Intelligent identification method for gas enrichment zone based on discrete element method and finite element method combined modeling

Abstract

A kind of block discrete element-finite element combined modeling gas enrichment zone intelligent identification method, collects the stratum geological data and mine production data of abandoned mining area;Obtain stratum mechanical parameters and gas occurrence parameters;Establish a three-dimensional mine geological model in block discrete element UDEC;Carry out excavation, balance simulation of stoping section, and extract the stope fracture image after excavation;The stope fracture image is imported into image recognition software Coreldraw, and the coordinates of each stope fracture are obtained;A space grid model is established in MATLAB, and the permeability is given by using the relationship between the coordinates of the stope fracture and the space grid;The obtained permeability is imported into finite element software COMSOL in the form of interpolation method for gas flow simulation, and the gas emission and enrichment area are comprehensively determined. This method can accurately determine the enrichment area of underground gas in abandoned stope, and can provide scientific guidance for the layout of ground gas extraction well.

Description

Technical Field

[0001] This invention belongs to the field of intelligent recognition technology, specifically relating to an intelligent recognition method for gas-rich areas based on block discrete element-finite element joint modeling. Background Technology

[0002] With the adjustment of China's energy structure, coal mining has shifted from decentralized to refined, centralized, and precise operations. Currently, the number of mines has decreased significantly, with many resource-depleted and outdated mines facing closure or abandonment. It is estimated that the number of abandoned mines will reach approximately 15,000 by 2030. Based on extensive exploration and research, preliminary estimates suggest that nearly 500 billion cubic meters of unconventional natural gas still exist in closed / abandoned mines. 3 Methane gas is a clean and efficient energy source, widely used in heating, cooking, and power generation. The heat generated by methane combustion can be converted into electricity, providing convenience for people's lives and work. However, methane is also a highly dangerous gas, capable of causing explosions and air pollution. Without systematic and standardized extraction and remediation, it will have a significant impact on the environment and pose substantial safety risks. In 2019, methane emissions from abandoned mines in my country accounted for 15% of total emissions, and this proportion is expected to continue to increase with production development and rising living demands. The large accumulation of methane gas in goaf areas greatly increases the risk of methane explosions, posing a serious threat to methane extraction and the scientific management of abandoned mines. Therefore, conducting methane extraction and remediation operations in abandoned mines has significant economic, environmental, and safety benefits.

[0003] Currently, in order to ensure the safe and efficient extraction of gas, it is essential to conduct research on gas extraction in abandoned mines. Through preliminary analysis and research, the gas-rich areas can be identified, which is conducive to the scientific and rational guidance of the subsequent layout of gas extraction wells. At the same time, it can provide reliable technical support for the safe extraction of gas. Therefore, there is an urgent need to provide a new intelligent identification method for gas-rich areas. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides an intelligent identification method for gas-rich areas based on block discrete element-finite element joint modeling. This method is simple to operate and has low implementation costs. It can accurately determine the gas-rich areas underground in abandoned mining sites and provide scientific guidance for the layout of surface gas extraction wells.

[0005] To achieve the above objectives, the present invention provides an intelligent identification method for gas-rich areas based on block discrete element-finite element joint modeling, comprising the following steps:

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

[0007] Step 2: Based on the geological data of the rock strata, the mechanical parameters of the rock strata, and the gas occurrence parameters, establish a full-scale three-dimensional mine geological model in the block discrete element UDEC. At the same time, set the parameters of the full-scale three-dimensional mine geological model and calculate it to the stress equilibrium state.

[0008] Step 3: Based on the collected mine production data, use a scaled 3D mine geological model to simulate the excavation and balancing of the mining section; use the software's built-in joined-open function to extract images of the mining area fractures after excavation.

[0009] Step 4: Import the obtained stope fracture image into the image recognition software CorelDRAW, and use CorelDRAW to perform vectorization processing to obtain the coordinates of each stope fracture;

[0010] Step 5: Establish a spatial grid model in MATLAB, and assign permeability using the relationship between the coordinates of the mining area fractures and the spatial grid;

[0011] Step 6: Import the obtained permeability into the finite element software COMSOL in the form of interpolation to simulate gas flow, and make a comprehensive judgment on gas outburst and enrichment areas to finally obtain the gas enrichment area of ​​the abandoned mine.

[0012] As a preferred option, in step two, the parameters of the scaled three-dimensional mine geological model include its own weight and boundary conditions.

[0013] 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.

[0014] As a preferred option, in step four, the stope fracture image is binarized before being imported into the image recognition software CorelDRAW.

[0015] Furthermore, in order to accurately and efficiently allocate the permeability of the mining area fractures, the process of establishing a spatial grid model and assigning permeability in step five is as follows:

[0016] S51: Extract the spatial coordinates of the cracks and establish an i*4 crack coordinate matrix F in MATLAB, as shown in formula (1);

[0017] (1);

[0018] In the formula, The obtained crack number; x i1 , These are the x-coordinates of the two ends of the crack, respectively; , These are the y-coordinates of the two ends of the crack, respectively.

[0019] S52: In MATLAB, establish a space of the same size as the scale of the three-dimensional mine geological model, and grid the space to divide it into j 20*20 cm grids; obtain the coordinates of the four endpoints of each grid and establish a j*9 matrix G, as shown in formula (2);

[0020] (2);

[0021] In the formula, j is the obtained grid number; , , , These are the x-coordinates of the four endpoints of the grid; , , , 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;

[0022] 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:

[0023] 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, so j = j + 1 is set, and A1 is executed again until the condition is met.

[0024] A2: If the y-coordinates of the two ends of the current crack i are y i1 y i2The 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, so j = j + 1 is set, and A2 is executed again until the condition is met.

[0025] A3: Based on the significant difference in permeability of fractures with different dip angles, the dip angle of the fractures is determined as follows;

[0026] 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 (3).

[0027] (3);

[0028] A4: Order Repeat steps A1 through A3;

[0029] A5: Repeat A4 multiple times until all fracture permeability allocation is completed, and finally the permeability within the spatial grid is obtained.

[0030] In this invention, core samples are drilled in the mining area using a sampling drill, and then tested in a laboratory to obtain accurate rock strata mechanical parameters and gas occurrence parameters. By combining these parameters with previously collected geological data, a scaled-down three-dimensional mine geological model highly consistent with the real-world environment can be easily established using the Block Discrete Element Method (UDEC), providing a reliable technical guarantee for obtaining accurate analysis results. By simulating the excavation and balancing of the mining section using this scaled-down three-dimensional mine geological model, working conditions consistent with the real-world environment can be simulated efficiently and accurately while effectively reducing material and human resource costs. First, the software's built-in jointed-open function is used to extract images of fractures in the excavated stope. Then, the image recognition software CorelDRAW is used to obtain the coordinates of each fracture. Next, a spatial mesh model is built using MATLAB. The permeability is then assigned based on the correlation between the coordinates of the stope fractures and the spatial mesh. This allows for the efficient and accurate assignment of permeability to fractures in different parts of the constructed scaled-down 3D mine geological model, consistent with the real environment. This helps to intuitively and accurately determine effective gas migration channels. At the same time, it also facilitates the determination of potential gas migration paths through analysis. Thus, by using the gas flow simulation method of the finite element software COMSOL, the migration channels and potential migration paths can be effectively combined, thereby accurately determining the gas enrichment areas. This can then rationally guide the layout of surface gas extraction wells and provide reliable technical support for the safe and efficient extraction of gas in the future.

[0031] This method is simple to operate and has low implementation costs. It effectively combines the advantages of block discrete element and finite element simulations, and can accurately determine the gas-rich areas underground in abandoned mines, providing scientific guidance for the layout of surface gas extraction wells. Furthermore, it can be easily visualized using an app developer with COMSOL software, facilitating real-time guidance for the precise extraction of gas from abandoned mines. Attached Figure Description

[0032] Figure 1 This is a flowchart of the present invention;

[0033] Figure 2 This is a flowchart of the permeability distribution process in the mining area fractures in this invention;

[0034] Figure 3 This is a schematic diagram of the process of vectorization and spatial meshing of mining fractures in this invention;

[0035] Figure 4 This is a distribution characteristic map of the gas-rich area in the mining area in this invention;

[0036] Figure 5 This is a diagram illustrating the pattern of gas outbursts in the mining area in this invention. Detailed Implementation

[0037] The present invention will be further described below with reference to the embodiments.

[0038] like Figure 1 As shown, this invention provides an intelligent identification method for gas-rich areas based on block discrete element-finite element joint modeling, comprising the following steps:

[0039] Step 1: Collect geological data of rock strata and mine production data of abandoned mining areas; construct sampling drills on the surface of the mining area to perform in-situ core sampling of each coal and rock strata to obtain core samples of each coal and rock, and then obtain the rock strata mechanical parameters and gas occurrence parameters of each coal and rock core sample through laboratory testing.

[0040] Step 2: Based on the geological data of the rock strata, the mechanical parameters of the rock strata, and the gas occurrence parameters, establish a full-scale three-dimensional mine geological model in the block discrete element UDEC. At the same time, set the parameters of the full-scale three-dimensional mine geological model and calculate it to the stress equilibrium state.

[0041] Step 3: Based on the collected mine production data, use a scaled 3D mine geological model to simulate the excavation and balancing of the mining section; use the software's built-in joined-open function to extract images of the mining area fractures after excavation.

[0042] Step 4: Import the obtained stope fracture image into the image recognition software CorelDRAW, and use CorelDRAW to perform vectorization processing to obtain the coordinates of each stope fracture;

[0043] Step 5: Establish a spatial grid model in MATLAB, and assign permeability using the relationship between the coordinates of the mining area fractures and the spatial grid;

[0044] like Figure 3 As shown, it illustrates the process of vectorization and spatial meshing of mining-induced fractures;

[0045] Step 6: Import the obtained permeability into the finite element software COMSOL in the form of interpolation to simulate gas flow, and make a comprehensive judgment on gas outburst and enrichment areas to finally obtain the gas enrichment area of ​​the abandoned mine.

[0046] like Figure 4 As shown, it displays the distribution characteristics of the gas-rich area in the mining area; as Figure 5 As shown, it displays a diagram illustrating the pattern of gas outbursts in the mining area;

[0047] As a preferred option, in step two, the parameters of the scaled three-dimensional mine geological model include its own weight and boundary conditions.

[0048] 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.

[0049] As a preferred option, in step four, the stope fracture image is binarized before being imported into the image recognition software CorelDRAW.

[0050] 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 model and assigning permeability in step five is as follows:

[0051] S51: Extract the spatial coordinates of the cracks and establish an i*4 crack coordinate matrix F in MATLAB, as shown in formula (1);

[0052] (1);

[0053] In the formula, The obtained crack number; x i1 , These are the x-coordinates of the two ends of the crack, respectively; , These are the y-coordinates of the two ends of the crack, respectively.

[0054] S52: In MATLAB, establish a space of the same size as the scale of the three-dimensional mine geological model, and grid the space to divide it into j 20*20 cm grids; obtain the coordinates of the four endpoints of each grid and establish a j*9 matrix G, as shown in formula (2);

[0055] (2);

[0056] In the formula, j is the obtained grid number; , , , These are the x-coordinates of the four endpoints of the grid; , , , 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;

[0057] 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:

[0058] A1: If the x-coordinates of the two ends of the current crack i are x i1x 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, so j = j + 1 is set, and A1 is executed again until the condition is met.

[0059] 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, so j = j + 1 is set, and A2 is executed again until the condition is met.

[0060] A3: Based on the significant difference in permeability of fractures with different dip angles, the dip angle of the fractures is determined as follows;

[0061] 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 (3).

[0062] (3);

[0063] A4: Order Repeat steps A1 through A3;

[0064] A5: Repeat A4 multiple times until all fracture permeability allocation is completed, and finally the permeability within the spatial grid is obtained.

[0065] In this invention, core samples are drilled in the mining area using a sampling drill, and then tested in a laboratory to obtain accurate rock strata mechanical parameters and gas occurrence parameters. By combining these parameters with previously collected geological data, a scaled-down three-dimensional mine geological model highly consistent with the real-world environment can be easily established using the Block Discrete Element Method (UDEC), providing a reliable technical guarantee for obtaining accurate analysis results. By simulating the excavation and balancing of the mining section using this scaled-down three-dimensional mine geological model, working conditions consistent with the real-world environment can be simulated efficiently and accurately while effectively reducing material and human resource costs. First, the software's built-in jointed-open function is used to extract images of fractures in the excavated stope. Then, the image recognition software CorelDRAW is used to obtain the coordinates of each fracture. Next, a spatial mesh model is built using MATLAB. The permeability is then assigned based on the correlation between the coordinates of the stope fractures and the spatial mesh. This allows for the efficient and accurate assignment of permeability to fractures in different parts of the constructed scaled-down 3D mine geological model, consistent with the real environment. This helps to intuitively and accurately determine effective gas migration channels. At the same time, it also facilitates the determination of potential gas migration paths through analysis. Thus, by using the gas flow simulation method of the finite element software COMSOL, the migration channels and potential migration paths can be effectively combined, thereby accurately determining the gas enrichment areas. This can then rationally guide the layout of surface gas extraction wells and provide reliable technical support for the safe and efficient extraction of gas in the future.

[0066] This method is simple to operate and has low implementation costs. It effectively combines the advantages of block discrete element and finite element simulations, and can accurately determine the gas-rich areas underground in abandoned mines, providing scientific guidance for the layout of surface gas extraction wells. Furthermore, it can be easily visualized using an app developer with COMSOL software, facilitating real-time guidance for the precise extraction of gas from abandoned mines.

Claims

1. A method for intelligent identification of gas-rich zones by block discrete element-finite element combined modeling, characterized in that, The method comprises the following steps: Step one: collecting the stratum geological data and mine production data of the abandoned mine area; drilling a sampling hole on the surface of the mine area to obtain in-situ core samples of each coal rock stratum, and then obtaining the stratum mechanical parameters and gas occurrence parameters of the core samples of each coal rock stratum through laboratory testing; Step two: establishing a proportional three-dimensional mine geological model in the block discrete element UDEC according to the stratum geological data, stratum mechanical parameters and gas occurrence parameters, setting parameters of the proportional three-dimensional mine geological model, and operating to a stress balance state; Step three: excavating and balancing the mining section by using the proportional three-dimensional mine geological model according to the collected mine production data; and extracting a stope fracture image after excavation by using a jointed-open function built in the software; Step four: importing the obtained stope fracture image into an image recognition software Coreldraw, and obtaining the coordinates of each stope fracture after vectorization processing by using the image recognition software Coreldraw; Step five: establishing a space grid model in MATLAB, and assigning a permeability by using the relationship between the coordinates of the stope fracture and the space grid; The process of establishing the space grid model and assigning the permeability is as follows: S51: Extract the spatial coordinates of the fissure, and build the The fissure coordinate matrix F is shown in equation (1). （1）； wherein is the number of fractures obtained; x i1 , are the x-coordinates of the two ends of the fracture, respectively; , are the y-coordinates of the two ends of the fracture, respectively; S52: Establish a space with the same size as the equal-proportion three-dimensional mine geological model in MATLAB, and grid the space to divide out 20*20 cm grids; Get the coordinates of the four endpoints of each grid and establish a matrix G, as shown in formula (2); G = [x1, x2, x3, x4; y1, y2, y3, y4] (2) （2）； In the formula, j is the grid number obtained; 、 、 、 are respectively the x coordinates of four end points of the grid; 、 、 、 are respectively the y coordinates of four end points of the grid; the first column in 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 where each fracture is located by using MATLAB, and cyclically determining the dip angle of the fracture, and the specific process is as follows: A1: If the current crack x-coordinate x i1 , of the fourth endpoint of the first network is less than the maximum value of the x-coordinate x , , , , of the fourth endpoint of the second network, and the x-coordinate x x-coordinate x i1 , of the fourth endpoint of the third network is greater than the minimum value of the x-coordinate x , , , , of the fourth endpoint of the fourth network, the determination condition is satisfied, and A2 is executed, otherwise the determination condition is not satisfied, let , and re-execute A1 until the determination condition is satisfied; A2: If the current crack y coordinates of both ends , The minimum value is less than the first The y-coordinates of the four endpoints of the network , , , The maximum value, and the current crack y coordinates of both ends , The maximum value is greater than the first The y-coordinates of the four endpoints of the network , , , If the minimum value is found, the condition is met, and A3 is executed; otherwise, the condition is not met, and A3 is executed. Then re-execute A2 until the judgment condition is met; A3: the permeability of different dip angle fractures is obviously different, and the dip angle of the fracture is determined as follows: Permeability is assigned to the grid for fracture dip greater than 45° Permeability is assigned to the grid for fracture dip less than or equal to 45° Permeability is assigned to the grid for matrix G (j,1) still being zero As shown in equation (3); （3）； A4: Let A1 to A3 are repeatedly executed; A5: repeatedly executing A4 for multiple times until the distribution of the permeability of all fractures is completed, and finally obtaining the permeability in the space grid; Step six: importing the obtained permeability into a finite element software COMSOL in the form of an interpolation method to simulate gas flow, comprehensively determining the gas emission and enrichment area, and finally obtaining the gas enrichment area of the abandoned mine.

2. The method according to claim 1, wherein, In step two, the parameters of the proportional three-dimensional mine geological model include self-weight and boundary conditions.

3. The intelligent identification method of gas-rich zones by block discrete element-finite element combined modeling according to claim 1 or 2, characterized in that, In step one, the stratum geological data includes coal rock stratum distribution, coal seam dip angle and coal seam strike, the mine production data includes mining amount of the mining area, production and abandonment period information, and the gas occurrence parameters include permeability, gas content and gas pressure.

4. The intelligent identification method of gas-rich zones by block discrete element-finite element combined modeling according to claim 3, characterized in that, In step four, the stope fracture image is subjected to binary processing before being imported into the image recognition software Coreldraw.

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