A method and system for detecting thin coal seams based on the attenuation of the period amplitude of refracted waves

Abstract

The present invention discloses a method and system for detecting thin coal seams based on the attenuation of the period amplitude of refracted waves, including: S1 Instrument layout: The seismic survey line consists of S excitation points and R receiving points; the total number of seismic data d i (t) is formed through signal acquisition and data transmission between the excitation points and the receiving points; S2 Obtaining formation data and calculating the refracted wave period: Obtaining the longitudinal wave velocity v r of the surrounding rock and the longitudinal wave velocity v c of the coal seam, measuring the thickness h of the coal seam exposed in the roadway on the sidewall of the roadway, and calculating the refracted wave period T; S3 Processing d i (t) to obtain the seismic data s i (t) after deconvolution and in-trace equalization; obtaining the amplitude ratio of the seismic data s i (t) to the reference trace s0(t) at the n p th order as the refracted wave period amplitude coefficient a p of point P, and the numerical value of a p reflects the thickness of the coal seam at point P. The refracted wave of the coal seam used in the present invention is another underground seismic wave generated simultaneously with the trough wave. Using the refracted wave can more accurately interpret the boundary of the thin coal seam, improving the coal mining work efficiency and resource utilization rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of coalfield geophysical prospecting, and relates to an underground geophysical prospecting method and system for detecting thin coal zones in coal mining faces. The method separates refracted waves from the seismic waves excited and received in the coal seam, and estimates the detection method of the boundary of the thin coal zone by using the attenuation degree of the periodic amplitude of the refracted waves. Background Art

[0002] A thin coal zone is a region where the thickness of the coal seam is locally reduced due to bottom convex thinning or the influence of river erosion. The existence of thin coal zones in coal mining faces not only increases the mining difficulty, reduces the coal output, but also easily induces geological disasters such as gas outbursts or water inrusions. Therefore, accurately detecting the position and development of hidden thin coal zones in the working face before coal mining is one of the prerequisites for reasonable design of the mining plan and disaster prevention and mitigation. The existing underground thin coal zone detection mainly relies on the drilling method, which is inefficient and inaccurate. There is a lack of a method in underground geophysical prospecting that can accurately detect thin coal zones. At present, only the trough wave detection technology uses the dispersion characteristics of trough waves to detect the coal thickness, but the actual underground data has a large gap with the theoretical dispersion properties of trough waves, and the detection results of this method are not ideal. Summary of the Invention

[0003] The present invention provides a data acquisition and processing method, which realizes the detection of the position of hidden thin coal zones in the coal seam by using the periodic change of the amplitude of refracted waves propagating on the coal-rock interface. To solve the above technical problems, the present invention adopts the following technical solutions:

[0004] A thin coal zone detection method based on the attenuation of the periodic amplitude of refracted waves, comprising:

[0005] S1 Instrument layout: Layout seismic survey lines, which are composed of S excitation points and R receiving points; a seismic data d i (t) with a total number of channels N is formed through signal acquisition and data transmission between the excitation points and the receiving points, where t is time; i is the seismic channel number, i ∈ [1, N], and N = S × R;

[0006] S2 Obtain formation data and the refracted wave period T: Obtain the longitudinal wave velocity v of the surrounding rock r and the longitudinal wave velocity v of the coal seam c , measure the thickness h of the coal seam exposed in the roadway on the sidewall of the roadway, and calculate the refracted wave period T;

[0007]

[0008] S3 Obtain the refracted wave period amplitude coefficient a p :

[0009] Perform deconvolution and in-trace equalization processing on the seismic data d i (t) to obtain the seismic trace si (t); The imaging area corresponding to the coal mining face is divided into grids, and each grid corresponds to an imaging point P(x, y); Calculate the distances between the imaging point P(x, y) and the connecting lines between each shot point and geophone point, and select the connecting line with a distance less than the preset threshold L W corresponding to the seismic trace s i (t) to form a trace gather Φ P ; For the trace gather Φ P in each seismic trace s i (t), calculate the refraction wave order n corresponding to the point P(x, y) p , and the amplitude ratio of the seismic trace s i (t) and the reference trace s 0 (t) at the refraction wave order n p is used as the refraction wave period amplitude coefficient a of the point P(x, y) p .

[0010] Optionally, the instrument layout specifically includes: arranging seismic survey lines in the transportation roadway and / or return airway of the coal mining face. The seismic survey line consists of S shot holes arranged at intervals and R geophone holes arranged at intervals; Explosives are buried in the shot holes as excitation points, and geophones are buried in the geophone holes as receiving points; A seismic data d i (t) with a total number of traces N is formed through signal acquisition and data transmission between the excitation point and the receiving point, where t is time; i is the seismic trace number, i ∈ [1, N], and N = S × R.

[0011] Optionally, the method for obtaining the reference trace s 0 (t) includes:[[]]

[0012] Set the time window parameter t W , and intercept the seismic data d i -t W to t i +t W in the time period to form a seismic wavelet w(t); Use the seismic wavelet w(t) to perform deconvolution on the seismic data d i (t) to obtain the deconvolved seismic data d′ i (t); Using T as a parameter, perform in-trace equalization on the seismic data d′ i (t) with the automatic gain control algorithm to obtain the seismic trace s i (t); Statistically calculate the sum of amplitudes A i of each trace data on s i (kT + t i ), and select the trace with the largest sum of amplitudes as the reference trace s i (t); 0 .

[0013] K is a positive integer, and the value of K is less than 10, t i represents the first arrival time of the refracted wave of each seismic trace.

[0014] Optionally, S3 obtains the refracted wave period amplitude coefficient a p Specifically including:

[0015] Based on the position of the excitation point (x S , y S ), the position of the receiving point (x R , y R ) and the longitudinal wave velocity v of the surrounding rock r , calculate the first arrival time t of the refracted wave of each seismic trace i ;

[0016]

[0017] Divide the imaging area of the coal mining face into grids. Suppose the number of its units is X in the strike direction and Y in the dip direction; for each grid, the corresponding imaging point is P(x, y), where x ∈ [1, X] and y ∈ [1, Y];

[0018] Among them

[0019] Calculate according to the above formula for all imaging points in the imaging area, and the imaging result of the refracted wave period amplitude coefficient of this area can be obtained. The abnormal area in the imaging result corresponds to the boundary of the thin coal seam. M is the total number of traces in the trace gather Φ P .

[0020] Optionally, the method for obtaining the balanced seismic trace s i (t) includes:

[0021] Set the time window parameter t W , and intercept the data within the time period from t i - t i to t W + t i in the seismic data d W as the seismic wavelet w(t);

[0022] Perform deconvolution on the seismic data d i (t) with the seismic wavelet w(t), that is, obtain the frequency-domain seismic signal D′ i (ω) from the following formula, and then transform D′ i (ω) to the time domain by inverse Fourier transform to obtain the deconvolved seismic data d′ i (t);

[0023]

[0024] where ω is the frequency, D i (ω) is the frequency-domain form of d i (t), W(ω) is the frequency-domain form of w(t), and the frequency-domain form is obtained by Fourier transform. W * (ω) is the conjugate complex number of W(ω), and γ ranges from 0.1 to 0.01;

[0025] Taking the refraction wave period T as a parameter, the gain control algorithm is used to perform in-trace equalization on d′ i (t), and the equalized seismic signal s i (t);

[0026]

[0027] A thin coal seam belt detection system based on the amplitude attenuation of the refraction wave period is provided with:

[0028] Instrument layout module: Layout seismic survey lines. The seismic survey lines are composed of S excitation points and R receiving points; the total number of seismic data d i (t) is formed by signal acquisition and data transmission between the excitation points and the receiving points, where i is the seismic trace number, i ∈ [1, N], and t is the time; N = S × R;

[0029] Stratum data and refraction wave period T acquisition module: Obtain the longitudinal wave velocity v of the surrounding rock r and the longitudinal wave velocity v of the coal seam c , measure the thickness h of the coal seam exposed in the roadway on the sidewall of the roadway, and calculate the refraction wave period T;

[0030]

[0031] Refraction wave period amplitude coefficient a acquisition p module: After performing deconvolution and in-trace equalization processing on the seismic data d i (t), the seismic trace s i (t) is obtained; the imaging area corresponding to the coal mining face is divided into grids, and each grid corresponds to an imaging point P(x, y); calculate the distance between the imaging point P(x, y) and the connection lines between each shot point and geophone point, and select the connection line corresponding to the distance less than the preset threshold L W The corresponding seismic trace s i (t) forms a trace gather Φ P ; for each seismic trace s P in the trace gather Φ i (t), calculate the refraction wave order n p corresponding to the point P(x, y), and the amplitude ratio of the seismic trace s i (t) and the reference trace s 0 (t) at the refraction wave order n p is used as the refraction wave period amplitude coefficient a of the point P(x, y)p 。

[0032] Optionally, the instrument layout specifically includes: arranging seismic survey lines in the transportation roadway and / or the return airway of the coal mining face. The seismic survey line consists of S shot holes arranged at intervals and R geophone holes arranged at intervals. Explosives are buried in the shot holes as excitation points, and geophones are buried in the geophone holes as receiving points. The excitation points and the receiving points form seismic data d with a total number of channels N through signal acquisition and data transmission i (t), where t is time; i is the seismic trace number, i ∈ [1, N], and N = S × R.

[0033] Optionally, the acquisition method of the reference trace s 0 (t) includes:

[0034] Set the time window parameter t W , and intercept the seismic data d i -t W to t i +t W during the time period to form a seismic wavelet w(t); deconvolve the seismic data d i (t) with the seismic wavelet w(t) to obtain the deconvolved seismic data d′ i (t); use the automatic gain control algorithm to perform in-trace equalization on the seismic data d′ i (t) with T as a parameter to obtain the seismic trace s i (t); statistically calculate the sum of amplitudes A i of each trace of data on s i (kT + t i ), and select the trace with the largest sum of amplitudes as the reference trace s i (t); 0 (t);

[0035] K is a positive integer, the value of K is less than 10, and t i represents the first arrival time of the refracted wave of each seismic trace.

[0036] Optionally, the module for obtaining the refracted wave period amplitude coefficient a p specifically includes:

[0037] Based on the excitation point position (x S , y S ), the receiving point position (x R , y R ) and the longitudinal wave velocity v of the surrounding rock r , calculate the first arrival time t i of the refracted wave of each seismic trace;

[0038]

[0039] Divide the imaging area of the coal mining face into grids. Assume there are X grids in the strike direction and Y grids in the dip direction; for each grid, the corresponding imaging point is P(x, y), where x ∈ [1, X] and y ∈ [1, Y];

[0040] Among them

[0041] Calculate for all imaging points in the imaging area according to the above formula, and the imaging result of the refraction wave period amplitude coefficient of this area can be obtained. The abnormal area in the imaging result corresponds to the boundary of the thin coal seam belt, and M is the total number of traces in the trace gather Φ P of the total number of traces.

[0042] Optionally, it further includes an acquisition module for the balanced seismic trace s i (t):

[0043] Set the time window parameter t W , and intercept the data within the time period from t i (t) from t i -t W to t i +t W as the seismic wavelet w(t);

[0044] Use the seismic wavelet w(t) to perform deconvolution on the seismic data d i (t), that is, obtain the frequency-domain seismic signal D′ i (ω) from the following formula, and then use the inverse Fourier transform to transform D′ i (ω) to the time domain to obtain the deconvolved seismic data d′ i (t);

[0045]

[0046] where ω is the frequency, D i (ω) is the frequency-domain form of d i (t), W(ω) is the frequency-domain form of w(t), and the frequency-domain form is obtained by Fourier transform. W * (ω) is the conjugate complex number of W(ω), and γ takes values from 0.1 to 0.01;

[0047] Using the refraction wave period T as a parameter, perform in-trace equalization on d′ i (t) with the gain control algorithm to obtain the equalized seismic signal s i (t);

[0048]

[0049] Compared with the prior art, the present invention brings the following beneficial technical effects:

[0050] The layout method of the downhole observation system required by the present invention is similar to that of the trough wave detection project, and the equipment can be shared. During downhole construction, it can be completed simultaneously with the transmission trough wave detection project without increasing additional workload and construction costs. The coal seam refraction wave used in the present invention is another type of downhole seismic wave generated simultaneously with the trough wave. Its generation and propagation mechanism are different from those of the trough wave. Therefore, the imaging result of the thin coal seam belt boundary in the working face generated by the present invention is not affected by the quality of the trough wave, which is a favorable supplement and reference to the trough wave imaging result, conducive to more accurately explaining the thin coal seam belt boundary and improving the coal mining work efficiency and resource utilization rate. Description of the Drawings

[0051] The drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present disclosure, but do not constitute a limitation to the present disclosure. In the drawings:

[0052] Figure 1 It is a corresponding diagram of the refraction wave and the coal seam;

[0053] Figure 2 It is a cross-sectional view of the relationship between the blast hole, geophone hole, coal seam and roadway;

[0054] Figure 3 It is a plan view of the relationship between the blast hole, geophone hole, coal seam and roadway; Figure 3 The straight line connecting the blast hole and the geophone hole is the "connection line" mentioned in the present invention;

[0055] Figure 4 It is a schematic diagram of the working face model containing a thin coal seam belt, where a is a plan view and b is a cross-sectional view;

[0056] Figure 5 It is the three-dimensional elastic wave forward simulation result of the working face model;

[0057] Figure 6 It is the intercepted sub-wave;

[0058] Figure 7 It is the refraction wave signals of channels R81, R92 and R150;

[0059] Figure 8 It is the result after the refraction wave signals of channels R81, R92 and R150 are deconvolved and trace balanced;

[0060] Figure 9 It is the imaging result of the refraction wave period amplitude coefficient of the working face. Specific Embodiments

[0061] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0062] Seismic data d i (t) refers to the seismic wave signal within a period of time collected by a geophone after the source is excited.

[0063] A seismic trace refers to the seismic wave signal within a period of time collected by the geophone at a certain geophone point when a certain shot point excites the source; when multiple points are sequentially excited, multiple seismic traces collected by multiple geophone points constitute seismic data.

[0064] The "seismic trace corresponding to the connection" refers to the seismic trace formed by the seismic wave signal collected at this geophone point when the connection connects a certain shot point and a certain geophone point and the source is excited at this shot point.

[0065] The downhole seismic data not only contains channel waves, but also contains refracted waves propagating along the interface between the coal seam and the roof and floor rock strata. Research has found that the refracted waves at the coal-rock interface have strong periodicity, and their period is related to the coal seam thickness. The reason for this phenomenon is that the seismic waves continuously enter and reflect at the same angle at the two interfaces of the coal seam and the roof and floor. Each incidence will generate refracted waves. Therefore, the received refracted waves have periodicity, and their amplitudes will increase after the same time difference. When there are thin coal zones in the coal seam, the refraction conditions of the seismic waves entering the thinning zone change, and the periodic strong amplitudes weaken or disappear. As Figure 1 (a), under the condition of constant coal thickness, a strong amplitude appears every fixed time period for the refracted waves. When there are thin coal zones in the coal seam, such as Figure 1 (b) to (c), as the distance between the boundary of the thin coal zone and the source point is different, the strong amplitudes at different periods weaken or disappear (the arrows in the figure indicate the positions where the thin coal seams appear). Therefore, based on this principle, it is possible to determine whether there is a thin coal zone by comparing the changes in the period amplitudes of the refracted waves on different seismic traces, and calculate the position of the boundary of the thin coal zone by determining the number of periods of the strong amplitudes.

[0066] The method for detecting thin coal zones based on the attenuation of the period amplitude of refracted waves of the present invention adopts the following data acquisition method:

[0067] S1 Instrument layout: Seismic survey lines are simultaneously arranged in the haulage roadway and / or the return airway of the coal mining face. The survey line contains S blast holes arranged at intervals and R geophone holes arranged at intervals. Specifically, blast holes and geophone holes are drilled in the coal seam as close as possible to the interface between the coal seam and the roof (or the coal seam and the floor, choosing the nearest one according to the distance from the roadway). The depth of the blast hole is about 2 m, and the depth of the geophone hole is about 1 - 1.5 m. The distance between geophone holes (channels) is 10 - 20 m, and the blast hole spacing is 10 - 20 m. The arrangement of blast holes and geophone holes can be to arrange blast holes and geophone holes at intervals in the same haulage roadway or return airway, and at the same time arrange blast holes and geophone holes at intervals in the other haulage roadway or return airway. During the experiment, the blast holes in the same roadway are used as the excitation points, and the geophone points in the other roadway are used as the receiving points, and then they can be exchanged and used; or only blast holes are arranged at intervals or only geophone holes are arranged at intervals in the same haulage roadway or return airway. Similarly, only geophone holes are arranged at intervals or only blast holes are arranged at intervals in the other haulage roadway or return airway. The experimental principle is the same; for example Figure 2 and Figure 3 the layout form in

[0068] Explosives are buried in the blast holes. The explosives are excited in one roadway, and geophones are buried in the geophone holes to receive seismic wave signals, and the seismograph receives the seismic waves. The relationship between the blast holes, geophone holes, coal seam and roadway is as Figure 2 shown. The explosives in each blast hole are excited in turn, and all geophones receive during each shot. The signal acquisition and data transmission between the excitation point and the receiving point form seismic data d i (t), where t is the time, and the unit is millisecond; i is the seismic trace number, i ∈ [1, N], N = S × R; one signal acquisition and data transmission between each excitation point and the receiving point forms a seismic trace, and N seismic traces form seismic data d i (t). The signal transmission here is seismic wave. For example, the coal seam refraction wave used in the present invention is another underground seismic wave generated simultaneously with the channel wave.

[0069] S2 Obtaining formation data and refraction wave period T: Obtain the longitudinal wave velocity v r of the surrounding rock and the longitudinal wave velocity v c of the coal seam. Measure the thickness h of the coal seam exposed in the roadway on the sidewall of the roadway, and calculate the refraction wave period T;

[0070]

[0071] S3 Obtaining the refraction wave period amplitude coefficient a p :

[0072] Process d i (t) to obtain the seismic data s after deconvolution and in-trace equalization i(t); The imaging area corresponding to the coal mining face is divided into grids, and each grid corresponds to an imaging point P(x, y); calculate the distances between the imaging point P(x, y) and the connecting lines of each excitation point and detection point, and select the seismic data s W (t) corresponding to the connecting lines with all connection distances less than the preset threshold L i to form a trace gather Φ P ; For each trace data s P in the trace gather Φ i (t), calculate the refraction wave order n p corresponding to the point P(x, y), and use the amplitude ratio of the seismic trace s i (t) and the reference trace s 0 (t) at the order n p as the refraction wave period amplitude coefficient a p of the point P(x, y).

[0073] In the embodiments of the present disclosure, the method for obtaining the reference trace s 0 (t) includes:

[0074] Set the time window parameter t W , and intercept the seismic data d i from t W - t i to t W + t i (t) within the time period to form a seismic wavelet w(t); use w(t) as the wavelet to perform deconvolution on the seismic data d i (t) to obtain the deconvolved seismic data d' i (t); use the automatic gain control (AGC) algorithm to perform in-trace equalization on d' i (t) with T as a parameter to obtain s i (t); count the sum of amplitudes A i of each trace data on s i (kT + t i ), and select the trace with the largest amplitude sum as the reference trace s 0 (t);

[0075] K is a positive integer, and the value of K is less than 10.

[0076] In the embodiments of the present disclosure, S3 obtaining the refraction wave period amplitude coefficient a p specifically includes:

[0077] According to the excitation point position (x S , y s ), the receiver point position (x R , y R ) and the longitudinal wave velocity v of the surrounding rock r, find the first arrival time \(t\) of the refracted wave for each seismic trace i ;

[0078]

[0079] Divide the imaging area of the coal mining face into grids. Assume there are \(X\) grids along the strike direction and \(Y\) grids along the dip direction; for each grid, the corresponding imaging point is \(P(x, y)\), where \(x\in[1, X]\) and \(y\in[1, Y]\); \(M\) is the total number of traces in the trace gather \(\varPhi\) P , and \(M\) is a positive integer;

[0080] where

[0081] a p . The numerical value of \(a\) reflects the coal seam thickness at point \(P\). Calculate according to the above formula for all imaging points in the imaging area, and the refracted wave period amplitude coefficient imaging result of this area can be obtained. The abnormal area in the imaging result corresponds to the boundary of the thin coal zone.

[0082] The present invention will be described in detail below in conjunction with specific embodiments and the accompanying drawings of the specification.

[0083] The main steps of the data processing method in the present invention are as follows:

[0084] 1. Obtain the longitudinal wave velocity \(v\) of the surrounding rock from ultrasonic logging data or by ultrasonic measurement of rock samples r and the longitudinal wave velocity \(v\) of the coal seam c ; in two roadways of the target working face, measure the coal seam thickness \(h\) exposed on the side wall. Calculate the refracted wave period \(T\) according to the following formula based on the longitudinal wave velocity \(v\) of the surrounding rock r , the longitudinal wave velocity \(v\) of the coal seam c and the coal seam thickness \(h\).

[0085]

[0086] 2. After preprocessing the actual downhole seismic data such as time delay correction and denoising, find the first arrival time \(t\) of the refracted longitudinal wave for each trace i . The position of the excitation point \((x\) S , \(y\) S ), the position of the receiving point \((x\) R , \(y\) R ) and the longitudinal wave velocity \(v\) of the surrounding rock r , then the first arrival time \(t\) of the refracted longitudinal wave i is:

[0087]

[0088] 3. Set the time window parameter \(t\) W , and intercept from \(t\) in the seismic trace \(d\) i (t)i -t W to t i +t W The data within the time period is used as the wavelet w(t), where t W Generally, 100 - 200 ms is selected, and it can also be adjusted according to the actual waveform.

[0089] 4. Using w(t) as the wavelet, perform deconvolution on the seismic data, that is, calculate the frequency - domain seismic signal D′ i (ω) by the following formula, and then use the inverse Fourier transform to transform D′ i (ω) to the time domain to obtain the deconvolved seismic signal d′ i (t);

[0090]

[0091] where ω is the frequency, D i (ω) is the frequency - domain form of d i (t), W(ω) is the frequency - domain form of w(t), and the frequency - domain form is obtained by Fourier transform. W * (ω) is the conjugate complex number of W(ω), and γ is a positive constant. Generally, γ takes values from 0.1 to 0.01 and can be adjusted according to the noise level of the original data.

[0092] 5. Using the refraction - wave period T as a parameter, perform in - trace equalization on d′ i (t) with the gain - control (AGC) algorithm, and the equalized seismic trace is s i (t).

[0093]

[0094] 6. Statistically calculate the sum of amplitudes A i on s i (kT + t i ) for each trace of data, and select the trace with the maximum sum of amplitudes as the reference trace s 0 (t). K is a positive integer, and the value of K is less than 10;

[0095] 7. Divide the imaging area of the coal - mining face into grids. Assume that the number of its units is X along the strike direction and Y along the dip direction. Let x = 1, y = 1, and process each imaging point P(x, y) corresponding to each grid one by one.

[0096] 8. Select all the seismic traces s i (t) whose connecting lines pass through the point P(x, y) from the total trace set to form a new common - imaging - point trace gather Φ P , and the specific measures are as follows:

[0097] (1) Let i = 1, and Φ P is an empty set;

[0098] (2) Take out the i-th seismic trace s i (t) from the total trace gather, and obtain the shot point position (x S , y S ) and the receiver position (x R , y R ) of the i-th trace from the trace header;

[0099] (3) Calculate the distance L between the line connecting the shot point and the geophone of the i-th trace and P(x, y): i :

[0100]

[0101] When L i < L W , add the i-th trace s i (t) to Φ P , where L W is a preset threshold, generally 5 - 10 m;

[0102] (4) Let i = i + 1 until i = N, where N is the total number of traces, and repeat the process from step (2).

[0103] 9. Calculate the refraction wave period amplitude coefficient a(x, y) at point P. The specific measures are as follows:

[0104] (1) Let i = 1, a(x, y) = 0;

[0105] (2) Obtain the shot point position (x S , y S ) corresponding to the i-th trace from the trace header, and calculate the refraction wave order n of point P(x, y): p :

[0106]

[0107] where represents rounding down;

[0108] (3) Calculate the amplitude ratio a i of the i-th trace signal s 0 (t) and the reference trace s p (t) at the n i -th order refraction wave:

[0109]

[0110] (4) Let i = 1, until i = M, where M is the total number of traces in the trace gather Φ P , and repeat the process from step (2) of step 9.

[0111] Let \(x = x + 1\) until \(x = X\), and repeat the process from step 9.

[0112] Let \(y = y + 1\) until \(y = Y\), and repeat the process from step 9.

[0113] Obtain the imaging result \(a(x,y)\) of the refraction wave period amplitude coefficient for the entire imaging area. The abnormal area in the imaging result corresponds to the boundary of the thin coal seam zone in the coal mining face.

[0114] The following takes the theoretical model and actual data as examples to illustrate the effects of the present invention:

[0115] Example 1:

[0116] The model consists of three layers: the roof, the coal seam, and the floor. The lithology of the roof and the floor is the same. The longitudinal wave velocity of the surrounding rock is 4000 m / s, the transverse wave velocity of the surrounding rock is 2300 m / s, and the density is 2.56 g / cm 3 ; the longitudinal wave velocity of the coal seam is 2000 m / s, the transverse wave velocity of the coal seam is 1050 m / s, and the density is 1.4 g / cm 3 . The normal coal seam thickness is 20 m, and there is a thin coal seam zone where the coal seam thickness is 12 m. The schematic diagram of the model is as Figure 4 shown. (a) is the plan view of the model, and (b) is the cross-sectional view of the model. The three-dimensional elastic wave forward simulation technology is used to perform forward simulation on the model. The source is a 400 Hz Ricker wavelet, and a total of 78 shot simulation results are generated. The 20th shot is as Figure 5 shown. Now, the model data is processed according to the steps of the present invention.

[0117] Execute step 1, and the longitudinal wave velocity \(v\) of the surrounding rock r takes a value of 4000 m / s, and the longitudinal wave velocity \(v\) of the coal seam c takes a value of 2000 m / s.

[0118] Execute step 2, and the coal seam thickness \(h\) exposed on the side is 20 m.

[0119] Execute step 3, and calculate that the refraction wave period \(T\) is 17.3 ms.

[0120] Execute step 4, and find the arrival time \(t\) of the refracted longitudinal wave for each trace i . Taking the R150 trace in the 20th shot as an example, the excitation point position obtained from the trace head is (400, 55), and the receiver point position is (690, 247). Then, the arrival time \(t\) of the refracted longitudinal wave is calculated as i 93 ms.

[0121] Execute step 5, set \(t\) W to 2 ms. Taking the R150 trace as an example, intercept the signal from 91 ms to 95 ms as the wavelet \(w(t)\), as Figure 6 .

[0122] Perform Steps 6 and 7 to perform deconvolution and equalization processing on each trace. Taking Traces R81, R92, and R150 as examples respectively, the original signal is as Figure 7 , and the processed signal is as Figure 8 .

[0123] Perform Step 8. After calculating the amplitudes of each trace, select Trace R81 as the reference trace s 0 (t).

[0124] Perform Step 9. Divide the working face into 80×40 grids, and the size of each grid is 10m×5m.

[0125] Perform Step 10. Generate a common image point gather for each grid.

[0126] Perform Step 11. Calculate the refraction wave period amplitude coefficient of each point. Taking the point (550, 100) on the boundary of the thin coal seam as an example, Trace R150 passes through this point, and the excitation point position in the trace header is (400, 55). Then n p = 4 can be calculated, and then a i = 10.15 can be calculated from this. Taking the point (250, 100) on the normal coal seam as an example, Trace R92 passes through this point, and the excitation point position in the trace header is (400, 55). Then n p = 4 can be calculated, and then a i = 3.45 can be calculated from this. The difference between the two is as shown by the part enclosed by the dashed box in Figure 8 . The fourth order of R92 has a small difference from the reference trace R81, and the fourth order of R150 has a large difference from the reference trace R81. Therefore, the points on the boundary of the thin coal seam have a larger refraction wave period amplitude coefficient than the points on the normal coal seam.

[0127] When executed to Step 14, the imaging result of the refraction wave period amplitude coefficient of the model working face is as shown in Figure 9 , which is basically consistent with the position of the thin coal area in the model.

[0128] Generally speaking, the present invention can, on the premise of knowing the longitudinal wave velocities of the surrounding rock and the coal seam, utilize the periodicity of the refraction wave in the coal seam and the characteristic of amplitude attenuation when the coal thickness changes, and realize the detection of the boundary of the thin coal belt by performing imaging of the refraction wave period amplitude coefficient on the working face.

[0129] The preferred embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings. However, the present disclosure is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0130] In addition, it should be noted that, in the above specific embodiments, the various specific technical features described can be combined in any suitable manner without conflict. To avoid unnecessary repetition, the present disclosure will not separately describe various possible combination manners.

[0131] In addition, any combination can be made among the various different embodiments of the present disclosure as long as it does not violate the idea of the present disclosure, and it should also be regarded as the content disclosed by the present disclosure.

Claims

1. A method for detecting thin coal seams based on the attenuation of the period amplitude of refracted waves, Characterized in that, Comprising: S1 Instrument layout: Layout seismic survey lines, which are composed of S excitation points and R receiving points; The seismic data d i (t) with a total number of channels N is formed between the excitation point and the receiving point through signal acquisition and data transmission, where t is time; i is the seismic trace number, i ∈ [1, N], N = S × R; S2 Obtain formation data and refraction wave period T: Obtain the longitudinal wave velocity v of the surrounding rock r and the longitudinal wave velocity v of the coal seam c , measure the coal seam thickness h exposed in the roadway on the side wall of the roadway, and calculate the refraction wave period T; S3 Obtain the refraction wave period amplitude coefficient a p : For seismic data d i (t), after deconvolution and in-trace equalization processing, the seismic trace s i (t) is obtained; the imaging area corresponding to the coal mining face is divided into grids, and each grid corresponds to an imaging point P(x, y); calculate the distances between the imaging point P(x, y) and the connecting lines between each shot point and geophone point, and select the connecting line with a distance less than the preset threshold L W corresponding to the seismic trace s i (t) to form a trace gather Φ P ; for each seismic trace s P in the trace gather Φ i (t), calculate the refraction wave order n p corresponding to the point P(x, y), and use the amplitude ratio between the seismic trace s i (t) and the reference trace s 0 (t) at the refraction wave order n p as the refraction wave period amplitude coefficient a p of the point P(x, y).

2. The method for detecting thin coal seams based on the attenuation of the period amplitude of refracted waves according to claim 1, Characterized in that, The specific layout of the instruments includes: arranging seismic survey lines in the transportation roadway and / or the return airway of the coal mining face. The seismic survey line consists of S blast holes arranged at intervals and R geophone holes arranged at intervals. Explosives are buried in the blast holes as excitation points, and geophones are buried in the geophone holes as receiving points. The excitation points and the receiving points form seismic data d i (t) with a total number of channels N through signal acquisition and data transmission, where t is time; i is the seismic trace number, i ∈ [1, N], and N = S × R.

3. The method for detecting thin coal seams based on the attenuation of the period amplitude of refracted waves according to claim 1 or 2, Characterized in that, The reference path s 0 (t) acquisition method includes: Set the time window parameter t W , intercepted from t i -t W to i +t W Earthquake data within the time period d i (t) to form a seismic wavelet w(t); the seismic wavelet w(t) is used to i (t) Perform deconvolution to obtain the deconvolved seismic data d′ i (t); Taking T as parameter, the automatic gain control algorithm is used to adjust the seismic data d′ i (t) Perform intra-trace equalization to obtain seismic trace s i (t); count each data in s i (kT+t i ) The sum of the amplitudes A i , select the trace with the largest amplitude as the reference trace 0 (t); K is a positive integer, and the value of K is less than 10, t i represents the first arrival time of the refracted wave of each seismic trace.

4. The method for detecting thin coal seams based on the attenuation of the period amplitude of refracted waves according to claim 1 or 2, Characterized in that, S3 Obtain the refraction wave period amplitude coefficient a p Specifically include: According to the excitation point position (x S , y S ), the receiving point position (x R , y R ) and the longitudinal wave velocity v r of the surrounding rock, calculate the first arrival time t i of the refracted wave for each seismic trace; Divide the imaging area of the coal mining face into grids. Assume that the number of units along the strike direction is X in total, and the number of units along the dip direction is Y in total; The imaging point P(x, y) corresponding to each grid, x ∈ [1, X], y ∈ [1, Y]; wherein By calculating all the imaging points in the imaging area according to the above formula, the imaging result of the refraction wave period amplitude coefficient of this area can be obtained. The abnormal area in the imaging result corresponds to the boundary of the thin coal seam belt, and M is the total number of traces in the trace gather Φ P of the trace gather Φ 5. The method for detecting thin coal seams based on the attenuation of the period amplitude of refracted waves according to claim 1 or 2, Characterized in that, The method for obtaining the balanced seismic trace s i (t) includes: Set the time window parameter t W , and intercept the data within the time period from t i (t) from t i - t W to t i + t W as the seismic wavelet w(t); Deconvolve the seismic data d i (t) with the seismic wavelet w(t), that is, obtain the frequency-domain seismic signal D′ i (ω) from the following formula, and then use the inverse Fourier transform to transform D′ i (ω) to the time domain to obtain the deconvolved seismic data d′ i (t); where ω is the frequency, D i (ω) is the frequency domain form of d i (t), W(ω) is the frequency domain form of w(t), and the frequency domain form is obtained by Fourier transform. W * (ω) is the conjugate complex number of W(ω), and γ takes values from 0.1 to 0.01; With the refraction wave period T as a parameter, use the gain control algorithm to perform in-trace equalization on d′ i (t), and the equalized seismic signal s i (t); 6. A system for detecting thin coal seams based on the attenuation of the period amplitude of refracted waves, Characterized in that, Set: Instrument layout module: Layout seismic survey lines, where a seismic survey line consists of S shot points and R receiver points; the seismic data d i (t) with a total number of channels N is formed between the shot points and the receiver points through signal acquisition and data transmission, where i is the seismic trace number, i ∈ [1, N], and t is time; N = S × R; Stratum data acquisition and refraction wave period T module: Obtain the longitudinal wave velocity v of the surrounding rock r and the longitudinal wave velocity v of the coal seam c , Measure the thickness h of the coal seam exposed in the roadway on the sidewall of the roadway, and calculate the refraction wave period T; Obtain the refraction wave period amplitude coefficient a p Module: Perform deconvolution and in-trace equalization on the seismic data d i (t) to obtain the seismic trace s i (t); Divide the imaging area corresponding to the coal mining face into grids, and each grid corresponds to an imaging point P(x, y); Calculate the distances between the imaging point P(x, y) and the connecting lines between each shot point and geophone point, and select the connecting lines with distances less than the preset threshold L W The corresponding seismic trace s i (t) to form a trace gather Φ P ; For each seismic trace s P in the trace gather Φ i (t), calculate the refraction wave order n p corresponding to the point P(x, y), and use the amplitude ratio between the seismic trace s i (t) and the reference trace s 0 (t) at the refraction wave order n p as the refraction wave period amplitude coefficient a of the point P(x, y) p .

7. The system for detecting thin coal seams based on the attenuation of the period amplitude of refracted waves according to claim 6, Characterized in that, The specific arrangement of the instruments includes: arranging seismic survey lines in the transportation roadway and / or the return airway of the coal mining face. The seismic survey line is composed of S blast holes arranged at intervals and R geophone holes arranged at intervals. Explosives are buried in the blast holes as excitation points, and geophones are buried in the geophone holes as receiving points. The excitation points and the receiving points form seismic data d i (t) with a total number of channels N through signal acquisition and data transmission, where t is time; i is the seismic trace number, i ∈ [1, N], and N = S × R.

8. The system for detecting thin coal seams based on the attenuation of the period amplitude of refracted waves according to claim 6 or 7, Characterized in that, The reference path s 0 (t) is obtained by the following method: Set the time window parameter t W , intercepted from t i -t W to i +t W Earthquake data within the time period d i (t) to form a seismic wavelet w(t); the seismic wavelet w(t) is used to i (t) Perform deconvolution to obtain the deconvolved seismic data d′ i (t); Taking T as parameter, the automatic gain control algorithm is used to adjust the seismic data d′ i (t) Perform intra-trace equalization to obtain seismic trace s i (t); count each data in s i (kT+t i ) The sum of the amplitudes A i , select the trace with the largest amplitude as the reference trace 0 (t); K is a positive integer, and the value of K is less than 10, t i represents the first arrival time of the refracted wave of each seismic trace.

9. The system for detecting thin coal seams based on the attenuation of the period amplitude of refracted waves according to claim 6 or 7, Characterized in that, Obtain the refraction wave period amplitude coefficient a p The module specifically includes: According to the excitation point position (x S , y S ), the receiver point position (x R , y R ) and the longitudinal wave velocity v r of the surrounding rock, calculate the first arrival time t i of the refracted wave for each seismic trace; Divide the imaging area of the coal mining face into grids. Assume that the number of units along the strike direction is X in total, and the number of units along the dip direction is Y in total; The imaging point P(x, y) corresponding to each grid, x ∈ [1, X], y ∈ [1, Y]; Among them By calculating all the imaging points in the imaging area according to the above formula, the imaging result of the refraction wave period amplitude coefficient of this area can be obtained. The abnormal area in the imaging result corresponds to the boundary of the thin coal seam belt, and M is the total number of traces in the trace gather Φ P of the trace gather Φ 10. The system for detecting thin coal seams based on the attenuation of the period amplitude of refracted waves according to claim 6 or 7, Characterized in that, It also includes an equalized seismic trace s i (t) acquisition module: Set the time window parameter t W and intercept the data from t i - t i to t W + t i in the seismic data d W (t) as the seismic wavelet w(t); Deconvolve the seismic data d i (t) with the seismic wavelet w(t), that is, obtain the frequency-domain seismic signal D′ i (ω) from the following formula, and then transform D′ i (ω) to the time domain by inverse Fourier transform to obtain the deconvolved seismic data d′ i (t); where ω is the frequency, D i (ω) is the frequency domain form of d i (t), W(ω) is the frequency domain form of w(t), and the frequency domain form is obtained by Fourier transform. W * (ω) is the conjugate complex number of W(ω), and γ takes values from 0.1 to 0.01; Using the refraction wave period \(T\) as a parameter, the in - trace equalization is performed on \(d^{\prime}\) i (t) by using the gain control algorithm, and the equalized seismic signal is \(s\) i (t);

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