Ultra-wide coal face bottom plate electrical tomography method

Abstract

The invention belongs to the technical field of geophysical exploration transient electromagnetic detection, and particularly relates to an ultra-wide coal face bottom plate electrical tomography method, which adopts a transient electromagnetic perspective detection technology, and realizes full-coverage imaging of a working face bottom plate electrical structure through alternate arrangement of transmitting-receiving roadways and dynamic data fusion. A time-space mapping relation is established by combining a smoke ring effect diffusion model, and aiming at the ultra-wide coal face with the width larger than or equal to 300 m; according to the fine detection of the hidden geological structure of the bottom plate, bidirectional detection and mesh generation are adopted, a single-side detection blind area is eliminated through roadway transposition of a transmitting end and a receiving end, and omni-directional imaging of the bottom plate is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of geophysical prospecting transient electromagnetic detection, and in particular relates to an electrical tomography method for the floor of an ultra-wide coal mining face. Background Art

[0002] With advances in mining technology, the width of modern coal mine working faces has expanded from the traditional 100-200 meters to over 300 meters, placing higher demands on the accuracy of geological structure detection. Accurately identifying hidden floor structures (such as water-bearing fissures and sinkholes) is crucial for safe mining, but existing technologies struggle to meet the high-resolution detection requirements of ultra-wide working faces.

[0003] At present, the detection of hidden structures mainly relies on two methods: drilling and geophysical exploration (geophysical exploration):

[0004] (1) Drilling: Although it can directly verify the structure, it is costly and inefficient. Moreover, the view from a single hole cannot reflect the spatial distribution of the structure, and the coverage is limited.

[0005] (2) Geophysical exploration:

[0006] Channel wave seismic method: It can detect faults with a fault distance greater than 1 / 3 of the coal thickness and changes in coal seam thickness, but it relies on explosive sources, has strict requirements on mine ventilation, is labor-intensive and costly.

[0007] Radio wave perspective method: convenient construction and high resolution, but the electromagnetic waves attenuate quickly and the perspective distance is insufficient, making it difficult to cover ultra-wide working surfaces over 300 meters.

[0008] In response to the above problems, transient electromagnetic perspective technology has been proposed: a transmitting coil is arranged on one side of the tunnel to excite a pulsed magnetic field, and the induced eddy current field signal is received on the other side. This method utilizes the strong penetrability of low-frequency transient electromagnetic fields, and has a detection distance far exceeding that of high-frequency radio waves. It does not require explosive sources and is adaptable to complex underground environments. However, the existing transient electromagnetic perspective technology has the following problems: theoretical model limitations: the traditional uniform half-space assumption is difficult to characterize complex electrical structures, resulting in insufficient imaging resolution; one-sided detection blind area: the edge signal of the ultra-wide working face is severely attenuated, and a single transmission-reception is difficult to cover the entire area; lack of interpretation method: lack of efficient and reliable data processing means, it is difficult to accurately locate the boundaries of geological anomalies. For this reason, the present invention proposes a method for electrical tomography of the floor of an ultra-wide coal mining working face. Summary of the Invention

[0009] The purpose of the present invention is to provide an electrical tomography method for the floor of an ultra-wide coal mining working face. The method adopts transient electromagnetic perspective detection technology, and realizes full coverage imaging of the electrical structure of the working face floor through alternating arrangement of transmitting and receiving tunnels and dynamic data fusion; combines the smoke ring effect diffusion model, establishes a time-space mapping relationship, and uses bidirectional detection and grid subdivision for the refined detection of hidden geological structures in the floor of an ultra-wide coal mining working face (width ≥ 300 meters). By exchanging the transmitting and receiving tunnels, the blind spots on one side of the detection are eliminated, and all-round imaging of the floor is realized.

[0010] The technical solutions adopted by the present invention are as follows:

[0011] A method for electrical tomography of the floor of an ultra-wide coal mining face comprises the following steps:

[0012] Step 1: Data acquisition: Alternately use transmitting coils and magnetic probes in two lanes on both sides of the coal mining face. A three-component magnetic sensor is used as the magnetic probe. Continuously record the attenuation curve of the vertical component (Hz) of the magnetic field and the attenuation curve of the induced electromotive force to obtain forward and reverse detection data sets.

[0013] Step 2: Data processing; including the following steps:

[0014] Step 201: Preliminary processing: obtaining existing geological, hydrological, and well logging data of the mining area to gain a preliminary understanding of the distribution of electrical characteristics of the formation;

[0015] Step 202: Preprocessing: Filter the raw Hz data to eliminate early transitions and late background noise. Since the format of the collected raw data is not suitable for processing, the data transmitted to the central control console is formatted and interference distortion points are removed. After completion, the data is stored in order from the earliest measurement date to the latest measurement date or from the largest distance between the measurement line and the working surface to facilitate the next step of processing. The Hz data of each measuring point is normalized to a unit current response of 10A to eliminate the influence of emission current fluctuations.

[0016] Step 203: Apparent resistivity and detection range calculation: select time slices at equal logarithmic intervals, calculate the diffusion range through smoke ring diffusion, and for time t_i, use the smoke ring diffusion radius formula:

[0017]

[0018] Calculate the diffusion range of the smoke ring at different times t, that is, the detection range, and then calculate the induced electromotive force using the formula:

[0019]

[0020] Calculate the apparent resistivity of the detection range.

[0021] The initial conductivity is σ0; the corresponding background resistivity is ρ0, μ=4π×10 -7 H / m, solve for apparent resistivity and get t 1 1-2 , t 2 1-2 , t 3 1-2 , t n1-2 , t 1 2-1 , t 2 2-1 , t 3 2-1 , t n 2-1 The apparent resistivity value within each detection range grid in the magnetic field line area at that moment;

[0022] Step 204: Overlapping area determination: For each detection area, if it is covered by both the forward detection area and the reverse detection area, it is marked as an overlapping area; the resistivity arithmetic average of the overlapping area is performed:

[0023]

[0024] For non-overlapping area resistivity: only positive coverage: directly use ρ 1→2 ; Only reverse coverage: directly use ρ 2→1 ;

[0025] Step 205: Data interpretation: First, the resistivity calculation value is used to observe the resistivity change characteristics of the ultra-wide coal mining working face floor. In order to accurately delineate the abnormal area of ​​the ultra-wide coal mining working face floor, the low resistivity layer is analyzed through the resistivity change cross-section diagram, and then the abnormal area is delineated to achieve full coverage and fine detection.

[0026] Preferably, in step 1, there are two ways to set up the transmitting coil and the magnetic probe:

[0027] The first method is to set up a transmitting coil in one roadway on both sides of the coal mining face, and set up an array of equally spaced magnetic probes in the other roadway. After the forward detection data set is acquired, the transmitting coil and magnetic probe in the roadway are swapped, and the reverse detection data set is acquired again after the swap.

[0028] The second method: transmitting coils and magnetic probes distributed in an equidistant array are set in the two tunnels on both sides of the coal mining face. The radiation coil in the current tunnel is used simultaneously with the magnetic probe in the other tunnel. The magnetic probe in the current tunnel is used simultaneously with the radiation coil in the other tunnel. This scheme uses them alternately without the need to disassemble and reassemble the radiation coil and magnetic probe.

[0029] Preferably, the transmitter outputs a square wave current to the transmitting coil, and the magnetic probe is used as a measuring point to continuously record the attenuation curve of the vertical component (Hz) of the magnetic field and the attenuation curve of the induced electromotive force to obtain a forward detection data set, and then the transmitting coils and magnetic probes in the two lanes are exchanged, and the data acquisition steps are repeated to obtain a reverse detection data set. The transmitting coil adopts a rectangular transmitting coil, and the transmitting coil is wound with a multi-core copper cable; the peak current output by the transmitter is 10A; several magnetic probes are arranged in an array with a spacing of 10m; after exchanging the transmitting coils and magnetic probes in the two lanes, the coil parameters are kept consistent with the transmitting current; the forward detection data set and the reverse detection data set are stored as time series files.

[0030] The technical effects achieved by the present invention are:

[0031] The present invention adopts transient electromagnetic perspective detection technology, and realizes full coverage imaging of the electrical structure of the working face floor through the alternating arrangement of transmitting and receiving tunnels and dynamic data fusion; combined with the smoke ring effect diffusion model, a time-space mapping relationship is established, and for the refined detection of hidden geological structures in the floor of ultra-wide coal mining working faces (width ≥ 300 meters), two-way detection and grid subdivision are adopted. By exchanging the transmitting and receiving end tunnels, the single-sided detection blind spot is eliminated and all-round imaging of the floor is realized.

[0032] In response to the problems of existing transient electromagnetic perspective technology in the application of ultra-wide coal mining working faces, such as large single-sided detection blind areas, low lateral resolution, and insufficient geological boundary identification accuracy, the present invention proposes a floor electrical tomography method based on the fusion of bidirectional transient electromagnetic perspective and dynamic resistivity, aiming to achieve high-precision, full-coverage detection of hidden geological structures in the floor of ultra-wide working faces of more than 300 meters, providing reliable geological protection for safe and efficient mining in coal mines. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a schematic diagram of the observation system of the present invention;

[0034] Figure 2 This is a schematic diagram of the bidirectional full coverage detection of the bottom plate in the present invention;

[0035] Figure 3 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0036] In order to make the purpose and advantages of the present invention more clearly understood, the present invention is described in detail below with reference to the following examples. It should be understood that the following text is only used to describe one or more specific embodiments of the present invention and does not strictly limit the scope of protection of the present invention.

[0037] Example 1:

[0038] like Figure 1 as well as Figure 3 As shown, a method for electrical tomography of the floor of an ultra-wide coal mining face comprises the following steps:

[0039] Step 1: Data acquisition: Alternately use transmitting coils and magnetic probes in two lanes on both sides of the coal mining face. A three-component magnetic sensor is used as the magnetic probe. Continuously record the attenuation curve of the vertical component (Hz) of the magnetic field and the attenuation curve of the induced electromotive force to obtain forward and reverse detection data sets.

[0040] Step 2: Data processing; including the following steps:

[0041] Step 201: Preliminary processing: obtaining existing geological, hydrological, and well logging data of the mining area to gain a preliminary understanding of the distribution of electrical characteristics of the formation;

[0042] Step 202: Preprocessing: Filter the original forward detection data set and the reverse detection data set to eliminate early transition process and late background noise. Since the format of the collected original data is not suitable for processing, the data transmitted to the central control console is formatted and interference distortion points are removed. After completion, the data is stored in order from the earliest measurement date to the latest measurement date or from the largest distance between the measurement line and the working surface at the time of measurement to facilitate the next step of processing. The Hz data of each measuring point is normalized to a unit current response of 10A to eliminate the influence of transmission current fluctuations.

[0043] In the present invention, the preliminary processing of data: since the format of the collected original data is not suitable for processing, the data transmitted to the central control console is format converted and interference distortion points are eliminated. After completion, the data is stored in order from the earliest to the latest measurement date or from the largest to the smallest distance between the measuring line and the working surface during measurement, so as to facilitate the next step of processing;

[0044] Step 203: Apparent resistivity and detection range calculation: select time slices at equal logarithmic intervals, calculate the diffusion range through smoke ring diffusion, and for time t_i, use the smoke ring diffusion radius formula:

[0045]

[0046] Calculate the smoke ring diffusion range at different times t, that is, the detection range, such as Figure 2 In, t 1 1-2 , t 2 1-2 , t 3 1-2 , t n 1-2 , t 1 2-1 , t 2 2-1 , t 3 2-1 , t n 2-1 The detection area within the magnetic field lines shown at the time, Figure 2 The area above the middle dotted line is the entire detection range, and the induced electromotive force is calculated using the formula:

[0047]

[0048] Calculate the apparent resistivity of the detection range.

[0049] The initial conductivity is σ0; the corresponding background resistivity is ρ0, μ=4π×10 -7 H / m, solve for the apparent resistivity and we get Figure 2 in;t 1 1-2 , t 2 1-2 , t 3 1-2 , t n1-2 , t 1 2-1 , t 2 2-1 , t 3 2-1 , t n 2-1 The apparent resistivity value within each detection range grid in the magnetic field line area at that moment;

[0050] In this method, resistivity calculation begins by first calculating the resistivity within the area where one lane transmits and the other lane receives, using the time-dependent resistivity calculation formula for the split-loop device and the equivalent current loop horizontal diffusion calculation formula. A sign change in the received data indicates that the smoke ring has reached the boundary. The resistivity within this area is then calculated using data from the other lane transmitting and the other lane receiving data. Full coverage of the detection area is achieved, with the resistivity averaged within overlapping areas. Single-sided data is used within non-overlapping areas.

[0051] Step 204: Overlapping area determination: For each detection area, if it is covered by both the forward detection area and the reverse detection area, it is marked as an overlapping area; the resistivity arithmetic average of the overlapping area is performed:

[0052]

[0053] For non-overlapping area resistivity: only positive coverage: directly use ρ 1→2 ; Only reverse coverage: directly use ρ 2→1 ;

[0054] Step 205: Data interpretation: First, the resistivity calculation value is used to observe the resistivity change characteristics of the ultra-wide coal mining working face floor. In order to accurately delineate the abnormal area of ​​the ultra-wide coal mining working face floor, the low resistivity layer is analyzed through the resistivity change cross-section diagram, and then the abnormal area is delineated to achieve full coverage and fine detection.

[0055] Imaging display: Imaging is performed based on the obtained apparent resistivity value to circle the abnormal area of ​​the bottom plate.

[0056] The present invention adopts bidirectional detection and grid subdivision, eliminates the blind spot of unilateral detection by transposing the transmitting and receiving lanes, and realizes full coverage of the grid within the detection range.

[0057] Preferably, in step 1, the transmitting coil and the magnetic probe are arranged as follows: a transmitting coil is arranged in a roadway on both sides of the coal mining working face, and magnetic probes are arranged in an array with equal spacing in another roadway; after the forward detection data set is acquired, the transmitting coil and the magnetic probe in the roadway are interchanged, and after the interchange, the reverse detection data set is acquired again; assuming that the roadway is 1000m long and 5m wide, and the working face is 300m long, a 1000m×5m long rectangular transmitting coil is laid along the ground in one of the roadways.

[0058] Preferably, the transmitter outputs a square wave current to the transmitting coil, and the magnetic probe is used as a measuring point to continuously record the attenuation curve of the vertical component (Hz) of the magnetic field and the attenuation curve of the induced electromotive force to obtain a forward detection data set. Then, the transmitting coils and the magnetic probes in the two lanes are exchanged, and the data acquisition steps are repeated to obtain a reverse detection data set. The transmitting coil adopts a rectangular transmitting coil, and the transmitting coil is wound with a multi-core copper cable; the peak current output by the transmitter is 10A; several magnetic probes are arranged in an array with a spacing of 10m; after exchanging the transmitting coils and the magnetic probes in the two lanes, the coil parameters are kept consistent with the transmitting current; the forward detection data set and the reverse detection data set are stored as time series files.

[0059] Example 2:

[0060] The difference from Example 1 is that the transmitting coil and the magnetic probe are set up differently. In Example 2, transmitting coils and magnetic probes distributed in an equidistant array are set up in the two tunnels on both sides of the coal mining working face. The radiation coil in the current tunnel is used simultaneously with the magnetic probe in the other tunnel. The magnetic probe in the current tunnel is used simultaneously with the radiation coil in the other tunnel. This solution is used alternately without the need to disassemble and reassemble the radiation coil and the magnetic probe.

[0061] The foregoing is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications are also within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described or explained herein shall, unless otherwise specified or limited, be implemented in accordance with conventional means in the art.

Claims

1. A method for electrical tomography of the floor of an ultra-wide coal mining face, characterized by: The following steps are involved: Step 1: Data acquisition: Alternately use transmitting coils and magnetic probes in two lanes on both sides of the coal mining face. A three-component magnetic sensor is used as the magnetic probe. Continuously record the attenuation curve of the vertical component (Hz) of the magnetic field and the attenuation curve of the induced electromotive force to obtain forward and reverse detection data sets. Step 2: Data processing; including the following steps: Step 201: Preliminary processing: obtaining existing geological, hydrological, and well logging data of the mining area to gain a preliminary understanding of the distribution of electrical characteristics of the formation; Step 202: Preprocessing: Filter the original forward detection data set and the reverse detection data set to eliminate early transition process and late background noise; convert the format of the data transmitted to the central control console and remove interference distortion points. After completion, the data are stored in order from the earliest measurement date to the latest measurement date or from the largest distance between the measurement line and the working surface at the time of measurement; Step 203: Apparent resistivity and detection range calculation: select time slices at equal logarithmic intervals, calculate the diffusion range through smoke ring diffusion, and for time t_i, use the smoke ring diffusion radius formula: Calculate the diffusion range of the smoke ring at different times t, that is, the detection range, and then calculate the induced electromotive force using the formula: Calculate the apparent resistivity of the detection range. The initial conductivity is σ0; the corresponding background resistivity is ρ0, μ=4π×10 -7 H / m, solve for apparent resistivity and get: t 11-2 , t 21-2 , t 31-2 , t n1-2 , t 12-1 , t 22-1 , t 32-1 , t n2-1 The apparent resistivity value within each detection range grid in the magnetic field line area at that moment; Step 204: Overlapping area determination: For each detection area, if it is covered by both the forward detection area and the reverse detection area, it is marked as an overlapping area; the resistivity arithmetic average of the overlapping area is performed: For non-overlapping area resistivity: only positive coverage: directly use ρ 1→2 ; Only reverse coverage: directly use ρ 2→1 ; Step 205: Data interpretation: First, the resistivity calculation value is used to observe the resistivity change characteristics of the floor of the ultra-wide coal mining face, and the low-resistivity layer is analyzed through the resistivity change cross-section diagram. Then, the abnormal area is circled to achieve full coverage and fine detection.

2. The method for electrical tomography of the floor of an ultra-wide coal mining face according to claim 1, characterized in that: In step 1, a transmitting coil is set in one lane on both sides of the coal mining face, and a magnetic probe distributed in an array with equal intervals is set in the other lane.

3. The method for electrical tomography of the floor of an ultra-wide coal mining face according to claim 1, characterized in that: In step 1, transmitting coils and magnetic probes distributed in an equidistant array are set in the two tunnels on both sides of the coal mining face. The radiation coil in the current tunnel is used simultaneously with the magnetic probe in the other tunnel, and the magnetic probe in the current tunnel is used simultaneously with the radiation coil in the other tunnel.

4. The method for electrical tomography of the floor of an ultra-wide coal mining face according to claim 2 or 3, characterized in that: The transmitter outputs a square wave current to the transmitting coil. The magnetic probe is used as a measuring point to continuously record the attenuation curve of the vertical component (Hz) of the magnetic field and the attenuation curve of the induced electromotive force to obtain a forward detection data set. Then, the transmitting coils and magnetic probes in the two lanes are exchanged, and the data acquisition steps are repeated to obtain a reverse detection data set.

5. The method for electrical tomography of the floor of an ultra-wide coal mining face according to claim 4, characterized in that: In step 1, the transmitting coil is a rectangular transmitting coil, and the transmitting coil is wound with a multi-core copper cable; the peak current output by the transmitter is 10A; and the plurality of magnetic probes are arranged in an array with a spacing of 10m.

6. The method for electrical tomography of the floor of an ultra-wide coal mining face according to claim 5, characterized in that: In step 1, after exchanging the transmitting coils and magnetic probes in the two lanes, the coil parameters and the transmitting current are kept consistent.

7. The method for electrical tomography of the floor of an ultra-wide coal mining face according to claim 6, characterized in that: The forward detection data set and the reverse detection data set are stored as time series files.

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