A transient electromagnetic perspective detection method for a coal mining face water-containing distribution area

Abstract

The present application belongs to the field of exploration geophysics, and particularly relates to a transient electromagnetic perspective detection method for water-bearing area in a coal mining face. Measurement points are arranged in two roadways of the coal mining face. A transmitting wire frame is fixed at a first point of a transmitting roadway for transmission, and a receiving wire frame receives at different positions in a certain range of the opposite roadway. The transmitter and the receiver are consistent in time and can synchronously collect. After the first point transmits, the transmitting coil is moved to a next position for transmission at a second point. Similarly, the receiving coil can receive in a certain range of the opposite roadway. After the second point transmits, the third point transmits, and so on until the transmission of the whole roadway is completed. The transmitting roadway and the receiving roadway are exchanged, and the above steps are repeated until the whole face is detected, and then inversion calculation is performed. The present application can solve the problems of low positioning accuracy of water-bearing abnormal body and inaccurate abnormal shape discrimination of the existing mine transient electromagnetic method.

Description

Technical Field

[0001] This invention belongs to the field of exploration geophysics, and in particular relates to a transient electromagnetic perspective detection method for water-bearing distribution areas in coal mining faces. Background Technology

[0002] To ensure safe coal mining, geophysical methods are generally used to investigate the hidden geological structures and water content within the working face after its formation.

[0003] Currently, radio wave imaging and channel wave seismic methods are commonly used to detect hidden geological structures inside the working face; while transient electromagnetic methods, audio-frequency electromagnetic imaging, and DC resistivity methods are commonly used to detect water content inside the working face. The transient electromagnetic method has the advantages of convenient construction, less spatial restriction, and sensitive response to water-bearing anomalies, and is the most widely used for water detection inside the working face.

[0004] However, during the construction of the mine transient electromagnetic method, it is shielded by the metal anchor mesh in the roadway. The shielding effect of the metal anchor mesh will have the following impacts on the use of the mine transient electromagnetic method: inaccurate spatial positioning of water-bearing anomalies, inconsistency between the interpreted shape of water-bearing anomalies and the actual situation, and inaccurate time-depth conversion. Summary of the Invention

[0005] The technical problem solved by this invention is to provide a transient electromagnetic perspective detection method for water-bearing distribution areas in coal mining faces, so as to solve the problems of low positioning accuracy and inaccurate identification of abnormal morphology in existing transient electromagnetic methods for mines.

[0006] The basic solution provided by this invention is: a transient electromagnetic perspective detection method for water-bearing distribution areas in coal mining faces, comprising:

[0007] S1: Measuring points are arranged at preset intervals in the intake and return air roadways of the coal mining face, and one of the intake or return air roadways is selected as the transmitting roadway, and the corresponding roadway is selected as the receiving roadway.

[0008] S2: Arrange the transmitter and transmitter frame in the transmission lane, and arrange the receiver and receiver frame in the receiving lane, and perform time synchronization processing on the transmitter and receiver;

[0009] S3: The transmitter supplies pulse current to the transmitting frame at a fixed time interval at the first transmitting point in the transmitting roadway, generating a secondary induced field in the coal mining face. During the pulse current turn-off period, the receiver receives the change of the secondary induced field over time in the area of ​​the receiving roadway.

[0010] S4: After the first transmission point is detected, the transmitter moves to the second transmission point to supply pulse current. The receiver receives the secondary induction field in the area of ​​the receiving tunnel, completing the detection of the second transmission point. This process continues until the entire transmission tunnel is detected.

[0011] S5: Swap the transmitting roadway and the receiving roadway, and repeat S1-S4 until the entire coal mining face has been detected.

[0012] S6: The data obtained from the two roadway explorations are combined using the inversion method to determine the water content distribution in the coal mining face.

[0013] Furthermore, the inversion method described in S6 includes:

[0014] Based on the principle of equivalent eddy current, a calculation model of the transient electromagnetic response of a water-bearing sphere under full-space conditions in a coal mining face is constructed.

[0015] Based on the particle swarm optimization algorithm, transient electromagnetic nonlinear inversion under full-space conditions of the coal mining face is performed using a transient electromagnetic response calculation model.

[0016] Furthermore, the calculation model for the transient electromagnetic response of a water-bearing sphere under full-space conditions in a coal mining face, based on the principle of equivalent eddy currents, is specifically as follows:

[0017] Calculation of background field: A uniform model of the entire space is preset. When the transmitter supplies a pulse current, the excitation source at t <t of The pulse current is constant at t=t of If the pulse current is turned off at a certain moment, then the magnetic field at a distance r from the source point after the turn-off is:

[0018]

[0019] Among them, u x u y u z Let m be the unit vector in the x, y, and z directions, t be the emitted magnetic moment, t be the time, and r be the distance from the observation point to the source point.

[0020] The Where μ is the magnetic permeability and σ is the electrical conductivity;

[0021] Abnormal field calculation: With the pulse current turned off, the available current in the induced magnetic field of the water-containing sphere with diameter d in the secondary induced field is i(t). The magnetic field generated by the current in the square ring with side length a is equivalently represented as:

[0022] i(t) = 0e -t / τ

[0023] The magnetic field it generates is:

[0024]

[0025] Where τ=σμ0d 2 / 4 2 d = 0.7, i0 = 0.6H 1n a and r′ are the distances from the center of the sphere to the observation point, and H is the distance from the center of the sphere to the observation point. 1n The expression is:

[0026]

[0027] in, This represents the distance from the source point to the center of the sphere;

[0028] Total field calculation:

[0029]

[0030]

[0031] Where S represents the area of ​​the receiving coil.

[0032] Furthermore, the transient electromagnetic nonlinear inversion under full-space conditions of the coal mining face based on the particle swarm inversion algorithm combined with the transient electromagnetic response calculation model specifically includes:

[0033] Acquire detection data, perform equivalent eddy current forward modeling on the detection data, and calculate the fitness. The formula for calculating the fitness is as follows:

[0034]

[0035] Among them, U obs U represents the set of observation data. forward Represents the forward-modeled dataset;

[0036] If the fitness requirement is met, the calculation terminates and the result is output. If the fitness requirement is not met, the iterative formula is used for calculation, specifically:

[0037]

[0038]

[0039] Where i represents the particle index in the detection dataset, and k represents the iteration number. V represents the position of the i-th particle in the k-th iteration. i () Let ω represent the iteration increment of the i-th particle in the k-th iteration, ω be the inertia factor, c1 and c2 be the learning factors, and r1 and r2 be two random numbers uniformly distributed between (0, 1). G represents the optimal position of particle i in the first k iterations. (k) The optimal position of all particles in the first k iterations;

[0040] After the iteration is completed, the equivalent eddy current forward modeling calculation is performed again. If the fitness meets the requirements, the iteration calculation is terminated and the result is output. If the fitness does not meet the requirements, the next iteration calculation is performed until the fitness meets the requirements and the result is output.

[0041] Furthermore, the transmitting frame is vertically arranged in the tunnel, and the normal of the transmitting frame is perpendicular to the tunnel direction; the receiving frame is vertically arranged in the tunnel, and the normal of the receiving frame is perpendicular to the tunnel direction.

[0042] Advantages of this invention: This invention utilizes the perspective detection theory to deploy a transmitter in one roadway of the coal mining face and receive secondary induction fields at different locations within a region in another roadway. By leveraging the propagation and diffusion characteristics of transient electromagnetic fields and employing a perspective detection construction method, the transmitter and receiver positions are determined, the propagation path of electromagnetic waves is restricted, and the cross-constraint of multiple paths is combined. Based on the data obtained from the detection, equivalent eddy current forward modeling and particle swarm inversion are performed, thereby achieving the detection and precise location of water-bearing anomalies within the coal mining face. Attached Figure Description

[0043] Figure 1 This is a flowchart of an embodiment of the present invention;

[0044] Figure 2 This is a diagram showing the layout of measuring points within the coal mining face in an embodiment of the present invention;

[0045] Figure 3 This is a flowchart of the particle swarm inversion algorithm in an embodiment of the present invention. Detailed Implementation

[0046] The following detailed description illustrates the specific implementation methods:

[0047] To ensure safe coal mining, after the coal face is formed, geophysical methods are needed to investigate the hidden geological structures and water content within the face. Currently, methods such as mine transient electromagnetic methods, audio-visual radiometry, and DC resistivity methods are used to investigate the water content within the face. Mine transient electromagnetic valves are the most widely used due to their advantages of convenient construction, minimal space constraints, and sensitive response to water-bearing anomalies. However, during construction, mine transient electromagnetic valves are shielded by metal anchor mesh in the roadway, resulting in inaccurate spatial positioning of water-bearing anomalies, inconsistencies between the interpreted shape of the anomaly and the actual situation, and inaccurate time-depth conversion. To address this, an analogy with radiometry is used, employing a "one-to-many" transmission method for transient electromagnetic detection. By utilizing the cross-constraint property of the transmission method, the problems of low positioning accuracy of water-bearing anomalies, inaccurate anomaly morphology identification, and insufficient effective detection depth in conventional detection methods are solved.

[0048] Therefore, this application proposes a transient electromagnetic perspective detection method for the water-bearing distribution area of ​​a coal mining face, and the embodiments are basically as follows. Figure 1 and Figure 2 As shown, it includes:

[0049] S1: Measuring points are arranged at preset intervals in the intake and return air roadways of the coal mining face, and one of the intake or return air roadways is selected as the transmitting roadway, and the corresponding roadway is selected as the receiving roadway. In this embodiment, the measuring points are arranged at intervals of 10m. The measuring points in the return air roadway are numbered 0-100#, and the measuring points in the intake air roadway are numbered 500-600#.

[0050] S2: A transmitter and a transmitter frame are arranged in the transmitting tunnel, and a receiver and a receiver frame are arranged in the receiving tunnel. Timing synchronization is performed on the transmitter and receiver. In this embodiment, the transmitter frame is 3m × 3m, vertically arranged in the tunnel, with its normal perpendicular to the tunnel's direction. The receiver frame is also 3m × 3m, vertically arranged in the tunnel, with its normal perpendicular to the tunnel's direction.

[0051] Before the detection begins, accurate timing processing is performed on the transmitter and receiver to ensure that they can collect data synchronously.

[0052] S3: The transmitter supplies pulse current to the transmitting frame at a fixed time interval at the first transmitting point in the transmitting roadway, generating a secondary induced field in the coal mining face. During the pulse current turn-off period, the receiver receives the change of the secondary induced field over time in the area of ​​the receiving roadway.

[0053] At the start of detection, the transmitter first supplies a pulsed current to the transmitting frame at the first transmitting point, transmitting a secondary induced field from the transmitting frame into the opposite tunnel. This secondary induced field is a transient electromagnetic field. A receiving frame is deployed in the opposite tunnel, receiving the changes in the secondary induced field over time during the period when the pulsed current is turned off. Specifically, the receiving frame and receiver move within a certain range in the receiving tunnel to receive the secondary induced field emitted by the transmitting frame. The range of movement is the target detection length, such as... Figure 2 As shown, a transmitting frame emits a secondary induction field in a fan shape, and a receiving frame receives signals from 10 pre-set receiving points within the range of the fan-shaped secondary induction field.

[0054] S4: After the first transmission point is detected, the transmitter moves to the second transmission point to supply pulse current. The receiver receives the secondary induction field in the area of ​​the receiving tunnel, completing the detection of the second transmission point. This process continues until the entire transmission tunnel is detected.

[0055] S5: Swap the transmitting roadway and the receiving roadway, and repeat S1-S4 until the entire coal mining face has been detected.

[0056] S6: The data obtained from the two roadway explorations are combined using the inversion method to determine the water content distribution in the coal mining face.

[0057] The inversion method described in S6 includes: based on the equivalent eddy current principle, constructing a calculation model of the transient electromagnetic response of a water-bearing sphere under full-space conditions in a coal mining face;

[0058] Based on the particle swarm optimization algorithm, transient electromagnetic nonlinear inversion under full-space conditions of the coal mining face is performed using a transient electromagnetic response calculation model.

[0059] Specifically, based on the principle of equivalent eddy current, the calculation model for the transient electromagnetic response of a water-bearing sphere under full-space conditions in a coal mining face is constructed as follows:

[0060] Calculation of background field: A uniform model of the entire space is preset. When the transmitter supplies a pulse current, the excitation source at t <t of The pulse current is constant at t=t of If the pulse current is turned off at a certain moment, then the magnetic field at a distance r from the source point after the turn-off is:

[0061]

[0062] Among them, u x u y u z Let m be the unit vector in the x, y, and z directions, t be the emitted magnetic moment, t be the time, and r be the distance from the observation point to the source point.

[0063] The Where μ is the magnetic permeability and σ is the electrical conductivity;

[0064] Abnormal field calculation: With the pulse current turned off, the available current in the induced magnetic field of the water-containing sphere with diameter d in the secondary induced field is i(t). The magnetic field generated by the current in the square ring with side length a is equivalently represented as:

[0065] i(t) = 0e -t / τ

[0066] The magnetic field it generates is:

[0067]

[0068] Where τ=σμ0d 2 / 4 2 d = 0.7, i0 = 0.6H 1n a and r′ are the distances from the center of the sphere to the observation point, and H is the distance from the center of the 1n The expression is:

[0069]

[0070] in, This represents the distance from the source point to the center of the sphere;

[0071] Total field calculation:

[0072]

[0073]

[0074] Where S represents the area of ​​the receiving coil.

[0075] Based on the particle swarm optimization algorithm and combined with the transient electromagnetic response calculation model, the transient electromagnetic nonlinear inversion under full-space conditions of the coal mining face is specifically performed as follows:

[0076] Acquire probe data, perform equivalent eddy current forward modeling on the probe data, and calculate the fitness. Specifically, first read multi-time channel probe data U obs The probe data group is assumed to consist of m particles: x1, x2, ... x i ,…x m Each particle contains n unknown parameters, such as the diameter, conductivity, and spatial position of the water-containing sphere. The position of the i-th particle is randomly assigned as follows:

[0077]

[0078] Based on the aforementioned transient electromagnetic response calculation model, a full-space equivalent eddy current forward model is performed to calculate the fitness. The formula for calculating the fitness is as follows:

[0079]

[0080] Among them, U obs U represents the set of observation data. forward Represents the forward-modeled dataset;

[0081] If the fitness requirement is met, the calculation terminates and the result is output. If the fitness requirement is not met, the iterative formula is used for calculation, specifically:

[0082]

[0083]

[0084] Where i represents the particle index in the probe dataset, k represents the iteration number, k = 1, 2, ..., itermax, and itermax is the maximum number of iterations allowed in the particle swarm optimization process. This represents the position of the i-th particle during the k-th iteration. V i (k) V represents the iteration increment of the i-th particle in the k-th iteration. i (k) =(V i,1 (k) V i,2 (k) ,…,V i,n (k) ), where ω is the inertia factor, and:

[0085]

[0086] c1 and c2 are learning factors, usually taken as c1 = 2, and r1 and r2 are two random numbers uniformly distributed between (0, 1). G represents the optimal position of particle i in the first k iterations. (k) The optimal position of all particles in the first k iterations;

[0087] After each iteration, the equivalent eddy current forward modeling is performed again. If the fitness requirement is met, the iteration is terminated and the result is output. If the fitness requirement is not met, the next iteration is performed until the fitness requirement is met, and the result is output. Figure 3 This is a flowchart of the inversion process.

[0088] In this embodiment, the requirement is met if the error between the actual value and the theoretical value of fitness is within 1%.

[0089] Table 1 below shows the results of the pseudo-3D inversion using this application, which was iterated 100 times:

[0090] Table 1

[0091] Model parameters Theoretical value Range of values Inversion value Horizontal position x / m 50 -100～100 50.17 Vertical position z / m -80 -20～100 -79.93 diameter / m 60 10～100 60.41 σ / (S / m) 1 0.1～10 0.99

[0092] The inverted value, after 100 iterations, has an error of less than 1% compared to the theoretical value, thus demonstrating high accuracy and meeting the requirements for on-site detection.

[0093] The above are merely embodiments of the present invention. Commonly known structures and characteristics are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, under the guidance of this application, improve and implement this solution in combination with their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A transient electromagnetic induction detection method for water-bearing distribution areas in coal mining faces, characterized in that: include: S1: Measuring points are arranged at preset intervals in the intake and return air roadways of the coal mining face, and one of the intake or return air roadways is selected as the transmitting roadway, and the corresponding roadway is selected as the receiving roadway. S2: Arrange the transmitter and transmitter frame in the transmission lane, and arrange the receiver and receiver frame in the receiving lane, and perform time synchronization processing on the transmitter and receiver; S3: The transmitter supplies pulse current to the transmitting frame at a fixed time interval at the first transmitting point in the transmitting roadway, generating a secondary induced field in the coal mining face. During the pulse current turn-off period, the receiver receives the change of the secondary induced field over time in the area of ​​the receiving roadway. S4: After the first transmission point is detected, the transmitter moves to the second transmission point to supply pulse current. The receiver receives the secondary induction field in the area of ​​the receiving tunnel, completing the detection of the second transmission point. This process continues until the entire transmission tunnel is detected. S5: Swap the transmitting roadway and the receiving roadway, and repeat S1-S4 until the entire coal mining face has been detected. S6: The data obtained from the two roadway explorations are combined using an inversion method to determine the water content distribution in the coal mining face; The inversion method described in S6 includes: Based on the principle of equivalent eddy current, a calculation model of the transient electromagnetic response of a water-bearing sphere under full-space conditions in a coal mining face is constructed. Based on the particle swarm inversion algorithm, combined with the transient electromagnetic response calculation model, transient electromagnetic nonlinear inversion under full-space conditions of the coal mining face is performed. The transient electromagnetic response calculation model of a water-bearing sphere under full-space conditions in a coal mining face, based on the equivalent eddy current principle, is specifically as follows: Calculation of background field: A pre-defined uniform model of the entire space is used. When the transmitter supplies a pulsed current, the excitation source is in... The pulse current is constant during the time period. ,exist If the pulse current is turned off at a certain moment, then the magnetic field at a distance r from the source point after the turn-off is: in, , , for , , The unit vector of direction. To emit magnetic moments, For time, The distance from the observation point to the source point; The ,in, Permeability, Electrical conductivity; Abnormal field calculation: Pulse current is turned off, and the diameter in the secondary induced field is... The available current for inducing the magnetic field of a water-containing sphere is The side length is The magnetic field generated by the square ring current is equivalent to that generated by the current in the ring, and the equivalent current is expressed as: The magnetic field it generates is: in, , , , The distance from the center of the sphere to the observation point. The expression is: in, This represents the distance from the source point to the center of the sphere; Total field calculation: Where S represents the area of ​​the receiving coil.

2. The transient electromagnetic induction detection method for water-bearing distribution areas in coal mining faces according to claim 1, characterized in that: The transient electromagnetic nonlinear inversion under full-space conditions of the coal mining face based on the particle swarm inversion algorithm combined with the transient electromagnetic response calculation model is specifically as follows: Acquire detection data, perform equivalent eddy current forward modeling on the detection data, and calculate the fitness. The formula for calculating the fitness is as follows: in, Represents the set of observation data. Represents the forward-modeled dataset; If the fitness requirement is met, the calculation terminates and the result is output. If the fitness requirement is not met, the iterative formula is used for calculation, specifically: in, This indicates the index of the particle in the detection dataset. Indicates the number of iterations. Indicates the first During the nth iteration, the 1st The position of each particle. Indicates the first During the nth iteration, the 1st The iteration increment of each particle, Inertia factor , As a learning factor, , Given two random numbers uniformly distributed between (0, 1), Indicates the preceding In the next iteration The optimal position of particle number 1 For the front The optimal position of all particles in the next iteration; After the iteration is completed, the equivalent eddy current forward modeling calculation is performed again. If the fitness meets the requirements, the iteration calculation is terminated and the result is output. If the fitness does not meet the requirements, the next iteration calculation is performed until the fitness meets the requirements and the result is output.

3. The transient electromagnetic induction detection method for water-bearing distribution areas in coal mining faces according to claim 1, characterized in that: The transmitting frame is vertically arranged in the tunnel, and the normal of the transmitting frame is perpendicular to the tunnel direction; the receiving frame is vertically arranged in the tunnel, and the normal of the receiving frame is perpendicular to the tunnel direction.

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