A seismic multi-wave fine exploration method for working face and underlying structures

Abstract

The present invention discloses a seismic multi-wave fine exploration method for the working face and underlying structures. First, a three-dimensional seismic observation system is arranged, which can simultaneously collect data for in-workface trough wave geological imaging and data for three-dimensional full waveform inversion imaging of the underlying structures of the working face. Then, when performing imaging within the working face, first, the qualified trough wave data are screened out from the collected seismic data, and then the trough waves are used for inversion to obtain the geological imaging within the working face. Next, all the collected seismic data are subjected to three-dimensional full waveform inversion, and the inversion area is limited to below the working face, so as to obtain the three-dimensional imaging of the underlying structures of the working face. Finally, the in-workface trough wave imaging and the three-dimensional imaging obtained by three-dimensional full waveform inversion below the working face are superimposed and integrated, so that the three-dimensional imaging of the working face and its underlying structures can be obtained, achieving the purpose of seismic multi-wave fine exploration of the coal mining working face and its underlying structures.

Description

Technical Field

[0001] The invention relates to a seismic multi-wave fine exploration method in a working face and underlying structures, belonging to the technical field of mineral resource exploration. Background Art

[0002] Deep coal mining faces the threat of high-pressure water in the floor. The activation of the underlying structure of the floor caused by mining and its communication with the Ordovician limestone aquifer with high pressure water will cause serious well flooding accidents. It is very important to identify the geological structures in and below the working face for the early treatment of floor water inrush disasters. Geophysical exploration technology can reveal accurate structural information and is a key means to achieve transparency of the geological structures in and below the working face. Seismic exploration in geophysical exploration has the ability to detect fine structures and has a strong ability to detect structures in the working face using the trough waves developed in the coal seams. It has been widely used in the exploration of working faces in deep coal mining.

[0003] Since channel waves are well developed in coal seams, but poorly effective in the rock mass below the working face, the current seismic exploration using channel waves is only applicable to the exploration of geological structures within the working face. The exploration of the underlying geological structures of the coal mining working face mainly uses other geophysical methods, such as transient electromagnetic, high-density electrical method, drilling and other methods; such methods as transient electromagnetic detection are affected by the volume effect, resulting in low accuracy, and high-density electrical method has a long construction period and low efficiency; drilling requires a high drilling density, resulting in high costs. Seismic exploration methods with high-precision imaging capabilities are rarely used in the exploration of the underlying geological structures of coal mining working faces, mainly due to the lack of advanced and effective three-dimensional exploration technology for the underlying structures of the working face floor, and it is impossible to achieve three-dimensional fine exploration of the working face and its underlying structures. Although some studies have attempted to use full waveform inversion technology to solve the problem of detecting underlying collapse columns, current research is limited to two-dimensional research on collapse columns in the working face floor (i.e., it only detects a certain section of the coal seam and the rock mass below it). In this case, only collapse columns that penetrate the coal seam can be detected, and it is impossible to conduct three-dimensional and detailed detection of hidden collapse columns under the working face floor.

[0004] Therefore, how to provide a new seismic multi-wave fine exploration method that can realize three-dimensional seismic multi-wave fine exploration of the coal mining face and its underlying structures is a technical problem that technical personnel in this field urgently need to solve. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention provides a method for fine seismic multi-wave exploration of the working face and the underlying structure, which combines slot wave inversion imaging with full waveform inversion imaging to realize three-dimensional seismic multi-wave fine exploration of the coal mining working face and the underlying structure.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a method for fine seismic multi-wave exploration of a working face and underlying structures, and the specific steps are as follows:

[0007] Step 1: A plurality of geophones are arranged in a row and at equal intervals along the roadway direction in the roadways on both sides of the coal seam working face. An inclined borehole is drilled obliquely into the coal seam and surrounding rock from a position away from the cutting eye of the coal seam working face. After completion, a plurality of geophones are arranged in a row and at equal intervals along the borehole direction in the inclined borehole; a plurality of seismic sources are arranged in a row and at equal intervals along the roadway direction in the roadways on both sides of the coal seam working face. The three rows of geophones and the two rows of seismic sources are all connected to the acquisition host through connection main lines, so that the geophones, seismic sources and data acquisition host form a three-dimensional seismic observation system;

[0008] Step 2: Each seismic source in the two rows of seismic sources is excited in turn. After each seismic source is excited, the three-dimensional seismic observation system receives the seismic source data collected by each geophone in real time; after all seismic sources are excited, the three-dimensional seismic observation system screens out the seismic data received by each geophone in the roadway on the other side of the working face when each seismic source is excited according to the seismic data received by each geophone recorded after each seismic source excitation (that is, when the seismic source is in the roadway on one side of the working face, the seismic data received by each geophone in this roadway and the inclined borehole is removed, and only the seismic data received by each geophone in the roadway on the other side of the working face is extracted, because only the seismic data received by each geophone in the roadway on the other side is the seismic wave transmitted through the working face when the current seismic source is excited), and then selects the trough wave data from the screened seismic data, and uses the trough wave data for seismic exploration imaging within the working face, so as to obtain a three-dimensional image within the working face;

[0009] Step 3: The seismic source data collected by each geophone in real time by the three-dimensional seismic observation system after each seismic source is excited in Step 2. In order to avoid the interference of strong-energy trough waves, three-dimensional full waveform inversion is performed on the area below the coal seam working face. The three-dimensional full waveform inversion algorithm uses the least squares objective function

[0010]

[0011] where ψ r,o b s is the observed data at the geophone point r, and ψ r,syn is the synthetic data of the wave equation at the geophone point r; the Lagrange multiplier method is used to derive the gradient of the objective function with respect to the model parameters; the three-dimensional elastic wave equation used for data simulation is as follows,

[0012]

[0013] where the velocity components of the particle vibrating along three directions are v = [v1 v2 v3] T = [vx v y v z T , The three normal stress and three shear stress components of the particle are:

[0014] σ = [σ1 σ2 σ3 σ4 σ5 σ6] T = [σ xx σ yy σ zz σ yz σ xz σ xy T , The source form with tensor property is f = [f1 f2 f3 f4 f5 f6] T = [f xx f yy f zz f yz f xz f xy T , The linking matrix is:

[0015] The Hooke's matrix related to the elastic parameters is

[0016] where, T represents the transpose of the vector, x, y and z represent the coordinates of the three-dimensional space coordinate system, t represents the time coordinate, represents the first-order time derivative operation, represents taking the partial derivative of the variable in the parentheses with respect to the subscript sub, ρ represents the density, C represents the Hooke's matrix, v i (i = 1, 2, 3) respectively represent the vibration velocities of the particle along the three directions, σ i (i = 1, 2,..., 6) represent the stress components of the particle, f represents the source term;

[0017] Using the Lagrange multiplier method to derive the gradient of the objective function with respect to the model parameters, the specific expression form of the adjoint equation is:

[0018]

[0019] where, and and

[0020]

[0021] Thus, the gradient expressions of the objective function with respect to velocity and density are obtained as follows:

[0022]

[0023] Define the model m = (v​​​p , v s , ρ) T is updated as follows:

[0024] m k+1 = m k + α k Δm k ,

[0025] where k represents the k - th iteration, α k represents the optimal step size at m k , and Δm k is the search direction constructed by the gradient. When using the steepest descent method, the search direction is the negative direction of the corresponding gradient; and the above - mentioned model is updated using the following conjugate gradient, and its specific form is

[0026]

[0027] where represents the gradient of the objective function with respect to the velocity parameter and density;

[0028] Finally, the updated model is used for full - waveform inversion to obtain the three - dimensional imaging of the structure underlying the working face;

[0029] Step Four: Superimpose and integrate the three - dimensional imaging within the working face obtained in Step Two and the three - dimensional imaging of the structure underlying the working face obtained in Step Three to finally obtain the three - dimensional fine imaging of the working face and its underlying structure.

[0030] Furthermore, the geophone is a three - component geophone.

[0031] Furthermore, the seismic source is an electronically controlled seismic source.

[0032] Compared with the prior art, the present invention combines the in - working - face trough - wave inversion imaging and the three - dimensional full - waveform inversion imaging below the working face, and has the following advantages:

[0033] 1. The three - dimensional seismic observation system arranged in the present invention can simultaneously collect data for in - working - face trough - wave geological imaging and data for three - dimensional full - waveform inversion imaging of the structure underlying the working face, ensuring that the collected data reaches the data volume required for imaging, and not only meeting the data requirements for transmitted trough waves for trough - wave imaging, but also meeting the data requirements for three - dimensional full - waveform inversion.

[0034] 2. Since the trough waves develop well within the working face, when performing imaging within the working face in the present invention, the required trough wave data is first screened out from the collected seismic data, and then the trough waves are used for inversion to obtain the geological imaging within the working face. However, the trough waves have extremely poor effects below the working face, so the existing methods cannot perform geological imaging below the working face. The present invention performs three-dimensional full waveform inversion on all the collected seismic data, and the inversion area is limited to below the working face, thereby obtaining the three-dimensional imaging of the underlying structure of the working face, solving the problem that the current conventional methods cannot achieve high-precision three-dimensional geological body exploration.

[0035] 3. The present invention superimposes and integrates the trough wave imaging within the working face and the three-dimensional imaging obtained by three-dimensional full waveform inversion below the working face, so as to obtain the three-dimensional imaging of the working face and its underlying structure, realizing the purpose of seismic multi-wave fine exploration of the working face and its underlying structure in the coal mining face, and can provide a direct and effective guiding role for coal mine resource development. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is the layout schematic diagram of the three-dimensional seismic observation system in the embodiment of the present invention;

[0037] Figure 2 is the three-dimensional imaging expansion schematic diagram of the underlying structure of the working face using the inversion velocity model in the embodiment of the present invention;

[0038] Figure 3 is the three-dimensional imaging expansion schematic diagram of the underlying structure of the working face using the theoretical velocity model in the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0039] The present invention will be further described below.

[0040] As Figure 1 shown, the specific steps of the present invention are as follows:

[0041] Step 1: A plurality of geophones are respectively arranged in a row and at equal intervals along the roadway direction in the roadways on both sides of the coal seam working face. An inclined borehole is drilled obliquely into the coal seam and surrounding rock from a position away from the cutting eye of the coal seam working face. After completion, a plurality of geophones are arranged in a row and at equal intervals along the borehole direction in the inclined borehole. A plurality of seismic sources are respectively arranged in a row and at equal intervals along the roadway direction in the roadways on both sides of the coal seam working face. The three rows of geophones and the two rows of seismic sources are all connected to the acquisition host through the connection main line, so that the geophones, seismic sources and data acquisition host form a three-dimensional seismic observation system; the geophones are three-component geophones; the seismic sources are electrically controlled seismic sources.

[0042] Step 2: Each of the two rows of seismic sources is excited in sequence. After each seismic source is excited, the 3D seismic observation system receives in real time the seismic source data collected by each geophone. After all the seismic sources are excited, the 3D seismic observation system screens out the seismic data received by each geophone in the roadway on the other side of the working face when each seismic source is excited (that is, when the seismic source is in the roadway on one side of the working face, the seismic data received by each geophone in this roadway and in the inclined boreholes is removed, and only the seismic data received by each geophone in the roadway on the other side of the working face is extracted, because only the seismic data received by each geophone in the roadway on the other side is the seismic wave excited by the current seismic source passing through the working face), then selects the trough wave data from the screened seismic data, and uses the trough wave data for seismic exploration imaging within the working face, so as to obtain the 3D imaging within the working face;

[0043] Step 3: After each seismic source in Step 2 is excited, the 3D seismic observation system receives in real time the seismic source data collected by each geophone. In order to avoid the interference of strong-energy trough waves, 3D full-waveform inversion is performed on the area below the coal seam working face. The 3D full-waveform inversion algorithm uses the least squares objective function

[0044]

[0045] where, ψ r,o b s is the observed data at the geophone point r, and ψ r,syn is the synthetic data of the wave equation at the geophone point r; The Lagrange multiplier method is used to derive the gradient of the objective function with respect to the model parameters; The 3D elastic wave equation used for data simulation is as follows,

[0046]

[0047] where, the velocity components of the particle vibrating along three directions are v = [v1 v2 v3] T =[v x v y v z T , and the three normal stresses and three shear stress components of the particle are:

[0048] σ = [σ1 σ2 σ3 σ4 σ5 σ6] T =[σ xx σ yy σ zz σ yz σ xz σ xy T , and the seismic source form with tensor properties is f = [f1 f2 f3 f4 f5 f6] T =[f​​xx f yy f zz f yz f xz f xy T , the link matrix is:

[0049] The Hooke's matrix related to the elastic parameters is

[0050] where T represents the transpose of a vector, x, y, and z represent the coordinates of a three-dimensional space coordinate system, t represents the time coordinate, represents the first-order time derivative operation, represents taking the partial derivative of the variable in the parentheses with respect to the subscript sub, ρ represents the density, C represents the Hooke's matrix, v i (i = 1, 2, 3) respectively represent the vibration velocities of the particle along three directions, σ i (i = 1, 2, …, 6) represent the stress components of the particle, f represents the source term;

[0051] Using the Lagrange multiplier method to derive the gradient of the objective function with respect to the model parameters, the specific expression of the adjoint equation is:

[0052]

[0053] where, and and

[0054]

[0055] Thus, the gradient expressions of the objective function with respect to velocity and density are obtained as follows:

[0056]

[0057] Define the update of the model m = (v p , v s , ρ) T as follows:

[0058] m k+1 = m k + α k Δm k ,

[0059] where k represents the k-th iteration, α k represents the optimal step size at m k , Δm k is the search direction constructed by the gradient. When using the steepest descent method, the search direction is the negative direction of the corresponding gradient; and the above model is updated using the following conjugate gradient, and its specific form is​

[0060]

[0061] Among them, represents the gradients of the objective function with respect to the velocity parameter and density;

[0062] Finally, the updated model is used for full waveform inversion to obtain the three-dimensional imaging of the structure underlying the working face;

[0063] Step 4: Superimpose and integrate the three-dimensional imaging within the working face obtained in Step 2 and the three-dimensional imaging of the structure underlying the working face obtained in Step 3, so as to finally obtain the three-dimensional fine imaging of the working face and its underlying structure.

[0064] Experimental verification:

[0065] The structure underlying the simulated working face is arranged, and the theoretical velocity model is obtained to perform inversion imaging on the structure underlying the simulated working face, as Figure 3 shown; then the inversion imaging of the structure underlying the simulated working face is obtained by using the three-dimensional full waveform inversion in the present invention, as Figure 2 shown. By Figure 2 and 3 comparison, it can be seen that the method of the present invention can effectively obtain the three-dimensional image of the geological structure hidden under the working face, and its position and contour are relatively close to the theoretical values, thus proving that the three-dimensional imaging of the structure underlying the working face by the present invention is relatively accurate and has practical value.

[0066] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A seismic multi-wave fine exploration method for the working face and underlying structures, characterized in that The specific steps are as follows: Step 1: Arrange a plurality of geophones in a row along the roadway direction at equal intervals in the roadways on both sides of the coal seam working face. Implement an inclined borehole into the coal seam and surrounding rock at a position far from the cutting eye of the coal seam working face. After completion, arrange a plurality of geophones in a row along the borehole direction at equal intervals in the inclined borehole. Arrange a plurality of seismic sources in a row along the roadway direction at equal intervals in the roadways on both sides of the coal seam working face. The three rows of geophones and the two rows of seismic sources are all connected to the acquisition host through the main connection line, so that the geophones, seismic sources and data acquisition host form a three-dimensional seismic observation system; Step 2: Excite each seismic source in the two rows of seismic sources in turn. After each seismic source is excited, the three-dimensional seismic observation system receives the seismic source data collected by each geophone in real time. After all the seismic sources are excited, the three-dimensional seismic observation system screens out the seismic data received by each geophone in the roadway on the other side of the working face when each seismic source is excited according to the seismic data recorded by each geophone after each seismic source excitation. Then, select the trough wave data from the screened seismic data, and use the trough wave data for seismic exploration imaging in the working face, so as to obtain the three-dimensional imaging in the working face; Step 3: For the seismic source data collected by each geophone in real time by the three-dimensional seismic observation system after each seismic source in Step 2 is excited, in order to avoid the interference of strong-energy trough waves, perform three-dimensional full waveform inversion on the area below the coal seam working face. The three-dimensional full waveform inversion algorithm uses the least squares objective function where, ψ r,obs is the observed data at the geophone point r, and ψ r,syn is the synthetic data of the wave equation at the geophone point r; the Lagrange multiplier method is used to derive the gradient of the objective function with respect to the model parameters; the three-dimensional elastic wave equation used in data simulation is as follows, Among them, the velocity components of the particle vibrating along three directions are \(v = [v_1\ v_2\ v_3]\) T = [v x v y v z T , and the three normal stresses and three shear stress components of the particle are as follows:​ σ = [σ1 σ2 σ3 σ4 σ5 σ6] T = [σ xx σ yy σ zz σ yz σ xz σ xy T , The source form with tensor properties is f = [f1 f2 f3 f4 f5 f6] T = [f xx f yy f zz f yz f xz f xy T , The link matrix is:​​ The Hooke's matrix related to the elastic parameters is where T represents the transpose of a vector, x, y, and z represent the coordinates of a three-dimensional space coordinate system, and t represents time, represents the first-order derivative operation with respect to time, represents taking the partial derivative of the variable in the parentheses with respect to the subscript sub, ρ represents density, C represents the Hooke's matrix, v i respectively represent the vibration velocities of the particle along three directions, where i = 1, 2, 3; σ i represents the stress component of the particle, where i = 1, 2,..., 6; f represents the source term; Adopt the Lagrange multiplier method to deduce the gradient of the objective function with respect to the model parameters, and the specific expression form of the adjoint equation obtained is: Among them, and and where i = 1, 2, …, 6; Thus, the gradient expressions of the objective function with respect to velocity and density are as follows: Define the update of model m=(v p ,v s ,ρ) T as follows: m k+1 = m k + α k Δm k , where k represents the k-th iteration, and α k represents the optimal step size at m k , Δm k is the search direction constructed from the gradient. When using the steepest descent method, the search direction is the negative direction of the corresponding gradient; and the above model is updated using the following conjugate gradient, and its specific form is Among them, represents the gradients of the objective function with respect to the velocity parameter and density; Finally, perform full waveform inversion using the updated model to obtain the three-dimensional imaging of the underlying structure of the working face; Step 4: Superimpose and integrate the three-dimensional imaging in the working face obtained in Step 2 and the three-dimensional imaging of the underlying structure of the working face obtained in Step 3, so as to finally obtain the three-dimensional fine imaging of the working face and its underlying structure.

2. The seismic multi-wave fine exploration method for the working face and underlying structures according to claim 1, characterized in that, The geophone is a three-component geophone.

3. The seismic multi-wave fine exploration method for the working face and underlying structures according to claim 1, characterized in that, The seismic source is an electronically controlled seismic source.

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