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

Abstract

The invention discloses a similar model-finite element simulation coupled abandoned mine gas emission height prediction method. The method comprises the following steps: collecting rock stratum geological data and mine production data of an abandoned mine area; rock stratum mechanical parameters and gas occurrence parameters are obtained; establishing a rock stratum excavation similar model according to the rock stratum geological data, the rock stratum mechanical parameters, the gas occurrence parameters and the similarity criterion; carrying out excavation and closed well balance simulation on a recovery section, and meanwhile, identifying a stope crack image by utilizing image processing software; the stope fracture image is imported into image recognition software Coreldraw, and the coordinate of each stope fracture is obtained; establishing a space grid model in MATLAB (matrix laboratory), and endowing permeability through the interrelation between fracture coordinates and space grids; and importing the obtained permeability into finite element software COMSOL in the form of an interpolation method, and comprehensively judging the gas emission height in a simulation manner. According to the method, the change condition of the gas emission height of the abandoned stope along with time can be accurately judged.

Description

Technical Field

[0001] The present invention belongs to the technical field of intelligent prediction, and in particular relates to a method for predicting the height of gas emission in abandoned mines by coupling a similarity model with finite element simulation. Background Art

[0002] At present, the number of abandoned mines in my country is increasing, and it is estimated that the number of abandoned mines will reach about 15,000 by 2030. Due to the constraints of the recovery rate, 45%-50% of the main coal seams and protective coal pillars are generally left underground in abandoned mines, which contain a large amount of gas resources. At the same time, the gas in the abandoned mines may enter the surface atmosphere through the stratum fissure channels to produce a greenhouse effect. At the same time, it may also be oxidized and ignited by the coal to cause gas explosions, which will cause safety accidents. If the abandoned mine gas is not systematically and standardizedly mined and scientifically managed, it will have a huge impact on the environment. At the same time, a large amount of gas accumulates in the goaf, which is very likely to cause gas explosion accidents. Therefore, carrying out gas extraction and management operations in abandoned mines has obvious economic, environmental and safety benefits.

[0003] Predicting the height of abandoned mine gas emission is of great significance for the safe and efficient extraction of gas, and is also conducive to improving the treatment effect of abandoned mine gas. The main characteristics of gas emission are long time period and lack of effective monitoring and prediction methods. Therefore, it is urgent to provide a method for predicting the height of abandoned mine gas emission, so as to effectively determine the evolution characteristics of abandoned mine cracks in the long period and the corresponding gas emission height. Summary of the invention

[0004] In view of the problems existing in the above-mentioned prior art, the present invention provides a method for predicting the gas emission height of abandoned mines by coupling a similarity model with finite element simulation. This method can greatly reduce the cost and risk of experiments and tests through simulation. It can accurately determine the change of the gas emission height of abandoned mining areas over time, and can provide scientific guidance for the arrangement of gas extraction drilling holes.

[0005] In order to achieve the above object, the present invention provides a method for predicting the gas emission height of abandoned mines by coupling similarity model and finite element simulation, comprising the following steps:

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

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

[0008] Step 3: Based on the collected mine production data, the excavation and closing balance simulation of the mining section is carried out on the rock formation excavation similar model. At the same time, the image of the similar model after excavation is collected, and the crack image of the mining field is identified by using image processing software;

[0009] Step 4: Import the obtained stope fissure image into the image recognition software Coreldraw, and obtain the coordinates of each stope fissure after vector processing;

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

[0011] Step 6: Import the obtained permeability into the finite element software COMSOL in the form of interpolation method, make a comprehensive judgment on the gas outburst height through simulation, and finally obtain the predicted result of the abandoned mine gas outburst height.

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

[0013] As a preference, in step 2, the similarity criteria include geometric similarity, density similarity, area similarity, and time similarity.

[0014] As a preferred embodiment, in step three, the recovery ratio of excavation is controlled according to the coal production in the mining area, and the mining time and balance time are determined according to the production abandonment years information.

[0015] Furthermore, in order to accurately determine the closed-well balance simulation time to obtain a more realistic simulation effect, in step 3, the closed-well 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 are the actual formation length and height respectively; l m 、h m is the length and height of the model stratum; v p ,t p is the speed and time of actual stope excavation; v m ,t m is the excavation speed and time of similar models; Kt is the temporal similarity ratio of the model; K l is the geometric similarity ratio of the model.

[0019] Furthermore, in order to ensure the recognition accuracy, in step 4, before importing the stope fissure image into the image recognition software Coreldraw, the stope fissure image is first binarized.

[0020] Furthermore, in order to accurately and efficiently distribute the permeability of the stope fractures, in step 5, the process of establishing a spatial grid module and assigning permeability is as follows:

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

[0022]

[0023] Where i is the crack number obtained; x mi1 、x mi2 is the x coordinate of the two ends of the crack; y mi1 ,y mi2 are the y coordinates of the two ends of the crack;

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

[0025]

[0026] Where j is the obtained grid number; x i1 、x i2 、x i3 、x i4 are the x coordinates of the four endpoints of the grid; y i1 ,y i2 ,y i3 ,y i4 are the y coordinates of the four endpoints of the grid respectively; the first column in the matrix is ​​the permeability of the grid, and the initial permeability of the grid is uniformly set to 0;

[0027] S53: Using MATLAB, determine the grid interval where each crack is located, and perform cyclic determination on the inclination angle of the crack. The specific process is as follows:

[0028] A1: If the x coordinates x at both ends of the current crack i i1 、x i2 The minimum value of is less than the x coordinates x of the four endpoints of the jth network j1 、x j2 、xj3 、x j4 The maximum value of the current crack i, and the x coordinates x at both ends of the crack i i1 、x i2 The maximum value of is greater than the x coordinates x of the four endpoints of the jth network j1 、x j2 、x j3 、x j4 If the minimum value of is reached, the judgment condition is met and A2 is executed. Otherwise, the judgment condition is not met, so let j=j+1 and re-execute A1 until the judgment condition is met.

[0029] A2: If the y coordinates y at both ends of the current crack i i1 ,y i2 The minimum value of is less than the y coordinates y of the four endpoints of the jth network j1 ,y j2 ,y j3 ,y j4 The maximum value of the current crack i, and the y coordinates y at both ends of the crack i i1 ,y i2 The maximum value of is greater than the y coordinates y of the four endpoints of the jth network j1 ,y j2 ,y j3 ,y j4 If the minimum value is reached, the judgment condition is met and A3 is executed. Otherwise, the judgment condition is not met, so let j=j+1 and re-execute A2 until the judgment condition is met.

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

[0031] The grids with fracture dip angles greater than 45° are assigned permeability k1, the grids with fracture dip angles less than or equal to 45° are assigned permeability k2, and the items in the matrix where G(j,1) is still 0 are assigned permeability k3, 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 is the maximum value of the fracture number, completing the allocation of all fracture permeabilities and finally obtaining the permeability within the spatial grid.

[0035] In the present invention, a sampling drill is used to drill core samples in the mining area, and then the core samples are placed in the laboratory for testing. The rock stratum mechanical parameters and gas storage parameters can be accurately obtained by experiment. In this way, by combining the rock stratum mechanical parameters, gas storage parameters, rock stratum geological data collected in the early stage and similarity criteria, a rock stratum excavation similarity model that is highly consistent with the actual environment can be conveniently established using modeling software, providing a reliable technical guarantee for obtaining accurate analysis results in the future. By performing excavation and balance simulation of the mining section on the rock stratum excavation similarity model, it is possible to efficiently and accurately simulate working conditions that are consistent with the actual environment while effectively reducing the material and human resource cost investment. First, the image of the cracks in the mining area after excavation is obtained, and then the coordinates of each crack are obtained after vector processing using the image recognition software Coreldraw. Then, a spatial grid model is established using MATLAB, and the permeability is assigned based on the correlation between the coordinates of the cracks in the mining area and the spatial grid. This can efficiently and accurately assign permeabilities that are consistent with the actual environment to the cracks in different parts of the constructed rock excavation similar model, which can help to intuitively and accurately determine the effective gas migration channel. At the same time, it can also facilitate the determination of the potential gas migration path through analysis. In this way, the gas emission height can be simulated through the finite element software COMSOL, and the prediction results of the gas emission height in abandoned mines can be obtained efficiently and accurately, which can provide reliable technical support for the subsequent safe and efficient gas extraction.

[0036] This method has a simple operation process and low implementation cost. It effectively combines the advantages of similar models and finite element simulation, and can greatly reduce the cost and risk of experiments and tests through simulation. It can accurately determine the change of gas outburst height over time in abandoned mining areas, and can provide scientific guidance for the arrangement of gas extraction drilling holes. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a flow chart of the present invention;

[0038] Figure 2 is a flow chart of the process of allocating the permeability of the stope fractures in the present invention;

[0039] Figure 3 It is a comparative schematic diagram of stope fracture extraction and spatial gridding in the present invention;

[0040] Figure 4 Schematic diagram of the simulation result of the gas emission height in the stope of the present invention, taking y=60 as an example;

[0041] Figure 5 It is a schematic diagram of the simulation results of the gas emission height in the mining area of ​​the present invention, taking y=80 as an example. DETAILED DESCRIPTION

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

[0043] like Figure 1 As shown, the present invention provides a method for predicting the gas emission height of abandoned mines by coupling similarity model and finite element simulation, comprising the following steps:

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

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

[0046] Step 3: Based on the collected mine production data, the excavation and closing balance simulation of the mining section is carried out on the rock formation excavation similar model. At the same time, the image of the similar model after excavation is collected, and the crack image of the mining field is identified by using image processing software;

[0047] Step 4: Import the obtained stope fissure image into the image recognition software Coreldraw, and obtain the coordinates of each stope fissure after vector processing;

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

[0049] Step 6: Import the obtained permeability into the finite element software COMSOL in the form of interpolation method, make a comprehensive judgment on the gas outburst height through simulation, and finally obtain the predicted result of the abandoned mine gas outburst height.

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

[0051] like Figure 4 As shown, Figure 4 The schematic diagram of the simulation results of the gas emission height in the stope is shown, taking y=60 as an example;

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

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

[0054] As a preference, in step 2, the similarity criteria include geometric similarity, density similarity, area similarity, and time similarity.

[0055] As a preferred embodiment, in step three, the recovery ratio of excavation is controlled according to the coal production in the mining area, and the mining time and balance time are determined according to the production abandonment years information.

[0056] In order to accurately determine the closed-well balance simulation time and obtain a more realistic simulation effect, in step 3, the closed-well 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 are the actual formation length and height respectively; l m 、h m is the length and height of the model stratum; v p ,t p is the speed and time of actual stope excavation; v m ,t m is the excavation speed and time of similar models; K t is the temporal similarity ratio of the model; K l is the geometric similarity ratio of the model.

[0059] In order to ensure the recognition accuracy, in step 4, before importing the stope fissure image into the image recognition software Coreldraw, the stope fissure image is first binarized.

[0060] like Figure 2 As shown in the figure, in order to accurately and efficiently distribute the permeability of the stope fractures, in step 5, the process of establishing the spatial grid module and assigning the permeability is as follows:

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

[0062]

[0063] Where i is the crack number obtained; x mi1 、x mi2 is the x coordinate of the two ends of the crack; y mi1 ,ymi2 are the y coordinates of the two ends of the crack;

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

[0065]

[0066] Where j is the obtained grid number; x i1 、x i2 、x i3 、x i4 are the x coordinates of the four endpoints of the grid; y i1 ,y i2 ,y i3 ,y i4 are the y coordinates of the four endpoints of the grid respectively; the first column in the matrix is ​​the permeability of the grid, and the initial permeability of the grid is uniformly set to 0;

[0067] S53: Using MATLAB, determine the grid interval where each crack is located, and perform cyclic determination on the inclination angle of the crack. The specific process is as follows:

[0068] A1: If the x coordinates x at both ends of the current crack i i1 、x i2 The minimum value of is less than the x coordinates x of the four endpoints of the jth network j1 、x j2 、x j3 、x j4 The maximum value of the current crack i, and the x coordinates x at both ends of the crack i i1 、x i2 The maximum value of is greater than the x coordinates x of the four endpoints of the jth network j1 、x j2 、x j3 、x j4 If the minimum value of is reached, the judgment condition is met and A2 is executed. Otherwise, the judgment condition is not met, so let j=j+1 and re-execute A1 until the judgment condition is met.

[0069] A2: If the y coordinates y at both ends of the current crack i i1 ,y i2 The minimum value of is less than the y coordinates y of the four endpoints of the jth network j1 ,y j2 ,y j3 ,y j4 The maximum value of the current crack i, and the y coordinates y at both ends of the crack i i1 ,y i2 The maximum value of is greater than the y coordinates y of the four endpoints of the jth networkj1 ,y j2 ,y j3 ,y j4 If the minimum value is reached, the judgment condition is met and A3 is executed. Otherwise, the judgment condition is not met, so let j=j+1 and re-execute A2 until the judgment condition is met.

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

[0071] The grids with fracture dip angles greater than 45° are assigned permeability k1, the grids with fracture dip angles less than or equal to 45° are assigned permeability k2, and the items in the matrix where G(j,1) is still 0 are assigned permeability k3, 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 is the maximum value of the fracture number, completing the allocation of all fracture permeabilities and finally obtaining the permeability within the spatial grid.

[0075] In the present invention, a sampling drill is used to drill core samples in the mining area, and then the core samples are placed in the laboratory for testing. The rock stratum mechanical parameters and gas storage parameters can be accurately obtained by experiment. In this way, by combining the rock stratum mechanical parameters, gas storage parameters, rock stratum geological data collected in the early stage and similarity criteria, a rock stratum excavation similarity model that is highly consistent with the actual environment can be conveniently established using modeling software, providing a reliable technical guarantee for obtaining accurate analysis results in the future. By performing excavation and balance simulation of the mining section on the rock stratum excavation similarity model, it is possible to efficiently and accurately simulate working conditions that are consistent with the actual environment while effectively reducing the material and human resource cost investment. First, the image of the cracks in the mining area after excavation is obtained, and then the coordinates of each crack are obtained after vector processing using the image recognition software Coreldraw. Then, a spatial grid model is established using MATLAB, and the permeability is assigned based on the correlation between the coordinates of the cracks in the mining area and the spatial grid. This can efficiently and accurately assign permeabilities that are consistent with the actual environment to the cracks in different parts of the constructed rock excavation similar model, which can help to intuitively and accurately determine the effective gas migration channel. At the same time, it can also facilitate the determination of the potential gas migration path through analysis. In this way, the gas emission height can be simulated through the finite element software COMSOL, and the prediction results of the gas emission height in abandoned mines can be obtained efficiently and accurately, which can provide reliable technical support for the subsequent safe and efficient gas extraction.

[0076] This method has a simple operation process and low implementation cost. It effectively combines the advantages of similar models and finite element simulation, and can greatly reduce the cost and risk of experiments and tests through simulation. It can accurately determine the change of gas outburst height over time in abandoned mining areas, and can provide scientific guidance for the arrangement of gas extraction drilling holes.

Claims

1. A method for predicting the gas emission height of abandoned mines by coupling similarity model and finite element simulation, characterized in that: The steps include: Step 1: Collect rock stratum geological data and mine production data from abandoned mining areas; at the same time, use sampling drills to perform in-situ coring operations on the surface of the mining area to obtain core samples of each coal stratum, and then obtain the rock stratum mechanical parameters and gas occurrence parameters of the core samples of each coal stratum through laboratory testing; Step 2: Establish a rock excavation similarity model based on rock geological data, rock mechanical parameters, gas storage parameters and similarity criteria; Step 3: Based on the collected mine production data, the excavation and closing balance simulation of the mining section is carried out on the rock formation excavation similar model. At the same time, the image of the similar model after excavation is collected, and the crack image of the mining field is identified by using image processing software; Step 4: Import the obtained stope fissure image into the image recognition software Coreldraw, and obtain the coordinates of each stope fissure after vector processing; Step 5: Establish a spatial grid model in MATLAB and assign permeability through the relationship between the fracture coordinates and the spatial grid; Step 6: Import the obtained permeability into the finite element software COMSOL in the form of interpolation method, make a comprehensive judgment on the gas outburst height through simulation, and finally obtain the predicted result of the abandoned mine gas outburst height.

2. The method for predicting the gas emission height of abandoned mines by coupling similarity model and finite element simulation according to claim 1 is characterized in that: In step one, the rock geological data include coal rock layer distribution, coal seam inclination, coal seam direction, the mine production data include mining area coal production, production and abandonment years information, the gas storage parameters include permeability, gas content, gas pressure.

3. The method for predicting the gas emission height of abandoned mines by coupling similarity model and finite element simulation according to claim 1 or 2, characterized in that: In step 2, the similarity criteria include geometric similarity, density similarity, area similarity, and time similarity.

4. The method for predicting the gas emission height of abandoned mines by coupling similarity model and finite element simulation according to claim 2 is characterized in that: In step three, the recovery ratio of excavation is controlled according to the coal mining volume in the mining area, and the mining time and balance time are determined according to the production abandonment years information.

5. The method for predicting the gas emission height of abandoned mines by coupling similarity model and finite element simulation according to claim 3 is characterized in that: In step 3, the time of the closed-well balance simulation is determined by formula (2) based on the area similarity relationship in formula (1); In the formula, l p 、h p are the actual formation length and height respectively; l m 、h m is the length and height of the model stratum; v p ,t p is the speed and time of actual stope excavation; v m ,t m is the excavation speed and time of similar models; K t is the temporal similarity ratio of the model; K l is the geometric similarity ratio of the model.

6. The method for predicting the gas emission height of abandoned mines by coupling similarity model and finite element simulation according to claim 5 is characterized in that: In step 4, before importing the stope fissure image into the image recognition software Coreldraw, the stope fissure image is firstly binarized.

7. The method for predicting the gas emission height of abandoned mines by coupling similarity model and finite element simulation according to claim 6 is characterized in that: In step 5, the process of establishing a spatial grid module and assigning permeability is as follows: S51: Extract the spatial coordinates of the cracks and establish an i*4 crack coordinate matrix F in MATLAB, as shown in formula (3); Where i is the crack number obtained; x mi1 、x mi2 is the x-coordinate of the two ends of the crack; y mi1 ,y mi2 are the y coordinates of the two ends of the crack; S52: In MATLAB, a space of the same size as the rock formation excavation model is established, and the space is gridded and divided into 1j 20*20 cm grids; the coordinates of the four endpoints of each grid are obtained and a j*9 matrix G is established, as shown in formula (4); Where j is the obtained grid number; x i1 、x i2 、x i3 、x i4 are the x coordinates of the four endpoints of the grid; y i1 ,y i2 ,y i3 ,y i4 are the y coordinates of the four endpoints of the grid respectively; the first column in the matrix is ​​the permeability of the grid, and the initial permeability of the grid is uniformly set to 0; S53: Using MATLAB, determine the grid interval where each crack is located, and perform cyclic determination on the inclination angle of the crack. The specific process is as follows: A1: If the x coordinates x at both ends of the current crack i i1 、x i2 The minimum value of is less than the x coordinates x of the four endpoints of the jth network j1 、x j2 、x j3 、x j4 The maximum value of the current crack i, and the x coordinates x at both ends of the crack i i1 、x i2 The maximum value is greater than the x coordinates x of the four endpoints of the jth network j1 、x j2 、x j3 、x j4 If the minimum value of is reached, the judgment condition is met and A2 is executed. Otherwise, the judgment condition is not met, so let j=j+1 and re-execute A1 until the judgment condition is met. A2: If the y coordinates y at both ends of the current crack i i1 ,y i2 The minimum value of is less than the y coordinates y of the four endpoints of the jth network j1 ,y j2 ,y j3 ,y j4 The maximum value of the current crack i, and the y coordinates y at both ends of the crack i i1 ,y i2 The maximum value of is greater than the y coordinates y of the four endpoints of the jth network j1 ,y j2 ,y j3 ,y j4 If the minimum value is reached, the judgment condition is met and A3 is executed. Otherwise, the judgment condition is not met, so let j=j+1 and re-execute A2 until the judgment condition is met. A3: Based on the obvious difference in permeability of fractures with different inclination angles, the inclination angle of the fracture is determined as follows; The grids with fracture dip angles greater than 45° are assigned permeability k1, the grids with fracture dip angles less than or equal to 45° are assigned permeability k2, and the items in the matrix where G(j,1) is still 0 are assigned permeability k3, as shown in formula (5); A4: Let i=i+1, and repeat A1 to A3; A5: Repeat A4 multiple times until i≥i max , where i max is the maximum value of the fracture number, completing the allocation of all fracture permeabilities and finally obtaining the permeability within the spatial grid.

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