Method and device for analyzing behavior of natural gas hydrate decomposition in porous medium

Abstract

The application relates to a method and device for analyzing natural gas hydrate decomposition behavior in a porous medium, wherein the method comprises the following steps: based on the basic principles of thermodynamics, mass conservation equations, momentum conservation equations, kinetic energy theorem equations, first law of thermodynamics equations, second law of thermodynamics equations, Clausius-Duhem inequality and energy conservation equations of the hydrate decomposition process in Euler coordinate system and Lagrange coordinate system are respectively established; based on the established equations, a thermodynamic coupling model of the hydrate decomposition process is constructed; the thermodynamic coupling model is used to describe the multiphase flow behavior and thermodynamic behavior of the hydrate decomposition process, and the analysis result of the hydrate decomposition behavior in the porous medium is obtained. Therefore, the problems that the decomposition behavior of the hydrate in the prior art is easy to cause the contact interface between soil particles, hydrates, water and gas to change, heat absorption is accompanied, and the decomposition rate of the whole hydrate reservoir and the gas production rate are affected are solved.

Description

Technical Field

[0001] This application relates to the field of deep-sea energy engineering technology, and in particular to a method and apparatus for analyzing the decomposition behavior of natural gas hydrates in porous media. Background Technology

[0002] Natural gas hydrates are abundant and have high energy density, making them a viable alternative to traditional fuels. However, existing hydrate extraction technologies are not yet mature enough to meet the demands of commercial extraction.

[0003] Hydrates typically occur in high-pressure and low-temperature environments, such as permafrost regions and shallow seabeds. When the equilibrium of hydrates is disrupted, such as by increased temperature, decreased pressure, or weakened equilibrium conditions, they will decompose into water and gas.

[0004] However, in existing technologies, the decomposition behavior of hydrates easily leads to changes in the contact interface between soil particles, hydrates, water, and gas, accompanied by heat absorption, which affects the decomposition rate and gas production rate of the entire hydrate reservoir, making it difficult to achieve commercial-level hydrate extraction, and this problem urgently needs to be solved. Summary of the Invention

[0005] This application provides a method and apparatus for analyzing the decomposition behavior of natural gas hydrates in porous media, in order to solve the problems in the prior art where the decomposition behavior of hydrates easily leads to changes in the contact interface between soil particles, hydrates, water and gas, accompanied by heat absorption, which affects the decomposition rate and gas production rate of the entire hydrate reservoir.

[0006] The first aspect of this application provides a method for analyzing the decomposition behavior of natural gas hydrates in porous media, comprising the following steps: based on fundamental thermodynamic principles, establishing the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation for the hydrate decomposition process in both Eulerian and Lagrange coordinate systems; constructing a thermodynamic coupling model of the hydrate decomposition process based on the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation; and using the thermodynamic coupling model to describe the multiphase flow behavior and thermodynamic behavior of the hydrate decomposition process, thereby obtaining the analysis results of the natural gas hydrate decomposition behavior in porous media.

[0007] Optionally, in one embodiment of this application, establishing the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation for the hydrate decomposition process in Eulerian and Lagrange coordinate systems respectively includes: calculating the decomposition rate and enthalpy of the hydrate; calculating the degree of mass change caused by the decomposition of the hydrate per unit time in both Eulerian and Lagrange coordinate systems based on the decomposition rate of the hydrate; and calculating the heat per unit time caused by the decomposition of the hydrate per unit time in both Eulerian and Lagrange coordinate systems based on the decomposition rate and enthalpy of the hydrate. Wherein, under phase transition conditions, the mass conservation equation for the hydrate decomposition process includes the solid matrix mass conservation equation and the pore component mass conservation equation.

[0008] In the Euler coordinate system, the mass conservation equation for the solid matrix is:

[0009]

[0010] In the formula, τ is the Euler porosity, t is time, and ρ is... s V is the intrinsic mass density of the soil particle solid matrix. s The velocity of the soil particle solid matrix;

[0011] In the Euler coordinate system, based on Darcy's law, Fourier's law, the degree of mass change, and the heat per unit time, the mass conservation equation for the pore component is calculated. The mass conservation equation for the pore component is as follows:

[0012]

[0013]

[0014]

[0015] In the formula, ρ H ρ is the density of the hydrate. W ρ is the density of water. G For gas density, Λ H→wG Λ represents the mass of hydrate decomposition per unit volume and per unit time. H→w Λ represents the mass of the hydrate converted into water. H→G V represents the mass of the hydrate converted into gas. H V is the velocity of the hydrate. W V is the velocity of the water. G τ is the velocity of the gas. H For the porosity of Euler hydrates, τW Let τ be the Euler water porosity. G Euler gas porosity;

[0016] In the Lagrange coordinate system, the mass conservation equation of the solid matrix is:

[0017]

[0018] In the formula, τ is the initial soil matrix density, and τ0 is the initial porosity;

[0019] In the Lagrange coordinate system, based on Darcy's law, Fourier's law, the degree of mass change, and the heat per unit time, the mass conservation equation for the pore component is calculated. The mass conservation equation for the pore component is as follows:

[0020]

[0021]

[0022]

[0023] In the formula, This represents the mass of hydrate converted into water and gas in the Lagrange formula. This represents the mass of hydrate converted to water in the Lagrange formula. m represents the mass of hydrate converted to gas in the Lagrange formula. H For the mass of hydrate, m W For water quality, m G For the mass of the gas, M w M is the Lagrange flux of water added to the initial configuration. G This refers to the Lagrange flux of the gas added to the initial configuration.

[0024] Optionally, in one embodiment of this application, the establishment of the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation for the hydrate decomposition process in Eulerian and Lagrange coordinate systems respectively includes:

[0025] In the Euler coordinate system, the momentum conservation equation for the hydrate decomposition process is:

[0026]

[0027] In the formula, γ s For the acceleration of the soil skeleton, γ αLet g be the acceleration of the hydrate, water, and gas, g be the gravity vector, σ be the Cauchy stress in the Euler coordinate system, and ρ be the acceleration of the hydrate, water, and gas. α τ is the mass density of the porous component. α Porosity of hydrates, water, and gas in the Euler coordinate system;

[0028] In the Lagrange coordinate system, the momentum conservation equation for the hydrate decomposition process is:

[0029]

[0030] In the formula, F is the deformation gradient, π is the Piola-Kirchhoff stress tensor in the Lagrange coordinate system, and m α The mass of the hydrate, water, and gas.

[0031] Optionally, in one embodiment of this application, the establishment of the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation for the hydrate decomposition process in Eulerian and Lagrange coordinate systems respectively includes:

[0032] In the Euler coordinate system, the kinetic energy theorem equation for the hydrate decomposition process is as follows:

[0033]

[0034] in,

[0035]

[0036] In the formula, K s K represents the kinetic energy of the soil skeleton. α V represents the kinetic energy of the hydrate, water, and gas. α Let d be the velocity of the hydrate, water, and gas. s Let w be the Euler strain rate tensor of the soil skeleton. α It is the Euler mass flux, p α The pressure of fluids with different components;

[0037] In the Lagrange coordinate system, the kinetic energy theorem equation for the hydrate decomposition process is:

[0038]

[0039] in, The strain power for unsaturated soil in the Lagrange formula is shown below:

[0040]

[0041] In the formula, h s Let h be the kinetic energy of the soil matrix in the Lagrange coordinates. α Let Δ be the kinetic energy of the fluid composed of the hydrate, water, and gas, and Δ be the Green-Lagrange strain tensor. Let be the porosity of different components in the Lagrange coordinates, g be the gravitational acceleration matrix, and J be the Jacobian number, i.e., the rank of the deformation gradient F.

[0042] Optionally, in one embodiment of this application, the step of establishing the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation for the hydrate decomposition process in Eulerian and Lagrange coordinate systems respectively includes:

[0043] In the Euler coordinate system, the first law of thermodynamics for the hydrate decomposition process is:

[0044]

[0045] In the formula, e is the total internal energy of the soil matrix and the pore components, and r Q and h Q These are the heat supply rate and the heat change rate caused by hydrate decomposition in the Euler coordinate system, respectively, and q is the output heat flux vector.

[0046] In the Lagrange coordinate system, the first law of thermodynamics for the hydrate decomposition process is:

[0047]

[0048] In the formula, E and Q are the Lagrange density-weighted total internal energy and Lagrange heat flux per unit initial volume, respectively, Δ is the Green-Lagrange strain tensor, and R... Q and H Q These represent the Lagrange density-weighted rate of heat supply per unit initial volume and the rate of heat change caused by hydrate decomposition, respectively.

[0049] Optionally, in one embodiment of this application, the establishment of the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation for the hydrate decomposition process in Eulerian and Lagrange coordinate systems respectively includes:

[0050] In the Euler coordinate system, the second law of thermodynamics for the hydrate decomposition process is:

[0051]

[0052] In the formula, θα (α=w,G) represents the specific entropy of component α, θ is the total entropy per unit volume, T represents the temperature, and n is the normal vector of the lower surface da in the Lagrange coordinate system.

[0053] Based on the second law of thermodynamics in the Euler coordinate system, the Clausius-Duhem inequality for the hydrate decomposition process in the Euler coordinate system is as follows:

[0054]

[0055] In the formula, ψ is the Helmholtz free energy, and g α (α=w,G) represents the free specific enthalpy of fluids with different components (α=c,w);

[0056] Based on the second law of thermodynamics in the Euler coordinate system and the Clausius-Duhem inequality, combined with Darcy's law, Fourier's law, the degree of mass change, and the heat per unit time in the Euler coordinate system, the energy conservation equation for the hydrate decomposition process in the Euler coordinate system is calculated. The energy conservation equation is as follows:

[0057]

[0058] In the formula, For the Eulerian dissipation volume density associated with open systems, For the Eulerian dissipative volume density related to thermal convection, The Euler dissipative volume density associated with the phase transition;

[0059] In the Lagrange coordinate system, the second law of thermodynamics for the hydrate decomposition process is:

[0060]

[0061] In the formula, Θ is the entropy density in the Lagrange coordinate system, and N is the normal vector of the surface dA in the Lagrange coordinate system.

[0062] Based on the second law of thermodynamics in the Lagrange coordinate system, the Clausius-Duhem inequality for the hydrate decomposition process in the Lagrange coordinate system is as follows:

[0063]

[0064] In the formula, Ψ is the Lagrange free energy density, and M α (α=w,g) represents the molar mass of different pore components;

[0065] Based on the second law of thermodynamics in the Lagrange coordinate system, the Clausius-Duhem inequality, Darcy's law in the Lagrange coordinate system, Fourier's law, the degree of mass change, and the heat per unit time, the energy conservation equation for the hydrate decomposition process in the Lagrange coordinate system is obtained. The energy conservation equation is:

[0066]

[0067] In the formula, Φ1 represents the inherent dissipation associated with the open system, and Φ3 and Φ → These are energy dissipation related to thermal convection and phase change, respectively.

[0068] A second aspect of this application provides an apparatus for analyzing the decomposition behavior of natural gas hydrates in porous media, comprising: a computation module for establishing, based on fundamental thermodynamic principles, the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation for the hydrate decomposition process in Eulerian and Lagrange coordinate systems, respectively; a modeling module for constructing a thermodynamically coupled model of the hydrate decomposition process based on the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation; and a simulation module for using the thermodynamically coupled model to describe the multiphase flow behavior and thermodynamic behavior of the hydrate decomposition process, and to obtain the analysis results of the natural gas hydrate decomposition behavior in porous media.

[0069] Optionally, in one embodiment of this application, the calculation module includes: a first calculation unit for calculating the decomposition rate and enthalpy of the hydrate; a second calculation unit for calculating, based on the decomposition rate of the hydrate, the degree of mass change caused by the decomposition of the hydrate per unit time in the Eulerian coordinate system and the Lagrange coordinate system, respectively; and a third calculation unit for calculating, based on the decomposition rate and enthalpy of the hydrate, the heat per unit time caused by the decomposition of the hydrate in the Eulerian coordinate system and the Lagrange coordinate system, respectively.

[0070] In the case of phase transition, the mass conservation equation for the hydrate decomposition process includes the solid matrix mass conservation equation and the pore component mass conservation equation.

[0071] An Euler mass conservation element is used in the Euler coordinate system, and the mass conservation equation of the solid matrix is:

[0072]

[0073] In the formula, τ is the Euler porosity, t is time, and ρ is... s V is the intrinsic mass density of the soil particle solid matrix. s The velocity of the soil particle solid matrix;

[0074] The fourth calculation unit is used to calculate the mass conservation equation of the pore component in the Euler coordinate system based on Darcy's law, Fourier's law, the degree of mass change, and the heat per unit time. The mass conservation equation of the pore component is as follows:

[0075]

[0076]

[0077]

[0078] In the formula, ρ H ρ is the density of the hydrate. W ρ is the density of water. G For gas density, Λ H→wG Λ represents the mass of hydrate decomposition per unit volume and per unit time. H→w Λ represents the mass of the hydrate converted into water. H→G V represents the mass of the hydrate converted into gas. H V is the velocity of the hydrate. W V is the velocity of the water. G τ is the velocity of the gas. H For the porosity of Euler hydrates, τ W Let τ be the Euler water porosity. G Euler gas porosity;

[0079] A Lagrange mass conservation element is used in the Lagrange coordinate system, and the mass conservation equation of the solid matrix is:

[0080]

[0081] In the formula, τ is the initial soil matrix density, and τ0 is the initial porosity;

[0082] The fifth calculation unit is used to calculate the mass conservation equation of the pore component in the Lagrange coordinate system based on Darcy's law, Fourier's law, the degree of mass change, and the heat per unit time. The mass conservation equation of the pore component is as follows:

[0083]

[0084]

[0085]

[0086] In the formula, This represents the mass of hydrate converted into water and gas in the Lagrange formula. This represents the mass of hydrate converted to water in the Lagrange formula. m represents the mass of hydrate converted to gas in the Lagrange formula. H For the mass of hydrate, m W For water quality, m G For the mass of the gas, M w M is the Lagrange flux of water added to the initial configuration. G This refers to the Lagrange flux of the gas added to the initial configuration.

[0087] Optionally, in one embodiment of this application, the computing module further includes:

[0088] In the Euler coordinate system, the momentum conservation equation for the hydrate decomposition process is:

[0089]

[0090] In the formula, γ s For the acceleration of the soil skeleton, γ α Let g be the acceleration of the hydrate, water, and gas, g be the gravity vector, σ be the Cauchy stress in the Euler coordinate system, and ρ be the acceleration of the hydrate, water, and gas. α n is the mass density of the porous component. α Porosity of hydrates, water, and gas in the Euler coordinate system;

[0091] In the Lagrange coordinate system, the momentum conservation equation for the hydrate decomposition process is:

[0092]

[0093] In the formula, F is the deformation gradient, π is the Piola-Kirchhoff stress tensor in the Lagrange coordinate system, and m α The mass of the hydrate, water, and gas.

[0094] Optionally, in one embodiment of this application, the computing module further includes:

[0095] In the Euler coordinate system, the kinetic energy theorem equation for the hydrate decomposition process is as follows:

[0096]

[0097] in,

[0098]

[0099] In the formula, K s K represents the kinetic energy of the soil skeleton. α V represents the kinetic energy of the hydrate, water, and gas. α Let d be the velocity of the hydrate, water, and gas. s Let w be the Euler strain rate tensor of the soil skeleton. α It is the Euler mass flux, p α The pressure of fluids with different components;

[0100] In the Lagrange coordinate system, the kinetic energy theorem equation for the hydrate decomposition process is:

[0101]

[0102] in, The strain power for unsaturated soil in the Lagrange formula is shown below:

[0103]

[0104] In the formula, h s Let h be the kinetic energy of the soil matrix in the Lagrange coordinates. α Let Δ be the kinetic energy of the fluid composed of the hydrate, water, and gas, and Δ be the Green-Lagrange strain tensor. Let be the porosity of different components in the Lagrange coordinates, g be the gravitational acceleration matrix, and J be the Jacobian number, i.e., the rank of the deformation gradient F.

[0105] Optionally, in one embodiment of this application, the computing module further includes:

[0106] In the Euler coordinate system, the first law of thermodynamics for the hydrate decomposition process is:

[0107]

[0108] In the formula, e is the total internal energy of the soil matrix and the pore components, and r Q and h Q These are the heat supply rate and the heat change rate caused by hydrate decomposition in the Euler coordinate system, respectively, and q is the output heat flux vector.

[0109] In the Lagrange coordinate system, the first law of thermodynamics for the hydrate decomposition process is:

[0110]

[0111] In the formula, E and Q are the Lagrange density-weighted total internal energy and Lagrange heat flux per unit initial volume, respectively, Δ is the Green-Lagrange strain tensor, and R... Q and H Q These represent the Lagrange density-weighted rate of heat supply per unit initial volume and the rate of heat change caused by hydrate decomposition, respectively.

[0112] Optionally, in one embodiment of this application, the computing module further includes:

[0113] In the Euler coordinate system, the second law of thermodynamics for the hydrate decomposition process is:

[0114]

[0115] In the formula, θα (α=w,G) represents the specific entropy of component α, θ is the total entropy per unit volume, T represents the temperature, and n is the normal vector of the lower surface da in the Lagrange coordinate system.

[0116] The sixth calculation unit is used to derive the Clausius-Duhem inequality for the hydrate decomposition process in the Euler coordinate system based on the second law of thermodynamics:

[0117]

[0118] In the formula, ψ is the Helmholtz free energy, and g α (α=w,G) represents the free specific enthalpy of fluids with different components (α=c,w);

[0119] The seventh calculation unit is used to calculate the energy conservation equation for the hydrate decomposition process in the Euler coordinate system based on the second law of thermodynamics in the Euler coordinate system and the Clausius-Duhem inequality, combined with Darcy's law, Fourier's law, the degree of mass change, and the heat per unit time in the Euler coordinate system. The energy conservation equation is as follows:

[0120]

[0121] In the formula, For the Eulerian dissipation volume density associated with open systems, For the Eulerian dissipative volume density related to thermal convection, The Euler dissipative volume density associated with the phase transition;

[0122] In the Lagrange coordinate system, the second law of thermodynamics for the hydrate decomposition process is:

[0123]

[0124] In the formula, Θ is the entropy density in the Lagrange coordinate system, and N is the normal vector of the surface dA in the Lagrange coordinate system.

[0125] The eighth calculation unit is used to derive the Clausius-Duhem inequality for the hydrate decomposition process in the Lagrange coordinate system based on the second law of thermodynamics:

[0126]

[0127] In the formula, Ψ is the Lagrange free energy density, and M α (α=w,g) represents the molar mass of different pore components;

[0128] The ninth calculation unit is used to derive the energy conservation equation for the hydrate decomposition process in the Lagrange coordinate system based on the second law of thermodynamics in the Lagrange coordinate system, the Clausius-Duhem inequality, Darcy's law in the Lagrange coordinate system, Fourier's law, the degree of mass change, and the heat per unit time. The energy conservation equation is as follows:

[0129]

[0130] In the formula, Φ1 represents the inherent dissipation associated with the open system, and Φ3 and Φ → These are energy dissipation related to thermal convection and phase change, respectively.

[0131] A third aspect of this application provides an electronic device, including: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the method for analyzing the decomposition behavior of natural gas hydrates in porous media as described in the above embodiments.

[0132] A fourth aspect of this application provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described method for analyzing the decomposition behavior of natural gas hydrates in porous media.

[0133] Therefore, the embodiments of this application have the following beneficial effects:

[0134] The embodiments of this application establish, based on fundamental thermodynamic principles, the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation for the hydrate decomposition process in both Eulerian and Lagrange coordinate systems. Based on these equations, a thermodynamic coupling model of the hydrate decomposition process is constructed. This coupled model is used to describe the multiphase flow and thermodynamic behavior of the hydrate decomposition process, yielding analytical results on the decomposition behavior of natural gas hydrates in porous media. By analyzing the multiphase flow, phase transition, and heat conversion of solid, liquid, and gas in the hydrate reservoir medium, this application avoids changes in the contact interfaces between soil particles, hydrates, water, and gas caused by hydrate decomposition, thereby ensuring the decomposition rate and gas production rate of the entire hydrate reservoir and providing theoretical support for achieving commercial-level hydrate extraction. This solves the problem in existing technologies that the decomposition behavior of hydrates easily leads to changes in the contact interface between soil particles, hydrates, water and gas, accompanied by heat absorption, which affects the decomposition rate and gas production rate of the entire hydrate reservoir.

[0135] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0136] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0137] Figure 1 This is a flowchart illustrating a method for analyzing the decomposition behavior of natural gas hydrates in porous media according to an embodiment of this application.

[0138] Figure 2 A schematic diagram of the pore composition in a porous medium containing hydrates is provided as an embodiment of this application;

[0139] Figure 3 This is an example diagram of an apparatus for analyzing the decomposition behavior of natural gas hydrates in porous media according to an embodiment of this application;

[0140] Figure 4 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application.

[0141] Among them, 10-analysis device for natural gas hydrate decomposition behavior in porous media, 100-computation module, 200-modeling module, 300-simulation module, 401-memory, 402-processor, and 403-communication interface. Detailed Implementation

[0142] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0143] The following describes a method and apparatus for analyzing the decomposition behavior of natural gas hydrates in porous media, based on embodiments of the present application, with reference to the accompanying drawings. Addressing the problems mentioned in the background section, this application provides a method for analyzing the decomposition behavior of natural gas hydrates in porous media. In this method, based on fundamental thermodynamic principles, mass conservation equations, momentum conservation equations, kinetic energy theorem equations, the first law of thermodynamics equations, the second law of thermodynamics equations, Clausius-Duhem inequalities, and energy conservation equations for the hydrate decomposition process are established in both Eulerian and Lagrange coordinate systems. Based on these equations, a thermodynamic coupling model of the hydrate decomposition process is constructed. Using this thermodynamic coupling model, the multiphase flow behavior and thermodynamic behavior of the hydrate decomposition process are described, yielding analytical results of the natural gas hydrate decomposition behavior in porous media. This application analyzes the multiphase flow, phase transition, and heat conversion of solid, liquid, and gas in hydrate reservoir media to prevent changes in the contact interface between soil particles, hydrates, water, and gas caused by hydrate decomposition, thereby ensuring the decomposition rate and gas production rate of the entire hydrate reservoir and providing theoretical support for achieving commercial-level hydrate extraction. This solves the problem in existing technologies where hydrate decomposition easily leads to changes in the contact interface between soil particles, hydrates, water, and gas, accompanied by heat absorption, affecting the decomposition rate and gas production rate of the entire hydrate reservoir.

[0144] Specifically, Figure 1 This is a flowchart illustrating a method for analyzing the decomposition behavior of natural gas hydrates in porous media, provided as an embodiment of this application.

[0145] like Figure 1 As shown, the method for analyzing the decomposition behavior of natural gas hydrates in this porous medium includes the following steps:

[0146] In step S101, based on the fundamental principles of thermodynamics, the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation for the hydrate decomposition process are established in both the Euler and Lagrange coordinate systems.

[0147] The embodiments of this application first establish, based on the fundamental principles of thermodynamics, the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation in the hydrate decomposition process in both Euler and Lagrange coordinate systems. This provides reliable data and theoretical support for establishing a thermodynamic coupling model involving multiphase flow and phase change in the hydrate decomposition process.

[0148] Optionally, in one embodiment of this application, the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation for the hydrate decomposition process are established in both the Eulerian and Lagrange coordinate systems, including: calculating the decomposition rate and enthalpy of the hydrate; calculating the degree of mass change caused by hydrate decomposition per unit time in both the Eulerian and Lagrange coordinate systems based on the decomposition rate of the hydrate; and calculating the heat per unit time caused by hydrate decomposition in both the Eulerian and Lagrange coordinate systems based on the decomposition rate and enthalpy of the hydrate. In the case of a phase transition, the mass conservation equation for the hydrate decomposition process includes the solid matrix mass conservation equation and the pore component mass conservation equation.

[0149] In the Euler coordinate system, the mass conservation equation for the solid matrix is:

[0150]

[0151] In the formula, τ is the Euler porosity, t is time, and ρ is... s V is the intrinsic mass density of the soil particle solid matrix. s The velocity of the solid matrix of soil particles;

[0152] In the Euler coordinate system, based on Darcy's law, Fourier's law, the degree of mass change, and the heat per unit time, the mass conservation equation for the pore components is calculated. The mass conservation equation for the pore components is as follows:

[0153]

[0154]

[0155]

[0156] In the formula, ρ H ρ is the density of the hydrate. W ρ is the density of water. G For gas density, Λ H→wGΛ represents the mass of hydrate decomposition per unit volume and per unit time. H→w Λ represents the mass of hydrate converted into water. H→G V represents the mass of hydrate converted into gas. H V represents the velocity of the hydrate. W V is the velocity of the water. G Let τ be the velocity of the gas. H For the porosity of Euler hydrates, τ W Let τ be the Euler water porosity. G Euler gas porosity;

[0157] In the Lagrange coordinate system, the mass conservation equation for the solid matrix is:

[0158]

[0159] In the formula, τ is the initial soil matrix density, and τ0 is the initial porosity;

[0160] In the Lagrange coordinate system, based on Darcy's law, Fourier's law, the degree of mass change, and the heat per unit time, the mass conservation equation for the pore components is calculated. The mass conservation equation for the pore components is as follows:

[0161]

[0162]

[0163]

[0164] In the formula, This represents the mass of hydrate converted into water and gas in the Lagrange formula. This represents the mass of hydrate converted to water in the Lagrange formula. m represents the mass of hydrate converted to gas in the Lagrange formula. H For the mass of hydrate, m W For water quality, m G For the mass of the gas, M w M is the Lagrange flux of water added to the initial configuration. G This refers to the Lagrange flux of the gas added to the initial configuration.

[0165] The embodiments of this application can be combined with the phase transition situation to analyze the calculation of the mass conservation equation, so as to give the expression forms of Euler coordinate system and Lagrange coordinate system respectively.

[0166] It should be noted that embodiments of this application may define ρ s and ρ α(α=H,w,G) represent the intrinsic mass densities of the solid matrix and the pore component, respectively. The pore component in the porous medium containing hydrates is as follows: Figure 2 As shown, the masses of the solid matrix and the pore component α currently contained in the volume dΩ are ρ and ρ, respectively. s (1-τ)dΩ and ρ α τs α dΩ. Therefore, the macroscopic (or apparent) mass densities of the solid matrix and the pore component α are ρ and dΩ, respectively. s (1-τ) and ρ α τs α When there is no phase transition, the mass conservation equations for the soil skeleton and pore components in Euler form are:

[0167]

[0168]

[0169] Therefore, the Euler continuity equation can be expressed as:

[0170]

[0171] and

[0172]

[0173] Among them, V s and V α (α = H, w, G) represent the velocities of the solid matrix and the pore components (hydrates, water, and gas), respectively.

[0174]

[0175] Where x represents the common position of all fluids and solids (π = s, H, w, G) at the current moment.

[0176] For the Lagrange formula, the Lagrange fluid mass m α for:

[0177] m α =ρ α φ α =ρ α φS α ,(α=H,w,G)(6)

[0178] Therefore, the Lagrange formula for the mass conservation of the phase (hydrate, water, or gas) within the pores can be obtained as follows:

[0179]

[0180] Where M α (X iLet w(t) be the Lagrange flux added to the initial configuration. α For Euler mass flux, its relationship with M α The relationship is:

[0181] w α ·ndα=M α ·NdA(8)

[0182] Where N is the unit normal to surface dA at the initial time, and n is the unit normal to surface da at the current time:

[0183]

[0184] Substituting equation (9) into equation (8), we get:

[0185]

[0186] but:

[0187]

[0188] Similarly:

[0189]

[0190] The mass flux of each fluid is:

[0191]

[0192] In this model, it is assumed that hydrates adhere to the surface of soil particles, causing them to move and deform together. Therefore,

[0193] V H =V s ,w H =M H =0(14)

[0194] The Lagrangian form of the mass conservation equation for the solid matrix, i.e., the soil skeleton, is:

[0195]

[0196] in, Let τ0 = φ0 be the initial soil matrix density, and τ0 = φ0 be the initial porosity. Therefore, the mass conservation equation for the soil skeleton is obtained:

[0197]

[0198] When considering hydrate decomposition, the phase transition involves only liquid water, gas, and hydrates. The mass conservation equations for the solid matrix in the equations still apply. The mass conservation equations for water, natural gas, and hydrates considering the phase transition are as follows:

[0199]

[0200]

[0201]

[0202] Among them, Λ wG→H ,Λ H→w and Λ H→G Let represent the mass per unit total volume and per unit time of water and gas converted into hydrates, hydrates converted into water, and hydrates converted into gas. Given the overall mass conservation requirement, then:

[0203] Λ H→G +Λ H→w =-Λ wG→H =Λ H→wG (20)

[0204] Among them, Λ H→wG Let represent the mass of hydrate decomposition per unit volume and per unit time. For any quantity Ξ, when its derivative is applied to its volume integral, we have:

[0205]

[0206] According to equation (21), equations (17), (18), and (19) can be written as:

[0207]

[0208] Using equation (21), the mass conservation equations for hydrates, water, and gas in Euler's formula can be obtained as follows:

[0209]

[0210] Based on a similar derivation of the previous Euler continuity equation, the Lagrange formulas for the continuity equations of hydrates, water, and gases are as follows:

[0211]

[0212]

[0213]

[0214] in, The mass of α converted to β in the Lagrange formula is shown below:

[0215]

[0216] Optionally, in one embodiment of this application, the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation for the hydrate decomposition process are established in both the Euler and Lagrange coordinate systems, including: In the Euler coordinate system, the momentum conservation equation for the hydrate decomposition process is:

[0217]

[0218] In the formula, γ s For the acceleration of the soil skeleton, γ α Let g be the acceleration of hydrates, water, and gas, g be the gravity vector, σ be the Cauchy stress in the Euler coordinate system, and ρ be the acceleration of hydrates, water, and gas. α τ is the mass density of the porous component. α Porosity of hydrates, water, and gas in the Euler coordinate system;

[0219] In the Lagrange coordinate system, the momentum conservation equation for the hydrate decomposition process is:

[0220]

[0221] In the formula, F is the deformation gradient, π is the Piola-Kirchhoff stress tensor in Lagrange coordinates, and m α The mass of hydrates, water, and gases.

[0222] Specifically, in the embodiments of this application, from a purely mechanical perspective, the unsaturated medium can be considered as a complex of hydrates, gas, and water, all of which interact with each other. In Euler's formula, ρ s (1-τ)V s and ρ α τ α V α (α = H, w, G) represent the linear momentum of the soil skeleton, hydrates, water, and gas, respectively. Λ H→w (V w -V H ) and Λ H→G (V G -V H This illustrates the change in linear momentum due to the mass rate of exchange. Therefore, in Euler's formula, the linear momentum conservation formula for unsaturated soil is:

[0223]

[0224] Where, γ s and γ α The accelerations of the soil skeleton, hydrates, water, and gases are expressed mathematically as follows:

[0225]

[0226] On the other hand, the linear rate of change of momentum of all matter within the material volume Ω is equivalent to the sum of all external forces applied to that matter. Therefore, the momentum conservation equation for all matter within a general porous medium Ω can be expressed as:

[0227]

[0228] Where ρ is the total mass density, i.e.:

[0229]

[0230] g is the gravity vector, and σ·n represents the surface force acting on the boundary of the material domain Ω.

[0231] Combining equations (26) and (28), we can obtain:

[0232]

[0233] therefore:

[0234]

[0235] The above formula can be expressed as:

[0236]

[0237] therefore:

[0238]

[0239] Assume that the Piola-Kirchhoff stress tensor π in the Lagrange formula is related to the Cauchy stress σ in the Euler formula, that is:

[0240] π=JF -1 ·σ· t F -1 (34)

[0241] Similarly, the material surface elements (both containing the same set of solid skeletal particles) at the initial time dA and the current time da are related, as follows:

[0242] F·π·NdA=σ·nda (35)

[0243] according to We can obtain:

[0244]

[0245] Combining equations (35) and (36), the momentum conservation equation in Euler's formula, i.e., equation (33), can be transformed into the Lagrange formula:

[0246]

[0247] Optionally, in one embodiment of this application, the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation for the hydrate decomposition process are established in both the Euler and Lagrange coordinate systems, including: the kinetic energy theorem equation for the hydrate decomposition process in the Euler coordinate system is as follows:

[0248]

[0249] in,

[0250]

[0251] In the formula, K s For the kinetic energy of the soil skeleton, K α V represents the kinetic energy of hydrates, water, and gases. α Let d be the velocity of hydrates, water, and gas. s Let w be the Euler strain rate tensor of the soil skeleton. α It is the Euler mass flux, p α The pressure of fluids with different components;

[0252] In the Lagrange coordinate system, the kinetic energy theorem equation for the hydrate decomposition process is:

[0253]

[0254] in, The strain power for unsaturated soil in the Lagrange formula is shown below:

[0255]

[0256] In the formula, h s h represents the kinetic energy of the soil matrix in Lagrange coordinates. α Let λ be the kinetic energy of the fluid composed of hydrates, water, and gas, and Δ be the Green-Lagrange strain tensor. Let be the porosity of different components in Lagrange coordinates, g be the gravitational acceleration matrix, and J be the Jacobian number, i.e., the rank of the deformation gradient F.

[0257] In embodiments of this application, the relative vector of fluid mass is introduced into equation (13) and the fluid pressure p αThis describes the movement of the soil skeleton. Therefore, for unsaturated soil in Eulerian form, the power of external objects and surface forces on the relative state of the reservoir is:

[0258]

[0259] Among them, T s and T α Let represent the traction forces of soil particles and component α, respectively. Equation (13) can be expressed as:

[0260]

[0261] Therefore, we can obtain:

[0262]

[0263] Combining equation (29), equation (40) can be expressed as:

[0264]

[0265] By applying the momentum balance equation to the soil framework and other components (hydrates, water, and gas), different local volumetric stress components emerge, where the local volumetric stress σ s and σ α (α = H, w, G) is associated with the soil framework and component α, that is:

[0266] T s (x,t,n)=(1-τ)σ s ·n,T α (x,t,n)=τ α σ α ·n(α=H,w,G) (42)

[0267] Where n is the normal vector of surface da. The intrinsic mean stresses of water and gas can be solved using the spherical tensor, as shown below:

[0268] σ α =-p α I,(α=w,G) (43)

[0269] Substituting equations (42) and (43) into equation (41), we get:

[0270]

[0271] Therefore, substituting equations (41) and (43) into equation (38), we get:

[0272]

[0273] Where T = Ts +T H +T w +T G It is the total traction vector.

[0274] Neglecting tortuosity, the kinetic energy of the soil matrix, hydrates, water, and gases in unsaturated soil is:

[0275]

[0276] Therefore, the kinetic energy of the soil skeleton K s The derivative is:

[0277]

[0278] Substituting equation (3) into equation (47), we get:

[0279]

[0280] Similarly, differentiating the kinetic energies of hydrates, water, and gases in unsaturated soil, we obtain:

[0281]

[0282] Combining equations (17), (19), and (39), equation (49) can be expressed as:

[0283]

[0284] Combining equations (47) and (50), the derivative of the total kinetic energy can be obtained as:

[0285]

[0286] According to equation (5), the Euler strain rate tensor d π for:

[0287]

[0288] The superscript t denotes the transpose of the matrix. According to equations (45) and (51), we have:

[0289]

[0290] Using the divergence theorem, we can obtain:

[0291]

[0292] Substituting equation (54) into equation (53), we get:

[0293]

[0294] Substituting the above equation into equation (33), and combining it with the following equation:

[0295]

[0296] Then equation (55) can be transformed into:

[0297]

[0298] Therefore, the Euler form of the kinetic energy theorem equation is obtained as follows:

[0299]

[0300] in,

[0301]

[0302] Similarly, the power of external objects and surface forces on unsaturated soil in Lagrange form can be derived as follows:

[0303]

[0304] Combining equation (46), the kinetic energy related to the soil matrix and the fluid composed of hydrates, water, and gas in the Lagrange formula is:

[0305]

[0306] Therefore, the work-energy theorem equation in the Lagrange formula can be obtained as follows:

[0307]

[0308] in, Let be the strain power of unsaturated soil in the Lagrange formula, i.e.:

[0309]

[0310] The Green-Lagrange strain tensor Δ can be defined as follows:

[0311]

[0312] Optionally, in one embodiment of this application, the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation for the hydrate decomposition process are established in both the Euler and Lagrange coordinate systems, including: In the Euler coordinate system, the first law of thermodynamics equation for the hydrate decomposition process is:

[0313]

[0314] In the formula, e is the total internal energy of the soil matrix and pore components, and r Q and h Q These represent the heat supply rate and the heat change rate caused by hydrate decomposition in the Euler coordinate system, respectively, and q is the output heat flux vector.

[0315] In the Lagrange coordinate system, the first law of thermodynamics for the decomposition of hydrates is:

[0316]

[0317] In the formula, E and Q are the Lagrange density-weighted total internal energy and Lagrange heat flux per unit initial volume, respectively, Δ is the Green-Lagrange strain tensor, and R... Q and H Q These represent the Lagrange density-weighted rate of heat supply per unit initial volume and the rate of heat change caused by hydrate decomposition, respectively.

[0318] The embodiments of this application can be based on the first law of thermodynamics, which states that the rate of change of energy over time is equal to the power P exerted on the substance by an external force. f,T (V s V α The sum of () and the external heating rate Q0, i.e.:

[0319]

[0320] Among them, e s and e α The specific internal energy (i.e., per unit mass) representing the volume density of the soil matrix and component α, and the total internal energy e are expressed as:

[0321]

[0322] The rate of external heating can be expressed as:

[0323]

[0324] Where, r Q and h Q These are the heat sources generated by external heat sources and hydrate decomposition within the volume density, respectively, while J Q The thermal conductivity rate through the surface.

[0325] Using equation (58), equation (65) can be expressed as:

[0326]

[0327] The left side of equation (68) is:

[0328]

[0329] Considering the relationship between other components and the soil skeleton:

[0330]

[0331] Combining equation (39), equation (69) can be expressed as:

[0332]

[0333] Therefore, we can obtain:

[0334]

[0335] Combined with the strain power P in equation (59) def (V s V α From equations (67), (68), and (72), we can obtain:

[0336]

[0337] Equation (73) can be written as:

[0338]

[0339] in,

[0340] J Q =-q·n,(75)

[0341] Where q is the output heat flux vector.

[0342] Substituting equation (11) into equation (10), the Euler form of the energy equation becomes:

[0343]

[0344] That is to say:

[0345]

[0346] therefore:

[0347]

[0348] Among them, the specific enthalpy h of water and gas α for:

[0349]

[0350] Let E, Q, R Q and H QThese are the Lagrange density-weighted total internal energy, Lagrange heat flux, heat supply rate within volume Ω0, and heat change rate caused by hydrate decomposition per unit initial volume dΩ0, respectively, as follows:

[0351] EdΩ0=edΩ,Q·NdA=q·nda,R Q dΩ0=r Q dΩ,H Q dΩ0=h Q dΩ(80)

[0352] Combination:

[0353]

[0354] Combining the energy equation in equation (80), equation (78) can be converted into Lagrange form, as follows:

[0355]

[0356] Optionally, in one embodiment of this application, the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation for the hydrate decomposition process are established in both the Euler and Lagrange coordinate systems, including: In the Euler coordinate system, the second law of thermodynamics for the hydrate decomposition process is:

[0357]

[0358] In the formula, θα (α=w,G) represents the specific entropy of component α, θ is the total entropy per unit volume, T represents the temperature, and n is the normal vector of the lower surface da in the Lagrange coordinate system.

[0359] Based on the second law of thermodynamics in the Euler coordinate system, the Clausius-Duhem inequality for the hydrate decomposition process in the Euler coordinate system is obtained as follows:

[0360]

[0361] In the formula, ψ is the Helmholtz free energy, and g α (α=w,G) represents the free specific enthalpy of fluids with different components (α=c,w);

[0362] Based on the second law of thermodynamics and the Clausius-Duhem inequality in the Euler coordinate system, and combined with Darcy's law, Fourier's law, the degree of mass change, and the heat per unit time in the Euler coordinate system, the energy conservation equation for the hydrate decomposition process in the Euler coordinate system is calculated. The energy conservation equation is as follows:

[0363]

[0364] In the formula, For the Eulerian dissipation volume density associated with open systems, For the Eulerian dissipative volume density related to thermal convection, The Euler dissipative volume density associated with the phase transition;

[0365] In the Lagrange coordinate system, the second law of thermodynamics for the decomposition of hydrates is:

[0366]

[0367] In the formula, Θ is the entropy density in the Lagrange coordinate system, and N is the normal vector of the surface dA in the Lagrange coordinate system;

[0368] Based on the second law of thermodynamics in the Lagrange coordinate system, the Clausius-Duhem inequality for the hydrate decomposition process in the Lagrange coordinate system is obtained as follows:

[0369]

[0370] In the formula, Ψ is the Lagrange free energy density, and M α (α=w,g) represents the molar mass of different pore components;

[0371] Based on the second law of thermodynamics and the Clausius-Duhem inequality in the Lagrange coordinate system, combined with Darcy's law, Fourier's law, the degree of mass change, and the heat per unit time in the Lagrange coordinate system, the energy conservation equation for the hydrate decomposition process in the Lagrange coordinate system is obtained as follows:

[0372]

[0373] In the formula, Φ1 represents the inherent dissipation associated with the open system, and Φ3 and Φ → These are energy dissipation related to thermal convection and phase change, respectively.

[0374] Furthermore, in embodiments of this application, according to the second law of thermodynamics, the increase in entropy θ (a comprehensive thermodynamic quantity) must be greater than or at least equal to the external entropy rate provided in the material subsystem Ω, i.e.:

[0375]

[0376] Where, θ π (π = s, H, w, G) represents the specific entropy of component π. According to equation (21), the left side of equation (83) can be expressed as:

[0377]

[0378] The last term in equation (84) can be expressed as:

[0379]

[0380] Substituting into equation (85), equation (84) can be derived as follows:

[0381]

[0382] Where θ is the total entropy per unit volume, such as:

[0383]

[0384] Substituting equation (86) into equation (83) and introducing the derivative equation, we get:

[0385]

[0386] That is to say:

[0387]

[0388] Equation (89) can be written as:

[0389]

[0390] Combining equation (78), we have:

[0391]

[0392] Furthermore, the Helmholtz free energy ψ is equal to:

[0393] ψ=e-Tθ(92)

[0394] therefore:

[0395] dψ=de-Tdθ-θdT(93)

[0396] Substituting equations (92) and (93) into equation (91), we get:

[0397]

[0398] Considering the fluid free specific enthalpy g α ,Right now:

[0399] g α =h α -Tθ α (α=w,G)

[0400]

[0401] Then we have:

[0402]

[0403] Substituting equation (92) into equation (90), we obtain the Euler form of the Clausius-Duhem inequality:

[0404]

[0405] In the Lagrange formula, the entropy density Θ is defined as:

[0406] ΘdΩ0=θdΩ. (98)

[0407] Combining equation (21), the rate of change of entropy of volume Ω0 with time is:

[0408]

[0409] Similar to equation (83), the second law of thermodynamics in Lagrange form is:

[0410]

[0411] Using the divergence theorem, equation (100) can be expressed as:

[0412]

[0413] Similarly:

[0414]

[0415] Equation (103) is shown below:

[0416]

[0417] Substituting equation (102) into equation (103), we get:

[0418]

[0419] The above formula can be written as:

[0420]

[0421] Combining equations (82) and (105), we can obtain:

[0422]

[0423] Combining equation (95), we can obtain:

[0424]

[0425] Substituting equation (107) into equation (106), we get:

[0426]

[0427] Let Ψ be the Lagrange free energy density, i.e.:

[0428] ΨdΩ0=ψdΩ, Ψ=E-TΘ, dΨ=dE-ΘdT-TdΘ. (109)

[0429] Substituting equations (24) and (109) into equation (108), the Euler form of the Clausius-Duhem inequality can be transformed into the Lagrange form, i.e.:

[0430]

[0431] The term on the left side of equation (110) can be defined as the total dissipation Φ per unit volume dΩ0, which can be decomposed into different physical terms, each of which is non-negative, such as:

[0432] Φ = Φ1 + Φ2 + Φ3 + Φ → (111)

[0433] in,

[0434]

[0435]

[0436]

[0437]

[0438] Where Φ1 represents the intrinsic dissipation associated with the open system dΩ0, which is consistent with the motion of the soil skeleton. Φ1 / T can describe the intrinsic entropy in internal production, which is part of the dissipation, Φ2, Φ3 and Φ → These are heat dissipation related to heat conduction, heat convection, and phase change, respectively.

[0439] According to equation (109), we can obtain:

[0440]

[0441] Combining equations (82) and (116), we can obtain:

[0442]

[0443] Combination:

[0444]

[0445] Substituting equation (118) into equation (117), we get:

[0446]

[0447] The above formula can be written as:

[0448]

[0449] Combination:

[0450]

[0451] and

[0452]

[0453] The Lagrange form of energy conservation associated with equation (120) is:

[0454]

[0455] Where, Φ M =Φ1+Φ3 represents the dissipation caused by irreversible motion.

[0456] Substituting equation (113) into equation (123), we get:

[0457]

[0458] That is to say:

[0459]

[0460] Combination:

[0461]

[0462] We can obtain:

[0463]

[0464] set up Let the volume density be the Euler dissipative density, then:

[0465]

[0466] Total dissipation in Euler's formula for:

[0467]

[0468] in

[0469]

[0470]

[0471]

[0472]

[0473] Combining equations (92) and (93), the energy conservation in equation (78) can be written as:

[0474]

[0475] The above formula can be written as:

[0476]

[0477] Combining equation (95), we can obtain:

[0478]

[0479] also

[0480]

[0481]

[0482] Substituting equation (139) into equation (138), we get:

[0483]

[0484] According to equations (130)-(135), the entropy balance in Euler's formula in equation (140) can be simplified to:

[0485]

[0486] In the specific implementation process, the embodiments of this application can calculate the energy conservation equation and the mass conservation equation through Darcy's law, Fourier's law, and the hydrate decomposition model.

[0487] The analysis of Darcy's law, Fourier's law, and the hydrate decomposition model is as follows:

[0488] First, regarding Darcy's law, for a fluid (α = c, w), its specific enthalpy can be expressed as:

[0489]

[0490] therefore:

[0491]

[0492] Substituting equation (143) into equation (134), we get:

[0493]

[0494] For water or gas, assume that dissipation is non-negative, that is:

[0495]

[0496] in

[0497]

[0498] Based on the assumption of normality of the dissipation mechanism, equation (146) can be expressed using the dissipation potential D. 3α (w α / ρ α To describe:

[0499]

[0500] When the dissipative potential D 3α (w α / ρ α When a function is chosen as a positively defined quadratic function, that is:

[0501]

[0502] Where, k α Given the permeability tensor, the fluid conduction law or Darcy's law is obtained from equations (147) and (148):

[0503]

[0504] For the Lagrange equations, corresponding to equations (144)-(149), we can obtain:

[0505]

[0506] It is assumed to be non-negative, such as:

[0507]

[0508] in

[0509]

[0510] Assume dissipation potential D 3α (M α / ρ α )for:

[0511]

[0512] therefore:

[0513]

[0514] and

[0515]

[0516] Where K α It is k α The conversion is as follows:

[0517] K α =JF -1 ·k α · t F -1 (156)

[0518] Regarding Fourier's law, according to the heat dissipation formula... nonnegativity but:

[0519]

[0520] Equation (157) dissipates heat to q / T and Connecting these points, according to the above inequality, heat spontaneously flows from high temperature to low temperature, and equation (157) corresponds to Fourier's law, namely:

[0521]

[0522] Here, κ is defined as the thermal conductivity tensor relative to the current configuration, and is positive definite and symmetric.

[0523] For the Lagrange form, we can obtain:

[0524]

[0525] Where Kis is the transformation of κ, such as:

[0526] K = JF -1 ·κ· t F -1 (160)

[0527] In Euler's formula, the mass change caused by the decomposition of hydrate per unit time is determined by the decomposition rate of the hydrate, that is:

[0528] Λ H→wG =M H r h

[0529] Λ H→w =N H M w r h ,

[0530] Λ H→G =M g r h (161)

[0531] Where, rh (kmol / s) is the decomposition rate of hydrate, M α (α = H, w, g) represents the molar mass of different components, N H It is the water element.

[0532] Similarly, in the Lagrange formula, we can obtain:

[0533]

[0534]

[0535]

[0536] Among them, R h (kmol / s) is the hydrate decomposition rate in the Lagrange formula.

[0537] Heat per unit time h caused by hydrate decomposition Q Determined by the decomposition rate and enthalpy of the hydrate, it can be obtained in the Eulerian form.

[0538] h Q =-ΔHr h (163)

[0539] ΔH is the latent heat caused by the phase transition of hydrates.

[0540] Similarly, in the Lagrange form, we can obtain:

[0541] H Q =-ΔHR h (164)

[0542] In step S102, a thermodynamic coupling model of the hydrate decomposition process is constructed based on the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality and energy conservation equation.

[0543] In step S103, a thermodynamic coupling model is used to describe the multiphase flow behavior and thermodynamic behavior of the hydrate decomposition process, and the analysis results of the natural gas hydrate decomposition behavior in porous media are obtained.

[0544] Furthermore, embodiments of this application can construct a thermodynamic coupling model involving multiphase flow and phase change during the hydrate decomposition process based on the established mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation. This establishes a comprehensive theoretical framework, yields analytical results of the natural gas hydrate decomposition behavior in porous media, and comprehensively describes the multiphase flow behavior and thermodynamic behavior during the hydrate decomposition process.

[0545] According to the method for analyzing the decomposition behavior of natural gas hydrates in porous media proposed in this application, based on the fundamental principles of thermodynamics, mass conservation equations, momentum conservation equations, kinetic energy theorem equations, the first law of thermodynamics equations, the second law of thermodynamics equations, Clausius-Duhem inequalities, and energy conservation equations for the hydrate decomposition process are established in both Eulerian and Lagrange coordinate systems. Based on these equations, a thermodynamic coupling model of the hydrate decomposition process is constructed. Using this thermodynamic coupling model, the multiphase flow behavior and thermodynamic behavior of the hydrate decomposition process are described, and the analysis results of the decomposition behavior of natural gas hydrates in porous media are obtained. This application analyzes the multiphase flow, phase change, and heat conversion of solid, liquid, and gas in hydrate reservoir media to prevent changes in the contact interface between soil particles, hydrates, water, and gas caused by hydrate decomposition behavior. This ensures the decomposition rate and gas production rate of the entire hydrate reservoir, providing theoretical support for the commercialization of hydrate extraction.

[0546] Secondly, the apparatus for analyzing the decomposition behavior of natural gas hydrates in porous media according to embodiments of this application is described with reference to the accompanying drawings.

[0547] Figure 3 This is a block diagram of an apparatus for analyzing the decomposition behavior of natural gas hydrates in porous media according to an embodiment of this application.

[0548] like Figure 3 As shown, the device 10 for analyzing the decomposition behavior of natural gas hydrates in porous media includes: a calculation module 100, a modeling module 200, and a simulation module 300.

[0549] The computation module 100 is used to establish, based on the fundamental principles of thermodynamics, the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, the first law of thermodynamics equation, the second law of thermodynamics equation, the Clausius-Duhem inequality, and the energy conservation equation for the hydrate decomposition process in the Euler coordinate system and the Lagrange coordinate system, respectively.

[0550] Modeling module 200 is used to construct a thermodynamically coupled model of the hydrate decomposition process based on the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality and energy conservation equation.

[0551] Simulation module 300 is used to describe the multiphase flow behavior and thermodynamic behavior of hydrate decomposition process using a thermodynamic coupling model, and to obtain the analysis results of natural gas hydrate decomposition behavior in porous media.

[0552] Optionally, in one embodiment of this application, the computation module 100 includes: a first computation unit, a second computation unit, a third computation unit, an Euler mass conservation unit, a fourth computation unit, a Lagrange mass conservation unit, and a fifth computation unit.

[0553] The first calculation unit is used to calculate the decomposition rate and enthalpy of the hydrate.

[0554] The second calculation unit is used to calculate the degree of mass change caused by hydrate decomposition per unit time in both Eulerian and Lagrange coordinate systems, based on the hydrate decomposition rate.

[0555] The third calculation unit is used to calculate the heat per unit time caused by the decomposition of hydrates in both Eulerian and Lagrange coordinate systems, based on the decomposition rate and enthalpy of the hydrates.

[0556] In the case of phase transition, the mass conservation equations for the hydrate decomposition process include the solid matrix mass conservation equation and the pore component mass conservation equation.

[0557] The Euler mass conservation element is used in the Euler coordinate system, where the mass conservation equation for the solid matrix is:

[0558]

[0559] In the formula, τ is the Euler porosity, t is time, and ρ is... s V is the intrinsic mass density of the soil particle solid matrix. s The velocity of the soil particle solid matrix.

[0560] The fourth calculation unit is used to calculate the mass conservation equation of the pore components in the Euler coordinate system based on Darcy's law, Fourier's law, the degree of mass change, and the heat per unit time. The mass conservation equation of the pore components is as follows:

[0561]

[0562]

[0563]

[0564] In the formula, ρ H ρ is the density of the hydrate. W ρ is the density of water. G For gas density, Λ H→wG Λ represents the mass of hydrate decomposition per unit volume and per unit time. H→w Λ represents the mass of hydrate converted into water. H→G V represents the mass of hydrate converted into gas. H V represents the velocity of the hydrate. W V is the velocity of the water. G Let τ be the velocity of the gas. H For the porosity of Euler hydrates, τ W Let τ be the Euler water porosity. G The value represents the Euler gas porosity.

[0565] The Lagrange mass conservation element is used to represent the mass conservation equation of a solid matrix in a Lagrange coordinate system.

[0566]

[0567] In the formula, n is the initial soil matrix density, and n0 is the initial porosity.

[0568] The fifth calculation unit is used to calculate the mass conservation equation of the pore components in the Lagrange coordinate system, based on Darcy's law, Fourier's law, the degree of mass change, and the heat per unit time. The mass conservation equation of the pore components is as follows:

[0569]

[0570]

[0571]

[0572] In the formula, This represents the mass of hydrate converted into water and gas in the Lagrange formula. This represents the mass of hydrate converted to water in the Lagrange formula. m represents the mass of hydrate converted to gas in the Lagrange formula. H For the mass of hydrate, m W For water quality, m G For the mass of the gas, M w M is the Lagrange flux of water added to the initial configuration. G This refers to the Lagrange flux of the gas added to the initial configuration.

[0573] Optionally, in one embodiment of this application, the computing module 100 further includes:

[0574] In the Euler coordinate system, the momentum conservation equation for the hydrate decomposition process is:

[0575]

[0576] In the formula, γ s For the acceleration of the soil skeleton, γ α Let g be the acceleration of hydrates, water, and gas, g be the gravity vector, σ be the Cauchy stress in the Euler coordinate system, and ρ be the acceleration of hydrates, water, and gas. α τ is the mass density of the porous component. α Let be the porosity of hydrates, water, and gas in the Euler coordinate system.

[0577] In the Lagrange coordinate system, the momentum conservation equation for the hydrate decomposition process is:

[0578]

[0579] In the formula, F is the deformation gradient, π is the Piola-Kirchhoff stress tensor in Lagrange coordinates, and m α The mass of hydrates, water, and gases.

[0580] Optionally, in one embodiment of this application, the computing module 100 further includes:

[0581] In the Euler coordinate system, the kinetic energy theorem equation for the hydrate decomposition process is as follows:

[0582]

[0583] in,

[0584]

[0585] In the formula, K s For the kinetic energy of the soil skeleton, K α V represents the kinetic energy of hydrates, water, and gases. α Let d be the velocity of hydrates, water, and gas. s Let w be the Euler strain rate tensor of the soil skeleton. α It is the Euler mass flux, p α The pressure is the pressure of the fluid with different components.

[0586] In the Lagrange coordinate system, the kinetic energy theorem equation for the hydrate decomposition process is:

[0587]

[0588] in, The strain power for unsaturated soil in the Lagrange formula is shown below:

[0589]

[0590] In the formula, h s h represents the kinetic energy of the soil matrix in Lagrange coordinates. α Let λ be the kinetic energy of the fluid composed of hydrates, water, and gas, and Δ be the Green-Lagrange strain tensor. Let be the porosity of different components in Lagrange coordinates, g be the gravitational acceleration matrix, and J be the Jacobian number, i.e., the rank of the deformation gradient F.

[0591] Optionally, in one embodiment of this application, the computing module 100 further includes:

[0592] In the Euler coordinate system, the first law of thermodynamics for the decomposition of hydrates is:

[0593]

[0594] In the formula, e is the total internal energy of the soil matrix and pore components, and r Q and h Q denoted as the heat supply rate and the heat change rate caused by hydrate decomposition in the Euler coordinate system, respectively, and q is the output heat flux vector.

[0595] In the Lagrange coordinate system, the first law of thermodynamics for the decomposition of hydrates is:

[0596]

[0597] In the formula, E and Q are the Lagrange density-weighted total internal energy and Lagrange heat flux per unit initial volume, respectively, Δ is the Green-Lagrange strain tensor, and R... Q and H Q These represent the Lagrange density-weighted rate of heat supply per unit initial volume and the rate of heat change caused by hydrate decomposition, respectively.

[0598] Optionally, in one embodiment of this application, the calculation module 100 further includes: a sixth calculation unit, a seventh calculation unit, an eighth calculation unit, and a ninth calculation unit.

[0599] In the Euler coordinate system, the second law of thermodynamics for the decomposition of hydrates is:

[0600]

[0601] In the formula, θα (α=w,G) represents the specific entropy of component α, θ is the total entropy per unit volume, T represents the temperature, and n is the normal vector of the lower surface da in the Lagrange coordinate system.

[0602] The sixth calculation unit, based on the second law of thermodynamics in the Euler coordinate system, derives the Clausius-Duhem inequality for the hydrate decomposition process in the Euler coordinate system as follows:

[0603]

[0604] In the formula, ψ is the Helmholtz free energy, and g α (α=w,G) represents the free enthalpy of fluids with different components (α=c,w).

[0605] The seventh calculation unit is used to calculate the energy conservation equation for the hydrate decomposition process in the Euler coordinate system based on the second law of thermodynamics and the Clausius-Duhem inequality, combined with Darcy's law, Fourier's law, the degree of mass change, and the heat per unit time in the Euler coordinate system. The energy conservation equation is as follows:

[0606]

[0607] In the formula, For the Eulerian dissipation volume density associated with open systems, For the Eulerian dissipative volume density related to thermal convection, The volumetric density of Euler dissipation associated with the phase transition.

[0608] In the Lagrange coordinate system, the second law of thermodynamics for the decomposition of hydrates is:

[0609]

[0610] In the formula, Θ is the entropy density in the Lagrange coordinate system, and N is the normal vector of the surface dA in the Lagrange coordinate system.

[0611] The eighth calculation unit, based on the second law of thermodynamics in the Lagrange coordinate system, derives the Clausius-Duhem inequality for the hydrate decomposition process in the Lagrange coordinate system as follows:

[0612]

[0613] In the formula, Ψ is the Lagrange free energy density, and M α (α = w, g) represents the molar mass of different pore components.

[0614] The ninth calculation unit is used to derive the energy conservation equation for the hydrate decomposition process in the Lagrange coordinate system based on the second law of thermodynamics, the Clausius-Duhem inequality, Darcy's law, Fourier's law, the degree of mass change, and the heat per unit time in the Lagrange coordinate system. The energy conservation equation is as follows:

[0615]

[0616] In the formula, Φ1 represents the inherent dissipation associated with the open system, and Φ3 and Φ → These are energy dissipation related to thermal convection and phase change, respectively.

[0617] It should be noted that the foregoing explanation of the embodiment of the method for analyzing the decomposition behavior of natural gas hydrates in porous media also applies to the apparatus for analyzing the decomposition behavior of natural gas hydrates in porous media in this embodiment, and will not be repeated here.

[0618] The apparatus for analyzing the decomposition behavior of natural gas hydrates in porous media according to the embodiments of this application includes a computation module for establishing, based on the fundamental principles of thermodynamics, the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, the first law of thermodynamics equation, the second law of thermodynamics equation, the Clausius-Duhem inequality, and the energy conservation equation for the hydrate decomposition process in Euler and Lagrange coordinate systems, respectively; a modeling module for constructing a thermodynamically coupled model of the hydrate decomposition process based on the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, the first law of thermodynamics equation, the second law of thermodynamics equation, the Clausius-Duhem inequality, and the energy conservation equation; and a simulation module for using the thermodynamically coupled model to describe the multiphase flow behavior and thermodynamic behavior of the hydrate decomposition process, and to obtain the analysis results of the decomposition behavior of natural gas hydrates in porous media. This application analyzes the multiphase flow, phase change, and heat conversion of solid, liquid, and gas in hydrate reservoir media to prevent changes in the contact interface between soil particles, hydrates, water, and gas caused by hydrate decomposition behavior. This ensures the decomposition rate and gas production rate of the entire hydrate reservoir, providing theoretical support for the commercialization of hydrate extraction.

[0619] Figure 4 A schematic diagram of the structure of an electronic device provided in an embodiment of this application. The electronic device may include:

[0620] The memory 401, the processor 402, and the computer program stored on the memory 401 and capable of running on the processor 402.

[0621] When the processor 402 executes the program, it implements the method for analyzing the decomposition behavior of natural gas hydrates in porous media provided in the above embodiments.

[0622] Furthermore, electronic devices also include:

[0623] Communication interface 403 is used for communication between memory 401 and processor 402.

[0624] The memory 401 is used to store computer programs that can run on the processor 402.

[0625] The memory 401 may include high-speed RAM memory, and may also include non-volatile memory, such as at least one disk storage device.

[0626] If the memory 401, processor 402, and communication interface 403 are implemented independently, then the communication interface 403, memory 401, and processor 402 can be interconnected via a bus to complete communication between them. The bus can be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, or an Extended Industry Standard Architecture (EISA) bus, etc. Buses can be divided into address buses, data buses, control buses, etc. For ease of representation, Figure 4 The bus is represented by a single thick line, but this does not mean that there is only one bus or one type of bus.

[0627] Optionally, in a specific implementation, if the memory 401, processor 402, and communication interface 403 are integrated on a single chip, then the memory 401, processor 402, and communication interface 403 can communicate with each other through an internal interface.

[0628] Processor 402 may be a central processing unit (CPU), an application specific integrated circuit (ASIC), or one or more integrated circuits configured to implement the embodiments of this application.

[0629] This application also provides a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the above-described method for analyzing the decomposition behavior of natural gas hydrates in porous media.

[0630] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0631] 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 indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "N" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0632] Any process or method described in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or N executable instructions for implementing custom logic functions or processes, and the scope of the preferred embodiments of this application includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as should be understood by those skilled in the art to which embodiments of this application pertain.

[0633] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0634] It should be understood that the various parts of this application can be implemented using hardware, software, firmware, or a combination thereof. In the above embodiments, the N steps or methods can be implemented using software or firmware stored in memory and executed by a suitable instruction execution system. If implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0635] Those skilled in the art will understand that all or part of the steps of the methods in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, the program includes one or a combination of the steps of the method embodiments.

[0636] Furthermore, the functional units in the various embodiments of this application can be integrated into a processing module, or each unit can exist physically separately, or two or more units can be integrated into a module. The integrated module can be implemented in hardware or as a software functional module. If the integrated module is implemented as a software functional module and sold or used as an independent product, it can also be stored in a computer-readable storage medium.

[0637] The storage medium mentioned above can be a read-only memory, a disk, or an optical disk, etc. Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of this application.

Claims

1. A method for analyzing the decomposition behavior of natural gas hydrates in porous media, characterized in that, Includes the following steps: Based on the fundamental principles of thermodynamics, the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation for the hydrate decomposition process are established in both Euler and Lagrange coordinate systems. Based on the mass conservation equation, the momentum conservation equation, the kinetic energy theorem equation, the first law of thermodynamics equation, the second law of thermodynamics equation, the Clausius-Duhem inequality, and the energy conservation equation, a thermodynamic coupling model of the hydrate decomposition process is constructed. The thermodynamic coupling model is used to describe the multiphase flow behavior and thermodynamic behavior of the hydrate decomposition process, and the analysis results of the natural gas hydrate decomposition behavior in porous media are obtained. The establishment of the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation for the hydrate decomposition process in Eulerian and Lagrange coordinate systems, respectively, includes: Calculate the decomposition rate and enthalpy of the hydrate; Based on the decomposition rate of the hydrate, the degree of mass change caused by the decomposition of the hydrate per unit time is calculated in both the Euler coordinate system and the Lagrange coordinate system. Based on the decomposition rate and enthalpy of the hydrate, the heat per unit time caused by the decomposition of the hydrate in the Euler coordinate system and the Lagrange coordinate system are calculated respectively. In the case of phase transition, the mass conservation equation for the hydrate decomposition process includes the solid matrix mass conservation equation and the pore component mass conservation equation. In the Euler coordinate system, the mass conservation equation for the solid matrix is: In the formula, τ Euler porosity, t For time, ρ s V is the intrinsic mass density of the soil particle solid matrix. s The velocity of the soil particle solid matrix; In the Euler coordinate system, based on Darcy's law, Fourier's law, the degree of mass change, and the heat per unit time, the mass conservation equation for the pore component is calculated. The mass conservation equation for the pore component is as follows: In the formula, ρ H The density of the hydrate. ρ W The density of water, ρ G For gas density, Λ H→wG Λ represents the mass of hydrate decomposition per unit volume and per unit time. H→w Λ represents the mass of the hydrate converted into water. H→G V represents the mass of the hydrate converted into gas. H V is the velocity of the hydrate. W V is the velocity of the water. G τ is the velocity of the gas. H For the porosity of Euler hydrates, τ W Let τ be the Euler water porosity. G Euler gas porosity; In the Lagrange coordinate system, the mass conservation equation of the solid matrix is: In the formula, τ is the initial soil matrix density, and τ0 is the initial porosity; In the Lagrange coordinate system, based on Darcy's law, Fourier's law, the degree of mass change, and the heat per unit time, the mass conservation equation for the pore component is calculated. The mass conservation equation for the pore component is as follows: In the formula, This represents the mass of hydrate converted into water and gas in the Lagrange formula. This represents the mass of hydrate converted to water in the Lagrange formula. This represents the mass of hydrate converted to gas in the Lagrange formula. For the mass of hydrates, For water quality, For gas mass, The Lagrange flux of water added to the initial configuration. The Lagrange flux of the gas added to the initial configuration; The establishment of the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation for the hydrate decomposition process in Eulerian and Lagrange coordinate systems respectively includes: In the Euler coordinate system, the momentum conservation equation for the hydrate decomposition process is: In the formula, γ s For the acceleration of the soil skeleton, γ α Let g be the acceleration of the hydrate, water, and gas, g be the gravity vector, and σ be the Cauchy stress in the Euler coordinate system. ρ α τ is the mass density of the porous component. α Porosity of hydrates, water, and gas in the Euler coordinate system; In the Lagrange coordinate system, the momentum conservation equation for the hydrate decomposition process is: In the formula, For deformation gradient, Let Piola-Kirchhoff stress tensor be in the Lagrange coordinate system. The mass of the hydrate, water, and gas; The establishment of the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation for the hydrate decomposition process in Eulerian and Lagrange coordinate systems respectively includes: In the Euler coordinate system, the kinetic energy theorem equation for the hydrate decomposition process is as follows: in, In the formula, K s This refers to the kinetic energy of the soil skeleton. K α V represents the kinetic energy of the hydrate, water, and gas. α Let d be the velocity of the hydrate, water, and gas. s Let w be the Euler strain rate tensor of the soil skeleton. α It is the Euler mass flux. p α The pressure of fluids with different components; In the Lagrange coordinate system, the kinetic energy theorem equation for the hydrate decomposition process is: in, The strain power for unsaturated soil in the Lagrange formula is shown below: In the formula, Let be the kinetic energy of the soil matrix in the Lagrange coordinates. Let Δ be the kinetic energy of the fluid composed of the hydrate, water, and gas, and Δ be the Green-Lagrange strain tensor. φ α Let be the porosity of different components in the Lagrange coordinates, g be the gravitational acceleration matrix, and J be the Jacobian number, i.e., the rank of the deformation gradient F. The establishment of the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation for the hydrate decomposition process in Euler and Lagrange coordinate systems respectively includes: In the Euler coordinate system, the first law of thermodynamics for the hydrate decomposition process is: In the formula, The total internal energy of the soil matrix and the pore components. r Q and h Q These are the heat supply rate and the heat change rate caused by hydrate decomposition in the Euler coordinate system, respectively, and q is the output heat flux vector. In the Lagrange coordinate system, the first law of thermodynamics for the hydrate decomposition process is: In the formula, E , Q Let be the total internal energy and Lagrange heat flux per unit initial volume, respectively, and Δ be the Green-Lagrange strain tensor. R Q and H Q These are the Lagrange density-weighted heat supply rate per unit initial volume and the heat change rate caused by hydrate decomposition, respectively. The establishment of the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality, and energy conservation equation for the hydrate decomposition process in Eulerian and Lagrange coordinate systems respectively includes: In the Euler coordinate system, the second law of thermodynamics for the hydrate decomposition process is: In the formula, θ ( =w, G) represents the components α The specific entropy, θ The total entropy per unit volume is T, where T represents temperature, and n is the lower surface d in the Lagrange coordinate system. a The normal vector; Based on the second law of thermodynamics in the Euler coordinate system, the Clausius-Duhem inequality for the hydrate decomposition process in the Euler coordinate system is as follows: In the formula, ψ For Helmholtz free energy, ( =w, G) represents fluids with different components ( α = c, w) free specific enthalpy; Based on the second law of thermodynamics in the Euler coordinate system and the Clausius-Duhem inequality, combined with Darcy's law, Fourier's law, the degree of mass change, and the heat per unit time in the Euler coordinate system, the energy conservation equation for the hydrate decomposition process in the Euler coordinate system is calculated. The energy conservation equation is as follows: In the formula, φ 1 represents the Eulerian dissipation volume density associated with the open system. φ 2 represents the Euler dissipative volume density related to thermal convection. φ → The Euler dissipative volume density associated with the phase transition; In the Lagrange coordinate system, the second law of thermodynamics for the hydrate decomposition process is: In the formula, Θ Let N be the entropy density in the Lagrange coordinate system, and let N be the normal vector of the surface dA in the Lagrange coordinate system. Based on the second law of thermodynamics in the Lagrange coordinate system, the Clausius-Duhem inequality for the hydrate decomposition process in the Lagrange coordinate system is as follows: In the formula, Ψ is the Lagrange free energy density. M α ( α =w, g) represents the molar mass of different pore components; Based on the second law of thermodynamics in the Lagrange coordinate system, the Clausius-Duhem inequality, Darcy's law in the Lagrange coordinate system, Fourier's law, the degree of mass change, and the heat per unit time, the energy conservation equation for the hydrate decomposition process in the Lagrange coordinate system is obtained. The energy conservation equation is: In the formula, Φ1 represents the inherent dissipation associated with the open system, and Φ3 and Φ → These are energy dissipation related to thermal convection and phase change, respectively.

2. An apparatus for analyzing the decomposition behavior of natural gas hydrates in porous media, used to implement the method for analyzing the decomposition behavior of natural gas hydrates in porous media as described in claim 1, characterized in that, include: The computation module is used to establish the mass conservation equation, momentum conservation equation, kinetic energy theorem equation, first law of thermodynamics equation, second law of thermodynamics equation, Clausius-Duhem inequality and energy conservation equation for the hydrate decomposition process in Euler coordinate system and Lagrange coordinate system, respectively, based on the basic principles of thermodynamics. The modeling module is used to construct a thermodynamic coupling model of the hydrate decomposition process based on the mass conservation equation, the momentum conservation equation, the kinetic energy theorem equation, the first law of thermodynamics equation, the second law of thermodynamics equation, the Clausius-Duhem inequality, and the energy conservation equation. The simulation module is used to describe the multiphase flow behavior and thermodynamic behavior of the hydrate decomposition process using the thermodynamic coupling model, and to obtain the analysis results of the natural gas hydrate decomposition behavior in porous media.

3. The apparatus according to claim 2, characterized in that, The computing module includes: The first calculation unit is used to calculate the decomposition rate and enthalpy of hydrates; The second calculation unit is used to calculate the degree of mass change caused by the decomposition of the hydrate per unit time in the Euler coordinate system and the Lagrange coordinate system, respectively, based on the decomposition rate of the hydrate. The third calculation unit is used to calculate the heat per unit time caused by the decomposition of the hydrate in the Euler coordinate system and the Lagrange coordinate system, respectively, based on the decomposition rate and enthalpy of the hydrate. In the case of phase transition, the mass conservation equation for the hydrate decomposition process includes the solid matrix mass conservation equation and the pore component mass conservation equation. An Euler mass conservation element is used in the Euler coordinate system, and the mass conservation equation of the solid matrix is: In the formula, τ Euler porosity, t For time, ρ s V is the intrinsic mass density of the soil particle solid matrix. s The velocity of the soil particle solid matrix; The fourth calculation unit is used to calculate the mass conservation equation of the pore component in the Euler coordinate system based on Darcy's law, Fourier's law, the degree of mass change, and the heat per unit time. The mass conservation equation of the pore component is as follows: In the formula, ρ H The density of the hydrate. ρ W The density of water, ρ G For gas density, Λ H→wG Λ represents the mass of hydrate decomposition per unit volume and per unit time. H→w Λ represents the mass of the hydrate converted into water. H→G V represents the mass of the hydrate converted into gas. H V is the velocity of the hydrate. W V is the velocity of the water. G τ is the velocity of the gas. H For the porosity of Euler hydrates, τ W Let τ be the Euler water porosity. G Euler gas porosity; A Lagrange mass conservation element is used in the Lagrange coordinate system, and the mass conservation equation of the solid matrix is: In the formula, τ is the initial soil matrix density, and τ0 is the initial porosity; The fifth calculation unit is used to calculate the mass conservation equation of the pore component in the Lagrange coordinate system based on Darcy's law, Fourier's law, the degree of mass change, and the heat per unit time. The mass conservation equation of the pore component is as follows: In the formula, This represents the mass of hydrate converted into water and gas in the Lagrange formula. This represents the mass of hydrate converted to water in the Lagrange formula. This represents the mass of hydrate converted to gas in the Lagrange formula. For the mass of hydrates, For water quality, For gas mass, The Lagrange flux of water added to the initial configuration. This refers to the Lagrange flux of the gas added to the initial configuration.

4. An electronic device, characterized in that, include: The method includes a memory, a processor, and a computer program stored in the memory and executable on the processor, the processor executing the program to implement the method for analyzing the decomposition behavior of natural gas hydrates in porous media as described in claim 1.

5. A computer-readable storage medium having a computer program stored thereon, characterized in that, The program is executed by a processor to implement the method for analyzing the decomposition behavior of natural gas hydrates in porous media as described in claim 1.

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