WO2020006818A1

WO2020006818A1 - Method for area-based coal rock water injection seepage-damage-stress coupling value simulation

Info

Publication number: WO2020006818A1
Application number: PCT/CN2018/100462
Authority: WO
Inventors: 周刚; 尹文婧; 张文政; 魏星; 张国宝
Original assignee: 山东科技大学
Priority date: 2018-07-02
Filing date: 2018-08-14
Publication date: 2020-01-09
Also published as: CN109063257B; RU2743121C1; CN109063257A

Abstract

Disclosed is a method for area-based coal rock water injection seepage-damage-stress coupling value simulation, comprising: establishing a coal seam model according to a geological survey result; performing area division and respectively simulating coal rock water injection seepage of a non-mining induced disturbance area and a mining induced disturbance area; in the non-mining induced disturbance area, performing programming to compare tension-shear torque values of meshes to determine whether deformation or even fracture occurs to coal rock under the action of water pressure stress; simultaneously simulating a coal fracture process using a meshfree method and simulating a seepage process using a boundary element method, wherein the advantages of the two simulation methods are combined on a micro scale; and in the mining induced disturbance area, respectively performing simulation using two mathematic models, i.e., the N-S equation and the Darcy's law, to accurately simulate coal damage and a water transfer law during an area-based coal rock water injection process. The method provides a solid data basis for coal seam water injection, greatly reduces the possibility that coal is crushed into dust particles, decreases the production amount of coal dust, and ensures the security of coal seam mining.

Description

Numerical simulation method for seepage-damage-stress coupling of water injection in coal and rock mass

Technical field

The present invention relates to the field of mine rock mechanics, and in particular, to a numerical simulation method for coupling water seepage-damage-stress coupling of coal rock masses containing geological structures.

Background technique

Coal seam water injection is the process of injecting pressurized water and aqueous solution into the coal body through drilling. The wetting effect of water makes the coal body plastic and the brittleness weakens. When the coal body is exposed to external forces, many brittle fractures become plastic deformation, which greatly reduces it. The possibility that the coal body is broken into dust particles is reduced, and the amount of coal dust generated is reduced. The whole process involves many disciplines such as computational fluid mechanics, fracture rock mechanics and fluid-structure coupling. The process of numerical simulation is more complicated.

At present, most of the numerical simulation studies on coal seam water injection are carried out from a macro perspective. The simulation of the seepage velocity field and seepage pressure field at the macro level is used to study the water transport law in the coal body. However, as a typical porous media material, the essence of coal body wetting is that water enters many fine pores in the coal body, and the simulation of macroscopic angle cannot reproduce this process for further research. In addition, most of the researches on water seepage in the prior art are based on separate analysis of finite element or discrete element, but it is difficult for finite element to achieve coal fracture, and discrete element cannot accurately describe the seepage process and moisture increment data.

Therefore, the existing technology needs to be further improved and developed.

Summary of the invention

In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide a numerical simulation method for seepage-damage-stress coupled numerical simulation of water injection in coal and rock masses containing geological structures, which can more accurately simulate coal body damage during the water injection process And water transport laws, providing data for coal seam water injection.

To solve the above technical problems, the solution of the present invention includes:

A coupled numerical simulation method for seepage-damage-stress coupling of water injection in coal and rock masses, comprising the following steps:

Step 1: Establish a coal and rock mass model including faults based on geological survey results;

Step 2: Scan the corresponding coal body in the coal rock body obtained from the geological survey, and combine the FDK 3D reconstruction algorithm to construct a 3D digital core model with real pore structure characteristics;

Step 3: In the boundary element environment, execute the "mining fissure" generation algorithm to determine whether it is a mining affected area, that is, determine whether the distance from the mining face is less than 80m. If it is a mining affected area, go to step 4; if it is not mining Move the affected area, go to step five;

Step 4. Determine whether the cross-sectional area of the watershed is greater than 30 μm ^2. If the cross-sectional area of the watershed is greater than 30 μm ² , perform NS calculation processing, store and output the result; if less than 30 μm ² , perform Darcy calculation processing, store and output the result;

Step 5. Determine whether the cross-sectional area of the watershed is greater than 30 μm ^2. If the cross-sectional area of the watershed is greater than 30 μm ² , go to step 6; if less than 30 μm ² , go to step 12;

Step 6. Based on the C # language, the programming generates initial stress concentration points based on burial depth, geological conditions, lithology of overlying strata, and coal seam inclination.

Step 7. Mesh the 3D digital core model processed in Step 6;

Step 8. Calculate the tensile and shearing moments of the coal body grid, compare the tensile and shearing moments of the grid with the tensile and shearing moments, and find the most vulnerable grid set; The grid of moments is marked as "Native Crack", and then step 9 is performed; if there is no grid with a tensile-shear moment greater than the tensile-shear moment, the calculation is terminated and step 11 is performed;

Step 9. Replace the material in the "primary fissure" grid with the gas in the coal seam;

Step 10. Determine whether the total area of the "primary fissures" after the processing in step 9 exceeds twice the fault area. If not, generate a new model after deleting the "primary fissure" grid, and return to repeat step 8. If it exceeds , The calculation is terminated and step 11 is executed;

Step 11: Construct a model of two types of coal seam fractures that ultimately include primary fractures in the geological structure and fractures generated during the calculation and re-mesh the mesh, derive the STL general geometry, perform N-S calculation processing, and store and output the results;

Step 12. In the boundary element environment, after coupling the custom equation to calculate the seepage field and stress parameters, go to Step 13.

Step 13. In the meshless simulation environment, determine whether there are points where the tensile-shear moment is greater than the relevant parameters of the coal and rock mass. If so, connect such points in turn, mark the closed area as "invalid coal and rock mass", and execute Step 14; if not, go to Step 15;

Step 14. Add the water inlet conditions to the marked "invalid coal and rock mass" boundary in step 13.

Step 15: Perform turbulence simulation separately, calculate the stress distribution, and store the simulation results of the node;

Step 16. Determine whether the fracture separation from the simulation result in step 15 reaches the surface of the coal body. If not, go to step 17; if it reaches the surface of the coal body, go to step 18.

Step 17. Check whether the accumulated storage time reaches the preset simulation time. If not, go back to Step 12. If the calculation time is reached, go to Step 18.

Step 18. Stop the calculation in the meshless simulation environment. After calculating turbulence and stress only in the boundary element environment, perform Darcy calculation processing, store and output the results;

Step 19: The output results of Step 4, Step 11 and Step 18 are integrated and output as an independent file to obtain a quantitative statistical result.

The numerical simulation method for the coupled seepage-damage-stress numerical simulation of coal-rock mass injection, wherein the N-S calculation processing includes:

Step A, N-S initialization;

Step B: Calculate water pressure and gas pressure;

Step C, determine whether the water pressure is greater than the gas pressure, and if it is greater, change the next grid material to water, and execute step D; if it is less, directly perform step D;

Step D: Determine whether the calculation time setting is reached. If the calculation time is not reached, return to step A. If the calculation time is reached, directly store and output the result.

The coupled numerical simulation method for seepage-damage-stress coupled injection of coal and rock mass, wherein the Darcy calculation process includes:

Step E, Darcy initialization;

Step F: Calculate water pressure and gas pressure;

Step J: Determine whether the water pressure is greater than the gas pressure, and if it is greater, change the next grid material to water, and perform step H; if it is less, directly perform step H;

Step H: Determine whether the calculation time setting is reached. If the calculation time is not reached, return to step E. If the calculation time is reached, directly store and output the result.

The numerical simulation method for coupled injection and seepage-damage-stress simulation of coal and rock masses, wherein the above-mentioned step 1 specifically further includes: reserve "fault start point" and "fault end point" in the process of establishing a coal rock mass model including fault "," Fault turning point "," Azimuth difference "," Drop "and" Dip angle "are provided for user input.

The method for numerically coupling seepage-damage-stress coupled numerical simulation of coal rock mass injection, wherein the above-mentioned step dimer further includes: using an image processing algorithm to perform a filtering operation on a three-dimensional digital core model, smoothing the model edges, and then implementing based on the threshold. Data segmentation was used to obtain the micropore structure of the coal body. The island pores with poor connectivity were eliminated, and the final numerical model of coal body pores in STL format was derived.

The numerical simulation method for coupled seepage-damage-stress numerical simulation of coal-rock mass injection, wherein the above-mentioned quantitative statistical results include simulation results of hydraulic pressure field, simulation results of gas pressure, simulation results of coal pressure, simulation results of water flow velocity, and simulation of gas flow velocity result.

The present invention provides a numerical simulation method for coupling water seepage-damage-stress coupled numerical simulation of coal rock masses containing geological structures, using two mathematical models of Navier-Stokes equation and Darcy's law, respectively, based on two methods: boundary element method and meshless method. Perform simulation; compared with finite element, the boundary element method has the advantages of fewer elements and simple data preparation. The boundary element method is used to simulate the seepage process, and the meshless method is used to simulate the coal body fracture process. The advantages of the simulation method can more accurately simulate the coal body damage and water movement during the regional injection of coal and rock masses, providing a solid data foundation for coal seam water injection, and greatly reducing the possibility of coal bodies being broken into dust particles. It reduces the amount of coal dust and ensures the safety of coal seam mining.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a numerical simulation method for seepage-damage-stress coupling of water injection in a coal rock mass according to the present invention;

2 is a schematic diagram of N-S calculation processing in the present invention;

3 is a schematic diagram of a Darcy calculation process in the present invention;

4 is a schematic diagram of removing island coal blocks in the present invention;

5 is a schematic view of a coal body model after removing islands in the present invention;

FIG. 6 is a simulation diagram of water pressure results in the present invention;

7 is a simulation diagram of gas pressure results of the present invention;

FIG. 8 is a simulation diagram of coal pressure results of the present invention; FIG.

FIG. 9 is a simulation diagram of the water flow velocity result of the present invention; FIG.

FIG. 10 is a simulation diagram of gas flow velocity results of the present invention.

detailed description

The present invention provides a numerical simulation method for coupling water seepage-damage-stress coupled numerical simulation of coal rock mass containing geological structures. In order to make the object, technical scheme and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

The invention provides a numerical simulation method for seepage-damage-stress coupling numerical simulation of water injection in coal and rock bodies, which includes the following steps:

Step 4. Determine whether the cross-sectional area of the watershed is greater than 30 μm ^2. If the cross-sectional area of the watershed is greater than 30 μm ² , as shown in FIG. 2, perform NS calculation processing, store and output the result; if less than 30 μm ² , as shown in FIG. 3 , Then perform Darcy calculation processing, store and output the results;

Step 7. Mesh the 3D digital core model processed in Step 6;

Step 8. Calculate the tensile and shearing moments of the coal body grid, compare the tensile and shearing moments of the grid with the tensile and shearing moments, and find the most vulnerable grid set; if there is a tensile and shearing moment greater than the tensile and shearing, The grid of moments is marked as "Native Crack", and then step 9 is performed; if there is no grid with a tensile-shear moment greater than the tensile-shear moment, the calculation is terminated and step 11 is performed;

Step 11: Construct a model of two types of coal seam fractures that ultimately include primary fractures in the geological structure and fractures generated during calculation, and re-mesh the mesh to derive the STL general geometry for N-S calculation processing, and store and output the results;

In another preferred embodiment of the present invention, the N-S calculation process includes:

Step A, N-S initialization;

Step B: Calculate water pressure and gas pressure;

Also Darcy calculation processing includes:

Step E, Darcy initialization;

Step F: Calculate water pressure and gas pressure;

Step J: determine whether the water pressure is greater than the gas pressure, and if it is greater, change the next grid material to water, and execute step H; if it is less, directly execute step H;

Furthermore, the above-mentioned step 1 specifically includes: reserve "fault start point", "fault end point", "fault turning point", "azimuth difference", "fall difference" and Six parameters of "tilt angle" are provided for user input.

In addition, the above-mentioned step dimer also includes: using an image processing algorithm to perform a filtering operation on the three-dimensional digital core model, smoothing the edges of the model, and then performing data segmentation based on the threshold to obtain the microscopic pore structure of the coal body, and removing island pores with poor connectivity, The final numerical model of coal pores in STL format was derived.

The above-mentioned quantitative statistical results include simulation results of water pressure field, simulation results of gas pressure, simulation results of coal pressure, simulation results of water flow velocity and simulation results of gas flow velocity.

In order to further describe the present invention, more detailed examples are listed below.

A coupled numerical simulation method for seepage-damage-stress coupling of water injection in a coal rock mass containing a geological structure includes the following steps:

Step 1. Based on the geological survey results, establish a coal and rock mass model including faults;

According to the results of actual geological surveys, a coal seam model is programmed and programmed, in which six parameters of "starting point of the fault", "end point of the fault", "turning point of the fault", "azimuth difference", "fall", and "dip angle" are reserved for user input. ;

Step 2: CT array model;

Scanning experiments were performed on the corresponding coal bodies in the coal and rock bodies obtained from the geological survey, and a 3D digital core model with real pore structure characteristics was constructed in combination with the FDK 3D reconstruction algorithm. The image processing algorithm is used to filter the 3D digital core model to smooth the edges of the model, and then the data is segmented based on the threshold to obtain the micro-pore structure of the coal body. The island pores with poor connectivity are eliminated, as shown in Figure 4. The resulting coal body pore structure is shown in Figure 5, which is derived as the final digital model of coal body pores in STL format.

Step 3: In the boundary element environment, execute the "mining fissure" generation algorithm to determine whether it is a mining affected area, that is, determine whether the distance from the mining surface is less than 80m. If it is a mining-affected area, go to step 4; if it is not a mining-affected area, go to step 5.

Step 4. Determine whether the cross-sectional area of the watershed is greater than 30 μm ^2. If the cross-sectional area of the watershed is greater than 30 μm ² , go to step 6; if it is less than 30 μm ² , go to step 7.

Step 5. Determine whether the cross-sectional area of the watershed is greater than 30 μm ^2. If the cross-sectional area of the watershed is greater than 30 μm ² , go to step 8; if it is less than 30 μm ² , go to step 14.

Step 6. Perform N-S calculations, store and output the results.

Step 7. Perform Darcy calculation, save and output the result.

Step 8. Based on the C # language, program to generate initial stress concentration points based on burial depth, geological conditions, lithology of overlying strata, and inclination of coal seams.

Step 9. Meshing.

Step 10. Calculate the tensile and shearing moments of the coal body grid, compare the tensile and shearing moments of the grid with the tensile and shearing moments, and find the most vulnerable grid set. If there is a mesh with a tensile-shear moment greater than the tensile-shear moment, mark it as "primary crack", and then perform step 11. If there is no mesh with a tensile-shear moment greater than the tensile-shear moment, the calculation is terminated and step 13 is performed.

Step 11: Replace the material in the "primary fissure" grid with the gas in the coal seam.

Step 12. Determine whether the total area of "primary fissures" exceeds twice the fault area. If not, generate a new model that deletes the original fissure mesh and return to repeat step 10. If it exceeds, terminate the calculation and perform step 10. three.

Step 13: Construct a model of the two types of coal seam fractures that ultimately include the primary fractures of the geological structure and the fractures generated during the calculation, and then re-mesh the grid to perform the sixth step after exporting the STL general geometry.

Step 14. In the boundary element environment, after coupling the custom equation to calculate the seepage field and stress parameters, go to step 15.

Step 15: In the meshless simulation environment, write the corresponding algorithm to determine whether there are points where the tensile-shear moment is greater than the relevant parameters of the coal rock mass. If so, connect such points and mark the closed area as "invalid coal rock mass." ", Go to step sixteen; if not, go to step seventeen.

Step 16. Add the water inlet conditions to the marked "invalid coal rock body" boundary in step 15.

Step 17: Perform turbulence simulation separately, calculate the stress distribution, and store the simulation results of this node.

Step 18. Determine whether the fracture separation has reached the surface of the coal body. If not, go to step 19; if it has reached the surface of the coal body, go to step 20.

Step 19: Check whether the accumulated storage time reaches the preset simulation time. If not, go back to step 14. If the calculation time is reached, go to step 20.

Step 20. Stop the calculation in the meshless environment and perform step 7 only after calculating turbulence and stress in the boundary element environment.

Step 21: The integrated result is output and stored as an independent file, and the statistical results are quantified, such as the hydraulic pressure field simulation result diagram of FIG. 6, the gas pressure simulation result diagram of FIG. 7, and the coal body pressure simulation diagram of FIG. 8. The simulation results of the water flow velocity in FIG. 9 and the simulation results of the gas flow velocity in FIG. 10.

It also includes the steps of N-S calculation processing and Darcy calculation processing:

N-S calculation processing steps;

Step 61: N-S initialization.

Step 62: Calculate water pressure and gas pressure.

Step 63: Determine whether the water pressure is greater than the gas pressure. If it is greater, change the next grid material to water and perform step 64. If it is less, proceed directly to step 64.

Step 64: Determine whether the calculation time setting is reached. If the calculation time is not reached, return to step 61 again. If the calculation time is reached, directly store and output the result.

Darcy calculation processing steps;

Step 71: Initialize Darcy.

Step 72: Calculate water pressure and gas pressure.

Step 73: Determine whether the water pressure is greater than the gas pressure. If it is greater, change the next grid material to water, and perform step 74. If it is less, directly perform step 74.

Step 74: Determine whether the calculation time setting is reached. If it cannot be reached, return to step 71 again. If the calculation time is reached, directly store and output the result.

Example 1

Step 1 Based on the results of the geological survey, a coal and rock mass model containing faults is established, which specifically includes the following steps:

(1) In the Cartesian coordinate system, a geometric model of the coal body is established based on the height, strike length, and inclination length of the water injection coal seam, and the model dimension is three-dimensional;

(2) Among them, six parameters of "starting point of the fault", "end point of the fault", "turning point of the fault", "azimuth difference", "fall" and "inclination angle" are reserved for user input.

(3) Then export the STL general geometry.

Step 2CT array model, which specifically includes the following steps:

(1) A nanoVoxel-2000 series-X-ray 3D microscope was used to scan the long-flame coal with an accuracy of 0.5 μm, and a 3D digital core model with real pore structure characteristics was constructed in combination with the FDK 3D reconstruction algorithm;

(2) The image processing algorithm is used to filter the three-dimensional digital core model to reduce noise, smooth the model edges, and then perform volume rendering based on the gray value, and then implement data segmentation based on the threshold to obtain the micro-pore structure of the coal body;

(3) Remove the island pores with poor connectivity, as shown in the non-light blue area in Figure 4 (see Figure 4 in other certification materials for details), and the pore structure of the coal body after processing is shown in Figure 5 (see other certifications for details) Figure 5) in the material, which is derived as the final digital model of coal pores in STL format

Step 3 In the boundary element environment, execute the "mining fissure" generation algorithm to determine whether it is a mining affected area, that is, whether the distance from the mining face is less than 80m. If it is a mining-affected area, go to step 4; if it is not a mining-affected area, go to step 5. In order to complete the theory itself, the following assumptions are introduced:

(1) Ignore or disregard the water permeability and water storage capacity of the matrix rock mass (because the water permeability and water storage performance of the matrix rock mass are particularly weak compared to "mining fractures").

(2) Seepage of "mining fracture" obeys Darcy's law

Where k = -b ^2/12

(3) The deformation law of "mining fracture" obeys the Goodman joint model.

Step 4 determines whether the cross-sectional area of the watershed is greater than 30 μm ^2. If the cross-sectional area of the watershed is greater than 30 μm ² , go to step 6; if it is smaller than 30 μm ² , go to step 7.

Step 5 determines whether the cross-sectional area of the watershed is greater than 30 μm ^2. If the cross-sectional area of the watershed is greater than 30 μm ² , go to step 8; if it is smaller than 30 μm ² , go to step 14.

Step 6: Perform N-S calculation, store and output the result.

(1) N-S initialization.

N-S is used to describe the free flow of water in water injection holes and cracks. It is expressed in Cartesian coordinate system as:

In the formula, t—time; ρ—water pressure in coal body, MPa; v—kinetic viscosity coefficient; u _x , u _y , u _z — axial unit mass forces of x, y, and z axes, respectively, mg · s ^-2 ; F _x , F _y , F _z are components of external force, N;

-Naples operator; u, v, w are the velocity components of the fluid at point (x, y, z) at time t.

(2) Calculate water pressure and gas pressure.

(3) Determine whether the water pressure is greater than the gas pressure. If it is greater, change the next grid material to water and perform (4). If it is less, directly perform (4).

(4) Determine whether the calculation time setting is reached. If it cannot be reached, return to re-execute (1). If the calculation time is reached, directly store and output the result.

Step 7 performs Darcy calculation, stores and outputs the result.

(1) Darcy initialization.

(2) Calculate water pressure and gas pressure.

Darcy's law describes the percolation motion of water in coal. Its differential equation is expressed in Cartesian coordinate system as:

In the formula, P is the water pressure MPa in the coal body, V _x and V _y are the velocity components in the x and y axis directions; K is the permeability, μ is the dynamic viscosity of water Pa · s, and g is the acceleration constant of gravity. ; Ρ is the density of the liquid.

Darcy's law states that the movement of coalbed methane in coal seams basically conforms to the law of linear permeability, namely:

Among them, V is the velocity vector m / s of the coal bed gas movement; gradp is the coal bed methane pore pressure gradient Pa / m; μ is the coal bed methane pore pressure function; k is the coal bed methane permeability coefficient is the absolute viscosity of the coal bed methane Pa · s;

The flow of gas along the coal seam generally obeys Darcy's law, that is, the seepage velocity of gas is proportional to the pressure gradient of gas:

Among them, q is gas seepage velocity, cm / s; λ is coal seam permeability coefficient, m ² / (MPa ² · d); μ is fluid dynamic viscosity coefficient, Pa · s; k is permeability, m ² ;

Is the gas pressure gradient, P / cm.

Step 8 is based on the C # language and is programmed to generate initial stress concentration points based on burial depth, geological conditions, lithology of overlying strata and inclination of coal seams.

Step 9 Divides the grid, which includes the following steps:

Tetrahedral meshing is performed on the coal body geometric model, and the meshing accuracy is increased as much as possible within the range allowed by the computing power of the computer to ensure the accuracy and reliability of the fracture calculation results.

Step 10 In the boundary element environment, calculate and compare the tensile and shear moment values of each mesh, which specifically includes the following steps:

(1) Describe the tensile-shear failure process of rock masses based on but not limited to the Coulomb-Mohr strength criterion. The Coulomb criterion states that the tensile shear failure value of the rock mass during the tensile-shear failure process in a certain plane exceeds the tensile-shear moment value, that is, the cohesion of the material and the constant plane method stress. Its mathematical expression is | τ | = C + γtanμ, where τ is the tensile-shear moment value; C is the cohesive force or cohesive force, which is the tensile-shear strength without positive pressure; μ is the internal friction angle; γ is a fixed constant.

(2) By calculating the tensile and shearing moments of the coal body grid, comparing the tensile and shearing moments of the grid with the tensile and shearing moments, find the most vulnerable grid set. If there is a mesh with a tensile-shear moment greater than the tensile-shear moment, it is marked as "moving crack", and then Step 11 is performed. If there is no mesh with a tensile-shear moment greater than the tensile-shear moment, the calculation is terminated and Step 13 is executed.

Step 11 replaces the material in the "primary fissure" grid with gas in the coal seam.

(1) In the coal body geometric model, remove the grid marked as "mining fracture" in Step 10;

(2) Change the removed geometric element material (grid) to gas in the coal seam, and change the porosity to 1;

(3) Set the same boundary conditions as the adjacent boundary to the newly generated boundary due to the unit being eliminated;

Step 12: Determine whether the total area of the "primary fissure" exceeds twice the fault area, which specifically includes the following steps:

(1) If not, generate a new model that deletes the original fissure mesh, and return to repeat Step 10. If it exceeds, terminate the calculation and execute Step 13.

Step 13 Build a model that finally includes two types of coal seam fractures, including primary fractures in the geological structure and fractures generated during the calculation.The specific steps include the following steps:

(1) Generate a coal rock model containing faults;

(2) Re-mesh the mesh;

(3) Export STL general geometry;

Step 14 In the boundary element environment, coupled with custom equations to calculate the seepage field and stress parameters.

(1) Describe the transport process of water in coal body according to but not limited to Darcy's law.

As a mathematical model for seepage simulation, where t is time; φk is the fracture-to-void ratio; s is the coordinate along the length of the fracture; k _f is the fracture permeability coefficient; W is the source-sink term; p is the water pressure in the coal body (MPa ). If researchers have other flow control equations that they need to add, they can add them manually;

(2) Under the action of pore fluid, the rock mass follows the modified stress law. The coal body stress distribution is calculated according to, but not limited to, the stress equation σ _ij = σ ' _ij + αpσ _ij based on the fluid seepage pressure, where α is called the effective stress coefficient. Practice has proved that α is a function of pore pressure p and volume stress θ, α = f (p, θ).

In coal seams that contain other stress distribution laws or special conditions, other constitutive equations can be programmed to simulate and analyze the stress distribution of the coal body closer to the actual.

Step 15 In the meshless simulation environment, write an algorithm to determine whether there are points where the tensile-shear moment is greater than the relevant parameters of the coal and rock mass, which specifically include the following steps:

(1) If it exists, connect the points where the tensile-shear moment is greater than the relevant parameters of the coal rock mass to form a closed area marked as "invalid coal rock mass" and continue with Step 16;

(2) If there is no point where the tensile-shear moment is greater than the relevant parameters of the coal rock mass, then Step 17 is continued.

Step 16 adds the water inlet conditions to the marked "invalid coal rock body" boundary in Step 15.

Step 18: Determine whether the fracture separation has reached the surface of the coal body, which specifically includes the following steps:

(1) If the fracture does not reach the surface of the coal body, then Step 19 is performed;

(2) If the fracture breaks off and reaches the surface of the coal body, perform Step 20.

Step 19 Whether the accumulated storage time reaches the preset simulation time, which specifically includes the following steps:

(1) If the storage time does not reach the preset simulation time, return to Step 14;

(2) If the storage time reaches the preset simulation time, execute Step 20.

Step 20 stops the calculation in the meshless method environment, calculates turbulence and stress only in the boundary element environment, and then executes Step 7.

Step 21 outputs the integrated result and stores it as an independent file to quantify the statistical results, such as the hydraulic pressure field simulation result chart in Fig. 6, the gas pressure simulation result chart in Fig. 7, the coal pressure result simulation chart in Fig. 8, and Fig. 9 The simulation results of water flow velocity and the simulation results of gas flow velocity in FIG.

According to the results calculated by the results of this numerical simulation method, it can be seen that as a larger range of coal bodies are wetted by water, the main source of power for water transport has become capillary force rather than water injection pressure. The average pressure gradually decreases; but the gradient of the water pressure is relatively constant, while the gas pressure is affected by the structure of irregular pores and fissures, and the gradient of the gradient is obvious. The coal body is gradually softened with the water injection operation, so the overall action pressure shows a downward trend. At the same time, the changes in the flow rate of water and gas are basically consistent with the changes in their respective pressures, but the flow rate of gas is higher than the flow rate of water.

The above phenomena are consistent with the application results in the engineering field, which shows that the results obtained by the simulation method of the present invention are reliable.

Of course, the above description is only a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It should be noted that all equivalent substitutions made by those skilled in the art under the teaching of this specification The obvious deformation forms all fall within the substantive scope of this specification and should be protected by the present invention.

Claims

A coupled numerical simulation method for seepage-damage-stress coupling of water injection in coal and rock masses, comprising the following steps:

Step 1: Establish a coal and rock mass model including faults based on geological survey results;

Step 2: Scan the corresponding coal body in the coal rock body obtained from the geological survey, and combine the FDK 3D reconstruction algorithm to construct a 3D digital core model with real pore structure characteristics;

Step 3: In the boundary element environment, execute the "mining fissure" generation algorithm to determine whether it is a mining affected area, that is, determine whether the distance from the mining face is less than 80m. If it is a mining affected area, go to step 4; if it is not mining Move the affected area, go to step five;

Step 4. Determine whether the cross-sectional area of the watershed is greater than 30 μm 2. If the cross-sectional area of the watershed is greater than 30 μm 2 , perform NS calculation processing, store and output the result; if less than 30 μm 2 , perform Darcy calculation processing, store and output the result;

Step 5. Determine whether the cross-sectional area of the watershed is greater than 30 μm 2. If the cross-sectional area of the watershed is greater than 30 μm 2 , go to step 6; if less than 30 μm 2 , go to step 12;

Step 6. Based on the C # language, the programming generates initial stress concentration points based on burial depth, geological conditions, lithology of overlying strata, and coal seam inclination.

Step 7. Mesh the 3D digital core model processed in Step 6;

Step 8. Calculate the tensile and shearing moments of the coal body grid, compare the tensile and shearing moments of the grid with the tensile and shearing moments, and find the most vulnerable grid set; if there is a tensile and shearing moment greater than the tensile and shearing, The grid of moments is marked as "Native Crack", and then step 9 is performed; if there is no grid with a tensile-shear moment greater than the tensile-shear moment, the calculation is terminated and step 11 is performed;

Step 9. Replace the material in the "primary fissure" grid with the gas in the coal seam;

Step 10. Determine whether the total area of the "primary fissures" after the processing in step 9 exceeds twice the fault area. If not, generate a new model after deleting the "primary fissure" grid, and return to repeat step 8. If it exceeds , The calculation is terminated and step 11 is executed;

Step 11: Construct a model of two types of coal seam fractures that ultimately include primary fractures in the geological structure and fractures generated during calculation, and re-mesh the mesh to derive the STL general geometry for N-S calculation processing, and store and output the results;

Step 12. In the boundary element environment, after coupling the custom equation to calculate the seepage field and stress parameters, go to Step 13.

Step 13. In the meshless simulation environment, determine whether there are points where the tensile-shear moment is greater than the relevant parameters of the coal and rock mass. If so, connect such points in turn, mark the closed area as "invalid coal and rock mass", and execute Step 14; if not, go to Step 15;

Step 14. Add the water inlet conditions to the marked "invalid coal and rock mass" boundary in step 13.

Step 15: Perform turbulence simulation separately, calculate the stress distribution, and store the simulation results of the node;

Step 16. Determine whether the fracture separation from the simulation result in step 15 reaches the surface of the coal body. If not, go to step 17; if it reaches the surface of the coal body, go to step 18.

Step 17. Check whether the accumulated storage time reaches the preset simulation time. If not, go back to Step 12. If the calculation time is reached, go to Step 18.

Step 18. Stop the calculation in the meshless simulation environment. After calculating turbulence and stress only in the boundary element environment, perform Darcy calculation processing, store and output the results;

Step 19: The output results of Step 4, Step 11 and Step 18 are integrated and output as an independent file to obtain a quantitative statistical result.
The method for numerically coupling seepage-damage-stress coupled numerical simulation of water injection in a coal rock mass according to claim 1, wherein the N-S calculation process includes:

Step A, N-S initialization;

Step B: Calculate water pressure and gas pressure;

Step C, determine whether the water pressure is greater than the gas pressure, and if it is greater, change the next grid material to water, and execute step D; if it is less, directly perform step D;

Step D: Determine whether the calculation time setting is reached. If the calculation time is not reached, return to step A. If the calculation time is reached, directly store and output the result.
The numerical simulation method for seepage-damage-stress coupled numerical simulation of water injection in a coal rock mass according to claim 1, wherein the Darcy calculation process includes:

Step E, Darcy initialization;

Step F: Calculate water pressure and gas pressure;

Step J: Determine whether the water pressure is greater than the gas pressure, and if it is greater, change the next grid material to water, and perform step H; if it is less, directly perform step H;

Step H: Determine whether the calculation time setting is reached. If the calculation time is not reached, return to step E. If the calculation time is reached, directly store and output the result.
The method for numerical simulation of seepage-damage-stress coupling of zoned water injection in a coal rock mass according to claim 1, wherein a specific step of the above step further comprises: "faults are reserved in the process of establishing a coal rock mass model including faults" The starting point, the end point of the fault, the turning point of the fault, the azimuth difference, the drop, and the inclination are provided for user input.
The method for numerically coupling water injection seepage-damage-stress coupling of a coal rock mass according to claim 1, wherein the step dimer further comprises: using an image processing algorithm to perform a filtering operation on a three-dimensional digital core model to smooth the model. The edge, and then based on the threshold to achieve data segmentation to obtain the micro-pore structure of the coal body, remove the island pores with poor connectivity, and derive the final digital model of coal body pores in STL format.
The method for numerical simulation of seepage-damage-stress coupling of water injection in a coal rock mass according to claim 1, wherein the quantitative statistical results include simulation results of hydraulic pressure field, simulation results of gas pressure, simulation results of coal pressure, and water flow velocity Simulation results and gas velocity simulation results.