential point (40m) is less than the preset value, it is determined that the suspected location point is directly above the underground good conductor (water source).

[0173] In summary, there is an obvious low-potential anomaly at 39.5m in the pseudo-section of the two-pole profile, and there are obvious distortions in the contour lines and multiple relatively low-potential anomaly areas. It is speculated that this area is a favorable location for finding groundwater. The final well location is 39.5m at the second survey line, the final drilling depth is 219.0m, the main water depth is around 90-100m, 150m and 190m, the static water level after pumping is 28.80m deep, and the daily water inflow is 1920t / d; it proves that there is indeed a water source below the suspected location point, confirming the accuracy of the detection work.

Claims

1. A frequency-selective exploration method based on natural electromagnetic phase observation, It is characterized in that A frequency-selective exploration system is applied to phase observation based on natural electromagnetic method; the system comprises a detection host and a detection electrode communicatively connected to the detection host; The number of detection electrodes is 2; The method comprises: Determine a region to be tested and a plurality of first detection points within the region to be tested, wherein the plurality of first detection points are equally spaced and arranged in a straight line within the region to be tested, and the detection electrodes are used to be embedded in the first detection points for detection; Acquire, by a detection host, a horizontal electric field component along a first measurement line direction obtained by the detection electrode at a plurality of different detection frequencies, wherein a common direction of a plurality of the first detection points is the first measurement line direction; The potential curve diagrams at different detection frequencies are obtained by detecting the host based on the horizontal electric field component along the first measuring line direction; Determining whether there is an abnormal potential point in the first detection point based on the potential curve diagram; If it exists, a dipole profile multi-frequency detection is carried out on the abnormal potential point to determine the horizontal position of the underground good conductor.

2. A frequency selective exploration method based on natural electromagnetic phase observation according to claim 1, It is characterized in that The acquiring, by the detection host, the horizontal electric field component along the first measuring line direction obtained by the detection electrode at a plurality of different detection frequencies comprises: Let the harmonic factor be e -iωt , to obtain the frequency domain electromagnetic field equations: Where, E is the electric field strength in the detection area, H is the magnetic field strength in the detection area; J s represents the field source term, μ 0 is the magnetic permeability in vacuum, i is an imaginary unit, and satisfies: i 2 =-1, t is the time variable, ω is the circular frequency, σ is the conductivity of the medium; Ignore the displacement current to find the curl on both sides of formula (1), and substitute formula (2) to obtain the second-order vector Helmholtz equation satisfied by the electric field in the medium: Let the field source term be 0 and apply the first-type boundary condition on the boundary to obtain formula (5), where the first-type boundary condition is as shown in formula (4): nE=nE 0 , (5) Where n is the outer normal vector of the boundary mesh, E 0 is the electric field response of the one-dimensional medium on the boundary.

3. A frequency selective exploration method based on natural electromagnetic phase observation according to claim 2, It is characterized in that The field source term is set to 0 and the first type of boundary condition is applied on the boundary to obtain formula (5), which then includes: An unstructured tetrahedral grid is used to discretize the underground good conductors in the test area, where the six edges of the underground good conductors satisfy the following formula: In the formula, E k is the tangential electric field value defined on the kth edge of the underground good conductor, N k is the vector shape function on the kth edge of the underground good conductor; Assume that the kth edge of the underground good conductor is connected by nodes i→j, then: Where λ is the barycentric coordinate of the node; shape function N k The curl of is expressed accordingly as: Based on formula (8), the discrete form of the first boundary condition is constructed to obtain an N DoF ×N DoF The complex system matrix A is symmetrical but not self-adjoint, and the linear equation (9) constructed by the complex system matrix A is solved to obtain the distribution of the electric field on the edge, where the linear equation (9) is: Ax=b, (9) Where N DoF Represents the number of all edges of good underground conductors.

4. A frequency selective exploration method based on natural electromagnetic phase observation according to claim 3, It is characterized in that The discrete form of the first boundary condition is constructed based on formula (8) to obtain an N DoF ×N DoF The complex system matrix A is symmetric but not self-adjoint. The linear equation (9) constructed by the complex system matrix A is solved to obtain the distribution of the electric field on the edge, which is then followed by: Assume that the conductivity distribution of the background in the area to be measured is σ 0 (r), and there are multiple underground good conductors distributed near the surface of the area to be measured, and the conductivity of the mth underground good conductor is determined as σ m (r),σ m (r) and σ 0 The difference between (r) is δσ m (r) = σ m (r)-σ 0 (r), the integral equation solution of the electric field E(r) at any position r inside or outside the mth underground good conductor is: Where μ is the magnetic permeability of the underground medium in the test area, r is the spatial position of any point in the underground good conductor, V m is the volume of the mth underground good conductor; E(r′) is the electric field vector at r′, g(r,r′) is the scalar full-space Green’s function; E 0 (r) is the normal field or the regional field; e 1 (r) is the inductive distorted electric field generated by a good conductor near the surface, e G (r) is the current-type distorted electric field generated by a good conductor in the local underground near the surface; Using the Born approximation, replace E(r′) in the integral of formula (10) and formula (11) with the normal electric field E 0 (r) to obtain the observed electric field E(r) and E 0 The relationship between (r): E(r)=|I+G(r)(I-G(r) -1 )|E 0 (r)=c(r)E 0 (r), (12) Where G(r) is the Green's vector tensor function; the distortion tensor c(r) is simplified to a second-order real tensor that is independent of frequency; The observed electric field E(r) is taken as the horizontal electric field component along the direction of the first survey line.

5. A frequency selective exploration method based on natural electromagnetic phase observation according to claim 4, It is characterized in that The method of obtaining potential curves at different detection frequencies based on the horizontal electric field component along the first measuring line direction by the detection host includes: The horizontal electric field component along the first measuring line direction is used as the ordinate of the potential curve graph, and the positions of the first detection points distributed along the first measuring line direction are used as the ordinate of the potential curve graph to obtain potential curve graphs under multiple different detection frequencies, wherein the number of detection frequencies corresponding to the potential curve graph is 3.

6. A frequency selective exploration method based on natural electromagnetic phase observation according to claim 5, It is characterized in that The determining whether there is an abnormal potential point in the first detection point based on the potential curve diagram includes: Determine whether there is a first detection point that meets the preset conditions in the potential curve graph; If so, it is determined that there is an abnormal potential point in the first detection point, and the first detection point that meets the preset conditions is marked as an abnormal potential point, wherein the preset conditions are: at each detection frequency, the horizontal electric field component collected by the abnormal potential point is greater than the horizontal electric field component collected by the first adjacent detection point before the abnormal potential point, and the horizontal electric field component collected by the abnormal potential point is greater than the horizontal electric field component collected by the first adjacent detection point after the abnormal potential point.

7. A frequency selective exploration method based on natural electromagnetic phase observation according to claim 6, It is characterized in that The method of performing a dipole profile multi-frequency detection on the abnormal potential point to determine the horizontal position of the underground good conductor includes: Determine a plurality of second detection points in the area to be tested, wherein the plurality of second detection points are equally spaced and arranged in a straight line in the area to be tested, the distance between two adjacent first detection points is a first point distance, the distance between two adjacent second detection points is a second point distance, and the second point distance is smaller than the first point distance, the abnormal potential point is one of the second detection points, and the abnormal potential point is located in the middle of the plurality of second detection points; The detection electrodes are sequentially embedded in each second detection point respectively, so as to obtain the horizontal electric field components along the second survey line direction obtained by each detection electrode at multiple different detection frequencies through the detection host, wherein the direction in which multiple second detection points are located together is the second survey line direction, the distance between the two detection electrodes when embedded in the first detection point for detection is the first pole distance, the distance between the two detection electrodes when embedded in the second detection point for detection is the second pole distance, and the second pole distance is consistent with the first pole distance, and the number of detection frequencies corresponding to the two detection electrodes when embedded in the second detection point for detection is greater than the number of detection frequencies corresponding to the potential curve graph; A pseudo-section diagram of a dipole profile is obtained based on the horizontal electric field component along the second survey line direction; Determine the horizontal position of underground good conductors based on the pseudo-section diagram of the dipole profile.

8. A frequency selective exploration method based on natural electromagnetic phase observation according to claim 7, It is characterized in that The method of obtaining a dipole profile pseudo-section diagram based on the horizontal electric field component along the second survey line direction comprises: The horizontal electric field component along the second survey line direction is used as the section line of the dipole profile pseudo-section diagram, the apparent depth is used as the ordinate of the dipole profile pseudo-section diagram, and the positions of the second detection points distributed along the second survey line direction are used as the upper abscissa of the dipole profile pseudo-section diagram to obtain the dipole profile pseudo-section diagram, wherein the ordinate apparent depth of the dipole profile pseudo-section diagram is obtained by inverting the skin depth formula of the electromagnetic wave and the empirical coefficient.

9. A frequency selective exploration method based on natural electromagnetic phase observation according to claim 8, It is characterized in that The method of determining the horizontal position of the underground good conductor based on the pseudo-section diagram of the dipole profile includes: The horizontal position corresponding to the maximum value of the horizontal electric field component in the pseudo-section diagram of the dipole section is marked as a suspected position point; Determine whether the horizontal distance between the suspected position point and the abnormal position point is less than a preset value; If so, the suspected position point is taken as the horizontal position of the underground good conductor.

10. A frequency selective exploration method based on natural electromagnetic phase observation according to claim 8, It is characterized in that When there is a high-voltage cable near the area to be measured, the first measuring line direction is set to be parallel to the extending direction of the high-voltage cable.

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