Multi-scale electromagnetic exploration method based on single electrode potential detection

Abstract

The present invention discloses a multi-scale electromagnetic exploration method based on single-electrode potential detection, which relates to the field of exploration geophysical technology. The method includes: determining the measurement area, clarifying the exploration target, and determining the measurement area and measurement point density based on the depth of the exploration target; deploying a number of transmitting sources and receiving arrays in the measurement area to collect surface potential data of the measurement area in real time, and processing the data frequency by frequency according to a preset frequency sequence; generating a surface potential distribution surface based on the single-electrode potential data, constraining and suppressing the field source effect, obtaining electric field distribution information of the measurement surface, and calculating apparent resistivity parameters in combination with magnetic field measurement data; using a multi-directional excitation mode and a multi-source emission scheme to suppress the field source effect, and constructing a three-dimensional resistivity profile to identify low-resistance or high-resistance bodies. The present invention solves the static effect and volume effect, breaking through the limitations of existing electromagnetic instruments on detection accuracy and depth.

Description

Technical Field

[0001] The present invention relates to the field of exploration geophysical technology, and in particular to a multi-scale electromagnetic exploration method based on single-electrode potential detection. Background Art

[0002] Electromagnetic exploration uses the amplitude / phase characteristics (frequency domain) and attenuation characteristics (time domain) of ground electromagnetic signals to extract information on parameters such as resistivity, dispersion, polarizability, magnetic susceptibility, and dipole. This allows for intuitive geoelectrical signatures and, combined with forward and inversion techniques, allows for the detection of stratum structure. Therefore, observing the amplitude / phase and attenuation characteristics of electromagnetic signals is a key task for electromagnetic exploration instruments.

[0003] The current surface electric field detection method uses a mode of measuring the potential difference between the two electrodes of MN. The electric field observation scale is fixed. This surface electric field detection method not only requires a large amount of construction, but also cannot overcome the influence of the rock mass near the field source, the low surface resistance of the survey area, and the high resistance of the shallow layer.

[0004] Foreign detection methods are difficult to adapt to the complex geological conditions in my country. When a geological body of a certain size exists near the transmitting source or between the transmitter and receiver, the secondary field excited by this geological body acts as part of the total excitation field on the measurement area, forming a field source effect. When there are uneven areas on the surface of the measurement area (such as rivers and lakes), the induced charges around this uneven area form an induced electric field as part of the total measurement field, causing the measured electric field to shift and form a static effect. When a large-scale high-resistance body (such as granite) exists in the shallow part of the measurement area, this high-resistance body hinders the conduction of current, forming an electromagnetic energy reflection area, making it impossible to identify the deeper geological bodies, resulting in a volume effect.

[0005] my country's extremely complex geological conditions make electromagnetic exploration in the country almost inevitable. Existing electric field detection methods, which rely on a two-electrode potential difference, are unable to address these issues. There is an urgent need to develop a new detection method and corresponding new detection equipment to overcome the limitations of existing electromagnetic instruments on detection accuracy and depth. Summary of the Invention

[0006] The present invention proposes a multi-scale electromagnetic exploration method based on single-electrode potential detection, which overcomes the problems of field source effect, static effect and volume effect that cannot be overcome by existing detection instruments, and realizes fine scanning of strata from shallow to deep.

[0007] To achieve the above objectives, the present invention provides a multi-scale electromagnetic exploration method based on single-electrode potential detection, comprising:

[0008] Determine the survey area, clarify the exploration target, and determine the survey area and measurement point density based on the depth of the exploration target;

[0009] Arrange a number of transmitting sources and receiving arrays in the measurement area to collect surface potential data of the measurement area in real time, and process the data frequency by frequency according to a preset frequency sequence;

[0010] Based on the single-electrode potential data, the surface potential distribution surface is generated, the field source effect is constrained and suppressed, the electric field distribution information of the measurement surface is obtained, and the apparent resistivity parameters are calculated in combination with the magnetic field measurement data;

[0011] A multi-directional excitation mode and multi-source emission scheme are used to suppress the field source effect, and a three-dimensional resistivity profile is constructed to identify low-resistance or high-resistance bodies.

[0012] Preferably, the measurement area and the measurement point density need to cover the structural trend of the exploration target.

[0013] Preferably, a plurality of transmitting sources and receiving arrays are arranged in the measurement area, including:

[0014] The transmitting source is arranged at the edge of the measurement area, and the proportion of low-frequency signals is adjusted according to the exploration depth;

[0015] The receiving magnetic sensors are arranged in an orthogonal manner, the electric field is measured using a single-point potential, and the transmission time and reception time are synchronized through satellite or wireless modules.

[0016] Preferably, real-time acquisition of surface potential data of the measurement area includes:

[0017] Interpolation filtering is performed on the potentials of the receiving array measurement points to obtain the potential measurement surface. The curvature distribution characteristics of the potential measurement surface are obtained based on the degree of concavity of the potential measurement surface. The degree of influence of the surface or shallow part is analyzed based on the curvature distribution of the potential surface. According to the required detection depth, the density of the detection electrodes is adjusted to reduce the curvature distribution of the potential surface and complete the detection from shallow to deep.

[0018] Preferably, an interpolation algorithm is used to generate the surface potential distribution surface, and static effects and volume effects caused by shallow low-resistance or high-resistance bodies are eliminated by filtering;

[0019] The interpolation algorithm is Kriging interpolation or polynomial fitting interpolation, and the filtering method is spatial domain low-pass filtering or adaptive threshold filtering.

[0020] Preferably, constraining and suppressing the field source effect includes:

[0021] By placing sparse detection points between the transmitting source and the receiving array, or adopting a multi-directional excitation mode, the field source effect can be constrained and suppressed.

[0022] Preferably, the electric field distribution information of the measurement surface is obtained as follows:

[0023] E = σ·J;

[0024] Where E is the electric field, σ is the conductivity, and J is the current density.

[0025] Preferably, the apparent resistivity parameter is calculated as:

[0026]

[0027] Where ω represents the angular frequency, μ represents the magnetic permeability, and E x Indicates the electric field strength in the direction of the emission source, H y It represents the magnetic field strength perpendicular to the emission source direction, and ρ is the apparent resistivity parameter.

[0028] Preferably, the method further comprises:

[0029] By comparing resistivity anomalies with known geological information through the resistivity distribution interface, lithologic boundaries, fault zones or hydrothermal channels can be delineated, and the scale and economic value of the target body can be assessed.

[0030] Compared with the prior art, the present invention has the following advantages and technical effects:

[0031] (1) The present invention adopts a multi-directional multi-source excitation mode to solve the influence of field source effects, completes multi-scale surface electric field measurement based on single-electrode potential detection, solves static effects and volume effects, and breaks through the limitations of existing electromagnetic instruments on detection accuracy and depth; the single-electrode potential receiving station automatically obtains the longitude and latitude of the measuring point through the satellite module, without the need for manual point positioning;

[0032] (2) The present invention includes information on a single source excitation mode and a multi-source multi-directional excitation mode through multi-directional excitation and single-electrode potential measurement, can complete geometric sounding and induction sounding functions, can perform electromagnetic exploration in the time domain and frequency domain, and realize multi-scale electromagnetic field detection on the surface, thus solving the drawbacks of traditional electromagnetic methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0034] Figure 1 A schematic diagram of a conventional electromagnetic detection mode according to an embodiment of the present invention;

[0035] Figure 2 Schematic diagram of the static effect mechanism of an embodiment of the present invention;

[0036] Figure 3 Schematic diagram of the volume effect mechanism of an embodiment of the present invention;

[0037] Figure 4Schematic diagram of the suppression mechanism of the shallow low-resistance static effect according to an embodiment of the present invention;

[0038] Figure 5 Schematic diagram of the suppression mechanism of the volume effect of shallow high-resistance body according to an embodiment of the present invention;

[0039] Figure 6 This is a diagram showing the impact of a shallow geological body according to an embodiment of the present invention;

[0040] Figure 7 A schematic diagram of a field construction method according to an embodiment of the present invention;

[0041] Figure 8 Schematic diagram of the construction mode of the present invention according to an embodiment of the present invention. DETAILED DESCRIPTION

[0042] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0043] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0044] Traditional electromagnetic exploration methods such as Figure 1 As shown. The transmitter transmits current into the ground through electrodes AB (about 1 km apart). As an excitation, a receiver array is arranged on a survey line parallel to AB 5 km away from the transmitter. The receiver measures the potential difference of the electrodes through MN. Since the potential difference of the MN electrodes is the integral of the electric field between MN, it is calculated using formula (1):

[0045]

[0046] Where M and N represent the position coordinates of the two electrodes along the measuring line, E represents the electric field strength between MN, and V MN represents the electric potential between MN, and dl is the line integral variable.

[0047] For the sake of convenience in engineering, the electric field between MNs is considered to be uniform, so the detection is completed using formula (2):

[0048]

[0049] Where V N and V M Represent the electric potentials at points N and M, respectively, |MN| represents the distance between the electrodes at point M and N, and E MN Indicates the electric field strength in the MN direction.

[0050] At the same time, the magnetic field information is measured, and different detection information is extracted according to different parameter definitions. For example, the apparent resistivity parameter is extracted using formula (3):

[0051]

[0052] Where ω represents the angular frequency, μ represents the magnetic permeability, and E x Indicates the electric field strength in the direction of the emission source; H y It represents the magnetic field strength perpendicular to the emission source direction, and ρ is the apparent resistivity parameter.

[0053] Therefore, the electromagnetic detection capability depends on the measurement accuracy of the surface electric and magnetic fields. When there is an interference source near the measurement site, the interference source is superimposed on the surface background field, causing errors in the actual measured electromagnetic field and failing to accurately reflect the underground information. For example, if there are inhomogeneous bodies such as rivers and lakes near the measurement site, induced charges will be generated around them due to the influence of the background field, forming an induced electric field as part of the total measurement field, causing the measured electric field to shift by a certain amplitude from low frequency to high frequency. The mechanism is as follows: Figure 2 shown.

[0054] For example, in shallow underground areas, there are large-scale high-resistance bodies (such as granite bodies), which hinder the conduction of current and "squeeze" the current to the surface. Figure 3 shown.

[0055] Since the magnitude of the electric field E is related to the current density J and the conductivity σ, as shown in formula (4):

[0056] E = σ·J(4);

[0057] Therefore, shallow underground high-resistance bodies will raise the overall electric field on the surface by a certain amplitude, thus affecting the detection of deep geological bodies.

[0058] There are large areas of low-resistance areas on the surface (such as lakes, rivers, etc.). Traditional dual electrodes need to stretch a line across the area to conduct detection. The actual construction is extremely difficult or even impossible to complete. This embodiment overcomes the influence of shallow low-resistance bodies on detection construction by measuring the potential of a single electrode. It is only necessary to place a receiving station in an area at a certain distance around the low-resistance area on the surface without pulling electrode lines. In addition, by increasing the detection scale of the electrode, the influence area of ​​the shallow geological body is bypassed, the detection of deep structures is completed, and the influence of the static effect of shallow low resistance is overcome. Figure 4 As shown, in the low-resistance area, the surface electric field is distorted due to the influence of induced charges and returns to normal after leaving the low-resistance area for a certain distance. This embodiment can directly cross the area where the electric field is distorted and use the interpolation method to "smooth" the affected area within the crossing area to obtain reliable detection data.

[0059] When there is a high-resistance rock mass in the shallow underground, the high-resistance rock mass blocks the flow of current, causing the current to be "squeezed" to the surface, forming a strong electric field. The current returns to normal after leaving the shallow high-resistance area for a certain distance. In this embodiment, a large number of single-electrode receiving stations can be placed on the surface to "outline" the distribution of the surface potential by analyzing the data, such as Figure 5 As shown in the figure, the distance between the electrodes is gradually increased based on the required depth of detection, crossing areas where the electric field is distorted. Interpolation is then used to "smooth" the affected area within the crossing area to obtain reliable detection data. By increasing the detection scale of the electrodes, the influence area of ​​shallow underground high-resistance bodies is bypassed, and detailed detection of the stratum structure from shallow to deep is completed.

[0060] The multi-scale electromagnetic exploration method based on single-electrode potential detection provided in this embodiment includes:

[0061] Determine the survey area, clarify the exploration target, and determine the survey area and measurement point density based on the depth of the exploration target;

[0062] Several transmitting sources and receiving arrays are deployed in the measurement area to collect the surface potential data of the measurement area in real time, and process the data frequency by frequency according to the preset frequency sequence;

[0063] Based on the single-electrode potential data, the surface potential distribution surface is generated, the field source effect is constrained and suppressed, the electric field distribution information of the measurement surface is obtained, and the apparent resistivity parameters are calculated in combination with the magnetic field measurement data;

[0064] A multi-directional excitation mode and multi-source emission scheme are used to suppress the field source effect, construct a three-dimensional resistivity profile, and identify low-resistance or high-resistance bodies.

[0065] The specific implementation steps are as follows:

[0066] Step 1: Data Collection and Target Location. Collect data on the survey area's geology, geophysics, topography, and electromagnetic interference sources (e.g., high-voltage lines, substations). Define the exploration target (e.g., fault location, ore body depth). Based on the target depth (e.g., 1-3 km), determine the survey area and measurement point density (100-200 m / point). The survey area and measurement points must cover the structural direction.

[0067] During actual field construction, electrodes can be placed at any suitable location. There are no strict requirements for electrode placement except avoiding water areas. Each electrode is equipped with a receiving station, which records the location information of the point through a satellite module and collects the surface potential of the point in real time. The site information is sent to the collection host through wireless / wired transmission mode, such as Figure 7 shown.

[0068] Step 2: Layout of the transmitter and receiving array. The transmitter (dipole source) is placed at the edge of the survey area, away from interference sources, and the ground resistance must be less than 20Ω (the resistance can be reduced by connecting multiple electrodes in parallel or treating with brine). The transmission frequency range is usually 0.1Hz-10kHz, the current intensity is 50-100A, and the proportion of low-frequency signals is adjusted according to the exploration depth (low frequency penetrates deeper). The receiving magnetic sensor adopts an orthogonal layout (Hx, Hy, Hz), the electric field is measured using a single-point potential, the electrode is buried 20-30cm deep to reduce ground noise, and the magnetic probe must be away from metal interference. Ensure synchronization of transmission and reception time through satellite or wireless modules.

[0069] Step 3: Data collection: Data is collected point by point according to a preset frequency sequence (eg, 10 frequency points / decade). In this embodiment, the number of superpositions of a single frequency point is ≥ 3 to improve the signal-to-noise ratio.

[0070] Step 4: Data processing and interpretation. Eliminate bad point data, change the electrode density data through single-electrode surface potential detection, interpolate and filter the external potential of the surface measurement point, and correct the terrain effects (such as the static effects caused by valleys / ridges / lakes / rivers) and high-resistance layer shielding (shallow high-resistance volume effects) based on multi-scale electric field measurement. By placing sparse detection points between the transmitter and receiver, or using a multi-directional excitation mode, the field source effect is constrained and suppressed. The electric field distribution information of the measurement surface is obtained through formula (4), and the apparent resistivity is calculated using formula (3), or other different detection information is extracted according to different parameter definitions.

[0071] Step 5: Invert the resistivity profile and optimize the model by incorporating geological constraints (such as drillhole data). For complex structures, finite element or integral equation methods are used to construct a three-dimensional resistivity structure to identify low-resistivity bodies (mineralized zones) or high-resistivity bodies (bedrock).

[0072] Step 6: Comprehensive geological interpretation. Compare resistivity anomalies with known geological information to delineate lithologic boundaries, fault zones, or hydrothermal channels, and assess the target volume and economic value.

[0073] Specifically, the resistivity distribution interface (line) between the resistivity anomaly and the background resistivity is verified by the interface (line) of the resistivity distribution. This interface is then verified with the interface (line) of the large fault or stratigraphic structure in the known geological section. Furthermore, it can identify small faults or stratigraphic structure interfaces (lines) not found in the geological section, thus achieving detailed detection of underground structures. Simply put, the large structure is used to verify the correctness of the resistivity anomaly detection, and then more detailed, smaller-scale lithologic boundaries, fault zones, or hydrothermal channels can be identified.

[0074] Compared with the traditional MN two-electrode potential difference detection, which requires a very long electrode line to complete this task, the single-electrode potential detection does not require a long line. As long as the distance is appropriate, the degree of influence can be intuitively seen through the potential surface. If the equipotential lines are too dense, it means that the near-surface influence is very large, and it is necessary to appropriately increase the observation scale and adjust to the appropriate equipotential line density. Figure 6 The superficial impact is shown to be greater.

[0075] When there is a low-resistance body on the surface, the surface electric field around the low-resistance body is distorted relative to the background field, and the equipotential lines formed are relatively dense, such as Figure 6 As shown by the dotted line in . After a certain distance from the low-resistance surface body, the surface electric field returns to normal. If the electric field is measured using the traditional fixed-scale MN electrode potential difference, the limited length of the electrode line cannot cross the electric field "contamination" area, so the picked-up electric field information is seriously affected by the low-resistance surface body. After adopting this technical solution, the surface potential is measured with a single electrode, without the need for electrode line extension. Electrodes 10, 11, 16, 17, 22, and 23 are ineffective electrodes. Crossing the electric field "contamination" area, the potential measured by the remaining electrodes is used, through interpolation filtering, to obtain the calculated potential values ​​of electrodes 10, 11, 16, 17, 22, and 23, thus overcoming the influence of the low-resistance surface body.

[0076] This method uses a multi-directional, multi-source excitation model to address the influence of field source effects. Based on single-electrode potential detection, it performs multi-scale surface electric field measurements, addressing both static and volume effects, and overcoming the limitations of existing electromagnetic instruments on detection accuracy and depth. The single-electrode potential receiving station automatically acquires the longitude and latitude of the measurement point via a satellite module, eliminating the need for manual positioning.

[0077] Through multi-directional excitation and single electrode potential measurement, it includes information on single field source excitation mode and multi-field source multi-directional excitation mode, which can complete geometric sounding and induction sounding functions, and can perform time domain and frequency domain electromagnetic exploration, realize multi-scale electromagnetic field detection on the surface, and solve the shortcomings of traditional electromagnetic methods. Its construction mode is as follows Figure 8 shown.

[0078] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A multi-scale electromagnetic exploration method based on single-electrode potential detection, characterized in that: include: Determine the survey area, clarify the exploration target, and determine the survey area and measurement point density based on the depth of the exploration target; Arrange a number of transmitting sources and receiving arrays in the measurement area to collect the surface potential data of the measurement area in real time, and process the data frequency by frequency according to a preset frequency sequence; Based on the single-electrode potential data, the surface potential distribution surface is generated, the field source effect is constrained and suppressed, the electric field distribution information of the measurement surface is obtained, and the apparent resistivity parameters are calculated in combination with the magnetic field measurement data; A multi-directional excitation mode and multi-source emission scheme are used to suppress the field source effect, construct a three-dimensional resistivity profile, and identify low-resistance or high-resistance bodies.

2. The multi-scale electromagnetic exploration method based on single electrode potential detection according to claim 1, characterized in that: The survey area and the density of the survey points must cover the structural trend of the exploration target.

3. The multi-scale electromagnetic exploration method based on single electrode potential detection according to claim 1, characterized in that: Several transmitting sources and receiving arrays are arranged in the measurement area, including: The transmitting source is arranged at the edge of the measurement area, and the proportion of low-frequency signals is adjusted according to the exploration depth; The receiving magnetic sensors are arranged in an orthogonal manner, the electric field is measured using a single-point potential, and the transmission time and reception time are synchronized through satellite or wireless modules.

4. The multi-scale electromagnetic exploration method based on single electrode potential detection according to claim 1, characterized in that: Real-time collection of surface potential data of the measurement area, including: Interpolation filtering is performed on the potentials of the receiving array measurement points to obtain the potential measurement surface. The curvature distribution characteristics of the potential measurement surface are obtained based on the degree of concavity of the potential measurement surface. The degree of influence of the surface or shallow part is analyzed based on the curvature distribution of the potential surface. According to the required detection depth, the density of the detection electrodes is adjusted to reduce the curvature distribution of the potential surface and complete the detection from shallow to deep.

5. The multi-scale electromagnetic exploration method based on single electrode potential detection according to claim 1, characterized in that: An interpolation algorithm is used to generate the surface potential distribution surface, and static effects and volume effects caused by shallow low-resistance or high-resistance bodies are eliminated by filtering; The interpolation algorithm is Kriging interpolation or polynomial fitting interpolation, and the filtering method is spatial domain low-pass filtering or adaptive threshold filtering.

6. The multi-scale electromagnetic exploration method based on single electrode potential detection according to claim 1, characterized in that: The field source effect is constrained and suppressed, including: By placing sparse detection points between the transmitting source and the receiving array, or adopting a multi-directional excitation mode, the field source effect can be constrained and suppressed.

7. The multi-scale electromagnetic exploration method based on single electrode potential detection according to claim 6, characterized in that: The electric field distribution information of the measurement surface is obtained as follows: E = σ·J; Where E is the electric field, σ is the conductivity, and J is the current density.

8. The multi-scale electromagnetic exploration method based on single electrode potential detection according to claim 1, characterized in that: The apparent resistivity parameter is calculated as: Where ω represents the angular frequency, μ represents the magnetic permeability, and E x Indicates the electric field strength in the direction of the emission source, H y It represents the magnetic field strength perpendicular to the emission source direction, and ρ is the apparent resistivity parameter.

9. The multi-scale electromagnetic exploration method based on single electrode potential detection according to claim 1, characterized in that: The method further comprises: By comparing resistivity anomalies with known geological information through the resistivity distribution interface, lithologic boundaries, fault zones or hydrothermal channels can be delineated, and the scale and economic value of the target body can be assessed.

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