Natural gas hydrate exploitation simulation method and system with two coupled fluidization fields

Abstract

The invention provides a fluidization two-field coupled natural gas hydrate exploitation simulation method and system, and relates to the field of natural gas hydrate exploitation. A fluidization two-field coupled natural gas hydrate exploitation simulation method comprises the following steps: establishing a geometric model of a natural gas hydrate reservoir on the basis of reservoir parameters and physical parameters of the natural gas hydrate reservoir; based on a mass conservation equation, establishing a control equation set of the natural gas hydrate fluidization two-field coupling model; adjusting the control equation set based on the intrinsic dynamic behavior of the natural gas hydrate phase change decomposition and the two-phase seepage law of the natural gas hydrate to obtain a target control equation set; based on initial conditions and boundary conditions, solving the target control equation set to obtain two-phase seepage field and chemical decomposition field distribution; based on the distribution of the two-phase seepage field and the chemical decomposition field, calculating the accumulated decomposition, water production and gas production quality of the natural gas hydrate. Therefore, simulation accuracy can be improved, and engineering practicability is facilitated.

Description

Technical Field

[0001] The present disclosure relates to the field of natural gas hydrate exploitation, and particularly to a simulation method and system for natural gas hydrate exploitation coupling two fluidization processes. Background Art

[0002] Natural Gas Hydrate (NGH) is a cage-shaped crystalline compound formed by natural gas (mainly composed of methane) and water molecules under low-temperature and high-pressure conditions. Under standard conditions, 1 cubic meter of natural gas hydrate can decompose to produce approximately 164 cubic meters of natural gas and 0.8 cubic meters of water. Its energy density far exceeds that of compressed natural gas or liquefied natural gas of the same volume, and is several to more than a dozen times that of traditional fossil energy such as coal and oil. Due to its huge high energy density and resource reserves, natural gas hydrate is a new clean energy source with great potential.

[0003] Currently, the exploitation of natural gas hydrates faces many challenges. Among the numerous problems to be explored and solved, the issue of the impact of dynamic changes in reservoir parameters on production capacity has received particular attention. The existing technology mainly determines the impact of dynamic changes in reservoir parameters on production capacity through numerical simulation methods. The numerical simulation method can provide in real time the evolution characteristics of reservoir physical and chemical parameters that cannot be observed in on-site tests, can also solve the limitations of laboratory experiments, and has a highly flexible parameter sensitivity analysis ability. It can quickly adjust the initial reservoir conditions (such as hydrate saturation, sediment type, etc.) or exploitation schemes, quantitatively evaluate the contribution of different parameters to production capacity, and provide a theoretical basis for optimizing exploitation strategies.

[0004] However, the existing numerical simulation methods have problems such as simplified model assumptions and inaccurate boundary condition handling, difficult parameter acquisition with high uncertainty, high computational cost, complex models prone to errors, and limited engineering applications. The simulation accuracy is relatively low and it is not suitable for engineering practical use. Summary of the Invention

[0005] The present disclosure provides a simulation method and system for natural gas hydrate exploitation coupling two fluidization processes to at least solve the above technical problems existing in the prior art.

[0006] According to a first aspect of the present disclosure, a simulation method for exploiting natural gas hydrates by coupling two fluidization fields is provided, including: obtaining reservoir parameters and physical property parameters of a natural gas hydrate reservoir; establishing a geometric model of the natural gas hydrate reservoir based on the reservoir parameters and physical property parameters; establishing a control equation set for the two-fluidization-field coupling model of natural gas hydrates based on the law of conservation of mass; adjusting the control equation set based on the intrinsic kinetic behavior of the phase change decomposition of natural gas hydrates and the two-phase seepage law of natural gas hydrates to obtain a target control equation set; solving the target control equation set based on initial conditions and boundary conditions to obtain a two-phase seepage field and a chemical decomposition field; calculating the cumulative decomposition of natural gas hydrates, the mass of produced water and produced gas, and dynamically analyzing the influence of key parameters on the production capacity based on the two-phase seepage field and the chemical decomposition field.

[0007] In one implementable manner, the control equation set is:

[0008] Wherein, is expressed as:

[0009] Wherein, , , are the gas-phase density, the water-phase density and the natural gas hydrate density respectively; , and are the gas saturation, the water saturation and the natural gas hydrate saturation respectively; are the gas-phase viscosity and the water-phase viscosity respectively; is the alkane gas pressure; is the porosity; are the mass decomposition rate of natural gas hydrates, the mass generation rate of gas and the mass generation rate of water respectively; K is the dynamic permeability of the reservoir; , are the gas-phase relative permeability and the water-phase relative permeability respectively; is the inlet reference pressure; is a parameter related to the pore size distribution; is the effective water saturation; is the gradient operator; , are the irreducible water saturation and the irreducible gas saturation respectively; is the time.

[0010] In one implementable manner, the formula for adjusting the control equation set based on the intrinsic kinetic behavior of the phase change decomposition of natural gas hydrates is:

[0011] Among them, is the decomposition kinetic constant of natural gas hydrate, is the activation energy of hydrate decomposition; R is the ideal gas constant; T is the temperature of the porous medium; , , are the molar mass of natural gas hydrate, the molar mass of the gas phase and the molar mass of the aqueous phase, respectively; is the effective porosity of the reservoir; is the three-phase equilibrium pressure of natural gas hydrate; is the hydration number; Among them, , , ; Among them, , are the phase equilibrium pressure regression coefficients, respectively.

[0012] In an implementable manner, the formula for adjusting the control equation set based on the two-phase seepage law of natural gas hydrate is:

[0013] Among them, is the relative permeability coefficient; Among them, ; ; Among them, is the absolute permeability of the reservoir, is the permeability decline index.

[0014] In an implementable manner, the formula for the initial conditions is:

[0015] Among them, is the initial pressure of the hydrate reservoir, is the initial temperature of the hydrate reservoir, is the saturation of each phase of the hydrate, are the three coordinate axes of the space coordinate system.

[0016] In an implementable manner, the formula for the boundary conditions is:

[0017] Among them, is the gas phase pressure of natural gas hydrate; is the pressure of the production well; is the boundary water saturation.

[0018] In one possible implementation, the formulas for calculating the cumulative decomposition of natural gas hydrate, the mass of produced water and gas, and dynamically analyzing the influence of key parameters on production capacity are as follows:

[0019] Wherein, 、 and are respectively t i the cumulative decomposition mass of natural gas hydrate, the cumulative gas production of natural gas hydrate, and the cumulative water production of natural gas hydrate at time is the start time of hydrate decomposition; is the standard methane gas concentration.

[0020] According to the second aspect of the present disclosure, a simulation system for exploiting natural gas hydrate with a fluidized two-field coupling is provided, including: an acquisition module for acquiring reservoir parameters and physical property parameters of a natural gas hydrate reservoir; a model establishment module for establishing a geometric model of the natural gas hydrate reservoir based on the reservoir parameters and physical property parameters; an equation establishment module for establishing a control equation set of a natural gas hydrate fluidized two-field coupling model based on the law of conservation of mass; an adjustment module for adjusting the control equation set based on the intrinsic kinetic behavior of natural gas hydrate phase change decomposition and the two-phase seepage law of natural gas hydrate to obtain a target control equation set; a calculation module for solving the target control equation set based on initial conditions and boundary conditions to obtain a two-phase seepage field and a chemical decomposition field; the calculation module is further configured to calculate the cumulative decomposition of natural gas hydrate, the mass of produced water and gas, and dynamically analyze the influence of key parameters on production capacity based on the two-phase seepage field and the chemical decomposition field.

[0021] In one possible implementation, the equation establishment module is further configured to generate the following control equation set:

[0022] Wherein, is expressed as:

[0023] Wherein, 、 、 are the gas phase density, the water phase density, and the natural gas hydrate density respectively; 、 and are the gas saturation, the water saturation, and the natural gas hydrate saturation respectively; are the gas phase viscosity and the water phase viscosity respectively; is the alkane gas pressure; is the porosity; They are the mass decomposition rate of natural gas hydrate, the mass generation rate of gas, and the mass generation rate of water, respectively; K is the dynamic reservoir permeability; 、 They are the relative permeability of the gas phase and the relative permeability of the water phase, respectively; is the inlet reference pressure; is the parameter related to the pore size distribution; is the effective water saturation; is the gradient operator; 、 They are the irreducible water saturation and the irreducible gas saturation, respectively; is the time.

[0024] In an implementable embodiment, the adjustment module is used to adjust the control equations based on the intrinsic kinetic behavior of the phase change decomposition of natural gas hydrate through the following formula:

[0025] where, is the decomposition kinetic constant of natural gas hydrate, is the activation energy of hydrate decomposition; R is the ideal gas constant; T is the temperature of the porous medium; 、 、 They are the molar mass of natural gas hydrate, the molar mass of the gas phase, and the molar mass of water, respectively; is the effective porosity of the reservoir; is the three-phase equilibrium pressure of natural gas hydrate; is the hydration number; where, , , ; where, 、 They are the phase equilibrium pressure regression coefficients, respectively.

[0026] A simulation method and system for natural gas hydrate production coupling two fluidization fields according to the present disclosure, based on reservoir parameters and physical property parameters of a natural gas hydrate reservoir, establish a geometric model of the natural gas hydrate reservoir; based on the law of conservation of mass, establish a control equation set for the natural gas hydrate two-fluidization-field coupling model; based on the intrinsic kinetic behavior of natural gas hydrate phase change decomposition and the two-phase seepage law of natural gas hydrate, adjust the control equation set to obtain a target control equation set; based on initial conditions and boundary conditions, solve the target control equation set to obtain a two-phase seepage field and a chemical decomposition field; based on the two-phase seepage field and the chemical decomposition field, calculate the cumulative decomposition of natural gas hydrate, the mass of produced water and produced gas, and dynamically analyze the influence of key parameters on production capacity. Thereby, problems such as inaccurate model assumption simplification and boundary condition processing, difficult parameter acquisition with large uncertainties, high computational cost, complex model prone to errors, and limited engineering applications can be avoided, the simulation accuracy can be improved, and it is applicable to engineering practicality.

[0027] It should be understood that the content described in this part is not intended to identify the key or important features of the embodiments of the present disclosure, nor is it used to limit the scope of the present disclosure. Other features of the present disclosure will become easily understood through the following description. Brief Description of the Drawings

[0028] By reading the following detailed description with reference to the accompanying drawings, the above and other objects, features, and advantages of the exemplary embodiments of the present disclosure will become easily understood. In the drawings, several embodiments of the present disclosure are shown in an exemplary rather than restrictive manner, wherein: In the drawings, the same or corresponding reference numerals represent the same or corresponding parts.

[0029] Figure 1 A schematic flow chart showing a simulation method for natural gas hydrate production coupling two fluidization fields according to an embodiment of the present disclosure is shown; Figure 2 A schematic structural diagram showing a simulation system for natural gas hydrate production coupling two fluidization fields according to an embodiment of the present disclosure is shown. Detailed Embodiments

[0030] To make the purpose, features, and advantages of the present disclosure more obvious and understandable, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below with reference to the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present disclosure.

[0031] Figure 1 A schematic flow chart showing a simulation method for natural gas hydrate production coupling two fluidization fields according to an embodiment of the present disclosure is shown, asFigure 1 As shown in Figure 1 , a simulation method for natural gas hydrate production coupling two fluidization fields includes: Step S101, obtaining reservoir parameters and physical property parameters of the natural gas hydrate reservoir.

[0032] In this embodiment, at the initial stage of natural gas hydrate production simulation, various parameters of the natural gas hydrate reservoir need to be obtained, such as reservoir parameters and physical property parameters. Reservoir parameters mainly include reservoir pressure and reservoir temperature, etc. These parameters can reflect the basic energy state of the reservoir and the environmental conditions where substances are located; physical property parameters mainly include core radius, core length, phase saturations, absolute permeability, and phase densities, etc. These parameters describe the physical structure of the reservoir and the distribution of fluids from a microscopic perspective.

[0033] In an implementable manner, these parameters can be obtained through various means such as laboratory tests, field production tests, and literature research. For example, laboratory tests can measure the physical properties of the collected core samples through experimental analysis; field production tests can directly obtain the real-time parameters of the reservoir from the actual production process; literature research can refer to existing research results and data to provide basic data support for model establishment.

[0034] Step S102, establishing a geometric model of the natural gas hydrate reservoir based on the reservoir parameters and physical property parameters.

[0035] In this embodiment, after obtaining the reservoir parameters and physical property parameters, a geometric model of the natural gas hydrate reservoir needs to be constructed according to the reservoir parameters and physical property parameters. The geometric model is a mathematical description of the physical space structure of the reservoir and can provide a spatial framework for subsequent simulation calculations. The establishment of the geometric model needs to consider the shape and size of the reservoir. At the same time, parameters such as phase saturations also need to be reasonably distributed in the model to ensure that the model can truly reflect the actual situation of the reservoir. By establishing an accurate geometric model, an accurate spatial basis can be provided for subsequent fluid flow and chemical reaction simulations.

[0036] Step S103, establishing a control equation set for the natural gas hydrate fluidization two-field coupling model based on the law of conservation of mass.

[0037] In this embodiment, the control equation set is used to simulate the fluid flow and chemical reactions during the exploitation of natural gas hydrates. The control equation set is based on the law of conservation of mass and gas-related parameters (such as gas phase density, gas phase viscosity, gas phase pressure, etc.) and water-related parameters (such as water phase density, water phase viscosity, etc.) to describe the flow laws of gas and water phases in the reservoir. Specifically, the control equation set can include the mass conservation equation, the momentum conservation equation, the energy conservation equation, etc. Among them, the mass conservation equation is used to describe the change of the saturation of gas and water phases over time, reflecting the accumulation and consumption of fluids in the reservoir; the momentum conservation equation is used to describe the flow state of fluids in the reservoir, including the pressure distribution and velocity field of the fluids; the energy conservation equation is used to describe the heat transfer and conversion process in the reservoir, which is closely related to the decomposition process of natural gas hydrates. This embodiment is simplified and only the mass conservation equation is used to establish the control equation set, which can transform complex physical phenomena into mathematical problems and provide a basis for further solution and analysis.

[0038] Step S104: Based on the intrinsic kinetic behavior of the phase change decomposition of natural gas hydrates and the two-phase seepage law of natural gas hydrates, adjust the control equation set to obtain the target control equation set.

[0039] In this embodiment, the phase change decomposition of natural gas hydrates is a complex chemical reaction process, and its intrinsic kinetic behavior is affected by various factors. At the same time, the seepage law of gas and water phases in the reservoir also has an important impact on the exploitation process. Therefore, after establishing the initial control equation set, it is necessary to adjust the control equation set according to the intrinsic kinetic behavior of the phase change decomposition of natural gas hydrates and the two-phase seepage law. Specifically, it is necessary to incorporate kinetic parameters such as the chemical reaction rate and activation energy during the decomposition process of natural gas hydrates into the control equation set, and at the same time consider the influence of factors such as relative permeability and capillary pressure on fluid flow during the two-phase seepage process. Through this adjustment, the control equation set can more accurately reflect the physical and chemical phenomena during the exploitation of natural gas hydrates, thereby obtaining a target control equation set that is more in line with the actual situation.

[0040] Step S105: Based on the initial conditions and boundary conditions, solve the target control equation set to obtain the distribution of the two-phase seepage field and the chemical decomposition field.

[0041] In this embodiment, after establishing the target control equations, it is also necessary to determine the corresponding initial conditions and boundary conditions before solving can be carried out. The initial conditions include the initial pressure of the reservoir, the initial temperature, and the initial saturation of each phase, etc. These conditions reflect the initial state of the reservoir at the beginning of exploitation; the boundary conditions include the pressure of the production well, the boundary water saturation, etc. These conditions are used to describe the interaction between the reservoir and the external environment. After determining the initial conditions and boundary conditions, numerical calculation methods (such as the finite difference method, the finite element method, etc.) can be used to solve the target control equations, so as to obtain the distribution of the two-phase seepage field and the chemical decomposition field inside the reservoir, including information such as the pressure, saturation of the gas and water phases, and the decomposition rate of natural gas hydrate.

[0042] Step S106, based on the two-phase seepage field and the chemical decomposition field, calculate the cumulative decomposition of natural gas hydrate, the produced water and the produced gas quality, and at the same time dynamically analyze the influence of key parameters on the production capacity.

[0043] In this embodiment, after obtaining the distribution of the two-phase seepage field and the chemical decomposition field, the cumulative decomposition mass, the cumulative gas production and the cumulative water production of natural gas hydrate can be calculated according to these results. In one example, the cumulative decomposition mass, the cumulative gas production and the cumulative water production of natural gas hydrate can be calculated by integrating within the reservoir volume. For example, the cumulative decomposition mass can be obtained by integrating the decomposition rate of natural gas hydrate in time and space, which reflects the total decomposition amount of natural gas hydrate during the exploitation process; the cumulative gas production is calculated by integrating the gas phase generation rate, which represents the total amount of natural gas produced during the exploitation process; the cumulative water production is obtained by integrating the water phase generation rate, which reflects the total amount of water produced during the exploitation process. These calculation results can intuitively reflect the effect and efficiency of natural gas hydrate exploitation, and provide key data support for the evaluation and optimization of the exploitation plan.

[0044] In the present disclosure, a geometric model is established by obtaining reservoir parameters and physical property parameters, the control equations of the fluidization two-field coupling model are constructed based on the law of conservation of mass combined with gas-water related parameters, and adjusted according to the phase change decomposition kinetic behavior and the two-phase seepage law. Finally, the two-phase seepage field and the chemical decomposition field are solved, and then the cumulative decomposition mass, the cumulative gas production and the cumulative water production of natural gas hydrate are calculated. Moreover, the influence of key parameters on the production capacity can also be dynamically analyzed. Thus, it can accurately characterize the interaction mechanism between gas-water two-phase seepage and hydrate decomposition in the reservoir, overcome the deficiencies of the existing methods in the research on the influence mechanism of dynamic changes of reservoir parameters on the production capacity, provide a theoretical basis for optimizing the exploitation process parameters, help improve the exploitation efficiency, reduce uncertainty, promote the process of natural gas hydrate exploitation, and is applicable to engineering practical application.

[0045] In another embodiment, the control equations are as follows:

[0046] Wherein, Is expressed as:

[0047] Wherein, , , Are the gas-phase density, water-phase density, and natural gas hydrate density, respectively; , And Are the gas saturation, water saturation, and natural gas hydrate saturation, respectively; Are the gas-phase viscosity and water-phase viscosity, respectively; Is the alkane gas pressure; Is the porosity; Are the natural gas hydrate decomposition mass rate, gas generation mass rate, and water generation mass rate, respectively; K Is the reservoir dynamic permeability; , Are the gas-phase relative permeability and water-phase relative permeability, respectively; Is the inlet reference pressure; Is the pore size distribution related parameter; Is the effective water saturation; Is the gradient operator; , Are the irreducible water saturation and irreducible gas saturation, respectively; Is the time.

[0048] In another embodiment, the formula for adjusting the control equations based on the intrinsic kinetic behavior of natural gas hydrate phase change decomposition is:

[0049] Wherein, Is the natural gas hydrate decomposition kinetic constant, Is the hydrate decomposition activation energy; R Is the ideal gas constant; T Is the porous medium temperature; , , Are the natural gas hydrate molar mass, gas-phase molar mass, and water-phase molar mass, respectively; Is the reservoir effective porosity; Is the natural gas hydrate three-phase equilibrium pressure; Is the hydration number; Wherein, , , ; The ideal gas effect is considered, i.e., the influence of temperature and pressure on the gas density in the natural gas hydrate reservoir; The temperature and pressure relationship for the stable existence (solid phase) of natural gas hydrates is considered; The influence of the change in hydrate saturation caused by the phase change of natural gas hydrates on the effective porosity of the reservoir is considered.

[0050] Among them, 、 are the phase equilibrium pressure regression coefficients respectively.

[0051] In another embodiment, the formula for adjusting the control equations based on the two-phase seepage law of natural gas hydrates is:

[0052] Among them, is the relative permeability coefficient; Among them, ; ; Among them, The influence of the change in water saturation caused by the phase change of natural gas hydrates on the effective water saturation is considered, The influence of the change in hydrate saturation caused by the phase change of natural gas hydrates on the dynamic permeability of the reservoir is considered.

[0053] Among them, is the absolute permeability of the reservoir, is the permeability decline exponent.

[0054] In another embodiment, the formula for the initial conditions is:

[0055] Among them, is the initial pressure of the hydrate reservoir, is the initial temperature of the hydrate reservoir, is the saturation of each phase of the hydrate, are the three coordinate axes of the space coordinate system.

[0056] In another embodiment, the formula for the boundary conditions is:

[0057] Among them, is the gas phase pressure of natural gas hydrates (which can be used to replace the pore pressure of the hydrate reservoir under certain conditions); is the pressure of the production well; is the boundary water saturation.

[0058] In one feasible embodiment, the established geometric model, governing equations, initial conditions, and boundary conditions are imported into mathematical calculation software for solution, and the numerical solutions of the dependent variables of the governing equations (i.e., P g , S w , S h ) with respect to the changes over time and space can be obtained, thereby obtaining the distribution of the two-phase seepage field and chemical decomposition field inside the core.

[0059] In another embodiment, the formulas for calculating the cumulative decomposition of natural gas hydrate, water production, and gas production mass are as follows:

[0060] Wherein, , and are respectively the cumulative decomposition mass of natural gas hydrate, the cumulative gas production volume of natural gas hydrate, and the cumulative water production volume of natural gas hydrate at time t i ; is the start time of hydrate decomposition; is the standard methane gas concentration.

[0061] In one feasible embodiment, the data from the indoor depressurization production test of natural gas hydrate and those obtained in steps S101 to S106 can also be used for comparison to verify the reliability of the model. , and

[0062] In one feasible embodiment, the dynamic changes of key parameters in the model, including the production well pressure ( P out ), hydrate number ( N w ), initial absolute permeability ( K 0), pore size distribution of porous media ( ), initial water saturation ( S w0 ), initial gas saturation ( S g0 ), and different phase equilibrium conditions ( e 1, e 2) and other reservoir parameters on the production capacity change can be analyzed to identify key influencing factors, reduce uncertainties, and provide a theoretical basis for optimizing production process parameters.

[0063] In one feasible embodiment, the laboratory core scale can also be extended to the reservoir scale of field production to obtain the reservoir pressure ( P 0), production well pressure (P out ), initial saturation of reservoir hydrate ( S h0 ), initial water saturation of reservoir ( S w0 ), etc. By repeating steps S101 to S106, the cumulative decomposition mass of natural gas hydrate, the cumulative gas production volume of natural gas hydrate, and the cumulative water production volume of natural gas hydrate can be predicted.

[0064] Figure 2 FIG. shows a schematic structural diagram of a fluidized two-field coupled simulation system for natural gas hydrate production according to an embodiment of the present disclosure. As Figure 2 shown, a fluidized two-field coupled simulation system for natural gas hydrate production includes: An acquisition module 10 for acquiring reservoir parameters and physical property parameters of a natural gas hydrate reservoir; a model establishment module 11 for establishing a geometric model of the natural gas hydrate reservoir based on the reservoir parameters and physical property parameters; an equation establishment module 12 for establishing a control equation set of the fluidized two-field coupled model of natural gas hydrate based on gas-related parameters and water-related parameters; an adjustment module 13 for adjusting the control equation set based on the intrinsic kinetic behavior of natural gas hydrate phase change decomposition and the two-phase seepage law of natural gas hydrate to obtain a target control equation set; a calculation module 14 for solving the target control equation set based on initial conditions and boundary conditions to obtain a two-phase seepage field and a chemical decomposition field; the calculation module 14 is further configured to calculate the cumulative decomposition, water production, and gas production mass of natural gas hydrate based on the two-phase seepage field and the chemical decomposition field, and dynamically analyze the influence of key parameters on the production capacity.

[0065] In an implementable manner, the equation establishment module 12 is configured to generate the following control equation set:

[0066] Wherein, is expressed as:

[0067] Wherein, , , are the gas phase density, the water phase density, and the natural gas hydrate density respectively; , and are the gas saturation, the water saturation, and the natural gas hydrate saturation respectively; are the gas phase viscosity and the water phase viscosity respectively; is the alkane gas pressure; is the porosity; They are the decomposition mass rate of natural gas hydrate, the gas generation mass rate, and the water generation mass rate, respectively; K is the dynamic permeability of the reservoir; 、 are the gas-phase relative permeability and the water-phase relative permeability, respectively; is the inlet reference pressure; is the parameter related to the pore size distribution; is the effective water saturation; is the gradient operator; 、 are the irreducible water saturation and the irreducible gas saturation, respectively; is the time.

[0068] In an implementable manner, the adjustment module 13 is used to adjust the control equation set based on the intrinsic kinetic behavior of the phase change decomposition of natural gas hydrate through the following formula:

[0069] Among them, is the decomposition kinetic constant of natural gas hydrate, is the activation energy of hydrate decomposition; R is the ideal gas constant; T is the temperature of the porous medium; 、 、 are the molar mass of natural gas hydrate, the molar mass of the gas phase, and the molar mass of the water phase, respectively; is the effective porosity of the reservoir; is the three-phase equilibrium pressure of natural gas hydrate; is the hydration number; Among them, , , ; Among them, 、 are the phase equilibrium pressure regression coefficients, respectively.

[0070] In an implementable manner, the adjustment module 13 is used to adjust the control equation set based on the two-phase seepage law of natural gas hydrate through the following formula:

[0071] Among them, is the relative permeability coefficient; Among them, ; ; Among them, is the absolute permeability of the reservoir, is the permeability decline index.

[0072] In one implementable manner, the formula for the initial conditions in the calculation module 14 is as follows:

[0073] wherein, is the initial pressure of the hydrate reservoir; is the initial temperature of the hydrate reservoir; is the saturation of each phase of the hydrate; are the three coordinate axes of the space coordinate system.

[0074] In one implementable manner, the formula for the boundary conditions in the calculation module 14 is as follows:

[0075] wherein, is the gas-phase pressure of the natural gas hydrate; is the pressure of the production well; is the boundary water saturation.

[0076] In one implementable manner, the calculation module 14 calculates the cumulative decomposition, water production, and gas production mass of the natural gas hydrate based on the following formula:

[0077] wherein, , and are respectively t i the cumulative decomposition mass of the natural gas hydrate, the cumulative gas production of the natural gas hydrate, and the cumulative water production of the natural gas hydrate at time; is the start time of hydrate decomposition; is the standard methane gas concentration.

[0078] It should be understood that various forms of the processes shown above can be used, steps can be reordered, added, or deleted. For example, the steps described in this disclosure can be executed in parallel, sequentially, or in a different order, as long as the desired results of the technical solution of this disclosure can be achieved, and no limitations are imposed herein.

[0079] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of this disclosure, "a plurality" means two or more unless otherwise specifically defined.

[0080] As described above, this is only a specific embodiment of the present disclosure. However, the protection scope of the present disclosure is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present disclosure can easily think of changes or substitutions, which should all be covered within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be subject to the protection scope of the claims described above.

Claims

1. A simulation method for natural gas hydrate production by coupling two fluidization fields, characterized in that, Including: Obtain the reservoir parameters and physical property parameters of the natural gas hydrate reservoir; wherein, the reservoir parameters include reservoir pressure and reservoir temperature, and the physical property parameters include core radius, core length, saturation of each phase, absolute permeability, and density of each phase; Based on the reservoir parameters and physical property parameters, establish a geometric model of the natural gas hydrate reservoir; Based on the law of conservation of mass, establish a control equation set for the two-field coupling model of natural gas hydrate fluidization; Based on the intrinsic kinetic behavior of natural gas hydrate phase change decomposition and the two-phase seepage law of natural gas hydrate, adjust the control equation set to obtain a target control equation set; Based on the initial conditions and boundary conditions, solve the target control equation set to obtain a two-phase seepage field and a chemical decomposition field; Based on the two-phase seepage field and the chemical decomposition field, calculate the cumulative decomposition of natural gas hydrate, the mass of produced water and produced gas, and dynamically analyze the influence of key parameters on the production capacity.

2. The method according to claim 1, wherein The control equation set is: Among them, It is expressed as: wherein, 、 、 are the gas phase density, the aqueous phase density, and the natural gas hydrate density, respectively; 、 and are the gas saturation, the aqueous saturation, and the natural gas hydrate saturation, respectively; are the gas phase viscosity and the aqueous phase viscosity, respectively; is the gas pressure; is the porosity; are the natural gas hydrate decomposition mass rate, the gas generation mass rate, and the water generation mass rate, respectively; K is the reservoir dynamic permeability; 、 are the gas phase relative permeability and the aqueous phase relative permeability, respectively; is the inlet reference pressure; is the pore size distribution related parameter; is the effective water saturation; is the gradient operator; 、 are the irreducible water saturation and the irreducible gas saturation, respectively; is the time.

3. The method according to claim 2, wherein The formula for adjusting the control equation set based on the intrinsic kinetic behavior of natural gas hydrate phase change decomposition is: Among them, is the decomposition kinetic constant of natural gas hydrate, is the activation energy of hydrate decomposition; R is the ideal gas constant; T is the temperature of the porous medium; 、 、 are the molar mass of natural gas hydrate, the molar mass of the gas phase, and the molar mass of water respectively; is the effective porosity of the reservoir; is the three-phase equilibrium pressure of natural gas hydrate; is the hydration number; Among them, , , ; Among them, and are the regression coefficients of the phase equilibrium pressure respectively.

4. The method according to claim 2, wherein The formula for adjusting the control equation set based on the two-phase seepage law of natural gas hydrate is: wherein, is the relative permeability coefficient; Among them, ; ; Among them, is the absolute permeability of the reservoir, is the permeability decline index.

5. The method according to claim 1, characterized in that, The formula for the initial conditions is: wherein, is the initial pressure of the hydrate reservoir, is the initial temperature of the hydrate reservoir, is the saturation of each phase of the hydrate, are the three coordinate axes of the space coordinate system.

6. The method according to claim 1, wherein, The formula for the boundary conditions is: wherein, is the gas phase pressure of natural gas hydrate; is the pressure of the production well; is the boundary water saturation.

7. The method according to any one of claims 1 to 6, characterized in that, The formula for calculating the cumulative decomposition of natural gas hydrate, the mass of produced water and produced gas is as follows: Among them, , and are respectively t i the cumulative decomposition mass of natural gas hydrate, the cumulative gas production of natural gas hydrate, and the cumulative water production of natural gas hydrate at a certain moment; is the moment when the hydrate starts to decompose; is the standard methane gas concentration.

8. A simulation system for natural gas hydrate production with fluidization and two-field coupling, characterized in that, Including: An acquisition module for obtaining the reservoir parameters and physical property parameters of the natural gas hydrate reservoir; wherein, the reservoir parameters include reservoir pressure and reservoir temperature, and the physical property parameters include core radius, core length, saturation of each phase, absolute permeability, and density of each phase; A model establishment module for establishing a geometric model of the natural gas hydrate reservoir based on the reservoir parameters and physical property parameters; An equation establishment module for establishing a control equation set for the two-field coupling model of natural gas hydrate fluidization based on the law of conservation of mass; An adjustment module for adjusting the control equation set based on the intrinsic kinetic behavior of natural gas hydrate phase change decomposition and the two-phase seepage law of natural gas hydrate to obtain a target control equation set; A calculation module for solving the target control equation set based on the initial conditions and boundary conditions to obtain a two-phase seepage field and a chemical decomposition field; The calculation module is further used to calculate the cumulative decomposition of natural gas hydrate, the mass of produced water and produced gas based on the two-phase seepage field and the chemical decomposition field, and dynamically analyze the influence of key parameters on the production capacity.

9. The system according to claim 8, wherein, The equation establishment module is further used to generate the following control equation set: Among them, It is expressed as: wherein, , , are the gas-phase density, the aqueous-phase density, and the natural gas hydrate density, respectively; , and are the gas saturation, the aqueous saturation, and the natural gas hydrate saturation, respectively; are the gas-phase viscosity and the aqueous-phase viscosity, respectively; is the alkane gas pressure; is the porosity; are the natural gas hydrate decomposition mass rate, the gas generation mass rate, and the water generation mass rate, respectively; K is the reservoir dynamic permeability; , are the gas-phase relative permeability and the aqueous-phase relative permeability, respectively; is the inlet reference pressure; is the parameter related to the pore size distribution; is the effective aqueous saturation; is the gradient operator; , are the irreducible water saturation and the irreducible gas saturation, respectively; is the time.

10. The system according to claim 8, characterized in that, The adjustment module is used to adjust the control equation set based on the intrinsic kinetic behavior of natural gas hydrate phase change decomposition through the following formula: Among them, is the decomposition kinetic constant of natural gas hydrate, is the activation energy of hydrate decomposition; R is the ideal gas constant; T is the temperature of the porous medium; , , are the molar mass of natural gas hydrate, the molar mass of the gas phase and the molar mass of water respectively; is the effective porosity of the reservoir; is the three-phase equilibrium pressure of natural gas hydrate; is the hydration number; Among them, , , ; Among them, and are the regression coefficients of the phase equilibrium pressure respectively.

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