Position detection method and system for low-resistance anomalous body of mine working face

Abstract

The invention provides a method and system for detecting the position of a low-resistance abnormal body in a mine working face, and belongs to the technical field of mine detection.The method comprises the steps that a power-on wire is arranged on a roadway on one side of the mine working face, and a receiving device is arranged on a roadway on the other side of the mine working face to receive induced electromotive force excited when the power-on wire is powered off; when the change rate of the induced electromotive force in the early stage is smaller than the threshold value and is higher than the threshold value after the threshold value in the late stage, the low-resistance anomalous body is located outside the receiving point; if the induced electromotive force excited by the transient electromagnetic field and received by the receiving point does not change obviously in the early stage and the late stage, the low-resistance anomalous body is located on the outer side of the electrified wire; and when the early change rate of the induced electromotive force excited by the transient electromagnetic field received by the receiving point is large and is higher than the threshold value after the later time threshold value, the anomalous body is located between transmitting and receiving. The method can detect the position of the low-resistance abnormal body in the well.

Description

Technical Field

[0001] This invention belongs to the field of mine detection technology, specifically relating to a method and system for detecting the location of low-resistivity anomalies in a mine working face. Background Technology

[0002] With the advent of intelligent mining models characterized by "no coal on the surface and no personnel underground" and the introduction of "long-face mining" (working face with a mining length greater than 300m), the requirements for detecting geological information within the coal seam are becoming increasingly stringent. Through mining trials, the long-face mining scheme (working face length greater than 300m) has proven to be a reasonable investment, technically feasible, and possesses significant advantages. Compared to back-pull mining, it requires less equipment, is easier to manage, requires fewer operators, and has a simpler production system. However, the construction of long-face mining places higher demands on mine geological geophysical exploration techniques and mine disaster management engineering technologies.

[0003] Currently, methods for investigating hidden water inrush disaster sources inside working faces, both domestically and internationally, can be broadly categorized into two types: seismic and electromagnetic. Seismic methods primarily involve channel wave seismic exploration; however, because seismic methods rely on the density of rocks and ores for detection, they struggle to distinguish the water-bearing properties of hidden disaster-causing factors within coal seams.

[0004] Electromagnetic methods mainly include direct current (DC) methods, radio wave imaging, and transient electromagnetic methods. These methods detect the differences in electrical properties between coal seams and roof and floor strata, effectively identifying hidden water inrush hazards within typical working faces. However, they have blind spots for some wide working faces. DC methods have limited detection range due to underground space constraints. Two-dimensional observation models using same-side transmission and reception can only detect geological information directly below the roadway. For three-dimensional methods like mine DC imaging, the detection capability for shallow geological information decreases as the working face length increases. Radio wave imaging commonly uses electromagnetic wave frequencies of 0.3MHz, 0.5MHz, and 1.5MHz. Higher frequencies result in smaller detectable working face widths; at 0.3MHz, the effective detectable width is less than 200m. Therefore, this method is meaningless for most working faces wider than 200m.

[0005] The transient electromagnetic method in mines is increasingly used to detect water-conducting (including) anomalies in front of coal mine roadways, the roof and floor of the working face, and the working face itself, due to its advantages such as convenient construction, high efficiency, high longitudinal and transverse resolution, and sensitivity to low resistance. However, its effective detection depth is generally no more than 110m, and the width of the working face that can be detected is no more than 220m when both roadways of the working face are available.

[0006] Existing technologies include a transient electromagnetic field detection method using a same-side transmission and reception approach to detect low-resistivity anomalies. This method involves placing an energized conductor on one side of the mine face to generate an electromagnetic field, receiving the induced electromotive force generated by the transient electromagnetic field when the conductor is de-energized on the same side, and determining the location of the low-resistivity anomaly based on the value of the induced electromotive force.

[0007] However, the induced electromotive force received by the same-side transmission and reception transient electromagnetic transmission detection method is very weak, so it cannot effectively detect the location of small low-resistivity anomalies. Summary of the Invention

[0008] To overcome the shortcomings of the existing technology, the present invention provides a method and system for detecting the location of low-resistivity anomalies in a mine working face.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] A method for detecting the location of a low-resistivity anomaly in a mine working face, comprising:

[0011] A live conductor is laid in a roadway on one side of the mine working face, and a receiving point is set in a roadway on the other side to receive the induced electromotive force generated when the live conductor is de-energized. The induced electromotive force and time are used as the vertical axis and the horizontal axis, respectively, to construct the relationship curve between induced electromotive force and time, and early time threshold and late time threshold are set on the time axis.

[0012] The position of the low-resistivity anomaly at the mine working face relative to the energized conductor and the receiving point is determined using the relationship curve.

[0013] If the rate of change of the induced electromotive force excited by the received transient electromagnetic field is lower than the early induced electromotive force rate of change threshold before the early time threshold and higher than the late induced electromotive force rate of change threshold after the late time threshold, then the low-resistance anomaly is located on the side of the receiving point away from the energized conductor.

[0014] If the rate of change of the induced electromotive force excited by the received transient electromagnetic field is lower than the threshold before the early time threshold and after the late time threshold, the low-resistance anomaly is located on the side of the current-carrying conductor away from the receiving point.

[0015] If the rate of change of the induced electromotive force excited by the received transient electromagnetic field is higher than the early induced electromotive force rate of change threshold before the early time threshold and higher than the late induced electromotive force rate of change threshold after the late time threshold, then the low-resistance anomaly is located between the energized conductor and the receiving point.

[0016] Furthermore, it also includes:

[0017] The location of the two low-resistivity anomalies in the mine is determined by using the induced electromotive force data received by the receiving point before the early time threshold.

[0018] If the rate of change of the induced electromotive force received by the receiving point before the early time threshold is negative, then the current receiving point is facing a low-resistivity anomaly.

[0019] If the rate of change of the induced electromotive force received by the receiving point before the early time threshold is positive, then the current receiving point is located in the middle of the left and right low-resistivity anomalies.

[0020] If the rate of change of the induced electromotive force received by the receiving point before the early time threshold is at the positive-negative boundary, then the receiving point is located at the boundary of the low-resistivity anomaly along the measurement line direction.

[0021] Furthermore, the energized conductor is a long strip-shaped transmitting return line.

[0022] Furthermore, the dimensions of the elongated emission loop are 1000m × 5m.

[0023] Furthermore, the extreme values ​​of the induced electromotive force generated by the elongated emission loop are concentrated around the elongated emission loop before the early time threshold;

[0024] The extreme values ​​of the induced electromotive force generated by the elongated emission loop concentrate at the center of the elongated emission loop after the late time threshold.

[0025] Furthermore, the magnetic induction intensity generated by the elongated emission loop in the surrounding space is:

[0026]

[0027] Where B is the magnetic flux density, I is the current, a is the distance from the point to the line, and μ is the permeability of the medium.

[0028] Furthermore, in free space, the magnetic permeability μ of the medium is:

[0029] μ = μ0 = 4π × 10 -7

[0030] Where μ0 is the vacuum permeability.

[0031] Furthermore, the rate of change of the induced electromotive force is between -73.49% and 24.94%.

[0032] A system for detecting the location of low-resistivity anomalies in a mine working face, characterized in that it comprises:

[0033] The information acquisition module is used to lay a energized conductor in one roadway of the mine working face and set a receiving point in the other roadway to receive the induced electromotive force generated when the energized conductor is de-energized.

[0034] The relationship curve construction module is used to construct the relationship curve between induced electromotive force and time, with induced electromotive force and time as the vertical and horizontal axes, respectively, and to set early time thresholds and late time thresholds on the time axis.

[0035] Judgment module; used to determine the position of the low-resistivity anomaly in the mine working face relative to the energized conductor and the receiving point using the relationship curve;

[0036] If the rate of change of the induced electromotive force excited by the received transient electromagnetic field is below the threshold before the early time threshold and above the threshold after the late time threshold, the low-resistance anomaly is located on the side of the receiving point away from the energized conductor.

[0037] If the rate of change of the induced electromotive force excited by the received transient electromagnetic field is lower than the threshold before the early time threshold and after the late time threshold, the low-resistance anomaly is located on the side of the current-carrying conductor away from the receiving point.

[0038] If the rate of change of the induced electromotive force excited by the received transient electromagnetic field is higher than the threshold before the early time threshold and higher than the threshold after the late time threshold, then the low-resistance anomaly is located between the energized conductor and the receiving point.

[0039] The method and system for detecting the location of low-resistivity anomalies in a mine working face provided by this invention have the following beneficial effects:

[0040] This invention utilizes a transient electromagnetic induction detection method with contralateral transmission and reception to detect the relative position of low-resistivity anomalies in a mine working face with respect to the transmitting and receiving ends. Compared to existing same-side reception methods, its early data is hundreds or even thousands of times larger than the same-side observation data. Small low-resistivity anomalies have a relatively small impact on the induced electromotive force (EMF). If a same-side reception method is used, it is difficult to detect small low-resistivity anomalies based on the EMF data because the influence of the low-resistivity anomaly on the observed EMF data is extremely weak. However, the contralateral transmission and reception transient electromagnetic induction detection method can amplify the observed data by hundreds or even thousands of times, making it much easier to detect small low-resistivity anomalies.

[0041] Specifically, by leveraging the varying characteristics of induced electromotive force data received via transient electromagnetic induction detection at different locations of low-resistivity anomalies, the position of the low-resistivity anomaly relative to the energized conductor and the receiving point can be determined. This enables the location detection of relatively small low-resistivity anomalies. Attached Figure Description

[0042] To more clearly illustrate the embodiments and design schemes of the present invention, the accompanying drawings required for this embodiment will be briefly described below. The drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a schematic diagram of the mine transient electromagnetic perspective detection technology observation system of the present invention;

[0044] Figure 2 This is a schematic diagram of the transient electromagnetic perspective data feature analysis model of the present invention;

[0045] Figure 3 This is a schematic diagram of the induced electromotive force and its rate of change over time according to the present invention.

[0046] Figure 4 Multi-channel cross-sectional view drawn using transient electromagnetic imaging data of the present invention;

[0047] Figure 5 This is a schematic diagram of the low-resistance anomaly body located outside the receiving point according to the present invention;

[0048] Figure 6 This is a schematic diagram of a model of the low-resistance anomaly located outside the transmitting coil according to the present invention;

[0049] Figure 7 This is a schematic diagram showing the horizontal positions of the left and right dual abnormal bodies in this invention;

[0050] Figure 8 Multichannel cross-sectional views drawn using transient electromagnetic perspective data of the present invention. Detailed Implementation

[0051] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0052] Example

[0053] This invention provides a method for detecting the location of low-resistivity anomalies in a mine working face, specifically as follows: Figure 1 As shown, it includes:

[0054] A conductive wire is laid in one roadway of the mine working face, and a receiving point is set in the other roadway to receive the induced electromotive force (EMF) generated when the conductive wire is de-energized. A curve is constructed to represent the relationship between the induced EMF and time, using time as the vertical and horizontal axes, respectively. Early and late time thresholds are set on the time axis. Using the curve, the position of the low-resistivity anomaly at the mine working face relative to the conductive wire and the receiving point is determined: if the rate of change of the induced EMF generated by the received transient electromagnetic field is lower than the threshold before the early time threshold and higher than the threshold after the late time threshold, the low-resistivity anomaly is located on the side of the receiving point away from the conductive wire; if the rate of change of the induced EMF generated by the received transient electromagnetic field is lower than the threshold before and after the early and late time thresholds, the low-resistivity anomaly is located on the side of the conductive wire away from the receiving point; if the rate of change of the induced EMF generated by the received transient electromagnetic field is higher than the threshold before the early time threshold and higher than the threshold after the late time threshold, the low-resistivity anomaly is located between the conductive wire and the receiving point.

[0055] Specifically, it also includes: using early data received by the receiving point to determine the relative positions of the left and right low-resistivity anomalies in the mine, wherein the rate of change of the measuring point directly opposite the low-resistivity anomaly is negative, the rate of change of the middle of the two low-resistivity anomalies is positive, and the positive-negative interface is the boundary of the low-resistivity anomaly along the measuring line direction.

[0056] The following is the principle behind the implementation of this invention:

[0057] Basic principles of transient electromagnetic imaging technology:

[0058] Transient electromagnetic imaging (TEM) technology, like conventional transient electromagnetic methods, is based on Maxwell's equations and observes transient electromagnetic fields (i.e., the secondary electromagnetic field or induced electromotive force induced by the primary magnetic field). However, there are two differences: First, the observation system: the target object detected by TEM is located between the transmitting coil and the receiving point, a construction characteristic consistent with the underground tunnel transient electromagnetic method. Second, the time period of focus for the observation data differs: this detection technology focuses on early-stage data, mainly influenced by the primary magnetic field during field construction, accurately determining the relative position of the target object along the survey line. It also considers the later electromagnetic field induced and diffused by the secondary field near the coil. These are detailed below:

[0059] 1.1 Observation System

[0060] Drawing inspiration from the transient electromagnetic method's transmission and reception modes in underground tunnels, the mine transient electromagnetic perspective detection technology utilizes a long, narrow transmitting loop deployed in one side of the working face to increase the transmitting magnetic moment. It then analyzes the transient electromagnetic field received in the other side of the working face after the long, narrow transmitting loop has been charged and de-energized. This allows for the interpretation of geological information within the working face, revealing the spatial location of geological isomorphisms affecting safe mining operations. The deployment method is as follows: Figure 1 As shown in the diagram. The red rectangle represents the transmitter, and the blue dots represent the receivers.

[0061] 1.2 Concept of Transient Electromagnetic Vision

[0062] Similar to conventional transient electromagnetic methods, transient electromagnetic imaging still observes the secondary field generated by a step current. However, unlike conventional methods, transient electromagnetic imaging primarily interprets geological anomalies using early data. According to the Biot-Saffar law, the magnetic field strength produced by an infinitely long straight conductor in the surrounding space can be expressed as:

[0063]

[0064] In the formula, I is the current in the long straight conductor (A); B is the magnetic flux density (Wb / m²); a is the distance from the point to the line (m); and μ is the permeability of the medium (H / m). In free space:

[0065] μ = μ0 = 4π × 10 -7

[0066] As shown in the above equation, for rectangular emission loops and electric source emission loops, when power is supplied, the primary magnetic field generated in the surrounding medium is independent of the medium's conductivity, depending only on the medium's permeability and the distance from the emission source. However, at the instant of power failure, the rapid disappearance of the primary magnetic field will generate a changing secondary field (secondary magnetic field and electric field) in the surrounding medium. In the time domain, the changing electromagnetic field relationship can be expressed using Maxwell's method:

[0067]

[0068] In the formula, H is the magnetic field strength (A / m); E is the electric field strength (V / m); D is the electric displacement (C / m²); σ is the dielectric conductivity (S / m); and ε is the dielectric constant of the medium (F / m). In free space:

[0069] ε=ε0=8.854×10 -12

[0070] Under active conditions, the first and second equations in equation (2) can be written as:

[0071]

[0072]

[0073] Equation (3) vividly illustrates the relationship between the changing magnetic field and the changing electric field. The conductivity σ in the first equation indicates that the electric field generated by the changing magnetic field is related to the conductivity of the medium. The transient electromagnetic method utilizes the above electromagnetic field relationship to detect geological information. As can be seen from equation (1), the closer to the emission source, the greater the influence of the primary field. In the early stage after the step current is turned off, the secondary field generated is stronger.

[0074] Transient electromagnetic induction (TEM) technology employs reception at a certain distance from the transmission loop. The secondary field received at the receiving point is relatively less affected by the transmission source in its early stages, allowing for a clearer distinction between anomalies and secondary fields generated by the surrounding rock. Therefore, it can be assumed that the early TEM data is primarily caused by the attenuation of the initial primary field, while the later stages are caused by the cyclical diffusion of the larger secondary field near the transmission loop over time. The transient electromagnetic observation method using a contralateral transmission and reception primarily analyzes the early data, hence it is termed transient electromagnetic induction detection technology caused by primary magnetic field transmission.

[0075] 2. Numerical Analysis:

[0076] Since transient electromagnetic induction (TEM) detection technology is applied in long-length / ultra-wide working faces, operating within the entire space, and because it uses a long strip-shaped emission source, its electromagnetic field diffusion characteristics differ from those in half-space. Analyzing the transient electromagnetic field diffusion characteristics formed by the long strip-shaped emission source in the entire space will help interpret the measured data. Therefore, this study constructs a uniform model of the entire space to analyze the variation of the electromagnetic field over time and to investigate the data characteristics and detection capabilities of TEM detection technology, aiming to provide theoretical support for the practical measurement of TEM in long-length working faces.

[0077] 2.1 Transient Electromagnetic Field Characteristics of a Full-Space Long Strip-Shaped Transient Electromagnetic Loop Ground and mine transient electromagnetic methods typically interpret geological information by observing the z-component of the induced electromotive force (EMF). (In this paper, the z-direction is defined as the direction of the normal to the transmitting loop, i.e., the rate of change of magnetic induction intensity Bz with time, in units of V·m⁻²·A⁻¹). Therefore, this section mainly analyzes the spatial distribution characteristics of the induced EMF generated by a full-space long strip-shaped transmitting loop over time. This invention uses a 1000m × 5m long strip-shaped transmitting loop as an example, and sets the uniform full-space resistivity to 100 Ω·m for experiments. Experimental data shows that in the early stages (time < 10⁻⁵ s), the extreme values ​​of the induced EMF are mainly concentrated near the long strip-shaped transmitting loop. The extreme values ​​are opposite in sign inside and outside the plane where the transmitting coil is located (the z = 0m plane). This is mainly because the primary magnetic field generated at the moment of power supply is distributed around the transmitting loop. The z-component of the magnetic field in the x = 2.5m and x = -2.5m planes where the edge of the transmitting loop is located is 0, while the z-components of the magnetic field inside and outside the coil are opposite in direction.

[0078] Based on equation (1), it can be seen that the magnitude of the primary field is inversely proportional to the distance from the source, meaning that the primary magnetic field is largest near the edge of the transmission loop, thus the secondary field induced near the transmission loop is largest. As time increases, the negative poles on the outside of the transmitting coil move away from the transmission loop, while the positive poles converge at the center of the transmission loop and remain at the center. The extreme values ​​of the induced electromotive force generated by the long strip-shaped transmission loop in the entire space are mainly concentrated near the transmission loop in the early stage, caused by the strong primary magnetic field generated when the transmission loop is charging and not disconnected. Although the z-component of the induced electromotive force is relatively weaker at locations farther from the transmission loop, it still exists. In the later stage, the extreme values ​​of the induced electromotive force are concentrated at the center of the transmission loop, but its influence range gradually increases. Therefore, in the later stage, the induced electromotive force at locations farther from the transmission loop is mainly caused by the extreme values ​​near the transmission loop, which is caused by the cyclical and cross-induced diffusion of the secondary field.

[0079] 2.2 Characteristics of transient electromagnetic imaging data

[0080] To provide guidance for practical work and determine the quality of data, this invention constructs a geophysical electrical model to simulate an ultra-wide working face with a mining length of 300m, analyzing the characteristics of transient electromagnetic perspective data from the mine during transmission and reception on the opposite side. The transmission loop is 1000m × 5m in size. Red dots represent transmission and reception points on the same side, and blue dots represent transmission and reception points on the opposite side. The light blue cuboid is a low-resistivity body with a resistivity of 1Ω·m and dimensions of 100m × 100m × 5m. The thickness of this cuboid is consistent with the coal seam, used to simulate the post-mining water accumulation zone of old workings within the mine face. The background resistivity of the model is 100Ω·m.

[0081] Figure 3The figure shows the characteristic curves of the measurement points at the center of the above model's measurement line. The horizontal axis represents time, and the left vertical axis represents the induced electromotive force (EMF). The red and blue solid lines represent the induced EMF calculated by the model containing only the coal seam, while the purple and blue solid lines represent the induced EMF calculated by the model containing both the coal seam and the low-resistivity body. As can be seen from the figure, during same-side transmission and reception, the induced EMF curves with and without the low-resistivity body are almost identical, indistinguishable in both the early and late stages. However, during opposite-side transmission and reception, the induced EMF curves obtained from the two models show a significant divergence in the early stages, but are almost identical in the later stages. For the same-side transmission and reception mode, the induced EMF continuously decreases over time, hence it can be called the induced EMF decay curve. The opposite-side transmission and reception induced EMF curve shows a trend of first rising and then falling, called the time-varying induced EMF curve. Since the induced EMF curves are almost identical and difficult to distinguish during same-side transmission and reception, we used the formula shown in the figure's right vertical axis title to calculate the rate of change of the induced EMF. EMFa is the induced EMF calculated by the model containing the low-resistivity body, and EMFb is the induced EMF obtained without the low-resistivity body. The red and black dashed lines in the figure represent the induced electromotive force change rates calculated during same-side and opposite-side transmission and reception, respectively. During same-side transmission and reception, the induced electromotive force change rate is basically at 0%, while the change rate during opposite-side transmission and reception is less than -3% in the early stage (before 3×10-5s). The earlier the time, the larger the absolute value of the change rate, far exceeding 10%.

[0082] To further illustrate the characteristics of mine transient electromagnetic imaging data under the contralateral transmit-receive model, this study focuses on... Figure 2The two receiving survey lines shown in the figure calculate the rate of change of induced electromotive force (EMF) at different times for each measuring point and plot it. The horizontal axis of the figure represents the horizontal position of each measuring point, and the vertical axis represents time. The induced EMF rate of change profile calculated from the same-side transmitting and receiving survey line ranges from -0.027 to 0.032. Since the observed data typically contains 4% to 5% random noise, the rate of change from the same-side transmitting and receiving in this model cannot accurately reflect the information of a low-resistivity anomaly. If random noise is ignored, there is a region with a relatively large rate of change in the horizontal range of -50m to 50m and the vertical range of 6×10⁻⁴s to 2×10⁻³s, which can be considered as caused by a low-resistivity anomaly. The induced EMF rate of change profile calculated under the transient electromagnetic induction detection method of the opposite-side transmitting and receiving has a value between -73.49% and 24.94%, which is much larger than that of the same-side transmitting and receiving mode. Due to the large early rate of change, the changes in later data were not clearly visible. Therefore, the profile of the induced electromotive force (EMF) change rate of the opposite side transmitter and receiver was divided into two segments with a time of less than 10⁻⁴ s and a time of more than 10⁻⁴ s, using 10⁻⁴ s as the boundary. In the results with a time of less than 10⁻⁴ s, the rate of change of the measuring point directly opposite the low-resistivity anomaly was negative, while the values ​​on both sides were positive. The interface between the positive and negative values ​​was the boundary of the low-resistivity anomaly along the measuring line. In the results with a time of more than 10⁻⁴ s, the rate of change of the induced EMF was between -0.025% and 0.04%, and its distribution pattern was basically consistent with the late-stage induced EMF change rate of the same side transmitter and receiver, but the rate of change was greater than that of the same side transmitter and receiver.

[0083] In actual detection, it is impossible to obtain background data (EMFb) without low-resistivity anomalies. Furthermore, the spatiotemporal distribution characteristics of the electromagnetic field excited by the long, strip-shaped emission loop in full space differ from those in half-space, making it impossible to directly use surface processing methods for transient electromagnetic imaging data interpretation. Without a suitable method for transient electromagnetic imaging interpretation, multi-channel mapping of the original data becomes the only method that can be directly used for data interpretation. Figure 4 As shown.

[0084] Figure 4 (a) Early multi-channel profiles plotted for data before 0.14774 ms. The black dashed line in the figure represents the multi-channel profile without the low-resistivity anomaly, while the solid lines of each color represent the multi-channel profile with the low-resistivity anomaly. As can be seen from the figure, the induced electromotive force (EMF) on both sides of the early multi-channel profile is greater than the midpoint. Based on the aforementioned electromagnetic field distribution characteristics, the location of the extreme values ​​of the early induced EMF is similar to the shape of the emission loop, i.e., the closer to the loop, the greater the induced EMF. The early multi-channel profiles indicate that the influence of the low-resistivity anomaly can still be effectively observed in the multi-channel profiles before 0.022695 ms. Figure 4(b) The late multi-channel profile is plotted for data at times greater than 0.16609ms. As time increases, the induced electromotive force at x=0m is greater than that on both sides. According to the electromagnetic field distribution characteristics, the extreme value of the late induced electromotive force is concentrated at the center of the transmission loop, that is, the induced electromotive force in the middle of the measurement line is slightly greater than that on both sides.

[0085] In summary, the time-varying curve of the induced electromotive force (EMF) during transmission and reception on the opposite side differs from that during transmission and reception on the same side; the induced EMF initially increases and then decreases over time. For the thin-plate model described in this paper, there is no significant response during transmission and reception on the same side, either in the early or late stages, while the early response of transmission and reception on the opposite side is very significant. This fully demonstrates that the initial secondary field directly caused by the early primary magnetic field has a higher resolution, while the induced EMF caused by the cross-induced diffusion of the secondary field near the transmission loop in the late stage has a relatively weaker resolution. In the early multi-channel profile, the influence of the low-resistivity anomaly in this model can be clearly seen.

[0086] 2.3 Spatial Localization Ability Analysis of Low-Resistivity Anomalies

[0087] For the same-side transmit-receive transient electromagnetic method / mine transient electromagnetic method, the ambiguity of the spatial location of anomalies in the detection results has always been a difficult problem to solve. This section is based on... Figure 2 The model was used to move the low-resistivity anomaly to the outside of the transmit loop and the receive point to study the ability of transient electromagnetic induction detection technology to locate the low-resistivity anomaly along the plane of the coal seam.

[0088] 1) The low-resistivity anomaly is located outside the receiver point.

[0089] Figure 5 This is a schematic diagram of a model showing a low-resistivity anomaly located 100m outside the receiving point. The model parameters are set as follows: Figure 2 Consistent. At this time, the rate of change of induced electromotive force ranges from -0.38 to 0.39. Although there is a distinct light blue negative rate of change band and a small yellow-green positive rate of change region after 10⁻⁴ s, which is caused by the diffusion of the secondary field of the low-resistivity anomaly, there is no large rate of change caused by the rapid decay of the primary magnetic field in the early stage. Therefore, it can be determined whether the low-resistivity anomaly is inside the working surface or outside the receiving point.

[0090] 2) The low-resistivity anomaly is located outside the transmit loop.

[0091] Figure 6 This is a schematic diagram of a low-resistivity anomaly located 100m outside the transmitting coil. The rate of change of its induced electromotive force ranges from -0.29 to 0.24. The region with a larger rate of change is in the early stage and the changes are more chaotic and irregular, while the later stage basically shows no obvious changes.

[0092] The above simple simulation shows that in actual operation, if there is no obvious perspective effect in the early stage of the observation data, the low-resistivity anomaly is not inside the working surface. If the secondary field diffusion effect occurs in the later stage, the low-resistivity anomaly is located outside the receiving point; otherwise, it is located outside the transmitting coil.

[0093] 2.4 Analysis of the ability to distinguish between left and right dual anomalies

[0094] In the actual working face, multiple water-rich areas may exist simultaneously. To analyze the ability of transient electromagnetic imaging technology to distinguish between two anomalies, in Figure 2 Based on this, such as Figure 7 The model shown is a double anomaly model. The horizontal distance between the transmitting coil and the measuring line is 300m (simulating a 300m wide working surface). The two anomalies are located between the transmitting coil and the receiving point, spaced 100m apart along the measuring line. The resistivity is 1Ω·m, and the dimensions of each are 100m×100m×5m.

[0095] This invention constructs a profile of the induced electromotive force (EMF) change rate obtained from two anomalous bodies. When using the same-side transmit / receive transient electromagnetic operating mode, the induced EMF change rate ranges from -0.09 to 0.23. There is a region with a relatively large change rate within the horizontal range of -150m to 150m and the vertical range of 6×10⁻⁴s to 2×10⁻³s, making it impossible to distinguish between the two low-resistivity anomalous bodies. When using the opposite-side transmit / receive transient electromagnetic perspective detection method, the induced EMF change rate ranges from -54.53% to 60.35%, which is hundreds of times greater than that of the same-side transmit / receive mode. Dividing the profile of the induced EMF change rate of the opposite-side transmit / receive mode into two segments with a 10⁻⁴s boundary, in results with times less than 10⁻⁴s, the change rate at the measurement point directly opposite the low-resistivity anomalous body is negative, while the rate between the two anomalous bodies is positive. The interface between the positive and negative values ​​represents the boundary of the low-resistivity anomalous body along the measurement line direction. In results with a time greater than 10⁻⁴ s, the rate of change of induced electromotive force ranged from -0.343% to 0.293%. Its distribution pattern was basically consistent with the rate of change of induced electromotive force in the late stage of transmission and reception on the same side. It was impossible to effectively distinguish the two low-resistance anomaly regions, but the rate of change was greater than that of transmission and reception on the same side.

[0096] Figure 8 This is a multi-channel profile of the transmission and reception of the two low-resistivity anomalies on the left and right sides. Its overall shape is consistent with the single anomaly mentioned above, but two obvious concave areas can be seen in the early stage (x=100m and x=-100m positions), which correspond to the positions of the two low-resistivity anomalies along the measurement line, respectively.

[0097] In summary, compared to the conventional same-side transmit and receive transient electromagnetic method, the opposite-side transmit and receive transient electromagnetic perspective observation mode has higher horizontal resolution in the early data, which is mainly affected by the transient changes in the primary magnetic field. In the later stages, it is the same as the same-side transmit and receive method, mainly affected by the diffusion of the secondary field, and its horizontal resolution is relatively weak.

[0098] According to the method of the present invention, the following implementation system is also proposed, comprising:

[0099] The information acquisition module is used to lay an energized conductor in one roadway of the mine working face and set a receiving point in the other roadway to receive the induced electromotive force generated when the energized conductor is de-energized.

[0100] The relationship curve construction module is used to construct a relationship curve between induced electromotive force and time, with induced electromotive force and time as the vertical and horizontal axes, respectively, and to set early time thresholds and late time thresholds on the time axis.

[0101] Judgment module; used to determine the position of the low-resistivity anomaly in the mine working face relative to the energized conductor and the receiving point using the relationship curve.

[0102] If the rate of change of the induced electromotive force excited by the received transient electromagnetic field is below the threshold before the early time threshold and above the threshold after the late time threshold, then the low-resistance anomaly is located on the side of the receiving point away from the energized conductor.

[0103] If the rate of change of the induced electromotive force excited by the received transient electromagnetic field is lower than the threshold before the early time threshold and after the late time threshold, the low-resistance anomaly is located on the side of the energized conductor away from the receiving point.

[0104] If the rate of change of the induced electromotive force excited by the received transient electromagnetic field is higher than the threshold before the early time threshold and higher than the threshold after the late time threshold, then the low-resistance anomaly is located between the energized conductor and the receiving point.

[0105] in conclusion:

[0106] Through theoretical research, numerical simulation, and analysis of measured data, a detailed study was conducted on transient electromagnetic imaging technology suitable for long mining faces, leading to the following conclusions:

[0107] (1) Compared with the traditional same-side transmission and reception working mode, the transient electromagnetic perspective detection method of opposite-side transmission and reception can observe low-resistivity anomalies in a smaller range, and the impact of the anomalies on early data is hundreds or even thousands of times greater than that of same-side observation data.

[0108] (2) The transient electromagnetic method of same-side transmission and reception cannot distinguish the left and right dual-anomaly model established in this paper, while the boundary of the two low-resistance anomalies can be clearly distinguished in the early segment of the opposite-side transmission and reception data.

[0109] (3) The late data received on the same side and the opposite side have the same characteristics, namely, they are all caused by the diffusion of the secondary field over time. The early data is affected by the initial secondary field generated by the instantaneous disappearance of the primary magnetic field of the transmission loop. The diffusion of the secondary field near the non-transmission coil is caused by the diffusion of the secondary field. Therefore, the transient electromagnetic vision technology has a higher ability to identify abnormal objects in the early data.

[0110] The above-described embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited thereto. Any simple changes or equivalent substitutions of the technical solutions that can be obviously obtained by those skilled in the art within the scope of the technology disclosed in the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for detecting the location of a low-resistivity anomaly in a mine working face, characterized in that, include: A live conductor is laid in a roadway on one side of the mine working face, and a receiving point is set in a roadway on the other side to receive the induced electromotive force generated when the live conductor is de-energized. The induced electromotive force and time are used as the vertical axis and the horizontal axis, respectively, to construct the relationship curve between induced electromotive force and time, and early time threshold and late time threshold are set on the time axis. The position of the low-resistivity anomaly at the mine working face relative to the energized conductor and the receiving point is determined using the relationship curve. If the rate of change of the induced electromotive force excited by the received transient electromagnetic field is lower than the early induced electromotive force rate of change threshold before the early time threshold and higher than the late induced electromotive force rate of change threshold after the late time threshold, then the low-resistance anomaly is located on the side of the receiving point away from the energized conductor. If the rate of change of the induced electromotive force excited by the received transient electromagnetic field is lower than the threshold before the early time threshold and after the late time threshold, the low-resistance anomaly is located on the side of the current-carrying conductor away from the receiving point. If the rate of change of the induced electromotive force excited by the received transient electromagnetic field is higher than the early induced electromotive force rate of change threshold before the early time threshold and higher than the late induced electromotive force rate of change threshold after the late time threshold, then the low-resistance anomaly is located between the energized conductor and the receiving point.

2. The method for detecting the location of a low-resistivity anomaly in a mine working face according to claim 1, characterized in that, Also includes: The location of the two low-resistivity anomalies in the mine is determined by using the induced electromotive force data received by the receiving point before the early time threshold. If the rate of change of the induced electromotive force received by the receiving point before the early time threshold is negative, then the current receiving point is facing a low-resistivity anomaly. If the rate of change of the induced electromotive force received by the receiving point before the early time threshold is positive, then the current receiving point is located in the middle of the left and right low-resistivity anomalies. If the rate of change of the induced electromotive force received by the receiving point before the early time threshold is at the positive-negative boundary, then the receiving point is located at the boundary of the low-resistivity anomaly along the measurement line direction.

3. The method for detecting the location of a low-resistivity anomaly in a mine working face according to claim 1, characterized in that, The energized conductor is a long strip-shaped transmitting return line.

4. The method for detecting the location of a low-resistivity anomaly in a mine working face according to claim 3, characterized in that, The dimensions of the elongated emission loop are 1000m × 5m.

5. The method for detecting the location of a low-resistivity anomaly in a mine working face according to claim 3, characterized in that, The extreme values ​​of the induced electromotive force generated by the elongated emission loop are concentrated around the elongated emission loop before the early time threshold. The extreme values ​​of the induced electromotive force generated by the elongated emission loop concentrate at the center of the elongated emission loop after the late time threshold.

6. The method for detecting the location of a low-resistivity anomaly in a mine working face according to claim 3, characterized in that, The magnetic field strength generated by the elongated emission loop in the surrounding space is: Where B is the magnetic flux density, I is the current, a is the distance from the point to the line, and μ is the permeability of the medium.

7. The method for detecting the location of a low-resistivity anomaly in a mine working face according to claim 6, characterized in that, In free space, the magnetic permeability μ of the medium is: μ=μ0=4π×10 -7 Where μ0 is the vacuum permeability.

8. The method for detecting the location of a low-resistivity anomaly in a mine working face according to claim 1, characterized in that, The rate of change of the induced electromotive force is between -73.49% and 24.94%.

9. A system for detecting the location of a low-resistivity anomaly in a mine working face, characterized in that, include: The information acquisition module is used to lay an energized conductor in one roadway of the mine working face and set a receiving point in the other roadway to receive the induced electromotive force generated when the energized conductor is de-energized. The relationship curve construction module is used to construct the relationship curve between induced electromotive force and time, with induced electromotive force and time as the vertical and horizontal axes, respectively, and to set early time thresholds and late time thresholds on the time axis. Judgment module; Used to determine the position of a low-resistivity anomaly at the mine working face relative to the energized conductor and the receiving point using the relationship curve; If the rate of change of the induced electromotive force excited by the received transient electromagnetic field is below the threshold before the early time threshold and above the threshold after the late time threshold, the low-resistance anomaly is located on the side of the receiving point away from the energized conductor. If the rate of change of the induced electromotive force excited by the received transient electromagnetic field is lower than the threshold before the early time threshold and after the late time threshold, the low-resistance anomaly is located on the side of the current-carrying conductor away from the receiving point. If the rate of change of the induced electromotive force excited by the received transient electromagnetic field is higher than the threshold before the early time threshold and higher than the threshold after the late time threshold, then the low-resistance anomaly is located between the energized conductor and the receiving point.

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