Similar model-finite element simulation coupled prediction method of gas emission height in abandoned mine

Abstract

A kind of abandoned mine gas emission height prediction method coupling similar model-finite element simulation, collects stratum geological data and mine production data of abandoned mining area;Obtain stratum mechanical parameters and gas occurrence parameters;According to stratum geological data, stratum mechanical parameters, gas occurrence parameters and similarity criterion, establish stratum excavation similar model;Excavation of stoping section is carried out, closed well balance simulation is carried out, simultaneously, image processing software is used to identify stope fissure image;Stope fissure image is imported into image recognition software Coreldraw, and the coordinates of each stope fissure are obtained;Space grid model is established in MATLAB, and permeability is given through the relationship between fissure coordinates and space grid;The obtained permeability is imported into finite element software COMSOL in the form of interpolation method, and the gas emission height is comprehensively determined by simulation method.The method can accurately determine the change of abandoned stope gas emission height with time.

Description

Technical Field

[0001] This invention belongs to the field of intelligent prediction technology, specifically relating to a method for predicting the gas emission height in abandoned mines using a similar model-finite element simulation coupling. Background Technology

[0002] Currently, the number of abandoned mines in my country is continuously increasing, and it is estimated that by 2030, the number of abandoned mines will reach approximately 15,000. Due to constraints on recovery rates, 45%-50% of the main coal seam and protective coal pillars are typically left underground in these abandoned mines, containing substantial amounts of methane resources. Simultaneously, methane from abandoned mines may enter the surface atmosphere through geological fissures, contributing to the greenhouse effect. Furthermore, it may be oxidized and ignited by residual coal, causing methane explosions and potentially leading to safety accidents. Without systematic and standardized extraction and scientific management of methane from abandoned mines, there will be a significant impact on the environment, and the accumulation of large amounts of methane in goaf areas greatly increases the risk of methane explosions. Therefore, carrying out methane drainage and management operations in abandoned mines has significant economic, environmental, and safety benefits.

[0003] Predicting the gas emission height in abandoned mines is of great significance for the safe and efficient extraction of gas and also helps improve the effectiveness of gas control in abandoned mines. The main characteristics of gas emission are long time periods and a lack of effective monitoring and prediction methods. Therefore, there is an urgent need to provide a method for predicting the gas emission height in abandoned mines, which can effectively determine the evolution characteristics of fractures in abandoned mine stopes over long periods and the corresponding gas emission height. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method for predicting the gas emission height in abandoned mines using a similar model-finite element simulation coupling method. This method can significantly reduce the cost and risk of experiments and tests through simulation, and can accurately determine the changes in gas emission height in abandoned mines over time, providing scientific guidance for the layout of gas drainage boreholes.

[0005] To achieve the above objectives, this invention provides a method for predicting the gas emission height in abandoned mines using a similar model-finite element simulation coupling method, comprising the following steps:

[0006] Step 1: Collect geological data of rock strata and mine production data of abandoned mining areas; at the same time, use sampling drills to carry out in-situ core sampling operations on the surface of the mining area to obtain core samples of each coal and rock strata, and then obtain the rock strata mechanical parameters and gas occurrence parameters of each coal and rock strata core samples through laboratory testing.

[0007] Step 2: Establish a similar model for rock excavation based on geological data, rock mechanical parameters, gas occurrence parameters, and similarity criteria;

[0008] Step 3: Based on the collected mine production data, conduct excavation and shaft closure balance simulation of the mining section of the rock stratum excavation similar model. At the same time, collect images of the similar model after excavation and use image processing software to identify the images of the mining area fractures.

[0009] Step 4: Import the obtained images of the stope fractures into the image recognition software CorelDRAW, and obtain the coordinates of each stope fracture after vectorization.

[0010] Step 5: Establish a spatial grid model in MATLAB, and assign permeability by the relationship between fracture coordinates and spatial grid;

[0011] Step Six: Import the obtained permeability into the finite element software COMSOL using interpolation. Through simulation, comprehensively determine the gas emission height and finally obtain the predicted result of the gas emission height in the abandoned mine.

[0012] As a preferred embodiment, in step one, the geological data of the rock strata includes the distribution of coal and rock strata, the dip angle of the coal seam, and the strike of the coal seam; the mine production data includes the coal mining volume of the mining area, and information on the production and abandonment years; and the gas occurrence parameters include permeability, gas content, and gas pressure.

[0013] As a preferred embodiment, in step two, the similarity criteria include geometric similarity, density similarity, area similarity, and time similarity.

[0014] As a preferred option, in step three, the recovery ratio of the excavation is controlled based on the amount of coal mined in the mining area, and the mining time and balancing time are determined based on the information on the number of years of production abandonment.

[0015] Furthermore, in order to accurately determine the well closure balance simulation time and obtain a more realistic simulation effect, in step three, the well closure balance simulation time is determined by formula (2) based on the area similarity relationship in formula (1).

[0016]

[0017]

[0018] In the formula, l p h p These represent the actual stratigraphic length and height, respectively; m h m v represents the length and height of the model strata; p t p This represents the actual speed and time of excavation in a mining area; v m t m For the excavation speed and time of similar models; Kt K represents the temporal similarity ratio of the model. l This represents the geometric similarity ratio of the models.

[0019] Furthermore, to ensure recognition accuracy, in step four, before importing the mine fracture image into the image recognition software CorelDRAW, the mine fracture image is first binarized.

[0020] Furthermore, in order to accurately and efficiently allocate the permeability of the mining area fractures, the process of establishing a spatial grid module and assigning permeability in step five is as follows:

[0021] S51: Extract the spatial coordinates of the fracture and establish an i*4 fracture coordinate matrix F in MATLAB, as shown in formula (3);

[0022]

[0023] In the formula, i is the obtained crack number; x mi1 x mi2 These are the x-coordinates of the two ends of the fracture; y-coordinates are the x-coordinates of the two ends of the fracture. mi1 y mi2 These are the y-coordinates of the two ends of the crack;

[0024] S52: In MATLAB, establish a space of the same size as the rock excavation model, and mesh the space into 1j 20*20cm grids; obtain the coordinates of the four endpoints of each grid and establish a j*9 matrix G, as shown in formula (4);

[0025]

[0026] In the formula, j is the obtained grid number; x i1 x i2 x i3 x i4 These are the x-coordinates of the four endpoints of the grid; y-coordinates of the grid. i1 y i2 y i3 y i4 These are the y-coordinates of the four endpoints of the grid; the first column of the matrix is ​​the grid's permeability, with the initial permeability of the grid uniformly set to 0;

[0027] S53: The grid interval where each crack is located is determined using MATLAB, and the dip angle of the crack is determined iteratively. The specific process is as follows:

[0028] A1: If the x-coordinates of the two ends of the current crack i are x i1 x i2 The minimum value is less than the x-coordinates of the four endpoints of the j-th network. j1 x j2 xj3 x j4 The maximum value, and the x-coordinates x at both ends of the current crack i. i1 x i2 The maximum value is greater than the x-coordinates of the four endpoints of the j-th network. j1 x j2 x j3 x j4 If the minimum value is found, the condition is met and A2 is executed; otherwise, the condition is not met, and j = j + 1 is set, and A1 is executed again until the condition is met.

[0029] A2: If the y-coordinates of the two ends of the current crack i are y i1 y i2 The minimum value is less than the y-coordinates of the four endpoints of the j-th network. j1 y j2 y j3 y j4 The maximum value, and the y-coordinates of the two ends of the current crack i. i1 y i2 The maximum value is greater than the y-coordinates of the four endpoints of the j-th network. j1 y j2 y j3 y j4 If the minimum value is found, the condition is met and A3 is executed; otherwise, the condition is not met, and j = j + 1 is set, and A2 is executed again until the condition is met.

[0030] A3: Based on the significant difference in permeability of fractures with different dip angles, the dip angle of the fractures is determined as follows;

[0031] A permeability k1 is assigned to the grid with a fracture dip angle greater than 45°, a permeability k2 is assigned to the grid with a fracture dip angle less than or equal to 45°, and a permeability k3 is assigned to the term in the matrix where G(j,1) is still 0, as shown in formula (5).

[0032]

[0033] A4: Let i = i + 1, and repeat A1 to A3;

[0034] A5: Repeat A4 multiple times until i ≥ i max , where i max The maximum value of the fracture number is used to complete the allocation of permeability for all fractures, ultimately obtaining the permeability within the spatial grid.

[0035] In this invention, core samples are drilled in the mining area using a sampling drill, and then tested in a laboratory. This allows for the precise acquisition of rock strata mechanical parameters and gas occurrence parameters through experimentation. By combining these parameters with previously collected geological data and similarity criteria, a rock strata excavation similarity model that closely resembles the real-world environment can be easily established using modeling software. This provides a reliable technical guarantee for obtaining accurate analysis results. By simulating the excavation and balancing of the mining section using the rock strata excavation similarity model, working conditions consistent with the real-world environment can be simulated efficiently and accurately while effectively reducing material and human resource costs. First, images of the fractures in the excavated mining area are acquired. Then, the coordinates of each fracture are obtained by vectorization using the image recognition software CorelDRAW. Next, a spatial mesh model is built using MATLAB. The permeability is assigned by the correlation between the coordinates of the mining area fractures and the spatial mesh. This allows for the efficient and accurate assignment of permeability to fractures in different parts of the constructed rock excavation similar model, which is consistent with the real environment. This helps to intuitively and accurately determine the effective gas migration channels. At the same time, it also facilitates the determination of potential gas migration paths through analysis. In this way, the gas emission height can be simulated using the finite element software COMSOL, thereby efficiently and accurately obtaining the prediction results of the gas emission height in abandoned mines. This provides reliable technical support for the safe and efficient extraction of gas in the future.

[0036] This method is simple to operate and has low implementation costs. It effectively combines the advantages of similarity models and finite element simulation, which can greatly reduce the cost and risk of experiments and tests through simulation. It can accurately determine the change of gas outburst height in abandoned mining areas over time and provide scientific guidance for the layout of gas drainage boreholes. Attached Figure Description

[0037] Figure 1 This is a flowchart of the present invention;

[0038] Figure 2 This is a flowchart of the permeability distribution process in the mining area fractures in this invention;

[0039] Figure 3 This is a comparative schematic diagram of the extraction of mining area fractures and spatial gridding in this invention;

[0040] Figure 4 This is a schematic diagram of the simulation results of the gas outburst height in the mining area according to the present invention, taking y=60 as an example;

[0041] Figure 5 This is a schematic diagram of the simulation results of the gas outburst height in the mining area according to the present invention, taking y=80 as an example. Detailed Implementation

[0042] The present invention will be further described below.

[0043] like Figure 1 As shown, this invention provides a method for predicting the gas emission height in abandoned mines using a similar model-finite element simulation coupling method, comprising the following steps:

[0044] Step 1: Collect geological data of rock strata and mine production data of abandoned mining areas; at the same time, use sampling drills to carry out in-situ core sampling operations on the surface of the mining area to obtain core samples of each coal and rock strata, and then obtain the rock strata mechanical parameters and gas occurrence parameters of each coal and rock strata core samples through laboratory testing.

[0045] Step 2: Establish a similar model for rock excavation based on geological data, rock mechanical parameters, gas occurrence parameters, and similarity criteria;

[0046] Step 3: Based on the collected mine production data, conduct excavation and shaft closure balance simulation of the mining section of the rock stratum excavation similar model. At the same time, collect images of the similar model after excavation and use image processing software to identify the images of the mining area fractures.

[0047] Step 4: Import the obtained images of the stope fractures into the image recognition software CorelDRAW, and obtain the coordinates of each stope fracture after vectorization.

[0048] Step 5: Establish a spatial grid model in MATLAB, and assign permeability by the relationship between fracture coordinates and spatial grid;

[0049] Step Six: Import the obtained permeability into the finite element software COMSOL using interpolation. Through simulation, comprehensively determine the gas emission height and finally obtain the predicted result of the gas emission height in the abandoned mine.

[0050] like Figure 3 As shown, Figure 3 A comparative schematic diagram showing the extraction of fractures in the stope and spatial gridding is presented;

[0051] like Figure 4 As shown, Figure 4 A schematic diagram showing the simulation results of gas outburst height in a mining area is presented, with y=60 as an example;

[0052] like Figure 5 As shown, Figure 5 A schematic diagram showing the simulation results of gas outburst height in the mining area is presented, with y=80 as an example.

[0053] As a preferred embodiment, in step one, the geological data of the rock strata includes the distribution of coal and rock strata, the dip angle of the coal seam, and the strike of the coal seam; the mine production data includes the coal mining volume of the mining area, and information on the production and abandonment years; and the gas occurrence parameters include permeability, gas content, and gas pressure.

[0054] As a preferred embodiment, in step two, the similarity criteria include geometric similarity, density similarity, area similarity, and time similarity.

[0055] As a preferred option, in step three, the recovery ratio of the excavation is controlled based on the amount of coal mined in the mining area, and the mining time and balancing time are determined based on the information on the number of years of production abandonment.

[0056] In order to accurately determine the well closure balance simulation time and obtain a more realistic simulation effect, in step three, the well closure balance simulation time is determined by formula (2) based on the area similarity relationship in formula (1).

[0057]

[0058] In the formula, l p h p These represent the actual stratigraphic length and height, respectively; m h m v represents the length and height of the model strata; p t p This represents the actual speed and time of excavation in a mining area; v m t m For the excavation speed and time of similar models; K t K represents the temporal similarity ratio of the model. l This represents the geometric similarity ratio of the models.

[0059] To ensure recognition accuracy, in step four, before importing the mining area fracture image into the image recognition software CorelDRAW, the mining area fracture image is first binarized.

[0060] like Figure 2 As shown, in order to accurately and efficiently allocate the permeability of the mining area fractures, the process of establishing a spatial grid module and assigning permeability in step five is as follows:

[0061] S51: Extract the spatial coordinates of the fracture and establish an i*4 fracture coordinate matrix F in MATLAB, as shown in formula (3);

[0062]

[0063] In the formula, i is the obtained crack number; x mi1 x mi2 These are the x-coordinates of the two ends of the fracture; y-coordinates are the x-coordinates of the two ends of the fracture. mi1 ymi2 These are the y-coordinates of the two ends of the crack;

[0064] S52: In MATLAB, establish a space of the same size as the rock excavation model, and mesh the space into 1j 20*20cm grids; obtain the coordinates of the four endpoints of each grid and establish a j*9 matrix G, as shown in formula (4);

[0065]

[0066] In the formula, j is the obtained grid number; x i1 x i2 x i3 x i4 These are the x-coordinates of the four endpoints of the grid; y-coordinates of the grid. i1 y i2 y i3 y i4 These are the y-coordinates of the four endpoints of the grid; the first column of the matrix is ​​the grid's permeability, with the initial permeability of the grid uniformly set to 0;

[0067] S53: The grid interval where each crack is located is determined using MATLAB, and the dip angle of the crack is determined iteratively. The specific process is as follows:

[0068] A1: If the x-coordinates of the two ends of the current crack i are x i1 x i2 The minimum value is less than the x-coordinates of the four endpoints of the j-th network. j1 x j2 x j3 x j4 The maximum value, and the x-coordinates x at both ends of the current crack i. i1 x i2 The maximum value is greater than the x-coordinates of the four endpoints of the j-th network. j1 x j2 x j3 x j4 If the minimum value is found, the condition is met and A2 is executed; otherwise, the condition is not met, and j = j + 1 is set, and A1 is executed again until the condition is met.

[0069] A2: If the y-coordinates of the two ends of the current crack i are y i1 y i2 The minimum value is less than the y-coordinates of the four endpoints of the j-th network. j1 y j2 y j3 y j4 The maximum value, and the y-coordinates of the two ends of the current crack i. i1 y i2 The maximum value is greater than the y-coordinates of the four endpoints of the j-th network.j1 y j2 y j3 y j4 If the minimum value is found, the condition is met and A3 is executed; otherwise, the condition is not met, and j = j + 1 is set, and A2 is executed again until the condition is met.

[0070] A3: Based on the significant difference in permeability of fractures with different dip angles, the dip angle of the fractures is determined as follows;

[0071] A permeability k1 is assigned to the grid with a fracture dip angle greater than 45°, a permeability k2 is assigned to the grid with a fracture dip angle less than or equal to 45°, and a permeability k3 is assigned to the term in the matrix where G(j,1) is still 0, as shown in formula (5).

[0072]

[0073] A4: Let i = i + 1, and repeat A1 to A3;

[0074] A5: Repeat A4 multiple times until i ≥ i max , where i max The maximum value of the fracture number is used to complete the allocation of permeability for all fractures, ultimately obtaining the permeability within the spatial grid.

[0075] In this invention, core samples are drilled in the mining area using a sampling drill, and then tested in a laboratory. This allows for the precise acquisition of rock strata mechanical parameters and gas occurrence parameters through experimentation. By combining these parameters with previously collected geological data and similarity criteria, a rock strata excavation similarity model that closely resembles the real-world environment can be easily established using modeling software. This provides a reliable technical guarantee for obtaining accurate analysis results. By simulating the excavation and balancing of the mining section using the rock strata excavation similarity model, working conditions consistent with the real-world environment can be simulated efficiently and accurately while effectively reducing material and human resource costs. First, images of the fractures in the excavated mining area are acquired. Then, the coordinates of each fracture are obtained by vectorization using the image recognition software CorelDRAW. Next, a spatial mesh model is built using MATLAB. The permeability is assigned by the correlation between the coordinates of the mining area fractures and the spatial mesh. This allows for the efficient and accurate assignment of permeability to fractures in different parts of the constructed rock excavation similar model, which is consistent with the real environment. This helps to intuitively and accurately determine the effective gas migration channels. At the same time, it also facilitates the determination of potential gas migration paths through analysis. In this way, the gas emission height can be simulated using the finite element software COMSOL, thereby efficiently and accurately obtaining the prediction results of the gas emission height in abandoned mines. This provides reliable technical support for the safe and efficient extraction of gas in the future.

[0076] This method is simple to operate and has low implementation costs. It effectively combines the advantages of similarity models and finite element simulation, which can greatly reduce the cost and risk of experiments and tests through simulation. It can accurately determine the change of gas outburst height in abandoned mining areas over time and provide scientific guidance for the layout of gas drainage boreholes.

Claims

1. A method for predicting the height of gas emission from an abandoned mine by coupling a similar model and a finite element simulation, characterized by, The method comprises the following steps: Step one: collecting stratum geological data and mine production data of abandoned mine; meanwhile, using sampling drill to make in-situ coring operation on the surface of the mine area to obtain core samples of each coal rock stratum, and obtaining stratum mechanical parameters and gas occurrence parameters of the core samples of each coal rock stratum through laboratory testing; Step two: establishing a stratum excavation similar model according to the stratum geological data, stratum mechanical parameters, gas occurrence parameters and similarity criteria; Step three: according to the collected mine production data, excavating the stoping section of the stratum excavation similar model, simulating the closed well balance, collecting the image of the similar model after excavation, and identifying the mining fissure image by using image processing software; Step four: importing the obtained mining fissure image into image recognition software Coreldraw, and obtaining the coordinates of each mining fissure after vectorization processing; Step five: establishing a space grid model in MATLAB, and giving the permeability through the mutual relationship between the fissure coordinates and the space grid; Step six: importing the obtained permeability into finite element software COMSOL in the form of interpolation method, comprehensively determining the gas emission height through simulation, and finally obtaining the prediction result of the gas emission height of the abandoned mine.

2. The method for predicting the height of gas emission in an abandoned mine according to claim 1, wherein, In step one, the stratum geological data includes coal rock stratum distribution, coal seam inclination and coal seam strike, the mine production data includes mining quantity of the mining area, production and abandoned time information, and the gas occurrence parameters include permeability, gas content and gas pressure.

3. The similar model-finite element simulation coupled abandoned mine gas emission height prediction method according to claim 1 or 2, characterized in that, In step two, the similarity criteria include geometric similarity, density similarity, area similarity and time similarity.

4. The similar model-finite element simulation coupled abandoned mine gas emission height prediction method according to claim 2, characterized in that, In step three, the mining ratio of the excavation is controlled according to the mining quantity of the mining area, and the mining time and balance time are determined according to the production and abandoned time information.

5. The similar model-finite element simulation coupled abandoned mine gas emission height prediction method according to claim 3, characterized in that, In step three, the time of the closed well balance simulation is determined through formula (2) based on the area similarity relationship in formula (1); （1）； （2）； wherein, l p , h p are the true length and height of the formation, respectively; l m , h m are the length and height of the model formation; v p , t p are the true stope excavation velocity and time; v m , t m are the model excavation velocity and time; K t is the time similarity ratio of the model; and K l is the geometric similarity ratio of the model.

6. The similar model-finite element simulation coupled abandoned mine gas emission height prediction method according to claim 5, characterized in that, In step four, the mining fissure image is binarized before being imported into the image recognition software Coreldraw.

7. The similar model-finite element simulation coupled abandoned mine gas emission height prediction method according to claim 6, characterized in that, In step five, the process of establishing the space grid module and giving the permeability is as follows: S51: extracting the space coordinates of the fissure, and establishing an i*4 fissure coordinate matrix F in MATLAB, as shown in formula (3); （3）； where i is the number of the fracture obtained; x mi1 , x mi2 is the x coordinate of the two ends of the fracture; y mi1 , y mi2 is the y coordinate of the two ends of the fracture; S52: establishing a space equal to the stratum excavation similar model in MATLAB, and meshing the space into j 20*20 cm grids; obtaining the coordinates of four end points of each grid and establishing a j*9 matrix G, as shown in formula (4); （4）； where j is the number of the grid obtained; , , , are the x coordinates of the four end points of the grid respectively; y i1 , y i2 , y i3 , y i4 are the y coordinates of the four end points of the grid respectively; the first column of the matrix is the permeability of the grid, and the initial permeability of the grid is uniformly set as 0; S53: determining the grid interval of each fissure by MATLAB, and cyclically determining the inclination of the fissure, and the specific process is as follows: A1: If the minimum value of the x coordinates x i1 , x i2 of the current crack i at both ends is less than the maximum value of the x coordinates x j1 , x j2 , x j3 , x j4 of the four end points of the jth network, and the maximum value of the x coordinates x i1 , x i2 of the current crack i at both ends is greater than the minimum value of the x coordinates x j1 , x j2 , x j3 , x j4 of the four end points of the jth network, then the determination condition is satisfied, and A2 is executed, otherwise the determination condition is not satisfied, j = j + 1, and A1 is re-executed until the determination condition is satisfied; A2: If the minimum value of y-coordinate y i1 , y i2 of the current crack i at both ends is less than the minimum value of y-coordinate y j1 , y j2 , y j3 , y j4 of the four end points of the jth network, and the maximum value of y-coordinate y i1 , y i2 of the current crack i at both ends is greater than the maximum value of y-coordinate y j1 , y j2 , y j3 , y j4 of the four end points of the jth network, then the determination condition is satisfied, and A3 is executed, otherwise the determination condition is not satisfied, j = j + 1, and A2 is re-executed until the determination condition is satisfied; A3: the permeability of the fissure with different inclination has obvious difference, and the inclination of the fissure is determined as follows; For the grid with fissure inclination greater than 45°, the permeability k1 is given, for the grid with fissure inclination less than or equal to 45°, the permeability k2 is given, and for the item with G (j, 1) still being 0 in the matrix, the permeability k3 is given, as shown in formula (5); （5）； A4: let i=i+1, and repeat A1 to A3; A5: repeatedly perform A4 until wherein, is the maximum value of the fracture number, and the distribution of the permeability of all fractures is completed to obtain the permeability in the spatial grid.

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