CN115128679A - Frequency domain electromagnetic sounding method and system and electronic equipment - Google Patents
Frequency domain electromagnetic sounding method and system and electronic equipment Download PDFInfo
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- CN115128679A CN115128679A CN202210617459.0A CN202210617459A CN115128679A CN 115128679 A CN115128679 A CN 115128679A CN 202210617459 A CN202210617459 A CN 202210617459A CN 115128679 A CN115128679 A CN 115128679A
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- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
- G01V3/082—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices operating with fields produced by spontaneous potentials, e.g. electrochemical or produced by telluric currents
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
- G01V3/088—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices operating with electric fields
Abstract
The application discloses a frequency domain electromagnetic sounding method, a frequency domain electromagnetic sounding system and electronic equipment, electromagnetic wave field signals of multiple frequencies can be transmitted and received at one time through the method, the acquisition area of electromagnetic field data is not limited to a remote area of a traditional controllable source audio frequency geoelectromagnetic method and a frequency sounding method, the application range of frequency domain electromagnetic sounding is expanded, a new frequency sounding method is formed by adopting a full-term apparent resistivity formula of a single electric field or magnetic field component, the observation range of an artificial source electromagnetic method is greatly expanded, and the observation speed, the observation precision and the field efficiency are improved.
Description
Technical Field
The present disclosure relates to the field of electronic technologies, and in particular, to a method and a system for frequency domain electromagnetic sounding, and an electronic device.
Background
Currently, electromagnetic sounding can be divided into natural and artificial field sourcesTwo types of common natural field source electromagnetic sounding methods are called a magnetotelluric sounding method and an audio magnetotelluric sounding method, and the artificial field source electromagnetic sounding method can be divided into a frequency domain electromagnetic sounding method (frequency sounding method for short) and a time domain electromagnetic sounding method, and a field source of the frequency sounding method can be an electric source (an earth electrode supplies power to provide an artificial field source) or a magnetic source (an ungrounded wire frame provides an artificial field source). The frequency sounding research of the electric source is considered to be that the horizontal Y component of the uniform half-space earth surface electric field is generated when the ground couple source AB emits
It does not contain frequency-dependent quantities, and therefore cannot be used for electromagnetic sounding, but only for direct current electrical methods (depth measurement in geometric dimensions).
The mode is based on that the thermocouple source AB emits an artificial field source, and the electric field component Ex of the parallel AB or the electric field component Ey of the vertical AB is measured in a certain range far away from the AB. However, in practical construction projects, the MN electrodes for collecting Ex and Ey are difficult to arrange due to the limitation of surface water bodies such as rivers and ponds and various civil buildings, and more complete data needs to be collected, or the field workload is increased to reduce the production efficiency, or the completeness of data is sacrificed by abandoning points.
Disclosure of Invention
The application provides a frequency domain electromagnetic sounding method, a frequency domain electromagnetic sounding system and electronic equipment, which are used for expanding the observation range of a manual source electromagnetic method and improving the observation speed, the observation precision and the field efficiency.
In a first aspect, the present application provides a frequency domain electromagnetic sounding method, including:
calculating to obtain an electric field and a magnetic field under a cylindrical coordinate system of the uniform earth surface based on the uniform earth surface electric dipole;
carrying out conversion operation on the electric field and the magnetic field in the cylindrical coordinate system in a Cartesian coordinate system to obtain an electromagnetic field in the Cartesian coordinate system;
calculating the full-term 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 performing frequency domain electromagnetic sounding based on the full-term apparent resistivity.
In one possible design, the calculating of the electric field and the magnetic field in the cylindrical coordinate system of the uniform earth surface based on the uniform earth surface electric dipole comprises:
determining a dipole current based on the uniform earth surface electric dipole;
according to the dipole current, calculating to obtain the vector bit component of the outer upper space and the vector bit component of the outer lower space of the surface of the uniform earth;
and calculating to obtain the electric field and the magnetic field under the uniform earth surface cylindrical coordinate system according to the outer upper space vector position and the outer lower space vector position.
In one possible design, the electric field in the cylindrical coordinate system is calculated by the following formula:
E z ＝0
the magnetic field under the cylindrical coordinate system is calculated by the following formula:
wherein, in 0 、I 1 、K 0 、K 1 Bessel function of deficiencyAnd (4) counting.
In one possible design, the electromagnetic field in the cartesian coordinate system is calculated by the following formula:
wherein ρ represents a uniform half-space resistivity,
an implicit term for uniform half-space resistivity.
In one possible design, the method for calculating the full-term 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 comprises the following steps:
acquiring a horizontal electric field in the direction of an included angle between any point and the electric dipole moment;
calculating the apparent resistivity of frequency or electromagnetic depth according to the electromagnetic field in the Cartesian coordinate system;
calculating to obtain the apparent resistivity of the electric field in any direction based on the horizontal electric field and the apparent resistivity of the electric field in any point and the included angle direction of the electric dipole moment;
and (4) iteratively calculating the apparent resistivity of the electric field in any direction to obtain the full-period apparent resistivity.
In one possible design, the horizontal electric field in the direction of the included angle between any point and the electric dipole moment is calculated by the following formula:
wherein rho represents uniform half-space resistivity, and theta is an included angle between any one point and the electric dipole moment.
In one possible design, the apparent resistivity of the electric field in any direction is calculated by the following formula:
where ρ is a And (3) characterizing the apparent resistivity of an electric field in any direction, wherein MN is an electrode of Ex and Ey.
In one possible design, the full apparent resistivity of the horizontal electric field in any direction is calculated by the following formula:
wherein the content of the first and second substances,
the full-term apparent resistivity is characterized.
In a second aspect, the present application provides a frequency domain electromagnetic sounding system, the system comprising:
the calculation module is used for calculating and obtaining an electric field and a magnetic field under a cylindrical coordinate system of the uniform earth surface based on the uniform earth surface electric dipole;
the conversion module is used for carrying out conversion operation on the electric field and the magnetic field under the cylindrical coordinate system under a Cartesian coordinate system to obtain an electromagnetic field under the Cartesian coordinate system;
the processing module is used for calculating the full-term 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 performing frequency domain electromagnetic sounding based on the full-term apparent resistivity.
In a second aspect, the present application provides an electronic device comprising:
a memory for storing a computer program;
and the processor is used for realizing the steps of the frequency domain electromagnetic sounding method when executing the computer program stored in the memory.
For each of the second to fourth aspects and possible technical effects of each aspect, please refer to the above description of the first aspect or the possible technical effects of each of the possible solutions in the first aspect, and no repeated description is given here.
Drawings
Fig. 1 is a flowchart of a frequency domain electromagnetic sounding method provided in the present application;
FIG. 2 is a schematic view of a coordinate system in a uniform earth surface as provided herein;
FIG. 3 is a schematic diagram of fast Hankel transform coefficients provided in the present application
FIG. 4 is a graph showing the comparison of apparent resistivities of two G-shaped sections provided herein;
FIG. 5 is a schematic diagram showing the comparison of apparent resistivities of two D-shaped sections provided in the present application;
FIG. 6 is a schematic diagram showing the comparison of apparent resistivities of three H-shaped sections provided in the present application;
FIG. 7 is a schematic diagram showing the comparison of apparent resistivities of three layers of K-type sections provided herein;
FIG. 8 is a schematic comparison of apparent resistivities of a multi-layer cross-section provided herein;
FIG. 9 is a schematic view of the current horizontal electric field characteristics provided herein;
FIG. 10 is a schematic diagram of the contour lines of the horizontal electric field plane in the horizontal and vertical directions provided by the present application;
FIG. 11 is E provided for the present application y A fast apparent resistivity curve diagram;
FIG. 12 is a schematic structural diagram of a frequency domain electromagnetic sounding system provided in the present application;
fig. 13 is a schematic structural diagram of an electronic device provided in the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more clear, the present application will be further described in detail with reference to the accompanying drawings. The particular methods of operation in the method embodiments may also be applied to apparatus embodiments or system embodiments. It should be noted that "a plurality" is understood as "at least two" in the description of the present application. "and/or" describes the association relationship of the associated objects, meaning that there may be three relationships, e.g., a and/or B, which may mean: a exists alone, A and B exist simultaneously, and B exists alone. A is connected with B and can represent: a and B are directly connected and A and B are connected through C. In the description of the present application, the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or order.
The embodiments of the present application will be described in detail below with reference to the accompanying drawings.
The electromagnetic sounding can be divided into a natural field source and an artificial field source, a common natural field source electromagnetic sounding method is called a magnetotelluric sounding method and an audio magnetotelluric sounding method, and an artificial field source electromagnetic sounding method can be divided into a frequency domain electromagnetic sounding method (frequency sounding method for short) and a time domain electromagnetic sounding method, wherein the field source of the frequency sounding method can be an electric source (the grounding electrode supplies power to provide the artificial field source) or a magnetic source (a non-grounding wire frame provides the artificial field source). The frequency sounding research of the electric source is considered to be that the horizontal Y component of the uniform half-space earth surface electric field is generated when the ground couple source AB emits
It does not contain frequency-dependent quantities, and therefore cannot be used for electromagnetic sounding, but only for direct current electrical methods (depth measurement in geometric dimensions). The research of ' frequency domain electromagnetic sounding method technology research based on AB-Ey mode ' of science and technology project of China coal geological institute geophysical exploration research institute 2020 ' considers that although an expression is irrelevant to frequency, the conductivity sigma is a quantity sigma (f) relevant to frequency, and the research of numerical calculation and field practice simultaneously shows that the AB-Ey (E-Ey) working device has the function of frequency sounding.
The above studies are based on a galvanic source AB emitting an artificial field source, measuring the electric field component Ex of the parallel AB or the electric field component Ey of the perpendicular AB over a certain range remote from the AB. However, in practical construction projects, the MN electrodes for collecting Ex and Ey are difficult to arrange due to the limitation of surface water bodies such as rivers and ponds and various civil buildings, and more complete data needs to be collected, or the field workload is increased to reduce the production efficiency, or the completeness of data is sacrificed by abandoning points. The frequency sounding method for studying the horizontal electric field E (E-E device) in any direction becomes a technical basis for solving the above-mentioned difficulties.
Based on the above problems, the present application provides a frequency domain electromagnetic sounding method, which provides a method for measuring horizontal electric field in any direction of power supply to perform frequency sounding. The corresponding calculation process of the full-term apparent resistivity is realized through forward calculation programs of transmitting by the ground galvanic couple source AB and receiving the horizontal electric field E in any direction on the ground. The apparent resistivity sounding curve of a horizontal electric field E (including Ex and Ey directions) in any direction is analyzed and compared, and the AB-E working system can carry out frequency domain electromagnetic sounding.
In addition, the method can enlarge the acquisition range of the sounding data of the electromagnetic frequency of the same field source, improve the field production efficiency and save the field construction cost. Meanwhile, when Ex and Ey are measured by fixing the direction of the MN electrode, if the MN electrode is consistent with the directions of electromagnetic interference sources such as a high-voltage wire, a power wire and an optical fiber, the generated electromagnetic interference is large, and a mode that the direction of the MN electrode is vertical to the direction of the interference source can be selected to collect data, so that the electromagnetic interference is inhibited.
Fig. 1 shows a flowchart of a frequency domain electromagnetic sounding method provided by the present application, where the method includes:
s1, calculating to obtain an electric field and a magnetic field under a cylindrical coordinate system of the uniform earth surface based on the uniform earth surface electric dipole;
s2, performing conversion operation on the electric field and the magnetic field in the cylindrical coordinate system in a Cartesian coordinate system to obtain an electromagnetic field in the Cartesian coordinate system;
s3, calculating the full-term 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;
s4, performing frequency domain electromagnetic sounding based on the full-term apparent resistivity.
Specifically, the frequency domain electromagnetic sounding method uses 2 ground electrodes A, B to supply power to the ground, and measures a pair of electric field and magnetic field components in a relatively far region. Since the distance between AB is much smaller than the distance between AB and MN (transmit-receive distance), the power supply A, B field source can be regarded as an electric dipole, and therefore the electromagnetic field generated by an electric dipole of a uniform earth surface is first explained here.
FIG. 2 is a schematic representation of a Cartesian coordinate system with a uniform large earth surface established by electric dipoles with electric dipole moments along the x-axis. Assuming the dipole current is a sine wave:
E＝E 0 e -iwt H＝H 0 e -iwt (3-1)
maxwell's equations for the steady field are:
where E and H are both complex functions describing the field, the vector bit A of the electric dipole can be defined as follows:
the combination formulas 3-1 and 3-2 are as follows:
in the formula k 2 I σ μ ω, which is the square of the wave number. The vector bit a is 0 in the Y direction, i.e. the vector bit a can be written as:
A＝(A X ,0,A Z ) (3-6)
through derivation calculation, X, Z components of upper and lower half space vector bits a outside the uniform earth surface (z ═ 0) can be obtained:
in the formula
J 0 、J 1 Are 0 th order and 1 st order bessel functions, respectively. The electric field expression under the cylindrical coordinate system of the uniform ground surface can be obtained through the operations of (3-4) and (3-7):
the magnetic field expression under the cylindrical coordinate system of the uniform earth surface is as follows:
in the formula I 0 、I 1 、K 0 、K 1 Bessel function which is a virtual quantity.
The above (3-8), (3-9) are expressions of the electromagnetic field of the uniform earth surface in a cylindrical coordinate system, and they are converted in a cartesian coordinate system by applying the following formula:
obtaining:
due to the implicit term of uniform half-space resistivity rho contained in the electric field Ex
E-ExThe Ex expression is rewritten in the wide-area electromagnetic sounding as:
using Δ V MN ＝E x MN, forming an apparent resistivity iterative solution formula:
the formula (3-13) is defined similarly to the DC-method resistivity, but includes F ex The apparent resistivity implication of (ikr) requires iterative determination of the full apparent resistivity. (3-12) formula Medium electric field E y Proportional to the uniform half-space earth resistivity ρ, E-E is easily derived y Apparent resistivity expression for frequency or electromagnetic sounding:
equations (3-14) are similar to the DC-TV resistivity equation, with the preceding terms being the device coefficients. For a horizontal electric field with an included angle theta between any point and the X axis (electric dipole moment), the horizontal electric field is as follows:
like Ex, order
The above formula is rewritten as:
the apparent resistivity of the electric field E in any direction is obtained as follows:
and the expression (3-15) is an expression for iteratively calculating the full-term apparent resistivity of the horizontal electric field in any direction.
In the controllable source audio frequency magnetotelluric sounding (CSAMT) theory, under the remote zone condition that kr is greater than 1, E x /H y And E y /H x As with magnetotelluric sounding, the ratio is only related to frequency, resistivity, and not to transmission and reception distances, and the corresponding apparent resistivity is also called kania resistivity, and the expression is:
for a horizontal electric field E-E in the direction where an angle theta is formed between any point and the X axis (electric dipole moment) x cosθ+E y sin θ, vertical horizontal magnetic field H thereof + ＝-H x sinθ+H y cos θ, also has a similar apparent resistivity expression:
that is, at the far zone position emitted by the current source, the horizontal electric field in any direction of any point and the horizontal magnetic field in the vertical direction thereof all satisfy the Carniian resistivity condition, and can be independent of the E in the controllable source audio magnetotelluric sounding (CSAMT) x /H y And E y /H x 。
Further, resistivity ρ that prevents a flow of a parallel interlayer interface current l And resistivity p preventing current flow perpendicular to the interface n Is different, the anisotropy coefficient of a layer is defined as
This value is always greater than 1, Table 1 being for certain rocksTypical values.
| Rock | λ | ρ n /ρ l |
| Layered mudstone | 1.02-1.05 | 1.04-1.10 |
| Shale sandstone interbed | 1.05-1.15 | 1.10-1.32 |
| Layered sandstone | 1.10-1.29 | 1.20-1.65 |
| Plate-shaped shale | 1.10-1.59 | 1.20-2.50 |
| Coal measure strata | 1.73-2.55 | 3.00-6.50 |
| Anthracite coal | 2.00-2.55 | 4.00-6.50 |
| Interbed of graphite slate and carbonaceous rock | 2.00-2.75 | 4.00-7.50 |
TABLE 1
Deriving the resistivity p from the layers n And resistivity p in the layer l The method starts with the difference of (1) to obtain the recursion relation between interfaces, and finally obtains the electric field expression of the horizontal layered large ground surface electric dipole:
magnetic field expression of horizontal layered large ground surface electric dipole:
where ρ is the resistivity ρ in the layer l ，R * And R and other parameters are respectively:
the expression in the cylindrical coordinate system is used for solving the E in the Cartesian coordinate system by using the expression (3-10) as well as the uniform earth surface electromagnetic field x 、E y 、H x 、H y And then respectively calculating the modes of the horizontal electric field and the magnetic field in any direction and the ratio of the horizontal electric field and the magnetic field.
Furthermore, the electromagnetic field expressions of the horizontal layered large surface electric dipoles are all integrals of the Bessel function in the (0, ∞) interval, the integrals are actually Hankel transformation expressions, and the electromagnetic field numerical calculation of the layered large surface electric dipoles and the magnetic dipoles is generally realized by fast Hankel transformation. The principle steps of the fast hankel transform forward computation are briefly described here.
The electromagnetic fields of the layered earth surface electric dipole and the magnetic dipole can be uniformly written as follows:
in the formula J n Is a first Bessel function of n orders, the real number n is more than-1, and a transformation formula is introduced:
wherein mu and v are new variables in the fast Hankel transformation, and the interval is (- ∞, ∞); r is a radical of hydrogen 0 Is a selected constant. Introducing a new function:
F(μ)＝f(λ) λG(ν)＝g(r)r
the formula (3-21) is rewritten as:
that is, G is functions F and H n Convolution of (2), here H n (μ)＝J n (μ)e μ . Its discrete form is:
from equations (3-23), the actual numerical calculation of the above discrete-form expression can be written as:
in the formula
Called fast Hankel transformThe filter coefficients can be obtained by fourier transform or by a number of public sources.
Referring to the fast hankerr transform coefficient shown in fig. 3, the hankerr coefficients have different lengths as required, and the calculation results are slightly different, several groups of hankerr coefficients published in the public are tested in the research process and compared with the coefficients obtained by the programmed fourier transform calculation, and the calculation results are not much different, and the relative change is less than 0.01%, and can be ignored. FIG. 3 is a graph of 0-order and 1-order Hankel transform coefficients between-100 and 150, which are obtained by Fourier transform calculation, and it can be seen that when n is greater than 0, the oscillation attenuation of the coefficients is reduced along with the increase of n, so that the Hankel coefficient range is generally asymmetrically intercepted.
Further, in the embodiment of the present application, the wide-area electromagnetic method is used as a frequency domain electromagnetic prospecting method, the artificial field source can be an electrical source or a magnetic source, and the combination of transmission and reception is various, and an AB-Ex (also referred to as E-Ex) method is commonly used at present. And comparing the full-term apparent resistivity curves defined by the horizontal electric fields in different directions through model calculation. The specific analysis results are as follows:
1. g-shaped section
Model parameters of the G-type section: the transmitting field source is located at A (-500, 0), B (500, 0), the receiving point is located at (2480, 4300), the shallow resistivity is 50 ohm meter, the thickness is 200 meter, and the substrate resistivity is 500 ohm meter. FIG. 4 is a graph of resistivity over time for a horizontal electric field in the X direction (AB-Ex), the Y direction (AB-Ey), the X axis at 30 degrees to the X axis, and the X axis at 60 degrees, at frequencies above 100Hz, with 4 curves substantially coincident; the frequency is 100-10Hz, the 4 curves are forked, but the change trends are consistent; the frequency is less than 10HZ, the apparent resistivity of the electric field in the AB-Ey and 60-degree directions tends to a fixed value, and the apparent resistivity of the electric field in the AB-Ex and 30-degree directions is still slowly increased; after the frequency is less than 1Hz, the apparent resistivity of the electric fields in 4 directions tends to a fixed value, namely 511 ohm-meter, 357 ohm-meter, 279 ohm-meter and 337 ohm-meter, which are also the apparent resistivity of the direct current method. The full-term apparent resistivity curves defined by the 4 directional electric fields all reflect the change characteristics of the formation resistivity, namely, all can detect the high-resistance substrate under 200 metersAnd (3) a layer. Depth of investigation by skin depth
It is estimated that the rms relative error of the full term apparent resistivity defined by the electric fields in 4 directions at depths less than 300m is less than 5% (as shown in table 2), and the rms error of the full term apparent resistivity at all frequencies at depths less than 1000m (at frequencies greater than 24Hz) is 9.60%.
TABLE 2
2. D-shaped section
D-type section model parameters: the transmitting field sources are located at A (-500, 0), B (500, 0), the receiving points are located at (2480, 4300), the shallow resistivity is 500 ohm-meters, the thickness is 200 meters, and the substrate resistivity is 50 ohm-meters. Fig. 5 is a full-term apparent resistivity curve defined by 4-direction horizontal electric fields, the 4 curves are basically overlapped, the final apparent resistivity tends to a fixed value of 50 ohm-meter, and the relative difference between the full-term apparent resistivity in all frequencies in 4 directions and the total pitch direction is 2.72%. Indicating that they can all detect the low resistance substrate and have the same frequency depth measurement function.
3. Three-layer H-shaped section
H-shaped section model parameters: the transmitting field source is positioned at A (-500, 0) and B (500, 0), the receiving point is positioned at (2480, 4300), the resistivities of the three layers from shallow to deep are respectively 100, 10 and 200 ohm.m, the thickness of the cover layer is 200 m, and the thickness of the middle layer is 50 m. FIG. 6 is a full-term apparent resistivity curve defined by 4 directional horizontal electric fields, the frequency is higher than 50Hz, 4 curves are basically overlapped, and the apparent resistivity curve form is consistent with a D-shaped section; within the frequency of 50-7Hz, 4 curves have differentiation phenomena, which are shown that the full-term apparent resistivity of a horizontal electric field in the direction of 60 degrees of the x axis has a false minimum value, the subsequent change trends are consistent, and the full-term apparent resistivity of the 4 curves is increased along with the reduction of the frequency; the frequency is less than 7HZ, the full-term apparent resistivities of AB-Ey and AB-Ex60 begin to tend to a fixed value, and the full-term apparent resistivities of AB-Ex and AB-Ex30 still slowly increase; finally, apparent resistivities of horizontal electric fields in 4 directions tend to fixed values, namely 208.3 ohm-meter, 161.6 ohm-meter, 138.0 ohm-meter and 155.7 ohm-meter. The 4 modes reflect the change characteristics of the formation resistivity of the H-shaped section, namely, the high-resistance layer (substrate) at the lower part of 250 meters can be detected by 4 directional horizontal electric fields.
4. Three-layer K-shaped section
Parameters of the K-shaped section model: the transmitting field source is positioned at A (-500, 0) and B (500, 0), the receiving point is positioned at (2480, 4300), the resistivities of the three layers from shallow to deep are respectively 50, 500 and 50 ohm.m, the thickness of the cover layer is 200 m, and the thickness of the middle layer is 100 m. FIG. 6 is a graph of the full term apparent resistivity defined by 4 directional horizontal electric fields at frequencies above 10Hz with the two curves substantially coincident; the apparent resistivity of the 10 Hz-0.1 Hz section is changed in a cross way, the frequency is lower than 0.1Hz, 4 curves tend to a fixed value which is respectively 45.8 ohm/meter, 55.4 ohm/meter, 60.2 ohm/meter and 56.6 ohm/meter, and the apparent resistivity corresponds to the direct current electrical apparent resistivity of the device. The 4 modes reflect the change characteristics of the formation resistivity from shallow to deep and low to high and low, that is, the 4-direction horizontal electric fields can detect the low-resistance substrate at the lower part of 300 meters. Numerically, the probe depth 848m was within 2% of the total rms relative difference of 5.66% for the shallow (greater than 10Hz frequency) 4 directions apparent resistivity (as shown in table 3).
TABLE 3
From the above 4 typical earth sections 4-direction horizontal electric field full-term resistivity curve comparative analysis, the following recognition can be obtained:
1. in the high frequency band, apparent resistivity sounding curves of horizontal electric fields (4 devices) in 4 directions are basically overlapped.
2. In the medium frequency range, the apparent resistivity sounding curves of 4 device modes have a bifurcation phenomenon, but the change rules are consistent, and the formation electrical property change characteristics are reflected.
3. In the low frequency band, when the frequency is lower than a specific frequency, the full-term resistivity curve tends to a certain fixed value, but the starting frequencies of the full-term resistivity defined by horizontal electric fields in different directions are different, and the AB-Ex device mode tends to the lowest starting frequency of the fixed value. From this point of analysis, because the frequency is low to a certain extent, the skin depth is compared with the transceiving distance, the skin depth is already close to the transceiving distance, even is greater than the transceiving distance, the function of depth measurement is not generated when the frequency is changed, and the apparent resistivity fixed value is the direct current method apparent resistivity of the device.
In addition, the D-type section and the K-type section are low-resistance substrates, the low-frequency band apparent resistivity curves of the 4 device modes of the K-type section (figure 6) are branched (inconsistent), and the D-type section (figure 4) is basically consistent. In general, the total root mean square relative error of the visual resistivity of the horizontal electric fields in 4 directions of the D-type and K-type sections (low-resistance substrates) is smaller than that of the G-type and H-type sections (high-resistance substrates).
5. Section of multi-layer model
The above analysis is based on a two-layer and three-layer geoelectric model, and electrical stratification (shown in table 4) is performed below according to a resistivity logging curve of a certain mine of coal from Shanxi Jin, a horizontal laminar geoelectric model is established, and forward modeling of 4 devices such as AB-Ex, AB-Ex30, AB-Ex60 and AB-Ey is performed to calculate the full-term apparent resistivity.
| Depth (Rice) | Thickness (Rice) | Resistivity (ohm, meter) | Formation of earth |
| 60 | 60 | 18 | Box group for newly-born kingdom and stone |
| 172 | 112 | 50 | Go up stone box group |
| 220 | 48 | 91 | Stone feeding box group |
| 262 | 42 | 36 | Stone feeding box group |
| 326 | 64 | 93 | Stone-discharging box group |
| 346 | 20 | 56 | Stone-discharging box group |
| 416 | 70 | 152 | Shanxi group and Taiyuan group |
| 516 | 100 | 180 | Taiyuan group |
| 536 | 20 | 20 | Taiyuan group and |
| 1000 | Ordovician series |
TABLE 4
The spatial position of the transmitting field source and the receiving point MN is kept unchanged, the transmitting-receiving distance is 4.9km, and the included angle between the electric dipole AB and the OMN (O is the midpoint of the AB) is 60 degrees. FIG. 7 is an apparent resistivity curve obtained by calculation, wherein 4 types of apparent resistivity curves are basically overlapped when the frequency is higher than 100Hz, the resistivity curve is branched between 100Hz and 10Hz, and 4 curves in a low frequency band tend to be a fixed value. As with the layered model above, the apparent resistivity changes in the 4-direction horizontal electric field all reflect the formation electrical characteristics.
The technical solution of the present application is further described below by specific application scenarios.
In the frequency domain electromagnetic depth measurement method provided by the application, the X, Y component of a horizontal electric field and apparent resistivity obtained by measuring components 30 and 60 degrees with an X axis can reflect the electrical property change of the stratum by using a current source of AB emission, and the frequency depth measurement can be carried out. Except for the restrictions of the terrain and the interference conditions, the formation resistivity of 50 ohm meters, the AB length of 1000m and the frequency of 6Hz can be selected for calculation, and FIG. 8 is a contour map of the total electric field size and direction angle, and it can be seen in FIG. 8 that electric field signals with enough strength can be measured when the electric field measurement direction is selected.
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 described by using fig. 9, and different measurement directions are selected in different sections according to the measurement range with larger values. Equally, the contour lines of the horizontal electric field at the angle directions of 15, 30, 45, 60 and 75 degrees of measurement can be calculated, and the corresponding measurement ranges are selected.
Further, CSAMT apparent resistivity of frequency domain electromagnetic sounding method
The apparent resistivity of the AB-E device mode of the frequency electromagnetic sounding method is deduced in the front
F e (ikr) is a function containing a multiplicity index, and the computation of the apparent resistivity can only be done by iterative methods, with the initial value of the iteration affecting the speed of the computation. As a special case, AB-E y Apparent resistivity of device frequency domain electromagnetic sounding method
Simple expression relation, apparent resistivity and E y I is in direct proportion, apparent resistivity can be rapidly obtained in the field, and even U is utilized MN And judging whether the electromagnetic sounding detects the target layer to be detected or not by the I curve.
Fig. 10 is a plot of current normalized MN potential difference versus apparent resistivity in the measured Y direction for a coal mine, and it can be seen in fig. 10 that 2 curves are parallel in logarithmic coordinates. The apparent resistivity curve can be indirectly analyzed by analyzing the potential difference curve, and whether a target layer is detected or not can be judged according to the known electrical condition of the exploration area. As shown in fig. 10, when the frequency of the resistivity curve is less than 100HZ, the resistivity increases along with the reduction of the frequency, which reflects that the low-resistance bauxite rock stratum of the benxi group enters the high-resistance limestone rock stratum of the Ordovician system, and the analysis and acquisition parameters meet the requirements of exploration tasks.
Further, one of the problems that the artificial source frequency domain electromagnetic sounding cannot be avoided is that the target sounding depth can be achieved when the transmitting and receiving distances are large or small, the maximum sounding depth with the transmitting and receiving distance of more than 4 times is considered to be appropriate in the CSAMT sounding in the early stage, and with the development of technical application, the skin depth (13 times of the sounding depth) with the transmitting and receiving distance of more than 9 times can meet the far-zone condition only at present. In practical application, in order to balance far-zone conditions and high signal-to-noise ratio, the receiving-transmitting distance generally adopts 6-8 times of exploration depth. The method is characterized in that the distance zone, the transition zone and the near zone of an electromagnetic field source manually established in frequency domain electromagnetic exploration are 3 sub-zones, an electromagnetic wave field of the distance zone is a plane wave, and depth measurement is achieved by changing the frequency; the electromagnetic wave of the transition region is between the plane wave and the spherical wave, the depth measurement can be carried out by changing the frequency, and the advancement of the wide-area electromagnetic method is to utilize the transition region information of the artificial field source; the electromagnetic wave field in the near region is spherical wave, the change frequency has no depth sounding function, the depth sounding is determined by the space position relation (geometric dimension) of the transmitting-receiving device, and the apparent resistivity is actually the apparent resistivity of the direct current electrical method.
In practical application, CSAMT exploration judges that the sounding enters a near field region through 45-degree rising of a Carniian apparent resistivity-frequency curve under a double logarithmic coordinate. By researching the apparent resistivity curve of the AB-E device mode, the apparent resistivity tends to a certain fixed value along with the reduction of the frequency, the apparent resistivity is basically not changed when the frequency is reduced, namely, the apparent resistivity enters a near field region, the apparent resistivity is the direct current method apparent resistivity of a corresponding device, and the frequency depth measurement cannot be carried out. Fig. 11 is a comprehensive graph of the transceiving distance-skin depth ratio and the apparent resistance depth measurement curve of the AB-Ex and AB-Ey device modes, and it can be seen that if the near field region is defined according to the skin depth range with the transceiving distance being less than 4 times, that is, the frequency is less than 9HZ, and the apparent resistivity of the 4 device modes for frequency depth measurement is still in the rise period, and the frequency depth measurement can also be performed. The graph shows that the apparent resistivity of the AB-Ey device mode tends to a fixed value when the receiving and transmitting distance is less than 1.3 times of the skin depth (the frequency is less than 4HZ), the frequency is changed again, the frequency electromagnetic depth measurement cannot be carried out, but the apparent resistivity of the AB-Ex device mode is changed.
For detecting depth in electromagnetic sounding exploration
The skin depth is estimated, the DC electrical prospecting depth is estimated by the distance between AB and MN, and the maximum prospecting depth of the AB-E device frequency sounding is considered to be the maximum prospecting depth of the device DC electrical method.
In addition, electromagnetic depth measurement is performed by measuring horizontal electric fields in any direction, but since the full-term apparent resistivity defined by the horizontal electric fields in different directions has a bifurcation phenomenon (a certain difference in numerical value) at the low-frequency asymptotic end, although the detection of a normal target layer is not affected, the same horizontal electric field in the same direction is measured in the same exploration area as much as possible, or the direction of MN is not changed too much.
In summary, the embodiments of the present application provide a frequency domain electromagnetic sounding method, by which electromagnetic field signals of multiple frequencies can be transmitted and received at one time, the acquisition region of electromagnetic field data is not limited to the "far region" of the traditional controllable source audio frequency magnetotelluric method and the "frequency sounding method", the application range of frequency domain electromagnetic sounding is extended, the apparent resistivity calculation neither follows the kania apparent resistivity formula of the controllable source audio frequency magnetotelluric method nor the "far region" apparent resistivity formula simplified by the "frequency sounding method", but adopts the full-term apparent resistivity formula of a single electric field or magnetic field component, a new frequency sounding method is formed, the observation range of the artificial source electromagnetic method is greatly expanded, and the observation speed, the observation precision and the field efficiency are improved.
Based on the same inventive concept, an embodiment of the present application further provides a frequency domain electromagnetic sounding system, as shown in fig. 12, which is a schematic structural diagram of the frequency domain electromagnetic sounding system provided by the present application, and the system includes:
the calculation module 301 is configured to calculate an electric field and a magnetic field in a cylindrical coordinate system of the uniform earth surface based on the uniform earth surface electric dipole;
a conversion module 302, configured to perform conversion operation on the electric field and the magnetic field in the cylindrical coordinate system in a cartesian coordinate system to obtain an electromagnetic field in the cartesian coordinate system;
the processing module 303 is configured to calculate a full-term apparent resistivity of a horizontal electric field in any direction of the frequency domain electromagnetic sounding according to the electromagnetic field in the cartesian coordinate system; and performing frequency domain electromagnetic sounding based on the full-term apparent resistivity.
Based on the same inventive concept, an embodiment of the present application further provides an electronic device, where the electronic device can implement the function of the foregoing frequency domain electromagnetic sounding system, and with reference to fig. 13, the electronic device includes:
at least one processor 401 and a memory 402 connected to the at least one processor 401, in this embodiment, a specific connection medium between the processor 401 and the memory 402 is not limited in this application, and fig. 13 illustrates an example in which the processor 401 and the memory 402 are connected through a bus 400. The bus 400 is shown in fig. 13 by a thick line, and the connection between other components is merely illustrative and not limited thereto. The bus 400 may be divided into an address bus, a data bus, a control bus, etc., and is shown with only one thick line in fig. 13 for ease of illustration, but does not represent only one bus or one type of bus. Alternatively, processor 401 may also be referred to as a controller, and is not limited by name.
In the embodiment of the present application, the memory 402 stores instructions executable by the at least one processor 401, and the at least one processor 401 may execute the frequency domain electromagnetic sounding method discussed above by executing the instructions stored in the memory 402. The processor 401 may implement the functions of the various modules in the system shown in fig. 12.
The processor 401 is a control center of the apparatus, and may connect various parts of the entire control device by using various interfaces and lines, and perform various functions and process data of the apparatus by operating or executing instructions stored in the memory 402 and calling data stored in the memory 402, thereby performing overall monitoring of the apparatus.
In one possible design, processor 401 may include one or more processing units and processor 401 may integrate an application processor that handles primarily operating systems, user interfaces, application programs, and the like, and a modem processor that handles primarily wireless communications. It will be appreciated that the modem processor described above may not be integrated into the processor 401. In some embodiments, processor 401 and memory 402 may be implemented on the same chip, or in some embodiments, they may be implemented separately on separate chips.
The processor 401 may 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, discrete hardware components, or the like, that may implement or perform the methods, steps, and logic blocks disclosed in embodiments of the present application. A general purpose processor may be a microprocessor or any conventional processor or the like. The steps of the frequency domain electromagnetic sounding method disclosed in the embodiments of the present application may be directly implemented by a hardware processor, or implemented by a combination of hardware and software modules in the processor.
By programming the processor 401, the code corresponding to the frequency domain electromagnetic sounding method described in the foregoing embodiment may be solidified into a chip, so that the chip can execute the steps of the frequency domain electromagnetic sounding method of the embodiment shown in fig. 1 when running. How to program the processor 401 is well known to those skilled in the art and will not be described in detail herein.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may 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, and so forth) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may 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, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present application without departing from the spirit and scope of the application. Thus, if such modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is intended to include such modifications and variations as well.
Claims (10)
1. A method of frequency domain electromagnetic sounding, the method comprising:
calculating to obtain an electric field and a magnetic field under a cylindrical coordinate system of the uniform earth surface based on the uniform earth surface electric dipole;
carrying out conversion operation on the electric field and the magnetic field in the cylindrical coordinate system in a Cartesian coordinate system to obtain an electromagnetic field in the Cartesian coordinate system;
calculating the full-term 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 performing frequency domain electromagnetic sounding based on the full-term apparent resistivity.
2. The method of claim 1, wherein the calculating the electric field and the magnetic field in the cylindrical coordinate system of the uniform earth surface based on the uniform earth surface electric dipoles comprises:
determining a dipole current based on the uniform earth surface electric dipole;
according to the dipole current, calculating to obtain the components of the outer upper space vector position and the outer lower space vector position of the uniform earth surface;
and calculating to obtain the electric field and the magnetic field under the uniform earth surface cylindrical coordinate system according to the outer upper space vector position and the outer lower space vector position.
3. The method of claim 2, wherein the electric field in the cylindrical coordinate system is calculated by the following formula:
E z ＝0
the magnetic field under the cylindrical coordinate system is calculated by the following formula:
wherein, in 0 、I 1 、K 0 、K 1 Bessel function which is a virtual quantity.
4. The method of claim 1, wherein the electromagnetic field in the cartesian coordinate system is calculated by the formula:
wherein ρ represents a uniform half-space resistivity,
an implicit term for uniform half-space resistivity.
5. The method of claim 1, wherein calculating the full-term apparent resistivity of the horizontal electric field in any direction for frequency domain electromagnetic sounding from the electromagnetic field in the cartesian coordinate system comprises:
acquiring a horizontal electric field in the direction of an included angle between any point and the electric dipole moment;
calculating the apparent resistivity of frequency or electromagnetic depth according to the electromagnetic field in the Cartesian coordinate system;
calculating to obtain apparent resistivity of the electric field in any direction based on the horizontal electric field and the apparent resistivity in the direction of the included angle between any point and the electric dipole moment;
and (4) iteratively calculating the apparent resistivity of the electric field in any direction to obtain the full-period apparent resistivity.
6. The method of claim 5, wherein the horizontal electric field in the direction of the included angle between any point and the electric dipole moment is calculated by the following formula:
wherein rho represents uniform half-space resistivity, and theta is an included angle between any one point and the electric dipole moment.
7. The method of claim 5, wherein the apparent resistivity of the electric field in any direction is calculated by the formula:
where ρ is a And (3) characterizing the apparent resistivity of an electric field in any direction, wherein MN is an electrode of Ex and Ey.
8. The method of claim 5, wherein the full apparent resistivity of the horizontal electric field in any direction is calculated by the formula:
wherein the content of the first and second substances,
the full-term apparent resistivity is characterized.
9. A frequency domain electromagnetic sounding system, the system comprising:
the calculation module is used for calculating and obtaining an electric field and a magnetic field under a cylindrical coordinate system of the uniform earth surface based on the uniform earth surface electric dipole;
the conversion module is used for carrying out conversion operation on the electric field and the magnetic field under the cylindrical coordinate system under a Cartesian coordinate system to obtain an electromagnetic field under the Cartesian coordinate system;
the processing module is used for calculating the full-term 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 performing frequency domain electromagnetic sounding based on the full-term apparent resistivity.
10. An electronic device, comprising:
a memory for storing a computer program;
a processor for implementing the method steps of any one of claims 1-8 when executing the computer program stored on the memory.
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| CN117473272B (en) * | 2023-12-26 | 2024-03-15 | 齐鲁工业大学(山东省科学院) | Object position identification method, system, equipment and medium based on magnetic field data |
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