Unit dense filling overburden permeability simulation method

Abstract

The application discloses a unit dense filling overburden rock permeability simulation method, comprising the following steps: dividing the whole area into CO2 mineralization sealing block segments and high-pressure CO2 sealing block segments; determining the post-peak softening law of the key parameters of the CO2 mineralization filling material; determining the strain hardening mechanical parameters of the high-pressure CO2 gas gangue double medium coupling body; adopting FLAC 3D to obtain the deformation and breakage of the overburden rock; extracting the unit dense filling stress path characteristics of different horizons of the overburden rock three zones; carrying out rock triaxial seepage experiments under the unit dense filling stress path; obtaining a rock permeability evolution model under the unit dense filling stress path; introducing the permeability segmented model into COMSOL, using MATLAB as an intermediate coordinator, and obtaining the unit dense filling overburden rock permeability evolution law. The application obtains the overburden rock permeability distribution characteristics, is beneficial to widening the CO2 sealing path under the conditions of protecting the overlying water resources and ensuring the safety of the unit dense filling site, and can provide strong support for the realization of the double-carbon target.

Description

Technical Field

[0001] This invention relates to the field of coal mining and CO2 geological storage technology, specifically to a method for simulating the permeability of overburden in densely packed unit filling, which is particularly suitable for simulating and analyzing the evolution law of overburden permeability under CO2 mineralized coal-based solid waste and CO2 original state densely packed unit filling conditions. Background Technology

[0002] In CO2-mineralized coal-based solid waste and CO2-preserved unit compaction backfilling projects, overburden permeability directly relates to groundwater resource protection and the safety of CO2 geological storage space. Accurately grasping the spatiotemporal evolution of overburden permeability is a fundamental prerequisite for optimizing backfilling process parameters. Existing overburden permeability simulation mainly relies on two types of numerical tools: one is FLAC... 3D Finite difference mechanics calculation software, represented by COMSOL, excels at simulating the redistribution of overburden stress and the collapse of rock strata caused by mining. However, its seepage function has significant limitations; it can only solve the pore water pressure field and cannot directly output the permeability variation law. The evolution law of overburden permeability during mining needs to be established by researchers using empirical formulas or secondary development, resulting in large fluctuations in the calculation results. Another type is the finite element multiphysics platform, represented by COMSOL. This type of software has advantages in solving continuous medium problems such as seepage fields and can provide detailed seepage distribution results. However, it cannot handle the compaction evolution process of the collapsed accumulation in the goaf. However, there is a close coupling relationship between the compaction state of the goaf and the permeability of the overburden. The bearing capacity of the collapse zone increases with the degree of compaction, which correspondingly inhibits the further subsidence of the overburden. If the compaction of the collapse body is insufficient, the range of overburden failure extends to the depth, and the permeability increases accordingly. This feedback chain of "goaf compaction - overburden stress adjustment - permeability change" is an unavoidable core link in the simulation of overburden permeability.

[0003] Existing single simulation methods cannot fully capture this coupling process, FLAC 3D While both software programs can reproduce stress fields and collapse processes, they cannot calculate permeability. COMSOL can solve seepage fields, but lacks a realistic mechanical process of pressure in goaf areas as a driving boundary. Using either alone, it is difficult to provide results that accurately reflect the evolution of overburden permeability in engineering practice, thus hindering the reliable support for optimizing engineering parameters such as backfill material composition and the widths of CMSB and HPCSB (CMSB represents CO2 mineralized storage blocks, HPCSB represents high-pressure CO2 storage blocks, and CMFM represents CO2 mineralized backfill material or backfill body). Therefore, there is an urgent need to develop a coupled simulation method that integrates the advantages of both software programs. Summary of the Invention

[0004] (a) Purpose of the invention

[0005] To address the shortcomings of CO2 mine sequestration technology, this invention provides a method for simulating overburden permeability under conditions of CO2 mineralized coal-based solid waste and dense filling of CO2 original units. The aim is to expand CO2 sequestration pathways while controlling the evolution of overburden permeability to ensure the safety of CO2 sequestration space.

[0006] (II) Technical Content

[0007] To solve the above-mentioned technical problems, the technical solution of the present invention is: a method for simulating the permeability of densely packed overburden, comprising the following steps:

[0008] S1. When the distance between the top of the unit compacted filling area and the bottom of the overlying aquifer is greater than or equal to a predetermined threshold, the entire unit compacted filling area is divided into mutually spaced CMSB and HPCSB.

[0009] S2. Determine the post-peak softening law of key CMFM parameters;

[0010] S3. Determine the strain hardening mechanical parameters of the high-pressure CO2 gas-collapsed gangue dual-medium coupled body;

[0011] S4, using FLAC 3D Secondary development was carried out to obtain the deformation and fracture of the overburden under the joint support of the CMFM and the high-pressure CO2 gas-collapse gangue dual-medium coupling body;

[0012] S5. Tecplot was used to extract the unit compaction stress path characteristics of different layers in the three zones of the overburden.

[0013] S6. Use high-pressure CO2 to cure rock specimens, and then carry out triaxial flow test of rock under unit compaction stress path;

[0014] S7. Considering CO2 adsorption and desorption and the coupling effect of CO2-water on rocks, a staged evolution model of rock permeability under the unit dense filling stress path is obtained.

[0015] S8. Import the permeability segmentation model into COMSOL and use MATLAB as an intermediate coordinator to control FLAC. 3D By exchanging data with COMSOL's execution process, the evolution law of permeability of the overlying strata under dense filling unit was obtained.

[0016] Furthermore, in step S1, the widths of CMSB and HPCSB are determined by the geological and hydrogeological conditions of the unit compaction filling project:

[0017]

[0018] In the formula, The critical threshold of equivalent permeability coefficient required for an intact rock stratum to isolate the water body from the overlying aquifer; The pressure difference between the upper and lower boundaries of the intact rock strata; It is the water recharge rate of shallow aquifers; The depth of the compacted filling site for the unit; This refers to the height of the coal seam. The proportion of rigid rock strata; CMSB width; The width of HPCSB; , , , , , These are the fitting coefficients, and all are greater than 0.

[0019] Furthermore, in step S2, the attenuation law of the post-peak parameters in CMFM is as follows:

[0020]

[0021] in, and These represent the pre-peak and post-peak cohesion of CMFM, respectively. and These are the internal friction angles before and after the CMFM peak, respectively. and These are the pre-peak and post-peak shear dilatation angles of CMFM, respectively. is the cumulative plastic shear strain; m, n, and p are CMFM characteristic parameters.

[0022] Furthermore, in step S3, the strain hardening mechanical parameters of the high-pressure CO2 gas-collapsed gangue dual-medium coupling body are determined by the following formula:

[0023]

[0024] in, and These represent the vertical stress and vertical strain of the coupled body, respectively. and The values ​​are used to characterize the strain hardening parameters.

[0025] Furthermore, in step S5, the unit compaction filling stress path monitoring points include: boundary coal pillars, HPCSB goaf, the middle of CMSB, and the midpoints of the three zones of rock strata on both sides of CMSB.

[0026] Furthermore, in step S7, the staged evolution model of rock permeability under the unit compaction stress path, considering CO2 adsorption and desorption and the coupling effect of CO2-water on the rock, is as follows:

[0027]

[0028] In the formula, The rock permeability during the compaction filling process; It is a deviatoric stress; and The nonlinear parameters, determined by fitting triaxial seepage experimental data under stress path, are used to reflect the seepage characteristics.

[0029] Furthermore, in step S8, during the COMSOL simulation, the bottom boundary of the overlying aquifer is used as the first head boundary, and the boundary of the high-pressure CO2 storage block is used as the second head boundary. The high-pressure CO2 gas-collapsed gangue dual-medium support only participates in the support effect of the Solid module on the overlying rock and does not participate in the seepage calculation of the Darcy law module.

[0030] Furthermore, in step S8, a grid node data interpolation mapping method is used to implement FLAC. 3D Transfer of field quantity data between COMSOL and the software; adopting a weak coupling scheme, establishing a time step coordination mechanism between the two software programs to achieve transient coupling between mechanical deformation and seepage evolution.

[0031] (III) Technical Effects

[0032] The advantages of this invention compared to existing technologies are: this invention utilizes FLAC 3D Cross-platform coupling with COMSOL integrates the advantages of both numerical simulation software, solving the problem of insufficient functionality when simulating overburden permeability with a single software. FLAC 3D COMSOL is responsible for reconstructing the real mechanical processes of overburden stress redistribution and goaf collapse and compaction during mining. Based on this, COMSOL completes the fine solution of the seepage field. The two are interconnected and linked by MATLAB data, which saves researchers the extra work of establishing the relationship between stress and permeability by relying on empirical formulas. It also avoids the unrealistic approach of the traditional finite element method, which simplifies the goaf as a homogeneous continuous medium with fixed permeability parameters. The core value of this coupling method is that it can fully present the entire feedback chain of how changes in the degree of goaf compaction affect the overburden stress distribution and thus permeability. This makes the physical mechanism of the simulation results clearer and more reliable. The evolution law of overburden permeability obtained is closer to the actual engineering situation. It can provide reliable numerical support for optimizing key parameters such as the filling body ratio, CMSB and HPCSB width in CO2 mineralized coal-based solid waste and CO2 original unit compaction filling projects. It has practical engineering significance for ensuring the safety of groundwater resources and the stability of CO2 storage space. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the unit dense filling in this invention;

[0034] Figure 2 FLAC in this invention 3D Secondary development numerical calculation flowchart;

[0035] Figure 3 This invention describes the post-peak parameter decay law of CMFM with a fly ash content of 75% and an age of 14 days.

[0036] Figure 4 This is the strain hardening curve of the high-pressure CO2-collapsed gangue dual-medium coupling body in this invention;

[0037] Figure 5 It uses FLAC 3D The secondary development yielded the morphology of the collapsed and deposited top slab and overlying rock.

[0038] Figure 6 This is the stress path of the leakage zone corresponding to the middle part of HPCSB in this invention;

[0039] Figure 7 This is the stress path of the leakage zone in the middle of the CMSB in this invention;

[0040] Figure 8 This refers to the stress path of the leakage zone on both sides of the CMSB in this invention;

[0041] Figure 9 This is the stress path of the seepage zone corresponding to the middle part of HPCSB in this invention;

[0042] Figure 10 This is the stress path of the seepage zone in the middle of the CMSB in this invention;

[0043] Figure 11 This is the stress path of the seepage isolation zone in the middle of HPCSB in this invention;

[0044] Figure 12 This is the stress path of the seepage isolation zone in the middle of the CMSB in this invention;

[0045] Figure 13 This invention is a segmented evolution model of permeability under the unit dense filling stress path that considers the effect of CO2-water coupling;

[0046] Figure 14 This invention is based on FLAC 3D -Permeability distribution characteristics of overburden under dense-filled units in MATLAB-COMSOL.

[0047] Explanation of reference numerals in the attached figures:

[0048] 1. Coal seam where the unit compacted filling area is located; 2. Overlying aquifer; 3. HPCSB; 4. CMSB; 5. First-stage stope branch roadway; 6. Second-stage stope branch roadway; 7. Chimney; 8. Factory; 9. CO2 gas; 10. Mine CO2 gas tank; 11. Fly ash; 12. Coal gangue; 13. Filling station; 14. Filling pump; 15. Filling pipeline; 16. High-pressure CO2 compressor; 17. Gas transport pipeline; 18. Leakage zone; 19. Seepage zone; 20. Seepage isolation zone. Detailed Implementation

[0049] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0050] Reference Appendix Figure 1 To be continued Figure 14 A method for simulating the permeability of densely packed overburden in a single unit includes the following steps:

[0051] S1. When the distance between the top of the unit compacted filling area and the bottom of the overlying aquifer is greater than or equal to a predetermined threshold, the predetermined threshold is 580 meters, and the entire unit compacted filling area is divided into mutually spaced CMSB and HPCSB.

[0052] S2. Determine the post-peak softening law of key CMFM parameters;

[0053] S3. Determine the strain hardening mechanical parameters of the high-pressure CO2 gas-collapsed gangue dual-medium coupled body;

[0054] S4, using FLAC 3D Secondary development was carried out to obtain the deformation and fracture of the overburden under the joint support of the CMFM and the high-pressure CO2 gas-collapse gangue dual-medium coupling body;

[0055] S5. Tecplot was used to extract the unit compaction stress path characteristics of different layers in the three zones of the overburden.

[0056] S6. Rock specimens were cured using high-pressure CO2, followed by triaxial flow tests under unit compaction stress paths. First, rock samples from three overlying zones were collected, including sandy mudstone, sandstone, mudstone, and fine sandstone. Each sample was processed into a standard cylindrical specimen with a diameter of φ×h of 50×100mm. The specimens were then dried at 105℃ for 24 hours to constant weight. After cooling, a vacuum was applied to negative pressure, and distilled water was injected to submerge the specimens. This vacuum was maintained for 24 hours to simulate in-situ water content. The saturated specimens were then placed in a curing vessel, and the curing temperature was set to 35℃ to simulate ground temperature. Once the temperature stabilized, CO2 was slowly injected, and the pressure was increased to preset values ​​(2MPa, 4MPa, 6MPa, 8MPa, 10MPa). The pressure was kept constant, and curing was carried out for 7, 30, and 90 days, respectively. Then, a high-temperature, high-pressure flow-coupled true triaxial rock mechanics testing system was used to conduct triaxial flow tests under unit compaction stress paths on specimens with different CO2 pressures and curing times.

[0057] S7. Considering CO2 adsorption and desorption and the coupling effect of CO2-water on rocks, a staged evolution model of rock permeability under the unit dense filling stress path is obtained.

[0058] S8. Import the permeability segmentation model into COMSOL and use MATLAB as an intermediate coordinator to control FLAC. 3D By exchanging data with COMSOL's execution process, the evolution law of permeability of the overlying strata under dense filling unit was obtained.

[0059] In step S1 of this embodiment, the widths of CMSB and HPCSB are determined by the geological and hydrogeological conditions of the unit compaction filling project:

[0060]

[0061] In the formula, The critical threshold of equivalent permeability coefficient required for an intact rock stratum to isolate the water body from the overlying aquifer; The pressure difference between the upper and lower boundaries of the intact rock strata; It is the recharge rate of water in shallow aquifers; The depth of the compacted filling site for a unit is measured in meters. The height of the coal seam is in meters (m). The proportion of rigid rock strata; CMSB width, in meters; denoted as HPCSB width, m; a, b, c, d, e, and f are fitting coefficients, all greater than 0. In this embodiment, the values ​​of a, b, c, d, e, and f are 0.987, 5.6, 17.86, 61.6, 29.02, and 2.68, respectively.

[0062] In step S2 of this embodiment, the attenuation law of the post-peak parameters of CMFM is as follows:

[0063]

[0064] in, N and N represent the pre-peak and post-peak cohesion of CMFM, respectively; and These are the internal friction angles before and after the CMFM peak, respectively. and These are the pre-peak and post-peak shear dilatation angles of CMFM, respectively. denoted as cumulative plastic shear strain; m, n, and p are parameters characterizing the properties of CMFM.

[0065] In step S3 of this embodiment, the strain hardening mechanical parameters of the high-pressure CO2 gas-collapsed gangue dual-medium coupling body are determined by the following formula:

[0066]

[0067] in, and The vertical stress and vertical strain of the coupled body are respectively, and h and k are values ​​characterizing strain hardening parameters. In this embodiment, the CO2 pressure is 2 MPa, and when the rock type of the collapsed gangue is sandstone, h is 45.44 and k is 0.56.

[0068] In step S5 of this embodiment, the monitoring points for the stress path of the unit compaction filling mainly include: the boundary coal pillar, the HPCSB goaf, the middle of the CMSB, and the midpoints of the three-zone strata on both sides of the CMSB.

[0069] In step S7 of this embodiment, the phased evolution model of rock permeability under the unit compaction stress path, considering CO2 adsorption and desorption and the coupling effect of CO2-water on rock, is as follows:

[0070]

[0071] In the formula, The rock permeability during the compaction filling process; It is a deviatoric stress; and The nonlinear parameters, determined by fitting triaxial seepage experimental data under stress path, are used to reflect the seepage characteristics.

[0072] In step S8 of this embodiment, during COMSOL simulation, the bottom boundary of the overlying aquifer is used as the first head boundary, and the boundary of the high-pressure CO2 storage block is used as the second head boundary. The high-pressure CO2 gas-collapsed gangue dual-medium support only participates in the support effect of the Solid module on the overlying rock and does not participate in the seepage calculation of the Darcy law module.

[0073] In step S8 of this embodiment, FLAC is used. 3D -A loosely coupled computing architecture combining MATLAB, COMSOL, and FLAC 3D The system is responsible for solving the mechanical problems of the evolution of mining stress field and the collapse and compaction process of overburden. COMSOL is responsible for solving the multi-field coupling of seepage field, and MATLAB is the intermediate data management platform, responsible for data reading and writing, inter-grid interpolation mapping, convergence determination, and coordination and control of coupling time steps.

[0074] The data transmission link is divided into four directions:

[0075] FLAC 3D For MATLAB: Data output functions are written using the FISH language. After each mechanical calculation is completed, the field quantities such as grid node coordinates, displacement, stress, and porosity are written to a formatted text file for easy parsing and reading by MATLAB.

[0076] MATLAB to COMSOL: Data interaction is achieved through the Livelink for MATLAB interface. The MATLAB side starts the COMSOL server and loads the pre-built seepage calculation model. The interpolated field data is organized into a COMSOL-recognizable format and written into the model. Material parameters such as permeability are directly assigned values ​​through the global variable interface. After the data is written, the COMSOL solver is triggered to execute the seepage calculation for the current time step.

[0077] COMSOL to MATLAB: After the seepage calculation is completed, the pore water pressure and seepage velocity are extracted by interpolation of the node coordinates through the interface function, and the extracted data is stored in MATLAB.

[0078] MATLAB to FLAC 3D Seepage field data was converted to FLAC via interpolation mapping. 3D After the grid system is established, MATLAB will configure it according to FLAC. 3D Write data to a readable format, FLAC 3D The end reads the file through the FISH function, assigns the pore water pressure value to the corresponding grid node, and then proceeds to the next mechanical calculation after the update is completed.

[0079] The grid interpolation mapping module is implemented in MATLAB, using the radial basis function interpolation method. This method belongs to the gridless interpolation technique and constructs the interpolation function based on the distance weighting principle. The interpolation calculation process is as follows:

[0080] Let the source mesh contain N nodes, with coordinate matrix X and corresponding field vector f. Let the target mesh contain M interpolation points, with coordinate matrix Y. First, calculate the Euclidean distance from each target point to all source nodes:

[0081]

[0082] Multiple quadratic radial basis functions are selected as interpolation basis functions:

[0083]

[0084] Where c is the shape parameter, its value is 0.5-1.0 times the average node spacing of the source mesh. An interpolation equation system containing N radial basis function terms and 4 linear polynomial terms is constructed, with 4 constraints added to ensure linear regeneration. In MATLAB, the equation system is solved directly by matrix left division. After obtaining the interpolation coefficient vector α and the polynomial coefficient vector β, the field interpolation value of each target point is calculated according to the following formula:

[0085]

[0086] A local support domain strategy is adopted. For each target point, only 20-50 source nodes within a range of 3-5 times the average node spacing are selected to participate in the interpolation calculation. The k-nearest neighbor algorithm is used to quickly filter the neighboring nodes. After the interpolation is completed, the accuracy is checked. The volume weighted average of the field quantities on the source grid and the target grid is compared. If the relative error is less than 1%, it is considered to meet the accuracy requirements. Otherwise, the support domain radius is reduced and the calculation is repeated.

[0087] Coupling time step coordination is controlled by MATLAB. The coupling time step size Δt must simultaneously satisfy two constraints: mechanical calculation stability and seepage calculation accuracy. The mechanical stability condition is determined by FLAC. 3D The explicit time step criterion is determined, and the seepage accuracy condition is controlled by the Fourier number Fo≤0.5.

[0088]

[0089] In the formula, k is the permeability; μ is the fluid viscosity; is the unit water storage rate; L is the characteristic length.

[0090] The coupling time step is taken as the smaller of the two upper limits of the constraints. A variable step size method is used in the calculation process. When the field changes are large in the early stage of the calculation, a small step size is used, and when the field changes are small in the later stage, the step size is increased to a large step size. The step size is adjusted by MATLAB based on the iteration convergence. When the number of iterations in three consecutive time steps is less than 3, the time step size is appropriately increased.

[0091] The final convergence criterion is the relative error of the L2 norm of the pore pressure field.

[0092]

[0093] In the formula, and These are the pore pressure fields after the k-th and (k-1)-th iterations, respectively; It is an L2 norm; This represents the relative error between two iterations.

[0094] Convergence tolerance is set to 10 -3 -10 -4 If the convergence condition is met, proceed to the next time step; otherwise, continue iterating. Each time step iterates 3-8 times.

[0095] The following detailed description is based on specific embodiments.

[0096] Example:

[0097] A method for simulating the permeability of densely packed overburden in a single unit includes the following steps:

[0098] Schematic diagram of unit compaction filling is shown below Figure 1 As shown, when the coal seam 1 where the unit compacted filling area is located is far from the overlying aquifer 2, the entire unit compacted filling area is divided into HPCSB3 and CMSB4 that are spaced apart from each other. The working face is 240m long, the coal seam is 3.0m thick and 600m deep, HPCSB3 is 30m wide, CMSB4 is 10m wide, the rigid rock layer accounts for 0.6, the distance between the coal seam 1 where the unit compacted filling area is located and the overlying aquifer 2 is 580m, and the recharge rate of the overlying aquifer 2 is 0.0675~0.1610L / s·m.

[0099] CMSB4 is further divided into Phase 1 stope roadway 5 and Phase 2 stope roadway 6. The specific process is as follows: First, CO2 gas 9 emitted from the chimney 7 and factory 8 is captured and transported to the mine CO2 tank 10. Using fly ash 11 and coal gangue 12 as aggregates, and water, silicate additives, and CO2 gas as auxiliary materials, fresh CMFM slurry is prepared at normal temperature and pressure and stored in the filling station 13. Then, through the filling pump 14, it is filled into Phase 1 stope roadway 5 and Phase 2 stope roadway 6 along the filling pipeline 15. After all the CMSB4 stope roadways are filled with CMFM, the coal body within HPCSB3 is mined. Then, after the roof collapses and accumulates, it is injected into HPCSB3 through the high-pressure CO2 compressor 16 along the gas transport pipeline 17. Considering the strain softening and strain hardening characteristics of CMFM and the dual-medium coupling body, FLAC is used... 3D FLAC has built-in FISH functionality for secondary development. 3D The secondary development numerical calculation process is as follows: Figure 2 As shown, the secondary development mainly includes four steps: CMFM filling, roof collapse, gangue accumulation, and dual-medium coupling body compaction.

[0100] (1) CMFM filling simulation

[0101] Excavate the coal body in CMSB4 using the null command, change the goaf to the Strain-softening model, and assign pre-peak parameters (bulk modulus , shear modulus , tensile strength ), as shown in the following table:

[0102] Table 1 shows the pre-peak parameters of CMFM with 14d age and 75% fly ash content in the present invention

[0103]

[0104] Based on Figure 3 the variation law of internal friction angle and cohesion with plastic cumulative shear strain, post-peak parameters (cohesion and internal friction angle ) are assigned through the Def function of FISH language.

[0105] (2) Roof caving simulation

[0106] ① Use FISH function to design a loop to traverse all units, obtain three-dimensional principal stresses (σ1, σ2, σ3) and volumetric strain , and calculate the overburden damage variable D.

[0107]

[0108] ② Use the IF function of FISH to compare the overburden damage variable D with the critical damage threshold D T , if D T <D, it means that the roof has caved, the constitutive model is changed from Mohr-Coulomb to null element, and the null element is classified into the caving group.

[0109] ③ Repeat steps ① and ② to complete the judgment of all elements.

[0110] (3) Gangue accumulation simulation

[0111] Use FISH function to obtain the maximum and minimum ordinates of each element in the caving group (Z max and Z min ), determined by determine the cumulative thickness of the roof rock that is about to cave and calculate the cumulative height of caved gangue and the height of caving zone .

[0112]

[0113] In the formula, and are the thickness and bulking coefficient of the i-th caved rock stratum respectively, This refers to the thickness of the coal seam.

[0114] like If the collapsed gangue does not contact the roof, continue the mechanical calculation; otherwise, if the collapsed gangue does contact the roof, replace the model at the corresponding (x,y) coordinate with the elastic model, and repeat until all elements have been judged.

[0115] (4) Compaction of dual-medium coupling body

[0116] ① Identify and index the collapse group units into a linked list.

[0117] ② The collapse model was changed to a nonlinear elastic model with strain hardening characteristics.

[0118] ③ Assign bulk modulus K, shear modulus G, density ρ, and Poisson's ratio μ according to the table below:

[0119] Table 2 shows the mechanical parameters of the dual-medium coupling body in this invention.

[0120]

[0121] Initial tangent modulus and maximum vertical strain Depend on Figure 4 Decide.

[0122] ④ Perform mechanical calculations.

[0123] ⑤ Based on vertical strain The change continuously updates the bulk modulus K to simulate strain hardening of a dual-medium coupled body, as the vertical strain increases. At the same time, K increases synchronously. :

[0124]

[0125] ⑥ Repeat steps ③ to ⑤ to obtain the morphology of the collapsed overlying slab, such as... Figure 5 As shown.

[0126] The stress path of mining in the middle of HPCSB3 and CMSB4, and the corresponding seepage zone 18 on both sides of CMSB4, is as follows: Figure 6-8 As shown; the mining stress path of the seepage zone 19 corresponding to the middle of HPCSB3 and CMSB4 in the densely filled unit is as follows. Figure 9-10 As shown; the mining stress paths of the corresponding seepage isolation zones 20 in the middle of the densely filled HPCSB3 and CMSB4 units are respectively as follows: Figure 11-12 As shown; according to Figures 6 to 12The stress path characteristics of the overlying strata are considered, taking into account the conditions of laboratory triaxial seepage experiments. These conditions are then equivalently transformed into loading and unloading conditions for laboratory triaxial seepage experiments. Based on the results of the triaxial seepage experiments and using a theoretical model, a segmented evolution model of rock permeability under the unit compaction stress path considering CO2-water coupling is obtained, such as... Figure 13 As shown; then using the above FLAC 3D The MATLAB-COMSOL weakly coupled scheme yielded the permeability distribution characteristics of densely filled overburden units, such as... Figure 14 As shown.

[0127] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A method for simulating the permeability of densely packed overburden in a single unit, characterized in that, Includes the following steps: S1. When the distance between the top of the unit compacted filling area and the bottom of the overlying aquifer is greater than or equal to a predetermined threshold, the entire unit compacted filling area is divided into mutually spaced CMSB and HPCSB. S2. Determine the post-peak softening law of key CMFM parameters; S3. Determine the strain hardening mechanical parameters of the CO2 gas-collapsed gangue dual-medium coupled body; S4, using FLAC 3D Secondary development was carried out to obtain the deformation and fracture of the overburden under the combined support of the CMFM and CO2 gas-collapse gangue dual-medium coupling body; S5. Tecplot was used to extract the unit compaction stress path characteristics of different layers in the three zones of the overburden. S6. Curing rock specimens with CO2, and then conducting triaxial flow tests of rock under unit compaction stress path; S7. Considering CO2 adsorption and desorption and the coupling effect of CO2-water on rocks, a staged evolution model of rock permeability under the unit dense filling stress path is obtained. S8. Import the permeability segmentation model into COMSOL and use MATLAB as an intermediate coordinator to control FLAC. 3D By exchanging data with COMSOL's execution process, the evolution law of permeability of the overlying strata under dense filling unit was obtained.

2. The method for simulating the permeability of densely packed overburden as described in claim 1, characterized in that, In step S1, the widths of CMSB and HPCSB are determined by the geological and hydrogeological conditions of the unit compaction filling project: In the formula, The critical threshold of equivalent permeability coefficient required for an intact rock stratum to isolate the water body from the overlying aquifer; The pressure difference between the upper and lower boundaries of the intact rock strata; It is the water recharge rate of shallow aquifers; The depth of the compacted filling site for the unit; This refers to the height of the coal seam. The proportion of rigid rock strata; CMSB width; The width of HPCSB; , , , , , The fitting coefficients are denoted as .

3. The method for simulating the permeability of densely packed overburden as described in claim 1, characterized in that, In step S2, the attenuation law of post-peak parameters in CMFM is as follows: in, and These represent the pre-peak and post-peak cohesion of CMFM, respectively. and These are the internal friction angles before and after the CMFM peak, respectively. and These are the pre-peak and post-peak shear dilatation angles of CMFM, respectively. is the cumulative plastic shear strain; m, n, and p are CMFM characteristic parameters.

4. The method for simulating the permeability of densely packed overburden as described in claim 1, characterized in that, In step S3, the strain hardening mechanical parameters of the CO2 gas-collapsed gangue dual-medium coupling body are determined by the following formula: in, and These represent the vertical stress and vertical strain of the coupled body, respectively. and The values ​​are used to characterize the strain hardening parameters.

5. The method for simulating the permeability of densely packed overburden as described in claim 1, characterized in that, In step S5, the unit compaction filling stress path monitoring points include: boundary coal pillar, HPCSB goaf, CMSB center, and the midpoint of the three-zone strata on both sides of CMSB.

6. The method for simulating the permeability of densely packed overburden as described in claim 1, characterized in that, In step S7, the staged evolution model of rock permeability under the unit compaction stress path, considering CO2 adsorption and desorption and the coupling effect of CO2-water on the rock, is as follows: In the formula, The rock permeability during the compaction filling process; It is a deviatoric stress; and The nonlinear parameters, determined by fitting triaxial seepage experimental data under stress path, are used to reflect the seepage characteristics.

7. The method for simulating the permeability of densely packed overburden as described in claim 1, characterized in that, In step S8, during the COMSOL simulation, the bottom boundary of the overlying aquifer is used as the first head boundary, and the boundary of HPCSB is used as the second head boundary. The CO2 gas-collapsed gangue dual-medium support only participates in the support effect of the Solid module on the overlying rock and does not participate in the seepage calculation of the Darcy law module.

8. The method for simulating the permeability of densely packed overburden rock according to claim 7, characterized in that, In step S8, a grid node data interpolation mapping method is used to implement FLAC. 3D Transfer of field quantity data between COMSOL and the software; adopting a weak coupling scheme, establishing a time step coordination mechanism between the two software programs to achieve transient coupling between mechanical deformation and seepage evolution.

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