Mine transient electromagnetic advanced detection method based on high and low voltage switching

Abstract

The invention relates to a mine transient electromagnetic advanced detection method based on high and low voltage switching. The method comprises the following steps: S1, alternately transmitting a low-voltage short pulse and a high-voltage long pulse; s2, starting data acquisition at 10 microseconds at the turn-off moment of the high-voltage pulse and the low-voltage pulse, and capturing a complete secondary field attenuation signal; s3, background noise is collected in the non-emission time period, and the induction signals are corrected; s4, establishing a mapping relation model of the double-voltage attenuation curve and the stratum conductivity; and S5, judging the geological anomalous body according to the curve change and the resistivity. According to the invention, the low-voltage short pulse energy is relatively concentrated, the attenuation speed is low, and clearer electromagnetic response can be generated in shallow geology. By emitting low-voltage short pulses, fine geological structures such as shallow water-containing fractures and small faults can be accurately detected, and the problem that the shallow resolution of a traditional transient electromagnetic method is insufficient is effectively solved.

Description

Technical Field

[0001] The present invention relates to the field of geological detection, and in particular to a mine transient electromagnetic advance detection method based on high-low voltage switching. Background Art

[0002] In mine excavation projects, the advance detection of hidden geological structures such as aquifers, fault fracture zones, and karst cavities is a core link in ensuring safe production. Such geological anomalies are prone to cause major accidents such as water inrush and landslides. Especially under high stress and complex hydrogeological conditions, it is crucial to accurately identify the distribution range and spatial form of geological hazards in front of the excavation face. As a non-contact geophysical detection method, transient electromagnetic method (TEM) is widely used in mine advanced geological prediction due to its high sensitivity to low-resistance water-bearing structures. However, traditional transient electromagnetic methods are limited to a single voltage emission mode and have the following technical bottlenecks:

[0003] Although high-pressure transmission can penetrate deep strata, the shallow signal attenuates too quickly, resulting in insufficient resolution; although low-pressure transmission can improve shallow imaging accuracy, it sacrifices the ability to effectively detect deep anomalies, making it difficult to meet the needs of multi-depth synchronous monitoring of mine excavation faces. Summary of the Invention

[0004] In view of this, the present invention aims to propose a mine transient electromagnetic advance detection method based on high and low voltage switching to solve the problems in the prior art.

[0005] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0006] The present invention proposes a mine transient electromagnetic advance detection method based on high and low voltage switching.

[0007] The detection method comprises the following steps:

[0008] S1, alternately emits low-voltage short pulses and high-voltage long pulses;

[0009] S2, start data acquisition 10μs after the high-voltage pulse and low-voltage pulse are turned off to capture the complete secondary field decay signal;

[0010] S3, collecting background noise during the non-transmitting period and correcting the sensing signal;

[0011] S4, establishing a mapping relationship model between the dual voltage attenuation curve and the formation conductivity;

[0012] S5, determine the geological anomaly based on curve changes and resistivity.

[0013] Furthermore, in the S1, the low voltage short pulse voltage is 9V, the pulse width is 10ms, and the off time is 120μs;

[0014] The high-voltage long pulse voltage is 36V, the pulse width is 10ms, and the off time is 300μs.

[0015] Furthermore, in S2, the time for capturing the low-voltage pulse signal is selected to be 0.05ms to 2ms, and the time for capturing the high-voltage pulse signal is selected to be 0.2ms to 6ms.

[0016] Furthermore, the noise elimination in S3 is performed by the following formula:

[0017] Vclean(t)=Vraw(t)―αN(t)

[0018] Where Vclean(t) is the transient electromagnetic response signal after removing the ambient noise, Vraw(t) is the mixed signal containing the target signal and the ambient noise, α is a constant coefficient, and N(t) is the pure ambient noise collected during the no-transmission period.

[0019] Furthermore, in S4, a mapping relationship model between the dual voltage attenuation curve and the formation conductivity is established by the following formula:

[0020]

[0021] Where VL(t) is the attenuation curve formula at low voltage, VH(t) is the attenuation curve formula at high voltage, M and N are fixed parameter values, i is the index summed from 1 to M, j is the index summed from 1 to N, σi and σj are conductivity, e is a natural constant, t is time, and wH(zj) and wL(zi) are weight functions.

[0022] Furthermore, in S5, if the resistivity ρ<10Ω / m or ρ<10Ω / m within 50 meters of the high-voltage curve or the low-voltage curve, and the gradient change is >20% / m, it indicates a shallow risk. If the resistivity mutation is >50% above 120 meters, it indicates a deep risk.

[0023] Furthermore, the switching time between the low-voltage short pulse and the high-voltage long pulse is less than 1 second.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] In the present invention, the energy of the low-voltage short pulse is relatively concentrated and the decay rate is slow, which can produce a clearer electromagnetic response in shallow geology. By emitting low-voltage short pulses, it is possible to accurately detect subtle geological structures such as shallow water-bearing fissures and small faults, effectively solving the problem of insufficient shallow resolution of traditional transient electromagnetic methods, providing more detailed shallow geological information for mine excavation, and reducing the risk of accidents such as water inrush and landslides caused by shallow geological anomalies. High-voltage long pulses have stronger penetration capabilities and can penetrate deep into the strata in front of the mine excavation face. Emitting high-voltage long pulses can detect large aquifers, caves and other geological anomalies that may exist in the deep, making up for the shortcomings of traditional methods in terms of limited deep detection capabilities, and realizing comprehensive detection of geological hazards at multiple depths in front of the mine excavation face, thereby ensuring the safety of the excavation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0027] Figure 1 It is a schematic diagram of the overall process of the present invention;

[0028] Figure 2 This is a schematic diagram of the high and low voltage emission timing of the present invention;

[0029] Figure 3 A schematic diagram of the capture time of high-voltage and low-voltage pulse signals of the present invention;

[0030] Figure 4 This is the mapping relationship model between the dual voltage attenuation curve and the formation conductivity of the present invention. DETAILED DESCRIPTION

[0031] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0032] In the description of the present invention, it should be noted that the terms "upper," "lower," "inner," and "back" and other terms indicating orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0033] Furthermore, in the description of the present invention, unless otherwise expressly defined, the terms "mounted," "connected," "connect," and "connector" should be interpreted broadly. For example, these terms may refer to fixed, removable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediary; or internal communication between two components. Those skilled in the art will appreciate the specific meanings of these terms in the present invention based on the specific circumstances.

[0034] The following will refer to the attached Figures 1 to 4 The present invention is described in detail with reference to the embodiments.

[0035] In general, the present invention proposes a mine transient electromagnetic advance detection method based on high-low voltage switching, which includes the following steps:

[0036] S1, alternately emits low-voltage short pulses and high-voltage long pulses;

[0037] S2, start data acquisition 10μs after the high-voltage pulse and low-voltage pulse are turned off to capture the complete secondary field decay signal;

[0038] S3, collecting background noise during the non-transmitting period and correcting the sensing signal;

[0039] S4, establishing a mapping relationship model between the dual voltage attenuation curve and the formation conductivity;

[0040] S5, determine the geological anomaly based on curve changes and resistivity.

[0041] In this embodiment, the energy of the low-voltage short pulse is relatively concentrated and decays slowly, which can produce a clearer electromagnetic response in shallow geology. By emitting low-voltage short pulses, subtle geological structures such as shallow water-bearing fissures and small faults can be accurately detected, effectively solving the problem of insufficient shallow resolution of traditional transient electromagnetic methods, providing more detailed shallow geological information for mine excavation, and reducing the risk of accidents such as water inrush and landslides caused by shallow geological anomalies. High-voltage long pulses have stronger penetration ability and can penetrate deep into the strata ahead of the mine excavation face. Emitting high-voltage long pulses can detect large aquifers, caves and other geological anomalies that may exist at depth, making up for the limited deep detection capabilities of traditional methods, and achieving comprehensive detection of geological hazards at multiple depths ahead of the mine excavation face, ensuring the safety of the excavation process.

[0042] Data acquisition begins 10μs after the high-voltage and low-voltage pulses are turned off. This precise timing ensures the capture of the complete secondary field attenuation signal. This signal contains rich geological information. Acquisition of this complete signal provides a reliable data foundation for subsequent signal processing and geological interpretation, helping to more accurately determine the location, scale, and nature of geological anomalies.

[0043] During periods of no transmission, background noise is collected and used to correct the sensing signal. This method effectively removes the effects of environmental noise and electromagnetic interference on the detection signal, improving the signal-to-noise ratio, making the detection results more accurate and reliable, and reducing false positives and missed detections caused by noise interference.

[0044] like Figure 4 As shown in the figure, a mapping model between dual voltage attenuation curves and formation conductivity is established, correlating the attenuation curves collected at different voltages with the formation conductivity. This model provides a quantitative basis for geological interpretation, allowing geologists to quickly and accurately infer the electrical characteristics of the formation based on changes in the attenuation curves, and thus determine the presence of geological anomalies.

[0045] By directly identifying geological anomalies based on curve changes and resistivity, the geological interpretation process is simplified. Geologists no longer need to perform complex calculations and analysis; simply by observing the changing trends of the attenuation curve and resistivity, they can intuitively identify areas of geological anomalies. This significantly improves the efficiency and accuracy of geological interpretation and provides timely and effective support for mine excavation decision-making.

[0046] It should be noted that the high-low voltage switching detection method allows for flexible adjustment of transmission parameters based on actual geological conditions. When encountering areas with complex geological structures and significant electrical differences, properly selecting the high-low voltage transmission ratio and pulse parameters can better adapt to geological variations, improving the applicability and reliability of the detection method in different geological environments.

[0047] During specific implementation, the transmitting device and the receiving device are installed in the preset position, and the transmitting device first transmits a low-voltage short pulse according to the preset transmission parameters. The low-voltage short pulse transmits a pulsed magnetic field to the underground medium through the transmitting coil, and the magnetic field excites induced eddy currents in the underground medium. During the transmission process, the transmission voltage, current and other parameters are monitored in real time to ensure the stability and accuracy of the transmission process. After the low-voltage short pulse is transmitted, after a short interval (which can be adjusted according to actual conditions), the transmitting device switches to the high-voltage long pulse transmission mode. The high-voltage long pulse transmits a pulsed magnetic field into the underground with stronger energy to further detect deep geological structures. Similarly, during the high-voltage long pulse transmission process, the transmission parameters are monitored and adjusted in real time.

[0048] 10 μs after the high-voltage and low-voltage pulses are switched off, the receiver immediately activates and begins collecting the secondary field decay signal. The receiving coil detects the temporal variation of the secondary induced eddy current field generated in the underground medium and converts it into an electrical signal, which is then transmitted to the data acquisition card in the receiving device. The data acquisition card acquires the signal at a preset sampling rate and stores the acquired data in a storage device.

[0049] It's important to note that the low-voltage short pulse voltage is set at 9V. This relatively low voltage generates a relatively mild electromagnetic field in shallow geological layers, preventing the rapid attenuation and distortion of shallow signals caused by excessive energy. The 10ms pulse width ensures the electromagnetic field has sufficient action time in the shallow medium to fully stimulate the induced eddy currents in the shallow geological bodies, thereby obtaining richer shallow geological information.

[0050] The high-voltage long pulse voltage is set to 36V, significantly increasing the energy of the transmitted electromagnetic field and giving it greater penetration. During mine excavation, deep geological structures are often more complex and may contain large geological anomalies, such as deep aquifers and large caves. The 36V high-voltage transmission can overcome the shielding and attenuation of shallow geological structures, effectively transmitting the electromagnetic field to deeper strata, stimulating induced eddy currents in the deep geological bodies, and thus enabling the detection of deep geological anomalies.

[0051] It needs to be further explained that, Figure 3 As shown in Figure 2, in S2, the time for capturing the low-voltage pulse signal is selected to be 0.05ms to 2ms, and the time for capturing the high-voltage pulse signal is selected to be 0.2ms to 6ms. In shallow geological exploration, the early stage of the secondary field signal excited by the low-voltage pulse contains rich geological details. The capture time window of the full time domain can completely cover the early process of the secondary field signal from generation to rapid decay. The signal at this stage is extremely sensitive to the electrical differences of shallow geological bodies and can accurately reflect the electromagnetic response characteristics of different shallow media (such as water-bearing fractures, and the boundary between loose rock layers and dense rock layers). This allows exploration personnel to clearly identify subtle changes in shallow geological structures and effectively reduce the risk of accidents such as water inrush and landslides caused by the failure to timely discover shallow geological anomalies.

[0052] The noise elimination in the above S3 is performed by the following formula:

[0053] Vclean(t)=Vraw(t)―αN(t)

[0054] Where Vclean(t) is the transient electromagnetic response signal after removing the ambient noise, Vraw(t) is the mixed signal containing the target signal and the ambient noise, α is a constant coefficient, and N(t) is the pure ambient noise collected during the no-transmission period.

[0055] It should be noted that in S4, the mapping relationship model between the dual voltage attenuation curve and the formation conductivity is established by the following formula:

[0056]

[0057] Where VL(t) is the attenuation curve formula at low voltage, VH(t) is the attenuation curve formula at high voltage, M and N are fixed parameter values, i is the index summed from 1 to M, j is the index summed from 1 to N, σi and σj are conductivity, e is a natural constant, t is time, and wH(zj) and wL(zi) are weight functions.

[0058] In addition, based on the above settings, in S5, if the resistivity ρ<10Ω / m or ρ<10Ω / m within 50 meters of the high-voltage curve or the low-voltage curve, and the gradient change is >20% / m, it indicates a shallow risk. If the resistivity suddenly changes by >50% above 120 meters, it indicates a deep risk.

[0059] Setting a resistivity of ρ < 10Ω·m within 50 meters of the high- or low-pressure curve as the shallow risk assessment standard is based on reasonable considerations of shallow geological characteristics such as water content. In mine geological environments, resistivity below this threshold often indicates water-rich areas, such as water-rich fracture zones, waterlogged caves, or loose aquifers. This threshold setting can quickly identify locations of potential shallow geological hazards, providing early warning during mine excavation and allowing operators ample time to take preventative measures to avoid casualties and property damage from accidents such as water inrush.

[0060] Furthermore, a resistivity gradient variation of >20% / m within 50 meters further enhances the ability to identify shallow risk areas. Resistivity gradient variations reflect dramatic spatial shifts in the electrical parameters of geological bodies, often closely associated with discontinuities in geological structures, sudden changes in lithology, or the boundaries of anomalous water-bearing bodies. When the gradient variation exceeds a set threshold, it indicates significant anomalies in the shallow geological structure, potentially indicating potential water channels or geological weaknesses. This allows for more precise delineation of shallow risk areas and improves the accuracy of risk warnings.

[0061] It should be noted that the criteria for resistivity changes exceeding 50% above 120 meters are optimized based on the electromagnetic response characteristics of deep geological bodies. Due to their greater burial depth, deep geological bodies are less susceptible to shallow geological disturbances, and their resistivity changes better reflect the essential characteristics of deep geological structures. A resistivity change exceeding 50% may indicate the presence of large geological anomalies at depth, such as fault fracture zones, karst development zones, or ore-rich strata. This criterion helps identify potential geological risks at greater depths, providing deep geological safety assurance for mine excavation.

[0062] Furthermore, the switching time between low-voltage short pulses and high-voltage long pulses is less than 1 second. In mine transient electromagnetic detection, pulse transmitting and receiving equipment must switch between low-voltage and high-voltage modes. If the switching time is too long, the equipment will be idle during the mode conversion process, and data collection will be impossible. When the switching time is less than 1 second, the equipment idle time is greatly compressed, allowing the detection equipment to quickly switch between different pulse modes and continue to operate, effectively reducing the total time spent at each detection point, significantly increasing the number of detection points per unit time, and thus accelerating the overall detection progress.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A mine transient electromagnetic advance detection method based on high and low voltage switching, characterized by: The detection method comprises the following steps: S1, alternately emits low-voltage short pulses and high-voltage long pulses; S2, start data acquisition 10μs after the high-voltage pulse and low-voltage pulse are turned off to capture the complete secondary field decay signal; S3, collecting background noise during the non-transmitting period and correcting the sensing signal; S4, establishing a mapping relationship model between the dual voltage attenuation curve and the formation conductivity; S5, determine the geological anomaly based on curve changes and resistivity.

2. The mine transient electromagnetic advance detection method based on high and low voltage switching according to claim 1 is characterized in that: In S1, the low-voltage short pulse voltage is 9V, the pulse width is 10ms, and the off time is 120μs; The high-voltage long pulse voltage is 36V, the pulse width is 10ms, and the off time is 300μs.

3. The mine transient electromagnetic advance detection method based on high and low voltage switching according to claim 1 is characterized in that: In the above S2, the time for capturing the low-voltage pulse signal is selected to be 0.05ms to 2ms, and the time for capturing the high-voltage pulse signal is selected to be 0.2ms to 6ms.

4. The mine transient electromagnetic advance detection method based on high and low voltage switching according to claim 1 is characterized in that: The noise elimination in S3 is performed by the following formula: Vclean(t)=Vraw(t)―αN(t) Where Vclean(t) is the transient electromagnetic response signal after removing the ambient noise, Vraw(t) is the mixed signal containing the target signal and the ambient noise, α is a constant coefficient, and N(t) is the pure ambient noise collected during the no-transmission period.

5. The mine transient electromagnetic advance detection method based on high and low voltage switching according to claim 1 is characterized in that: In S4, a mapping relationship model between the dual voltage attenuation curve and the formation conductivity is established by the following formula: Where VL(t) is the attenuation curve formula at low voltage, VH(t) is the attenuation curve formula at high voltage, M and N are fixed parameter values, i is the index summed from 1 to M, j is the index summed from 1 to N, σi and σj are conductivity, e is a natural constant, t is time, and wH(zj) and wL(zi) are weight functions.

6. The mine transient electromagnetic advance detection method based on high and low voltage switching according to claim 1 is characterized in that: In S5, if the resistivity ρ<10Ω / m or ρ<10Ω / m within 50 meters of the high-voltage curve or the low-voltage curve, and the gradient change is >20% / m, it indicates a shallow risk. If the resistivity mutation is >50% above 120 meters, it indicates a deep risk.

7. A mine transient electromagnetic advance detection method based on high and low voltage switching according to claims 1 to 6, characterized in that: The switching time between the low-voltage short pulse and the high-voltage long pulse is less than 1 second.

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