Non-grounding magnetic coil single-frequency and multi-frequency combined stratum exploration method

Abstract

The invention discloses a non-contact geomagnetic coil single-frequency and multi-frequency combined stratum exploration method. The method comprises the following steps that S1, observation parameters are calculated according to exploration requirements; s2, transmitting a single-frequency vertical coil, and moving and scanning a three-component coil; s3, the apparent resistivity and the apparent polarizability of the earth are quickly found through transverse and longitudinal table look-up; s4, quickly identifying a regional stratum, and dividing abnormal sections; s5, abnormal section multi-frequency static data acquisition; s6, multi-frequency data longitudinal underground layering inversion is carried out; and S7, performing combined output of plane quick sweeping and section layering results. According to the method, the precision of the exploration result and the data accuracy are guaranteed, the final exploration result is combined with the plane section and the longitudinal section, the exploration efficiency is guaranteed, the exploration precision can be guaranteed, and the exploration cost is greatly reduced on the premise that the exploration precision is guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of railway engineering survey, in particular to a non-grounding magnetic coil single-multi-frequency combined stratum survey method. Background Art

[0002] At present, railway projects often use electromagnetic methods to conduct stratigraphic surveys, but the current main method of conducting surveys is to evenly distribute survey points. Especially for area surveys, this is time-consuming and difficult to ensure the survey timeliness, which affects subsequent engineering survey and design work. At the same time, large-scale surveys are very costly, so it is necessary to study new survey methods and algorithms to improve survey efficiency and save exploration funds.

[0003] In summary, the application significance of the present invention is:

[0004] The non-grounded magnetic coil single-multi-frequency joint formation exploration method of the present invention firstly obtains regional exploration data quickly by transmitting a magnetic field at a single frequency of the non-grounded magnetic coil and scanning with a receiving coil, then finds the earth resistivity and polarizability in a pre-calculated resistivity polarizability vector diagram, quickly delineates the abnormal section, further carries out multi-frequency static data acquisition and vertical underground stratification inversion in the abnormal section, and finally outputs the plane quick scan and section stratification results jointly. The exploration system has the advantages of no need for grounding, mobile observation, joint horizontal and vertical sections, high efficiency, and exploration cost saving, and the exploration results include two parameters, resistivity and polarizability, which are convenient for subsequent engineering survey and design. Summary of the invention

[0005] According to the above problems, the present invention proposes a non-grounding magnetic coil single-multi-frequency combined formation exploration method, the specific scheme is as follows:

[0006] A non-grounded magnetic coil single-multi-frequency combined formation exploration method comprises the following steps:

[0007] Step S1: Calculate observation parameters according to exploration requirements;

[0008] Calculate the fast scanning frequency f according to the burial depth and resistivity attributes of the exploration target 0 , abnormal section transmission frequency band f, transmission and reception distance r and point distance p;

[0009] Step S2: single frequency vertical coil transmission and three component coil movement scanning;

[0010] In the moving state, according to the fast scanning frequency f calculated in step S1 0 , the vertical transmitting coil emits a vertical magnetic field The vertical magnetic field is received by a three-component receiving coil at a distance r from the transmitting coil. and horizontal magnetic field Through the horizontal magnetic field Synthetic radial magnetic field

[0011] Step S3: Look up the table horizontally and vertically to quickly find the apparent resistivity and apparent polarizability of the earth;

[0012] According to the resistivity and polarizability vector diagrams calculated by numerical simulation of the uniform earth model in advance, the apparent resistivity ρ of each measuring point is found by looking up the table. s , apparent polarizability η s ;

[0013] Step S4: quickly identify regional strata and divide abnormal sections;

[0014] The apparent resistivity ρ of the earth quickly found according to step S3 s , apparent polarizability η s As well as the horizontal and vertical geodetic coordinates x,y of the point, plot the apparent resistivity ρ s , apparent polarizability η s The plane image is obtained and the abnormal area is circled therein;

[0015] Step S5: multi-frequency static data collection of abnormal section;

[0016] In the abnormal area delineated in step S4, the device in step S2 is used to transmit the frequency band f, and the three-component receiving coil is used to collect multi-frequency data d in the corresponding frequency band for use in the vertical underground layer inversion;

[0017] Step S6: vertical subsurface layer inversion of multi-frequency data;

[0018] Based on the data d collected in step S5, an objective function δ and an initial formation model are established to solve the sensitivity matrix F of resistivity and polarizability, and then an iterative inversion of the underground formation is performed to obtain the resistivity ρ and polarizability η of the underground formation;

[0019] Step S7: Joint output of plane quick scan and cross-section stratification results;

[0020] According to the plane data obtained in step S4 and the underground formation resistivity ρ, polarizability η, and formation thickness h data obtained in step S6, a plane result map and a longitudinal section result map are drawn, and the map includes the north-south coordinates x, y and the depth z.

[0021] Preferably, in step S1, the fast scanning frequency calculation formula is f 0 =ρ t / (πμ 0 H t 2 ), the unit is Hz, where H t is the burial depth of the exploration target, H t The unit is m, ρt is the regional formation resistivity value, in Ω·m; π is the circumference of a circle, μ 0 is the magnetic permeability, μ 0 =4π×10 -7 H / m;

[0022] The frequency band f of the abnormal area is 10000Hz~(1-20%)f 0 The receiving and transmitting distance r ranges from 1m to 20m, and the exploration point distance p is selected to be between 5m and 20m according to the size of the exploration target.

[0023] Preferably, the regional formation resistivity value ρ t In the range of values, the resistivity in loess areas is 30 to 200Ω·m; the resistivity in relatively wet soil areas is 10 to 20Ω·m; the resistivity in sandy soil areas is approximately 500 to 1000Ω·m; and the resistivity in rock and gravel areas is 5000Ω·m.

[0024] Preferably, in step S3, establishing a resistivity and polarizability vector diagram comprises the following steps:

[0025] S31: Establish a one-dimensional uniform geogeological model, the model thickness is set to be infinite, and the model contains two physical variables: earth resistivity and polarizability. The resistivity value range is 10Ω·m to 10000Ω·m, and the polarizability value range is 0.01 to 0.90;

[0026] S32: Calculation formula based on uniform vertical magnetic field of the earth;

[0027] Determine the series vertical magnetic field H z , radial magnetic field calculation formula Determine the series radial magnetic field H r ;

[0028] Where z is the height of the transmitting coil from the ground, h is the height of the receiving coil from the ground (h>0 means above the ground), r is the transmitting and receiving distance, a is the radius of the transmitting coil, I is the transmitting current, ω=2πf 0 is the circular frequency, μ 0 =4π×10 -7 H / m,u 0 =(λ 2 -ω 2 μ 0 ε 0 +iωμ 0 σ 0 ) 1 / 2 , ρ is the earth resistivity, η is the earth polarizability;

[0029] Then according to the vertical magnetic field Hz and radial magnetic field H r Calculate two parameters: vertical diameter ratio Apparent Phase Where Δφ is H z and H r The phase difference;

[0030] S33: Based on the series of vertical diameter ratios τ and apparent phases α obtained in step S32, a resistivity polarizability vector diagram is drawn, where the horizontal axis is the apparent phase α and the vertical diameter ratio τ is the vertical axis. The variables in the diagram include resistivity and polarizability. Then the vertical magnetic field collected in step S2 is plotted. Radial magnetic field Convert it into the vertical diameter ratio τ and the apparent phase α, so as to find the corresponding apparent resistivity ρ of the earth in the vector diagram s and apparent polarizability η s .

[0031] Preferably, the step S6 specifically includes the following steps:

[0032] S61: Multi-frequency static data collection import;

[0033] Importing the multi-frequency data d collected in step S5;

[0034] S62: Establishing the objective function;

[0035] Based on the multi-frequency data d collected in step S5 and the vertical magnetic field and radial magnetic field calculation formula in step S32:

[0036]

[0037]

[0038] Establish the objective function δ(x), δ(x) = (dF(x)) T (dF(x)) = R(x) T R(x), further Taylor expand the objective function and ignore the terms above the second order to obtain the following formula:

[0039] J(x) T J(x)ΔP=-J(x) T R(x),

[0040] Where F is the forward response, which is given by H z and H r The calculation formula is combined, ΔP is the model parameter correction between two adjacent iterations, J(x) is the sensitivity matrix J(X) = R′(X), x is the model vector (N×1), and d is the collected data vector (2M×1);

[0041] S63: constructing an initial stratigraphic model;

[0042] Construct an initial stratum model in one-dimensional space, including stratum thickness, resistivity and polarizability of each stratum;

[0043] S64: forward calculation;

[0044] Calculate vertical magnetic field based on formation model;

[0045] Forward calculation formula:

[0046] S65: calculation and judgment of fitting residuals;

[0047] Calculate the fitting residual e=|dF(x) 2 , fitting difference vector (2M×1), there is the following relationship: g=J T e, and determine whether the set target value has been reached;

[0048] If the result is reached, the process goes to step S68 to output the inversion result; if the result is not reached, the process goes to step S66 to perform sensitivity matrix calculation;

[0049] S66: Calculate sensitivity matrix;

[0050] Solve the sensitivity matrix of resistivity and polarizability. The sensitivity matrix is ​​the field F(x) to the formation resistivity ρ, polarizability η, formation thickness h c The derivatives of the three model parameters are solved according to the following formula:

[0051]

[0052] In the formula, Δx j is the difference step size corresponding to a certain parameter, which is selected as 10 -3 x j , the range should be adjusted appropriately. If the step size is too large, the differential result will lose the meaning of partial derivative. If the step size is too small, the differential result will oscillate, affecting the inversion efficiency.

[0053] S67: Model modification;

[0054] Calculate the correction value ΔP, ΔP k =-(J T J) -1 ·J·[F(x) k -d], and modify the model. The model vector for the k+1th iteration is x k+1 =x k +ΔP k Then, enter step S64, forward calculation, continuous iteration, (J(x) T J(x)+αI)ΔP=-J(x) TR(x), where I is the unit vector and α is the damping coefficient;

[0055] S68: inversion result output;

[0056] When the fitting residual e=|dF(x) 2 When the set target is reached, the stratification results of each layer thickness h, resistivity ρ, and polarizability η are output.

[0057] Preferably, in step S67, different α may be selected according to the linear characteristics of the model vector F(x);

[0058] When the convergence is stable, a smaller α can be selected to speed up the convergence. Otherwise, increasing α ensures the inversion convergence.

[0059] Preferably, in step S4, the standard for defining the abnormal area is the apparent resistivity ρ s Significantly reduced apparent polarizability η s The areas with obvious elevation were identified as abnormal areas.

[0060] Preferably, in step S5, the specific steps of collecting multi-frequency data d in the corresponding frequency band are as follows:

[0061] The transmission frequency band f is divided into multiple frequencies at equal intervals according to the logarithm, and then in the abnormal area circled in step S4, the vertical transmitting coil transmits a vertical magnetic field according to this frequency series The three-component receiving coil at a distance r from the transmitting coil receives the vertical magnetic field of the corresponding frequency and horizontal magnetic field Thus, multi-frequency data d is formed. Data d contains 4 columns of data. The first column is the frequency and the second column is the vertical magnetic field. The third column is H x R , the fourth column is

[0062] The beneficial effects of the present invention are:

[0063] 1. The present invention uses a magnetic coil with a single frequency to transmit a magnetic field and a receiving coil to move and scan. The exploration system does not need to be grounded, and the exploration efficiency is high;

[0064] 2. Single-frequency regional exploration data, by looking up the table in the pre-calculated resistivity and polarizability vector diagram to find the earth resistivity and polarizability, so as to quickly identify the abnormal section and target area, which can effectively improve the exploration efficiency;

[0065] 3. In the rapidly delineated abnormal sections, further multi-frequency static data collection and stratigraphic inversion are carried out to enrich the detection data volume of the abnormal sections, ensure the precision of the exploration results and the accuracy of the information. Finally, the exploration results are combined with horizontal and vertical sections, which not only ensures the exploration efficiency, but also ensures the exploration accuracy. On the premise of ensuring the exploration accuracy, the exploration cost is also greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments, but it should be understood that these drawings are designed only for explanation purposes and are not intended to limit the scope of the present invention. In addition, unless otherwise specified, these drawings are intended only to conceptually illustrate the structural configurations described herein and are not necessarily drawn to scale.

[0067] Figure 1 It is a flow chart of the non-grounded magnetic coil single-multi-frequency combined formation exploration method of the present invention;

[0068] Figure 2 is the pre-calculated resistivity polarizability vector diagram of the present invention;

[0069] Figure 3 It is a multi-frequency formation inversion flow chart of the present invention;

[0070] Figure 4 It is a plane diagram of regional earth apparent resistivity and apparent polarizability of the present invention;

[0071] Figure 5 It is a multi-frequency inversion result diagram of the abnormal area of ​​the present invention;

[0072] Figure 6 It is a comprehensive result diagram of the present invention. DETAILED DESCRIPTION

[0073] First of all, it should be noted that the specific structure, features and advantages of the present invention will be specifically described below by way of example, but all descriptions are only for illustration and should not be understood as limiting the present invention in any way. In addition, any single technical feature described or implied in the embodiments mentioned herein, or any single technical feature displayed or implied in the drawings, can still be combined or deleted between these technical features to obtain more other embodiments of the present invention that may not be directly mentioned in this document. In addition, in order to simplify the drawings, the same or similar technical features may be marked only in one place in the same drawing.

[0074] In the present invention, unless otherwise clearly stipulated and limited, the terms such as "installation", "setting", "connection", "fixation" and "screw-on" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. Unless otherwise clearly defined, ordinary technicians in this field can understand the specific meanings of the above terms in the present invention according to the specific circumstances.

[0075] The following is combined with Figure 1 -Attached Figure 6 The present invention will be described in detail.

[0076] Embodiment 1:

[0077] like Figure 1 As shown, a non-grounded magnetic coil single-multi-frequency combined formation exploration method includes the following steps:

[0078] Step S1: Calculate observation parameters according to exploration requirements;

[0079] Calculate the fast scanning frequency f according to the burial depth and resistivity attributes of the exploration target 0 , abnormal section transmission frequency band f, transmission and reception distance r and point distance p;

[0080] Step S2: single frequency vertical coil transmission and three component coil movement scanning;

[0081] In the moving state, according to the fast scanning frequency f calculated in step S1 0 , the vertical transmitting coil emits a vertical magnetic field The vertical magnetic field is received by a three-component receiving coil at a distance r from the transmitting coil. and horizontal magnetic field Through the horizontal magnetic field Synthetic radial magnetic field

[0082] Step S3: Look up the table horizontally and vertically to quickly find the apparent resistivity and apparent polarizability of the earth;

[0083] According to the resistivity and polarizability vector diagrams calculated by numerical simulation of the uniform earth model in advance, the apparent resistivity ρ of each measuring point is found by looking up the table. s , apparent polarizability η s ;

[0084] Step S4: quickly identify regional strata and divide abnormal sections;

[0085] The apparent resistivity ρ of the earth quickly found according to step S3 s , apparent polarizability η sAs well as the horizontal and vertical geodetic coordinates x,y of the point, plot the apparent resistivity ρ s , apparent polarizability η s A planar image such as Figure 4 As shown in the figure, the upper part is the regional earth apparent resistivity plane distribution map, and the lower part is the regional apparent polarizability plane distribution map, in which we can find the area of ​​low resistivity and high polarizability, that is, circle the anomaly, such as Figure 4 As shown in the figure, 60-70m in the x direction and 0-30m in the y direction are overlapping areas of low apparent resistivity and high apparent polarizability, so it is possible to consider arranging multi-frequency static data acquisition lines in this area, such as Figure 4 At 65m in the x direction, a multi-frequency static data acquisition survey line is arranged along 0-40m in the y direction to further obtain underground stratum information;

[0086] Step S5: multi-frequency static data collection of abnormal section;

[0087] In the static data acquisition survey line arranged in step S4, the device in step S2 is used to transmit the frequency band f, and the three-component receiving coil is used to collect multi-frequency data d in the corresponding frequency band for use in the vertical underground layer inversion;

[0088] Step S6: vertical subsurface layer inversion of multi-frequency data;

[0089] Based on the data d collected in step S5, establish the objective function δ and the initial formation model, solve the sensitivity matrix F of resistivity and polarizability, and then perform iterative inversion of the underground formation to obtain the resistivity ρ, polarizability η and formation thickness h of the underground formation;

[0090] Step S7: Joint output of plane quick scan and cross-section stratification results;

[0091] According to the plane data obtained in step S4 and the underground formation resistivity ρ, polarizability η, and formation thickness h data obtained in step S6, a plane result map and a longitudinal section result map are drawn, and the map includes the north-south coordinates x, y and the depth z.

[0092] Working principle:

[0093] The method of the present invention calculates the parameters required for observation according to the exploration requirements before the exploration work, such as the fast scanning frequency, the transmission frequency band of the abnormal section, the transmission and reception distance and the point spacing; then, a plane fast mobile scanning is performed based on the fast scanning frequency, and then the earth resistivity and polarizability of each point are found in the resistivity and polarizability vector diagram by using the horizontal and vertical table lookup method, and the abnormal section is quickly divided. The abnormal section is further subjected to multi-frequency static data collection and underground layer inversion, and finally the plane fast scanning and cross-section layering results are jointly output to complete the exploration work.

[0094] Furthermore, in the embodiment, it can also be considered that in step S1, the fast scanning frequency calculation formula is f 0 =ρ t / (πμ 0 H t 2 ), the unit is Hz, where H t is the burial depth of the exploration target, H t The unit is m, ρ t is the regional formation resistivity value, in Ω·m; π is the circumference of a circle, μ 0 is the magnetic permeability, μ 0 =4π×10 -7 H / m;

[0095] The frequency band f of the abnormal area is 10000Hz~(1-20%)f 0 The receiving and transmitting distance r ranges from 1m to 20m, and the exploration point distance p is selected to be between 5m and 20m according to the size of the exploration target.

[0096] Furthermore, in the embodiment, it can also be considered that the regional formation resistivity value ρ t In the range of values, the resistivity in loess areas is 30 to 200Ω·m; the resistivity in relatively wet soil areas is 10 to 20Ω·m; the resistivity in sandy soil areas is approximately 500 to 1000Ω·m; and the resistivity in rock and gravel areas is 5000Ω·m.

[0097] Furthermore, it can also be considered in the embodiment that in step S3, establishing the resistivity and polarizability vector diagram includes the following steps:

[0098] S31: Establish a one-dimensional uniform geogeological model, the model thickness is set to be infinite, and the model contains two physical variables: earth resistivity and polarizability. The resistivity value range is 10Ω·m to 10000Ω·m, and the polarizability value range is 0.01 to 0.90;

[0099] S32: Calculation formula based on uniform vertical magnetic field of the earth;

[0100] Determine the series vertical magnetic field H z , radial magnetic field calculation formula Determine the series radial magnetic field H r ;

[0101] Where z is the height of the transmitting coil from the ground, h is the height of the receiving coil from the ground (h>0 means above the ground), r is the transmitting and receiving distance, a is the radius of the transmitting coil, I is the transmitting current, ω=2πf 0 is the circular frequency, μ 0 =4π×10 -7 H / m,u0 =(λ 2 -ω 2 μ 0 ε 0 +iωμ 0 σ 0 ) 1 / 2 , ρ is the earth resistivity, η is the earth polarizability;

[0102] Then according to the vertical magnetic field H z and radial magnetic field H r Calculate two parameters: vertical diameter ratio Apparent Phase Where Δφ is H z and H r The phase difference;

[0103] S33: Based on the series of vertical diameter ratios τ and apparent phases α obtained in step S32, a resistivity polarizability vector diagram is drawn, where the horizontal axis is the apparent phase α and the vertical diameter ratio τ is the vertical axis. The variables in the diagram include resistivity and polarizability. Then the vertical magnetic field collected in step S2 is plotted. Radial magnetic field Convert it into the vertical diameter ratio τ and the apparent phase α, so as to find the corresponding apparent resistivity ρ of the earth in the vector diagram s and apparent polarizability η s .

[0104] Resistivity polarizability vector diagram Figure 2 shown.

[0105] Furthermore, it can also be considered in the embodiment that step S6 specifically includes the following steps:

[0106] S61: Multi-frequency static data collection import;

[0107] Importing the multi-frequency data d collected in step S5;

[0108] S62: Establishing the objective function;

[0109] Based on the multi-frequency data d collected in step S5 and the vertical magnetic field and radial magnetic field calculation formula in step S32:

[0110]

[0111]

[0112] Establish the objective function δ(x), δ(x) = (dF(x)) T (dF(x)) = R(x) T R(x), further Taylor expand the objective function and ignore the terms above the second order to obtain the following formula:

[0113] J(x) T J(x)ΔP=-J(x) T R(x),

[0114] Where F is the forward response, which is given by H z and H r The calculation formula is combined, ΔP is the model parameter correction between two adjacent iterations, J(x) is the sensitivity matrix J(X) = R′(X), x is the model vector (N×1), and d is the collected data vector (2M×1);

[0115] S63: constructing an initial stratigraphic model;

[0116] Construct an initial stratum model in one-dimensional space, including stratum thickness, resistivity and polarizability of each stratum;

[0117] S64: forward calculation;

[0118] Calculate vertical magnetic field based on formation model;

[0119] Forward calculation formula:

[0120] S65: calculation and judgment of fitting residuals;

[0121] Calculate the fitting residual e=|dF(x) 2 , fitting difference vector (2M×1), there is the following relationship: g=J T e, and determine whether the set target value has been reached;

[0122] If the result is reached, the process goes to step S68 to output the inversion result; if the result is not reached, the process goes to step S66 to perform sensitivity matrix calculation;

[0123] S66: Calculate sensitivity matrix;

[0124] Solve the sensitivity matrix of resistivity and polarizability. The sensitivity matrix is ​​the field F(x) to the formation resistivity ρ, polarizability η, formation thickness h c The derivatives of the three model parameters are solved according to the following formula:

[0125]

[0126] In the formula, Δx j is the difference step size corresponding to a certain parameter, which is selected as 10 -3 x j , the range should be adjusted appropriately. If the step size is too large, the differential result will lose the meaning of partial derivative. If the step size is too small, the differential result will oscillate, affecting the inversion efficiency.

[0127] S67: Model modification;

[0128] Calculate the correction value ΔP, ΔP k =-(J T J) -1 ·J·[F(x) k -d], and modify the model. The model vector for the k+1th iteration is x k+1 =x k +ΔP k Then, enter step S64, perform forward calculation, and iterate continuously, (J(x) T J(x)+αI)ΔP=-J(x) T R(x), where I is the unit vector and α is the damping coefficient;

[0129] S68: inversion result output;

[0130] When the fitting residual e=|dF(x) 2 To achieve the set goal, output the layered results of each layer thickness h, resistivity ρ, polarizability η, the inversion results are as follows Figure 5 As shown, the upper figure is the result of underground formation resistivity, and the lower figure is the result of underground formation polarizability. The horizontal axis in the figure is the measurement point position, and the vertical axis is the depth of the underground formation, the unit is meter, and the attributes in the figure are the resistivity and polarizability of the underground formation respectively.

[0131] Furthermore, in the embodiment, it can also be considered that in step S67, different α can be selected according to the linear characteristics of the model vector F(x);

[0132] When the convergence is stable, a smaller α can be selected to speed up the convergence. Otherwise, increasing α ensures the inversion convergence.

[0133] The inversion process is as follows Figure 3 shown.

[0134] Furthermore, in the embodiment, it can also be considered that in step S4, the standard for delineating the abnormal area is the apparent resistivity ρ s Significantly reduced apparent polarizability η s The areas with obvious elevation were identified as abnormal areas.

[0135] In this embodiment, the specific values ​​of the apparent resistivity and apparent polarizability of the anomaly zone boundary are generally determined based on the geological conditions of the survey area and working experience.

[0136] Furthermore, in the embodiment, it can also be considered that in step S5, the specific steps of collecting multi-frequency data d in the corresponding frequency band are as follows:

[0137] The transmission frequency band f is divided into multiple frequencies at equal intervals according to the logarithm, generally divided into 10 to 20 frequencies, and then in the abnormal area circled in step S4, the vertical transmitting coil emits a vertical magnetic field according to this frequency series The three-component receiving coil at a distance r from the transmitting coil receives the vertical magnetic field of the corresponding frequency and horizontal magnetic field Thus, multi-frequency data d is formed, which contains 4 columns of data, the first column is the frequency, and the second column is the vertical magnetic field. The third column is The fourth column is

[0138] In step S7, the combined output of the plane quick scan and cross-section stratification results is as follows: Figure 6 As shown:

[0139] Regional apparent resistivity ρ s The result map is combined with the underground layer inversion results of multi-frequency static data in the abnormal section to form a three-dimensional detection result. Figure 6 In the figure, x and y are the plane coordinate axes, z is the vertical coordinate axis, and the units are all meters.

[0140] The above embodiments describe the present invention in detail, but the contents are only preferred embodiments of the present invention and cannot be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A non-grounded magnetic coil single-multi-frequency combined formation exploration method, characterized in that: The following steps are involved: Step S1: Calculate observation parameters according to exploration requirements; According to the burial depth and resistivity attributes of the exploration target, the fast scanning frequency f0, the transmission frequency band f of the abnormal section, the transmission and reception distance r and the point distance p are calculated; Step S2: single frequency vertical coil transmission and three component coil movement scanning; In the moving state, according to the fast scanning frequency f0 calculated in step S1, the vertical transmitting coil emits a vertical magnetic field The vertical magnetic field is received by a three-component receiving coil at a distance r from the transmitting coil. and horizontal magnetic field Through the horizontal magnetic field Synthetic radial magnetic field Step S3: Look up the table horizontally and vertically to quickly find the apparent resistivity and apparent polarizability of the earth; According to the resistivity and polarizability vector diagrams calculated by numerical simulation of the uniform earth model in advance, the apparent resistivity ρ of each measuring point is found by looking up the table. s , apparent polarizability η s ; Step S4: quickly identify regional strata and divide abnormal sections; The apparent resistivity ρ of the earth quickly found according to step S3 s , apparent polarizability η s As well as the horizontal and vertical geodetic coordinates x,y of the point, plot the apparent resistivity ρ s , apparent polarizability η s The plane image is obtained and the abnormal area is circled therein; Step S5: multi-frequency static data collection of abnormal section; In the abnormal area delineated in step S4, the device in step S2 is used to transmit the frequency band f, and the three-component receiving coil is used to collect multi-frequency data d in the corresponding frequency band for use in the vertical underground layer inversion; Step S6: vertical subsurface layer inversion of multi-frequency data; Based on the data d collected in step S5, establish the objective function δ and the initial formation model, solve the sensitivity matrix F of resistivity and polarizability, and then perform iterative inversion of the underground formation to obtain the resistivity ρ, polarizability η and formation thickness h of the underground formation; Step S7: Joint output of plane quick scan and cross-section stratification results; According to the plane data obtained in step S4 and the underground formation resistivity ρ, polarizability η, and formation thickness h data obtained in step S6, a plane result map and a longitudinal section result map are drawn, and the map includes the north-south coordinates x, y and the depth z.

2. The non-grounding magnetic coil single-multi-frequency combined formation exploration method according to claim 1 is characterized by: In step S1, the fast scanning frequency calculation formula is: The unit is Hz, where H t is the burial depth of the exploration target, H t The unit is m, ρ t is the regional formation resistivity value, in Ω·m; π is pi, μ0 is the magnetic permeability, μ0=4π×10 -7 H / m; The transmission frequency band f in the abnormal area is 10000Hz~(1-20%)f0, the transmitting and receiving distance r ranges from 1m to 20m, and the exploration point distance p is selected to be between 5m and 20m according to the size of the exploration target.

3. The non-grounded magnetic coil single-multi-frequency combined formation exploration method according to claim 2 is characterized by: Regional formation resistivity value ρ t In the range of values, the resistivity in loess areas is 30 to 200Ω·m; the resistivity in relatively wet soil areas is 10 to 20Ω·m; the resistivity in sandy soil areas is approximately 500 to 1000Ω·m; and the resistivity in rock and gravel areas is 5000Ω·m.

4. The method for single-frequency and multi-frequency combined stratum exploration of a non-grounded magnetic coil according to claim 2 is characterized in that: In step S3, establishing a resistivity and polarizability vector diagram includes the following steps: S31: Establish a one-dimensional uniform geogeological model, the model thickness is set to be infinite, and the model contains two physical variables: earth resistivity and polarizability. The resistivity value range is 10Ω·m to 10000Ω·m, and the polarizability value range is 0.01 to 0.90; S32: Calculation formula based on uniform vertical magnetic field of the earth; Determine the series vertical magnetic field H z , radial magnetic field calculation formula Determine the series radial magnetic field H r ; Where z is the height of the transmitting coil from the ground, h is the height of the receiving coil from the ground (h>0 means above the ground), r is the transmitting and receiving distance, a is the radius of the transmitting coil, I is the transmitting current, ω=2πf0 is the circular frequency, μ0=4π×10 -7 H / m,u0=(λ 2 -ω 2 μ0ε0+iωμ0σ0) 1 / 2 , ρ is the earth resistivity, η is the earth polarizability; Then according to the vertical magnetic field H z and radial magnetic field H r Calculate two parameters: vertical diameter ratio Apparent Phase Where Δφ is H z and H r The phase difference; S33: Based on the series of vertical diameter ratios τ and apparent phases α obtained in step S32, a resistivity polarizability vector diagram is drawn, where the horizontal axis is the apparent phase α and the vertical diameter ratio τ is the vertical axis. The variables in the diagram include resistivity and polarizability. Then the vertical magnetic field collected in step S2 is plotted. Radial magnetic field Convert it into the vertical diameter ratio τ and the apparent phase α, so as to find the corresponding apparent resistivity ρ of the earth in the vector diagram s and apparent polarizability η s .

5. The non-grounded magnetic coil single-multi-frequency combined formation exploration method according to claim 4 is characterized in that: The step S6 specifically comprises the following steps: S61: Multi-frequency static data collection import; Importing the multi-frequency data d collected in step S5; S62: Establishing the objective function; Based on the multi-frequency data d collected in step S5 and the vertical magnetic field and radial magnetic field calculation formula in step S32: Establish the objective function δ(x), δ(x) = (dF(x)) T (dF(x)) = R(x) T R(x), further Taylor expand the objective function and ignore the terms above the second order to obtain the following formula: J(x) T J(x)ΔP=-J(x) T R(x), Where F is the forward response, which is given by H z and H r The calculation formula is combined, ΔP is the model parameter correction between two adjacent iterations, J(x) is the sensitivity matrix J(X) = R′(X), x is the model vector (N×1), and d is the collected data vector (2M×1); S63: constructing an initial stratigraphic model; Construct an initial stratum model in one-dimensional space, including stratum thickness, resistivity and polarizability of each stratum; S64: forward calculation; Calculate vertical magnetic field based on formation model; Forward calculation formula: S65: calculation and judgment of fitting residuals; Calculate the fitting residual e=|dF(x) 2 , fitting difference vector (2M×1), there is the following relationship: g=J T e, and determine whether the set target value has been reached; If the result is reached, the process goes to step S68 to output the inversion result; if the result is not reached, the process goes to step S66 to perform sensitivity matrix calculation; S66: Calculate sensitivity matrix; Solve the sensitivity matrix of resistivity and polarizability. The sensitivity matrix is ​​the field F(x) to the formation resistivity ρ, polarizability η, formation thickness h c The derivatives of the three model parameters are solved according to the following formula: In the formula, Δx j is the difference step size corresponding to a certain parameter, which is selected as 10 -3 x j , the range should be adjusted appropriately. If the step size is too large, the differential result will lose the meaning of partial derivative. If the step size is too small, the differential result will oscillate, affecting the inversion efficiency. S67: Model modification; Calculate the correction value ΔP, ΔP k =-(J T J) -1 ·J·[F(x) k -d], and modify the model. The model vector for the k+1th iteration is x k+1 =x k +ΔP k Then, enter step S64, perform forward calculation, and iterate continuously, (J(x) T J(x)+αI)ΔP=-J(x) T R(x), where I is the unit vector and α is the damping coefficient; S68: Inversion result output: When the fitting residual e=|dF(x) 2 When the set target is reached, the stratification results of each layer thickness h, resistivity ρ, and polarizability η are output.

6. The non-grounded magnetic coil single-multi-frequency combined formation exploration method according to claim 5 is characterized by: In step S67, different α may be selected according to the linear characteristics of the model vector F(x); When the convergence is stable, a smaller α can be selected to speed up the convergence. Otherwise, increasing α ensures the inversion convergence.

7. The non-grounded magnetic coil single-multi-frequency combined formation exploration method according to claim 1 is characterized by: In step S4, the standard for defining the abnormal area is the apparent resistivity ρ s Significantly reduced apparent polarizability η s The areas with obvious elevation were identified as abnormal areas.

8. The non-grounded magnetic coil single-multi-frequency combined formation exploration method according to claim 7 is characterized in that: In step S5, the specific steps of collecting multi-frequency data d in the corresponding frequency band are as follows: The transmission frequency band f is divided into multiple frequencies at equal intervals according to the logarithm, and then in the abnormal area circled in step S4, the vertical transmitting coil transmits a vertical magnetic field according to these frequencies The three-component receiving coil at a distance r from the transmitting coil receives the vertical magnetic field of the corresponding frequency and horizontal magnetic field Thus, multi-frequency data d is formed. Data d contains 4 columns of data. The first column is the frequency and the second column is the vertical magnetic field. The third column is The fourth column is

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