A forward modeling method for seismic data during mine excavation

Abstract

The present invention discloses a forward simulation method for seismic data during tunneling in a mine, comprising the following steps: S1. Establish a forward model and an observation system; S2. According to the requirements of forward simulation, set the forward parameters for the forward model, and conduct forward simulation stability analysis and numerical dispersion condition judgment; S3. If the forward parameters meet the stability and numerical dispersion conditions, then perform source loading and set the source wavelet F t ; S4. Set the boundary conditions to obtain the elastic wave control equation in the boundary region; S5. Use a high-order staggered grid to perform finite-difference wavefield solution for the elastic wave control equation in the boundary region and the elastic wave equation in the internal region. By constructing the source equation for seismic data during tunneling, the present invention can achieve true and effective forward simulation of seismic data during tunneling. The simulated seismic data is consistent with the signal characteristics of actual mining data, and can well assist the research of seismic exploration technology during tunneling, providing a reliable technical guarantee for the development of rapid and intelligent tunneling of roadways.

Description

Technical Field

[0001] The present invention relates to the technical field of mine geophysical exploration, and more particularly to a forward modeling method for seismic data of mine excavation. Background Art

[0002] Intelligent coal mines are the core technical support for adapting to the development trend of the modern industrial technological revolution, achieving the "dual carbon" goals, ensuring national energy security, and realizing high-quality development of the coal industry. As one of the two core links of coal mine production, the demand for intelligent tunneling is extremely urgent, but in the process of tunneling, disasters such as coal and gas outbursts and water inrush seriously threaten the safety of tunneling production and the personal safety of miners. Geological support technology is the basis for the safety guarantee of intelligent coal production. It is the basic data source for geological prediction, disturbance perception and risk assessment before, during and after tunneling construction. It is the prerequisite for the implementation of all key technologies for intelligent tunneling. Among them, integrating the detection instrument with the tunneling machinery and carrying out on-the-spot detection is one of the most effective ways to ensure the rapid tunneling. It can realize parallel exploration and excavation, precise disaster control, and give full play to the production efficiency of tunneling machinery. It is the most urgently needed guarantee technology for the rapid intelligent tunneling development of tunnels in the future. The mine excavation seismic exploration technology has attracted extensive attention from scholars in the industry for its advanced advantages such as safety, greenness, and compliance with the scientific concept of intelligent and unmanned mining in coal mines. However, the technology is still in the experimental research stage, and many key basic research breakthroughs have not been made.

[0003] Forward modeling is one of the most important research methods in geophysical exploration technology, and is the most important research method and foundation for theoretical research and inversion imaging. In order to carry out in-depth basic research on mine seismic exploration technology, the assistance of corresponding forward modeling methods is also needed. Since the seismic source of the tunnel boring machine is quite different from conventional seismic sources such as explosives in terms of excitation mode, wavelet form, energy, frequency, etc., conventional cognition and forward modeling methods can no longer achieve results.

[0004] Therefore, how to provide an effective forward modeling method suitable for mine excavation seismic data is an urgent problem to be solved by those skilled in the art. Summary of the invention

[0005] In view of this, the present invention provides a forward simulation method for mine excavation seismic data, which aims to effectively simulate the mine excavation seismic data.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A forward modeling method for seismic data during mine excavation, comprising the following steps:

[0008] S1. Establish forward model and observation system;

[0009] S2. According to the needs of forward modeling, set the forward modeling parameters for the forward modeling model, and perform forward simulation stability analysis and numerical dispersion condition judgment;

[0010] S3. If the forward modeling parameters meet the stability and numerical dispersion conditions, the source is loaded and the source wavelet F is set. t ;

[0011] The specific method of source loading is as follows:

[0012] s(x,z,t)=exp{-α[(x-x0) 2 +(z-z0) 2 ]}·F t

[0013] In the formula, x represents the horizontal coordinate, z represents the vertical coordinate, t represents the time, (x0,z0) is the center position of the earthquake source, α is the attenuation coefficient, and α>0;

[0014] Set source wavelet F t The specific method is:

[0015] (1) Select n multi-source basic wavelets f with different main frequencies t i ;

[0016] (2) Select the main frequency range of the earthquake source for forward modeling as needed;

[0017] (3) Within the main frequency range, set m randomly distributed frequency values, where m ≥ n, and compare the m frequency values ​​with the n multi-source basic wavelets f t i Randomly combine and superimpose to obtain superimposed multi-source wavelets

[0018] (4) Set the upper and lower limits of different excitation delays during continuous excitation:

[0019] (5) Setting j randomly distributed excitation delay values ​​τ according to the upper and lower limits j :

[0020]

[0021] τ1≤τ j ≤τ2

[0022] In the formula, τ1 is the lower limit of the excitation delay, τ2 is the upper limit of the excitation delay, and nt is the time length of the seismic data;

[0023] (6) Repeat step (3) j times to obtain j superimposed multi-source wavelets. Compare the j superimposed multi-source wavelets with j randomly distributed excitation delay values ​​τ j Combine them one by one;

[0024] (7) The superposition and combination of the seismic source wavelet F is obtained by t ;

[0025] S4. Setting boundary conditions and obtaining elastic wave control equations in the boundary area;

[0026] S5. Perform finite difference wave field solutions on the elastic wave control equations in the boundary region and the elastic wave equations in the internal region using a high-order staggered grid.

[0027] Preferably, the forward modeling parameters include: model grid transverse spacing dx, model grid longitudinal spacing dz, sampling time interval dt, and sampling point number nt.

[0028] Preferably, the specific contents of the forward simulation stability analysis in S2 include:

[0029] The stability condition in two dimensions using the staggered grid difference scheme is:

[0030]

[0031] Where: (V p ) max represents the maximum value of the longitudinal wave velocity model in the forward model, the model grid transverse spacing dx, the model grid longitudinal spacing dz, the sampling time interval dt, C n is the finite difference coefficient, and 2N is the finite difference order.

[0032] Preferably, the numerical dispersion condition in S2 is:

[0033]

[0034] Where: dx&dz represents dx and dz, λ min is the minimum wavelength, n w is the number of grid points occupied by the minimum wavelength, f max Represents superposition of multi-source wavelets The maximum frequency (V s ) min Represents the minimum value of the shear wave velocity in the forward model.

[0035] Preferably, the specific content of S4 includes:

[0036] The boundary conditions include conventional boundaries and free interfaces, wherein the conventional boundaries adopt perfectly matched layer absorbing boundary layer boundary conditions, and the specific calculation method of the free cross section includes:

[0037] Assume that the tunnel roof is located at z = jdz, and there is a cavity below. The method for setting the free boundary of the tunnel roof is:

[0038]

[0039] Where: h, k represent the positions of the grid nodes in the z and x directions respectively, σ xz and σ zz They are all stress components of elastic wave field;

[0040] The tunnel floor is located at z = kdz, with a cavity above it. The free boundary setting method of the tunnel floor is:

[0041]

[0042] The tunnel face is located at x = hdx, and there is a cavity behind it. The method for setting the free boundary of the tunnel face is:

[0043]

[0044] Preferably, the specific content of S5 includes: solving the wave field of the isotropic medium elastic wave equation using a staggered grid difference format with second-order time and 2N-order space accuracy:

[0045]

[0046] Where: V x ,V z represents the velocity of the particle, σ xx , σ xz , σ zz represents the stress component of the elastic wave field, λ,μ are the Lame constants, ρ represents the density, e represents the time node, h,k represent the position of the grid node in the z and x directions respectively, C n is the difference coefficient;

[0047] In the process of wave field solution, given the initial condition, that is, source loading, add s(x,z,t) in S3 to σ xx With σ zz superior:

[0048]

[0049] It can be seen from the above technical solutions that, compared with the prior art, the present invention discloses a forward modeling method for seismic data during mine excavation, which has the following beneficial effects:

[0050] (1) The present invention can realize the real and effective forward simulation of the excavation seismic data by constructing the earthquake source equation of the excavation seismic data, and the seismic data obtained by simulation has the same signal characteristics as the actual excavation data;

[0051] (2) The forward modeling method of seismic data during excavation disclosed in the present invention can well assist the research of seismic exploration technology during excavation and provide a reliable technical guarantee for the development of rapid and intelligent tunnel excavation. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0053] Figure 1 A schematic diagram of the characteristics of seismic data signals during actual mining provided in an embodiment of the present invention;

[0054] Figure 2 A schematic diagram of a conventional forward modeling seismic exploration signal provided in an embodiment of the present invention;

[0055] Figure 3 The present invention provides a flow chart of a forward modeling method for seismic data during mine excavation;

[0056] Figure 4 A schematic diagram of an advanced fault fracture zone model (P-wave velocity) provided in an embodiment of the present invention;

[0057] Figure 5 A schematic diagram of a forward modeling record of an earthquake during excavation provided in an embodiment of the present invention;

[0058] Figure 6 It is a schematic diagram of the characteristics of the forward simulation of the seismic recording signal during excavation provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0059] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0060] The seismic data is a complex, variable frequency, continuous signal with a certain duration. Its sub-wave form is uncertain and generally shows a pseudo-random signal characteristic of multi-source superposition. Its original signal characteristics are as follows: Figure 1 shown.

[0061] However, conventional forward modeling of seismic exploration data uses a single wavelet with a fixed main frequency, a certain starting time and limited energy, and decays in a very short time, such as the Ricker wavelet. The simulated signal is a regular pulse vibration signal, such as Figure 2 As shown, conventional methods cannot be used to simulate the seismic data while digging. Therefore, in order to effectively simulate the seismic data while digging, the embodiment of the present invention discloses a forward modeling method for seismic data while digging a mine, such as Figure 3 As shown, the following steps are included:

[0062] S1. Establish forward model and observation system;

[0063] S2. According to the needs of forward modeling, set the forward modeling parameters for the forward modeling model, conduct forward simulation stability analysis and determine the numerical dispersion conditions;

[0064] S3. If the forward modeling parameters meet the stability and numerical dispersion conditions, the source is loaded and the source wavelet F is set. t ;

[0065] The specific method of source loading is as follows:

[0066] s(x,z,t)=exp{-α[(x-x0) 2 +(z-z0) 2 ]}·F t

[0067] In the formula, x represents the horizontal coordinate, z represents the vertical coordinate, t represents the time, (x0,z0) is the center position of the earthquake source, α is the attenuation coefficient, and α>0;

[0068] Set source wavelet F t The specific method is:

[0069] (1) Select n multi-source basic wavelets f with different main frequencies t i ;

[0070] (2) Select the main frequency range of the earthquake source for forward modeling as needed;

[0071] (3) Within the main frequency range, set m randomly distributed frequency values, where m ≥ n, and compare the m frequency values ​​with the n multi-source basic wavelets f t i Randomly combine and superimpose to obtain superimposed multi-source wavelets

[0072] (4) Set the upper and lower limits of different excitation delays during continuous excitation:

[0073] (5) Set j randomly distributed excitation delay values ​​τ according to the upper and lower limits j :

[0074]

[0075] τ1≤τ j ≤τ2

[0076] In the formula, τ1 is the lower limit of the excitation delay, τ2 is the upper limit of the excitation delay, and nt is the time length of the seismic data;

[0077] (6) Repeat step (3) j times to obtain j superimposed multi-source wavelets. Compare the j superimposed multi-source wavelets with j randomly distributed excitation delay values ​​τ j Combine them one by one;

[0078] (7) The superposition and combination of the seismic source wavelet F is obtained by t ;

[0079] S4. Setting boundary conditions and obtaining elastic wave control equations in the boundary area;

[0080] S5. Finite difference wave field solutions are performed for the boundary region elastic wave governing equations and the interior region elastic wave equations using high-order staggered grids.

[0081] It should be noted that:

[0082] The source wavelet F t Specifically, it can be expressed as:

[0083]

[0084] Where n is the number of multi-source basic wavelets, nt is the time length of seismic data, For different frequency values ​​and multi-source basic wavelets f t i The superimposed multi-source wavelet obtained by random combination and superposition, τ j is the jth randomly distributed excitation delay value;

[0085] Wave equation forward modeling is actually a process of solving the wave equation under given initial conditions and boundary conditions, and then the wave field value at any position and any time can be calculated. In seismic wave forward modeling, the source term is the initial condition.

[0086] During the forward modeling process, different directional force sources or longitudinal wave sources can be selected according to the source form to be simulated and the force source setting method.

[0087] The forward model includes P-wave velocity model, S-wave velocity model and density model;

[0088] The observation system includes detection points and seismic sources, which are arranged and distributed in the middle of the coal seam.

[0089] The present invention performs elastic wave forward simulation of excavation seismic data, and three sets of parameter models are designed when designing the forward model, namely, a longitudinal wave velocity model, a shear wave velocity model and a density model.

[0090] In addition, due to the special source form of mine excavation seismic exploration technology, that is, the excavation seismic source, the vibration accompanying the tunnel production process is used as the seismic source, so its seismic source is generally a point source. Figure 4 As shown, the observation system is arranged and distributed in the middle of the coal seam, where the black circles are the detection points and the red stars are the seismic sources.

[0091] In order to further implement the above technical solution, the forward modeling parameters include: model grid transverse spacing dx, model grid longitudinal spacing dz, sampling time interval dt, and sampling point number nt.

[0092] In order to further implement the above technical solutions, the specific contents of the forward simulation stability analysis in S2 include:

[0093] The stability condition in two dimensions using the staggered grid difference scheme is:

[0094]

[0095] Where: (V p ) max represents the maximum value of the longitudinal wave velocity model in the forward model, the model grid transverse spacing dx, the model grid longitudinal spacing dz, the sampling time interval dt, C n is the finite difference coefficient, and 2N is the finite difference order.

[0096] In order to further implement the above technical solution, the numerical dispersion condition in S2 is:

[0097]

[0098] Where: dx&dz represents dx and dz, λ min is the minimum wavelength, n w is the number of grid points occupied by the minimum wavelength, f max Represents superposition of multi-source wavelets The maximum frequency (V s ) min Represents the minimum value of the shear wave velocity in the forward model.

[0099] In order to further implement the above technical solution, the specific contents of S4 include:

[0100] The boundary conditions include conventional boundaries and free interfaces. The conventional boundaries use the perfectly matched layer absorbing boundary layer boundary conditions. The specific calculation methods of the free cross section include:

[0101] Assume that the tunnel roof is located at z = jdz, and there is a cavity below. The method for setting the free boundary of the tunnel roof is:

[0102]

[0103] Where: h, k represent the positions of the grid nodes in the z and x directions respectively, σ xz and σ zz They are all stress components of elastic wave field;

[0104] The tunnel floor is located at z = kdz, with a cavity above it. The free boundary setting method of the tunnel floor is:

[0105]

[0106] The tunnel face is located at x = hdx, and there is a cavity behind it. The method for setting the free boundary of the tunnel face is:

[0107]

[0108] In order to further implement the above technical solution, the specific content of S5 includes: solving the wave field of the elastic wave equation of isotropic medium with the staggered grid difference format of the second order in time and 2N order in space:

[0109]

[0110] Where: V x ,V z represents the velocity of the particle, σ xx , σ xz , σ zz represents the stress component of the elastic wave field, λ,μ are the Lame constants, ρ represents the density, e represents the time node, h,k represent the position of the grid node in the z and x directions respectively, C n is the difference coefficient;

[0111] In the process of wave field solution, given the initial condition, that is, source loading, add s(x,z,t) in S3 to σ xx With σ zz superior:

[0112]

[0113] It should be noted that:

[0114] The boundary condition setting of the present invention includes two parts:

[0115] (1) Conventional boundaries use perfectly matched layer (PML) absorbing boundary layer boundary conditions;

[0116] (2) Since the interface of a mine tunnel is similar to the free interface on the ground, in a two-dimensional case, there are three free interfaces in the tunnel, namely, the tunnel roof, the floor (or the left and right side walls, depending on the section direction) and the head. These free interfaces need to be specially processed during the forward simulation process. The present invention adopts an improved mirror method to process the free interfaces.

[0117] The present invention adopts a high-order staggered grid finite difference method to solve the forward simulation process. Different from the staggered grid setting method inside the boundary, the staggered grid of the free interface of the tunnel sets the normal stress at the center of the grid. It is particularly important to note that, unlike the free boundary of the surface in the forward simulation of conventional seismic exploration, the free interface of the tunnel roof is above the cavity. Contrary to the surface, for discrete grids, the surface interface is set on the upper surface of the grid, but for the tunnel roof surface, the free interface is set on the lower surface of the grid, and the mirror equation has changed.

[0118] The present invention will be further described below through specific experiments:

[0119] In order to verify the effectiveness and accuracy of the forward modeling method of mine excavation seismic data in this patent, the scheme proposed in this invention is used in the advanced fault fracture zone model ( Figure 4 ), and the forward simulation record is obtained as Figure 5 shown.

[0120] and Figure 1 The analysis of the actual excavation seismic data is consistent with that of the previous one. The 1000ms single-channel record is used as the analysis unit. The forward simulation of the excavation seismic record signal characteristics are analyzed from the time domain, frequency domain and time-frequency domain. For example, Figure 6 shown.

[0121] contrast Figure 1 and Figure 6 It can be seen that the forward simulated earthquake records obtained by the present invention are consistent with the measured earthquake records in the time domain, frequency domain and time-frequency domain, which proves the effectiveness and accuracy of the forward simulation method of mine seismic data while digging.

[0122] The present invention analyzes the signal characteristics of the measured excavation seismic data and finds that the excavation seismic data is a complex, variable frequency, continuous signal with a certain duration, and its sub-wave form is uncertain, and generally shows a pseudo-random signal characteristic of multi-source superposition. Based on the signal characteristic analysis, the present invention proposes a solution to the excavation seismic source equation. The data characteristics simulated by the method provided by the present invention are consistent with the characteristics of the measured excavation seismic data. Therefore, the present invention can realize the real and effective forward simulation of the excavation seismic data.

[0123] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0124] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A forward modeling method for seismic data during mine excavation, characterized in that: The following steps are involved: S1. Establish forward model and observation system; S2. According to the needs of forward modeling, set the forward modeling parameters for the forward modeling model, and perform forward simulation stability analysis and numerical dispersion condition judgment; S3. If the forward modeling parameters meet the stability and numerical dispersion conditions, the source is loaded and the source wavelet F is set. t ; The specific method of source loading is as follows: s(x,z,t)=exp{-α[(x-x0) 2 +(z-z0) 2 ]}·F t In the formula, x represents the horizontal coordinate, z represents the vertical coordinate, t represents the time, (x0,z0) is the center position of the earthquake source, α is the attenuation coefficient, and α>0; Set source wavelet F t The specific method is: (1) Select n multi-source basic wavelets with different main frequencies (2) Select the main frequency range of the earthquake source for forward modeling as needed; (3) Within the main frequency range, set m randomly distributed frequency values, where m ≥ n, and compare the m frequency values ​​with the n multi-source basic wavelets f t i Randomly combine and superimpose to obtain superimposed multi-source wavelets (4) Set the upper and lower limits of different excitation delays during continuous excitation: (5) Setting j randomly distributed excitation delay values ​​τ according to the upper and lower limits j : τ1≤τ j ≤τ2 In the formula, τ1 is the lower limit of the excitation delay, τ2 is the upper limit of the excitation delay, and nt is the time length of the seismic data; (6) Repeat step (3) j times to obtain j superimposed multi-source wavelets. Compare the j superimposed multi-source wavelets with j randomly distributed excitation delay values ​​τ j Combine them one by one; (7) The superposition and combination of the seismic source wavelet F is obtained by t ; S4. Setting boundary conditions and obtaining elastic wave control equations in the boundary area; S5. Perform finite difference wave field solutions on the elastic wave control equations in the boundary region and the elastic wave equations in the internal region using a high-order staggered grid.

2. A forward modeling method for mine seismic data while digging according to claim 1, characterized in that: The forward modeling parameters include: model grid transverse spacing dx, model grid longitudinal spacing dz, sampling time interval dt, and sampling point number nt.

3. A forward simulation method for mine excavation seismic data according to claim 1, characterized in that: The specific contents of the forward simulation stability analysis in S2 include: The stability condition in two dimensions using the staggered grid difference scheme is: Where: (V p ) max represents the maximum value of the longitudinal wave velocity model in the forward model, the model grid transverse spacing dx, the model grid longitudinal spacing dz, the sampling time interval dt, C n is the finite difference coefficient, and 2N is the finite difference order.

4. A forward simulation method for mine seismic data while digging according to claim 1, characterized in that: The numerical dispersion condition in S2 is: Where: dx&dz represents dx and dz, λ min is the minimum wavelength, n w is the number of grid points occupied by the minimum wavelength, f max Represents superposition of multi-source wavelets The maximum frequency (V s ) min Represents the minimum value of the shear wave velocity in the forward model.

5. The forward modeling method for mine excavation seismic data according to claim 1, characterized in that: The specific contents of S4 include: The boundary conditions include conventional boundaries and free interfaces, wherein the conventional boundaries adopt perfectly matched layer absorbing boundary layer boundary conditions, and the specific calculation method of the free interface includes: Assume that the tunnel roof is located at z = jdz, and there is a cavity below. The method for setting the free boundary of the tunnel roof is: Where: h, k represent the positions of the grid nodes in the z and x directions respectively, σ xz and σ zz They are all stress components of elastic wave field; The tunnel floor is located at z = kdz, with a cavity above it. The free boundary setting method of the tunnel floor is: The tunnel face is located at x = hdx, and there is a cavity behind it. The method for setting the free boundary of the tunnel face is:

6. A forward modeling method for mine excavation seismic data according to claim 1, characterized in that: The specific contents of S5 include: solving the wave field of the elastic wave equation of isotropic medium with the staggered grid difference format of the second order in time and 2N order in space: Where: V x ,V z represents the velocity of the particle, σ xx , σ xz , σ zz represents the stress component of the elastic wave field, λ,μ are the Lame constants, ρ represents the density, e represents the time node, h,k represent the position of the grid node in the z and x directions respectively, C n is the difference coefficient; In the process of wave field solution, given the initial condition, that is, source loading, add s(x,z,t) in S3 to σ xx With σ zz superior:

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