Geological exploration method and device based on ultra-near-source electromagnetism

Abstract

The invention provides a geological exploration method and device based on ultra-near-source electromagnetism, and relates to the technical field of geological exploration, and the method comprises the steps: obtaining a landform feature vector XL of a to-be-explored region; obtaining the similarity eta1 between the XL and the first preset landform feature vector XL1 and the similarity eta2 between the XL and the second preset landform feature vector XL2; if eta 1 is greater than eta 2, geological exploration is carried out on the to-be-explored area by using a preset line source device; if eta 1 is smaller than eta 2, geological exploration is conducted on the to-be-explored area through a preset loop source device; if eta 1 is equal to eta 2, performing geological exploration on the to-be-explored area by using a preset line source device or a return line source device; according to the invention, comprehensive improvement of geological exploration in adaptability, efficiency and accuracy can be realized.

Description

Technical Field

[0001] The present invention relates to the field of geological exploration technology, and in particular to a geological exploration method and equipment based on ultra-near-source electromagnetics. Background Art

[0002] As a basic work in the fields of resource development and engineering construction, geological exploration requires the acquisition of underground geological information. Existing electromagnetic exploration methods such as controlled source electromagnetic method, wide-area electromagnetic method, time-frequency electromagnetic method, etc. have many problems: First, the measurement parameters are single. For example, controlled source electromagnetic method and wide-area electromagnetic method can only measure resistivity, which makes it difficult to comprehensively judge the occurrence status of geological bodies. For example, it is impossible to effectively distinguish low-resistance ore bodies from non-ore low-resistance bodies, and it is difficult to directly identify laterally inhomogeneous geological bodies. Secondary exploration is required, which is inefficient. Second, there is no breakthrough in the measurement of key parameters. "Time-frequency electromagnetic method" has failed to achieve engineering measurement of polarizability at different frequencies, and lacks the "eddy current electromagnetic method". Third, it is difficult to balance exploration efficiency and adaptability. Traditional line-source methods are greatly affected by ground resistance, and the voltage needs to be increased in high-resistance formations, which increases equipment difficulty and safety risks. Traditional loop devices have high requirements for terrain and are difficult to deploy in complex terrain. In addition, most methods require parameter measurements in batches, which takes a long time and is labor-intensive. Fourth, the signal-to-noise ratio and exploration depth are insufficient. Conventional methods have weak signals in the near-source area, poor signal-to-noise ratio, fuzzy shallow information, and insufficient deep detection accuracy, which cannot meet the needs of deep resource exploration. Summary of the Invention

[0003] In view of the above technical problems, the technical solution adopted by the present invention is: According to a first aspect of the present application, a geological exploration method based on ultra-near source electromagnetics is provided, the method comprising the following steps: S100, obtaining a topographic feature vector XL of the area to be surveyed; the XL is obtained by obtaining the elevation, slope, slope direction, topographic relief, and surface roughness of the area to be surveyed; S200, obtaining a similarity η1 between a first preset topographic and geomorphic feature vector XL1 and a similarity η2 between a first preset topographic and geomorphic feature vector XL1 and a second preset topographic and geomorphic feature vector XL2; wherein XL1 corresponds to geological exploration using a preset line source device, and XL2 corresponds to geological exploration using a preset loop source device; S300, if η1>η2, use a preset line source device to perform geological survey on the area to be surveyed; S400, if η1 < η2, use a preset loop source device to perform geological survey on the area to be surveyed; S500: If η1=η2, a preset line source device or a loop source device is used to perform geological survey on the area to be surveyed.

[0004] Furthermore, the line source device includes a power supply, a first power supply wire and a second power supply wire; wherein, one end of the first power supply wire is connected to the power supply, and the other end is used for grounding; one end of the second power supply wire is connected to the power supply, and the other end is used for grounding.

[0005] Furthermore, step S300 includes the following steps: S310, in the area to be surveyed, supplying an AC signal of a preset frequency f and a preset waveform to a grounding point A of the first power supply wire and a grounding point B of the second power supply wire through the power supply, the first power supply wire, and the second power supply wire; S320, using a first measuring electrode M and a second measuring electrode N, sequentially measure each preset geological parameter of the preset point along the direction from A to B; wherein the straight line between M and N is parallel to the straight line between A and B; each preset measuring point is the midpoint between M and N.

[0006] Furthermore, if the alternating current is a sine wave, the preset geological parameters include: resistivity and ratio; if the alternating current is other preset non-sinusoidal waves, the preset geological parameters include: resistivity, polarizability, ratio and vortex rate; wherein, ratio B s =△U n / △U n-1 ; △U n is the observed value of the potential difference between MN at the nth preset point; △U n-1 is the observed value of the potential difference between MN at the n-1th preset point; the vortex rate W s =△U a / △U b ; △U a is the early secondary potential during the time period t0-t1 when the vortex electric field is generated, △U b is the primary potential.

[0007] Furthermore, the loop source device includes a power supply and a third wire; wherein both ends of the third wire are connected to the power supply to form a rectangular loop.

[0008] Furthermore, step S400 includes the following steps: S410, forming a rectangular loop in the area to be surveyed by the power supply and the third conductor; the power supply applies an AC signal of a preset frequency f and a preset waveform; the endpoints of the longitudinal sides of the rectangular loop are A and B and A' and B'; S420, using a first measuring electrode M and a second measuring electrode N, sequentially measure each preset geological parameter of a preset point along the direction from A to B or from A' to B'; wherein the straight line between M and N is parallel to the straight line between A and B; each preset measuring point is the midpoint between M and N.

[0009] Furthermore, the preset waveforms include: a triangle wave, a steamed bun wave and a positive sine wave; wherein the steamed bun wave is a wave in which all values ​​on the time axis are positive; and the positive sine wave is a sine wave with a minimum value of 0.

[0010] According to another aspect of the present application, there is also provided a device for the geological exploration method based on ultra-near source electromagnetics according to any one of the first aspects, the device comprising: a power transmission part and a measurement part; The power transmission part includes a signal generating circuit, a signal biasing circuit, a rectifier and filter circuit, an audio amplifier circuit, an output rectifier and filter circuit, a voltage stabilizing and limiting circuit, a current stabilizing and limiting circuit, a protection circuit and an auxiliary power supply circuit; the output power of the power transmission part is 0-100 kilowatts, the output voltage is 0-2 kilovolts, the output current is 0-50 amperes, the output frequency is 0.01-30,000 hertz, and the output waveform is a sine wave, a triangle wave or a steamed bun wave; The measuring part includes a data acquisition circuit, an overvoltage protection circuit, a current and voltage stabilization circuit, a computer control part, and a computer calculation and storage part; the measuring part is used to measure the primary field potential difference △U1 in the power supply time period and the secondary field potential difference △U2 in the power-off time period in the induced electromagnetic field, and calculate the resistivity, polarizability, ratio rate and vortex rate based on △U1 and △U2.

[0011] Furthermore, the power transmitting part can control the output parameters through manual control or programming, and the output parameters include power supply time, power off time, output power, output voltage, output current and output frequency; the power transmitting part has constant current and constant voltage characteristics and automatic power supply and automatic stop functions.

[0012] Furthermore, the measuring part is common to the line source device and the return line source device; in the power transmitting part, the power output voltage applicable to the line source device is higher than the power output voltage applicable to the return line source device, and the power applicable to the line source device can be used for the return line source device.

[0013] The present invention has at least the following beneficial effects: The geological exploration method based on ultra-near source electromagnetics of the present invention obtains the topographic and geomorphic feature vectors XL of the area to be explored, such as elevation, slope, slope direction, terrain undulation, and surface roughness, and compares the similarity with the topographic and geomorphic feature vectors XL1 and XL2 corresponding to the preset line source device and loop source device, thereby selecting an adapted exploration device. This method can specifically solve the problem of the difficulty in balancing exploration efficiency and adaptability in traditional exploration methods, avoid the power supply problem of the line source device in high-resistance strata due to the influence of ground resistance, and avoid the power supply problem of the traditional loop source device in complex terrain. At the same time, relying on the advantage of ultra-near source electromagnetic method itself in measuring multiple parameters such as resistivity, polarizability, ratio rate, vortex rate, etc., it solves the problem of single measurement parameters and no breakthrough in key parameter measurement of existing methods, reduces the need for secondary exploration, and reduces labor intensity; and combined with the characteristics of strong signal, high signal-to-noise ratio (several millivolts to several thousand millivolts) and the ability to correspond to different exploration depths through frequency under ultra-near source measurement, it improves the problems of insufficient signal-to-noise ratio and exploration depth of conventional methods, and finally realizes the comprehensive improvement of geological exploration in adaptability, efficiency and accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0015] Figure 1 A flow chart of a geological exploration method based on ultra-near source electromagnetics provided in an embodiment of the present invention; Figure 2 A schematic diagram of a line source device provided by an embodiment of the present invention; Figure 3 A schematic diagram of a loop source device provided in an embodiment of the present invention; Figure 4 A schematic diagram of a triangle wave provided by an embodiment of the present invention; Figure 5 A schematic diagram of a sine wave provided in an embodiment of the present invention; Figure 6 A schematic diagram of a steamed bun wave provided in an embodiment of the present invention; Figure 7 Schematic diagram of power supply and power off and primary and secondary fields provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0016] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making any creative efforts shall fall within the scope of protection of the present invention.

[0017] It should be noted that, based on this disclosure, those skilled in the art will appreciate that an aspect described herein can be implemented independently of any other aspect, and that two or more of these aspects can be combined in various ways. For example, any number of the aspects described herein can be used to implement an apparatus and / or practice a method. In addition, other structures and / or functionalities other than one or more of the aspects described herein can be used to implement such an apparatus and / or practice such a method.

[0018] The following will refer to Figure 1 The flowchart of the geological exploration method based on ultra-near source electromagnetics is shown, which introduces a geological exploration method based on ultra-near source electromagnetics.

[0019] The geological exploration method based on ultra-near source electromagnetics may include the following steps: S100, obtaining a topographical feature vector XL of the area to be surveyed; the XL is obtained by obtaining the elevation, slope, slope direction, topographic relief, and surface roughness of the area to be surveyed.

[0020] In this embodiment, a feature vector XL can be generated by collecting topographic information such as elevation, slope, aspect, terrain relief, and surface roughness of the area to be surveyed. These features directly reflect the complexity of the regional terrain. For example, areas with high terrain relief and surface roughness (such as mountainous areas and gully areas) are considered complex terrain, while areas with small elevation changes and gentle slopes (such as plains and gentle slopes) are considered simple terrain.

[0021] It provides an objective and quantitative terrain basis for subsequent device selection, avoiding the poor adaptability problem caused by "selecting devices based on experience" in traditional exploration (such as forcibly laying return line sources in mountainous areas, resulting in construction difficulties), reducing ineffective labor from the beginning of the process, and improving the efficiency of early preparations.

[0022] S200, obtaining the similarity η1 between the first preset topographic feature vector XL1 and the similarity η2 between the first preset topographic feature vector XL1 and the second preset topographic feature vector XL2; wherein XL1 corresponds to geological exploration using a preset line source device, and XL2 corresponds to geological exploration using a preset loop source device.

[0023] Furthermore, the line source device includes a power supply, a first power supply wire and a second power supply wire; wherein, one end of the first power supply wire is connected to the power supply, and the other end is used for grounding; one end of the second power supply wire is connected to the power supply, and the other end is used for grounding.

[0024] In this embodiment, the line source device is as follows Figure 2 As shown in the figure, a line source device supplies power underground from A and B, with a long power supply wire between A and B and the power supply equipment located between A and B. Alternating current with a frequency ranging from 0.01 to 30,000 Hz is supplied underground through A and B and the long wire between A and B, generating an induced electromagnetic field near the wire. By measuring the electric field signals of different frequencies in the induced electromagnetic field, geological information at different depths can be obtained. High frequencies reflect shallow geological information, while low frequencies reflect deep geological information.

[0025] According to the principle of the truncation, the truncation depth of each frequency is calculated as follows: ; Where δ is the skin depth, ω is the angular frequency, μ is the magnetic permeability, and σ is the electrical conductivity; ω=2πf; f is the frequency of the alternating current; the skin depth of each frequency is regarded as the exploration depth of each frequency.

[0026] The measuring electrode MN is parallel to the long wire at a distance of one to tens of meters and measures the induced electric field of various frequencies generated by the wire point by point. MN moves point by point along the AB direction, and the recording point is at the midpoint of MN.

[0027] Line source devices are simple to deploy, and can be laid out in straight lines or along curved paths or ditches, making them flexible and convenient to construct. However, the supply current is significantly affected by ground resistance. When ground resistance is high, the supply current is relatively low. To increase the supply current, the voltage must be increased, which not only increases the difficulty of equipment manufacturing but also results in a situation where high power is required but low current is required.

[0028] Furthermore, the loop source device includes a power supply and a third wire; wherein both ends of the third wire are connected to the power supply to form a rectangular loop.

[0029] like Figure 3As shown, a loop source device is a loop power supply consisting of one or more turns of wire, without the need to directly supply power to the ground. The loop device is rectangular, with long sides ranging from 100 to several thousand meters and short sides ranging from tens to hundreds of meters. The power supply equipment is located between the loops. The loop transmits an alternating electric field signal with a frequency ranging from 0.01 to 30,000 Hz, generating an induced electromagnetic field near the wire. By measuring the different frequency electric field signals in the induced electromagnetic field, geological information at different depths can be obtained. High frequencies reflect shallow geological information, while low frequencies reflect deeper geological information. Based on the tachist principle, the calculation method for the tachist depth at each frequency is similar to the skin depth calculation method for the line source device and is not detailed here.

[0030] The measuring electrode MN is positioned parallel to the conductor at a distance of one to several tens of meters from the long side, measuring the induced electric field of different frequencies generated by the conductor at each point. The measuring electrode MN can be moved point by point along the AB line or along the A'B' line.

[0031] The power supply current of the loop source device is not affected by the grounding resistance, and can supply low power and high current. Compared with the line source method, it reduces the difficulty of equipment manufacturing and can measure the profile along the two long sides. However, the construction difficulty is greater than that of the line source method, and the terrain must not be too complex.

[0032] Based on the characteristics of the above two devices, the line source device and the loop source device each adapt to different terrain and landform features. Therefore, several types of terrain and landform features can be divided into two types, one is complex terrain and the other is flat terrain. The corresponding feature vectors, namely XL1 and XL2, can be generated in advance, XL1 represents complex terrain and XL2 represents flat terrain.

[0033] XL1 and XL2 can be obtained in the following ways: Obtain a characteristic vector corresponding to each known complex terrain and a characteristic vector corresponding to each known flat terrain; calculate an average vector for the characteristic vectors corresponding to each known complex terrain and an average vector for the characteristic vectors corresponding to each known flat terrain; determine the average vector corresponding to the characteristic vectors corresponding to each complex terrain as XL1, and determine the average vector of the characteristic vectors corresponding to each known flat terrain as XL2.

[0034] By using quantitative similarity comparison, we replace the traditional subjective judgment of terrain compatibility, making device selection more scientific. For example, if the regional terrain is more similar to the XL1 (line source adaptation), it indicates that it is more suitable for line source devices. This can avoid deployment failures caused by incorrectly selecting a line source and reduce rework costs.

[0035] S300: If η1>η2, a preset line source device is used to perform geological survey on the area to be surveyed.

[0036] In this embodiment, if η1>η2, it means that the topographic and geomorphological characteristics of the area to be surveyed are relatively similar to those of the complex topographic and geomorphological characteristics, and the area to be surveyed belongs to complex terrain. Therefore, a line source device is selected to conduct geological survey of the area to be surveyed. The core of the line source device is "AB power supply point + long wire", which can be laid out in a straight line or curved along a path (such as along a road or ditch), without a strict rectangular layout, and can adapt to complex terrain.

[0037] Leveraging the flexible construction capabilities of line source systems, the difficulty of deploying return line sources in complex terrain can be avoided. For example, in mountainous areas or areas with ravines, line source conductors can be laid along existing paths, reducing the workload of terrain modification (such as land leveling) and lowering construction difficulty and labor intensity.

[0038] Furthermore, step S300 may include the following steps: S310 , in the area to be surveyed, supplying an AC signal of a preset frequency f and a preset waveform to a grounding point A of the first power supply wire and a grounding point B of the second power supply wire through the power supply, the first power supply wire, and the second power supply wire.

[0039] In the area to be surveyed, the power supply in the line source device, along with the first and second power conductors, supplies an AC signal with a preset frequency f (ranging from 0.01 to 30,000 Hz) and a preset waveform to the grounding points A and B of the two conductors, respectively. The core of this operation is to transmit AC power underground via the power conductors. Based on the principle of electromagnetic induction, AC power generates an induced electromagnetic field underground. Signals of different frequencies correspond to different exploration depths (high frequencies reflect shallow geological information, while low frequencies reflect deep geological information). Different waveforms (such as triangular waves, mantou waves, and sine waves) determine the type of geological parameters that can be measured. For example, sine waves can only measure resistivity and ratio, while other waveforms can measure resistivity, polarizability, ratio, and vortex ratio.

[0040] Through this step, signals of specific frequencies can be transmitted in a targeted manner to meet the requirements of different exploration depths, solving the problem that some traditional methods have limited exploration depth or cannot flexibly adjust the exploration depth.

[0041] By selecting an appropriate preset waveform, multi-parameter measurement can be achieved (such as when using waveforms such as triangular waves). Compared with methods such as controlled source electromagnetic method that can only observe resistivity, richer geological information can be obtained, laying the foundation for subsequent accurate judgment of geological conditions.

[0042] The power supply process is stable and controllable, which ensures the stable generation of the induced electromagnetic field, reduces the measurement error caused by unstable power supply, and improves the reliability of measurement.

[0043] S320, using a first measuring electrode M and a second measuring electrode N, sequentially measure each preset geological parameter of the preset point along the direction from A to B; wherein the straight line between M and N is parallel to the straight line between A and B; each preset measuring point is the midpoint between M and N.

[0044] Using a first measuring electrode M and a second measuring electrode N, measurements are taken at predetermined measurement points along the line from A to B, obtaining the predetermined geological parameters at each point. The line between M and N is parallel to the line between A and B, and each predetermined measurement point is set at the midpoint between M and N. This measurement method is based on the distribution characteristics of the induced electromagnetic field generated by the line source device. A direction parallel to the AB conductor can more accurately capture the electromagnetic field signal. Using the midpoint of MN as the recording point ensures the uniformity and standardization of measurement point locations, facilitating subsequent data comparison and analysis.

[0045] The measuring electrodes are measured along a specific direction (A to B direction) and at a standardized measuring point (MN midpoint), which ensures the consistency and comparability of the measurement data, avoids data deviation caused by confusion in the measurement position, and improves the reliability of the data.

[0046] When measuring with M and N parallel to the AB wires, the induced electromagnetic field signal can be received to the greatest extent, with high signal strength (usually a few millivolts to several thousand millivolts) and high signal-to-noise ratio. Compared with other similar methods with weak signals, the impact of external interference on the measurement results is reduced.

[0047] By measuring the preset points in sequence, the geological parameters of the area to be surveyed can be systematically obtained, which facilitates a comprehensive understanding of the regional geological conditions and improves the comprehensiveness and accuracy of the exploration.

[0048] Furthermore, if the alternating current is a sine wave, the preset geological parameters include: resistivity and ratio; if the alternating current is other preset non-sinusoidal waves, the preset geological parameters include: resistivity, polarizability, ratio and vortex rate; wherein, ratio B s =△U n / △U n-1 ; △U n is the observed value of the potential difference between MN at the nth preset point; △U n-1 is the observed value of the potential difference between MN at the n-1th preset point; the vortex rate W s =△U a / △U b ; △U a is the early secondary potential during the time period t0-t1 when the vortex electric field is generated, △U b is the primary potential.

[0049] In this embodiment, the sinusoidal AC current can only measure the resistivity ρ sand ratio B s This is because the sine wave is a symmetrical waveform, and it is difficult to stably capture the polarization effect and the attenuation signal of the eddy electric field after power failure, so the polarization rate and eddy rate cannot be obtained.

[0050] Non-sinusoidal AC (such as triangle wave, steamed bun wave, and sine wave): can measure resistivity ρ s , polarizability η s , ratio B s , vortex rate W s The non-sinusoidal wave is a unidirectional positive waveform that can form a stable primary field when powered. After power failure, the polarization effect and the attenuation signal of the eddy electric field are easier to identify, providing conditions for the measurement of polarization rate and eddy rate. Furthermore, the preset waveforms include: triangle wave, steamed bun wave and sine wave; wherein, the steamed bun wave is a wave whose values ​​on the time axis are all positive; the sine wave is a sine wave whose minimum value is 0. Figure 4 As shown, the sine wave is Figure 5 As shown, the steamed bun wave is as Figure 6 shown.

[0051] Schematic diagram of power supply and power outage and primary field and secondary field as shown below Figure 7 As shown, the calculation logic of the core parameters is: Ratio B s : The potential difference observation value of the same frequency between two adjacent points (point n and point n-1) (△U n and △U n-1 ) is calculated by the ratio (B s =△U n / △U n-1 ). When the normal geological body is laterally uniform, B s ≈1; when there are horizontally inhomogeneous bodies such as faults, inclined plate-shaped or lens-shaped low-resistance ore bodies, B s Anomalies greater than 1 or less than 1 will appear, thereby realizing the identification of lateral anomalies.

[0052] Vortex rate W s : Early secondary potential generated by the vortex electric field (△U a , within the time period t0-t1 after power failure, t0-t1≤50 milliseconds) and the primary field potential (△U b , the ratio of the early potential difference when powering on) is calculated (W s =△U a / △U b ). Low-resistance bodies such as metal ore bodies will generate strong eddy electric fields under the action of alternating electric fields. s The value is much larger than that of the surrounding rock, which is used to distinguish between mineral and non-mineral geological bodies.

[0053] Resistivity ρ s: It is calculated based on the ratio of the primary field potential difference to the current combined with the device coefficient to reflect the conductivity of the geological body; the primary field potential △U refers to the potential difference between the earlier MNs during the power supply period. It is the potential difference of the induced field generated by the conductor during the power supply time, rather than the potential difference generated by the power supply current at points AB. The potential difference generated by the power supply current at points AB is also called the primary field in the conduction electrical method. It is essentially different from the primary field described in this embodiment. This measurement regards it as interference, so MN is far away from AB. Generally, the distance between MN and AB is not less than 50 meters to prevent the current at the two power supply points AB from interfering with the measurement results.

[0054] Polarizability η s : Calculated based on the ratio of the secondary field potential to the primary field potential in the t1-t2 time period (t1-t2≤3000 milliseconds) after power failure, reflecting the polarization characteristics of the geological body (measurable under non-sinusoidal waves).

[0055] The above steps have at least the following beneficial effects: 1. Targeted and flexible parameter measurement: Select measurement parameters according to the AC type, simplify measurement under sine wave (only measure ρ s 、B s ), suitable for rapid preliminary survey; multi-parameter measurement under non-sinusoidal wave (ρ s ,η s 、B s 、W s ), which is suitable for detailed exploration, takes into account both efficiency and accuracy, and solves the problems of single parameters or fixed measurement processes in traditional methods.

[0056] 2. Accuracy of anomaly identification: unique parameter ratio B s and vortex rate W s It targets laterally inhomogeneous bodies and low-resistance ore bodies (ore and non-ore) respectively, filling the gap in special anomaly identification of traditional electromagnetic methods (such as controlled source electromagnetic method and wide-area electromagnetic method that can only measure resistivity), and reducing misjudgments caused by insufficient parameters (such as misjudging faults as ordinary rock formations and misjudging non-ore low-resistance bodies as ore bodies).

[0057] 3. Adaptability to device characteristics: Combined with the power supply characteristics of the line source device (which can be flexibly deployed), by matching parameters and waveforms, key geological information can still be efficiently obtained in complex terrain, avoiding the technical bottleneck of methods such as "time-frequency electromagnetic method" that cannot achieve polarizability measurement, and improving the practicality of field exploration.

[0058] S400: If η1 < η2, a preset loop source device is used to perform geological survey on the area to be surveyed.

[0059] In this embodiment, if η1<η2, it means that the topographic features of the area to be surveyed are relatively similar to those of the gentle topography, and the area to be surveyed belongs to the gentle terrain. Therefore, a loop source device is selected to conduct geological survey on the area to be surveyed; the loop source device is a "rectangular loop conductor" that does not need to be grounded, and the supply current is not affected by the grounding resistance (it can supply low power and high current), but the terrain must be gentle to ensure a rectangular layout.

[0060] Leveraging the stable power supply advantages of loop-source devices, the advantage of line-source devices in flat terrain is eliminated, as the problem of low current when ground resistance is high often occurs with line-source devices. For example, in plain areas, loop-source devices can transmit a strong, stable signal without increasing voltage to maintain current, reducing equipment load and improving signal strength (higher signal-to-noise ratio).

[0061] Furthermore, step S400 may include the following steps: S410, forming a rectangular loop in the area to be surveyed by the power supply and the third conductor; the power supply applies an AC signal of a preset frequency f and a preset waveform; the endpoints of the longitudinal sides of the rectangular loop are A and B and A' and B'.

[0062] Using a power supply and a third conductor, a rectangular loop is constructed in the area to be surveyed (this is the core structure of the loop source device, consisting of one or more turns of wire). The lengthwise sides of the rectangular loop correspond to endpoints A and B, and A' and B', respectively. The power supply then applies an AC signal with a preset frequency f (according to the attached data, the frequency range is 0.01-30,000 Hz) and a preset waveform (such as a triangle wave, a bun wave, or a sine wave) to this rectangular loop.

[0063] When AC current passes through a rectangular loop, it generates an induced electromagnetic field around the loop and underground. Signals of different frequencies correspond to different exploration depths. High-frequency signals reflect shallow geological information, while low-frequency signals reflect deeper geological information (based on the principle of skin depth, δ is related to frequency; the lower the frequency, the greater δ). Furthermore, the choice of preset waveform affects the parameters that can be measured subsequently (for example, a sine wave can only measure resistivity and ratio, while other non-sinusoidal waves can measure all four parameters).

[0064] The rectangular loop structural design does not need to rely on grounding like the line source device, avoiding the problem of "the power supply current is greatly affected by the ground resistance" of the line source device (the appendix mentions that the line source needs to increase the voltage in high-resistance formations, which increases the difficulty of equipment installation). It can achieve low-power and high-current power supply, reducing the manufacturing difficulty and use risk of power supply equipment.

[0065] The flexible selection of preset frequencies can meet the needs of different exploration depths. There is no need to replace the device multiple times to adjust the depth. A single power supply can lay the foundation for the subsequent acquisition of geological information at different depths, which improves the convenience of exploration.

[0066] The clarification of the preset waveform provides a prerequisite for subsequent parameter measurement, ensuring that the appropriate waveform can be selected according to the exploration objectives (such as whether it is necessary to distinguish between mines and non-mines), creating conditions for accurately obtaining the required geological parameters.

[0067] S420, using a first measuring electrode M and a second measuring electrode N, sequentially measure each preset geological parameter of a preset point along the direction from A to B or from A' to B'; wherein the straight line between M and N is parallel to the straight line between A and B; each preset measuring point is the midpoint between M and N.

[0068] Using a first measuring electrode M and a second measuring electrode N, measure predetermined measurement points along the length of the rectangular loop (from A to B or from A' to B') to obtain the predetermined geological parameters at each point. The line between M and N must be parallel to the line between A and B (i.e., the long side of the rectangle), and each predetermined measurement point is set at the midpoint between M and N.

[0069] The long side of a rectangular loop is the primary signal transmission direction. The induced electromagnetic field generated near this long side is more stable and produces a stronger signal. The measurement electrode MN is placed parallel to the long side to maximize the reception of the electric field signal from the induced electromagnetic field, ensuring signal strength and stability. Using the midpoint of the MN as the measurement point unifies the spatial coordinate reference of the measurement points, ensuring comparability of data from different measurement points (avoiding data errors caused by positional deviations).

[0070] Measuring along the long side of the rectangle with MN parallel to the long side fully utilizes the advantage of strong signals near the long side (the appendix mentions that the signal-to-noise ratio of ultra-near source measurements is high, with signals ranging from a few millivolts to several thousand millivolts), solving the problem of "weak signals and low signal-to-noise ratio in the near-source area" in traditional electromagnetic methods and improving the accuracy of measurement data.

[0071] It allows measurement along the two long sides, A to B or A' to B', which is equivalent to obtaining geological information of two profiles in one deployment, thus expanding the exploration coverage, reducing the workload of repeated deployment of the device, and improving exploration efficiency.

[0072] Taking the midpoint of MN as the measurement point unifies the spatial reference of data recording, avoids the confusion in subsequent data comparison caused by unclear definition of measurement points, provides standardized original data for parameter calculation (such as the ratio rate requires comparison of adjacent point data), and ensures the reliability of parameter calculation.

[0073] The geological parameters measured by the loop source device are the same as those measured by the line source device in the above embodiment, and are not described in detail here.

[0074] S500: If η1=η2, a preset line source device or a loop source device is used to perform geological survey on the area to be surveyed.

[0075] In this embodiment, if η1=η2, it means that the terrain of the area to be surveyed is between complex terrain and flat terrain. In theory, geological survey can be carried out using either a line source device or a loop source device. Therefore, the preset line source device or loop source device can be used to conduct geological survey of the area to be surveyed, and one of them can be selected according to actual needs; for example, if fast construction is required, a simpler line source can be selected; if a more stable power supply signal is required, a loop source can be selected.

[0076] Maintain flexibility to accommodate scenarios where terrain has no apparent bias. Avoid selection limitations due to rigid rules and optimize solutions based on survey objectives (e.g., prioritizing efficiency or signal stability) to further enhance operational adaptability.

[0077] The method in this embodiment uses the logic of "terrain feature quantification → similarity comparison → device adaptation selection" to specifically solve the problem of "difficulty in balancing exploration efficiency and adaptability" in the traditional method mentioned in the appendix: for complex terrain, line sources are given priority to avoid the difficulty of laying out return line sources; for flat terrain, return line sources are given priority to avoid the problem of unstable power supply of line sources; quantitative comparison replaces subjective judgment, reducing efficiency loss caused by device selection errors.

[0078] Ultimately, the "optimal match between terrain and equipment" is achieved, laying the foundation for subsequent multi-parameter measurements (the core advantage of the accessories), and indirectly improving the accuracy and efficiency of exploration.

[0079] In this embodiment, a topographic and geomorphic feature vector XL, such as elevation, slope, aspect, terrain relief, and surface roughness, of the area to be surveyed, is obtained and compared for similarity with the topographic and geomorphic feature vectors XL1 and XL2 corresponding to preset line-source and loop-source devices, thereby selecting an appropriate survey device. This approach specifically addresses the difficulty in balancing exploration efficiency and adaptability in traditional survey methods, avoiding power supply difficulties associated with line-source devices in high-resistance formations due to ground resistance, as well as the difficulty in deploying traditional loop-source devices in complex terrain. Furthermore, leveraging the advantages of the ultra-near-source electromagnetic method, which can measure multiple parameters such as resistivity, polarizability, ratio, and vortex rate, it addresses the limitations of existing methods, such as the single measurement parameter and the lack of breakthroughs in key parameter measurement, thereby reducing the need for secondary surveys and lowering labor intensity. Furthermore, the ultra-near-source method, with its strong signal and high signal-to-noise ratio (from a few millivolts to several thousand millivolts), and the ability to map frequencies to different survey depths, improves the signal-to-noise ratio and survey depth limitations of conventional methods, ultimately achieving comprehensive improvements in the adaptability, efficiency, and accuracy of geological surveys.

[0080] In an exemplary embodiment, a device for the ultra-near source electromagnetic based geological exploration method described in the above embodiment is also provided. The device includes: a power transmission part and a measurement part.

[0081] The measurement equipment is essentially the same for both methods; however, the power supply differs slightly. When using the line source method, the output voltage is higher than when using the loop source method. In other words, power supply equipment suitable for the line source method is also suitable for the loop source method, but not necessarily suitable for the line source method.

[0082] The power supply transmitting part includes a signal generating circuit, a signal bias circuit, a rectifier and filter circuit, an audio amplifying circuit, an output rectifier and filter circuit, a voltage stabilizing and limiting circuit, a current stabilizing and limiting circuit, a protection circuit and an auxiliary power supply circuit; the output power of the power supply transmitting part is 0-100 kilowatts, the output voltage is 0-2 kilovolts, the output current is 0-50 amps, the output frequency is 0.01-30,000 Hz, and the output waveform is a sine wave, a triangle wave or a steamed bun wave.

[0083] The measuring part includes a data acquisition circuit, an overvoltage protection circuit, a current and voltage stabilization circuit, a computer control part, and a computer calculation and storage part; the measuring part is used to measure the primary field potential difference △U1 in the power supply time period and the secondary field potential difference △U2 in the power-off time period in the induced electromagnetic field, and calculate the resistivity, polarizability, ratio rate and vortex rate based on △U1 and △U2.

[0084] Furthermore, the power transmitting part can control the output parameters through manual control or programming, and the output parameters include power supply time, power off time, output power, output voltage, output current and output frequency; the power transmitting part has constant current and constant voltage characteristics and automatic power supply and automatic stop functions.

[0085] Furthermore, the measuring part is common to the line source device and the return line source device; in the power transmitting part, the power output voltage applicable to the line source device is higher than the power output voltage applicable to the return line source device, and the power applicable to the line source device can be used for the return line source device.

[0086] Although some specific embodiments of the present invention have been described in detail by way of examples, it should be understood by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the present invention. It should also be understood by those skilled in the art that various modifications may be made to the embodiments without departing from the scope and spirit of the present invention.

Claims

1. A geological exploration method based on ultra-near source electromagnetics, characterized in that: The method comprises the following steps: S100, obtaining a topographic feature vector XL of the area to be surveyed; the XL is obtained by obtaining the elevation, slope, slope direction, topographic relief, and surface roughness of the area to be surveyed; S200, obtaining a similarity η1 between a first preset topographic and geomorphic feature vector XL1 and a similarity η2 between a first preset topographic and geomorphic feature vector XL1 and a second preset topographic and geomorphic feature vector XL2; wherein XL1 corresponds to geological exploration using a preset line source device, and XL2 corresponds to geological exploration using a preset loop source device; S300, if η1>η2, use a preset line source device to perform geological survey on the area to be surveyed; S400, if η1 < η2, use a preset loop source device to perform geological survey on the area to be surveyed; S500: If η1=η2, a preset line source device or a loop source device is used to perform geological survey on the area to be surveyed.

2. The geological exploration method based on ultra-near source electromagnetics according to claim 1, characterized in that: The line source device includes a power supply, a first power supply wire and a second power supply wire; wherein one end of the first power supply wire is connected to the power supply and the other end is grounded; one end of the second power supply wire is connected to the power supply and the other end is grounded.

3. The geological exploration method based on ultra-near source electromagnetics according to claim 2, characterized in that: Step S300 includes the following steps: S310, in the area to be surveyed, supplying an AC signal of a preset frequency f and a preset waveform to a grounding point A of the first power supply wire and a grounding point B of the second power supply wire through the power supply, the first power supply wire, and the second power supply wire; S320, using a first measuring electrode M and a second measuring electrode N, sequentially measure each preset geological parameter of the preset point along the direction from A to B; wherein the straight line between M and N is parallel to the straight line between A and B; each preset measuring point is the midpoint between M and N.

4. The geological exploration method based on ultra-near source electromagnetics according to claim 3, characterized in that: If the alternating current is a sine wave, the preset geological parameters include: resistivity and ratio; if the alternating current is other preset non-sinusoidal waves, the preset geological parameters include: resistivity, polarizability, ratio and vortex rate; wherein, ratio B s =△U n / △U n-1 ; △U n is the observed value of the potential difference between MN at the nth preset point; △U n-1 is the observed value of the potential difference between MN at the n-1th preset point; the vortex rate W s =△U a / △U b ; △U a is the early secondary potential during the time period t0-t1 when the vortex electric field is generated, △U b is the primary potential.

5. The geological exploration method based on ultra-near source electromagnetics according to claim 1, characterized in that: The loop source device includes a power supply and a third wire; wherein two ends of the third wire are connected to the power supply to form a rectangular loop.

6. The geological exploration method based on ultra-near source electromagnetics according to claim 5, characterized in that: Step S400 includes the following steps: S410, forming a rectangular loop in the area to be surveyed by the power supply and the third conductor; the power supply applies an AC signal of a preset frequency f and a preset waveform; the endpoints of the longitudinal sides of the rectangular loop are A and B and A' and B'; S420, using a first measuring electrode M and a second measuring electrode N, sequentially measure each preset geological parameter of a preset point along the direction from A to B or from A' to B'; wherein the straight line between M and N is parallel to the straight line between A and B; each preset measuring point is the midpoint between M and N.

7. The geological exploration method based on ultra-near source electromagnetics according to claim 3 or 6, characterized in that: The preset waveforms include: triangle wave, steamed bun wave and sine wave; among them, the steamed bun wave is a wave in which all values ​​on the time axis are positive; the sine wave is a sine wave with a minimum value of 0.

8. A device for the geological exploration method based on ultra-near source electromagnetics according to any one of claims 1 to 7, characterized in that: The device comprises: a power transmission part and a measurement part; The power transmission part includes a signal generating circuit, a signal biasing circuit, a rectifier and filter circuit, an audio amplifier circuit, an output rectifier and filter circuit, a voltage stabilizing and limiting circuit, a current stabilizing and limiting circuit, a protection circuit and an auxiliary power supply circuit; the output power of the power transmission part is 0-100 kilowatts, the output voltage is 0-2 kilovolts, the output current is 0-50 amperes, the output frequency is 0.01-30,000 hertz, and the output waveform is a sine wave, a triangle wave or a steamed bun wave; The measuring part includes a data acquisition circuit, an overvoltage protection circuit, a current and voltage stabilization circuit, a computer control part, and a computer calculation and storage part; the measuring part is used to measure the primary field potential difference △U1 in the power supply time period and the secondary field potential difference △U2 in the power-off time period in the induced electromagnetic field, and calculate the resistivity, polarizability, ratio rate and vortex rate based on △U1 and △U2.

9. The device according to claim 7, characterized in that The power transmitting part can control the output parameters through manual control or programming, and the output parameters include power supply time, power off time, output power, output voltage, output current and output frequency; the power transmitting part has constant current and constant voltage characteristics and automatic power supply and automatic stop functions.

10. The device according to claim 7, characterized in that The measuring part is common to the line source device and the return line source device; in the power transmitting part, the power output voltage applicable to the line source device is higher than the power output voltage applicable to the return line source device, and the power applicable to the line source device can be used for the return line source device.

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