Method for detecting fault displacement of coal face fault based on combination of reflection and transmission slot waves

Abstract

The invention discloses an underground coal mine fault displacement slot wave earthquake quantitative detection method, and a high-precision detection result can be obtained due to the fact that the distance between the underground coal mine fault displacement slot wave earthquake quantitative detection method and a detection target body is closer in mine seismic exploration. The characteristics that traditional slot wave detection is sensitive to fault position, direction and coal thickness change response are utilized, parameters capable of accurately exploring fault displacement are extracted through collected seismic records, reference is provided for coal mine production, production efficiency is improved, and losses caused by coal seam breakage and loss are reduced. And the specific fault displacement of the fault is directly given, and the detection precision is good. Through mutual verification from multiple angles, the accuracy of fault displacement judgment is improved, fine detection of detection is improved, exploration, mining and safety management work of mines are guided, and the method is suitable for large-scale industrial use and popularization.

Description

Technical Field

[0001] The present invention belongs to the technical field of geophysical exploration, and in particular relates to a method for detecting fault distances in a coal mining face based on the combination of reflection and transmission channel waves. Background Art

[0002] my country is a major coal producer and user. With the continuous advancement of intelligent coal mine construction, the safety and efficiency of coal mine production are constantly improving. The safety and production problems caused by small structures inside the working face are becoming more and more prominent. It is crucial to identify the underground structure of coal mines for construction design, reserve estimation, geological disaster prevention and coal mining.

[0003] In existing technologies, channel-wave seismic exploration in coal mines is achieved by placing excitation and receiving points directly around the working face being detected, which is closer to the target and avoids the influence of complex surface low-velocity zones. This significantly improves detection accuracy and reliability. Channel-wave seismic exploration is currently the most widely used and effective detection technology in mine seismic exploration. Channel-wave seismic exploration in coal mines has made significant progress in detecting faults and coal thickness distribution within the coal mining face. However, in terms of detecting fault throw, dip, and properties, both transmitted and reflected channel waves can obtain the direction of the fault and roughly determine whether the fault throw is greater than half the coal thickness based on the relative amplitude. However, they cannot quantitatively determine the fault throw, fault properties, and cross-section dip. This is still a qualitative and semi-quantitative detection method that cannot meet the needs of precise detection. There is an urgent need for relevant research on theories and methods. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for detecting fault distances in coal mining working faces based on a combination of reflection and transmission slot waves, so as to solve the problem that the fault detection methods in the prior art cannot meet the requirements of fine detection.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A method for detecting fault distance in a coal mining face based on a combination of reflection and transmission channel waves comprises the following steps:

[0007] Step 1: Establish an observation system based on the channel wave seismic data of the area to be measured;

[0008] Step 2: Use the channel wave seismic inversion method to obtain the distribution of all faults in the area to be measured;

[0009] Step 3: arbitrarily select a fault in the area to be measured, determine the channel wave dispersion equation of the selected fault, and obtain the corresponding theoretical dispersion curve;

[0010] Step 4: determine the amplitude of the fundamental mode L wave in the selected fault according to the rock-coal-rock three-layer symmetry model;

[0011] Step 5, calculate the reflection coefficient R of the reflected wave and transmitted wave within the selected fault SS and the transmission coefficient T SS ;

[0012] Step 6, calculate the equivalent reflection coefficient R according to the parameters obtained in Steps 4 and 5;

[0013] Step 7, determine the preferred seismic record according to the distribution of all faults, and select the quantitative detection area in the preferred seismic record in combination with the theoretical dispersion curve obtained in Step 3 according to the distribution of observation points within the observation system;

[0014] Step 8, convert the energies of the transmitted wave and reflected wave within the quantitative detection area into amplitudes respectively, and compensate the converted amplitudes to the corresponding positions in the quantitative detection area;

[0015] Step 9, obtain the corresponding equivalent reflection coefficient R1 by using the compensated amplitudes to get the theoretical characteristic parameter R'; perform a linear regression equation of R1 with respect to the wavelength to get the characteristic parameter R'1, and further obtain the fault throw size of the corresponding fault in the quantitative detection area;

[0016] Step 10, use the above method to traverse all faults in the area to be measured, and obtain the fault throw size of each fault.

[0017] The present invention also has the following features:

[0018] Further, Step 3 includes the following sub-steps:

[0019] Step 31, arbitrarily select a fault, and use the following formula to obtain the slot wave dispersion equation of the selected fault;

[0020]

[0021] where ω represents the circular frequency;

[0022] d represents the semi-coal thickness;

[0023] C L represents the phase velocity of the love-type slot wave;

[0024] ν s1 and ν s2 respectively represent the shear wave velocities of the surrounding rock and coal rock;

[0025] μ1 and μ2 respectively represent the shear moduli of the surrounding rock and coal rock;

[0026] n = 0, 1, 2,... represents the order of the vibration mode;

[0027] Step 32, obtain the corresponding theoretical dispersion curve according to the slot wave dispersion equation of this fault.

[0028] Further, in step 4, according to the three-layer symmetric model of rock - coal - rock, determine the amplitude f of the fundamental mode L-wave within the selected fault A , as follows:

[0029]

[0030] where β1 and β2 represent functions of the wavelength;

[0031] z represents the depth of the SH-wave in the z-direction;

[0032] A represents a coefficient related to the seismic source.

[0033] Further, step 5 includes the following sub-steps:

[0034] Step 51, use the following formula to calculate the reflection coefficient R of the reflected wave and the transmitted wave within the selected fault SS and the transmission coefficient T SS :

[0035]

[0036]

[0037] where ρ1 and ρ2 respectively represent the densities of the surrounding rock and the coal seam within the selected fault.

[0038] Further, in step 6, according to the amplitude f of the fundamental mode L-wave within the selected fault A and the reflection coefficient R SS and the transmission coefficient T SS , use the following formula to calculate the equivalent reflection coefficient R:

[0039]

[0040] where a and b respectively represent the positions of the top and bottom of the coal seam after the selected fault is offset;

[0041] dz represents the differentiation with respect to z.

[0042] Further, step 8 includes the following sub-steps:

[0043] Step 81, use the following formula to convert the transmitted wave energy and the reflected wave energy of the selected fault into amplitudes respectively:

[0044]

[0045] where A i represents the amplitude, and E i represents the energy; Step 82, use the following formula to calculate the two-way attenuation TL of the channel wave within the selected fault:

[0046]

[0047] Among them, x represents the one-way distance from the seismic source to the receiving point in the observation system;

[0048] λ A represents the wavelength of the fundamental mode Rayleigh wave;

[0049] δ represents the absorption attenuation rate, δ = αλ; λ represents the wavelength;

[0050] α represents the absorption coefficient of the medium absorption effect;

[0051] Step 83: Combine the two-way attenuation of the trough wave in the selected fault to compensate the amplitude at the corresponding position of the selected fault.

[0052] Furthermore, Step 9 includes the following sub-steps:

[0053] Step 91: Use the compensated amplitude to obtain its equivalent reflection coefficient R1;

[0054]

[0055] Among them, E r 、E t respectively represent the energies of the transmitted wave and the reflected wave of the selected fault; Step 92: In the quantitative detection area, take the derivative of R obtained in Step 6 with respect to the wavelength and then take the average to obtain the theoretical characteristic parameter R′ of the monotonic curve with respect to the fault throw h;

[0056] Step 93: In the quantitative detection area, obtain the linear regression equation for the wavelength as follows:

[0057]

[0058] Among them, the characteristic parameter R′1 is the coefficient of the first-order term of the linear regression equation. Let R′ = R′1, and use the one-to-one correspondence between the characteristic parameter R′1 and the fault throw h to determine the fault throw h.

[0059] Furthermore, during the process of traversing all the faults in the area to be measured, when the petrophysical properties of the working face in the area to be measured change greatly, repeat Steps 3 - 9;

[0060] When the petrophysical properties of the working face in the area to be measured are stable, select an untraversed fault and repeat Steps 7 - 9.

[0061] Furthermore, the great change in the petrophysical properties of the working face in the area to be measured includes the following situations:

[0062] The lithology of the roof and floor in the area to be measured changes, such as from sandstone to mudstone;

[0063] The coal thickness property in the area to be measured changes;

[0064] There is a sunken column in the area to be measured, which changes the physical properties of the strata near the fault;

[0065] The degree of coal rock fragmentation in the area to be measured changes.

[0066] Compared with the prior art, the present invention has the following technical effects:

[0067] In the method for quantitatively detecting the fault throw of trough waves in underground coal mines of the present invention, since mine seismic exploration is closer to the target body to be detected, high-precision detection results can be obtained. At the same time, due to the sensitivity of the sensor, the dispersion signals in the seismic waves can be effectively received. These signals contain detailed structural information in the coal seam, which provides reliable data support for predicting the fault throw. Utilizing the characteristics of traditional trough wave detection that is sensitive to the fault position, strike, and coal thickness change, through the collected seismic records, parameters that can accurately detect the fault throw are extracted, providing a reference for coal mine production, improving production efficiency, and reducing losses caused by problems such as coal seam loss. The specific fault throw is directly given and has good detection accuracy.

[0068] The method for quantitatively detecting the fault throw of trough waves in underground coal mines of the present invention accurately detects the fault throw without increasing additional costs and the workload of technical personnel, expanding the application scope of trough wave detection technology. It provides a more accurate geological basis for the reasonable layout of the working face in the mining area, and also provides strong technical support for the safe production and efficient mining of coal mines. Combining with the geological information in the mining area and verifying each other from multiple angles can improve the accuracy of judging the fault throw size and enhance the fine detection, thus guiding the exploration, mining, and safety management work of the mine, and being suitable for large-scale industrial use and promotion. Brief Description of the Drawings

[0069] Figure 1 is the flow chart of the method for quantitatively detecting the fault throw of trough waves in underground coal mines of the present invention;

[0070] Figure 2 is the theoretical dispersion curve graph in an embodiment of the present invention;

[0071] Figure 3 is the amplitude distribution function graph of different frequencies in an embodiment of the present invention;

[0072] Figure 4 is the fault mode relationship graph in an embodiment of the present invention;

[0073] Figure 5 is the relationship graph between the wavelength λ and the reflection coefficient R in an embodiment of the present invention;

[0074] Figure 6This is a CT image of the working surface and slot wave in one embodiment of the present invention.

[0075] Figure 7 This is a transmission energy pickup diagram of a certain channel in one embodiment of the present invention;

[0076] Figure 8 is a picking diagram of characteristic parameter R′1 at H1 in one embodiment of the present invention;

[0077] Figure 9 This is a quantitative diagram of the break distance in one embodiment of the present invention;

[0078] Figure 10 It is a distribution diagram of fault distance along fault strike in one embodiment of the present invention. DETAILED DESCRIPTION

[0079] It should be noted that, unless otherwise specified, all methods in the present invention adopt methods known in the prior art. For example, the channel wave seismic inversion method adopts a known method.

[0080] Specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made on the basis of the technical solution of this application fall within the protection scope of the present invention.

[0081] The purpose of this embodiment is to provide a method for quantitatively detecting fault pitch in underground coal mines using channel wave seismic analysis, addressing production issues caused by unclear identification of fault pitch elements in coal mines. Channel waves undergo energy conversion when passing through a fault, with some energy being transmitted and some being reflected. By analyzing and identifying the specific response characteristics of reflected and transmitted channel waves as they pass through a fault, information such as the fault's location, strike, and coal seam thickness can be detected. Therefore, conventional channel wave seismic technology is used to explore the fault's location, strike, and coal seam thickness.

[0082] At the same time, due to the strong dispersion characteristics of channel waves, the amplitudes of wavelets of different frequencies vary significantly in depth distribution. When crossing a fault, the reflection areas vary due to the varying fault throws, resulting in different proportions of reflected and transmitted channel wave energy. By combining information such as the shear and longitudinal wave velocities of the coal seam and surrounding rock, density, and coal thickness, the distribution relationship between reflected and transmitted channel wave energy at different fault throws can be determined.

[0083] Extract the energy of the reflected slot wave and the transmitted slot wave according to the principles of vertical incidence of slot waves, clear dispersion curves, and concentrated energy. Since slot waves form converted waves at the fault plane when passing through a fault, the energy is distributed to the reflected slot wave and the transmitted slot wave according to the transmission relationship. Considering the effects of wavefront diffusion, dispersion attenuation, and absorption attenuation of the medium, etc., perform energy compensation on the extracted energy to restore the energy distribution relationship affected by the original fault. Determine the fault throw size by matching with the equivalent reflection coefficient obtained from theoretical calculations. Then, combined with the geological information in the mining area, verify each other from multiple angles to improve the accuracy of fault throw size identification, so as to guide the exploration, mining, and safety management work of the mine.

[0084] As Figure 1 shown, a method for detecting the fault throw of a coal mining face based on the combination of reflected and transmitted slot waves includes the following steps:

[0085] Step 1, establish an observation system according to the slot wave seismic data of the area to be measured;

[0086] Step 2, use the slot wave seismic inversion method to obtain the distribution of all faults in the area to be measured;

[0087] Both Step 1 and Step 2 are conventional methods in this field and will not be elaborated here.

[0088] Step 3, arbitrarily select a fault in the area to be measured, determine the slot wave dispersion equation of the selected fault, and obtain the corresponding theoretical dispersion curve. The theoretical dispersion curve is as shown in Figure 2 ;

[0089] Step 4, determine the amplitude of the fundamental mode L wave in the selected fault according to the three-layer symmetric model of rock - coal - rock;

[0090] Step 5, calculate the reflection coefficient R S′ of the reflected wave and the transmitted wave in the selected fault and the transmission coefficient T SS ;

[0091] Step 6, calculate the equivalent reflection coefficient R according to the parameters obtained in Steps 4 and 5;

[0092] Step 7, determine the preferred seismic record according to the distribution of all faults, and select the quantitative detection area in the preferred seismic record in combination with the theoretical dispersion curve obtained in Step 3 according to the distribution of observation points in the observation system;

[0093] Step 8, convert the energies of the transmitted wave and the reflected wave in the quantitative detection area into amplitudes respectively, and compensate the converted amplitudes to the corresponding positions in the quantitative detection area;

[0094] Step 9: Obtain the corresponding equivalent reflection coefficient R1 using the compensated amplitude to get the theoretical characteristic parameter R′; perform a linear regression equation on R1 with respect to the wavelength to obtain the characteristic parameter R′1, and further obtain the fault throw size of the fault corresponding to the quantitative detection area.

[0095] Step 10: Use the above method to traverse all the faults in the area to be measured and obtain the fault throw size of each fault.

[0096] Specifically, step 3 includes the following sub - steps:

[0097] Step 31: Arbitrarily select a fault and use the following formula to obtain the slot - wave dispersion equation of the selected fault;

[0098]

[0099] where ω represents the circular frequency;

[0100] d represents the semi - coal thickness;

[0101] C L represents the love - type slot - wave phase velocity;

[0102] v s1 and v s2 respectively represent the shear wave velocities of the surrounding rock and coal - rock;

[0103] μ1 and μ2 respectively represent the shear moduli of the surrounding rock and coal - rock;

[0104] n = 0, 1, 2,... represents the order of the vibration mode, where when n = 0, it is the fundamental vibration mode, and when n>0, it is the higher - order vibration mode;

[0105] The above data are all contents that can be directly determined or directly obtained.

[0106] Step 32: Obtain the corresponding theoretical dispersion curve according to the slot - wave dispersion equation of the fault.

[0107] Specifically, in step 4, for the selected fault, take the displacement field of the SH - wave that satisfies the wave equation and substitute it into the rock - coal - rock three - layer symmetric model v:

[0108]

[0109] where β1 and β2 are expressed as the following formula:

[0110]

[0111] Substitute the displacement field of the SH - wave into the boundary conditions, and then determine the following parameters:

[0112]

[0113] Step 42: Obtain the amplitude f of the fundamental mode L-wave within the selected fault according to the above coefficients A , as follows:

[0114]

[0115] A represents the coefficient related to the seismic source and is directly determined by the above formula.

[0116] As Figure 3 shown, the amplitude of the fundamental Love trough wave is related to frequency and vertical position. The amplitude shows a trend of concentrating from the surrounding rock to the coal seam as the frequency increases. Vertically, the amplitude is symmetrically distributed on both sides with respect to the center of the coal seam and rapidly decays from the center of the coal seam to both sides. Since the coal seam is a non-rigid body, its energy is also distributed in the rock formation. Usually, the amplitude decays to 0 at one wavelength. Since the low-frequency component in the rock formation is much higher than the high-frequency component, when it passes through the fault and enters the coal seam, it will cause the low-frequency component of the transmitted trough wave to be significantly enhanced, and the larger the fault throw, the more significant the low-frequency component should be.

[0117] In step 5, use v s1 , ν s2 to solve for the reflection coefficient R SS and the transmission coefficient T SS .

[0118] Since the Love trough wave is a trough wave formed by the constructive interference of two SH waves in different directions in the coal seam, the particle vibration direction is perpendicular to the wave propagation direction and only vibrates in the horizontal plane. Therefore, the calculation formula in step 5 is also determined under the condition of normal incidence.

[0119] Specifically, step 5 includes the following sub-steps:

[0120] Step 51: Use the following formula to calculate the reflection coefficient R SS of the reflected wave and the transmission coefficient T SS in the selected fault:

[0121]

[0122]

[0123] where ρ1 and ρ2 respectively represent the densities of the surrounding rock and the coal seam in the selected fault.

[0124] Specifically, in step 6, use the amplitude distribution function for calculation to obtain the equivalent reflection coefficient R under different fault throws;

[0125] According to the amplitude f A of the fundamental mode L-wave in the selected fault and the reflection coefficient R SS and the transmission coefficient T SS , substitute them into the following formula to calculate the equivalent reflection coefficient R:

[0126]

[0127] Among them, a and b respectively represent the positions of the top and bottom of the coal seam after the selected fault is offset;

[0128] dz represents the differential with respect to z.

[0129] Such as Figure 4 As shown, the Love trough wave propagates along the ray direction in a medium with a coal thickness of 2d, vertically incident on a fault with a vertical offset of h, and is affected by the fault to form a reflected wave and a transmitted wave.

[0130] Due to the fault offset, part of the energy of the incident wave enters the rock formation from the coal seam, and part of the energy enters the coal seam from the rock formation. Therefore, the energies of the reflected wave and the transmitted wave in the coal seam are not conserved, and the degree of energy leakage is related to the fault offset and the physical properties of the strata. Therefore, the fault offset size can be calculated based on the characteristics of energy leakage, and the equivalent reflection coefficient is used to describe the energy leakage characteristics to calculate the fault offset size.

[0131] According to the above formula, a theoretical curve cluster of "wavelength λ - equivalent reflection coefficient R" under different fault offsets h can be obtained, such as Figure 5 shown.

[0132] Figure 6 It is a specific example of the working face and the trough wave CT imaging situation. S represents the shot point number, H represents the fault offset prediction point number, R represents the geophone point number. The red dots in the figure represent the shot point positions, the green triangles represent the geophone point positions, the red squares represent the fault offset prediction point positions, the white dashed lines represent the positions and distributions of the predicted trough wave faults, the white lines represent the connections between the received points of the predicted reflected trough waves and the transmitted trough waves, and the intersection of the white line and the white dashed line is the fault offset prediction point. The geophone points on the working face are arranged at intervals of 10 m in the middle of the two side roadways, the excitation points are excited at intervals of 20 m, the selected area is 530 m long and 250 m wide. The trough wave reflection CT imaging results show that a fault with an offset less than the coal thickness is detected at about 50 m from the north side.

[0133] Specifically, in step 7, according to all the fault distribution situations obtained in step 2, the preferred seismic records are determined, and based on the fault distribution situations and the distribution of the observation points in the observation system, combined with the preferred seismic records, the records with clear dispersion curves and concentrated energy relative to the theoretical dispersion curves are found (the preferred records are as Figure 7 shown), and then the corresponding transmitted and reflected energies are determined; the frequency band with the strongest transmitted and reflected energies and the highest resolution among these records is selected as the dominant frequency band, and the dominant frequency band is used as the quantitative detection area.

[0134] Specifically, in step 8, according to the positional relationship between the receiving points of the transmitted wave and the reflected wave energy in the observation system and the selected fault, the transmitted wave energy and the reflected wave energy are compensated.

[0135] First, convert the energy into amplitude. Since the trough wave propagation is confined in the coal seam and approximately propagates in a two-dimensional space with a cylindrical wavefront, the amplitude will decay according to x. -1 / 2 The dispersion of the trough wave causes its wave train to continuously spread out with the increase of the propagation distance and the amplitude of the trough wave to continuously decrease. Due to the dispersion phenomenon, the amplitude of the trough wave will decay according to x. -1 / 2 Decay, and the amplitude of the Airy phase decays according to x. -1 / 3 Decay.

[0136] Generally, it is considered that due to the attenuation caused by the absorption effect of the formation medium during the propagation process, the amplitude of the trough wave will decay according to Decay. Combining the wavefront diffusion, dispersion attenuation, and absorption attenuation of the medium, the converted amplitude is compensated to the fault position.

[0137] Furthermore, step 8 includes the following sub-steps:

[0138] Step 81, use the following formula to convert the transmitted wave energy and the reflected wave energy of the selected fault into amplitudes respectively:

[0139]

[0140] where A i represents the amplitude, and E i represents the energy;

[0141] Step 82, use the following formula to calculate the two-way attenuation of the trough wave within the selected fault:

[0142]

[0143] where x represents the one-way distance from the seismic source to the target; since the receiving points of the reflected wave and the transmitted wave are not in the same place, compensation needs to be carried out separately.

[0144] λ A represents the wavelength of the fundamental mode Airy phase;

[0145] δ represents the absorption attenuation rate, δ = αλ;

[0146] α represents the absorption coefficient of the medium absorption effect;

[0147] In the above formula, the first term on the right is related to the cylindrical wavefront diffusion and geometric dispersion, and the second term is related to the absorption attenuation.

[0148] Step 83, combine the two-way attenuation of the trough wave within the selected fault and compensate the amplitude at the corresponding position of the selected fault.

[0149] Specifically, step 9 includes the following sub-steps:

[0150] Step 91: Using the compensated amplitude, calculate its equivalent reflection coefficient R1;

[0151]

[0152] Among them, E r and E t respectively represent the energies of the transmitted wave and the reflected wave of the selected fault;

[0153] The amplitude and the energy can be directly converted through step 81, and there is actually no difference between them.

[0154] Step 92: In the quantitative detection area, take the derivative of R with respect to the fundamental mode Airy phase wavelength and then average it to obtain the theoretical characteristic parameter R′ of the monotonic curve with respect to the fault throw h;

[0155] In the quantitative detection area, take the derivative of R with respect to the wavelength λ and then average it to obtain the theoretical characteristic parameter R′. R′ is a monotonic curve with respect to the fault throw h. Since the picked-up energy is discrete data, a linear regression equation is obtained for R1 with respect to the fundamental mode Airy phase wavelength within the dominant frequency band. Figure 8 It is the pick-up diagram of the characteristic parameter R′1 at the example H1. Using this pick-up result, the fault throw size can be obtained in the fault throw quantitative relationship.

[0156] Step 93: In the quantitative detection area, obtain a linear regression equation for the fundamental mode Airy phase wavelength, as follows:

[0157]

[0158] Among them, the characteristic parameter R′1 is the coefficient of the first-order term of the linear regression equation. Let R′ = R′1, and the fault throw h is determined by using the one-to-one correspondence between the theoretical characteristic parameter R′1 and the fault throw h. Other parameters in the above formula are the corresponding terms of the linear regression equation and are well-known information.

[0159] Figure 9 It is the fault throw quantitative diagram of a specific embodiment. The characteristic parameters of H1, H2, and H3 obtained from the measured data are 0.99, 1.18, and 2.39 respectively, and their corresponding fault throws are 4.75, 3.98, and 1.89 m respectively.

[0160] Figure 10 It is the diagram of the fault throw of a specific embodiment extending along the fault strike. The on-site actual exposure shows that there is a normal fault with a dip angle of 70° and a fault throw of 4.5 m here, which gradually sharpens along the strike direction. The predicted absolute error is 0.58 m and the relative error is 12.9%. It conforms to the predicted result.

[0161] In step 10, during the process of traversing all the faults in the area to be measured, when the petrophysical properties of the working face rock in the area to be measured are stable, select an untraversed fault and repeat steps 7-9;

[0162] Specifically, when the petrophysical properties of the working face rock in the area to be measured change greatly, repeat steps 3-9.

[0163] Furthermore, the great change in the petrophysical properties of the working face rock in the area to be measured includes the following situations:

[0164] The lithology of the roof and floor rocks in the area to be measured changes, such as from sandstone to mudstone;

[0165] The coal thickness in the area to be measured changes, for example, locally from a medium coal seam to a thick coal seam;

[0166] There are subsidence columns in the area to be measured, which change the physical properties of the strata near the faults;

[0167] The degree of coal rock fragmentation in the area to be measured changes. For example, from fragmented coal to granular coal and mylonite coal.

Claims

1. A method for detecting the fault throw of a coal mining face based on the combination of reflected and transmitted trough waves, characterized in that, It includes the following steps: Step 1: Establish an observation system based on the slot wave seismic data of the area to be measured; Step 2: Use the slot wave seismic inversion method to obtain the distribution of all faults in the area to be measured; Step 3: Arbitrarily select a fault in the area to be measured, determine the slot wave dispersion equation of the selected fault, and obtain the corresponding theoretical dispersion curve; Step 4: Determine the amplitude of the fundamental mode L wave in the selected fault according to the three-layer symmetric model of rock - coal - rock; Step 5, calculate the reflection coefficient R of the reflected wave and the transmitted wave within the selected fault SS and the transmission coefficient T SS ; Step 6: Calculate the equivalent reflection coefficient R according to the parameters obtained in Steps 4 and 5; Step 7: Determine the optimal seismic record according to the distribution of all faults, and select the quantitative detection area in the optimal seismic record by combining the theoretical dispersion curve obtained in Step 3 according to the distribution of observation points in the observation system; Step 8: Convert the transmitted wave and reflected wave energies in the quantitative detection area into amplitudes respectively, and compensate the converted amplitudes to the corresponding positions in the quantitative detection area; Step 9: Use the compensated amplitudes to obtain the corresponding equivalent reflection coefficient R1, and get the theoretical characteristic parameter R′; perform a linear regression equation of R1 with respect to the wavelength to obtain the characteristic parameter R′1, and further obtain the fault throw size of the corresponding fault in the quantitative detection area; Step 10: Traverse all faults in the area to be measured using the above method to obtain the fault throw size of each fault.

2. The fault throw detection method for the coal mining face based on the combination of reflected and transmitted trough waves as claimed in claim 1, wherein Step 3 includes the following sub - steps: Step 31: Arbitrarily select a fault and use the following formula to obtain the slot wave dispersion equation of the selected fault; where ω represents the circular frequency; d represents the semi - coal thickness; C L represents the phase velocity of the love-type trough wave; ν s1 and ν s2 respectively represent the shear wave velocities of the surrounding rock and coal-rock; μ1 and μ2 respectively represent the shear moduli of the surrounding rock and coal - rock; n = 0, 1, 2,... represents the order of the vibration mode; Step 32: Obtain the corresponding theoretical dispersion curve according to the slot wave dispersion equation of the fault.

3. The fault throw detection method for the coal mining face based on the combination of reflected and transmitted trough waves according to claim 1, wherein In step 4, according to the three-layer symmetric model of rock-coal-rock, determine the amplitude F of the fundamental mode L-wave within the selected fault, as follows: A , as shown in the following formula: where β1, β2 are functions of the wavelength; z represents the depth of the SH wave in the z - direction; A represents the coefficient related to the seismic source.

4. The fault throw detection method for the coal mining face based on the combination of reflected and transmitted trough waves as claimed in claim 1, wherein, Step 5 includes the following sub - steps: Step 51, calculate the reflection coefficient R of the reflected wave and the transmitted wave within the selected fault using the following formula SS and the transmission coefficient T SS : where ρ1, ρ2 respectively represent the densities of the surrounding rock and coal seam in the selected fault.

5. The fault throw detection method for the coal mining face based on the combination of reflected and transmitted trough waves as claimed in claim 1, wherein In step 6, according to the amplitude f of the fundamental mode L wave within the selected fault A and the reflection coefficient R SS and the transmission coefficient T SS , the equivalent reflection coefficient R is calculated using the following formula: where a, b respectively represent the positions of the top and bottom of the coal seam after the selected fault is offset; dz represents the differential of z.

6. The fault throw detection method for the coal mining face based on the combination of reflected and transmitted trough waves according to claim 1, characterized in that In Step 7, determine the optimal seismic record according to the distribution of all faults obtained in Step 2, and find the record with clear dispersion curve and concentrated energy relative to the theoretical dispersion curve based on the fault distribution and the distribution of observation points in the observation system, and then determine the corresponding transmitted and reflected energies; Select the frequency band with the strongest transmitted and reflected energies and the highest resolution among these records as the dominant frequency band, and take the dominant frequency band as the quantitative detection area.

7. The fault throw detection method for the coal mining face based on the combination of reflected and transmitted trough waves as claimed in claim 1, wherein Step 8 includes the following sub - steps: Step 81: Use the following formula to convert the transmitted wave energy and reflected wave energy of the selected fault into amplitudes respectively: Among them, A i represents the amplitude, and E i represents the energy; Step 82, use the following formula to calculate the two-way attenuation TL of the trough wave within the selected fault: where x represents the one - way distance from the seismic source to the receiving point in the observation system; λ A represents the fundamental mode Airy phase wavelength; δ represents the absorption attenuation rate, δ = αλ; λ represents the wavelength; α represents the absorption coefficient of the medium absorption effect; Step 83: Combine the two - way attenuation of the slot wave in the selected fault to compensate the amplitude at the corresponding position of the selected fault.

8. The fault throw detection method for the coal mining face based on the combination of reflection and transmission trough waves according to claim 1, characterized in that Step 9 includes the following sub - steps: Step 91: Use the compensated amplitude to obtain its equivalent reflection coefficient R1; Among them, E r and E t respectively represent the energies of the transmitted wave and the reflected wave of the selected fault; Step 92: Derive R obtained in Step 6 with respect to the wavelength in the quantitative detection area and then take the average to obtain the theoretical characteristic parameter R′ of the monotonic curve with respect to the fault offset h; Step 93, obtain a linear regression equation for the wavelength in the quantitative detection area as follows: Among them, the characteristic parameter R′1 is the coefficient of the first-order term of the linear regression equation. Let R′ = R′1, and determine the fault throw h using the one-to-one correspondence between the characteristic parameter R′1 and the fault throw h.

9. The fault throw detection method for the coal mining face based on the combination of reflected and transmitted trough waves according to claim 1, wherein In step 10, during the process of traversing all the faults in the area to be measured, when the physical properties of the working face rock in the area to be measured change greatly, repeat steps 3-9; When the physical properties of the working face rock in the area to be measured are stable, select an untraversed fault and repeat steps 7-9.

10. The fault throw detection method for the coal mining face based on the combination of reflected and transmitted trough waves according to claim 10, characterized in that The great change in the physical properties of the working face rock in the area to be measured includes the following situations: The lithology of the roof and floor in the area to be measured changes, such as from sandstone to mudstone; The coal thickness property in the area to be measured changes; There are subsidence columns in the area to be measured, which change the physical properties of the strata near the faults; The degree of coal and rock fragmentation in the area to be measured changes.

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