Advanced detection method for gas occurrence area of excavation-following earthquake of excavation working face

Abstract

The method comprises the following steps: according to a response relationship between coal seam gas and a Poisson's ratio parameter, acquiring a complete vibration signal of a heading machine seismic source by means of a high-definition distributed optical fiber sound wave sensing system, and extracting longitudinal waves and transverse waves in a heading seismic record; poisson ratios at different positions are obtained through the longitudinal waves and the transverse waves. And finally, accurately corresponding the Poisson's ratio parameter to the gas content condition, thereby detecting the gas enrichment area, and exploring the gas risk in a certain range in front of and on two sides of the tunneling working face in real time. And the gas risk of the area is predicted by collecting excavation-following seismic records in front of and on the two sides of the excavation working face. Compared with the prior art, the method has high accuracy for solving the outburst problem dominated by gas and has a large monitoring range, meanwhile, the method is not prone to being affected by other signals due to the processing mode that data are overlaid along with excavation for multiple times, limitation in the prior art is overcome, and the early warning effect is improved.

Description

Technical Field

[0001] The present invention belongs to the field of geophysical exploration, and particularly relates to a method for advanced detection of gas occurrence areas in a tunneling working face by seismic exploration while tunneling. Background Art

[0002] Coal is the main energy source in China. With the continuous development of mining equipment, the intensity of coal mining and tunneling in coal mines has gradually increased, and the number of kilometer-deep wells has gradually increased, with the maximum mining depth exceeding 1500 m. In actual production, some areas with high predicted index values did not experience outburst accidents, while outbursts sometimes occurred in areas with low predicted index values. It can be seen that the prediction of outburst accidents, as an important link in preventing outbursts, directly determines the effectiveness of prevention work.

[0003] In the early warning of coal and gas outburst disasters, different methods have their own characteristics. The electromagnetic radiation prediction method has the advantages of non-contact and little influence by rock mass occurrence, but has a small monitoring range and is easily affected by other electromagnetic signals; the acoustic-electric early warning has high sensitivity and accuracy for gas outburst problems dominated by ground stress, but has low accuracy for outburst problems dominated by gas; microseismic monitoring also has the same deficiency, and has good early warning effect for coal and gas outburst problems controlled by stress and structure, but lacks effectiveness for outburst problems dominated by gas. Therefore, it is necessary to find a prediction method that can effectively early warn of coal and gas outburst problems dominated by gas and break through the limitations of existing technologies in this regard. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for advanced detection of gas occurrence areas in a tunneling working face by seismic exploration while tunneling, so as to solve the problem that the early warning is not effective enough due to limitations in the existing technology for gas early warning.

[0005] In order to solve the above technical problems, the present invention is implemented by adopting the following technical solutions:

[0006] A method for advanced detection of gas occurrence areas in a tunneling working face by seismic exploration while tunneling, comprising the following steps:

[0007] Step 1, collect the mining engineering plan of the working face to be measured, and determine the position of the roadway in the tunneling working face according to the mining engineering plan; establish an observation system in the working face roadway;

[0008] Step 2, conduct directional drilling construction at each signal receiving point in the observation system to obtain corresponding monitoring boreholes; arrange fixed distributed optical fibers inside each monitoring borehole, and connect each fixed distributed optical fiber to an external monitoring system;

[0009] Step 3, carry out tunneling operations on the roadway of the tunneling working face, and obtain the vibration signals of the corresponding seismic traces through each fixed distributed optical fiber;

[0010] Step 4: Determine the position of each signal receiving point and the corresponding substation channel number according to the vibration signals of each seismic trace, and perform band-pass filtering on the vibration signals of all seismic traces;

[0011] Step 5: Select a reference trace, and obtain the correlation records of the reference trace and each of the remaining seismic traces respectively;

[0012] Step 6: Conduct quality evaluation, screening and data processing on all correlation records to obtain seismic trace records with improved signal-to-noise ratio;

[0013] Step 7: Extract the velocities of direct P-waves and S-waves respectively from all seismic trace records with improved signal-to-noise ratio and perform velocity scanning to obtain the velocity values of direct P-waves and S-waves corresponding to each pairwise combination of adjacent seismic traces;

[0014] Step 8: Calculate the Poisson's ratio at the corresponding position of the working face to be measured according to the velocity values of direct P-waves and S-waves corresponding to each seismic trace;

[0015] Step 9: Draw a curve of the change of Poisson's ratio with position according to the Poisson's ratios at different positions of the working face to be measured, and determine the gas content in front of and on both sides of the tunneling working face through the curve of the change of Poisson's ratio with position.

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

[0017] Further, in Step 5, when performing band-pass filtering on the vibration signals of the seismic while tunneling, the filtering range is 5 - 200 Hz.

[0018] Further, in Step 5, select the seismic trace closest to the roadheader as the reference trace;

[0019] Use the following formula to correlate the vibration signal of the reference trace after band-pass filtering with the vibration signals of each of the remaining seismic traces after band-pass filtering to obtain the correlation record φ of the vibration signals of the reference trace and each of the remaining seismic traces;

[0020]

[0021] where x i represents the vibration signal of the reference trace after band-pass filtering;

[0022] x j represents the vibration signal of the j-th seismic trace after band-pass filtering;

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

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

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

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

[0027] δt represents the sampling rate.

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

[0029] Step 61, optionally select a relevant record, and take a time window along the direct wave travel time 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 seismic trace;

[0034] f represents the amplitude;

[0035] f i,t(i) represents the amplitude of the i-th seismic trace with an up travel time of t(i);

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

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

[0038] Step 71, set the velocity scanning range Vmin - Vmax and the scanning interval dv;

[0039] Step 72, perform a velocity loop from Vmin to Vmax with a scanning interval dv, and use the following formula to calculate the direct wave arrival time difference of each seismic trace with each loop velocity:

[0040]

[0041] where Δt i represents the direct wave arrival time difference of the i-th seismic trace;

[0042] v k represents the loop velocity selected this time, v k ∈(Vmin, Vmax);

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

[0044] Step 73, traverse each seismic trace using the following formula, and perform time difference correction through the corresponding direct wave arrival time difference:

[0045]

[0046] wherein, represents the data of the i-th seismic trace after eliminating the influence of the direct wave propagation time difference;

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

[0048]

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

[0050] Step 75, substitute each loop velocity, and take the velocities corresponding to the maximum value and the second maximum value of Ψ ij as the longitudinal wave velocity V p (i, j) and the shear wave velocity V s (i, j) of the direct wave between the i-th and j-th seismic traces;

[0051] Step 76, repeat Steps 74 - 75, traverse all pairwise combinations of adjacent seismic traces, and obtain their corresponding longitudinal wave velocities and shear wave velocities.

[0052] Furthermore, in Step 71, the value of Vmin is 1500 m / s;

[0053] The value of Vmax is 3000 m / s;

[0054] The scanning interval dv is 5 m / s.

[0055] Furthermore, in Step 8, according to the longitudinal wave velocity and shear wave velocity corresponding to the pairwise adjacent seismic traces obtained in Step 76, use the following formula to calculate the Poisson's ratio μ at the corresponding position:

[0056]

[0057] wherein, V p represents the longitudinal wave velocity;

[0058] V s represents the shear wave velocity.

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

[0060] The advanced detection method for the gas occurrence area along with the excavation in the driving face of the present invention is based on the response relationship between the coal seam gas and the Poisson's ratio parameter. With the help of a high-definition distributed optical fiber acoustic sensing system, the complete vibration signal of the roadheader vibration source is obtained, the longitudinal wave and the transverse wave in the seismic record along with the excavation are extracted, and the Poisson's ratio at different positions is obtained from the longitudinal and transverse waves. Finally, the Poisson's ratio parameter is accurately corresponded to the gas content situation, so as to detect the gas enrichment area and real-time explore the gas risk within a certain range in front of and on both sides of the driving face. By collecting the seismic records along with the excavation in front of and on both sides of the driving face, the gas risk in this area is predicted, making up for the deficiency of "taking a point as a surface and overgeneralizing" when predicting the unexplored area by the method of detecting the gas concentration. It has a high accuracy for solving the outburst problem dominated by gas, has a large monitoring range, and at the same time, the processing method of multiple superpositions of the data along with the excavation makes it not easily affected by other signals, overcoming the limitations in the prior art, improving the early warning effect, and being suitable for large-scale industrial use and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 FIG. is the technical flow chart of the advanced detection method for the gas occurrence area along with the excavation in the driving face of the present invention;

[0062] Figure 2 FIG. is the optical fiber observation system diagram in the borehole for the seismic exploration along with the excavation in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0063] It should be noted that all components in the present invention, unless otherwise specified, all adopt the components known in the prior art. For example, the fixed distributed optical fiber adopts the known and commonly used fixed distributed optical fiber.

[0064] The following gives specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent transformations made on the basis of the technical solution of the present application fall within the protection scope of the present invention.

[0065] In step 8, according to step 76 as Figure 1 As shown, an advanced detection method for the gas occurrence area along with the excavation in the driving face includes the following steps:

[0066] Step 1: Collect the mining engineering plan of the working face to be measured, and determine the position of the driving face roadway according to the mining engineering plan; establish an observation system in the working face roadway;

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

[0068] Step 3: Carry out tunneling operations on the roadway of the tunneling face, and obtain the vibration signals of the corresponding seismic traces through each fixed distributed optical fiber. The seismic source of the vibration signals here is the roadheader.

[0069] Step 4: Determine the position of each signal receiving point and the corresponding substation channel number according to the vibration signals of each seismic trace, and perform band-pass filtering on the vibration signals of all seismic traces.

[0070] Step 5: Select a reference trace and obtain the correlation records of the reference trace and each of the remaining seismic traces respectively.

[0071] Step 6: Conduct quality evaluation and screening on all correlation records and perform data processing to obtain seismic trace records with improved signal-to-noise ratio.

[0072] Among them, when the tunneling machinery cuts the coal wall, the energy of the generated effective vibration signal is very strong and can be received by the geophone array. Therefore, the signals received on the entire receiving array have high similarity and thus high correlation. Utilizing this feature, by performing correlation processing on the signals received near the roadheader and other receiving traces, the seismic single-shot record can be extracted.

[0073] Since the signal-to-noise ratio of the seismic data during tunneling is relatively low, the background noise energy is strong, and it is difficult to identify the effective signals. It is difficult to directly extract the direct longitudinal wave and transverse wave from the seismic data during tunneling. Therefore, the data processing process includes performing quality evaluation on the correlation records obtained in Step 5. The basis for quality evaluation is to take a time window along the travel time path of the direct wave in the correlation record, calculate the normalized cross-correlation summation coefficient for the records within the time window, and evaluate the quality of the correlation records through this coefficient.

[0074] Step 7: Respectively extract the velocities of the direct longitudinal wave and transverse wave for all seismic trace records with improved signal-to-noise ratio and perform velocity scanning to obtain the velocity values of the direct longitudinal wave and transverse wave corresponding to each seismic trace.

[0075] Step 8: Calculate the Poisson's ratio at the corresponding position of the working face to be measured according to the velocity values of the direct longitudinal wave and transverse wave corresponding to each seismic trace.

[0076] Step 9: Draw a curve of the Poisson's ratio varying with position for different positions of the working face to be measured, and determine the gas-bearing conditions in front of and on both sides of the tunneling face through the curve of the Poisson's ratio varying with position.

[0077] After drawing the curve of the Poisson's ratio varying with position, analyze the gas-bearing conditions in front of and on both sides of the tunneling face through the Poisson's ratio curve.

[0078] A low Poisson's ratio corresponds to oil and gas in the formation. The higher the degree of consolidation of the rock, the smaller the Poisson's ratio. The Poisson's ratio of loose weathered ground can reach 0.45, and its variation range is between 0 and 0.5. Under the static equilibrium state of in-situ stress, the distribution of gas shows that when the gas content in the coal seam is high, the propagation velocities of longitudinal and transverse seismic waves are slow, and the Poisson's ratio increases. Therefore, the high anomaly area on the Poisson's ratio curve can be defined as the outburst danger area.

[0079] Specifically, in step 5, when performing band-pass filtering on the vibration signals of the seismic while tunneling, the filtering range is 5 - 200 Hz.

[0080] Specifically, in step 5, select the seismic trace closest to the roadheader as the reference trace;

[0081] Use the following formula to correlate the vibration signal of the reference trace after band-pass filtering with the vibration signals of each of the remaining band-pass filtered seismic traces, and obtain the correlation record φ of the vibration signals of the reference trace and each of the remaining seismic traces;

[0082]

[0083] where, x i represents the vibration signal of the reference trace after band-pass filtering;

[0084] x j represents the vibration signal of the j-th seismic trace after band-pass filtering;

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

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

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

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

[0089] δt represents the sampling rate.

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

[0091] Step 61, randomly select one correlation record, and take a time window along the direct wave travel time path in the selected correlation 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 seismic trace;

[0096] f represents the amplitude;

[0097] f i,t(i) represents the amplitude of the i-th seismic trace with an up-going travel time of t(i);

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

[0099] During the data processing here, when the roadheader is working normally, a direct wave in-phase axis will be generated accordingly. Therefore, the amplitudes are stacked along the in-phase axis travel time to obtain a relatively high normalized cross-correlation summation coefficient;

[0100] When the roadheader is in a stopped state, a direct wave in-phase axis cannot be formed in the relevant records, and thus the calculated value of the normalized cross-correlation summation coefficient is relatively low.

[0101] Based on this, quality evaluation and screening are carried out on a large amount of seismic data during tunneling. The data with relatively high quality evaluation coefficients are stacked, and a seismic trace record with improved signal-to-noise ratio can be obtained.

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

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

[0104] Step 72: Conduct a velocity loop from Vmin to Vmax with a scanning interval of dv. Using the following formula, calculate the direct wave arrival time difference of each seismic trace with each loop velocity:

[0105]

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

[0107] v k represents the loop velocity selected this time, v k ∈(Vmin, Vmax);

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

[0109] When the velocity takes different values, the arrival time difference of the direct wave in the seismic trace obtained will also be different, but the arrival time difference of the direct wave obtained for a certain determined velocity value is also determined. When cycling to a certain velocity, subsequent operations such as time difference correction and calculation of the square modulus of the cross-correlation coefficient are performed based on the arrival time difference of the direct wave obtained for this velocity. The square modulus of the cross-correlation coefficient obtained each time is also different. Find the cycling velocities corresponding to the maximum and the second maximum of the square modulus of the cross-correlation coefficient, which are the P-wave velocity and S-wave velocity of the direct wave.

[0110] Step 73, use the following formula to traverse each seismic trace and perform time difference correction through its corresponding arrival time difference of the direct wave:

[0111]

[0112] where, represents the data of the i-th seismic trace after eliminating the influence of the propagation time difference of the direct wave;

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

[0114]

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

[0116] Step 75, substitute each cycling velocity, and take the velocities corresponding to the maximum and the second maximum of Ψ ij as the P-wave velocity V p (i,j) and S-wave velocity V s (i,j) of the direct wave between the i-th and j-th seismic traces;

[0117] Step 76, repeat Steps 74 - 75, traverse all pairwise combinations of adjacent seismic traces, and obtain their corresponding P-wave velocities and S-wave velocities.

[0118] As a specific implementation manner, in Step 71, the value of Vmin is 1500 m / s;

[0119] the value of Vmax is 3000 m / s;

[0120] the scanning interval dv is 5 m / s.

[0121] The scanning range and scanning interval here are a general value given in combination with the physical properties of the coal seam. In actual work, those skilled in the art can also select other value ranges in combination with the actual working conditions.

[0122] Specifically, for the longitudinal wave velocity and the shear wave velocity corresponding to two adjacent seismic traces obtained in step, the Poisson's ratio μ at the corresponding position is calculated using the following formula:

[0123]

[0124] where V p represents the longitudinal wave velocity;

[0125] V s represents the shear wave velocity.

Claims

1. A method for advanced detection of gas-bearing areas during excavation of a working face, characterized in that: The following steps are involved: Step 1: Collect the mining engineering plan of the working face to be measured, determine the location of the tunnel of the excavation working face according to the mining engineering plan; establish an observation system in the tunnel of the working face; Step 2: perform directional drilling at each signal receiving point in the observation system to obtain a corresponding monitoring borehole; arrange a fixed distributed optical fiber in each monitoring borehole, and connect each fixed distributed optical fiber to an external monitoring system; Step 3, excavating the tunnel of the excavation working face, and obtaining the vibration signal of the corresponding seismic trace through each fixed distributed optical fiber; Step 4, according to the vibration signal of each seismic channel, determine the position of each signal receiving point and the corresponding substation channel number, and perform bandpass filtering on the vibration signals of all seismic channels; Step 5, select a reference trace, and obtain the correlation records between the reference trace and each of the remaining seismic traces; Step 6: perform quality evaluation and screening on all relevant records and perform data processing to obtain seismic trace records with improved signal-to-noise ratio; Step 7, extracting the velocities of direct P-waves and S-waves from all seismic traces with improved signal-to-noise ratios and performing velocity scanning to obtain the velocity values ​​of direct P-waves and S-waves corresponding to the combinations of all adjacent seismic traces; Step 8, calculating the Poisson's ratio at the corresponding position of the working surface to be measured according to the velocity values ​​of the direct longitudinal wave and the transverse wave corresponding to each seismic trace; Step 9, plotting a curve of Poisson's ratio versus position based on the Poisson's ratio at different positions of the working face to be tested, and determining the gas content in front of and on both sides of the excavation working face through the curve of Poisson's ratio versus position.

2. The method for advanced detection of gas-bearing areas during excavation of a tunneling working face according to claim 1, characterized in that: In step 5, when the vibration signal of the excavation earthquake is band-pass filtered, the filtering range is 5-200 Hz.

3. The method for advanced detection of gas-bearing areas during excavation of a tunneling working face according to claim 1, characterized in that: In step 5, the seismic trace closest to the tunnel boring machine is selected as the reference trace; The vibration signal of the reference trace after bandpass filtering is correlated with the vibration signal of each of the remaining seismic traces after bandpass filtering using the following formula to obtain a correlation record φ between the vibration signal of the reference trace and each of the remaining seismic traces; Among them, x i represents the bandpass filtered vibration signal of the reference track; x j represents the vibration signal after bandpass filtering of the jth seismic trace; t i and t j denote the initial travel time of the reference trace and the jth seismic trace respectively; τ represents the delay time relative to the initial travel time; T represents the length of the correlation window; t0 represents the time between the initial travel time and the starting point of the correlation window; δt represents the sampling rate.

4. The method for advanced detection of gas-bearing areas during excavation of a tunneling working face according to claim 3, characterized in that: Step 6 includes the following sub-steps: Step 61, select any one of the related records, and take a time window along the direct wave travel time path in the selected related record; Step 62, using the following formula, obtain the normalized cross-correlation sum coefficient NCC for the records in the time window; Where m represents the total number of seismic traces; i represents the i-th seismic trace; f represents the amplitude; f i,t(i) represents the amplitude of the i-th seismic trace with the upward travel time t(i); Step 63, traverse all relevant records, obtain corresponding normalized cross-correlation sum coefficients and perform data processing respectively to obtain seismic single shot records with improved signal-to-noise ratio.

5. The method for advanced detection of gas-bearing areas during excavation of a working face according to claim 1, characterized in that: Step 7 includes the following sub-steps: Step 71, setting the speed scanning range Vmin-Vmax and the scanning interval dv; Step 72, perform velocity cycles from Vmin to Vmax at a scanning interval dv, and use the following formula to calculate the direct wave arrival time difference of each seismic trace using each cycle velocity: Among them, Δt i represents the direct wave arrival time difference of the i-th seismic trace; v k Indicates the cycle speed selected this time, v k ∈(Vmin, Vmax); s i represents the distance between the ith seismic trace and the first seismic trace; Step 73, using the following formula, traverse each seismic trace and perform time difference correction using the corresponding direct wave arrival time difference: in, It represents the data of the i-th seismic trace after eliminating the influence of the direct wave propagation time difference; Step 74, using the following formula, calculate the square modulus of the zero-delay correlation coefficient between two adjacent seismic traces through the seismic trace data after time difference correction: Among them, ij represents the square modulus of the zero-delay mutual correlation coefficient between the i-th and j-th seismic traces; Step 75, substitute each cycle speed and change Ψ ij The velocities corresponding to the maximum and second maximum values ​​are taken as the longitudinal wave velocity V of the direct wave between the i-th and j-th seismic traces. p (i, j) and shear wave velocity V s (i,j); Step 76, repeating steps 74-75, traversing all the combinations of two adjacent seismic traces, and obtaining their corresponding longitudinal wave velocity and shear wave velocity.

6. The method for advanced detection of gas-bearing areas during excavation of a tunneling working face according to claim 5, characterized in that: In step 71, Vmin is set to 1500 m / s; Vmax value is 3000m / s; The scanning interval dv is 5m / s.

7. The method for advanced detection of gas-bearing areas during excavation of a tunneling working face according to claim 6, characterized in that: In step 8, the Poisson's ratio μ at the corresponding position is calculated using the following formula based on the P-wave velocity and S-wave velocity corresponding to the two adjacent seismic traces obtained in step 76: Among them, V p represents the longitudinal wave velocity; V s Represents the shear wave velocity.

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