A numerical simulation method for gas-liquid two-phase flow considering desorption hysteresis of coal-bed methane

Abstract

The application discloses a kind of gas-liquid two-phase flow numerical simulation method considering coalbed gas desorption lag, comprising the following steps: using well logging, indoor experiment means to obtain productivity calculation parameter;Desorption equation of matrix system is defined in combination with desorption lag effect, diffusion equation;Gas-water two-phase percolation equation of fracture system is defined, and desorption equation of matrix system, diffusion equation is combined, and double medium gas-water two-phase coupling flow equation set is formed;The porosity and permeability change of matrix system and fracture system in production process is calculated respectively, and the physical property change equation set of double medium is deduced;Using the numerical solver of COMSOL, the coupling equation set is solved using iterative method, and the gas production and water production are calculated.The application is simple to operate, can more scientific and reasonable assess the influence of coalbed gas desorption lag effect on gas well productivity, while greatly reducing the cost and time of gas well numerical simulation calculation, and also has important inspiration for other unconventional gas reservoir development affected by desorption lag.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coalbed methane development, and particularly relates to a gas-liquid two-phase flow numerical simulation method considering coalbed methane desorption hysteresis. BACKGROUND

[0002] Coalbed methane resources are abundant in China and have broad development prospects. Coalbed methane mainly exists in coal matrix in adsorbed state, and is desorbed and diffused to the fracture system when the pressure decreases, and is transported to the production well through seepage. Compared with conventional natural gas reservoirs, coalbed methane reservoirs have obvious low porosity and low permeability characteristics, and their occurrence and migration are controlled by the heterogeneity of coal seams, stress sensitivity and desorption hysteresis effect. Desorption hysteresis effect refers to the hysteresis phenomenon between desorption process and adsorption process during the change of coalbed methane pressure. Specifically, when the pressure of coalbed methane decreases, the desorption process cannot be completely symmetrical with the adsorption process, and the desorption curve lags behind the adsorption curve, that is, the desorption process experiences a longer time delay than the adsorption process. This hysteresis phenomenon shows that the desorption process is affected by the pressure state, so that the coalbed methane cannot immediately reach a new equilibrium desorption state when the pressure changes. How to accurately evaluate the influence of desorption hysteresis on gas-liquid two-phase flow and then optimize the coalbed methane development plan is one of the current research focuses.

[0003] At present, engineers usually use numerical simulation methods to predict productivity and optimize analysis in the development of coalbed methane reservoirs. The mainstream commercial numerical simulation software (such as CMG, ECLIPSE, etc.) can simulate the seepage characteristics of coalbed methane by establishing a complex geological model and dividing fine grids. However, such software needs to model the dual medium characteristics and dynamic seepage mechanism of coal seams in the simulation process, which has a large amount of calculation, high requirements for computer hardware, and a long simulation process, and it is difficult to meet the needs of efficient decision-making in the development of coalbed methane. In addition, the traditional numerical simulation method is mainly based on the assumption of equilibrium desorption, and does not fully consider the dynamic influence of desorption hysteresis on gas-liquid two-phase flow, which leads to deviation of the prediction results and affects the optimization of the coalbed methane reservoir development plan. Therefore, in view of the desorption hysteresis effect of coalbed methane and the complex seepage mechanism of gas-liquid two-phase flow, it is necessary to develop a gas-liquid two-phase flow numerical simulation method considering coalbed methane desorption hysteresis, so as to improve the prediction accuracy of coalbed methane reservoir productivity and provide theoretical and technical support for the scientific development of coalbed methane. SUMMARY

[0004] To solve the above problems, the present application provides a gas-liquid two-phase flow numerical simulation method considering coalbed methane desorption hysteresis, which considers the desorption hysteresis effect of coalbed methane and the complex seepage mechanism of gas-liquid two-phase flow, and can reasonably evaluate the development of coalbed methane.

[0005] To achieve the above technical purposes, the present application adopts the following technical scheme:

[0006] A gas-liquid two-phase flow numerical simulation method considering coalbed methane desorption hysteresis, characterized in that it comprises the following steps:

[0007] S1: obtaining productivity prediction parameters by using well logging and laboratory experiments;

[0008] S2: establishing a calculation domain of a coalbed methane dual medium two-phase model in COMSOL, and defining a desorption equation and a diffusion equation of a matrix system in combination with a desorption hysteresis effect;

[0009] S3: defining a gas-water two-phase seepage flow equation of a fracture system by using a finite element method of COMSOL, and forming a dual medium two-phase coupling flow equation set in combination with the desorption equation and the diffusion equation of the matrix system;

[0010] S4: considering the desorption hysteresis effect and the gas-water two-phase seepage flow characteristics, calculating the porosity and the permeability changes of the matrix system and the fracture system respectively, and deducing a physical property change equation set of the dual medium;

[0011] S5: using a numerical solver of COMSOL, setting corresponding initial conditions, solving the coupling equation set in steps S2-S4 by using an iterative method, and obtaining gas production and water production through calculation.

[0012] Further, the steps S1-S5 have the following assumptions:

[0013] 1) The coal body is divided into a matrix and a fracture system, adsorbed gas mainly exists in the matrix system, the fracture is the main seepage channel of the fluid, and water only exists in the fracture system;

[0014] 2) The strain of the coal body is regarded as infinitesimal;

[0015] 3) Adsorbed gas desorbed from the matrix pore enters the fracture system and then flows into the wellbore;

[0016] 4) The effects of gravity and temperature are ignored;

[0017] 5) The gas is equivalent to an ideal gas, and its viscosity is constant during the flow process, and the water is an incompressible fluid;

[0018] 6) The adsorption of methane in the matrix is saturated adsorption.

[0019] Further, the productivity prediction parameters in step S1 include:

[0020] 1) coal seam parameters

[0021] coal seam length, coal seam width, coal seam thickness, coal seam density, matrix initial porosity, matrix initial permeability, fracture initial porosity, fracture initial permeability, coal seam temperature, coal seam initial pressure, coal seam Young's modulus, initial water saturation, irreducible water saturation;

[0022] 2) Adsorption and desorption parameters

[0023] Langmuir pressure, Langmuir volume, desorption hysteresis coefficient;

[0024] 3) Fluid parameters

[0025] Methane viscosity, methane density, water viscosity, water density, bottom hole flowing pressure, standard temperature.

[0026] Further, the desorption equation of the matrix system in step S2 is:

[0027] W de = W ad +a·exp(b·p m )

[0028] In the formula, a is a hysteresis gas content coefficient, m 3 / kg; b is a hysteresis gas pressure coefficient, MPa -1 , the coefficients a and b can be fitted in actual experimental adsorption and desorption experiments. p m is the pressure of the matrix system, MPa; W de is the gas content when the coal rock desorbs, m 3 / kg, W ad is the adsorbed gas content in the coal seam, m 3 / kg, which can be defined by the following formula:

[0029]

[0030] In the formula, V L is the Langmuir volume constant of the adsorption process, m 3 / kg; P L is the Langmuir pressure constant of the adsorption process, MPa; V L-de is the Langmuir volume constant of the desorption process, m 3 / kg; P L-de is the Langmuir pressure constant of the desorption process, MPa; W re is the residual adsorption amount, m 3 / kg.

[0031] The desorption hysteresis pressure is a threshold pressure in the desorption state, defined as p q , MPa, which can be calculated according to the following formula:

[0032]

[0033] In the formula, ρ c is the density of coal rock, kg / m 3 ; VM Gas molar volume of methane, m 3 / mol; R is gas molar constant, J / (mol-K); T is temperature, K

[0034] According to Fick diffusion law, the gas mass conservation equation in matrix is:

[0035]

[0036] where Q m = Dσ c (c m -c f ), represents the mass transfer rate of methane between matrix and fracture system, kg / (m 3 ·s); m m is the mass of methane in unit volume of coal matrix, kg / m 3 . σ c is the shape factor of coal rock matrix, m -2 , defined as L is the fracture spacing, m; D is the diffusion coefficient, m 2 / s.

[0037] c m and c f are the concentrations of methane in matrix and in fracture system, kg / m 3 . According to ideal gas law:

[0038]

[0039] where M g is the molar mass of methane, kg / mol; p fg is the gas pressure in fracture system, MPa. Considering the desorption hysteresis effect, the mass transfer rate of methane between matrix and fracture system is:

[0040]

[0041] The adsorbed gas in matrix is represented by Langmuir equation, and the free gas satisfies ideal gas state equation. The total gas content in matrix system can be calculated by:

[0042]

[0043] where φ m is the matrix porosity, dimensionless.

[0044] Further, the diffusion equation of matrix system in step S2 is:

[0045]

[0046] Further, the gas-water two-phase percolation equation of the fracture system in step S3 can be written as:

[0047]

[0048] wherein m g = ρ g φ f S g represents the mass of free gas in the fracture per unit volume of coal, kg / m 3 ; m w = ρ w φ f S w represents the mass of water in the fracture per unit volume of coal, kg / m 3 ; ρ g is the gas density, kg / m 3 ; ρ w is the water density, kg / m 3 ; S g and S w are the gas and water saturations, respectively, dimensionless; φ f is the porosity of the fracture, dimensionless; k f is the permeability of the fracture, mD; μ g and μ w are the dynamic viscosities of methane and water, respectively, Pa·s; b1 is the Klinkenberg coefficient, Pa; k rg and k rw are the relative permeabilities of the gas and water phases, respectively, dimensionless; and p fw is the water phase partial pressure of the fracture system.

[0049] The gas-water relative permeability of the fracture system can be given by the following formula:

[0050]

[0051] wherein m is the relative permeability fitting coefficient, dimensionless, and in the present study, m = 0.65; S e is the effective water saturation, dimensionless, and can be defined by the following formula:

[0052]

[0053] wherein S wr is the residual water saturation, and S gr is the residual gas saturation.

[0054] Further, the two-phase coupled flow equation set of the dual medium in step S3 is:

[0055]

[0056] Further, the step S4 considers desorption hysteresis, the matrix system porosity change can be expressed as follows:

[0057]

[0058] Where S = ε V + (p m / K s )- ε sq , ε V is the volumetric strain of coal, dimensionless; K s is the volumetric modulus of coal skeleton, GPa; ε sq represents the strain when gas desorbs, ε sq = α sg W de , dimensionless; α sg is the matrix expansion coefficient, kg / m 3 , wherein subscript '0' represents the initial value of the strain.

[0059] Further, the step S4 considers desorption hysteresis, the fracture system porosity change can be expressed as follows

[0060]

[0061] Where M is the axial constraint modulus, MPa, M = E (1-v) / [(1+v) (1-2v)]. Considering the cubic law between the permeability and porosity of porous media, the matrix and fracture system permeability can be expressed as:

[0062]

[0063] Further, the step S5 calculates the gas and water production formula as:

[0064]

[0065] Where Q g and Q w are the daily gas and water production, m 3 ; and are the average pressure of gas and water phases, MPa; p wf is the bottom hole flowing pressure, MPa; r w is the wellbore radius, m; r e is the drainage radius, m; S is the skin factor.

[0066] The application provides a gas-liquid two-phase flow numerical simulation method considering coalbed gas desorption hysteresis, combines logging and experimental data, defines a desorption equation of a matrix system, a diffusion equation and a gas-water two-phase percolation equation of a fracture system, forms a double medium gas-water two-phase coupling flow equation set, iteratively solves the coupling equation set based on COMSOL software, and calculates gas production and water production.

[0067] Beneficial effects:

[0068] Compared with the prior art, the application has the following beneficial effects:

[0069] The COMSOL software is used to quickly simulate gas-liquid two-phase flow under different desorption hysteresis characteristics, and the model accuracy is checked in combination with coalbed gas well production data. The method can more scientifically and reasonably evaluate the influence of desorption hysteresis effect on coalbed gas well productivity, improve numerical simulation calculation precision, and greatly reduce calculation cost and time. BRIEF DESCRIPTION OF DRAWINGS

[0070] Figure 1 A comparison chart of predicted production of a straight well and production data. DETAILED DESCRIPTION

[0071] In order to make the purpose, technical scheme and advantages of the application clearer, the application is further described in detail below in combination with examples.

[0072] Example:

[0073] A gas-liquid two-phase flow numerical simulation method considering coalbed gas desorption hysteresis, characterized in that the method comprises the following steps:

[0074] S1: Obtain productivity prediction parameters by using logging and indoor experiments;

[0075] The productivity calculation parameters comprise:

[0076] 1) Coalbed parameters

[0077] Coal seam length, coal seam width, coal seam thickness, coal seam density, matrix initial porosity, matrix initial permeability, fracture initial porosity, fracture initial permeability, coal seam temperature, coal seam initial pressure, coal seam Young's modulus, initial water saturation, irreducible water saturation;

[0078] 2) Adsorption and desorption parameters

[0079] Langmuir pressure, Langmuir volume, desorption hysteresis coefficient;

[0080] 3) Fluid parameters

[0081] Methane viscosity, methane density, water viscosity, water density, bottom hole flowing pressure, standard temperature.

[0082] S2: Establish the calculation domain of the coalbed methane dual medium two-phase model in COMSOL, and define the desorption equation and diffusion equation of the matrix system in combination with the desorption hysteresis effect;

[0083] The desorption equation of the matrix system is:

[0084] W de =W ad +a·exp(b·p m )

[0085] In the formula, a is a hysteresis gas content coefficient, m 3 / kg; b is a hysteresis gas pressure coefficient, MPa -1 , and the coefficients a and b can be fitted in actual experimental adsorption and desorption experiments. p m is the pressure of the matrix system, MPa; W de is the gas content when the coal rock desorbs, m 3 / kg, and W ad is the adsorbed gas content in the coal seam, m 3 / kg, which can be defined by the following formula:

[0086]

[0087] In the formula, V L is the Langmuir volume constant of the adsorption process, m 3 / kg; P L is the Langmuir pressure constant of the adsorption process, MPa; V L-de is the Langmuir volume constant of the desorption process, m 3 / kg; P L-de is the Langmuir pressure constant of the desorption process, MPa; W re is the residual adsorption amount, m 3 / kg.

[0088] The desorption hysteresis pressure is a threshold pressure in the desorption state, defined as p q , MPa, which can be calculated according to the following formula:

[0089]

[0090] where p c is the density of coal rock, kg / m 3 ; V M is the gas molar volume of methane, m 3 / mol; R is the gas molar constant, J / (mol·K); and T is the temperature, K

[0091] According to the Fick diffusion law, the gas mass conservation equation in the matrix is as follows:

[0092]

[0093] where Q m = Dσ c (c m -c f ), represents the mass transfer rate of methane between the matrix and the fissure system, kg / (m 3 ·s); m m is the mass of methane per unit volume of coal matrix, kg / m 3 . σ c is the shape factor of the coal rock matrix, m -2 , defined as L is the fissure spacing, m; and D is the diffusion coefficient, m 2 / s.

[0094] c m and c f are the concentrations of methane in the matrix and in the fissure system, respectively, kg / m 3 . According to the ideal gas law:

[0095]

[0096] where M g is the molar mass of methane, kg / mol; and p fg is the gas pressure in the fissure system, MPa. Considering the desorption hysteresis effect, the mass transfer rate of methane between the matrix and the fissure system is obtained as:

[0097]

[0098] The adsorbed gas in the matrix is represented by the Langmuir equation, and the free gas satisfies the ideal gas state equation. The total gas content in the matrix system can be calculated according to the following formula:

[0099]

[0100] where φ m is the matrix porosity, dimensionless.

[0101] The diffusion equation for the matrix system is:

[0102]

[0103] S3: Using the finite element method of COMSOL, the gas-water two-phase flow equation of the fracture system is defined, and combined with the desorption equation and diffusion equation of the matrix system, the two-phase coupling flow equation set of double medium is formed;

[0104] The gas-water two-phase flow equation of the fracture system can be written as:

[0105]

[0106] where m g = ρ g φ f S g , represents the mass of free gas in the fracture per unit volume of coal, kg / m 3 ; m w = ρ w φ f S w , represents the mass of water in the fracture per unit volume of coal, kg / m 3 ; ρ g is the gas density, kg / m 3 ; ρ w is the water density, kg / m 3 ; S g and S w are the gas and water saturation, respectively, dimensionless; φ f is the porosity of the fracture, dimensionless; k f is the fracture permeability, mD; μ g and μ w are the dynamic viscosities of methane and water, respectively, Pa·s; b1 is the Klinkenberg coefficient, Pa; k rg and k rw are the relative permeabilities of gas and water phases, respectively, dimensionless; p fw is the water phase partial pressure of the fracture system.

[0107] The gas-water relative permeability of the fracture system can be given by:

[0108]

[0109] where m is the relative permeability fitting coefficient, dimensionless, m = 0.65 in this study; S eFor effective water saturation, dimensionless, can be defined by the following formula:

[0110]

[0111] In the formula S wr is the residual water saturation, S gr is the residual gas saturation.

[0112] The two-phase coupling flow equation of dual media is:

[0113]

[0114] S4: Considering the desorption hysteresis effect and the gas-water two-phase seepage characteristics, the porosity and permeability changes of the matrix system and the fracture system are calculated respectively, and the physical property change equation set of dual media is derived;

[0115] Considering desorption hysteresis, the change of matrix system porosity can be expressed as follows:

[0116]

[0117] Where S = ε V +(p m / K s )-ε sq , ε V is the volumetric strain of coal, dimensionless; K s is the volumetric modulus of coal skeleton, GPa; ε sq represents the strain during gas desorption, ε sq = α sg W de , dimensionless; α sg is the matrix expansion coefficient, kg / m 3 , in which subscript '0' represents the initial value of the strain variable.

[0118] Considering desorption hysteresis, the change of fracture system porosity can be expressed as follows

[0119]

[0120] In the formula, M is the axial constraint modulus, MPa, M = E(1-v) / [(1+v)(1-2v)]. Considering the cubic law between the permeability and porosity of porous media, the permeability of matrix and fracture system can be expressed as:

[0121]

[0122] S5: Using the numerical solver of COMSOL, setting the corresponding initial conditions, solving the coupling equation set in steps S2-S4 by iteration method, and obtaining the gas and water production through calculation.

[0123] The gas and water production formula is:

[0124]

[0125] Where Q g and Q w are the daily gas and water production, m 3 ; and are the average pressure of gas phase and water phase, MPa; p wf is the bottom hole flowing pressure, MPa; r w is the wellbore radius, m; r e is the drainage radius, m; and S is the skin factor.

[0126] The steps S1-S5 have the following assumptions:

[0127] 1) The coal body is divided into two systems of matrix and fissure, the adsorbed gas mainly exists in the matrix system, the fissure is the main seepage channel of fluid, and water only exists in the fissure system;

[0128] 2) The strain of the coal body is regarded as infinitesimal;

[0129] 3) The adsorbed gas is desorbed from the matrix pore and enters the fissure system, and then flows into the wellbore;

[0130] 4) The effects of gravity and temperature are ignored;

[0131] 5) The gas is equivalent to an ideal gas, and its viscosity is constant during the flow process, and the water is an incompressible fluid;

[0132] 6) The adsorption of methane in the matrix is saturated adsorption.

[0133] Example 1

[0134] The data used in this example are from No. 1 well in the south area of Fanshuang block in Qinshui Basin. The calculation parameters are shown in the following table.

[0135] Table 1 Calculation parameters

[0136]

[0137] According to the present application, using the calculation data in Table 1, the time step is set to 1 day, and the total time length is 1000 days, and the daily gas and water production of the production well is calculated. Figure 1 The comparison of the horizontal well daily production calculated by the method of the present application with the actual production is shown, and Figure 1 It can be seen that the result calculated by the method of the present application is highly consistent with the actual data, which verifies the accuracy of the method of the present application.

[0138] The application provides a gas-liquid two-phase flow numerical simulation method considering coalbed gas desorption hysteresis, which combines logging and experimental data, defines desorption and diffusion equations of a matrix system and gas-water two-phase percolation equations of a fracture system according to desorption hysteresis effect, forms a double medium two-phase coupling flow equation set, iteratively solves the coupling equation set based on COMSOL software, and obtains gas production and water production through calculation. The application is simple to operate, can more scientifically and reasonably evaluate the influence of coalbed gas desorption hysteresis effect on gas well productivity, greatly reduces the numerical simulation calculation cost and time of the gas well, and has important enlightenment for the development of other unconventional gas reservoirs affected by desorption hysteresis.

[0139] The above description is not intended to limit the application in any form, although the application has been disclosed by the above examples. However, it is not intended to limit the application. Any person skilled in the art can make some changes or modifications to the equivalent examples of equivalent changes within the scope of the technical solutions of the application by using the disclosed technical content. Any simple modification, equivalent change and modification made to the above examples according to the technical essence of the application are still within the scope of the technical solutions of the application.

Claims

1. A numerical simulation method for gas-liquid two-phase flow considering the desorption hysteresis of coalbed methane, characterized in that, Includes the following steps: S1: Obtain production capacity prediction parameters by using well logging and laboratory experiments; S2: Establish the computational domain of the coalbed methane dual-medium two-phase model in COMSOL, and define the desorption equation and diffusion equation of the matrix system in combination with the desorption hysteresis effect; S3: Using the finite element method of COMSOL, the gas-water two-phase flow equation of the fracture system is defined, and combined with the desorption and diffusion equations of the matrix system, a set of two-phase coupled flow equations of dual media is formed. S4: Considering the desorption hysteresis effect and the gas-water two-phase flow characteristics, calculate the porosity and permeability changes of the matrix system and the fracture system respectively, and derive the equation set of physical property changes of the dual media. S5: Using the COMSOL numerical solver, set the corresponding initial conditions, and use the iterative method to solve the coupled equations in steps S2-S4, and calculate the gas production and water production. The following assumptions apply to steps S1 to S5: 1) The coal body is divided into two systems: matrix and fracture. Adsorbed gas mainly exists in the matrix system, while the fractures are the main seepage channels for fluids. Water only exists in the fracture system. 2) The strain of the coal body is considered infinitesimal; 3) The adsorbed gas desorbs from the matrix pores and enters the fracture system, then flows into the wellbore; 4) Ignore the effects of gravity and temperature; 5) The gas is equivalent to an ideal gas, and its viscosity remains unchanged during the flow process; water is an incompressible fluid. 6) The adsorption of methane in the matrix is ​​saturated adsorption; The desorption equation for the matrix system in step S2 is: W de =W ad +a·exp(b·p m ) In the formula, a is the hysteresis gas content coefficient, and m 3 / kg; b is the hysteresis gas pressure coefficient, MPa -1 The coefficients a and b can be fitted in actual adsorption and desorption experiments; p m The pressure of the matrix system is MPa; W de The gas content during coal and rock desorption, m 3 / kg, W ad The adsorbed gas content within the coal seam, m 3 / kg can be defined by the following formula: In the formula V L Let m be the Langmuir volume constant for the adsorption process. 3 / kg; P L V represents the Langmuir pressure constant for the adsorption process, in MPa; L-de Let m be the Langmuir volume constant for the desorption process. 3 / kg; P L-de Let be the Langmuir pressure constant for the desorption process, in MPa; W re m represents the residual adsorption amount. 3 / kg; The desorption hysteresis pressure in the desorption state manifests as a threshold pressure, defined as p. q MPa can be calculated using the following formula: In the formula ρ c The density of coal and rock is kg / m³. 3 V M m is the molar volume of methane gas. 3 / mol; R is the gas molar constant, J / (mol·K); T is the temperature, K. According to Fick's diffusion law, the mass conservation equation for the gas in the matrix is: Q m =Dσ c (c m -c f ), representing the mass transfer rate of methane between the matrix and fractured systems, kg / (m³). 3 ·s);m m The mass of methane per unit volume of coal matrix, kg / m³ 3 ; σ c It is the shape factor of the coal and rock matrix, m -2 Defined as L is the crack spacing, in meters; D is the diffusion coefficient, in meters. 2 / s; c m and c f The concentrations of methane in the matrix and in the fractured system are shown in kg / m³. 3 According to the ideal gas law: In the formula M g p is the molar mass of methane, kg / mol; fg Let be the gas pressure within the fractured system, in MPa; considering the desorption hysteresis effect, the mass transfer rate of methane between the matrix and the fractured system is: Adsorbed gases within the matrix are represented by the Langmuir equation, while free gases satisfy the ideal gas law. The total gas content within the matrix system can be calculated using the following formula: In the formula φ m The matrix porosity is dimensionless. The diffusion equation for the matrix system is: This equation can be used to characterize the diffusion behavior of gases in a matrix system.

2. The numerical simulation method for gas-liquid two-phase flow considering the desorption hysteresis of coalbed methane as described in claim 1, characterized in that, The capacity prediction parameters in step S1 include: 1) Coal seam parameters Coal seam length, coal seam width, coal seam thickness, coal seam density, initial matrix porosity, initial matrix permeability, initial fracture porosity, initial fracture permeability, coal seam temperature, initial coal seam pressure, coal seam Young's modulus, initial water saturation, and bound water saturation. 2) Adsorption and desorption parameters Langmuir pressure, Langmuir volume, desorption hysteresis coefficient; 3) Fluid parameters Methane viscosity, methane density, water viscosity, water density, bottom hole flowing pressure, standard temperature.

3. The numerical simulation method for gas-liquid two-phase flow considering the desorption hysteresis of coalbed methane as described in claim 1, characterized in that, The gas-water two-phase flow equation for the fractured system in step S3 can be written as follows: In the formula m g =ρ g φ f S g This represents the mass of free gas in the fissures of each volume of coal, expressed in kg / m³. 3 ; m w =ρ w φ f S w This represents the mass of water in the fissures of each volume of coal, expressed in kg / m³. 3 ; ρ g The density of the gas is kg / m³. 3 ; ρ w The density of water is kg / m³. 3 ; S g and S w These represent the gas content and water saturation, respectively, dimensionless; φ f k represents the porosity of the fracture, which is dimensionless. f For fracture permeability, mD; μ g and μ w λm and λwater are the dynamic viscosity of methane and water, respectively, in Pa·s; b1 is the Klinkenberg coefficient, in Pa; km is the dynamic viscosity of methane and water, respectively. rg and k rw p represents the relative permeability of the gas phase and the aqueous phase, respectively, dimensionless; fw The partial pressure of the water phase in the fractured system; The relative permeability of air and water in a fractured system can be given by the following formula: In the formula, m is the relative permeability fitting coefficient, which is dimensionless and is taken as m = 0.65 in this study; S e Effective water saturation, dimensionless, can be defined by the following formula: In the formula S wr S represents the residual water saturation. gr Residual gas saturation; The equations for two-phase coupled flow in a dual-medium medium are as follows: The above formula can characterize the flow law of two-phase coupling in a dual-medium medium.

4. The numerical simulation method for gas-liquid two-phase flow considering the desorption hysteresis of coalbed methane as described in claim 3, characterized in that, Considering desorption hysteresis in step S4, the change in porosity of the matrix system can be expressed as follows: Where S = ε V +(p m / K s )-ε sq , ε V K represents the volumetric strain of coal, which is dimensionless. s ε is the bulk modulus of the coal skeleton, in GPa; sq ε represents the strain during gas desorption. sq =α sg W de , dimensionless; α sg The matrix expansion coefficient is expressed in kg / m³. 3 In the formula, the subscript '0' indicates the initial value of the corresponding variable; Considering desorption hysteresis, the porosity change in a fractured system can be expressed as follows: In the formula, M is the axial constraint modulus, MPa, M=E(1-v) / [(1+v)(1-2v)]; considering the cubic law between the permeability and porosity of porous media, the permeability of the matrix and fractured system can be expressed as: This set of equations is the formula for calculating the permeability of the matrix and fracture system.

5. The numerical simulation method for gas-liquid two-phase flow considering the desorption hysteresis of coalbed methane as described in claim 4, characterized in that, The formula for calculating gas-water production in step S5 is as follows: Q g and Q w These represent daily gas production and daily water production, in m. 3 ; and The average pressures of the gas phase and the aqueous phase are respectively, in MPa; p wf The bottom hole flowing pressure is in MPa; r w r is the radius of the wellbore, in meters (m). e Where is the drainage radius, in meters; S is the epidermal coefficient.

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