Gas-gas diffusion concentration distribution calculation method considering gravity influence

Abstract

The invention discloses a gas-gas diffusion concentration distribution calculation method considering gravity influence, and relates to the field of oil-gas field development, the method introduces a gravity drift velocity item generated by density difference into a traditional diffusion equation to realize unified characterization of molecular diffusion and gravity differentiation, and the method is suitable for gas-gas diffusion concentration distribution calculation. A dynamic mass transfer model suitable for multi-temperature-pressure and multi-component conditions is constructed and used for calculating concentration distribution and corresponding dynamic diffusion coefficients of injected gas and formation gas in the vertical diffusion process, and a calculation basis with better consistency is provided for prediction of the migration front edge and the distribution pattern of the injected gas, gas injection parameter optimization and gas channeling risk assessment. The method has the applicable value of improving the recovery ratio of the gas reservoir and the operation safety of the gas storage.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oil and gas field development, in particular to a gas-gas diffusion concentration distribution calculation method considering gravity effect, which is particularly suitable for gas diffusion simulation in gas drive gas reservoir development. BACKGROUND

[0002] In the field of oil and gas field development and underground gas storage, gas injection displacement and gas peak shaving operation widely rely on accurate characterization of mass transfer process between different gases. In actual reservoirs, gas-gas systems often exhibit multi-factor coupled mass transfer under high temperature and high pressure conditions. In addition to molecular diffusion and dispersion, gravity differentiation and natural convection caused by density difference will change the vertical component and concentration distribution, and then affect the injection gas migration front, fingering pattern and overall development effect.

[0003] Existing researches are generally divided into experimental and theoretical two paths. For CO2 and natural gas system, some scholars use stratified sampling and time sequence monitoring to measure component concentration at different depths and times, and use analytical formula based on Fick's law or convection-dispersion framework to carry out fitting regression to obtain molecular diffusion coefficient, equivalent diffusion / dispersion coefficient and other characterization parameters. One method for determining the gravity diffusion coefficient of carbon dioxide in natural gas, CN119164838B); some works further introduce dimensionless gravity parameter to induce observation phenomena. Some scholars measure the longitudinal dispersion coefficient of supercritical CO2 and CH4 in porous media through core displacement experiment, and establish a one-dimensional convection-dispersion model. Such method has engineering operability and can reflect the macroscopic migration characteristics when density difference exists to a certain extent, but often includes the effect of "gravity induced drift / convection" into the equivalent parameters, and the physical interpretability of the parameters is limited. (CO2 sequestration for enhanced gas recovery: New measurements of supercritical CO2-CH4 dispersion in porous media and a review of recent research. [J]. International Journal of Greenhouse Gas Control, 2012, Vol.9: 457-468.).

[0004] In the theoretical model research, the mainstream method is based on Fick's law or Maxwell-Stefan equation to establish a multi-component diffusion coefficient matrix, discuss the influence of thermodynamic non-ideality and molecular interaction on equivalent diffusion, and give the approximate relationship with Fick's coefficient under certain conditions (Calculation of multi-component gas-gas diffusion coefficient[J]. Natural Gas Industry, 2015, (8): 39-43.). Some scholars have established a diffusion coefficient calculation model based on Fick's second law for dry gas and condensate gas system under supercritical conditions. However, compared with gas-oil diffusion, the modeling work directly facing gas-gas system and introducing gravity effect under supercritical conditions is still limited (A supercritical dry gas-condensate dynamic diffusion coefficient calculation method, CN115081217A). The existing models focus on the expression of "concentration gradient-driven flux", and lack explicit inclusion and unified description of the drift term caused by density difference-gravity, the triggering condition of natural convection under stable / unstable density stratification, and the coupling mechanism of gravity and dispersion at the control equation level.

[0005] In summary, the existing methods can reflect the gravity-related phenomena at the experimental level, but the theoretical level generally lacks explicit inclusion of the gravity term into the control equation; and the modeling method based on molecular diffusion is difficult to represent the gravity-driven characteristics of gas-gas system. Based on the theoretical simulation needs of engineering application, it is necessary to propose a gas-gas diffusion modeling and parameterization idea that can consider gravity differentiation and dynamic diffusion process simultaneously, to support the design and optimization of gas injection scheme. SUMMARY

[0006] The purpose of the present application is to provide a gas-gas diffusion concentration distribution calculation method considering the influence of gravity. This method introduces a gravity drift velocity term caused by density difference into the traditional diffusion equation, realizes the unified representation of molecular diffusion and gravity differentiation, constructs a dynamic mass transfer model suitable for multi-temperature and pressure and multi-component conditions, and is used to calculate the concentration distribution and corresponding dynamic diffusion coefficient of injected gas and formation gas in the vertical diffusion process, to provide calculation basis for front position prediction, gas injection parameter setting and gas channeling risk assessment, and to support the decision-making of gas reservoir enhanced recovery and gas storage operation.

[0007] To achieve the above technical purposes, the following technical solutions are adopted in the present application.

[0008] A gas-gas diffusion concentration distribution calculation method considering the influence of gravity, comprising the following steps in sequence: Step S1: Consider a certain PVT cylinder containing two gases in a non-equilibrium state with known initial composition, with the origin coordinate located at the gas-gas interface, and the interface being in equilibrium state, with the positive direction of z-axis upward and the negative direction of z-axis downward; Step S2: Based on S1, considering the influence of molecular diffusion and gravity, the total diffusion flux of the upper and lower gasesJ The expression is as follows: (1) In the formula: J is the total flux of diffusion, ; is the flux caused by molecular diffusion, ; is the flux caused by gravity, .

[0009] Step S3: Based on Fick's second law, the basic form of the diffusion flux is: (2) In the formula: D is the diffusion coefficient, ; is the molar concentration, ; z is the position coordinate, .

[0010] Step S4: The gas molecules in the system will be affected by gravity, and the mass transfer flux caused by gravity is: (3) In the formula: is the drift velocity caused by gravity, .

[0011] Step S5: Based on Stokes' law, the velocity expression of the gas caused by gravity is: (4) In the formula: D is the diffusion coefficient, m 2 / s; is the acceleration of gravity, m / s 2 ; is the difference between the densities of the two gases, kg / m 3 ; is the average molar mass of the gas, kg / mol; is the average density of the gas, kg / m 3 ; R is the universal gas constant, 8.314 kg·m 2 / (s 2 ·mol·K); T is the temperature, K.

[0012] Step S6: In the process of diffusion of two gases, when there is gravity, the gas-gas mass transfer equation is: (5) In the formula: tFor the diffusion time, .

[0013] Step S7: Combined with the physical simulation process of step S1 and the mass transfer equation of step S5, the upper gas diffusion model is as follows: (6) In the formula: subscript 1 represents the upper gas; is the initial molar concentration of the upper gas, ; is the molar concentration of the upper gas phase component when the gas-gas interface is balanced, ; is the height of the upper gas, m .

[0014] Step S8: Homogeneous boundary condition, the upper gas diffusion model in step S7 can be converted into the following form: (7) In the formula: is an auxiliary attenuation term, which satisfies ; is an intermediate function, which satisfies ; is an intermediate function, which satisfies .

[0015] Step S9: The upper gas model is solved by the mathematical physics method of separation of variables, and the expression of the upper gas concentration function is: (8) In which:

[0016] In the formula: is the characteristic coefficient of the upper gas concentration function.

[0017] Similarly, the expression of the lower gas concentration function is: (9) In which:

[0018] In the formula: subscript 2 represents the lower gas.

[0019] Step S10: The least square method is used to fit the experimental data to determine the diffusion coefficient considering the influence of gravity D : (10) In the formula: is the calculated gas molar concentration value from the model, ; is the measured gas molar concentration value, .

[0020] Further, the step S3 is processed as follows: Step S31: In Fick's second law, the basic driving force of the diffusion process is the concentration gradient, and the diffusion behavior of the gas is mainly determined by the concentration gradient Ccontrol, the diffusion flux expression is: (3.1) Step S32: Since diffusion only occurs in the z direction, the concentration gradient The expression is as follows: (3.2) Step S33: Substitute equation (3.2) into equation (3.1) to obtain: (2) Further, the step S5 is processed as follows: Step S51: and respectively, the density of the upper gas and the lower gas, is the difference between the densities of the two gases, and its form is as follows: (5.1) Step S52: y 1 and y 2 are the mass fractions of the upper gas and the lower gas, respectively, is the average density of the mixed gas, which is a weighted average of the densities of the two gases: (5.2) Step S53: is the average molar mass of the mixed gas, which is a weighted average of the molar masses of the two gases: (5.3) Step S54: Based on Stokes' law, The expression for (5.4) Step S55: Substitute equation (5.1), equation (5.2) and equation (5.3) into equation (5.4) to obtain: (4) Further, the step S6 is processed as follows: Step S61: The total flux in the diffusion process J is the sum of the diffusion flux driven by the concentration gradient and the drift flux caused by gravity, and substituting equation (2) and equation (3) into equation (1) to obtain: (6.1) Step S62: Substitute the total flux into the continuity equation to obtain the following equation: (6.2) Step S63: In the process of gas diffusion, the mass transfer equation of gas-gas is as follows: (6.3) Step S64: Assuming which is independent of the position z, the final form of the mass transfer equation is as follows: (5) Further, the process of step S7 is as follows: Step S71: According to the process of physical simulation of gas-gas diffusion described in step S1, the initial condition for the upper gas is as follows: (7.1) Step S72: The upper boundary of diffusion is a closed flux-free boundary, and the upper boundary condition is as follows: (7.2) Step S73: In the process of gas-gas diffusion, the pressure of the whole system is constant, and the interface is in equilibrium state, and the lower boundary condition is as follows: (7.3) Step S74: According to the initial condition and the boundary condition, and combining equation (5), the diffusion model of the upper gas is as follows: (6) Similarly, the diffusion model of the lower gas is as follows: (7.4) Further, the process of step S8 is as follows: Step S81: Let After the homogeneous boundary condition, equation (5) can be transformed into: (8.1) Step S82: Define , and the following equation is obtained: (7) Similarly, the diffusion model of the lower gas can be transformed into: (8.2) Further, the process of step S9 is as follows: Step S91: The separation of variables method is used to solve the diffusion model, and let (9.1) In the equation, X isz Functions in space; T for t A function of time.

[0021] Step S92: Substitute equation (9.1) into equation (9) and divide both sides simultaneously. , (9.2) In the formula: It is a parameter introduced to eliminate the convection term.

[0022] Step S93: The general solution for the time part is: (9.3) In the formula: These are coefficients to be determined.

[0023] Step S94: The spatial partial differential equation is: (9.4) Step S95: The general solution for the spatial part is: (9.5) In the formula: These are coefficients to be determined; These are coefficients to be determined.

[0024] Step S96: Therefore, the solution to equation (7) is: (9.6) Step S97: Combining the initial conditions, boundary conditions, and equation (9.6), the expression for the upper gas concentration function can be obtained as follows: (8) in: (9) Similarly, the expression for the lower gas concentration function can be obtained as follows: (10) in: (11) Furthermore, step S10 is as follows: Step S101: Obtain the concentration distribution of the upper and lower gas through a gas-to-gas diffusion experiment; Step S102: Provide initial values ​​for the diffusion coefficients of the upper and lower gases. D g1 and D g2 ; Step S103: Calculate the concentration distribution of the upper and lower gas according to formula (8) and formula (10), and determine whether the difference between the model calculation value and the experimental measured value is less than 10 by the least square method -5 , if the difference is less than 10 -5 , output the corresponding diffusion coefficient D ; (12) Step S104: if the difference between the model calculation value and the experimental measured value is greater than 10 -5 , return to step S102, re-adjust the diffusion coefficient value, and then perform subsequent calculation until the difference is less than 10 -5 .

[0025] Compared with the prior art, the present application is based on the natural convection mechanism caused by the density difference, and a gravity drift velocity term is explicitly introduced into the traditional diffusion equation to form a gas-gas diffusion coupling model which simultaneously describes molecular diffusion and gravity differentiation. Under the conditions of multi-temperature pressure and multi-component, the model can calculate the vertical concentration distribution and the dynamic diffusion coefficient varying with temperature and pressure, making up for the deficiency of not explicitly considering the gravity effect based on Fick's law, and more fully reflecting the vertical differentiation and convection behavior caused by the density difference. Therefore, it can provide a more consistent calculation basis for the prediction of injection gas migration front and distribution pattern, injection parameter optimization and gas channeling risk assessment, and has the application value of improving the recovery of gas reservoirs and the safety of gas storage operation. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a schematic diagram of the physical model; Figure 2 is a diagram of the distribution of CH4 mole fraction with position under 10MPa; Figure 3 is a diagram of the distribution of CO2 mole fraction with position under 10MPa; Figure 4 is a program calculation block diagram. DETAILED DESCRIPTION

[0027] The present application will be further described below according to the drawings and examples, so that those skilled in the art can understand the present application. However, it should be clear that the present application is not limited to the scope of the specific embodiments, and for those skilled in the art, as long as various changes are within the spirit and scope of the present application as defined and limited by the appended claims, they are all within the protection scope.

[0028] The gravity-considered gas-gas diffusion concentration distribution calculation method of the present embodiment comprises the following steps in turn: S1. Consider a certain PVT cylinder containing two gases, CO2 and CH4, in a non-equilibrium state with known initial composition. Diffusion experiments are conducted under constant temperature conditions, with CO2 at the top of the PVT cylinder and natural gas at the bottom of the PVT cylinder. The specific content of the model assumptions is as follows: no chemical reaction occurs at the gas-gas interface; the mass flux of the components relative to the interface is continuous; the origin coordinate is located at the gas-gas interface, which is in equilibrium state, with the z-axis positive direction upward and the z-axis negative direction downward, as shown in the physical model schematic diagram. Figure 1

[0029] Table 1: Basic parameter table

[0030] S2 Based on the physical process of S1, consider molecular diffusion and gravity effect, at this time the total diffusion flux of the upper and lower gases J is: (1) S31. In Fick's second law, the basic driving force of the diffusion process is the concentration gradient, and the diffusion behavior of the gas is mainly controlled by the concentration gradient C, and the diffusion flux is: (3.1) S32. Since diffusion only occurs in the z direction, the concentration gradient is as follows: (3.2) S3. For molecular diffusion, based on Fick's second law, the concentration gradient is the basic driving force of the diffusion process, and under the action of this driving force, the diffusion flux is: (2) S4. The gas molecules in the system will be affected by gravity, and gravity will cause the sinking of gas molecules with higher density and the relative rising of gas molecules with lower density, which will greatly affect the mass transfer of molecules. The mass transfer flux caused by gravity is: (3) S51. and are the densities of the upper gas and the lower gas, respectively, is the difference in density between the two gases.

[0031] (5.1) S52. y 1 and y 2 are the mass fractions of the upper gas and the lower gas, respectively, ​The average density of the mixed gas is a weighted average of the densities of the two gases.

[0032] (5.2) S53. The average molar mass of the mixed gas is a weighted average of the molar masses of the two gases.

[0033] (5.3) S54. Based on Stokes' law, the upper gas is: (5.4) The lower gas is: (5.5) S61. The total flux in the diffusion process J is the sum of the diffusion flux driven by the concentration gradient and the drift flux caused by gravity. Substituting equation (2) and equation (3) into equation (1) gives: (6.1) S62. Substituting the total flux into the continuity equation gives: (6.2) S63. In the process of diffusion of two gases, the mass transfer equation of gas-gas with gravity effect is: (6.3) S6. In the process of diffusion of two gases, the mass transfer equation of gas-gas with gravity effect is: (5) S71. According to the gas-gas diffusion physical simulation process of S1, the initial condition for the upper gas is: (7.1) In the formula: represents the initial molar concentration of the upper gas, .

[0034] S72. The upper boundary of diffusion is a closed flux-free boundary, and the upper boundary condition is: (7.2) S73. In the process of gas-gas diffusion, the pressure of the whole system is constant, and the interface is in equilibrium state, and the lower boundary condition is: (7.3) S7. Combined with the physical simulation process of S1 and the mass transfer equation of S5, the upper gas diffusion model is as follows: (6) Similarly, the lower gas diffusion model can be expressed as: (7) S8. Let The upper gas diffusion model in S7 can be transformed into the following form by using the homogeneous boundary condition: (8) Where: .

[0035] Similarly, the lower gas diffusion model can be transformed into: (9) S91. The diffusion model is solved by using the separation of variables method, and let: (9.1) S92. Substitute equation (9.1) into equation (9) and divide both sides by , (9.2) S93. The general solution of the time part is: (9.3) S94. The spatial part differential equation is: (9.4) S95. The general solution of the spatial part is: (9.5) S96. Therefore, the solution of equation (8) is (9.6) S9 The upper gas model is solved by using the separation of variables method of mathematical physics, and the upper gas concentration function is as follows: z = L g1 = 0.0175 m, t = 3600 s as an example: (11) (10) Similarly, the concentration distribution function of the lower gas is calculated as: (13) (12) The CH4 and CO2 concentration distributions at different times and different positions are calculated by the upper and lower gas concentration distribution functions as Figure 2 andFigure 3 The results are shown in Table 2. S101. The concentration distribution of the upper gas and the lower gas is obtained by the gas-gas diffusion experiment.

[0036] S102. The initial values of the diffusion coefficients of the upper gas and the lower gas are given as 0.51x10 -8 m 2 / s and 0.38x10 - 8 m 2 / s, respectively.

[0037] S103. The concentration distribution of the upper and lower gas is calculated according to the formula (11) and formula (12), and it is determined by the least square method whether the difference between the model calculation value and the measured value is less than 10 -5 . If the difference is less than 10 -5 , the corresponding diffusion coefficient D is output.

[0038] (14) S104. If the difference between the model calculation value and the measured value is greater than 10 -5 , return to step S102, adjust the diffusion coefficient value again, and then perform subsequent calculation until the difference is less than 10 -5 . Details are shown in formula (13). Figure 4

[0039] Table 2 Diffusion coefficient data table of CH4 and CO2 at 10 MPa .​

Claims

1. A method for calculating gas-to-gas diffusion concentration distribution considering the influence of gravity, characterized in that, Includes the following steps: Step S1: Now consider a certain volume PVT cylinder containing two gases with known initial composition in a non-equilibrium state. The origin coordinates are located at the gas-gas interface, where the interface is in equilibrium. The upward direction is the positive z-axis, and the downward direction is the negative z-axis. Step S2: Based on S1, considering the effects of molecular diffusion and gravity, calculate the total diffusion flux of the upper and lower gas sections. J The expression is as follows: (1) In the formula: J For the total diffusion flux, ; The flux caused by molecular diffusion, ; For the flux caused by gravity, ; Step S3: Based on Fick's second law, the basic form of diffusion flux is: (2) In the formula: D Where is the diffusion coefficient. ; molar concentration, z is the position coordinate. ; Step S4: Gas molecules in the system are affected by gravity. The mass transfer flux caused by gravity is: (3) In the formula: The drift velocity caused by gravity, ; Step S5: Based on Stokes' law, the expression for the velocity of a gas caused by gravity is: (4) In the formula: D m is the diffusion coefficient. 2 / s; The acceleration due to gravity is m / s². 2 ; The density difference between the two gases, in kg / m³ 3 ; The average molar mass of the gas is expressed in kg / mol. The average density of the gas is kg / m³. 3 ; R The universal gas constant is 8.314 kg·m. 2 / (s 2 (·mol·K); T Temperature, K; Step S6: During the diffusion of the two gases, when gravity is involved, the gas-to-gas mass transfer equation is: (5) In the formula: t For diffusion time, ; Step S7: Combining the physical simulation process in Step S1 and the mass transfer equation in Step S5, the upper gas diffusion model takes the following form: (6) In the formula: the subscript 1 represents the upper part of the air; The initial molar concentration of the upper gas. ; This represents the molar concentration of the upper gas phase component at equilibrium at the gas-gas interface. ; This refers to the height at which the upper gas enters. m ; Step S8: Homogeneous boundary conditions. The upper gas diffusion model in step S7 can be transformed into the following form: (7) In the formula: As an additional attenuation term, satisfying ; For intermediate functions, satisfying ; For intermediate functions, satisfying ; Step S9: Using the mathematical physics method of separation of variables, the upper gas model is solved, and the expression for the upper gas concentration function is obtained as follows: (8) in: In the formula: These are the characteristic coefficients of the upper gas concentration function; Similarly, the expression for the lower gas concentration function can be obtained as follows: (9) in: In the formula: the subscript 2 represents the lower part of the gas; Step S10: Fit the experimental data using the least squares method to determine the diffusion coefficient considering the effect of gravity. D : (10) In the formula: The values ​​represent the gas molar concentrations calculated by the model. ; The values ​​are the gas molar concentrations measured in the experiment. .

2. The method for calculating gas-to-gas diffusion concentration distribution considering the influence of gravity according to claim 1, characterized in that, The process of step S3 is as follows: Step S31: In Fick's second law, the fundamental driving force of diffusion is the concentration gradient; the diffusion behavior of a gas is mainly driven by the concentration gradient. C-controlled diffusion flux expression is: (3.1) Step S32: Since diffusion only occurs in the z-direction, the concentration gradient... The expression is as follows: (3.2) Step S33: Substituting equation (3.2) into equation (3.1) yields: (2)。 3. The method for calculating gas-to-gas diffusion concentration distribution considering the influence of gravity according to claim 1, characterized in that, The process of step S5 is as follows: Step S51: and These are the densities of the upper and lower gas layers, respectively. The density difference between the two gases is expressed as follows: (5.1) Step S52: y 1 and y 2 represents the mass fractions of the upper and lower gas components, respectively. The average density of the gas mixture is obtained by weighting the densities of the two gases together. (5.2) Step S53: The average molar mass of the gas mixture is obtained by weighting the molar masses of the two gases together. (5.3) Step S54: Based on Stokes' law, The expression is: (5.4) Step S55: Substituting equations (5.1), (5.2), and (5.3) into equation (5.4) yields: (4)。 4. The method for calculating gas-to-gas diffusion concentration distribution considering the influence of gravity according to claim 1, characterized in that, The process of step S6 is as follows: Step S61: Total flux during the diffusion process J It is the sum of the diffusion flux driven by the concentration gradient and the drift flux caused by gravity. Substituting equations (2) and (3) into equation (1) yields: (6.1) Step S62: Substituting the total flux into the continuity equation, we obtain the following equation: (6.2) Step S63: During the diffusion of the two gases, the gas-to-gas mass transfer equation under the influence of gravity is: (6.3) Step S64: Assume Independent of position z, the final form of the mass transfer equation is: （5）。 5. The method for calculating gas-to-gas diffusion concentration distribution considering the influence of gravity according to claim 1, characterized in that, The process of step S7 is as follows: Step S71: Based on the gas-to-gas diffusion physical simulation process described in step S1, the initial conditions for the upper gas are as follows: (7.1) Step S72: The upper boundary of diffusion is a closed, flux-free boundary, and the upper boundary condition is: (7.2) Step S73: During the gas-to-gas diffusion process, the pressure of the entire system remains constant, the interface is in equilibrium, and the lower boundary condition is: (7.3) Step S74: Based on the initial conditions and boundary conditions, combined with equation (5), the upper gas diffusion model takes the following form: (6) Similarly, the lower gas diffusion model takes the following form: (7.4)。 6. The method for calculating gas-to-gas diffusion concentration distribution considering the influence of gravity according to claim 1, characterized in that, The process of step S8 is as follows: Step S81: Let After homogenizing the boundary conditions, equation (5) can be transformed into: (8.1) Step S82: Define We can obtain: (7) Similarly, the lower gas diffusion model can be transformed into: (8.2)。 7. The method for calculating gas-to-gas diffusion concentration distribution considering the influence of gravity according to claim 1, characterized in that, The process of step S9 is as follows: Step S91: Solve the diffusion model using the method of separation of variables. Let: (9.1) In the formula: X for z Functions in space; T for t A function of time; Step S92: Substitute equation (9.1) into equation (9) and divide both sides simultaneously. , (9.2) In the formula: These are parameters introduced to eliminate the convection term; Step S93: The general solution for the time part is: (9.3) In the formula: These are coefficients to be determined; Step S94: The spatial partial differential equation is: (9.4) Step S95: The general solution for the spatial part is: (9.5) In the formula: These are coefficients to be determined; These are coefficients to be determined; Step S96: Therefore, the solution to equation (7) is: (9.6) Step S97: Combining the initial conditions, boundary conditions, and equation (9.6), the expression for the upper gas concentration function can be obtained as follows: (8) in: (9) Similarly, the expression for the lower gas concentration function can be obtained as follows: (10) in: (11)。 8. The method for calculating gas-to-gas diffusion concentration distribution considering the influence of gravity according to claim 1, characterized in that, The process of step S10 is as follows: Step S101: Obtain the concentration distribution of the upper and lower gas through a gas-to-gas diffusion experiment; Step S102: Provide initial values ​​for the diffusion coefficients of the upper and lower gases. D g1 and D g2 ; Step S103: Calculate the concentration distribution of the upper and lower gases according to equations (8) and (10), and determine whether the difference between the model-calculated value and the experimentally measured value is less than 10 using the least squares method. -5 If the difference is less than 10 -5 Then the corresponding diffusion coefficient will be output. D ; (12) Step S104: If the difference between the model calculated value and the experimental measured value is greater than 10... -5 Then return to step S102, readjust the diffusion coefficient value, and perform subsequent calculations until the difference is less than 10. -5 until.

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