A frequency domain electromagnetic sounding method, system and electronic device

Abstract

The application discloses a frequency domain electromagnetic sounding method, system and electronic equipment. The method can transmit and receive electromagnetic wave field signals of multiple frequencies at a time. The collection area of electromagnetic field data is not limited to the "far zone" of the traditional controllable source audio frequency magnetotelluric method and the "frequency sounding method", the application range of the frequency domain electromagnetic sounding is expanded, a single electric field or magnetic field component full-time apparent resistivity formula is used, a new frequency sounding method is formed, the observation range of the artificial source electromagnetic method is greatly expanded, and the observation speed, precision and field efficiency are improved.

Description

Technical Field

[0001] This application relates to the field of electronic technology, and in particular to a frequency domain electromagnetic depth sounding method, system and electronic equipment. Background Technology

[0002] Currently, electromagnetic sounding can be divided into two types: natural and artificial source. Commonly used natural source electromagnetic sounding methods are called magnetotelluric sounding and audio-frequency magnetotelluric sounding. Artificial source electromagnetic sounding methods can be further divided into frequency domain electromagnetic sounding (or frequency sounding) and time domain electromagnetic sounding. The field source in frequency sounding can be an electrical source (powered by grounded electrodes to provide the artificial field source) or a magnetic source (powered by an ungrounded wire frame to provide the artificial field source). In the study of frequency sounding using electrical sources, it is assumed that because the horizontal Y component of the uniform half-space electric field on the Earth's surface is emitted by the ground electric dipole source AB... It does not contain frequency-related quantities, so it cannot be used for electromagnetic depth sounding; it can only be used for direct current methods (geometric depth sounding).

[0003] The above method is based on an electric field source AB emitting an artificial field source, measuring the electric field component Ex parallel to AB or the electric field component Ey perpendicular to AB within a certain range at a medium to long distance from AB. However, in actual construction projects, due to the limitations imposed by surface water bodies such as rivers and ponds, as well as various human-made structures, it is difficult to deploy the MN electrodes for collecting Ex and Ey. To collect relatively complete data, either the amount of fieldwork is increased, reducing production efficiency, or the data collection points are abandoned, sacrificing data completeness. Summary of the Invention

[0004] This application provides a frequency domain electromagnetic sounding method, system, and electronic equipment to expand the observation range of artificial source electromagnetic methods and improve observation speed, accuracy, and field efficiency.

[0005] In a first aspect, this application provides a frequency-domain electromagnetic depth sounding method, the method comprising:

[0006] Based on the electric dipoles of a uniform earth surface, the electric and magnetic fields in the cylindrical coordinate system of a uniform earth surface are calculated.

[0007] The electric and magnetic fields in the cylindrical coordinate system are transformed and calculated in the Cartesian coordinate system to obtain the electromagnetic field in the Cartesian coordinate system.

[0008] Based on the electromagnetic field in the Cartesian coordinate system, the apparent resistivity of the horizontal electric field in any direction during the frequency domain electromagnetic sounding is calculated.

[0009] Frequency domain electromagnetic depth sounding is performed based on the apparent resistivity over the entire period.

[0010] In one possible design, based on a uniform earth surface electric dipole, the electric and magnetic fields in a uniform earth surface cylindrical coordinate system are calculated, including:

[0011] Determine the dipole current based on the electric dipoles of a uniform Earth surface;

[0012] Based on the dipole current, the upper and lower spatial vector potential components of the uniform Earth surface are calculated.

[0013] The electric and magnetic fields in the cylindrical coordinate system of the uniform Earth surface are calculated using the outer upper spatial vector position and the outer lower spatial vector position.

[0014] In one possible design, the electric field in the cylindrical coordinate system is calculated using the following formula:

[0015]

[0016]

[0017] E z =0

[0018] The magnetic field in cylindrical coordinates is calculated using the following formula:

[0019]

[0020]

[0021]

[0022] Among them, I0, I1, K0, and K1 are Bessel functions of the imaginary arguments.

[0023] In one possible design, the electromagnetic field in the Cartesian coordinate system is calculated using the following formula:

[0024]

[0025]

[0026] Where ρ represents the resistivity of a uniform half-space. This is an implicit term for the resistivity of a uniform half-space.

[0027] In one possible design, the apparent resistivity of the horizontal electric field in any direction during the frequency domain electromagnetic sounding is calculated based on the electromagnetic field in the Cartesian coordinate system, including:

[0028] Obtain the horizontal electric field at any point in the direction of the angle between the electric dipole moment and the point of interest.

[0029] Calculate the apparent resistivity of the frequency or electromagnetic depth based on the electromagnetic field in the Cartesian coordinate system.

[0030] Based on the horizontal electric field and apparent resistivity in the direction of the angle between any point and the electric dipole moment, the apparent resistivity of the electric field in any direction can be calculated.

[0031] The apparent resistivity of the electric field in any direction is calculated iteratively to obtain the apparent resistivity over the entire period.

[0032] In one possible design, the horizontal electric field at any point in the direction of the angle between the electric point and the electric dipole moment is calculated using the following formula:

[0033]

[0034] Where ρ represents the resistivity of a uniform half-space, and θ is the angle between any point and the electric dipole moment.

[0035] In one possible design, the apparent resistivity of the electric field in any direction is calculated using the following formula:

[0036]

[0037] Where, ρ a The apparent resistivity characterizes the electric field in any direction, and MN is the electrode of Ex and Ey.

[0038] In one possible design, the apparent resistivity of the horizontal electric field in any direction over the entire lifespan is calculated using the following formula:

[0039]

[0040] in, Characterizes the apparent resistivity over the entire period.

[0041] Secondly, this application provides a frequency-domain electromagnetic depth sounding system, the system comprising:

[0042] The calculation module is used to calculate the electric and magnetic fields in the cylindrical coordinate system of a uniform Earth surface based on the electric dipoles of a uniform Earth surface.

[0043] The conversion module is used to perform conversion operations on the electric field and magnetic field in the cylindrical coordinate system to the Cartesian coordinate system to obtain the electromagnetic field in the Cartesian coordinate system.

[0044] The processing module is used to calculate the apparent resistivity of the horizontal electric field in any direction during the entire period of frequency domain electromagnetic sounding based on the electromagnetic field in the Cartesian coordinate system; and to perform frequency domain electromagnetic sounding based on the apparent resistivity during the entire period.

[0045] Secondly, this application provides an electronic device, comprising:

[0046] Memory, used to store computer programs;

[0047] When the processor executes the computer program stored in the memory, it implements the steps of the frequency domain electromagnetic depth sounding method described above.

[0048] For the various aspects of the second to fourth aspects mentioned above, and the technical effects that each aspect may achieve, please refer to the above description of the technical effects that can be achieved for the first aspect or the various possible solutions in the first aspect, which will not be repeated here. Attached Figure Description

[0049] Figure 1 A flowchart of a frequency domain electromagnetic depth sounding method provided in this application;

[0050] Figure 2 A schematic diagram of the coordinate system in a uniform earth surface provided in this application;

[0051] Figure 3 A schematic diagram of the fast Hankel transform coefficients provided in this application

[0052] Figure 4 A schematic diagram comparing the apparent resistivity of the two-layer G-type cross-section provided in this application;

[0053] Figure 5 A schematic diagram comparing the apparent resistivity of a two-layer D-type cross-section provided in this application;

[0054] Figure 6 A schematic diagram comparing the apparent resistivity of the three-layer H-shaped cross-section provided in this application;

[0055] Figure 7 A schematic diagram comparing the apparent resistivity of the three-layer K-type cross-section provided in this application;

[0056] Figure 8 A schematic diagram comparing the apparent resistivity of multi-layer cross sections provided in this application;

[0057] Figure 9 A schematic diagram of the electric field characteristics of the current level provided in this application;

[0058] Figure 10 A schematic diagram of the horizontal and vertical electric field contour lines provided for this application;

[0059] Figure 11 E provided for this application y Schematic diagram of rapid apparent resistivity curve;

[0060] Figure 12 A schematic diagram of the structure of a frequency domain electromagnetic depth sounding system provided in this application;

[0061] Figure 13 This is a schematic diagram of the structure of an electronic device provided in this application. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. The specific operational methods in the method embodiments can also be applied to the device embodiments or system embodiments. It should be noted that in the description of this application, "multiple" is understood as "at least two". "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. A connected to B can represent: A and B directly connected, and A and B connected through C. Furthermore, in the description of this application, terms such as "first" and "second" are used only for distinguishing the purpose of description and should not be construed as indicating or implying relative importance or order.

[0063] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0064] Electromagnetic sounding can be divided into two types: natural and artificial source. Commonly used natural source electromagnetic sounding methods are called magnetotelluric sounding or audio-frequency magnetotelluric sounding. Artificial source electromagnetic sounding methods can be further divided into frequency domain electromagnetic sounding (or frequency sounding) and time domain electromagnetic sounding. The field source in frequency sounding can be an electrical source (powered by grounded electrodes) or a magnetic source (powered by an ungrounded wire frame). In studies of frequency sounding using electrical sources, it is assumed that the horizontal Y component of the uniform half-space electric field on the Earth's surface during the emission of the ground dipole source AB... Since it does not contain frequency-related quantities, it cannot be used for electromagnetic sounding; it can only be used for direct current methods (geometric sounding). The 2020 research project "Technical Research on Frequency Domain Electromagnetic Sounding Method Based on AB-Ey" by the Geophysical Exploration Research Institute of China Coal Geology Bureau concluded that although the expression is frequency-independent, the conductivity σ is a frequency-related quantity σ(f). Numerical calculations and field practice studies also show that the AB-Ey (E-Ey) working device has frequency sounding capabilities.

[0065] The aforementioned research is based on an artificial field source emitted by an electric dipole source AB, measuring the electric field component Ex parallel to AB or the electric field component Ey perpendicular to AB within a certain range at a considerable distance from AB. However, in actual construction projects, the deployment of MN electrodes for collecting Ex and Ey is difficult due to limitations imposed by surface water bodies such as rivers and ponds, as well as various human-made structures. To collect relatively complete data, either the workload in the field is increased, reducing production efficiency, or data collection points are abandoned, sacrificing data completeness. Researching a frequency-based depth sounding method for an arbitrary-direction horizontal electric field E (EE device) becomes the technical basis for solving the above difficulties.

[0066] To address the aforementioned issues, this application provides a frequency-domain electromagnetic sounding method, which proposes a method for frequency-domain sounding by measuring the horizontal electric field in any direction using a power source. A forward modeling program for transmitting from a ground-based electrocouple source AB and receiving a horizontal electric field E in any direction from the ground is used to calculate the corresponding apparent resistivity over the entire period. Apparent resistivity sounding curves for the horizontal electric field E in any direction (including the Ex and Ey directions) are analyzed and compared, and this AB-E system can perform frequency-domain electromagnetic sounding.

[0067] Furthermore, this method can expand the data acquisition range of electromagnetic frequency sounding from the same source, improve field production efficiency, and save field construction costs. Meanwhile, when measuring Ex and Ey using a fixed MN electrode direction, if the MN electrode is aligned with electromagnetic interference sources such as high-voltage lines, power lines, and optical fibers, the resulting electromagnetic interference can be significant. Therefore, data can be acquired by aligning the MN electrode perpendicular to the interference source direction to suppress electromagnetic interference.

[0068] like Figure 1 The flowchart shown below illustrates a frequency domain electromagnetic depth sounding method provided in this application. The method includes:

[0069] S1, based on the electric dipole of the uniform earth surface, the electric field and magnetic field in the cylindrical coordinate system of the uniform earth surface are calculated;

[0070] S2, the electric field and magnetic field in the cylindrical coordinate system are transformed into the Cartesian coordinate system to obtain the electromagnetic field in the Cartesian coordinate system;

[0071] S3. Calculate the apparent resistivity of the horizontal electric field in any direction during the frequency domain electromagnetic sounding based on the electromagnetic field in the Cartesian coordinate system.

[0072] S4, perform frequency domain electromagnetic depth sounding based on the apparent resistivity throughout the entire period.

[0073] Specifically, the frequency domain electromagnetic sounding method uses two grounded electrodes, A and B, to supply power to the ground and measure a pair of electric and magnetic field components in a relatively distant area. Since the distance between AB is much smaller than the distance between AB and MN (transmitter-receiver distance), the power supply sources A and B can be regarded as electric dipoles. Therefore, the electromagnetic field generated by an electric dipole on a uniform Earth surface will be explained first.

[0074] like Figure 2 The diagram shows a Cartesian coordinate system established on a uniform Earth surface with electric dipoles, where the dipole moment is along the x-axis. Assume the dipole current is sinusoidal.

[0075] E = E0e -iwt H = H0e -iwt (3-1)

[0076] Maxwell's equations for a stable field are:

[0077]

[0078] In the formula, E and H are both complex functions describing the field. The vector potential A of the electric dipole can be defined as follows:

[0079]

[0080] Combined formulas 3-1 and 3-2 include:

[0081]

[0082]

[0083] In the formula k 2 =iσμω, where i is the square of the wave number. Vector A is 0 in the Y direction, meaning vector A can be written as:

[0084] A=(A X ,0,A Z (3-6)

[0085] Through derivation and calculation, the X and Z components of the vector potential A in the upper and lower half-space outside the uniform Earth surface (z=0) can be obtained:

[0086]

[0087] In the formula J0 and J1 are the 0th and 1st order Bessel functions, respectively. From (3-4) and (3-7), the electric field expression in cylindrical coordinates of a uniform Earth surface can be obtained:

[0088]

[0089] The expression for the magnetic field in cylindrical coordinates of a uniform Earth surface:

[0090]

[0091] In the formula, I0, I1, K0, and K1 are Bessel functions of the imaginary arguments.

[0092] The above expressions (3-8) and (3-9) are expressions for the electromagnetic field of a uniform Earth surface in cylindrical coordinates. They are converted to Cartesian coordinates using the following formula:

[0093]

[0094] get:

[0095]

[0096]

[0097] Because the electric field Ex contains an implicit term for the resistivity ρ of a uniform half-space. In E-Ex wide-area electromagnetic sounding, the expression for Ex is rewritten as:

[0098]

[0099] Using ΔV MN =E x ·MN forms the iterative solution formula for apparent resistivity:

[0100]

[0101] Equation (3-13) is similar to the definition of apparent resistivity in DC resistivity, but includes F ex The implied term of apparent resistivity in (ikr) must be obtained through iteration to obtain the apparent resistivity over the entire period. In equation (3-12), the electric field E y Proportional to the resistivity ρ of the uniform half-space earth, EE can be easily derived. y The expression for apparent resistivity in frequency or electromagnetic depth sounding:

[0102]

[0103] Equation (3-14) is similar to the apparent resistivity formula for DC methods, where the preceding term is the device coefficient. For any point, the horizontal electric field in the direction making an angle θ with the X-axis (electric dipole moment) is:

[0104]

[0105] Similar to Ex, let The above formula can be rewritten as:

[0106]

[0107] The apparent resistivity of the electric field E in any direction is:

[0108]

[0109] Equation (3-15) is the expression for iteratively calculating the apparent resistivity of a horizontal electric field in any direction over the entire period.

[0110] In the theory of Controlled Source Audio-frequency Magnetotelluric Sounding (CSAMT), under the far-field condition where |kr|>1, E x / H y and E y / H x Similar to magnetotelluric sounding, the ratio is only related to frequency and resistivity, and is independent of transmission and reception distance. Its corresponding apparent resistivity is also known as Carnia resistivity, and its expression is:

[0111]

[0112] For any point, the horizontal electric field E = Ex in the direction where the angle θ with the X-axis (electric dipole moment) is given. x cosθ+E y sinθ, its vertical direction horizontal magnetic field H + =-H x sinθ+H y cosθ also has a similar expression for apparent resistivity:

[0113]

[0114] In other words, at any point in the far-field region from which the current source is emitted, the horizontal electric field in any direction and the horizontal magnetic field perpendicular to it satisfy the Carnia resistivity condition, which is not limited to the E in controlled-source audio-frequency magnetotelluric sounding (CSAMT). x / H y and E y / H x .

[0115] Furthermore, the resistivity ρ that prevents the flow of interlayer current in parallel layers. l and resistivity ρ which prevents the flow of current perpendicular to the interface n They are different; the anisotropy coefficient of a certain layer is defined as follows: This value is always greater than 1, and Table 1 shows typical values ​​for some rocks.

[0116] rock λ <![CDATA[ρ n / r l ]]> Layered mudstone 1.02-1.05 1.04-1.10 Shale and sandstone interbedded 1.05-1.15 1.10-1.32 Layered sandstone 1.10-1.29 1.20-1.65 tabular shale 1.10-1.59 1.20-2.50 Coal-bearing strata 1.73-2.55 3.00-6.50 anthracite 2.00-2.55 4.00-6.50 Interbedded graphitic slate and carbonaceous rock 2.00-2.75 4.00-7.50

[0117] Table 1

[0118] Derivation from interlayer resistivity ρ n With the resistivity ρ of the layer l By approaching the problem from different angles, we obtain the recursive relationships between the interfaces, ultimately leading to the electric field expression of the horizontally layered Earth surface electric dipole:

[0119]

[0120] Magnetic field representation of horizontally layered electric dipoles on the Earth's surface:

[0121]

[0122]

[0123] In the formula, ρ is the resistivity within the layer. l R * Other parameters such as R are as follows:

[0124]

[0125] The above is the expression in cylindrical coordinates. Similar to the electromagnetic field on a uniform Earth surface, E in Cartesian coordinates is first solved using equation (3-10). x E y H x H y Then, calculate the magnitudes of the horizontal electric and magnetic fields in any direction and their ratios.

[0126] Furthermore, the electromagnetic field expressions for electric dipoles on a horizontally layered Earth surface are all integrals of the Bessel function over the interval (0, ∞). These integrals are actually a type of Hankel transformation. Numerical calculations of the electromagnetic fields of electric and magnetic dipoles on a layered Earth surface are generally performed using the Fast Hankel Transform. Here, we briefly describe the principle and steps of forward modeling using the Fast Hankel Transform.

[0127] The electromagnetic fields of electric and magnetic dipoles on the layered Earth surface can be uniformly written as:

[0128]

[0129] In the formula J n It is an nth-order Bessel function of the first kind, where the real number n is greater than -1. We introduce the transformation formula:

[0130]

[0131] In the formula, μ and ν are new variables in the Fast Hankel Transform, with an interval of (-∞, ∞); r0 is a selected constant. A new function is introduced:

[0132] F(μ)=f(λ) λG(ν)=g(r)r

[0133] Equation (3-21) can be rewritten as:

[0134]

[0135] In other words, G is a function of F and H n The convolution, where H n (μ)=J n (μ)e μ Its discrete form is:

[0136]

[0137] According to equation (3-23), the actual numerical calculation formula of the above discrete form expression can be written as:

[0138]

[0139] In the formula These are called Fast Hankel Transform (FHH) filter coefficients, which can be obtained through Fourier Transform or from many publicly available sources.

[0140] Reference Figure 3 The fast Hankel transform coefficients shown are used. The calculation results will vary slightly depending on the length of the Hankel coefficients selected as needed. During the research, several sets of publicly published Hankel coefficients were tested and compared with the coefficients calculated by the programmed Fourier transform. The calculation results showed little difference, with a relative change of less than 0.01%, which can be ignored. Figure 3 - represents the 0th and 1st order Hankel transform coefficients between -100 and 150 obtained using Fourier transform. As can be seen from the figure, when n is greater than 0, the coefficients oscillate and decay at a faster rate as n increases. Therefore, the range of Hankel coefficients is generally not symmetrically truncated.

[0141] Furthermore, in this embodiment, the wide-area electromagnetic method, as a frequency-domain electromagnetic exploration method, uses artificial field sources that can be electrical or magnetic. The combination of transmission and reception can also vary, with the AB-Ex (also known as E-Ex) method being commonly used. The apparent resistivity curves for the entire period defined by horizontal electric fields in different directions are compared through model calculations. Specific analysis results are as follows:

[0142] 1. G-type cross section

[0143] G-type cross-section model parameters: the transmitting source is located at A(-500, 0) and B(500, 0), the receiving point is located at (2480, 4300), the shallow resistivity is 50 ohm-meters, the thickness is 200 meters, and the substrate resistivity is 500 ohm-meters. Figure 4 These are the apparent resistivity curves for the entire period in the horizontal electric field along the X-direction (AB-Ex), Y-direction (AB-Ey), at a 30-degree angle to the X-axis, and at a 60-degree angle to the X-axis. Above 100Hz, the four curves are essentially overlapping; between 100-10Hz, the four curves bifurcate, but the trend remains consistent; below 10Hz, the apparent resistivity in the AB-Ey and 60-degree directions begins to approach a fixed value, while the apparent resistivity in the AB-Ex and 30-degree directions continues to increase slowly; below 1Hz, the apparent resistivity in all four directions approaches a fixed value of 511, 357, 279, and 337 ohm-meters, respectively, which are also the apparent resistivity values ​​for DC resistivity methods. The apparent resistivity curves defined by the four electric fields all reflect the changing characteristics of the formation resistivity, meaning they can all detect the high-resistivity basement layer up to 200 meters below. The detection depth is based on the skin depth... It is estimated that the root mean square relative error of the apparent resistivity defined by the electric field in four directions for the whole period is less than 5% when the depth is less than 300m (as shown in Table 2), and the root mean square error of the apparent resistivity for all frequencies for the whole period is 9.60% when the exploration depth is less than 1000m (frequency greater than 24Hz).

[0144]

[0145]

[0146] Table 2

[0147] 2. D-type cross-section

[0148] D-type cross-section model parameters: the emission source is located at A(-500, 0) and B(500, 0), the receiving point is located at (2480, 4300), the shallow resistivity is 500 ohm-meters, the thickness is 200 meters, and the substrate resistivity is 50 ohm-meters. Figure 5 These are the apparent resistivity curves defined by the horizontal electric field in four directions throughout the entire period. The four curves basically overlap, and the final apparent resistivity tends to a fixed value of 50 ohm-meters. The total square relative difference of the apparent resistivity in the four directions throughout the entire period at all frequencies is 2.72%. This indicates that they can all detect low-resistivity substrates and have the same frequency sounding function.

[0149] 3. Three-layer H-shaped cross-section

[0150] H-shaped cross-section model parameters: the transmitting source is located at A(-500, 0) and B(500, 0), the receiving point is located at (2480, 4300), the resistivity of the three layers from shallow to deep are 100, 10, and 200 ohm-meters respectively, the thickness of the cap layer is 200 meters, and the thickness of the middle layer is 50 meters. Figure 6 These are the apparent resistivity curves defined by horizontal electric fields in four directions throughout the entire period. Above 50Hz, the four curves largely overlap, and their shape is consistent with the D-type section. Between 50-7Hz, the four curves diverge, exhibiting a false minimum with respect to the apparent resistivity of the horizontal electric field at 60 degrees to the x-axis throughout the entire period. Subsequently, the trend is consistent: the apparent resistivity of all four curves increases with decreasing frequency. Below 7Hz, the apparent resistivity of AB-Ey and AB-Ex60 begins to approach a fixed value, while the apparent resistivity of AB-Ex and AB-Ex30 continues to increase slowly. Ultimately, the apparent resistivity of the horizontal electric fields in all four directions tends to fixed values ​​of 208.3, 161.6, 138.0, and 155.7 ohm-meters, respectively. All four methods reflect the characteristics of the formation resistivity variation in the H-type section, meaning that the high-resistivity layer (basement) below 250 meters can be detected by all four horizontal electric fields.

[0151] 4. Three-layer K-shaped cross-section

[0152] K-type cross-section model parameters: the transmitting source is located at A(-500, 0) and B(500, 0), the receiving point is located at (2480, 4300), the resistivity of the three layers from shallow to deep are 50, 500, and 50 ohm-meters respectively, the thickness of the cap layer is 200 meters, and the thickness of the middle layer is 100 meters. Figure 6The figures show the apparent resistivity curves defined by the horizontal electric fields in four directions throughout the entire period. Above 10Hz, the two curves largely overlap. In the 10Hz–0.1Hz range, the apparent resistivity exhibits cross-variance. Below 0.1Hz, all four curves tend towards a fixed value: 45.8, 55.4, 60.2, and 56.6 ohm-meters, corresponding to the apparent resistivity of the device using DC resistivity. All four methods reflect the variation of formation resistivity from shallow to deep, indicating a low-resistivity basement up to 300 meters below the surface. Numerical analysis shows that the root mean square relative differences of the apparent resistivity in the four directions at depths shallower than 848m (frequency greater than 10Hz) are mostly within 2%, with a total root mean square relative difference of 5.66% (as shown in Table 3).

[0153]

[0154]

[0155] Table 3

[0156] The following conclusions can be drawn from the comparative analysis of the apparent resistivity curves of the horizontal electric field in four directions over the entire period for the four typical geoelectric cross sections:

[0157] 1. In the high-frequency band, the apparent resistivity depth measurement curves of the horizontal electric fields in four directions (four types of devices) basically overlap.

[0158] 2. In the mid-frequency band, the apparent resistivity sounding curves of the four device methods showed a bifurcation phenomenon, but the changing pattern was consistent, reflecting the characteristics of the formation's electrical changes.

[0159] 3. In the low-frequency range, when the frequency is below a certain range, the apparent resistivity curve will tend to a fixed value throughout the entire period. However, the starting frequency of the apparent resistivity defined by the horizontal electric field in different directions is different. The AB-Ex device has the lowest starting frequency at which the apparent resistivity tends to a fixed value. From this perspective, because the frequency is low enough, the skin depth is close to or even greater than the transmit / receive distance. Changing the frequency no longer has a depth-measuring effect, and the fixed value of the apparent resistivity is the DC apparent resistivity of the device.

[0160] In addition, both D-type and K-type cross-sections are low-resistivity substrates, and K-type cross-section ( Figure 6 The four device methods show bifurcated (inconsistent) apparent resistivity curves in the low-frequency band, while the D-type cross-section ( Figure 4 The results are basically the same. Overall, the root mean square relative error of the apparent resistivity of the horizontal electric field in the four directions of the D-type and K-type cross sections (low-resistivity substrates) is smaller than that of the G-type and H-type cross sections (high-resistivity substrates).

[0161] 5. Multi-layer model cross-section

[0162] The above analysis is based on two-layer and three-layer geoelectric models. The following analysis is based on the resistivity logging curves of a certain coal mine in Shanxi Province. The electrical properties are stratified (as shown in Table 4). A horizontal layered geoelectric model is established, and forward modeling is performed for four types of devices: AB-Ex, AB-Ex30, AB-Ex60, and AB-Ey. The apparent resistivity over the entire period is calculated.

[0163] Depth (meters) Thickness (meters) Resistivity (ohm-meter) strata 60 60 18 New World, Upper Stone Box Group 172 112 50 Upper Stone Box Group 220 48 91 Upper Stone Box Group 262 42 36 Upper Stone Box Group 326 64 93 Lower Stone Box Group 346 20 56 Lower Stone Box Group 416 70 152 Shanxi Group, Taiyuan Group 516 100 180 Taiyuan Group 536 20 20 Taiyuan Group, Benxi Group 1000 Ordovician

[0164] Table 4

[0165] The spatial positions of the transmitting source and the receiving point MN remain unchanged, the transmit-receive distance is 4.9km, and the angle between the electric dipole AB and OMN (O is the midpoint of AB) is 60°. Figure 7 These are the calculated apparent resistivity curves. At frequencies above 100Hz, the apparent resistivity curves of the four methods basically overlap. Between 100Hz and 10Hz, the resistivity curves exhibit bifurcation. In the low-frequency range, all four curves tend towards a fixed value. Similar to the layered model above, the changes in apparent resistivity in the horizontal electric field in the four directions reflect the electrical characteristics of the formation.

[0166] The technical solution of this application will be further explained below through specific application scenarios.

[0167] First, let's discuss the frequency-domain electromagnetic sounding method provided in this application. Using a current source emitted by AB, the apparent resistivity obtained by measuring the X and Y components of the horizontal electric field, as well as the components at 30 and 60 degrees to the X-axis, can reflect the electrical variations of the strata, enabling frequency sounding. Therefore, aside from limitations imposed by topography and interference conditions, a stratum resistivity of 50 ohm-meters, an AB length of 1000m, and a frequency of 6Hz can be selected for calculations. Figure 8 This is a contour map showing the magnitude and direction angle of the total electric field. Figure 8 As can be seen, by selecting the right electric field measurement direction, a sufficiently strong electric field signal can be measured.

[0168] In CSAMT detection, E can be measured. x H y or E y H x Two pairs of components, E x E y The magnitude of the electric field can be used Figure 9 The description states that different measurement directions can be selected for different locations based on the corresponding measurement range of the numerical value. Similarly, the contour lines of the horizontal electric field at 15, 30, 45, 60, and 75-degree angles can be calculated, and the corresponding measurement range can be selected.

[0169] Furthermore, the apparent resistivity of CSAMT in frequency domain electromagnetic sounding. The apparent resistivity of the frequency electromagnetic sounding AB-E device method was derived earlier. Fe (ikr) is a function containing the complex reluctance exponent. Apparent resistivity can only be calculated using iterative methods, and the initial values ​​of the iterations affect the calculation speed. As a special case, AB-E... y Apparent resistivity of the frequency domain electromagnetic sounding method The expression is simple, relating apparent resistivity to E. y It is proportional to I, and the apparent resistivity can be quickly calculated in the field, and even U can be used. MN The / I curve determines whether electromagnetic sounding has detected the target layer.

[0170] Figure 10 This is a measured curve of the normalized MN potential difference of the Y-direction current versus the apparent resistivity in a coal mine. Figure 10 The graph shows two parallel curves on a logarithmic scale. By analyzing the potential difference curve, the apparent resistivity curve can be indirectly analyzed. Based on the known electrical conditions of the exploration area, it can be determined whether the target layer has been detected. For example... Figure 10 The resistivity curve shows that the resistivity increases with decreasing frequency when the frequency is less than 100 Hz, which reflects that the low-resistivity bauxite strata of the Benxi Formation have entered the high-resistivity limestone strata of the Ordovician. The analyzed and collected parameters meet the requirements of the exploration task.

[0171] Furthermore, a crucial issue in artificial source frequency domain electromagnetic sounding is determining the optimal transmission and reception distance to achieve the desired depth. Early CSAMT exploration considered a transmission-reception distance of at least four times the depth to be suitable. However, with technological advancements, a skin depth (13 times the depth) of at least nine times the transmission-reception distance is now required to meet far-field conditions. In practical applications, to balance far-field conditions and a high signal-to-noise ratio, a transmission-reception distance of 6–8 times the depth is commonly used. This is because frequency domain electromagnetic sounding involves three zones: the far-field, transition zone, and near-field. The electromagnetic wave field in the far-field is a plane wave, and depth sounding is achieved by changing the frequency. The electromagnetic wave in the transition zone lies between a plane wave and a spherical wave, and depth sounding can also be achieved by changing the frequency; the advantage of wide-area electromagnetic methods lies in utilizing the transition zone information of the artificial source. The electromagnetic wave field in the near-field is a spherical wave, and changing the frequency has no depth sounding effect; the depth sounding is determined by the spatial relationship (geometric dimensions) of the transmitting and receiving devices, and the apparent resistivity is actually the apparent resistivity of the DC method.

[0172] In practical applications, CSAMT exploration uses a 45° rise in the Carnia apparent resistivity-frequency curve on a double logarithmic coordinate system to determine if depth sounding has entered the near-field zone. By studying the apparent resistivity curve of the AB-E device, it was found that as the frequency decreases, the apparent resistivity tends to a fixed value. Further decreases in frequency do not change the apparent resistivity significantly, indicating entry into the near-field zone. In this zone, the apparent resistivity is the DC resistivity of the corresponding device, making frequency-based depth sounding no longer feasible. Figure 11This is a combined graph of the transmit / receive distance to skin depth ratio and apparent resistivity depth measurement curves for the AB-Ex and AB-Ey device methods. The graph shows that if the near-field region is defined as a transmit / receive distance less than 4 times the skin depth (i.e., frequencies less than 9 Hz), the apparent resistivity of the above four device methods is still increasing, and frequency depth measurement can still be performed. The graph shows that the apparent resistivity of the AB-Ey device method only tends to a fixed value when the transmit / receive distance is less than 1.3 times the skin depth (frequency less than 4 Hz), and changing the frequency further prevents frequency electromagnetic depth measurement. However, the apparent resistivity of the AB-Ex device method continues to change.

[0173] Electromagnetic sounding is used to detect depth. The skin depth is estimated by multiples, and the DC electrical resistivity tomography exploration depth is estimated using the distance between AB-MN. Based on the above analysis, it is believed that the maximum exploration depth of the AB-E device's frequency sounding should be the maximum exploration depth of the device's DC electrical resistivity tomography.

[0174] It should also be noted that electromagnetic sounding is performed by measuring the horizontal electric field in any direction. However, since the apparent resistivity of the horizontal electric field in different directions is bifurcated at the low-frequency asymptotic end (the values ​​are somewhat different), although it does not affect the detection of normal target layers, the horizontal electric field in the same direction should be measured as much as possible in the same exploration area, or the MN direction should not change too much.

[0175] In summary, the proposed embodiment provides a frequency domain electromagnetic sounding method. This method can transmit and receive electromagnetic wave field signals of multiple frequencies simultaneously. The acquisition area of ​​electromagnetic field data is not limited to the "far-field" of traditional controlled-source audio-frequency magnetotellurics and "frequency sounding," thus expanding the applicability of frequency domain electromagnetic sounding. The apparent resistivity calculation does not use the Carnia apparent resistivity formula of controlled-source audio-frequency magnetotellurics, nor the simplified "far-field" apparent resistivity formula of "frequency sounding." Instead, it adopts the full-period apparent resistivity formula of a single electric or magnetic field component, forming a new frequency sounding method. This greatly expands the observation range of artificial source electromagnetic methods and improves observation speed, accuracy, and field efficiency.

[0176] Based on the same inventive concept, embodiments of this application also provide a frequency domain electromagnetic depth sounding system, such as... Figure 12 The diagram shown is a structural schematic of a frequency domain electromagnetic depth sounding system provided in this application. The system includes:

[0177] The calculation module 301 is used to calculate the electric field and magnetic field in the cylindrical coordinate system of the uniform earth surface based on the electric dipole of the uniform earth surface.

[0178] The conversion module 302 is used to perform conversion operations on the electric field and magnetic field in the cylindrical coordinate system to the Cartesian coordinate system to obtain the electromagnetic field in the Cartesian coordinate system.

[0179] The processing module 303 is used to calculate the apparent resistivity of the horizontal electric field in any direction during the entire period of frequency domain electromagnetic sounding based on the electromagnetic field in the Cartesian coordinate system; and to perform frequency domain electromagnetic sounding based on the apparent resistivity during the entire period.

[0180] Based on the same inventive concept, this application also provides an electronic device that can realize the functions of the aforementioned frequency domain electromagnetic depth sounding system. (Refer to...) Figure 13 The electronic device includes:

[0181] At least one processor 401 and a memory 402 connected to at least one processor 401. In this embodiment, the specific connection medium between the processor 401 and the memory 402 is not limited. Figure 13 The example shown is the connection between processor 401 and memory 402 via bus 400. Bus 400 is... Figure 13 The connections between other components are indicated by thick lines and are for illustrative purposes only, not as limiting information. The 400 bus can be divided into address bus, data bus, control bus, etc., for ease of representation. Figure 13 The term is represented by a single thick line, but this does not imply that there is only one bus or one type of bus. Alternatively, processor 401 can also be called a controller; there is no restriction on the name.

[0182] In this embodiment, memory 402 stores instructions executable by at least one processor 401. By executing the instructions stored in memory 402, at least one processor 401 can perform the frequency-domain electromagnetic depth sounding method described above. Processor 401 can implement... Figure 12 The system shown illustrates the functions of each module.

[0183] The processor 401 is the control center of the device. It can connect to various parts of the control device through various interfaces and lines. By running or executing instructions stored in memory 402 and calling data stored in memory 402, the processor can perform various functions and process data, thereby monitoring the device as a whole.

[0184] In one possible design, processor 401 may include one or more processing units. Processor 401 may integrate an application processor and a modem processor, wherein the application processor mainly handles the operating system, user interface, and applications, and the modem processor mainly handles wireless communication. It is understood that the modem processor may also not be integrated into processor 401. In some embodiments, processor 401 and memory 402 may be implemented on the same chip; in some embodiments, they may also be implemented separately on separate chips.

[0185] Processor 401 can be a general-purpose processor, such as a central processing unit (CPU), digital signal processor, application-specific integrated circuit, field-programmable gate array or other programmable logic device, discrete gate or transistor logic device, or discrete hardware component, capable of implementing or executing the methods, steps, and logic block diagrams disclosed in the embodiments of this application. The general-purpose processor can be a microprocessor or any conventional processor. The steps of the frequency domain electromagnetic depth sounding method disclosed in the embodiments of this application can be directly manifested as being executed by a hardware processor, or executed by a combination of hardware and software modules within the processor.

[0186] Memory 402, as a non-volatile computer-readable storage medium, can be used to store non-volatile software programs, non-volatile computer-executable programs, and modules. Memory 402 may include at least one type of storage medium, such as flash memory, hard disk, multimedia card, card-type memory, random access memory (RAM), static random access memory (SRAM), programmable read-only memory (PROM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), magnetic storage, magnetic disk, optical disk, etc. Memory 402 can be any other medium capable of carrying or storing desired program code in the form of instructions or data structures that can be accessed by a computer, but is not limited thereto. In the embodiments of this application, memory 402 can also be a circuit or any other device capable of implementing storage functions for storing program instructions and / or data.

[0187] By designing and programming the processor 401, the code corresponding to the frequency domain electromagnetic depth sounding method described in the foregoing embodiments can be embedded into the chip, thereby enabling the chip to execute the code during operation. Figure 1 The steps of the frequency domain electromagnetic depth sounding method shown in the embodiment are described below. How to design and program the processor 401 is a technique well-known to those skilled in the art and will not be elaborated upon here.

[0188] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0189] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0190] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0191] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0192] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A frequency domain electromagnetic sounding method, characterized in that, The method comprises: Based on the uniform earth surface electric dipole, the electric field and the magnetic field in the uniform earth surface cylindrical coordinate system are calculated; The electric field and the magnetic field in the cylindrical coordinate system are converted and calculated in the Cartesian coordinate system to obtain the electromagnetic field in the Cartesian coordinate system; According to the electromagnetic field in the Cartesian coordinate system, the full-time apparent resistivity of the horizontal electric field in any direction of the frequency domain electromagnetic sounding is calculated; Based on the full-time apparent resistivity, the frequency domain electromagnetic sounding is carried out; The calculation of the full-time apparent resistivity comprises: Obtaining the horizontal electric field in the direction of the angle between any point and the electric dipole moment; According to the electromagnetic field in the Cartesian coordinate system, the apparent resistivity of the frequency or electromagnetic depth is calculated; Based on the horizontal electric field in the direction of the angle between any point and the electric dipole moment and the apparent resistivity, the apparent resistivity of the electric field in any direction is calculated; Iterative calculation of the apparent resistivity of the electric field in any direction obtains the full-time apparent resistivity; The apparent resistivity of the electric field in any direction is calculated by the following formula: wherein, apparent resistivity representing the electric field in any direction, MN Ex, Ey are electrodes; when in the far zone condition of |kr| > 1, the horizontal electric field in any direction and its vertical direction horizontal magnetic field at any point satisfy the Cagniard resistivity condition.

2. The method of claim 1, wherein, Based on the uniform earth surface electric dipole, the electric field and the magnetic field in the uniform earth surface cylindrical coordinate system are calculated, comprising: Based on the uniform earth surface electric dipole, the dipole current is determined; According to the dipole current, the outer upper space vector potential and the outer lower space vector potential component of the uniform earth surface are calculated; The electric field and the magnetic field in the uniform earth surface cylindrical coordinate system are calculated through the outer upper space vector potential and the outer lower space vector potential.

3. The method of claim 2, wherein, The electric field in the cylindrical coordinate system is calculated by the following formula: Ez=0 The magnetic field in the cylindrical coordinate system is calculated by the following formula: wherein I 0 、I 1 、K 0 、K 1 Bessel function of imaginary argument.

4. The method of claim 1, wherein, The electromagnetic field in the Cartesian coordinate system is calculated by the following formula: wherein, characterizing the uniform half-space resistivity, is an implicit term for the uniform half-space resistivity.

5. The method of claim 1, wherein, The horizontal electric field in the direction of the angle between any point and the electric dipole moment is calculated by the following formula: wherein The uniform half-space resistivity is characterized by θ, the angle between the dipole moment and the arbitrary point.

6. The method of claim 1, wherein, The full-time apparent resistivity of the horizontal electric field in any direction is calculated by the following formula: wherein, Full-year apparent resistivity is characterized.

7. A frequency domain electromagnetic sounding system, characterized in that, The system comprises: A calculation module for calculating the electric field and the magnetic field in the uniform earth surface cylindrical coordinate system based on the uniform earth surface electric dipole; A conversion module for converting and calculating the electric field and the magnetic field in the cylindrical coordinate system in the Cartesian coordinate system to obtain the electromagnetic field in the Cartesian coordinate system; A processing module for calculating the full-time apparent resistivity of the horizontal electric field in any direction of the frequency domain electromagnetic sounding according to the electromagnetic field in the Cartesian coordinate system, and carrying out the frequency domain electromagnetic sounding based on the full-time apparent resistivity.

8. An electronic device, comprising: Comprise: A memory for storing a computer program; A processor for executing the computer program stored in the memory to realize the method steps of any one of claims 1-6.

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