A method for advanced detection of gas occurrence area in a tunneling face

Abstract

The application discloses a kind of tunneling working face with tunneling seismic gas occurrence zone advanced detection method according to the response relationship between coal seam gas and Poisson ratio parameter, complete vibration signal of tunneling machine seismic source is obtained by means of high-definition distributed optical fiber acoustic wave sensing system, longitudinal wave and transverse wave in tunneling seismic record are extracted, and Poisson ratio at different positions is obtained from longitudinal wave and transverse wave.Finally, Poisson ratio parameter is accurately corresponded with gas content, so as to detect gas enrichment zone, and real-time probe the gas risk in front of tunneling working face and within a certain range on both sides.By collecting tunneling seismic record in front of tunneling working face and on both sides, the gas risk in this area is predicted.This method has high accuracy in solving gas-dominated outburst problems, and has a large monitoring range.Multiple superposition processing of tunneling data makes it not easily affected by other signals, overcoming the limitations of the prior art and improving the early warning effect.

Description

Technical Field

[0001] This invention belongs to the field of geophysical exploration, and specifically relates to a method for advance detection of seismic gas occurrence zones during tunneling. Background Technology

[0002] Coal is my country's primary energy source. With the continuous development of mining equipment, the intensity of coal mine tunneling and extraction has gradually increased, and the number of deep mines exceeding 1,000 meters has gradually increased, with the maximum mining depth exceeding 1,500 meters. In actual production, some areas with high predicted index values ​​have not experienced coal gas outbursts, while areas with low predicted index values ​​have experienced frequent outbursts. Therefore, the prediction of coal gas outbursts is a crucial link in outburst prevention and control, and its accuracy directly determines the effectiveness of prevention and control efforts.

[0003] In early warning of coal and gas outburst disasters, different methods have their own characteristics. Electromagnetic radiation prediction has the advantages of being non-contact and less affected by rock mass occurrence, but its monitoring range is small and it is easily affected by other electromagnetic signals. Acoustic-electric early warning has high sensitivity and accuracy for gas outbursts dominated by geostress, but its accuracy is lower for gas-dominated outbursts. Microseismic monitoring also has similar shortcomings; it is effective for early warning of stress- and tectonic-controlled coal and gas outbursts, but lacks effectiveness for gas-dominated outbursts. Therefore, it is necessary to find a predictive method that can effectively warn of gas-dominated coal and gas outbursts and overcome the limitations of existing technologies in this regard. Summary of the Invention

[0004] The purpose of this invention is to provide a method for advanced detection of seismic gas occurrence zones during tunneling, so as to solve the problem that the existing technology has limitations in gas early warning, resulting in insufficient early warning effectiveness.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A method for advance detection of seismic gas occurrence zones during tunneling includes the following steps:

[0007] Step 1: Collect the mining engineering plan of the working face to be measured, and determine the location of the tunnel in the working face based on the mining engineering plan; establish an observation system in the tunnel of the working face;

[0008] Step 2: Conduct directional drilling at each signal receiving point within the observation system to obtain the corresponding monitoring borehole; arrange fixed distributed optical fibers inside each monitoring borehole and connect each fixed distributed optical fiber to the external monitoring system.

[0009] Step 3: Carry out tunneling operations on the tunneling face and acquire vibration signals of the corresponding seismic channels through each fixed distributed optical fiber;

[0010] Step 4: Based on the vibration signal of each seismic trace, determine the location of each signal receiving point and the corresponding substation channel number, and perform bandpass filtering on the vibration signals of all seismic traces.

[0011] Step 5: Select a reference trace and obtain the relevant records for the reference trace and each of the other seismic traces.

[0012] Step 6: Evaluate and screen all relevant records and process the data to obtain seismic trace records with improved signal-to-noise ratio;

[0013] Step 7: Extract the velocity of direct P-waves and S-waves from all seismic traces with improved signal-to-noise ratios and perform velocity scanning to obtain the velocity values ​​of direct P-waves and S-waves corresponding to pairwise combinations of all adjacent seismic traces.

[0014] Step 8: Calculate the Poisson's ratio at the corresponding location of the working surface under test based on the velocity values ​​of the direct P-wave and S-wave corresponding to each seismic trace.

[0015] Step 9: Plot the curve of Poisson's ratio as a function of position based on the Poisson's ratio at different locations on the working face to be tested. Determine the gas content in front of and on both sides of the tunneling working face by using the curve of Poisson's ratio as a function of position.

[0016] The present invention also has the following features:

[0017] Furthermore, in step 5, when bandpass filtering is performed on the vibration signal of the seismic event during excavation, the filtering range is 5-200Hz.

[0018] Furthermore, in step 5, the seismic tunnel closest to the tunneling machine is selected as the reference tunnel;

[0019] The following formula is used to correlate the vibration signal of the bandpass-filtered reference trace with the vibration signal of each of the other bandpass-filtered seismic traces to obtain the correlation record φ between the vibration signal of the reference trace and the vibration signal of each of the other seismic traces.

[0020]

[0021] Where, x i This represents the vibration signal after bandpass filtering of the reference track;

[0022] x j This represents the bandpass filtered vibration signal of the j-th seismic trace;

[0023] t i and t j These represent the initial travel times of the reference trace and the j-th seismic trace, respectively;

[0024] τ represents the delay time relative to the initial time travel;

[0025] T represents the length of the relevant window;

[0026] t0 represents the time between the initial time travel and the start point of the relevant window;

[0027] δt represents the sampling rate.

[0028] Furthermore, step 6 includes the following sub-steps:

[0029] Step 61: Select any relevant record and take the time window along the direct wave travel path in the selected relevant record;

[0030] Step 62: Use the following formula to calculate the normalized cross-correlation summation coefficient (NCC) for the records within the time window;

[0031]

[0032] Where m represents the total number of seismic traces;

[0033] i represents the i-th earthquake trace;

[0034] f represents the amplitude;

[0035] f i,t(i) Let t(i) represent the amplitude of the i-th seismic trace during its upward travel.

[0036] Step 63: Traverse all relevant records, obtain the corresponding normalized cross-correlation summation coefficients, and perform data processing respectively to obtain seismic single-shot records with improved signal-to-noise ratio.

[0037] Furthermore, step 7 includes the following sub-steps:

[0038] Step 71: Set the velocity scan range Vmin-Vmax and the scan interval dv;

[0039] Step 72: Cycle the velocity from Vmin to Vmax at scan intervals dv, and calculate the direct wave arrival time difference for each seismic trace using the following formula for each cycle velocity:

[0040]

[0041] Where, Δt i This represents the arrival time difference of the direct wave in the i-th seismic trace;

[0042] v k This indicates the selected cycle speed, v. k ∈(Vmin, Vmax);

[0043] s i This represents the distance between the i-th seismic trace and the first seismic trace;

[0044] Step 73: Use the following formula to iterate through each seismic trace and perform time difference correction based on the arrival time difference of its corresponding direct wave:

[0045]

[0046] in, This represents the data from the i-th seismic trace after eliminating the effects of direct wave propagation time difference;

[0047] Step 74, using the following formula, calculate the square modulus of the zero-delay cross-correlation coefficient between two adjacent seismic traces using the time-difference corrected seismic trace data:

[0048]

[0049] Where, ψ ij The square modulus of the zero-delay cross-correlation coefficient between the i-th and j-th seismic traces;

[0050] Step 75, substitute each cycle velocity, and set Ψ ij The velocities corresponding to the maximum and second-largest values ​​are respectively taken as the P-wave velocities V of the direct wave between the i-th and j-th seismic traces. p (i,j) and transverse wave velocity V s (i,j);

[0051] Step 76: Repeat steps 74-75 to iterate through all pairs of adjacent seismic traces and obtain their corresponding P-wave velocity and S-wave velocity.

[0052] Furthermore, in step 71, Vmin is set to 1500 m / s;

[0053] Vmax is set to 3000 m / s;

[0054] The scan interval dv is set to 5 m / s.

[0055] Further, in step 8, based on the P-wave velocity and S-wave velocity corresponding to each pair of adjacent seismic traces obtained in step 76, the Poisson's ratio μ at the corresponding location is calculated using the following formula:

[0056]

[0057] Among them, V p Indicates the longitudinal wave velocity;

[0058] V s This indicates the velocity of the transverse wave.

[0059] Compared with the prior art, the present invention has the following technical effects:

[0060] This invention presents a method for advanced detection of gas-bearing zones during tunneling face seismic activity. Based on the response relationship between coal seam gas and Poisson's ratio, it utilizes a high-definition distributed fiber optic acoustic sensing system to acquire complete vibration signals from the tunneling machine's seismic source. P-waves and S-waves are extracted from the seismic records, and the Poisson's ratio at different locations is calculated from these waves. Finally, the Poisson's ratio parameter is accurately correlated with gas content, thereby detecting gas-rich areas and providing real-time monitoring of gas risk within a certain range ahead and to both sides of the tunneling face. By collecting seismic records ahead and to both sides of the tunneling face, the gas risk in this area is predicted, overcoming the shortcomings of traditional methods that rely on gas concentration detection for predicting unexplored areas, which often suffer from inaccuracies and oversimplification. This method offers high accuracy in addressing gas-dominated issues and has a wide monitoring range. Furthermore, the multiple overlay processing of the data during tunneling makes it less susceptible to interference from other signals, overcoming limitations in existing technologies, improving early warning effectiveness, and making it suitable for large-scale industrial application and promotion. Attached Figure Description

[0061] Figure 1 This is a flowchart of the advanced detection method for seismic gas occurrence zones during tunneling in accordance with the present invention.

[0062] Figure 2 This is a diagram of the fiber optic observation system in the seismic borehole during excavation in this invention. Detailed Implementation

[0063] It should be noted that, unless otherwise specified, all components in this invention are known in the prior art. For example, the fixed distributed optical fiber uses a commonly known fixed distributed optical fiber.

[0064] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0065] In step 8, according to step 76 as follows Figure 1 As shown, a method for advance detection of seismic gas occurrence zones during tunneling includes the following steps:

[0066] Step 1: Collect the mining engineering plan of the working face to be measured, and determine the location of the tunnel in the working face based on the mining engineering plan; establish an observation system in the tunnel of the working face;

[0067] Step 2: Conduct directional drilling at each signal receiving point within the observation system to obtain the corresponding monitoring borehole; arrange fixed distributed optical fibers inside each monitoring borehole and connect each fixed distributed optical fiber to the external monitoring system.

[0068] Step 3: Conduct tunneling operations on the tunnel face and acquire vibration signals from the corresponding seismic channels through each fixed distributed optical fiber; the source of the vibration signals here is the tunneling machine.

[0069] Step 4: Based on the vibration signal of each seismic trace, determine the location of each signal receiving point and the corresponding substation channel number, and perform bandpass filtering on the vibration signals of all seismic traces.

[0070] Step 5: Select a reference trace and obtain the relevant records for the reference trace and each of the other seismic traces.

[0071] Step 6: Evaluate and screen all relevant records and process the data to obtain seismic trace records with improved signal-to-noise ratio;

[0072] When tunneling machinery cuts through the coal face, the resulting effective vibration signal energy is very strong and can be received by the detector array. Therefore, the signals received across the entire detector array have high similarity and thus high correlation. Utilizing this characteristic, by correlating the signals received near the tunneling machine with other receivers, the seismic single-shot record can be extracted.

[0073] Due to the low signal-to-noise ratio and strong background noise energy of seismic data obtained during tunneling, it is difficult to identify effective signals, making it challenging to directly extract direct P-waves and S-waves from the data. Therefore, the data processing procedure includes quality evaluation of the relevant records obtained in step 5. The quality evaluation is based on taking time windows along the travel paths of the direct waves in the relevant records, calculating the normalized cross-correlation summation coefficient for the records within the time window, and using this coefficient to evaluate the quality of the relevant records.

[0074] Step 7: Extract the velocity of direct P-waves and S-waves from all seismic traces with improved signal-to-noise ratios and perform velocity scanning to obtain the velocity values ​​of direct P-waves and S-waves for each seismic trace.

[0075] Step 8: Calculate the Poisson's ratio at the corresponding location of the working surface under test based on the velocity values ​​of the direct P-wave and S-wave corresponding to each seismic trace.

[0076] Step 9: Plot the curve of Poisson's ratio as a function of position based on the Poisson's ratio at different locations on the working face to be tested. Determine the gas content in front of and on both sides of the tunneling working face by using the curve of Poisson's ratio as a function of position.

[0077] After plotting the Poisson's ratio curve as a function of position, the gas content in front of and on both sides of the tunnel face is analyzed using the Poisson's ratio curve.

[0078] A low Poisson's ratio corresponds to oil and gas content in the formation. The higher the degree of rock consolidation, the lower the Poisson's ratio. The Poisson's ratio of loosely weathered surfaces can reach 0.45, and its range is between 0 and 0.5. Under static equilibrium of geostress, the distribution of gas is characterized by high gas content in gas-bearing coal seams, resulting in slow propagation velocities of seismic P-waves and S-waves, and an increased Poisson's ratio. Therefore, high anomaly areas on the Poisson's ratio curve can be identified as outburst hazard zones.

[0079] Specifically, in step 5, when bandpass filtering is performed on the vibration signal of the seismic event during excavation, the filtering range is 5-200Hz.

[0080] Specifically, in step 5, the seismic tunnel closest to the tunneling machine is selected as the reference tunnel;

[0081] The following formula is used to correlate the vibration signal of the bandpass-filtered reference trace with the vibration signal of each of the other bandpass-filtered seismic traces to obtain the correlation record φ between the vibration signal of the reference trace and the vibration signal of each of the other seismic traces.

[0082]

[0083] Where, x i This represents the vibration signal after bandpass filtering of the reference track;

[0084] x j This represents the bandpass filtered vibration signal of the j-th seismic trace;

[0085] t i and t j These represent the initial travel times of the reference trace and the j-th seismic trace, respectively;

[0086] τ represents the delay time relative to the initial time travel;

[0087] T represents the length of the relevant window;

[0088] t0 represents the time between the initial time travel and the start point of the relevant window;

[0089] δt represents the sampling rate.

[0090] Specifically, step 6 includes the following sub-steps:

[0091] Step 61: Select any relevant record and take the time window along the direct wave travel path in the selected relevant record;

[0092] Step 62: Use the following formula to calculate the normalized cross-correlation summation coefficient (NCC) for the records within the time window;

[0093]

[0094] Where m represents the total number of seismic traces;

[0095] i represents the i-th earthquake trace;

[0096] f represents the amplitude;

[0097] f i,t(i) Let t(i) represent the amplitude of the i-th seismic trace during its upward travel.

[0098] Step 63: Traverse all relevant records, obtain the corresponding normalized cross-correlation summation coefficients, and perform data processing respectively to obtain seismic single-shot records with improved signal-to-noise ratio.

[0099] During the data processing here, when the tunneling machine is working normally, the correlation will generate a direct wave phase axis. Therefore, when traveling along the phase axis, the superimposed amplitudes will result in a higher normalized cross-correlation summation coefficient.

[0100] When the tunneling machine is stopped, the direct wave phase axis cannot be formed in the relevant records, resulting in a lower calculated normalized cross-correlation summation coefficient.

[0101] Based on this, a quality assessment and screening of the massive amount of seismic data obtained during excavation can be carried out. By superimposing the data with higher quality assessment coefficients, seismic trace records with improved signal-to-noise ratio can be obtained.

[0102] Specifically, step 7 includes the following sub-steps:

[0103] Step 71: Set the velocity scan range Vmin-Vmax and the scan interval dv;

[0104] Step 72: Cycle the velocity from Vmin to Vmax at scan intervals dv, and calculate the direct wave arrival time difference for each seismic trace using the following formula for each cycle velocity:

[0105]

[0106] Where, Δt i This represents the arrival time difference of the direct wave in the i-th seismic trace;

[0107] v k This indicates the selected cycle speed, v. k ∈(Vmin, Vmax);

[0108] s i This represents the distance between the i-th seismic trace and the starting trace;

[0109] The arrival time difference of the direct wave in the seismic trace will vary depending on the velocity value, but the arrival time difference of the direct wave at a certain velocity value is also fixed. When cycling to a certain velocity, subsequent time difference corrections and cross-correlation coefficient square modulus calculations are performed based on the arrival time difference of the direct wave obtained at this velocity. The cross-correlation coefficient square modulus obtained each time is also different. Find the cyclic velocity corresponding to the maximum and second largest cross-correlation coefficient square modulus, which are the P-wave velocity and S-wave velocity of the direct wave.

[0110] Step 73: Use the following formula to iterate through each seismic trace and perform time difference correction based on the arrival time difference of its corresponding direct wave:

[0111]

[0112] in, This represents the data from the i-th seismic trace after eliminating the effects of direct wave propagation time difference;

[0113] Step 74, using the following formula, calculate the square modulus of the zero-delay cross-correlation coefficient between two adjacent seismic traces using the time-difference corrected seismic trace data:

[0114]

[0115] Among them, Ψ ij The square modulus of the zero-delay cross-correlation coefficient between the i-th and j-th seismic traces;

[0116] Step 75, substitute each cycle velocity, and set Ψ ij The velocities corresponding to the maximum and second-largest values ​​are respectively taken as the P-wave velocities V of the direct wave between the i-th and j-th seismic traces. p (i,j) and transverse wave velocity V s (i,j);

[0117] Step 76: Repeat steps 74-75 to iterate through all pairs of adjacent seismic traces and obtain their corresponding P-wave velocity and S-wave velocity.

[0118] In one specific implementation, in step 71, Vmin is set to 1500 m / s;

[0119] Vmax is set to 3000 m / s;

[0120] The scan interval dv is set to 5 m / s.

[0121] The scanning range and scanning interval here are general values ​​given in combination with the physical properties of coal seams. In actual work, those skilled in the art can also choose other value ranges based on the actual working conditions.

[0122] Specifically, the P-wave velocity and S-wave velocity corresponding to each pair of adjacent seismic traces obtained in the first step are used to calculate the Poisson's ratio μ at the corresponding location using the following formula:

[0123]

[0124] Among them, V p Indicates the longitudinal wave velocity;

[0125] V s This indicates the velocity of the transverse wave.

Claims

1. A method for advance detection of seismic gas occurrence zones during tunneling, characterized in that, Includes the following steps: Step 1: Collect the mining engineering plan of the working face to be measured, and determine the location of the tunnel in the working face based on the mining engineering plan; establish an observation system in the tunnel of the working face; Step 2: Conduct directional drilling at each signal receiving point within the observation system to obtain the corresponding monitoring borehole; arrange fixed distributed optical fibers inside each monitoring borehole and connect each fixed distributed optical fiber to the external monitoring system. Step 3: Carry out tunneling operations on the tunneling face and acquire vibration signals of the corresponding seismic channels through each fixed distributed optical fiber; Step 4: Based on the vibration signal of each seismic trace, determine the location of each signal receiving point and the corresponding substation channel number, and perform bandpass filtering on the vibration signals of all seismic traces. Step 5: Select a reference trace and obtain the relevant records for the reference trace and each of the other seismic traces. Step 6: Evaluate and screen all relevant records and process the data to obtain seismic trace records with improved signal-to-noise ratio; Step 7: Extract the velocity of direct P-waves and S-waves from all seismic traces with improved signal-to-noise ratios and perform velocity scanning to obtain the velocity values ​​of direct P-waves and S-waves corresponding to pairwise combinations of all adjacent seismic traces. Step 8: Calculate the Poisson's ratio at the corresponding location of the working surface under test based on the velocity values ​​of the direct P-wave and S-wave corresponding to each seismic trace. Step 9: Plot the curve of Poisson's ratio as a function of position based on the Poisson's ratio at different locations on the working face to be tested. Determine the gas content in front of and on both sides of the tunneling working face by using the curve of Poisson's ratio as a function of position.

2. The method for advance detection of seismic gas occurrence zones during tunneling as described in claim 1, characterized in that, In step 5, when bandpass filtering is performed on the vibration signal of the seismic event during excavation, the filtering range is 5-200Hz.

3. The method for advance detection of seismic gas occurrence zones during tunneling as described in claim 1, characterized in that, In step 5, the seismic tunnel closest to the tunneling machine is selected as the reference tunnel; The following formula is used to correlate the vibration signal of the bandpass-filtered reference trace with the vibration signal of each of the other bandpass-filtered seismic traces to obtain the correlation record φ between the vibration signal of the reference trace and the vibration signal of each of the other seismic traces. Where, x i This represents the vibration signal after bandpass filtering of the reference track; x j This represents the bandpass filtered vibration signal of the j-th seismic trace; t i and t j These represent the initial travel times of the reference trace and the j-th seismic trace, respectively; τ represents the delay time relative to the initial time travel; T represents the length of the relevant window; t0 represents the time between the initial time travel and the start point of the relevant window; δt represents the sampling rate.

4. The method for advanced detection of seismic gas occurrence zones during tunneling as described in claim 3, characterized in that, Step 6 includes the following sub-steps: Step 61: Select any relevant record and take the time window along the direct wave travel path in the selected relevant record; Step 62: Use the following formula to calculate the normalized cross-correlation summation coefficient (NCC) for the records within the time window; Where m represents the total number of seismic traces; i represents the i-th earthquake trace; f represents the amplitude; f i,t(i) Let t(i) represent the amplitude of the i-th seismic trace during its upward travel. Step 63: Traverse all relevant records, obtain the corresponding normalized cross-correlation summation coefficients, and perform data processing respectively to obtain seismic single-shot records with improved signal-to-noise ratio.

5. The method for advance detection of seismic gas occurrence zones during tunneling as described in claim 1, characterized in that, Step 7 includes the following sub-steps: Step 71: Set the velocity scan range Vmin-Vmax and the scan interval dv; Step 72: Cycle the velocity from Vmin to Vmax at scan intervals dv, and calculate the direct wave arrival time difference for each seismic trace using the following formula for each cycle velocity: Where, Δt i This represents the arrival time difference of the direct wave in the i-th seismic trace; v k This indicates the selected cycle speed, v. k ∈(Vmin, Vmax); s i This represents the distance between the i-th seismic trace and the first seismic trace; Step 73: Use the following formula to iterate through each seismic trace and perform time difference correction based on the arrival time difference of its corresponding direct wave: in, This represents the data from the i-th seismic trace after eliminating the effects of direct wave propagation time difference; Step 74, using the following formula, calculate the square modulus of the zero-delay cross-correlation coefficient between two adjacent seismic traces using the time-difference corrected seismic trace data: Among them, Ψ ij The square modulus of the zero-delay cross-correlation coefficient between the i-th and j-th seismic traces; Step 75, substitute each cycle velocity, and set Ψ ij The velocities corresponding to the maximum and second-largest values ​​are respectively taken as the P-wave velocities V of the direct wave between the i-th and j-th seismic traces. p (i,j) and transverse wave velocity V s (i,j); Step 76: Repeat steps 74-75 to iterate through all pairs of adjacent seismic traces and obtain their corresponding P-wave velocity and S-wave velocity.

6. The method for advance detection of seismic gas occurrence zones during tunneling as described in claim 5, characterized in that, In step 71, Vmin is set to 1500 m / s; Vmax is set to 3000 m / s; The scan interval dv is set to 5 m / s.

7. The method for advance detection of seismic gas occurrence zones during tunneling as described in claim 6, characterized in that, In step 8, based on the P-wave velocity and S-wave velocity corresponding to each pair of adjacent seismic traces obtained in step 76, the Poisson's ratio μ at the corresponding location is calculated using the following formula: Among them, V p Indicates the longitudinal wave velocity; V s This indicates the velocity of the transverse wave.

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