A natural gas hydrate production simulation method and system with fluidization and two-field coupling

Abstract

The present disclosure provides a fluidized two-field coupled natural gas hydrate mining simulation method and system, relating to the field of natural gas hydrate mining. A fluidized two-field coupled natural gas hydrate mining simulation method includes: establishing a geometric model of the natural gas hydrate reservoir based on the reservoir parameters and physical property parameters of the natural gas hydrate reservoir; establishing a control equation group of the natural gas hydrate fluidized two-field coupled model based on the mass conservation equation; adjusting the control equation group 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 group; solving the target control equation group based on initial conditions and boundary conditions to obtain the two-phase seepage field and chemical decomposition field distribution; and calculating the cumulative decomposition, water production, and gas production quality of the natural gas hydrate based on the two-phase seepage field and chemical decomposition field distribution. This can improve the simulation accuracy and facilitate engineering practicality.

Description

Technical Field

[0001] The present disclosure relates to the field of natural gas hydrate production, and in particular to a natural gas hydrate production simulation method and system with fluidization and two-field coupling. Background Art

[0002] Natural gas hydrate (NGH) is a cage-shaped crystalline compound formed by natural gas (primarily methane) and water molecules under low temperature and high pressure. Under standard conditions, one cubic meter of natural gas hydrate decomposes to produce approximately 164 cubic meters of natural gas and 0.8 cubic meters of water. Its energy density far exceeds that of the same volume of compressed natural gas or liquefied natural gas, and is several to dozens of times higher than that of traditional fossil fuels such as coal and oil. Due to its enormous energy density and resource reserves, natural gas hydrates represent a highly promising new clean energy source.

[0003] Currently, natural gas hydrate extraction faces numerous challenges. Among the many challenges awaiting exploration and resolution, the impact of dynamic changes in reservoir parameters on productivity has received particular attention and attention. Existing technologies primarily use numerical simulation methods to determine the impact of dynamic changes in reservoir parameters on productivity. These methods can provide real-time insights into the evolution of reservoir physical and chemical parameters that cannot be observed in field experiments, addressing the limitations of laboratory experiments, and offer highly flexible parameter sensitivity analysis capabilities. These methods can rapidly adjust reservoir initial conditions (such as hydrate saturation and sediment type) or extraction plans, quantitatively assess the contribution of different parameters to productivity, and provide a theoretical basis for optimizing extraction strategies.

[0004] However, existing numerical simulation methods have problems such as inaccurate simplification of model assumptions and boundary condition processing, difficulty in obtaining parameters and large uncertainty, high computational cost, complex models and prone to errors, which limit engineering applications. The simulation accuracy is low and it is not suitable for engineering practical application. Summary of the Invention

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

[0006] According to a first aspect of the present disclosure, a fluidization two-field coupled natural gas hydrate production simulation method is provided, comprising: 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 group of a natural gas hydrate fluidization two-field coupled model based on the law of conservation of mass; adjusting the control equation group 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 group; solving the target control equation group based on initial conditions and boundary conditions to obtain a two-phase seepage field and a chemical decomposition field; calculating the cumulative decomposition, water production and gas production quality of natural gas hydrates based on the two-phase seepage field and the chemical decomposition field, and dynamically analyzing the influence of key parameters on production capacity.

[0007] In one embodiment, the control equations are:

[0008]

[0009] in, Expressed as:

[0010]

[0011] in, 、 、 are the gas phase density, water phase density and gas hydrate density respectively; 、 and are gas saturation, water saturation, and 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 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 irreducible water saturation and irreducible gas saturation, respectively; For time.

[0012] In one embodiment, the formula for adjusting the control equations based on the intrinsic kinetic behavior of the natural gas hydrate phase transition decomposition is:

[0013]

[0014] in, is the kinetic constant for the decomposition of natural gas hydrate, is the activation energy for hydrate decomposition; R is the ideal gas constant; T is the porous medium temperature; 、 、 are the gas hydrate molar mass, gas phase molar mass, and water phase molar mass, respectively; is the effective porosity of the reservoir; is the three-phase equilibrium pressure of natural gas hydrate; is the hydration number;

[0015] in, , , ;

[0016] in, 、 are the phase equilibrium pressure regression coefficients, respectively.

[0017] In one embodiment, the formula for adjusting the control equations based on the two-phase seepage law of natural gas hydrate is:

[0018]

[0019] in, is the relative permeability coefficient;

[0020] in, ; ;

[0021] in, is the absolute permeability of the reservoir, is the permeability reduction index.

[0022] In one embodiment, the formula for the initial condition is:

[0023]

[0024] in, is the initial pressure of the hydrate reservoir, is the initial temperature of the hydrate reservoir, is the saturation of each hydrate phase, are the three coordinate axes of the spatial coordinate system.

[0025] In one embodiment, the boundary condition is formulated as follows:

[0026]

[0027] in, is the gas phase pressure of natural gas hydrate; is the production well pressure; is the boundary water saturation.

[0028] In one embodiment, the formula for calculating the cumulative decomposition of natural gas hydrates, water production, and gas production quality, while dynamically analyzing the impact of key parameters on production capacity is as follows:

[0029]

[0030] in, 、 and They are t i Cumulative decomposition mass of natural gas hydrate, cumulative gas production of natural gas hydrate and cumulative water production of natural gas hydrate at each moment; is the moment when the hydrate begins to decompose; is the standard methane gas concentration.

[0031] According to a second aspect of the present disclosure, a fluidized two-field coupled natural gas hydrate production simulation system is provided, comprising: 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 group of a natural gas hydrate fluidized two-field coupled model based on the law of conservation of mass; an adjustment module for adjusting the control equation group 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 group; a calculation module for solving the target control equation group based on 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, water production and gas production quality of natural gas hydrates based on the two-phase seepage field and the chemical decomposition field, and dynamically analyze the influence of key parameters on production capacity.

[0032] In one embodiment, the equation building module is further configured to generate the following control equations:

[0033]

[0034] in, Expressed as:

[0035]

[0036] in, 、 、 are the gas phase density, water phase density and gas hydrate density respectively; 、 and are gas saturation, water saturation, and 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 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 irreducible water saturation and irreducible gas saturation, respectively; For time.

[0037] In one embodiment, the adjustment module is configured to adjust the control equations based on the intrinsic kinetic behavior of the natural gas hydrate phase transition decomposition using the following formula:

[0038]

[0039] in, is the kinetic constant for the decomposition of natural gas hydrate, is the activation energy for hydrate decomposition; R is the ideal gas constant; T is the porous medium temperature; 、 、 are the gas hydrate molar mass, gas phase molar mass, and water molar mass, respectively; is the effective porosity of the reservoir; is the three-phase equilibrium pressure of natural gas hydrate; is the hydration number;

[0040] in, , , ;

[0041] in, 、 are the phase equilibrium pressure regression coefficients, respectively.

[0042] The present invention discloses a fluidized two-field coupled natural gas hydrate mining simulation method and system. The method establishes a geometric model of the natural gas hydrate reservoir based on the reservoir parameters and physical property parameters of the natural gas hydrate reservoir; establishes a control equation group of the natural gas hydrate fluidized two-field coupled model based on the law of conservation of mass; adjusts the control equation group 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 group; solves the target control equation group based on initial conditions and boundary conditions to obtain a two-phase seepage field and a chemical decomposition field; calculates the cumulative decomposition of the natural gas hydrate, the water production and the gas production quality based on the two-phase seepage field and the chemical decomposition field, and dynamically analyzes the impact of key parameters on production capacity. In this way, the method can avoid the problems of insufficient precision in model assumption simplification and boundary condition processing, difficulty in parameter acquisition and large uncertainty, high computational cost, complex model prone to errors, and limitations on engineering application, thereby improving simulation accuracy and being suitable for engineering practical application.

[0043] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present disclosure, nor are they intended to limit the scope of the present disclosure. Other features of the present disclosure will become readily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The above and other objects, features and advantages of the exemplary embodiments of the present disclosure will become readily understood by reading the detailed description below with reference to the accompanying drawings, in which several embodiments of the present disclosure are shown by way of example and not limitation, wherein:

[0045] In the drawings, the same or corresponding reference numerals denote the same or corresponding parts.

[0046] Figure 1 A schematic flow chart of a natural gas hydrate production simulation method with fluidization and two-field coupling according to an embodiment of the present disclosure is shown;

[0047] Figure 2 A structural schematic diagram of a natural gas hydrate production simulation system with fluidization two-field coupling according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0048] To make the purposes, features, and advantages of the present disclosure more apparent and understandable, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present disclosure, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present disclosure without creative work shall fall within the scope of protection of the present disclosure.

[0049] Figure 1A flow chart of a natural gas hydrate production simulation method with fluidization and two-field coupling according to an embodiment of the present disclosure is shown. Figure 1 As shown in FIG, a natural gas hydrate production simulation method with fluidization and two-field coupling includes:

[0050] Step S101: Acquire reservoir parameters and physical property parameters of a natural gas hydrate reservoir.

[0051] In this example, during the initial stages of the natural gas hydrate extraction simulation, various parameters of the natural gas hydrate reservoir, such as reservoir parameters and physical properties, need to be acquired. Reservoir parameters primarily include reservoir pressure and temperature, which reflect the reservoir's basic energy state and the environmental conditions in which the material resides. Physical properties primarily include core radius, core length, phase saturation, absolute permeability, and phase density, which describe the reservoir's physical structure and fluid distribution from a microscopic perspective.

[0052] In one possible implementation, these parameters can be obtained through a variety of methods, including laboratory testing, field trials, and literature research. For example, laboratory testing can measure the physical properties of collected core samples through experimental analysis; field trials can directly obtain real-time reservoir parameters from the actual mining process; and literature research can reference existing research results and data to provide basic data support for model establishment.

[0053] Step S102: establishing a geometric model of the natural gas hydrate reservoir based on reservoir parameters and physical property parameters.

[0054] In this embodiment, after obtaining reservoir parameters and physical properties, a geometric model of the natural gas hydrate reservoir is constructed based on these parameters. This geometric model is a mathematical description of the reservoir's physical spatial structure, providing a spatial framework for subsequent simulation calculations. The creation of this geometric model requires consideration of the reservoir's shape and size. Furthermore, parameters such as the saturation of each phase must be rationally distributed within the model to ensure that it accurately reflects the reservoir's actual conditions. By establishing a precise geometric model, an accurate spatial foundation is provided for subsequent fluid flow and chemical reaction simulations.

[0055] Step S103: Based on the law of conservation of mass, a control equation group of the two-field coupling model of natural gas hydrate fluidization is established.

[0056] In this embodiment, a set of governing equations is used to simulate fluid flow and chemical reactions during natural gas hydrate extraction. These governing equations describe the flow patterns of the gas and water phases in the reservoir based on the law of conservation of mass, as well as gas-related parameters (such as gas density, gas viscosity, and gas pressure) and water-related parameters (such as water density and viscosity). Specifically, the governing equations may include mass conservation equations, momentum conservation equations, and energy conservation equations. The mass conservation equation describes the temporal variation of the saturation of the gas and water phases, reflecting the accumulation and consumption of fluids in the reservoir; the momentum conservation equation describes the flow state of the fluid in the reservoir, including its pressure distribution and velocity field; and the energy conservation equation describes the heat transfer and conversion process in the reservoir, which is closely related to the decomposition of natural gas hydrates. This embodiment simplifies the governing equations by using only the mass conservation equation. This allows complex physical phenomena to be transformed into mathematical problems, providing a foundation for further solution and analysis.

[0057] Step S104 : Based on the intrinsic kinetic behavior of the phase transition decomposition of natural gas hydrates and the two-phase seepage law of natural gas hydrates, the control equations are adjusted to obtain the target control equations.

[0058] In this embodiment, the phase transition decomposition of natural gas hydrates is a complex chemical reaction process, and its intrinsic kinetic behavior is affected by multiple factors. Furthermore, the seepage patterns of the gas and water phases in the reservoir also have a significant impact on the extraction process. Therefore, after establishing the initial set of governing equations, they need to be adjusted based on the intrinsic kinetic behavior of the phase transition decomposition of natural gas hydrates and the two-phase seepage patterns. Specifically, kinetic parameters such as the chemical reaction rate and activation energy during the natural gas hydrate decomposition process need to be incorporated into the governing equations, while also considering the effects of factors such as relative permeability and capillary pressure on fluid flow during the two-phase seepage process. This adjustment allows the governing equations to more accurately reflect the physical and chemical phenomena during the natural gas hydrate extraction process, resulting in a target set of governing equations that better reflects actual conditions.

[0059] Step S105 , solving the target control equations based on the initial conditions and boundary conditions to obtain the two-phase seepage field and chemical decomposition field distribution.

[0060] In this embodiment, after establishing the target governing equations, the corresponding initial and boundary conditions must be determined before the solution can be performed. Initial conditions include the reservoir's initial pressure, initial temperature, and initial saturation of each phase; these conditions reflect the reservoir's initial state at the start of production. Boundary conditions include the well pressure and boundary water saturation; these conditions describe the interaction between the reservoir and the external environment. After determining the initial and boundary conditions, numerical calculation methods (such as the finite difference method and the finite element method) can be used to solve the target governing equations, thereby obtaining the distribution of the two-phase seepage field and chemical decomposition field within the reservoir, including information such as the pressure and saturation of the gas and water phases, and the decomposition rate of natural gas hydrates.

[0061] Step S106 , based on the two-phase seepage field and the chemical decomposition field, calculate the cumulative decomposition of natural gas hydrates, the quality of water production and gas production, and dynamically analyze the impact of key parameters on production capacity.

[0062] In this embodiment, after obtaining the distribution of the two-phase seepage field and the chemical decomposition field, the cumulative decomposition mass, cumulative gas production, and cumulative water production of the natural gas hydrate can be calculated based on these results. In one example, the cumulative decomposition mass, cumulative gas production, and cumulative water production of the natural gas hydrate can be calculated by integrating them within the reservoir volume. For example, the cumulative decomposition mass can be obtained by integrating the natural gas hydrate decomposition rate over time and space, reflecting the total amount of natural gas hydrate decomposition during the extraction process; the cumulative gas production is calculated by integrating the gas phase generation rate, representing the total amount of natural gas produced during the extraction process; and the cumulative water production is calculated by integrating the water phase generation rate, reflecting the total amount of water produced during the extraction process. These calculation results can intuitively reflect the effectiveness and efficiency of natural gas hydrate extraction, providing key data support for the evaluation and optimization of extraction plans.

[0063] In the present disclosure, a geometric model is established by obtaining reservoir parameters and physical property parameters, and a control equation group of the fluidization two-field coupling model is constructed based on the law of conservation of mass and gas-water related parameters. The equation group is adjusted according to the phase change decomposition kinetic behavior and the two-phase seepage law, and finally the two-phase seepage field and chemical decomposition field are solved to obtain the cumulative decomposition mass, cumulative gas production and cumulative water production of natural gas hydrates. In addition, the influence of key parameters on production capacity can be dynamically analyzed. As a result, the interaction mechanism between gas-water two-phase seepage and hydrate decomposition in the reservoir can be accurately characterized, overcoming the shortcomings of existing methods in studying the mechanism of the influence of dynamic changes in reservoir parameters on production capacity, providing a theoretical basis for optimizing mining process parameters, helping to improve mining efficiency, reduce uncertainty, promote the process of natural gas hydrate mining, and is suitable for engineering practical application.

[0064] In another embodiment, the governing equations are:

[0065]

[0066] in, Expressed as:

[0067]

[0068] in, 、 、 are the gas phase density, water phase density and natural gas hydrate density respectively; 、 and are gas saturation, water saturation, and 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 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 irreducible water saturation and irreducible gas saturation, respectively; For time.

[0069] In another embodiment, the formula for adjusting the control equations based on the intrinsic kinetic behavior of the natural gas hydrate phase transition decomposition is:

[0070]

[0071] in, is the kinetic constant for the decomposition of natural gas hydrate, is the activation energy for hydrate decomposition; R is the ideal gas constant; T is the porous medium temperature; 、 、 are the gas hydrate molar mass, gas phase molar mass, and water phase molar mass, respectively; is the effective porosity of the reservoir; is the three-phase equilibrium pressure of natural gas hydrate; is the hydration number;

[0072] in, , , ; The ideal gas effect, i.e. the influence of temperature and pressure on the gas density in gas hydrate reservoirs, was considered; The temperature and pressure relationship of the stable existence (solid phase) of natural gas hydrates is considered; The influence of hydrate saturation change caused by natural gas hydrate phase transition on the effective porosity of the reservoir is considered.

[0073] in, 、 are the phase equilibrium pressure regression coefficients, respectively.

[0074] In another embodiment, the formula for adjusting the control equations based on the two-phase seepage law of natural gas hydrate is:

[0075]

[0076] in, is the relative permeability coefficient;

[0077] in, ; ;in, The effect of water saturation change caused by natural gas hydrate phase transition on effective water saturation is considered. The influence of hydrate saturation change caused by natural gas hydrate phase transition on reservoir dynamic permeability is considered.

[0078] in, is the absolute permeability of the reservoir, is the permeability reduction index.

[0079] In another embodiment, the formula for the initial condition is:

[0080]

[0081] in, is the initial pressure of the hydrate reservoir, is the initial temperature of the hydrate reservoir, is the saturation of each hydrate phase, are the three coordinate axes of the spatial coordinate system.

[0082] In another embodiment, the boundary condition is formulated as follows:

[0083]

[0084] in, is the gas phase pressure of natural gas hydrate (which can be used to replace the pore pressure of hydrate reservoir under certain conditions); is the production well pressure; is the boundary water saturation.

[0085] In one embodiment, the geometric model, control equations, initial conditions and boundary conditions are imported into mathematical calculation software for solution, and the dependent variables of the control equations (i.e. P g 、 S w 、 S h ) with time and space, thereby obtaining the distribution of two-phase seepage field and chemical decomposition field inside the core.

[0086] In another embodiment, the formula for calculating the cumulative decomposition, water production, and gas production quality of natural gas hydrate is as follows:

[0087]

[0088] in, 、 and They are t i Cumulative decomposition mass of natural gas hydrate, cumulative gas production of natural gas hydrate and cumulative water production of natural gas hydrate at each moment; is the moment when the hydrate begins to decompose; is the standard methane gas concentration.

[0089] In one embodiment, the data from the indoor depressurization test of natural gas hydrate and the data from steps S101 to S106 can also be used. 、 and Make comparisons to verify the reliability of the model.

[0090] In one embodiment, key parameters in the model, including the production well pressure ( P out )、hydration 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) Analyze the impact of dynamic changes in reservoir parameters on production capacity changes to identify key influencing factors, reduce uncertainty, and provide a theoretical basis for optimizing mining process parameters.

[0091] In one embodiment, the laboratory core scale can be extended to the reservoir scale of field production to obtain the reservoir pressure ( P 0), production well pressure ( P out ), initial reservoir hydrate saturation ( S h0 ), initial reservoir water saturation ( S w0 ), and other parameters, repeating steps S101 to S106 can predict 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.

[0092] Figure 2 FIG. 1 shows a structural diagram of a fluidized two-field coupled natural gas hydrate production simulation system according to an embodiment of the present disclosure, as shown in FIG. Figure 2 As shown in FIG, a natural gas hydrate production simulation system with fluidization and two-field coupling includes:

[0093] An acquisition module 10 is used to obtain reservoir parameters and physical property parameters of the natural gas hydrate reservoir; a model establishment module 11 is used to establish a geometric model of the natural gas hydrate reservoir based on the reservoir parameters and physical property parameters; an equation establishment module 12 is used to establish a control equation group of a two-field coupling model of natural gas hydrate fluidization based on gas-related parameters and water-related parameters; an adjustment module 13 is used to adjust the control equation group 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 group; a calculation module 14 is used to solve the target control equation group based on initial conditions and boundary conditions to obtain a two-phase seepage field and a chemical decomposition field; the calculation module 14 is also used to calculate the cumulative decomposition, water production and gas production quality of natural gas hydrates based on the two-phase seepage field and the chemical decomposition field, and dynamically analyze the influence of key parameters on production capacity.

[0094] In one embodiment, the equation building module 12 is used to generate the following control equations:

[0095]

[0096] in, Expressed as:

[0097]

[0098] in, 、 、 are the gas phase density, water phase density and natural gas hydrate density respectively; 、 and are gas saturation, water saturation, and 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 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 irreducible water saturation and irreducible gas saturation, respectively; For time.

[0099] In one embodiment, the adjustment module 13 is configured to adjust the control equations based on the intrinsic kinetic behavior of the natural gas hydrate phase transition decomposition using the following formula:

[0100]

[0101] in, is the kinetic constant for the decomposition of natural gas hydrate, is the activation energy for hydrate decomposition; R is the ideal gas constant; T is the porous medium temperature; 、 、 are the gas hydrate molar mass, gas phase molar mass, and water phase molar mass, respectively; is the effective porosity of the reservoir; is the three-phase equilibrium pressure of natural gas hydrate; is the hydration number;

[0102] in, , , ;

[0103] in, 、 are the phase equilibrium pressure regression coefficients, respectively.

[0104] In one embodiment, the adjustment module 13 is configured to adjust the control equations based on the two-phase flow law of natural gas hydrates using the following formula:

[0105]

[0106] in, is the relative permeability coefficient;

[0107] in, ; ;

[0108] in, is the absolute permeability of the reservoir, is the permeability reduction index.

[0109] In one embodiment, the formula for the initial condition in the calculation module 14 is:

[0110]

[0111] in, is the initial pressure of the hydrate reservoir, is the initial temperature of the hydrate reservoir, is the saturation of each hydrate phase, are the three coordinate axes of the spatial coordinate system.

[0112] In one embodiment, the boundary condition in the calculation module 14 is calculated as follows:

[0113]

[0114] in, is the gas phase pressure of natural gas hydrate; is the production well pressure; is the boundary water saturation.

[0115] In one embodiment, the calculation module 14 calculates the cumulative decomposition, water production, and gas production quality of natural gas hydrate based on the following formula:

[0116]

[0117] in, 、 and They are t i Cumulative decomposition mass of natural gas hydrate, cumulative gas production of natural gas hydrate and cumulative water production of natural gas hydrate at each moment; is the moment when the hydrate begins to decompose; is the standard methane gas concentration.

[0118] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this disclosure can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solutions of this disclosure can be achieved, and this document is not limited here.

[0119] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. Throughout the present disclosure, "plurality" means two or more, unless otherwise specifically defined.

[0120] The above description is merely a specific embodiment of the present disclosure, but the scope of protection of the present disclosure is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this disclosure should be included in the scope of protection of the present disclosure. Therefore, the scope of protection of the present disclosure should be based on the scope of protection of the claims.

Claims

1. A natural gas hydrate production simulation method with fluidization and two-field coupling, characterized in that: include: Obtaining 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; Establishing a geometric model of the natural gas hydrate reservoir based on the reservoir parameters and physical property parameters; Based on the law of conservation of mass, the governing equations of the two-field coupled model of natural gas hydrate fluidization are established; Based on the intrinsic kinetic behavior of the phase transition decomposition of natural gas hydrates and the two-phase seepage law of natural gas hydrates, the control equations are adjusted to obtain the target control equations; Solving the target control equations based on initial conditions and boundary conditions to obtain a two-phase seepage field and a chemical decomposition field; Based on the two-phase seepage field and chemical decomposition field, the cumulative decomposition of natural gas hydrates, water production, and gas production quality are calculated, and the impact of key parameters on production capacity is dynamically analyzed; Wherein, the control equations are: in, Expressed as: in, 、 、 are the gas phase density, water phase density and natural gas hydrate density respectively; 、 and are gas saturation, water saturation, and gas hydrate saturation, respectively; are the gas phase viscosity and the water phase viscosity, respectively; is the gas phase pressure of natural gas hydrate; is the porosity; are the 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 irreducible water saturation and irreducible gas saturation, respectively; For time; The formula for adjusting the control equations based on the intrinsic kinetic behavior of the phase transition decomposition of natural gas hydrate is: in, is the kinetic constant for the decomposition of natural gas hydrate, is the activation energy for hydrate decomposition; R is the ideal gas constant; T is the porous medium temperature; 、 、 are the gas hydrate molar mass, gas phase molar mass, and water molar mass, respectively; is the effective porosity of the reservoir; is the three-phase equilibrium pressure of natural gas hydrate; is the hydration number; in, , , ; in, 、 are the phase equilibrium pressure regression coefficients; The formula for adjusting the control equations based on the two-phase seepage law of natural gas hydrate is: in, is the relative permeability coefficient; in, ; ; in, is the absolute permeability of the reservoir, is the permeability decline index; The formula for calculating the cumulative decomposition, water production, and gas production quality of natural gas hydrates is as follows: in, 、 and They are t i Cumulative decomposition mass of natural gas hydrate, cumulative gas production of natural gas hydrate and cumulative water production of natural gas hydrate at each moment; is the moment when the hydrate begins to decompose; is the standard methane gas concentration.

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

3. The method according to claim 1, characterized in that The boundary condition formula is: in, is the gas phase pressure of natural gas hydrate; is the production well pressure; is the boundary water saturation.

4. A natural gas hydrate production simulation system with fluidization and two-field coupling, characterized in that: include: An acquisition module is used to acquire 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 building module, used to build a geometric model of the natural gas hydrate reservoir based on the reservoir parameters and physical property parameters; Equation building module, used to establish the control equations of the two-field coupling model of natural gas hydrate fluidization based on the law of conservation of mass; An adjustment module is used to adjust the control equations based on the intrinsic kinetic behavior of the natural gas hydrate phase transition decomposition and the two-phase seepage law of the natural gas hydrate to obtain a target control equations; A calculation module, configured to solve the target control equations based on 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 hydrates, water production, and gas production quality based on the two-phase seepage field and chemical decomposition field, and dynamically analyze the impact of key parameters on production capacity; The equation building module is also used to generate the following control equations: in, Expressed as: in, 、 、 are the gas phase density, water phase density and natural gas hydrate density respectively; 、 and are gas saturation, water saturation, and gas hydrate saturation, respectively; are the gas phase viscosity and the water phase viscosity, respectively; is the gas phase pressure of natural gas hydrate; is the porosity; are the 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 irreducible water saturation and irreducible gas saturation, respectively; For time; The adjustment module is used to adjust the control equations based on the intrinsic kinetic behavior of natural gas hydrate phase change decomposition using the following formula: in, is the kinetic constant for the decomposition of natural gas hydrate, is the activation energy for hydrate decomposition; R is the ideal gas constant; T is the porous medium temperature; 、 、 are the gas hydrate molar mass, gas phase molar mass, and water molar mass, respectively; is the effective porosity of the reservoir; is the three-phase equilibrium pressure of natural gas hydrate; is the hydration number; in, , , ; in, 、 are the phase equilibrium pressure regression coefficients; The formula for adjusting the control equations based on the two-phase seepage law of natural gas hydrate is: in, is the relative permeability coefficient; in, ; ; in, is the absolute permeability of the reservoir, is the permeability decline index; The formula for calculating the cumulative decomposition, water production, and gas production quality of natural gas hydrates is as follows: in, 、 and They are t i Cumulative decomposition mass of natural gas hydrate, cumulative gas production of natural gas hydrate and cumulative water production of natural gas hydrate at each moment; is the moment when the hydrate begins to decompose; is the standard methane gas concentration.

Images