CN111812714B - Coal seam longitudinal and transverse wave velocity obtaining method based on refracted longitudinal waves and high-frequency trough waves - Google Patents
Coal seam longitudinal and transverse wave velocity obtaining method based on refracted longitudinal waves and high-frequency trough waves Download PDFInfo
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Abstract
The invention relates to a longitudinal wave and transverse wave velocity solving method, belongs to the technical field of coal detection, and particularly relates to a coal seam longitudinal wave and transverse wave velocity solving method based on refracted longitudinal waves and high-frequency trough waves. The method for obtaining the coal bed longitudinal wave and transverse wave speeds provided by the invention can obtain the coal bed longitudinal wave speed according to the relationship between the coal bed longitudinal wave and the refracted longitudinal wave period, the speed and the coal bed thickness and obtain the coal bed transverse wave speed according to the relationship between the coal bed transverse wave and the high-frequency trough wave on the premise of not increasing the cost by depending on a trough wave detection project, is simple and convenient to operate, has small artificial error, can provide accurate constraint parameters for lithological inversion, improves the accuracy of inversion, provides support for further delineating the position and the type of an abnormal area, and ensures safe and efficient mining of a coal mine.
Description
Technical Field
The invention relates to a longitudinal wave and transverse wave velocity solving method, belongs to the technical field of coal detection, and particularly relates to a coal seam longitudinal wave and transverse wave velocity solving method based on refracted longitudinal waves and high-frequency trough waves.
Background
For coal field exploration, the coal bed longitudinal wave velocity and the coal bed transverse wave velocity in a coal face are important geophysical parameters. The accurate calculation of the two velocities (coal bed longitudinal wave velocity and coal bed transverse wave velocity) plays an important role in the detection of disaster-causing areas such as a coal bed fracture zone, a stress concentration area, a gas gathering area and the like in a working face. Because seismic waves are transmitted in the coal bed in the form of trough waves, the conventional method cannot directly calculate the longitudinal wave velocity and the transverse wave velocity of the coal bed only from underground seismic data.
At present, the channel wave detection engineering is widely developed in the tunneling and stoping stages of a coal face, and collected underground seismic data not only comprise channel waves transmitted along a coal seam, but also comprise refracted waves transmitted along the interface of the coal seam and a top floor rock stratum. In fact, the velocities of the refracted wave and the trough wave are determined by the velocities of the coal seam and the surrounding rocks of the top and bottom floor together. The high frequency channel wave velocity is similar to the coal bed transverse wave velocity, and the velocity and period of the refraction longitudinal wave are related to the coal thickness and the coal bed longitudinal wave velocity. Therefore, the underground seismic data are processed, the arrival time of the refracted longitudinal wave and the arrival time of the high-frequency channel wave on each seismic channel data are picked up, the refracted wave and the channel wave are converted into the arrival time of the coal bed longitudinal wave and the arrival time of the coal bed transverse wave of each channel according to the relation between the refracted wave and the channel wave and the coal bed longitudinal wave and the coal bed transverse wave, and then the imaging results of the coal bed longitudinal wave and the coal bed transverse wave speed in the working face can be obtained through speed inversion. The coal bed longitudinal wave and coal bed transverse wave speeds in the whole working face range are obtained in the mode, and detection of disaster-causing areas in the working face can be achieved by inverting lithological parameters such as porosity and gas content of the coal bed in the working face.
Disclosure of Invention
The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.
The invention mainly aims to provide a method for solving the velocity of longitudinal waves and transverse waves of a coal bed based on refracted longitudinal waves and high-frequency trough waves.
In order to solve the problems, the scheme of the invention is as follows:
a method for solving the speed of longitudinal waves and transverse waves of a coal bed based on refracted longitudinal waves and high-frequency channel waves is characterized by comprising the following steps:
and calculating the wave mode speed of the coal bed in the working surface by using a tomography method and adopting the following iterative formula based on the obtained wave mode of the coal bed when the wave mode arrives:
where m is the number of steps in the iteration, a n Is the length of the n-th ray from the emitting point to the receiving point of the seismic channel in each grid, t n Is the waveform arrival time of the n-th track, λ is the relaxation factor, v (m-1) Is the waveform velocity, v, of the m-1 st iteration (m) Is the waveform velocity of the mth iteration.
Preferably, the method for obtaining the coal bed longitudinal wave and coal bed transverse wave velocity based on the refracted longitudinal wave and the high-frequency trough wave includes the arrival time t of the coal bed longitudinal wave pn The arrival time t of the longitudinal wave of the coal bed pn Is based on the following equation:
in the formula, L n Is the propagation distance of the nth ray, h is the thickness of the coal seam, T n Is the period of the refracted longitudinal wave, t rpn Is the refracted longitudinal wave arrival time.
Preferably, in the method for determining the velocity of the longitudinal wave and the transverse wave of the coal bed based on the refracted longitudinal wave and the high-frequency trough wave, the time t of the refracted longitudinal wave is rpn The calculation of (2) comprises:
by observing the seismic record, the minimum velocity v of the refracted longitudinal wave is given p0 So that v is p0 Above the time distance curve, only the wave train of the refracted longitudinal wave;
each path of seismic data d n (t) zeroing data points except for refracted longitudinal wave to obtain refracted longitudinal wave data p n (t)；
Constructed to refract longitudinal main frequency f p Minimum phase wavelet w as dominant frequency p (τ)；
For refracted longitudinal wave data p n (t) at each time point t, calculating the waveform and wavelet w before and after the point p (τ) similarity ratio r pn (t)；
Determining r in each trace of seismic data pn (t) t reaches the maximum max Then t is max Is the time t of the refracted longitudinal wave of the channel rpn 。
Preferably, in the method for determining the velocity of the longitudinal wave and the transverse wave of the coal bed based on the refracted longitudinal wave and the high-frequency trough wave, the period T of the refracted longitudinal wave n The obtaining of (1) comprises:
solving for p by short-time Fourier transform n (t) time frequency spectrum P n (t,f)；
Extracting principal frequency f of refracted longitudinal wave p Temporal spectral slice P of n (t,f p )；
To P n (t,f p ) Sampling with T as period to obtain average amplitude A at sampling point n (T)：
Wherein K is the number of periods T contained in the wave train length of the refracted longitudinal wave, namely:
find out the order of A n (T) T to the maximum max Then T is max Is the refracted longitudinal wave period T of the channel n 。
Preferably, in the method for obtaining the velocity of the longitudinal wave and the transverse wave of the coal bed based on the refracted longitudinal wave and the high-frequency channel wave, the principal frequency f of the refracted longitudinal wave p The calculation of (2) comprises:
solving for p by Fourier transform n (t) finding the frequency f corresponding to the maximum amplitude spectrum max Then f is max I.e. primary frequency f of refracted longitudinal waves p 。
Preferably, the method for obtaining the coal bed longitudinal wave and coal bed transverse wave velocity based on the refracted longitudinal wave and the high-frequency trough wave includes the arrival time t of the coal bed transverse wave sn The arrival time t of the coal bed transverse wave sn The obtaining of (1) comprises:
for each seismic data d n (t) high pass filtering, and determining the amplitude envelope E n (t)；
To E n (t) at each time point t, the average amplitude ratio r before and after the point is obtained En (t)；
Determining the distance r in each seismic data trace En (t) t reaches a maximum max Then t is max That is the arrival time t of the transverse wave of the coal bed on the road sn 。
Therefore, compared with the prior art, the invention has the following advantages: the method for solving the coal bed longitudinal wave velocity and the coal bed transverse wave velocity can accurately solve the coal bed longitudinal wave velocity and the coal bed transverse wave velocity of each area in the working face by means of a channel wave detection project on the premise of not increasing cost, is simple and convenient to operate, has small human error, can provide accurate constraint parameters for lithology inversion, and improves the accuracy of the inversion. On the basis of the inversion result, the position and the type of the abnormal area in the coal bed are further defined, so that the safety and the high-efficiency mining of the coal mine are better guaranteed.
Drawings
The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate embodiments of the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the disclosure.
Fig. 1 is a general flowchart of a method for determining the velocity of longitudinal waves and transverse waves of a coal seam based on refracted longitudinal waves and high-frequency channel waves.
FIG. 2 is a model diagram of a working face and parameters of an abnormal region containing coal seam velocity.
Fig. 3 shows the results of forward modeling of the three-dimensional elastic wave of the model.
FIG. 4 is a intercepted refracted longitudinal wave.
FIG. 5 is a constructed refracted longitudinal wave wavelet.
FIG. 6 is a wave train of two refracted longitudinal waves.
Fig. 7 is a time-frequency spectrum of two refracted longitudinal waves, in which (a) is a 142 th temporal frequency spectrum and (b) is a 100 th temporal frequency spectrum.
Fig. 8 is a time-frequency spectrum frequency slice on two main frequencies, in which (a) is a 142 th time-frequency spectrum frequency slice, and (b) is a 100 th time-frequency spectrum frequency slice.
FIG. 9 is a graph of the average amplitude over the period of two traces, where (a) is the average amplitude over the 142 th trace and (b) is the average amplitude over the 100 th trace.
FIG. 10 shows the arrival of high frequency channel waves and coal bed longitudinal waves and coal bed transverse waves.
Fig. 11 shows tomographic results of the determined coal bed compressional wave velocity and coal bed transverse wave velocity, where (a) is the coal bed compressional wave velocity and (b) is the coal bed transverse wave velocity.
Detailed Description
Examples
The refracted wave in this embodiment means: the seismic source is excited in the coal seam, and then generates seismic waves which propagate along the interface of the coal seam and the rock stratum and have strong periodicity under the influence of multiple reflections between the layers.
Referring to fig. 1, a method for determining the velocity of longitudinal waves and transverse waves of a coal seam based on refracted longitudinal waves and high-frequency channel waves is disclosed. The method specifically comprises the following steps:
the seismic waves received by each geophone during each seismic source excitation in the underground seismic data are recorded as a seismic trace. And after preprocessing such as time delay correction and denoising is carried out on the actual data, and the ray propagation distance corresponding to each channel is calculated according to the positions of the excitation point and the receiving point corresponding to each channel. For the nth data, the position of the excitation point is (x) sn ,y sn ) The receiving point is set to (x) rn ,y rn ) Then its corresponding ray propagation distance L n Comprises the following steps:
and analyzing the geological data of the working face, and obtaining the average coal seam thickness h of the working face according to the drilling histogram of the working face and the actual exposure condition of the roadway.
Then, the main frequency f of the refracted longitudinal wave is obtained p The concrete measures are as follows:
by observing the seismic record, the minimum velocity v of the refracted longitudinal wave is given p0 So that v is p0 Above the time-distance curve of (2) there is only the wave train of the refracted longitudinal wave. For v p0 The seismic record display software is operated only by approximate estimation, and only refracted shear wave trains with obviously stronger amplitudes are removed.
Each channel of seismic data d n (t) zeroing data points except for refracted longitudinal wave to obtain refracted longitudinal wave data p n (t) that is
Solving for p by Fourier transform n (t) amplitude spectrum P n (f) And after the amplitude spectrums of all tracks are superposed, finding out the frequency f corresponding to the maximum amplitude spectrum max Then f is max I.e. refraction of the primary longitudinal wave frequency f p 。
In finding main frequency f of refracted longitudinal wave p Then, the arrival time t of the refracted longitudinal wave of each channel is obtained rpn The concrete measures are as follows:
construction with f p Minimum phase wavelet w as dominant frequency p (τ)：
K is the ratio of the wave crest to the wave trough, and can be selected from 1.01 to 1.2 according to actual conditions; e is a natural constant; tau is a sampling point, tau is equal to 0]M is the wavelet length, typically 3-4 periods T p ，T p ＝1/f p 。
To p n (t) at each time point t, determining the wavelets w and the waveform in the range of one wavelet length M before and after the point p (τ) similarity ratio r pn (t)：
Determining r in each trace of seismic data pn (t) t reaches the maximum max Then t is max Is the time t of the refracted longitudinal wave of the channel rpn 。
The period T of the refracted longitudinal wave of each track is then determined n The concrete measures are as follows:
finding p by short-time Fourier transform n (t) time frequency spectrum P n (t,f)；
Let f = f p Taking out the main frequency f of the refracted longitudinal wave p Temporal spectral slice P n (t,f p )；
To P n (t,f p ) Sampling with T as period to obtain average amplitude A at sampling point n (T)：
Wherein K is the number of periods T which can be contained in the wave train length of the refracted longitudinal wave, namely:
find out the relation A n (T) T to the maximum max Then T is max Is the refracted longitudinal wave period T of the channel n 。
Then, the time t of the longitudinal wave of each coal seam is obtained pn . According to t pn And period T of refracted longitudinal wave n Coal seam thickness h, refracted longitudinal wave arrival time t rpn Can derive:
wherein L is n Is the propagation distance of the nth track. For the working surface with stable coal seam thickness, the time t of the coal seam longitudinal wave can be obtained by the formula pn 。
Then, the arrival time t of the transverse wave of each coal seam is obtained sn . Because the velocity of the high-frequency channel wave is infinitely close to that of the coalThe laminar transverse wave speed, and the high-pass filtering can effectively eliminate the Airy phase of the refracted wave and the trough wave and reserve the high-frequency trough wave, so that the speed of the coal-bed transverse wave can be replaced by the speed of the high-frequency trough wave. Solving for t using high-pass filtered seismic data sn . The concrete measures are as follows:
for each seismic data d n (t) high-pass filtering to obtain amplitude envelope E n (t)。
To E is to n (t) at each time point t, the average amplitude ratio r before and after the point is obtained En (t)：
Determining r in each trace of seismic data En (t) t reaches a maximum max Then t is max Namely the arrival time t of the transverse wave of the coal bed csn 。
The arrival time t of the longitudinal wave of the coal seam on each seismic channel is obtained pn And the arrival time t of the transverse wave of the coal bed sn Then, the longitudinal wave velocity v of the coal bed in the working face can be obtained by utilizing a tomography algorithm p Transverse wave velocity v of coal bed s The inversion result of (2). By the longitudinal wave velocity v of the coal bed p For example, the arrival time t of the coal bed longitudinal wave on each seismic channel is obtained pn Then, dividing the working surface into K grids, and setting the longitudinal wave velocity of the coal bed of each grid as v pk The length a of the ray from the emitting point to the receiving point of each seismic channel in each grid is obtained according to the space relation kn ，k∈[1，K]，n∈[1，N]K is the total number of grids and N is the total number of tracks. A is to kn Writing as matrix form A, v pk And t pn Written as vector form v and t, respectively, then there is a system of equations
Av＝t
Where A and t are known. Solving the system of equations to obtain v for each grid rpk Thereby obtaining the longitudinal wave velocity v of the surrounding rock in the working face rp Distribution of (2). The equation set can be solved by adopting an ART algorithm, and after an initial value is set for v according to experience, the following iterative formula is adopted for solving:
where m is the number of steps of the iteration, a n Is the length of the nth ray in each grid, and λ is the relaxation factor. t is t n The arrival time of the nth track, v is a vector formed by the values of the speed in each grid. When the longitudinal wave velocity v of the coal seam is obtained p When in the above formula, t n Is t pn (ii) a When the transverse wave velocity v of the coal bed is obtained s When in the above formula, t n Is t sn 。
Generally, after a plurality of iterations, a more ideal result can be obtained. Sequentially mixing t pn And t sn Substituting into the equation set, the v in the working surface can be obtained p And v s The distribution of (c).
The arrangement mode of the underground observation system required by the embodiment is the same as that of the channel wave detection project, and the underground observation system can be developed simultaneously with the channel wave detection project without additional construction.
The refracted longitudinal wave in the underground seismic data is not the longitudinal wave of the surrounding rock, the refracted longitudinal wave speed is less than that of the surrounding rock, the refracted longitudinal wave has strong periodicity, and the periodicity is related to the coal thickness.
The effect of the invention is illustrated below by taking a theoretical model as an example:
the model consists of three layers, namely a top plate, a coal bed and a bottom plate, and the lithology of the top plate is the same as that of the bottom plate. The longitudinal wave velocity of the surrounding rock is 4000m/s, the transverse wave velocity of the surrounding rock is 2300m/s, and the density is 2.56g/cm 3 (ii) a The thickness of the coal seam is 10m, the longitudinal wave velocity of the coal seam is 2000m/s, the transverse wave velocity of the coal seam is 1050m/s, and the density is 1.4g/cm 3 . The model comprises two coal seam low-speed areas, wherein the longitudinal wave speed of the low-speed area is 1600m/s, and the transverse wave speed of the low-speed area is 850m/s. The location and observation system arrangement of the low velocity zone is shown in fig. 2. Fig. 3 shows the results of the 25 th shot forward simulation obtained by the three-dimensional elastic wave forward simulation method, from which refracted longitudinal waves, refracted transverse waves, and channel waves can be distinguished after amplitude gain control processing. The coal bed compressional wave velocity and the coal bed shear wave velocity are determined from the data according to the steps of the invention.
The step 1 is carried out, and the step,calculating the propagation distance L of each channel n 。
And 2, executing the step, wherein the thickness of the coal seam is 10m.
Step 3 is performed by looking at FIG. 3, let v p0 And =2900m/s, intercepting the refracted longitudinal wave. The intercepted refracted longitudinal wave is shown in figure 4.
Step 4 is executed to obtain main frequency f of refracted longitudinal wave p Is 500Hz. Taking the k value as 1.02 and constructing a dominant frequency f p Is a 500Hz wavelet, as shown in FIG. 5.
Step 6 is executed, taking the 100 th channel and the 142 th channel as examples, the refracted longitudinal waves in the two channels are as shown in fig. 6, and short-time fourier transform is respectively performed to obtain time-frequency spectrums as shown in fig. 7.
Go to step 7, take out f p Temporal spectral slice P n (t,f p ) As in fig. 8.
Step 9 is executed of T n 、t rpn 、L n H, calculating the arrival time t of the longitudinal wave of each coal seam pn 。
And step 10 is executed, high-pass filtering of more than 500Hz is carried out on the data, and high-frequency slot waves are obtained.
Step 11 is executed to obtain the arrival time t of the coal bed transverse wave csn . FIG. 10 shows the arrival time t of the high frequency channel wave and the determined coal bed longitudinal wave pn And the arrival time t of the transverse wave of the coal bed sn 。
Step 12 is executed for t pn And t sn Carrying out velocity tomography to obtain the longitudinal wave velocity v of the coal bed of the working face p And coal bed transverse wave velocity v s The tomographic results of (a) are shown in fig. 11 (a) and fig. 11 (b), respectively. It can be seen that the reversed coal bed longitudinal wave velocity of fig. 11 (a) is 2000m/s, which is consistent with the model, wherein the velocity of the low velocity region is about 1650m/s, which is close to 1600m/s of the model; FIG. 11 (b) shows the inverted lateral wave velocity of the surrounding rockThe velocity is 1050m/s, which is consistent with the model, wherein the velocity of the low velocity region is about 810m/s, which is close to 850m/s of the model. In general, the method can accurately calculate the distribution condition of the coal bed longitudinal wave velocity and the coal bed transverse wave velocity on the working surface, and therefore the detection of the velocity abnormal area in the surrounding rock is achieved.
It is noted that references in the specification to "one embodiment," "an example embodiment," "some embodiments," etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.
The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (4)
1. A method for solving the speed of longitudinal waves and transverse waves of a coal bed based on refracted longitudinal waves and high-frequency trough waves is characterized by comprising the following steps:
and calculating the wave mode speed of the coal bed in the working surface by using a tomography method and adopting the following iterative formula based on the obtained wave mode of the coal bed when the wave mode arrives:
where m is the number of steps in the iteration, a n Is the first of a seismic trace from the point of emission to the point of receptionThe length of n rays in each grid forms a vector, | a n I is the length of this ray, λ is the relaxation factor, t n When the waveform of the n-th track arrives, v is a vector formed by values of the required speed in each grid, v is (m-1) Is the waveform velocity, v, of the m-1 th iteration (m) The waveform velocity for the mth iteration;
wherein, the longitudinal wave velocity v of the coal bed is obtained p Then, the waveform of the n-th track reaches time t n Taking the arrival time t of the longitudinal wave of the coal bed pn (ii) a When the transverse wave velocity v of the coal bed is obtained s Then, the waveform of the n-th track reaches time t n Taking the arrival time t of the transverse wave of the coal bed sn ；
Wherein,
the arrival time t of the longitudinal wave of the coal bed pn Is based on the following equation:
in the formula, L n Is the propagation distance of the nth ray, h is the thickness of the coal seam, T n Is the period of the refracted longitudinal wave, t, on the seismic trace rpn Is the arrival time of the refracted longitudinal wave on the channel;
the arrival time t of the coal bed transverse wave sn The obtaining of (1) comprises:
for each seismic data d n (t) high-pass filtering to obtain amplitude envelope E n (t)；
To E n (t) at each time point t, the average amplitude ratio r before and after the point is obtained En (t)；
Determining the distance r in each seismic data trace En (t) t reaches a maximum max Then t is max That is the arrival time t of the transverse wave of the coal bed on the road sn 。
2. The method for calculating the velocity of the compressional wave and the shear wave of the coal bed based on the refracted compressional wave and the high-frequency channel wave as claimed in claim 1, wherein the refracted compressional wave reaches time t rpn The obtaining of (1) comprises:
by observing the seismic records, giveMinimum velocity v of refracted longitudinal wave p0 So that v is p0 Above the time distance curve, there is only wave train of refracted longitudinal wave;
each channel of seismic data d n (t) zeroing data points other than the refracted longitudinal wave to obtain refracted longitudinal wave data p n (t)；
Constructed to refract longitudinal main frequency f p Minimum phase wavelet w as dominant frequency p (τ)；
For refracted longitudinal wave data p n (t) at each time point t, the waveform and wavelet w before and after the point are obtained p (tau) similarity ratio r pn (t)；
Determining r in each trace of seismic data pn (t) t reaches the maximum max Then t is max Is the time t of the refracted longitudinal wave of the channel rpn 。
3. The method for calculating the velocity of the compressional wave and the shear wave of the coal bed based on the refracted compressional wave and the high-frequency channel wave as claimed in claim 2, wherein the period T of the refracted compressional wave n The obtaining of (1) comprises:
finding p by short-time Fourier transform n (t) time-frequency spectrum P n (t,f)；
Extracting main frequency f of refracted longitudinal wave p Temporal spectral slice P of n (t,f p )；
To P n (t,f p ) Sampling with T as period to obtain average amplitude A at sampling point n (T)：
Wherein K is the number of periods T contained in the wave train length of the refracted longitudinal wave, namely:
find out the order of A n (T) T to the maximum max Then T is max Is the refracted longitudinal wave period T of the channel n 。
4. The method for calculating the velocity of the longitudinal wave and the transverse wave of the coal bed based on the refracted longitudinal wave and the high-frequency channel wave as claimed in claim 2, wherein the principal frequency f of the refracted longitudinal wave p The obtaining of (1) comprises:
solving for p by Fourier transform n (t) finding the frequency f corresponding to the maximum amplitude spectrum max Then f is max I.e. primary frequency f of refracted longitudinal waves p 。
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