Direct wave suppression method for coal mine underground slot wave advanced detection data processing

Abstract

The invention discloses a direct wave suppression method for slot wave advanced detection, and the method comprises the following steps: 1, designing an observation system according to the characteristics of a target body, and collecting data according to the observation system; 2, reading the slot wave data acquired in the step 1, converting the slot wave data into a standard seismic data format, and writing the acquired information into a data trace header; 3, extracting the wave velocity of the slot wave through the fitting of a time curve; 4, selecting a sampling point interval corresponding to the wave arrival time of the direct groove wave and setting the sampling point interval to zero; and 5, diffracted wave processing and imaging are carried out on the data after zero setting in the step 4. The method has the main advantages that the direct waves can be efficiently and quickly suppressed, effective wave information is completely reserved, and the imaging effect is remarkably improved after the direct waves are suppressed through the method.

Description

Technical Field

[0001] This invention belongs to the field of underground seismic exploration technology in coal mines, and more specifically, relates to a direct wave suppression method for processing data from underground channel wave advance detection in coal mines. Background Technology

[0002] During coal mine tunnel excavation, unfavorable geological structures such as faults, collapse columns, and goafs may exist ahead. These structures can lead to gas accumulation, water inrush, and roof collapse, seriously threatening tunneling safety. Advanced channel wave detection can identify these anomalies in advance, providing safety assurance for tunneling operations, optimizing tunneling plans, rationally arranging tunneling direction and support methods, improving tunneling efficiency, and reducing tunneling costs.

[0003] Trough wave advance detection is a detection technique based on the propagation characteristics of seismic waves in coal seams. It is mainly used for advance detection of geological structures ahead during coal mine roadway excavation. Coal seams are characterized by low velocity and low density. When a seismic source is excited in the coal seam, the seismic waves undergo total reflection and total refraction at the roof and floor interfaces, superimposing and reverberating to form a trough wave. Trough waves are characterized by high energy, long propagation distance, easily identifiable waveform features, and significant dispersion characteristics. When the trough wave propagates along the roadway in the coal seam, if it encounters geological structures ahead, such as faults or collapse columns, it will form reflected and diffracted waves. By analyzing the propagation characteristics of these reflected and diffracted waves, spatial information such as the location and orientation of the geological structures ahead can be obtained.

[0004] The channel wave advance detection employs a "one-shot, multiple-receiver" observation system, with the seismic source and receiving points arranged along the horizontal centerline of the coal seam. Detectors record the propagation information of the channel waves, primarily including direct waves and reflected waves. Through methods such as migration imaging, the channel wave propagation information is transformed into images of the geological structure, thereby more accurately determining the location of faults and other anomalies, providing guidance for tunneling operations.

[0005] A direct wave is a seismic wave that travels directly from the epicenter to the detector without any reflection or refraction. Direct waves have a short propagation path and relatively low energy loss, therefore the amplitude of the direct wave received by the detector is relatively large. Reflected waves are waves in which some of the energy of a seismic wave is reflected back when it encounters an interface between different media during propagation. In channel wave advance detection, reflected waves are mainly those reflected back from the interfaces of abnormal geological structures such as faults and collapse columns in coal seams.

[0006] The propagation path of a reflected wave is longer than that of a direct wave because it needs to reach the reflecting interface before being reflected back. Therefore, the arrival time of a reflected wave is usually later than that of a direct wave, and the reflected wave loses some energy during reflection, resulting in a smaller amplitude. The reflected wave carries detailed information about the reflecting interface, such as the location, strike, and dip angle of the fault. By analyzing the propagation events and waveform characteristics of the reflected wave, the geological structure ahead of the tunnel can be inferred.

[0007] When a seismic wave travels from its source to a reflecting interface, only a portion of its energy is reflected back. The amplitude of the reflected wave depends on the reflection coefficient.

[0008] Where R is the reflection coefficient. and Let the density and wave velocity of the first medium be the product of the wave impedance of the first medium. and Let be the density and wave velocity of the second medium, and their product be the wave impedance of the second medium. Typically, the reflection coefficient is less than 1, meaning the amplitude of the reflected wave is less than the amplitude of the incident wave. Assume a longitudinal wave is excited in a coal seam and reflects upon encountering sandstone. The density of the coal seam is approximately 1.3 × 10³ kg / m³, and the longitudinal wave velocity is approximately 2000 m / s. The density of the sandstone is approximately 2.7 × 10³ kg / m³, and the longitudinal wave velocity in the sandstone is around 4000 m / s. The calculated reflection coefficient is 0.73, meaning the amplitude of the reflected wave is 0.73 times the amplitude of the incident wave.

[0009] Whether it's a direct wave or a reflected wave, seismic waves experience energy attenuation during propagation. Assuming the seismic wave travels a distance of... x The formula for seismic wave attenuation is: A

[0010] Where A is the amplitude of the longitudinal wave at a distance x. It is the initial amplitude of the longitudinal wave at the source. This is the attenuation coefficient of seismic waves, which is related to the physical properties of the medium and the frequency of the wave. Specifically, the attenuation coefficient of the P-wave is... The attenuation coefficient is usually 2, with a shear wave attenuation coefficient of 1 / 2 and a channel wave attenuation coefficient of 5 / 6 (these are empirical values ​​and vary depending on the medium).

[0011] During seismic wave propagation, the amplitude of the direct wave decreases due to energy attenuation as the propagation distance increases. Similarly, the amplitude of the reflected wave also decreases with increasing distance. Reflected waves typically have longer propagation paths than direct waves, meaning they experience greater energy loss during propagation. Furthermore, the energy of the reflected wave is also affected by the reflection coefficient, which determines the ratio of reflected wave energy to incident wave energy. Since the reflection coefficient is usually less than 1, the energy of the reflected wave is generally less than that of the direct wave.

[0012] In summary, the energy of reflected waves is affected by both the reflection coefficient and the attenuation coefficient, and the propagation path is longer than that of direct waves. Therefore, the energy of reflected waves is much smaller than that of direct waves. This energy difference has a significant impact on the imaging effect, making it difficult to clearly identify the structures in front of the tunnel during the imaging process.

[0013] In current data processing, suppressing direct waves is an important step, and the commonly used methods are frequency domain filtering and deconvolution.

[0014] Direct waves and reflected waves have different characteristics in the frequency domain, and bandpass filters are typically used to achieve this. However, there is a significant overlap in the frequencies of direct and reflected waves. After filtering, the energy proportion of the direct wave remains relatively large. Furthermore, improper selection of filter parameters during bandpass filtering can cause signal distortion and may introduce noise, thus affecting image quality.

[0015] Deconvolution is a technique to enhance signal resolution by suppressing redundant information in seismic waves, allowing for clearer identification of direct and reflected waves. Deconvolution processing can enhance the signal of reflected waves to some extent. Commonly used deconvolution methods include predictive deconvolution and radial trace transform deconvolution. However, predictive deconvolution is suitable for suppressing short-period multiple waves but causes significant damage to the effective wave; radial trace transform deconvolution is ineffective for dispersive signals. Each method has its limitations. Summary of the Invention

[0016] The purpose of this invention is to provide a direct wave suppression method for data processing in underground coal mine channel wave advance detection, to solve the problem of low imaging quality caused by the low effective wave signal-to-noise ratio in advance detection. The method of this invention can flexibly suppress high-energy direct waves according to different observation systems, thereby enhancing reflected waves and improving the imaging quality of advance detection.

[0017] To achieve the above objectives, the present invention employs the following technical methods (taking direct slot waves and reflected slot waves as examples): Step 1: Design the observation system and collect data according to the observation system.

[0018] Step 2: Read the channel wave data acquired in Step 1, convert it into a standard seismic data format, and write the acquired information into the data header.

[0019] Specifically, according to the standard seismic data format, the acquisition information such as sampling rate, number of sample points, shot number, shot point coordinates, trace number, and receiver coordinates are written into the data trace header. Based on the number of shot points and the number of detectors, the data trace header (sgyhead) is transformed into a three-dimensional array, which consists of trace header information, trace number, and shot number. Similarly, the data volume (sgydata) is transformed into a three-dimensional array, which consists of the number of sample points, trace number, and shot number.

[0020] Step 3: Extract the wave velocity of the trough wave by fitting the time-distance curve.

[0021] The velocity of the trough wave can be obtained by fitting the time-distance curve. The time-distance curve represents the functional relationship between the time required for the trough wave to propagate from the source point to the geophone and the distance between the source and receiver. It is usually plotted with the number of sample points on the vertical axis and the number of channels on the horizontal axis. When a shot is fired, multiple geophones typically receive the signals. The line connecting the sample index values ​​of the seismic waves arriving at each geophone is plotted on the seismic record. When the curve coincides with the phase axis connecting the first arrival or crest of a wave train, it reflects the wave velocity of that wave train. Figure 1 As shown. Figure 1 The system uses 42 detectors, with each detector receiving a total of 8,000 samples. Figure 1 The curve shown represents the time-distance curve of the reflector wave using the accurate velocity.

[0022] Specifically, the distance-time curve is related to the length of the shot-detector connection, the wave velocity, and the sampling rate. It requires calculating the distance from one or more shots to each detector, then reading the sampling rate from the data header, and finally, given an initial velocity, the formula for calculating the distance-time curve of the direct wave can be derived. The calculation method is as follows: (1) in, Here are the coordinates of the m-th shot point, in meters. Here are the coordinates of the nth detector, in meters. Let m be the distance between the shot point and the detector n, Fs be the sampling rate (number of samples per second), and v be the velocity of a wave train in meters per second. This represents the sample index value of the direct wave train received by all detectors when a certain shot point is fired.

[0023] After calculation, the time-distance curve is plotted on a single-shot recorder. By changing the velocity v, the time-distance curve is made to coincide with the phase axis or first arrival of the direct wave train. The velocity v at this time is the wave velocity of the wave train.

[0024] The time-distance curve of the reflected wave requires first calculating the coordinates of the virtual source of the m-th shot. Assume the coordinates of the virtual source are... Then, the sample index value of the reflected wave from the m-th shot received by the n-th detector can be obtained.

[0025] (2) This represents the sample index value of the reflected wave train received by all detectors when a certain shot point is fired. Figure 1 The mid-time distance curve coincides with the reflected trough wave train, and the velocity v at this time is the wave velocity of the trough wave.

[0026] Step 4: Obtain the time-distance curves of all wave trains when all shot points are fired, in order to determine the relationship between the direct wave and the reflected wave in terms of arrival time.

[0027] In slot wave lead detection technology, the shape of the time-distance curve is significantly affected by a variety of factors, which can be mainly summarized into the following two aspects: ① Observation System Design: The design of the observation system is influenced by the target depth; different target depths require different observation system parameters. These parameters include the number of shot points, the number of detectors, the shot distance, the track distance, and whether in-hole detectors are used. Differences in these parameters will result in different characteristics in the time-distance curves.

[0028] ② The attitude of the geological structures ahead of the tunnel: The attitude of the geological structures ahead of the tunnel also has a significant impact on the time-distance curve. Taking a fault as an example, different angles between the fault and the tunnel will lead to significant changes in the shape of the time-distance curve. Different structural attitudes mean that the wave propagation paths and reflection and refraction characteristics are different, thus affecting the shape of the time-distance curve.

[0029] Therefore, the time-distance curve for each shot needs to be calculated and compared with actual seismic records. Numerical simulations were performed to determine the impact of different observation systems and tectonic attitudes on the wave train arrival time. For example... Figures 2-5 As shown.

[0030] in, Figure 2 The diagrams show the ray paths when the number of shot points, the number of detectors, the shot distance, the track distance, and the presence or absence of detectors in the holes are changed, and numerical simulations are performed using these observation systems. Figure 3 To calculate the time-distance curves obtained from different observation systems. Figure 3 In the diagram, the vertical axis represents the sample index value, and the horizontal axis represents the number of detector channels. The upper portion, with a larger number of samples (i.e., later arrival times), represents the time-distance curve of the reflected trough wave, while the lower portion, with a smaller number of samples (i.e., earlier arrival times), represents the time-distance curve of the direct trough wave. Figure 3 It can be seen that, regardless of how the observation system changes, the direct trough wave and the reflected trough wave do not overlap in time.

[0031] Figure 4 The diagrams show ray paths when the angle between the fault and the tunnel direction is different, and numerical simulations are performed using these observation systems. Figure 4 The simulated parameters include a channel wave velocity of 1000 m / s, 20 shot points, a shot distance of 10 m, 30 geophone channels with a channel spacing of 10 m, 6 geophone channels in the borehole with a channel spacing of 10 m, and the angle between the fault and the tunnel gradually increases from 30 degrees to 90 degrees. Figure 5 The display shows the time-distance curves for all shot points. The vertical axis represents the number of sample points. The upper portion, with a larger number of sample points (i.e., later arrival times), represents the time-distance curve for the reflected trough wave, while the lower portion, with a smaller number of sample points (i.e., earlier arrival times), represents the time-distance curve for the direct trough wave. Simulations show that the arrival time of the reflected trough wave train is always later than that of the direct trough wave. In other words, under this observation system, the reflected trough wave and the direct trough wave do not overlap in time, regardless of the angle between the fault and the tunnel.

[0032] Step 5: Select the sample interval corresponding to the arrival time of the direct trough wave and set it to zero.

[0033] From the simulation in step four, we can see that: (1) changes in the observation system have almost no impact on the non-overlapping relationship between the direct trough wave and the reflected trough wave in time; (2) the larger the angle between the fault and the tunnel, the greater the difference in arrival time between the direct trough wave and the reflected trough wave. Therefore, we only need to calculate the arrival time of the direct trough wave and set the corresponding sample interval to zero. Specifically, as follows: ① Read the coordinates of all shot points and all detectors in the slot wave data head; ② Calculate the sample index value of the direct wave received by the nth detector when the mth shot is fired, according to formula (1) in step three; ③ Filter out The maximum sample index value in the middle. direct .

[0034] ④ Assume the slot wave data is sgydata(p,n,m), where p is the number of samples, n is the number of traces, and m is the number of shot points. For each trace in sgydata, calculate the 1:max... direct Set the value of the point to zero, that is: (3) In the formula, max direct This represents the sample index value indicating the maximum amplitude of the direct wave; the range of this index value is clearly defined. The reflected wave arrives at the detector later than the direct wave, therefore 1:max direct The signals between them only include information such as direct waves and random interference.

[0035] ⑤ The zeroed data is then processed for diffraction and imaged. This operation yields an image of the structure ahead of the tunnel, reflecting its size and location.

[0036] Compared with existing technologies, the main advantage of this invention is that it can efficiently and quickly suppress direct waves while fully preserving effective wave information. The imaging effect is significantly improved after suppressing direct waves using this method. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the time-distance curve of the reflection slot wave; Figure 2 It involves changing the simulated ray path diagram of the observation system. The parameters that are changed include the number of shot points (20 shots and 40 shots), shot distance (10 meters and 20 meters), track spacing (10 meters and 20 meters), and the presence or absence of aperture detectors. Figure 2 The simulation included the fault in front of the tunnel, the shot points and detectors arranged on the side of the tunnel, and the ray paths of the seismic waves reflected back from the fault received by all the detectors when the shot points were fired. Figure 3 It is the time-distance curve calculated after changing the observation system, with the vertical axis representing the number of sample points and the horizontal axis representing the number of channels. Figure 3 It contains the time-distance curves corresponding to the firing of all shot points. The upper sample points have larger index values, which are wave trains with later arrival times, while the lower sample points have smaller index values, which are wave trains with earlier arrival times. Figure 4 It is a simulated ray path diagram that changes the angle between the fault and the tunnel, with angles including 30 degrees, 45 degrees, 60 degrees, 75 degrees and 90 degrees. Figure 4 The simulation showed the path of rays reflected back from the fault when the angle of the fault in front of the tunnel changed. Figure 5 This is a schematic diagram of the time-distance curve calculated after changing the angle between the fault and the tunnel. The vertical axis represents the number of sample points, and the horizontal axis represents the number of tunnels. Figure 3 It contains the time-distance curves corresponding to the firing of all shot points. The upper sample points have larger index values, which are wave trains with later arrival times, while the lower sample points have smaller index values, which are wave trains with earlier arrival times. Figure 6 This is a comparison of imaging effects before and after suppressing direct waves. Figure 6 a represents the original data imaging result. Figure 6 b represents the imaging result after suppressing the direct wave, where the abnormal location is the area with a large gray value. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0039] The method for suppressing direct waves for leading detection of slot waves provided in this invention specifically includes the following steps: Step 1: Design an observation system based on the characteristics of the target body, and collect channel wave data according to the observation system; Step 2: Read the channel wave data acquired in Step 1, convert it to a standard seismic data format, and write the acquired information into the data header. Assume the data header is sgyhead and the data volume is sgydata. Write important information such as sampling rate, number of samples, shot number, shot coordinates, channel number, and receiver coordinates into the data header according to the standard seismic data format. Based on the number of shot points and detectors, transform the data header sgyhead into a three-dimensional array, representing the header information, channel number, and shot number. Similarly, transform the data volume sgydata into a three-dimensional array, representing the number of samples, channel number, and shot number.

[0040] Step 3: Extract the wave velocity of the trough wave by fitting the time-distance curve.

[0041] Step 31: Read the horizontal and vertical coordinates of the shot point and detector from the specified position in the data header (sgyhead), and store them in the arrays shot_axis and rec_axis; read the sampling rate from the data header. Fs Set the initial speed to 1000 meters per second. Step 32: Calculate the sample index values ​​of the direct wave train received by all detectors when a certain shot point is fired using the following formula; and then obtain the time-distance curve of the direct slot wave.

[0042] in, Here are the coordinates of the m-th shot point, in meters. Here are the coordinates of the nth detector, in meters. Let m be the distance between the shot point and the detector n, Fs be the sampling rate (number of samples per second), and v be the velocity of a wave train in meters per second. This represents the sample index value of the direct wave train received by all detectors when a certain shot point is fired.

[0043] Step 33: Plot the time-distance curve of the direct-arrival trough wave on a single-shot recorder. By changing the velocity, make the curve coincide with the phase axis or first arrival of the direct-arrival wave train. The velocity at this point is the wave velocity of the wave train, which is the accurate wave velocity v of the direct-arrival trough wave. iss_direct .

[0044] Step 34: Calculate the virtual source coordinates of the m-th shot. The following formula is used to calculate the sample index value of the reflected wave from the m-th shot received by the n-th detector, and then the time-distance curve of the reflection groove wave is obtained.

[0045] in, This represents the sample index value of the reflected wave train received by all detectors when a certain shot point is fired.

[0046] Step 35: Plot the reflection trough wave time-distance curve on the single-shot record. When the reflection trough wave time-distance curve (such as...) Figure 1 When the wave train coincides with the wave train of the reflecting groove, the velocity at this moment is the wave velocity v of the reflecting groove wave. iss_reflected .

[0047] Step 36: Because the density of the coal seam will change, the wave velocity of each shot will fluctuate. The final wave velocity can be determined by averaging the values, and the calculation method is as follows:

[0048] Each shot yields a direct wave velocity and a reflected wave velocity. The average of the direct wave velocities of all shots and the average of the reflected wave velocities of all shots is taken as the final wave velocity.

[0049] Step 4: Since the above has demonstrated that changes in the observation system and the angle between the fault and the roadway have little impact on the overlap of arrival times of direct and reflected trough waves, we can directly select the sample interval corresponding to the arrival time of the direct trough wave and set it to zero. Specifically: ① Replace the initial wave velocity 1000 with the final wave velocity v obtained in step 36, and use the formula in step 32 to calculate the sample index value corresponding to the arrival time of the direct slot wave received by each detector when the m-th shot is fired, and then obtain the n sample index values ​​corresponding to the m-th shot. ② From the n index values ​​obtained for each shot, select the maximum sample index value (max) corresponding to that shot. direct .

[0050] ③ Set all sample point intervals in the seismic record of this shot to zero.

[0051] ; Step 5: Perform diffraction wave processing and imaging on the zeroed data obtained in Step 4.

[0052] Imaging effects before and after suppressing direct waves, such as Figure 6 As shown. Figure 6 The data processing methods are completely consistent, among which Figure 6 a represents the original data imaging result. Figure 6 b represents the imaging result after suppressing the direct wave. Figure 6 It can be seen that the imaging effect after suppressing the direct wave can accurately restore the location of the fault.

[0053] By following the steps described above, the slot wave data can be read, the slot wave velocity can be extracted, and the sample point interval where the direct arrival time of the slot wave is located can be calculated. After the zeroing operation, the imaging effect of the slot wave advance detection is more accurate.

[0054] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for suppressing direct waves in advance detection of slot waves, characterized in that, Specifically, the following steps are included: Step 1: Design an observation system based on the characteristics of the target object, and collect data according to the observation system; Step 2: Read the channel wave data acquired in Step 1, convert it into a standard seismic data format, and write the acquired information into the data header; Step 3: Extract the wave velocity of the trough wave by fitting the time-distance curve; Step 4: Select the sampling interval corresponding to the arrival time of the direct trough wave and set it to zero; Step 5: Perform diffraction wave processing and imaging on the data after zeroing in Step 4.

2. The method for suppressing direct waves for leading detection of slot waves as described in claim 1, characterized in that, In step two, the sampling rate, number of sample points, shot number, shot point coordinates, trace number, and receiver coordinates are written into the data header according to the standard seismic data format. Based on the number of shot points and the number of detectors, the data header sgyhead is transformed into a three-dimensional array, which contains the header information, trace number, and shot number. Similarly, the data volume sgydata is transformed into a three-dimensional array, which contains the number of sample points, trace number, and shot number.

3. The method for suppressing direct waves for leading detection of slot waves as described in claim 1, characterized in that, Step three includes the following sub-steps: Step 31: Read the horizontal and vertical coordinates of the shot point and the detector from the specified position in the data header (sgyhead) and store them in an array; read the sampling rate from the data header. Fs The wave velocity of the channel wave is approximately 1000 m / s; the initial velocity is set to 1000 m / s. Step 32: Calculate the sample index values ​​of the direct wave train received by all detectors when a certain shot point is fired using the following formula; and then obtain the time-distance curve of the direct slot wave. in, Here are the coordinates of the m-th shot point, in meters. Here are the coordinates of the nth detector, in meters. Let m be the distance between the shot point and the detector n, Fs be the sampling rate, and v be the velocity of a certain wave train in meters per second. The sample index value of the direct wave train received by all detectors when a shot point is fired; Step 33: Plot the time-distance curve of the direct-arrival trough wave on a single-shot recorder. By changing the velocity, make the curve coincide with the phase axis or first arrival of the direct-arrival wave train. The velocity at this point is the wave velocity of the wave train, which is the accurate wave velocity v of the direct-arrival trough wave. iss_direct ; Step 34: Calculate the virtual source coordinates of the m-th shot. The following formula is used to calculate the sample index value of the reflected wave from the m-th shot received by the n-th detector, and then the time-distance curve of the reflection slot wave is obtained. in, The sample index value is the value of the reflected wave train received by all detectors when a shot point is fired. Step 35: Plot the time-distance curve of the reflection groove wave on the single shot record. When the time-distance curve of the reflection groove wave coincides with the wave train of the reflection groove wave, the velocity v at this time is the wave velocity of the reflection groove wave. Step 36: For each shot, a direct wave velocity and a reflected wave velocity can be obtained. The average of the direct wave velocity and the reflected wave velocity of all shots is calculated as the final wave velocity, as shown in the following formula: 。 4. The method for suppressing direct waves for leading detection of slot waves as described in claim 1, characterized in that, The specific process for step four is as follows: ① Replace the initial wave velocity 1000 with the final wave velocity v obtained in step 36, and use the formula in step 32 to calculate the sample index value corresponding to the arrival time of the direct slot wave received by each detector when the m-th shot is fired, and then obtain the n sample index values ​​corresponding to the m-th shot. ② From the n index values ​​obtained for each shot, select the maximum sample index value (max) corresponding to that shot. direct ; ③ Set all sample point intervals in the seismic record of this shot to zero; 。

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