A method for predicting dynamic permeability of coal seam under gas-solid coupling effect

Abstract

This invention discloses a method for predicting the dynamic permeability of coal seams considering the synergistic effect of gas-solid coupling, comprising the following steps: S1, collecting coal and rock samples from the target coal seam, conducting relevant experiments, and determining the basic parameters required for the dynamic evolution model of permeability; S2, obtaining the methane desorption amount per unit coal body and the pore pressure in the matrix under non-equilibrium conditions; S3, obtaining the effective strain change of fractures and matrix in the coal under the synergistic effect of gas-solid coupling, and deriving the porosity evolution equation; S4, deriving the permeability evolution equation based on the relationship between porosity and permeability; S5, solving the equation using a numerical solver based on the above dynamic evolution equation of coal seam permeability. This invention can accurately predict the dynamic permeability of coal seams under non-equilibrium conditions. The proposed method fully considers the synergistic effect of gas-solid coupling in coal seams under non-equilibrium conditions, and the calculation results have clear physical meaning, which can guide coalbed methane exploration and development under reservoir conditions.

Description

Technical Field

[0001] This invention belongs to the field of coalbed methane exploration, development and utilization, and specifically relates to a method for predicting the dynamic permeability of coal seams considering gas-solid coupling. Background Technology

[0002] For a long time, conventional energy sources, mainly coal and oil, have dominated my country's energy system. However, given my country's energy landscape of "abundant coal, scarce oil, and limited gas," the commercial exploration and development of unconventional oil and gas resources has become an urgent need due to the continuous expansion of energy demand and the further depletion of conventional energy minerals. Coalbed methane (CBM), as an important type of unconventional natural gas, is considered a key mineral for improving my country's energy consumption structure, achieving green and efficient energy conversion, and ensuring energy security due to its clean, efficient, and abundant reserves. Unlike conventional gas reservoirs, the storage form and transmission mechanism of CBM in reservoirs are completely different, mainly in four aspects: 1. Most CBM exists in the pores of coal in the form of adsorption; 2. Multi-scale pores and fractures are developed in the reservoir, making the CBM transport mechanism complex and controlled by diffusion and seepage; 3. The volume of the coal matrix will expand / contract with the adsorption / desorption of adsorbed gas, changing the coal structure; 4. The increase in effective stress in the reservoir during production leads to changes in reservoir properties. Reservoir permeability undergoes dynamic changes under the synergistic effect of complex gas-solid coupling mechanisms, and permeability is directly related to the production efficiency of coalbed methane wells. Accurate and efficient quantitative characterization of the dynamic evolution process of reservoir permeability is helpful for the selection of "sweet spots" in coalbed methane production and the design of coalbed methane well drainage schemes, providing theoretical guidance for the commercial development of coalbed methane.

[0003] Current theoretical calculation methods for coalbed methane reservoir permeability typically treat the coal body as an ideal porous medium composed of cubes or matchsticks, using porous elasticity as a basis for theoretical derivation. Furthermore, the adsorption-induced effect is assumed to be linear elastic strain and superimposed on the coal body deformation constitutive equation to account for the evolution of pore and fracture sizes caused by matrix shrinkage and effective stress during depressurization development. This method can accurately obtain the permeability at adsorption equilibrium under different pressures, but it cannot effectively characterize the dynamic evolution of permeability under non-equilibrium conditions. Moreover, existing permeability models often only consider fracture gas pressure, neglecting the interaction between fractures and the matrix. However, the different gas pressures in fractures and the matrix under non-equilibrium conditions are the driving force for gas desorption and the controlling factor for matrix shrinkage. Therefore, comprehensively considering the dual deformation mechanism of the reservoir during coalbed methane extraction, the multi-scale gas transport mechanism in pores and fractures, and the gas-solid coupling synergy between the two, establishing a coalbed methane permeability evolution model to achieve accurate prediction of dynamic permeability is crucial for the efficient development of coalbed methane. Summary of the Invention

[0004] To address the shortcomings of current methods for calculating coal seam permeability, this invention provides a quantitative prediction method for dynamic coal seam permeability. This method fully considers the dynamic response of coal seam pore and fracture volume under complex gas-solid coupling during coalbed methane depressurization mining. It also considers the interaction between fractures and matrix in coal under non-equilibrium conditions caused by pressure lag, quantifies the evolution process of coal seam permeability under non-equilibrium conditions, and realizes the quantitative prediction of the dynamic evolution of relative coal seam permeability.

[0005] The technical means employed in this invention are as follows:

[0006] This invention discloses a method for predicting the dynamic permeability of coal seams, the method comprising:

[0007] S1. Collect coal and rock samples from the target coal seam and conduct basic rock mechanics tests and methane isothermal adsorption tests to obtain the basic parameters required for the dynamic evolution model of permeability.

[0008] S2. Based on Fick's second diffusion law, Langmuir's adsorption equation and the law of conservation of mass, the dynamic evolution equation of methane desorption and pore pressure in the matrix under non-equilibrium conditions is obtained, and the real-time methane desorption and matrix pore gas pressure are obtained.

[0009] S3. Based on the theory of porous elasticity, the constitutive equation of coal matrix and fracture under gas-solid coupling is constructed, the effective strain change of coal matrix and fracture under the current pressure condition is calculated, and the porosity evolution equation is obtained according to the relationship between porosity and effective strain change.

[0010] S4. Based on the coal porosity evolution equation, and according to the corresponding coupling relationship between porosity and permeability, the dynamic evolution equation of coal seam permeability considering the synergistic effect of gas-solid coupling is derived.

[0011] S5. Based on the above dynamic evolution equation of coal seam permeability, use a numerical solver to solve the equation and achieve accurate prediction of coal seam dynamic permeability.

[0012] The present invention also has the following technical features:

[0013] Specifically, the method includes the following steps:

[0014] S1. Collect coal and rock samples from the target coal seam and conduct basic rock mechanics tests and methane isothermal adsorption tests to obtain the basic parameters required for the dynamic evolution model of permeability.

[0015] Preferably, the basic rock mechanics test is a uniaxial compression and deformation test of rock, and the Young's modulus E and Poisson's ratio ν of the coal and rock are obtained based on the relationship between stress and strain in the coal and rock during the experiment.

[0016] Preferably, the methane isothermal adsorption test includes sample preparation and experimental stages;

[0017] The sample preparation stage requires crushing the coal and rock blocks into 60-80 mesh powder, and then placing the powder in a drying oven for drying for no less than 4 hours.

[0018] The experimental phase specifically involves checking the airtightness of the isothermal adsorption apparatus before the experiment, including the sample container, reference container, valves, and pipe connections. Before the adsorption experiment begins, helium is injected into the sample container, followed by vacuuming. This process is repeated multiple times to remove residual adsorbed gases from the coal sample. Subsequently, a methane adsorption experiment is conducted, recording the methane pressure, the corresponding methane adsorption amount, and the time consumed. An isothermal adsorption curve is plotted, and the Langmuir equation is applied to fit the curve to obtain the Langmuir volume V. L With Langmuir pressure P L .

[0019] S2. Based on Fick's second diffusion law, Langmuir's adsorption equation and the law of conservation of mass, the dynamic evolution equation of methane desorption and pore pressure in the matrix under non-equilibrium conditions is obtained, and the real-time methane desorption and matrix pore gas pressure are obtained.

[0020] Because coal has different gas transport mechanisms in its pore and fracture systems at different scales, this invention treats the coal body as a dual-medium system composed of fractured and matrix media in its theoretical derivation. Only diffusion occurs in the matrix media, while only seepage occurs in the fractured media. During depressurization mining, gas diffusion lags behind seepage, creating a pressure difference, which is the driving force for the desorption of adsorbed gas into free gas. Diffusion and seepage equations are established separately for the matrix and fractures, with the diffusion equation using fracture gas pressure as the boundary condition and the seepage equation using methane diffusion as the mass source. The dynamic parameter ΔP(t)=P f (t)-P m (t) to achieve coupling, and further obtain the methane desorption amount and matrix pore gas pressure under non-equilibrium conditions;

[0021] Preferably, the amount of methane desorption under the non-equilibrium state can be obtained by Fick's second diffusion law, the law of conservation of mass, and the methane single-pore diffusion model, as follows:

[0022]

[0023] In the formula: Q m D represents the amount of methane desorption; e M is the effective diffusion coefficient of methane; c R is the molar mass of the gas; R is the ideal gas constant; T is the temperature; P m P is the matrix gas pressure at time t; f Let t be the fracture gas pressure.

[0024] Furthermore, according to the law of conservation of mass, the change in the mass of gas in the coal matrix per unit time is:

[0025]

[0026] In the formula: This represents the methane mass flow rate.

[0027] By combining equations (1) and (2), the dynamic evolution equation of the matrix methane desorption can be obtained:

[0028]

[0029] The effective diffusion coefficient D e Considering the influence of micropore size on the diffusion rate, this method, compared to the diffusion coefficient D, can more accurately reflect the dynamic diffusion process. Its value can be calculated by the following formula:

[0030]

[0031] In the formula: P0 is the initial pressure; P t P represents the pressure at time t. ∞ To achieve pressure equilibrium; t is the diffusion time; n is the number of terms.

[0032] Preferably, based on the law of conservation of mass and the Langmuir equation, the equation for the amount of methane gas per unit coal mass can be obtained. Furthermore, by differentiating with respect to time t, the time-varying evolution equation for the matrix gas pressure can be derived.

[0033]

[0034] In the formula: P m D represents the gas pressure within the matrix; t represents time; D represents the pressure of the gas within the matrix. e V is the effective diffusion coefficient of methane; m P is the molar volume of the gas; f P represents the gas pressure within the fracture. L For Langmuir pressure; V L R is the Langmuir volume; T is the ideal gas constant; ρ is the temperature. c Φ represents the apparent density of coal. m The porosity of the coal matrix.

[0035] S3. Based on the theory of porous elasticity, the constitutive equation of coal matrix and fracture under gas-solid coupling is constructed, the effective strain change of coal matrix and fracture under the current pressure condition is calculated, and the porosity evolution equation is obtained according to the relationship between porosity and effective strain change.

[0036] Preferably, due to the presence of secondary minerals filling the coal matrix, the adsorption-induced strain exhibits spatial heterogeneity, and only deformation into the coal body affects permeability. The internal strain is quantified using an internal expansion factor f. The change in internal strain induced by adsorption during pressure drop is:

[0037]

[0038] In the formula: f is the internal expansion factor, and its range is [0,1]; ε f s This refers to the internal strain induced by adsorption; ε m s This refers to the external strain induced by adsorption.

[0039] The aforementioned adsorption-induced change in external strain can be obtained by combining the Gibbs surface adsorption equation and the Langmuir adsorption equation:

[0040]

[0041] In the formula: V L For Langmuir volume; P L R is the Langmuir pressure; T is the ideal gas constant; ρ is the temperature. c P is the apparent density of coal; P0 is the initial gas pressure; P t E is the gas pressure at time t. hi V0 is the solid expansion modulus of the coal matrix; V0 is the molar volume of the gas.

[0042] Preferably, the mechanical strain of the fractures and matrix caused by dynamic changes in reservoir pressure can be obtained through relevant theories of porous elasticity. By superimposing this strain with adsorption-induced strain, the effective strain of the fractures and matrix is:

[0043]

[0044]

[0045] Where: ε f For the effective variable of the crack; The effective variable of the crack caused by local effective stress; ε is the effective variable of the crack caused by methane desorption. m As a matrix-related effective variable; The effective matrix variable is caused by local effective stress; K represents the external strain induced by adsorption. f K represents the bulk modulus of fractures in coal. m P is the bulk modulus of the coal matrix. f P is the fracture pressure; mα is the matrix pressure; β is the Biot coefficient of the fractures in the coal; and β is the Biot coefficient of the coal matrix.

[0046] Furthermore, considering the pressure drop process during extraction and the evolution of fracture and matrix volume, the following method for calculating the effective strain change is proposed:

[0047]

[0048]

[0049] In the formula: P f,0 P is the initial fracture pressure; f,t P represents the fracture pressure at time t. m,0 P represents the initial matrix pore pressure. m,t Let t be the matrix pore pressure at time t.

[0050] Preferably, the evolution equation of coal seam porosity under the pressure drop condition is:

[0051]

[0052] Where: Φ f For porosity, Φ f,0 This represents the initial porosity.

[0053] S4. Based on the coal porosity evolution equation, and according to the corresponding coupling relationship between porosity and permeability, the dynamic evolution equation of coal seam permeability considering the synergistic effect of gas-solid coupling is derived.

[0054] Preferably, the corresponding coupling relationship between porosity and permeability is as follows:

[0055]

[0056] In the formula: k f For penetration rate, k f,0 This represents the initial penetration rate.

[0057] S5. Based on the above dynamic evolution equation of coal seam permeability, use a numerical solver to solve the equation and achieve accurate prediction of coal seam dynamic permeability.

[0058] Preferably, the above model involves solving partial differential equations, which can be solved analytically using numerical simulation software with secondary development capabilities (such as Ansys or COMSOL Multiphysics), and the solution can be used as the final prediction result. After obtaining the parameters required for the prediction model through rock mechanics tests and methane isothermal adsorption tests, numerical simulation software is selected, and by establishing a reasonable geometric model and setting the calculation step size and convergence conditions according to requirements, the dynamic relative permeability of coal seams under pressure drop conditions can be predicted.

[0059] Compared with existing technologies, the technical solution of the present invention has the following advantages:

[0060] 1. The permeability prediction method proposed in this invention fully considers the dynamic response of coal seam pore and fracture volume under complex gas-solid coupling synergy during coalbed methane depressurization mining. It focuses on the interaction between fractures and matrix in coal under non-equilibrium conditions caused by pressure lag, thus making up for the shortcomings of existing permeability models.

[0061] 2. This invention quantifies the dynamic evolution of coal seam permeability during coalbed methane depressurization mining. In addition, it can be combined with commercial numerical simulation software to simulate reservoir pressure, matrix pressure, and reservoir stress-strain state throughout the entire coalbed methane drainage process, achieving full-process visualization and providing theoretical reference for understanding the dynamic development law of coalbed methane for rational and efficient coalbed methane development.

[0062] 3. Compared with existing technologies, this method has a faster and simpler implementation path, higher accuracy in predicting dynamic relative permeability, and only requires routine experiments to obtain the required parameters.

[0063] The method proposed in this invention is simple, easy to operate, economical, and reliable. In production practice, it can guide the design and optimization of coalbed methane exploration and development plans. It has significant theoretical implications for exploring the dynamic laws of coalbed methane production and its efficient development. Attached Figure Description

[0064] Figure 1 A flowchart illustrating a method for predicting the dynamic permeability of coal seams considering gas-solid coupling.

[0065] Figure 2 A contour plot showing the change in gas pressure in the matrix pores when the equilibrium pressure drops from 1.71 MPa to 0.70 MPa.

[0066] Figure 3 A contour map showing the change in porosity in a coal column when the pressure drops from 1.71 MPa to 0.70 MPa.

[0067] Figure 4 A contour map showing the change in porosity in a coal column when the pressure drops from 1.71 MPa to 0.70 MPa.

[0068] Figure 5 The curve showing the relative permeability as a function of pressure, calculated when the pressure decreases from 5.50 MPa to 0.70 MPa;

[0069] Figure 6 The curve showing the change in relative permeability of the coal pillar over time before reaching various equilibrium pressures. Detailed Implementation

[0070] The following provides specific embodiments of the present invention for further description. It should be noted that the present invention is not limited to the following specific embodiments. All embodiments obtained by those skilled in the art based on the technical solutions of this application without creative effort fall within the protection scope of the present invention.

[0071] Example:

[0072] Reference Figure 1-6 This embodiment uses the dynamic relative permeability prediction of a coal pillar sample from a mine as an example for illustration. All equations involved in the method are solved using COMSOL Multiphysics 6.1 based on the finite element method. Permeability experiments were conducted on the coal pillar sample under different pressures. The initial injection pressure was 5.5 MPa, subsequently reduced to 4.24 MPa, 3.00 MPa, 1.71 MPa, and 0.70 MPa. The permeability at equilibrium was recorded to verify the accuracy of the relative permeability prediction method proposed in this application. Correspondingly, a physical model was established in the numerical solver using the actual size of the coal pillar sample. It was assumed that the methane pressure in the coal pillar was 5.5 MPa in the initial state, with its upper, left, and right boundaries being non-flowing boundaries, and the bottom boundary set as constant pressure boundaries of 4.24 MPa, 3.00 MPa, 1.71 MPa, and 0.70 MPa, to simulate the state of the coal pillar under various equilibrium gas pressures during the pressure drop process.

[0073] Reference Figure 1 The present invention provides a flowchart illustrating a method for predicting the dynamic relative permeability of coal seams considering gas-solid coupling, comprising the following steps:

[0074] S1: Collect coal and rock samples from the target coal seam, and conduct basic rock mechanics tests and methane isothermal adsorption tests to obtain the basic parameters required for the dynamic evolution model of permeability;

[0075] Coal and rock samples were collected from a mine in the Qinshui Basin of Shanxi Province, China. A portion of the samples was ground into powder with a particle size of 60–80 mesh, thoroughly dried, and then subjected to a methane isothermal adsorption experiment. A coal column with a diameter of 50 mm and a height of 100 mm was drilled from the same sample for rock mechanics testing. The test results are as follows:

[0076] Table 1. Test results of basic parameters of coal samples

[0077]

[0078] In Table 1: V L For Langmuir volume; P L R is Langmuir pressure; E is Young's modulus; ν is Poisson's ratio; ρ c For apparent density.

[0079] S2. Based on Fick's second diffusion law, Langmuir's adsorption equation and the law of conservation of mass, the dynamic evolution equation of methane desorption and pore pressure in the matrix under non-equilibrium conditions is obtained, and the real-time methane desorption and matrix pore gas pressure are obtained.

[0080] In this embodiment, the methane diffusion equation in the matrix is ​​established according to Fick's diffusion law, as follows:

[0081]

[0082] In the formula: Q m D represents the amount of methane desorption; e M is the effective diffusion coefficient of methane; c R is the molar mass of the gas; R is the ideal gas constant; T is the temperature; P m P represents the matrix pore gas pressure at time t. f Let t be the fracture gas pressure.

[0083] Furthermore, according to the law of conservation of mass, the change in the mass of gas in the coal matrix per unit time is:

[0084]

[0085] By combining equations (1) and (2), the dynamic evolution equation of the matrix methane desorption can be obtained:

[0086]

[0087] Based on the law of conservation of mass and the Langmuir equation, the equation for the amount of methane gas per unit volume of medium can be obtained. Furthermore, by differentiating with respect to time t, the time-varying evolution equation for the pore gas pressure in the matrix can be derived:

[0088]

[0089] In the formula: P m D represents the gas pressure within the matrix; t represents time; D represents the pressure of the gas within the matrix. e V is the effective diffusion coefficient of methane; m P is the molar volume of the gas; f P represents the gas pressure within the fracture. L For Langmuir pressure; V L R is the Langmuir volume; T is the ideal gas constant; ρ is the temperature. c Φ represents the apparent density of coal. m The porosity of the coal matrix.

[0090] The above partial differential equations are input into a numerical solver and solved using the finite element method. Figure 2To illustrate the change in gas pressure in the matrix pores when the equilibrium pressure decreases from 1.71 MPa to 0.70 MPa, similarly, the matrix pore gas pressure within any equilibrium pressure range can be obtained. Only the following is considered: Figure 2 As an example.

[0091] S3. Based on the theory of porous elasticity, construct the deformation constitutive equation of coal matrix and fracture under gas-solid coupling, calculate the effective strain change of coal matrix and fracture under the current pressure condition, and then derive the porosity evolution equation based on the relationship between porosity and effective strain change.

[0092] Under pressure drop conditions, the deformation of the matrix and fractures is controlled by three mechanisms: matrix shrinkage caused by methane desorption, fracture closure caused by increased effective stress in the coal seam, and the interaction between fractures and matrix under non-equilibrium conditions.

[0093] The amount of coal matrix shrinkage caused by methane desorption can be derived based on the Gibbs adsorption equation and the Langmuir adsorption equation, specifically:

[0094] Based on the pore gas pressure in the matrix obtained in S2, according to the formula:

[0095]

[0096] The change in coal matrix strain caused by methane desorption from the initial equilibrium state to the current equilibrium state was calculated.

[0097] In the formula: V L For Langmuir volume; P L R is the Langmuir pressure; T is the ideal gas constant; ρ is the temperature. c P is the apparent density of coal; P0 is the initial gas pressure; P t E is the gas pressure at time t. hi V0 is the solid expansion modulus of the coal matrix; V0 is the molar volume of the gas.

[0098] Based on the theory of porous elasticity, considering the anisotropy of matrix shrinkage and the interaction between the matrix and the cracks, according to the formula:

[0099]

[0100]

[0101] The strain of the matrix and the cracks was calculated.

[0102] Where: ε f For the effective variable of the crack; The effective variable of the crack caused by local effective stress; ε is the effective variable of the crack caused by methane desorption.m As a matrix-related effective variable; The effective matrix variable is caused by local effective stress; K represents the external strain induced by adsorption. f K represents the bulk modulus of fractures in coal. m P is the bulk modulus of the coal matrix. f P is the fracture pressure; m α is the matrix pressure; β is the Biot coefficient of the fractures in the coal; and β is the Biot coefficient of the coal matrix.

[0103] Furthermore, considering the pressure drop process, according to the formula:

[0104]

[0105]

[0106] The effective strain changes of the matrix and cracks were calculated.

[0107] In the formula: P f,0 P is the initial fracture pressure; f,t P represents the fracture pressure at time t. m,0 P represents the initial matrix pore pressure. m,t Let t be the matrix pore pressure at time t.

[0108] Based on the relationship between effective strain and porosity, according to the formula:

[0109]

[0110] Where: Φ f For porosity, Φ f,0 This represents the initial porosity.

[0111] The dynamic porosity of the coal seam under pressure drop conditions can then be obtained.

[0112] The above equations were substituted into COMSOL Multiphysics 6.1 and solved using the finite element method. The relevant parameter values ​​used in this embodiment are shown in Table 2. Figure 3 To obtain a contour map of porosity changes in the coal pillar when the equilibrium pressure decreases from 1.71 MPa to 0.70 MPa, similarly, porosity can be obtained within any equilibrium pressure variation range. Only by considering... Figure 3 As an example.

[0113] Table 2 shows the values ​​of the parameters input to the solver.

[0114]

[0115] *In the table: T is temperature; R is the ideal gas constant; M cρ is the molar mass of the gas. c Φ represents the apparent density of coal. f Coal porosity; D e f is the effective diffusion coefficient of methane; f is the internal expansion coefficient; E hi It represents the solid expansion modulus of the coal matrix.

[0116] S4. Based on the coal porosity evolution equation, and according to the corresponding coupling relationship between porosity and permeability, a dynamic evolution model of coal seam permeability is obtained.

[0117] Based on the porosity evolution equation obtained in S3, the dynamic permeability can be further calculated according to the relationship between porosity and permeability using the following formula:

[0118]

[0119] S5. Based on the above dynamic evolution equation of coal seam permeability, use a numerical solver to solve the equation and achieve accurate prediction of coal seam dynamic permeability.

[0120] Substituting the above equations into COMSOL Multiphysics 6.1 and solving them using the finite element method, the parameter values ​​used in S5 and S3 are the same. Figure 4 To obtain a contour map of permeability changes in the coal pillar when the equilibrium pressure decreases from 1.71 MPa to 0.70 MPa, similarly, permeability can be obtained within any range of equilibrium pressure changes, using only... Figure 4 As an example.

[0121] Figure 5 The curves showing the relative permeability change obtained when the pressure drops from 5.50 MPa to 0.70 MPa are shown. The results indicate that the prediction method for dynamic relative permeability of coal seams under gas-solid coupling proposed in this application has a small error between the predicted relative permeability value obtained by the finite element numerical method and the experimental measurement value, and can achieve accurate prediction of dynamic relative permeability of coal seams under pressure drop conditions. Figure 6 To obtain the curves showing the change of relative permeability of the coal pillar over time before each equilibrium pressure, similarly, this application can also obtain the stress or strain evolution curves under non-equilibrium conditions.

[0122] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for predicting the dynamic permeability of a coal seam under the synergistic effect of gas-solid coupling, characterized in that, The method includes the following steps: S1. Collect coal and rock samples from the target coal seam and conduct basic rock mechanics tests and methane isothermal adsorption tests to obtain the basic parameters required for the dynamic evolution model of permeability. S2. Based on Fick's second diffusion law, Langmuir's adsorption equation and the law of conservation of mass, the dynamic evolution equation of methane desorption and pore pressure in the matrix under non-equilibrium conditions is obtained, and the real-time methane desorption and matrix pore gas pressure are obtained. S3. Based on the theory of porous elasticity, the constitutive equation of coal matrix and fracture under gas-solid coupling is constructed, the effective strain change of coal matrix and fracture under the current pressure condition is calculated, and the porosity evolution equation is obtained according to the relationship between porosity and effective strain change. S4. Based on the coal porosity evolution equation, and according to the corresponding coupling relationship between porosity and permeability, the dynamic evolution equation of coal seam permeability considering the synergistic effect of gas-solid coupling is derived. S5. Based on the above dynamic evolution equation of coal seam permeability, use a numerical solver to solve the equation and achieve accurate prediction of coal seam dynamic permeability. In step S3, the calculation method for the effective strain change of coal matrix and fractures under gas-solid coupling based on porous elasticity theory is as follows: ； ； In the formula: This represents the effective strain change in the crack. This represents the change in effective strain in the crack caused by local effective stress. This represents the effective strain change in the crack caused by methane desorption. This represents the effective strain change of the matrix; This represents the change in effective strain of the matrix caused by local effective stress. α represents the effective strain change in the matrix caused by methane desorption; α is the Biot coefficient of the fracture; β is the Biot coefficient of the matrix; P f,0 P is the initial fracture pressure; f,t P represents the fracture pressure at time t. m,0 P represents the initial matrix pore pressure. m,t ΔP(t) represents the matrix pore pressure at time t; ΔP(t) represents the pressure difference between the fracture and the matrix at time t; f is the internal expansion factor; K f K represents the bulk modulus of fractures in coal. m P is the bulk modulus of the coal matrix. L For Langmuir pressure; V L For Langmuir volume; ρ c Φ represents the apparent density of coal. m R is the porosity of the coal matrix; T is the ideal gas constant; E is the temperature. hi V0 is the solid expansion modulus of the coal matrix; V0 is the molar volume of the gas. In step S3, the method for calculating the dynamic porosity of coal seams under the gas-solid coupling synergy based on porous elasticity theory is as follows: ； where: Φ f is the porosity; Φ f,0 is the initial porosity.

2. The method of claim 1, wherein, In step S1, the basic parameters required for the dynamic evolution model of permeability are obtained from rock mechanics tests and methane isothermal adsorption tests. The test samples are obtained from exploration boreholes or mining faces in the target area. The parameters include elastic modulus, Poisson's ratio, Langmuir pressure, Langmuir volume, and apparent density of coal.

3. The method of claim 1, wherein, In step S2, the method for calculating the amount of methane desorption under non-equilibrium conditions based on Fick's second diffusion law and the law of conservation of mass is as follows: ； wherein: is the methane mass flow rate; D e M is the effective diffusion coefficient of methane; c R is the molar mass of the gas; R is the ideal gas constant; T is the temperature; P m P represents the gas pressure within the matrix. f This represents the gas pressure inside the fissure.

4. The method of claim 1, wherein, In step S2, the method for calculating the gas pressure within the coal matrix based on the law of conservation of mass and the Langmuir equation is as follows: ； In the formula: P m D represents the gas pressure within the matrix; t represents time; D represents the pressure of the gas within the matrix. e V is the effective diffusion coefficient of methane; m P is the molar volume of the gas; f P represents the gas pressure within the fracture. L For Langmuir pressure; V L R is the Langmuir volume; T is the ideal gas constant; ρ is the temperature. c Φ represents the apparent density of coal. m The porosity of the coal matrix.

5. The method for predicting dynamic permeability of coalbed considering gas-solid coupling synergy of claim 1, wherein, The permeability evolution model established in step S4 is as follows: ； wherein: k f is the porosity; k f,0 is the initial porosity.

6. The method for predicting dynamic permeability of coalbed considering gas-solid coupling synergy of claim 1, wherein, The dynamic permeability of coal seams can be predicted by obtaining the coal and rock properties parameters of the target area, inputting them into the permeability evolution model established in step S4, and solving the model. The model involves solving complex partial differential equations, which requires the use of a numerical solver to obtain its numerical solution.

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