Method and apparatus for constructing stress-strain constitutive models of natural gas hydrate decomposition

Abstract

This application relates to a method and apparatus for constructing a stress-strain constitutive model for natural gas hydrate decomposition. The method includes: constructing a thermal porosity elastic constitutive model of the hydrate reservoir based on a pre-defined Lagrange saturation theory and solid-liquid-gas interface interaction; obtaining an ideal thermal porosity elastoplastic constitutive model of the hydrate and soil particles based on the thermal porosity elastic constitutive model of the hydrate reservoir and the plastic strain characteristics of the hydrate and soil particles; and establishing a generalized stiffness matrix of the hardening elastoplastic modulus based on the ideal thermal porosity elastoplastic constitutive model, the strain hardening characteristics of the hydrate and soil particles, and the associated or unassociated plastic potential energy, to construct a hardening elastoplastic constitutive model of the hydrate reservoir, thereby predicting the reservoir stability during the hydrate decomposition process. This solves the problem that the hydrate decomposition process easily leads to a decrease in hydrate saturation, pressure changes, and effective stress reconstruction, which greatly damages the geomechanical stability of the hydrate reservoir.

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 constructing a stress-strain constitutive model of natural gas hydrate decomposition. Background Technology

[0002] Natural gas hydrates are abundant and have high energy density, making them a viable alternative to traditional fuels. However, current hydrate extraction technologies are not yet mature enough to meet the demands of commercial exploitation. Hydrates typically occur in high-pressure and low-temperature environments, such as permafrost regions and shallow seabeds. When the hydrate equilibrium is disrupted, such as by increased temperature, decreased pressure, or weakened equilibrium conditions, it will decompose into water and gas. This decomposition process easily leads to changes in the contact interfaces between soil particles, hydrates, and water and gas, accompanied by heat absorption, thus affecting the decomposition rate and gas production rate of the entire hydrate reservoir.

[0003] Furthermore, the decomposition process of hydrates involves the transformation from solid to gaseous and liquid phases, which leads to a decrease in hydrate saturation, pressure changes, effective stress reconstruction, local temperature reduction, and changes in the mechanical properties of the solid skeleton. This may disrupt the geomechanical stability of the reservoir, such as wellbore collapse, submarine landslides, or damage to existing engineering structures, and may even trigger tsunamis and earthquakes.

[0004] In summary, in the existing technology, the decomposition process of hydrates can easily lead to a decrease in hydrate saturation, pressure changes, effective stress reconstruction, or changes in the mechanical properties of the solid skeleton, which greatly undermines the geomechanical stability of hydrate reservoirs and urgently needs to be addressed. Summary of the Invention

[0005] This application provides a method and apparatus for constructing a stress-strain constitutive model for the decomposition of natural gas hydrates, in order to solve the problems that the decomposition process of hydrates can easily lead to a decrease in hydrate saturation, pressure changes, and effective stress reconstruction, which greatly damage the geomechanical stability of hydrate reservoirs.

[0006] The first aspect of this application provides a method for constructing a stress-strain constitutive model for the decomposition of natural gas hydrates, comprising the following steps: constructing a thermal porosity elastic constitutive model of a hydrate reservoir based on a preset Lagrange saturation theory and solid-liquid-gas interface interaction; obtaining an ideal thermal porosity elastoplastic constitutive model of the hydrate and soil particles based on the thermal porosity elastic constitutive model of the hydrate reservoir and the plastic strain characteristics of the hydrate and soil particles; establishing a generalized stiffness matrix of the hardening elastoplastic modulus based on the ideal thermal porosity elastoplastic constitutive model, the strain hardening characteristics of the hydrate and soil particles, and the associated or unassociated plastic potential energy; and constructing a hardening elastoplastic constitutive model of the hydrate reservoir based on the generalized stiffness matrix, so as to predict the reservoir stability of the hydrate decomposition process through the hardening elastoplastic constitutive model of the hydrate reservoir.

[0007] Optionally, in one embodiment of this application, the step of constructing a thermoporous elastic constitutive model of a hydrate reservoir based on a preset Lagrange saturation theory and solid-liquid-gas interface interaction includes: analyzing the volume changes of the solid skeleton and the pore space to obtain the volume change results of the solid skeleton and the pore space; calculating the state equation of the unsaturated soil thermoporous elasticity based on the volume change results; and calculating the volume change results of the solid skeleton and the pore space under isotropic conditions and the state equation of the unsaturated soil thermoporous elasticity under isotropic conditions based on the state equation of the unsaturated soil thermoporous elasticity and a preset Legendre-Fenchel transformation strategy. The volume changes of the solid framework and the pore space under isotropic conditions are as follows:

[0008] The equation of state for the thermal porosity elasticity of the isotropic unsaturated soil is as follows:

[0009] In the formula, σ ij For the component form of Cauchy stress σ, f W This represents the change in the volume occupied by water. f G θ represents the change in the volume occupied by the gas. m Let ε be the entropy of the solid matrix. kk For volumetric strain, K , G and α These represent the bulk modulus, shear modulus, and coefficient of thermal expansion of the solid skeleton, respectively. b G For the generalized Biot coefficient of gases, b W For water, the generalized Biot coefficient, NJK For the generalized Biot coupling modulus, C T ε is the specific heat capacity of the solid matrix. ij For strain tensor, α W The coefficient of thermal expansion of water is 1. α G is the coefficient of thermal expansion of the gas. T m Temperature under relative conditions In order to effectively transfer gas pressure to the solid framework, In order to effectively transfer the water pressure to the solid framework, This is the Kronecker matrix.

[0010] Optionally, in one embodiment of this application, obtaining an ideal thermal porosity elastic-plastic constitutive model of the hydrate reservoir based on the thermal porosity elastic constitutive model of the hydrate reservoir and the plastic strain characteristics of the hydrate and soil particles includes: under ideal plastic conditions without hardening variables, the volume change results of the solid skeleton and the pore space under isotropic conditions and the state equation of the thermal porosity elasticity of the unsaturated soil under isotropic conditions are as follows:

[0011]

[0012] In the formula, These represent plastic strain and changes in plastic porosity of water and gas, respectively. The yield trajectory of the ideal elastoplastic constitutive model is obtained according to the preset maximum plastic work principle. When the smoothness of the yield trajectory is zero, the yield trajectory is a convex function, and the yield trajectory is as follows:

[0013] In the formula, λ is the relative change in stress or porosity caused by strain or volume change under yielding conditions; when f <0 or f =0 and d f When <0, then =0, =0 and =0, where, f This is related to the plastic potential.

[0014] Optionally, in one embodiment of this application, the step of establishing a generalized stiffness matrix of the hardening elastoplastic modulus based on the ideal thermal porosity elastoplastic constitutive model, the strain hardening characteristics of the hydrate and the soil particles, and combining correlated or uncorrelated plastic potential energy, and constructing a hardening elastoplastic constitutive model of the hydrate reservoir based on the generalized stiffness matrix, includes: obtaining a first hardening elastoplastic theory based on the correlated plastic potential energy, wherein the first hardening elastoplastic theory is:

[0015] in,

[0016] The second hardening elastoplastic theory is derived based on the non-correlated plastic potential energy. The second hardening elastoplastic theory is as follows:

[0017] in,

[0018] In the formula, H The hardening modulus is the plastic potential associated with hardening plasticity. The hardening modulus is the uncorrelated plastic potential. x J dλ is the hardening variable. E Let be the relative change in effective stress caused by strain under yield conditions, and be... , g J These are the hardening parameters; Based on the second hardening elastoplastic theory, the hardening elastoplastic modulus of the unassociated hardening elastoplastic constitutive model is calculated as follows:

[0019]

[0020] Based on the first hardening elastoplastic theory, the hardening elastoplastic modulus of the associated hardening elastoplastic constitutive model is calculated as follows:

[0021] In the formula, D e Let σ be the elastic modulus matrix. E For effective stress, The hardening modulus parameter is used to characterize the effective stress.

[0022] A second aspect of this application provides a device for constructing a stress-strain constitutive model for natural gas hydrate decomposition, comprising: a first modeling module for constructing a thermal porosity elastic constitutive model of a hydrate reservoir based on a preset Lagrange saturation theory and solid-liquid-gas interface interaction; a second modeling module for obtaining an ideal thermal porosity elastoplastic constitutive model of the hydrate and soil particles based on the thermal porosity elastic constitutive model of the hydrate reservoir and the plastic strain characteristics of the hydrate and soil particles; and a prediction module for establishing a generalized stiffness matrix of the hardening elastoplastic modulus based on the ideal thermal porosity elastoplastic constitutive model, the strain hardening characteristics of the hydrate and soil particles, and the associated or unassociated plastic potential energy, and constructing a hardening elastoplastic constitutive model of the hydrate reservoir based on the generalized stiffness matrix, so as to predict the reservoir stability of the hydrate decomposition process through the hardening elastoplastic constitutive model of the hydrate reservoir.

[0023] Optionally, in one embodiment of this application, the first modeling module includes: a first analysis unit, used to analyze the volume changes of the solid skeleton and the pore space, and obtain the volume change results of the solid skeleton and the pore space; a first calculation unit, used to calculate the state equation of unsaturated soil thermal porosity elasticity based on the volume change results; and a second calculation unit, used to calculate the volume change results of the solid skeleton and the pore space under isotropic conditions and the state equation of unsaturated soil thermal porosity elasticity under isotropic conditions based on the state equation of unsaturated soil thermal porosity elasticity and a preset Legendre-Fenchel transformation strategy; wherein, the volume change results of the solid skeleton and the pore space under isotropic conditions are:

[0024] The equation of state for the thermal porosity elasticity of the isotropic unsaturated soil is as follows:

[0025] In the formula, σ ij For the component form of Cauchy stress σ, f W This represents the change in the volume occupied by water. f G θ represents the change in the volume occupied by the gas. m Let ε be the entropy of the solid matrix. kk For volumetric strain, K , G and α These represent the bulk modulus, shear modulus, and coefficient of thermal expansion of the solid skeleton, respectively. b G For the generalized Biot coefficient of gases, b W For water, the generalized Biot coefficient, NJK For the generalized Biot coupling modulus, C T ε is the specific heat capacity of the solid matrix. ij For strain tensor, α W The coefficient of thermal expansion of water is 1. α G is the coefficient of thermal expansion of the gas. T m Temperature under relative conditions In order to effectively transfer gas pressure to the solid framework, In order to effectively transfer the water pressure to the solid framework, This is the Kronecker matrix.

[0026] Optionally, in one embodiment of this application, the second modeling module includes: a state determination unit, used to determine the volume change results of the solid skeleton and the pore space under isotropic conditions and the state equation of the thermal porosity elasticity of the unsaturated soil under isotropic conditions under ideal plasticity conditions where no hardening variables are present:

[0027]

[0028] In the formula, These represent plastic strain and changes in plastic porosity of water and gas, respectively. The second analysis unit is used to obtain the yield trajectory of the ideal elastoplastic constitutive model according to the preset maximum plastic work principle, wherein when the smoothness of the yield trajectory is zero, the yield trajectory is a convex function, and the yield trajectory is:

[0029] In the formula, λ is the relative change in stress or porosity caused by strain or volume change under yielding conditions; The third analysis unit is used when f <0 or f =0 and d f When <0, then =0, =0 and =0, where, f This is related to the plastic potential.

[0030] Optionally, in one embodiment of this application, the prediction module includes: a third calculation unit, configured to obtain a first hardening elastoplastic theory based on the correlated plastic potential energy, wherein the first hardening elastoplastic theory is:

[0031] in,

[0032] The fourth calculation unit is used to derive the second hardening elastoplastic theory based on the non-correlated plastic potential energy. The second hardening elastoplastic theory is as follows:

[0033] in,

[0034] In the formula, H The hardening modulus is the plastic potential associated with hardening plasticity. The hardening modulus is the uncorrelated plastic potential. x J dλ is the hardening variable. E Let be the relative change in effective stress caused by strain under yield conditions, and be... , g J These are the hardening parameters; The fifth calculation unit is used to calculate the hardening elastic-plastic modulus of the non-associated hardening elastic-plastic constitutive model based on the second hardening elastic-plastic theory:

[0035]

[0036] The sixth calculation unit is used to calculate the hardening elastic-plastic modulus of the associated hardening elastic-plastic constitutive model based on the first hardening elastic-plastic theory:

[0037] In the formula, D e Let σ be the elastic modulus matrix. E For effective stress, The hardening modulus parameter is used to characterize the effective stress.

[0038] 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 constructing a stress-strain constitutive model for natural gas hydrate decomposition as described in the above embodiments.

[0039] 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 constructing a stress-strain constitutive model for the decomposition of natural gas hydrates.

[0040] Therefore, the embodiments of this application have the following beneficial effects: The embodiments of this application construct a thermoporous elastic constitutive model of hydrate reservoirs based on a pre-defined Lagrange saturation theory and solid-liquid-gas interface interaction. Based on this thermoporous elastic constitutive model, and combined with the plastic strain characteristics of hydrates and soil particles, an ideal thermoporous elastoplastic constitutive model of hydrates and soil particles is obtained. Based on the ideal thermoporous elastoplastic constitutive model, the strain hardening characteristics of hydrates and soil particles, and combined with correlated or uncorrelated plastic potential energy, a generalized stiffness matrix of the hardening elastoplastic modulus is established. Based on this generalized stiffness matrix, a hardening elastoplastic constitutive model of hydrate reservoirs is constructed to predict reservoir stability during hydrate decomposition. This application establishes a correct stress-strain constitutive relationship for the hydrate decomposition process to predict reservoir stability during hydrate decomposition, thereby effectively ensuring the geomechanical stability of hydrate reservoirs and providing solid theoretical support for hydrate reservoir stability analysis. This solves the problem that the decomposition process of hydrates can easily lead to a decrease in hydrate saturation, pressure changes, and effective stress reconstruction, which greatly undermines the geomechanical stability of hydrate reservoirs.

[0041] 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

[0042] 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: Figure 1 This is a flowchart illustrating a method for constructing a stress-strain constitutive model for the decomposition of natural gas hydrates according to an embodiment of this application. Figure 2 A schematic diagram of the pore composition in a porous medium containing hydrates is provided as an embodiment of this application; Figure 3 This is an example diagram of an apparatus for constructing a stress-strain constitutive model of natural gas hydrate decomposition according to an embodiment of this application; Figure 4 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application.

[0043] Among them, 10-natural gas hydrate decomposition stress-strain constitutive model construction device, 100-first modeling module, 200-second modeling module, 300-prediction module, 401-memory, 402-processor, and 403-communication interface. Detailed Implementation

[0044] 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.

[0045] The following describes a method and apparatus for constructing a stress-strain constitutive model for natural gas hydrate decomposition, 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 constructing a stress-strain constitutive model for natural gas hydrate decomposition. In this method, a thermal porosity elastic constitutive model of the hydrate reservoir is constructed based on a preset Lagrange saturation theory and solid-liquid-gas interface interaction. Based on the thermal porosity elastic constitutive model of the hydrate reservoir, and combined with the plastic strain characteristics of hydrates and soil particles, an ideal thermal porosity elastoplastic constitutive model of hydrates and soil particles is obtained. Based on the ideal thermal porosity elastoplastic constitutive model, the strain hardening characteristics of hydrates and soil particles, and combined with correlated or uncorrelated plastic potential energy, a generalized stiffness matrix of the hardening elastoplastic modulus is established. Based on the generalized stiffness matrix, a hardening elastoplastic constitutive model of the hydrate reservoir is constructed to predict the reservoir stability during the hydrate decomposition process. This application establishes a correct stress-strain constitutive relationship for the hydrate decomposition process to predict reservoir stability during this process, thereby effectively ensuring the geomechanical stability of hydrate reservoirs and providing solid theoretical support for hydrate reservoir stability analysis. This solves the problem that the hydrate decomposition process easily leads to reduced hydrate saturation, pressure changes, and effective stress reconstruction, which greatly undermine the geomechanical stability of hydrate reservoirs.

[0046] Specifically, Figure 1 This is a flowchart illustrating a method for constructing a stress-strain constitutive model for the decomposition of natural gas hydrates, as provided in an embodiment of this application.

[0047] like Figure 1 As shown, the method for constructing the stress-strain constitutive model for natural gas hydrate decomposition includes the following steps: In step S101, a thermal porosity elastic constitutive model of the hydrate reservoir is constructed based on the preset Lagrange saturation theory and the solid-liquid-gas interface interaction.

[0048] In the embodiments of this application, it can be assumed that there is an adhesive connection between the hydrate and the soil particles, and that the two deform together. Thus, the embodiments of this application can construct a thermal porosity elastic constitutive model of the hydrate reservoir by combining the Lagrange saturation theory and considering the solid-liquid-gas interface interaction.

[0049] The specific principles of Lagrange saturation theory and solid-liquid-gas interface interaction are described below.

[0050] Those skilled in the art should understand that, under the assumptions of infinitesimal transformations and quasi-static deformations, the Lagrange formula and the Euler formula differ, and internal dissipation occurs when the acceleration of each component is neglected. int This can be simplified to the inherent dissipation associated with the open system dΩ0. 1. (This dissipation is consistent with the movement of the soil skeleton) Heat dissipation related to phase transition → The sum is as follows: (1) Where σ is the Cauchy stress, t For time variables, g α Specific enthalpy of fluid ( α = w, G), m α = r α α = r α S α For the mass density of the Lagrange fluid, r α , α and S α Components α The density, Lagrange porosity, and Lagrange saturation, For Lagrange porosity, variable i This represents the total entropy per unit volume. T Indicates temperature. ψ For Helmholtz free energy, In the Lagrange formula α Transform into β The mass. Furthermore, ε is the strain tensor, which can be expressed as: (2) Combining nonlocal interaction forces, equation (2) can be rewritten as: (3) Right now: (4) in, m α This represents the specific chemical potential of an unsaturated solution.

[0051] The last term in equation (4) describes the dissipation that may occur during the phase transition. Zero dissipation in a phase transition means that the coexisting phases of the same composition are in thermodynamic equilibrium, and therefore their chemical potentials are equal as shown in the following equation: (5) For natural gas and water, the following assumptions are made: (6) definition ψ s Let the free energy of the skeleton be: (7) in, m s = r s (1- ) represents the mass density of the soil skeleton. ψ Given the total free energy, according to equations (6) and (7), we can obtain the following equation: (8) Substituting equation (8) into equation (3) yields: (9) The above formula can be simplified to: (10) The last six terms in equation (10) can be written as: (11) Considering m α =p α α and i α Since it does not change over time, the embodiments of this application can be expressed as follows (12). (12) Substituting equations (11) and (12) into equation (10), we obtain the Clausius-Duhem inequality related to the skeleton: (13) Figure 2 This is a schematic diagram of the pore composition in a porous medium containing hydrates. Figure 2 It can be seen that due to the changes in the porosity of water and gas... f w and f GThis primarily reflects the infinitesimal deformation of porous networks, preventing any migration of liquid water within the porous space and maintaining a constant temperature to avoid hydrate transformation, thus ensuring the liquid density... r w and gas density r G and the saturation of water and gases S w and S g Each is in an infinitesimal state of change. This is achieved by ensuring that the pores continuously satisfy [the desired condition]. S w + S g =1- S H The volume ratio of gas to water can be calculated. G and w The subsequent changes were reduced to changes in volume. f G and f w .

[0052] Similarly, the total porosity (Lagrange porosity) at the current time ultimately only involves changes in the skeleton, that is: (14) and (15) in, 0 represents the initial porosity. Substituting equation (14) into equation (13), we obtain the following equation: (16) Equation (16) can be reformulated as follows: (17) In equation (17), the first three terms represent time. t and t +d t The strain work applied to the porous solid, the fourth and fifth terms are the work done on the interfacial forces required to establish a new interface between water and gas, and therefore, the free energy of the soil skeleton and hydrate. ψ s and ψ H It can be: (18) in, These represent the plastic strain and the changes in plastic porosity of water and gas, respectively. In equation (18), the first term represents the free energy of the solid. Ws It can be decomposed into elastic properties and irreversible plastic properties, and it is assumed that the plastic properties depend only on the hardening variable. x J ; second item ( 0 - H ) U The contribution of the interface depends on the volume distribution among water, gas, and the soil skeleton, as well as hydrates. It is assumed that the porous volume does not change significantly with deformation of the porous solid (small deformation assumption). Therefore, it is assumed that the interfacial energy U is related to ε. ij It is not related to, but rather to f w and f G Related.

[0053] Therefore, the embodiments of this application can construct a thermal porosity elastic constitutive model for hydrate reservoirs by combining Lagrange saturation theory and considering solid-liquid-gas interface interactions, thereby providing solid theoretical and technical support for the construction of an ideal thermal porosity elastoplastic constitutive model.

[0054] Optionally, in one embodiment of this application, a thermoporous elastic constitutive model of a hydrate reservoir is constructed based on a preset Lagrange saturation theory and solid-liquid-gas interface interaction, including: analyzing the volume changes of the solid skeleton and pore space to obtain the volume change results of the solid skeleton and pore space; calculating the state equation of unsaturated soil thermoporous elasticity based on the volume change results; and calculating the volume change results of the solid skeleton and pore space under isotropic conditions and the state equation of unsaturated soil thermoporous elasticity under isotropic conditions based on the state equation of unsaturated soil thermoporous elasticity and a preset Legendre-Fenchel transformation strategy; wherein, the volume change results of the solid skeleton and pore space under isotropic conditions are:

[0055] The equation of state for the thermal porosity elasticity of isotropic unsaturated soil is:

[0056] In the formula, σ ij For the component form of Cauchy stress σ, f W This represents the change in the volume occupied by water. f G θ represents the change in the volume occupied by the gas. m Let ε be the entropy of the solid matrix. kk For volumetric strain, K , G and αThese represent the bulk modulus, shear modulus, and coefficient of thermal expansion of the solid skeleton, respectively. b G For the generalized Biot coefficient of gases, b W For water, the generalized Biot coefficient, N JK For the generalized Biot coupling modulus, C T ε is the specific heat capacity of the solid matrix. ij For strain tensor, α W The coefficient of thermal expansion of water is 1. α G is the coefficient of thermal expansion of the gas. T m Temperature under relative conditions In order to effectively transfer gas pressure to the solid framework, In order to effectively transfer the water pressure to the solid framework, This is the Kronecker matrix.

[0057] It should be noted that the embodiments of this application can simplify the free energy of the solid medium based on the assumption of linear elastic behavior. ψ s and ψ H We get the following formula: (19) Therefore, we can conclude that: (20) Substituting equation (20) into equation (17), we get: (twenty one) Combining equation (14), we can obtain: (twenty two) therefore: (twenty three) It is understandable that the deformation of the solid skeleton and pore space, as well as temperature changes, can vary independently of fluid saturation. When fluid saturation remains constant, the inequality transforms into an equation representing elastic behavior, namely: (twenty four) Entropy of soil skeleton and hydrate m s i s + m H i HIt consists of two parts, among which, i m = W s / T is the entropy of the solid matrix. S int = U / T It is interface entropy.

[0058] Substituting equation (24) into equation (23), we get: (25) in, F hys The hysteresis dissipation of the phase transition is ignored here and requires further study. Under the above conditions, equation (25) can be transformed into an equation, considering small strain ( - 0) / 0 After making assumption 1, the following state equation can be obtained: (26) Assume the interface energy U is: (27) Gas pressure p G and water pressure p w satisfy (28) in, (29) Equation (29) represents the fluid pressure effectively transmitted to the pores of the solid skeleton, -2 / 3 U This illustrates the capillary force generated by the interface.

[0059] Therefore, the state equation for the unsaturated soil thermal porosity elasticity in this embodiment is: (30) Furthermore, embodiments of this application may incorporate [the following]: f w and f G Related W s Legendre-Fenchel transformation form : (31) Equation (30) can be converted to: (32) Generally speaking, in linear porosity elasticity, Its independent variable ε ij , p w , p G and T m T The second-order form, for isotropic linear thermal porosity elasticity, It can be represented as: (33) and (34) Where, ε kk Indicates volume expansion. K , G and α The bulk modulus, shear modulus, and coefficient of thermal expansion of the solid skeleton are respectively shown in the following formula: (35) b J It is the generalized Biot coefficient, that is: (36) N JK For the generalized Biot coupling modulus, according to Maxwell's symmetry relation, we can obtain... N JK = N KJ , α J and C T They are phases J Thermal expansion of the occupied pore volume and specific heat capacity of the solid matrix.

[0060] In step S102, based on the thermoporous elastic constitutive model of the hydrate reservoir and combined with the plastic strain characteristics of hydrates and soil particles, an ideal thermoporous elastic-plastic constitutive model of hydrates and soil particles is obtained.

[0061] After constructing the thermoporous elastic constitutive model of the hydrate reservoir, the embodiments of this application may further consider the plastic strain characteristics of the hydrate and soil particles to obtain the stress-strain relationship including hardening plasticity, thereby constructing an ideal thermoporous elastic-plastic constitutive model of the hydrate and soil particles.

[0062] Optionally, in one embodiment of this application, based on the thermoporous elastic constitutive model of hydrate reservoirs and combined with the plastic strain characteristics of hydrates and soil particles, an ideal thermoporous elastic-plastic constitutive model of hydrates and soil particles is obtained, including: under ideal plastic conditions without hardening variables, the volume change results of the solid skeleton and pore space under isotropic conditions and the state equation of unsaturated soil thermoporous elasticity under isotropic conditions are as follows:

[0063]

[0064] In the formula, These represent plastic strain and changes in plastic porosity of water and gas, respectively. The yield trajectory of the ideal elastoplastic constitutive model is obtained based on the pre-defined maximum plastic work principle. When the smoothness of the yield trajectory is zero, the yield trajectory is a convex function, and the yield trajectory is as follows:

[0065] In the formula, λ is the relative change in stress or porosity caused by strain or volume change under yielding conditions; when f <0 or f =0 and d f When <0, then =0, =0 and =0, where, f This is related to the plastic potential.

[0066] In actual implementation, embodiments of this application can generate mechanical dissipation and skeleton free energy during plastic deformation. ψ s and ψ H It can be decomposed into the recoverable elastic free energy, plasticity, and interfacial free energy of the solid skeleton, namely: (37) Therefore, we can obtain the following formula: (38) Substituting equations (22) and (38) into equation (17), we get: (39) Combining equations (24) and (25), we can obtain plastic dissipation: (40) For the absence of hardening variables x J Ideal plasticity conditions, It can be represented as: (41) Therefore, we can conclude that: (42) Therefore, the plastic dissipation in equation (40) can be expressed as: (43) in, (44) Therefore, the thermodynamic parameters related to plastic strain, plastic porosity of water and gas are σ, respectively. ij , and According to the principle of maximum plastic work, we can obtain: (45) Equation (45) shows that the elastic domain in stress space is independent of temperature, when (σ ij , The current stress state satisfies equation (45), while ( , The plastic work is maximized when the other pair of stress states in the equation is satisfied, i.e.: (46) In the embodiments of this application, a yield trajectory is assumed. f (σij, The smoothness of )=0 is 0 (no vertex effect), then f (σij, ) is a convex function and satisfies the following equation: (47) In other cases, namely f <0 or f =0 and d f <0 (representing elastic state or partial unloading state, respectively), then =0, =0 and =0. In equation (47), f This can be viewed as a correlation between plastic potential, i.e., the flow law and the plastic yield trajectory. f Related.

[0067] For isothermal conditions containing hardening variables x J The hardening plasticity, as expressed in equation (40), can also be represented as: (48) According to the principle of maximum plastic work, we can obtain: (49) when f ( s ij , , x J When is a strictly (smooth plastic) convex function, then the current elastic domain is determined by... f ( s ij , , x J Given that ≤0, the ideal plastic yield is as follows: (50) Combining equations (41) and (43), we can obtain: (51) in, (52) in, H This is the hardening modulus in hardening plasticity.

[0068] For unsaturated soil, since the plastic strain rate is not perpendicular to the yield trajectory, and f Since it cannot be used as a plastic potential, embodiments of this application may introduce a non-associated plastic potential. h (σ ij , , x J This allows the flow behavior under these conditions, i.e., the hardening elastic-plastic modulus of the hardening elastic-plastic constitutive model, to be expressed as: (53) in, (54) in, The hardening modulus is the uncorrelated plastic potential.

[0069] Therefore, the embodiments of this application combine the strain hardening characteristics of hydrates and soil particles to obtain a stress-strain relationship that includes hardening plasticity, thereby generating an ideal thermoporous elastoplastic constitutive model for hydrates and soil particles, thus providing data basis and support for the construction of a hardening elastoplastic constitutive model for hydrate reservoirs.

[0070] In step S103, based on the ideal thermal pore elastoplastic constitutive model and the strain hardening characteristics of hydrates and soil particles, combined with correlated or uncorrelated plastic potential energy, a generalized stiffness matrix of hardening elastoplastic modulus is established. Based on the generalized stiffness matrix, a hardening elastoplastic constitutive model of hydrate reservoir is constructed to predict the reservoir stability of hydrate decomposition process through the hardening elastoplastic constitutive model of hydrate reservoir.

[0071] After constructing an ideal thermal elastoplastic constitutive model, the embodiments of this application can further combine the strain hardening characteristics of hydrates and soil particles, and establish a generalized stiffness matrix of hardening elastoplastic modulus in a general form for associated and unassociated plastic potential energy, so as to construct a hardening elastoplastic constitutive model of hydrate reservoir, thereby enabling effective prediction of reservoir stability during hydrate decomposition.

[0072] Optionally, in one embodiment of this application, based on the ideal thermal porosity elastoplastic constitutive model and the strain hardening characteristics of hydrates and soil particles, combined with correlated or uncorrelated plastic potential energy, a generalized stiffness matrix of the hardening elastoplastic modulus is established, and based on the generalized stiffness matrix, a hardening elastoplastic constitutive model of the hydrate reservoir is constructed, including: obtaining a first hardening elastoplastic theory based on the correlated plastic potential energy, wherein the first hardening elastoplastic theory is:

[0073] in,

[0074] The second hardening elastoplastic theory is derived from the non-correlated plastic potential energy. The second hardening elastoplastic theory is as follows:

[0075] in,

[0076] In the formula, H The hardening modulus is the plastic potential associated with hardening plasticity. The hardening modulus is the uncorrelated plastic potential. x J dλ is the hardening variable. E Let be the relative change in effective stress caused by strain under yield conditions, and be... , g J These are the hardening parameters; Based on the second hardening elastoplastic theory, the hardening elastoplastic modulus of the unassociated hardening elastoplastic constitutive model is calculated as follows:

[0077]

[0078] Based on the first hardening elastoplastic theory, the hardening elastoplastic modulus of the associated hardening elastoplastic constitutive model is calculated as follows:

[0079] In the formula, D e Let σ be the elastic modulus matrix. E For effective stress, The hardening modulus parameter is used to characterize the effective stress.

[0080] It should be noted that, in the embodiments of this application, for unsaturated soil, stress and strain can be expressed as: (55) in, s k ( k =1,2,3) s m and s s These represent stress in different directions, mean stress, and generalized shear stress, respectively. e k (k=1,2,3), ε m , ε s and ε v These represent strain in different directions, average strain, shear strain, and volumetric strain, respectively. e ij , s ij These are the strain deviatoric tensor and the stress deviatoric tensor, respectively.

[0081] Generally speaking, the total strain of a porous medium corresponds to the deformation of the solid skeleton, while the total stress is the combination of the local stresses of the solid skeleton and the fluid within the pores. Therefore, the yield criterion should be expressed as the stress on the soil skeleton, which can be regarded as a combination of external load, water pressure, and gas pressure.

[0082] In the embodiments of this application, assuming that the solid soil particles are plastically incompressible, that is, plasticity is caused by irreversible sliding between indeformable solid particles, then we can obtain: (56) By introducing a coefficient χ ranging from 0 to 1, we can assume that: (57) Where, χ varies S α ( α = G, w, H) changes.

[0083] Plastic strain satisfies the following equation: (58) Substituting equation (57) into equation (48), we get: (59) Therefore, we can obtain the following formula: (60) Substituting equation (58) into equation (60), we get: (61) Thus, the following can be achieved: (62) Equation (62) is the expression for the effective stress, which is a combination of the total stress, water pressure, and gas pressure, as shown in the following equation: (63) use p por The pore pressure, representing the combination of water pressure and gas pressure, can be obtained as follows: (64) in, x Relative water saturation S w / (1- S G ), p por This is the average pressure of the pore fluid considering the influence of interfacial energy. Under the assumption of an incompressible solid particle skeleton, The effective stress that controls the deformation and strength of the soil skeleton and hydrates acts similarly to the Terzaghi effective stress in saturated soil or the Bishop effective stress in unsaturated soil.

[0084] Therefore, if the current elastic domain satisfies the following equation: (65) in f If the loading function is used, the ideal plastic yield result is shown in the following equation: (66) Furthermore, by combining the associated plasticity criterion and the non-associated plasticity criterion in the embodiments of this application, the hardening plasticity standard theory can be obtained as shown in the following formula: (67) in, (68) and (69) in, (70) It should be noted that, in the embodiments of this application, it is assumed that the physical properties of the hydrate reservoir are consistent with those of typical sandstone. Under low confining pressure, the hydrate reservoir exhibits stress softening behavior, that is, the volumetric strain first contracts and then expands. As the confining pressure increases, it gradually transforms into strain hardening behavior while maintaining continuous contraction.

[0085] Therefore, based on equation (53) under the loaded state, we can obtain: (71) and (72) Generally speaking, hardening parameters g J It can be identified as plastic strain α P The function, that is: (73) Therefore, we can conclude that: (74) Combining equation (66), under unrelated plastic potential, we can obtain: (75) but: (76) According to the consistency condition in equation (76), d l E It can be represented as: (77) in, (78) From equation (75), we can obtain the incremental form. and As shown in the following formula: (79) Therefore, equation (78) can be expressed as: (80) The above-mentioned plastic hardening modulus was obtained under non-associated plasticity criteria. The same result can be obtained under associated plasticity criteria, as shown in the following formula: (81) Then, according to equations (41) and (64), we can obtain: (82) Among them, D e Let be the elastic modulus matrix, and its mathematical expression is: (83) Substituting equation (75) into equation (82), we get: (84) Multiply both sides of equation (84) by Then we can obtain: (85) Substituting equation (75) into equation (85), we obtain the following equation: (86) and (87) Therefore, we can conclude that: (88) Substituting equation (88) into equation (84), we get: (89) in (90) For the associated flow patterns, satisfying h = f Then we can obtain: (91) Therefore, the embodiments of this application can predict the reservoir stability during the hydrate decomposition process by establishing a correct stress-strain constitutive relationship for the hydrate decomposition process. This effectively reduces the occurrence of situations that damage the geomechanical stability of the reservoir, such as wellbore collapse, submarine landslides, or damage to existing engineering structures, and provides solid theoretical support for the commercialization of hydrate mining.

[0086] According to the stress-strain constitutive model construction method for natural gas hydrate decomposition proposed in this application, a thermoporous elastic constitutive model of the hydrate reservoir is constructed based on a pre-set Lagrange saturation theory and solid-liquid-gas interface interaction. Based on this thermoporous elastic constitutive model, and combined with the plastic strain characteristics of hydrates and soil particles, an ideal thermoporous elastoplastic constitutive model of hydrates and soil particles is obtained. Based on the ideal thermoporous elastoplastic constitutive model, the strain hardening characteristics of hydrates and soil particles, and combined with correlated or uncorrelated plastic potential energy, a generalized stiffness matrix of the hardening elastoplastic modulus is established. Based on this generalized stiffness matrix, a hardening elastoplastic constitutive model of the hydrate reservoir is constructed to predict reservoir stability during the hydrate decomposition process. This application establishes a correct stress-strain constitutive relationship for the hydrate decomposition process to predict reservoir stability during hydrate decomposition, thereby effectively ensuring the geomechanical stability of hydrate reservoirs and providing solid theoretical support for hydrate reservoir stability analysis.

[0087] Secondly, the apparatus for constructing a stress-strain constitutive model of natural gas hydrate decomposition according to an embodiment of this application is described with reference to the accompanying drawings.

[0088] Figure 3 This is a block diagram of a device for constructing a stress-strain constitutive model of natural gas hydrate decomposition according to an embodiment of this application.

[0089] like Figure 3 As shown, the natural gas hydrate decomposition stress-strain constitutive model construction device 10 includes: a first modeling module 100, a second modeling module 200, and a prediction module 300.

[0090] The first modeling module 100 is used to construct a thermal porosity elastic constitutive model of hydrate reservoirs based on the preset Lagrange saturation theory and solid-liquid-gas interface interaction.

[0091] The second modeling module 200 is used to obtain an ideal thermal porosity elastic-plastic constitutive model of hydrates and soil particles based on the thermal porosity elastic constitutive model of hydrate reservoirs and the plastic strain characteristics of hydrates and soil particles.

[0092] The prediction module 300 is used to establish a generalized stiffness matrix of the hardening elastic-plastic modulus based on the ideal thermal porosity elastic-plastic constitutive model, the strain hardening characteristics of hydrates and soil particles, and the associated or unassociated plastic potential energy. Based on the generalized stiffness matrix, a hardening elastic-plastic constitutive model of hydrate reservoir is constructed to predict the reservoir stability of hydrate decomposition process through the hardening elastic-plastic constitutive model of hydrate reservoir.

[0093] Optionally, in one embodiment of this application, the first modeling module 100 includes: a first analysis unit, a first calculation unit, and a second calculation unit.

[0094] The first analysis unit is used to analyze the volume changes of the solid skeleton and pore space, and obtain the volume change results of the solid skeleton and pore space.

[0095] The first calculation unit is used to calculate the state equation of unsaturated soil thermal porosity elasticity based on the volume change results.

[0096] The second calculation unit is used to calculate the volume change results of the solid skeleton and pore space under isotropic conditions and the state equation of the thermal porosity of unsaturated soil under isotropic conditions, based on the state equation of unsaturated soil thermal porosity elasticity and the preset Legendre-Fenchel transformation strategy.

[0097] The volume changes of the solid framework and pore space under isotropic conditions are as follows:

[0098] The equation of state for the thermal porosity elasticity of isotropic unsaturated soil is:

[0099] In the formula, σ ij For the component form of Cauchy stress σ, f W This represents the change in the volume occupied by water. f G θ represents the change in the volume occupied by the gas. m Let ε be the entropy of the solid matrix. kk For volumetric strain, K , G and α These represent the bulk modulus, shear modulus, and coefficient of thermal expansion of the solid skeleton, respectively. b G For the generalized Biot coefficient of gases, b W For water, the generalized Biot coefficient, N JK For the generalized Biot coupling modulus, C T ε is the specific heat capacity of the solid matrix. ij For strain tensor, α W The coefficient of thermal expansion of water is 1. α G is the coefficient of thermal expansion of the gas. T m Temperature under relative conditions In order to effectively transfer gas pressure to the solid framework, In order to effectively transfer the water pressure to the solid framework, This is the Kronecker matrix.

[0100] Optionally, in one embodiment of this application, the second modeling module 200 includes: a state determination unit, a second analysis unit, and a third analysis unit.

[0101] Among them, the state determination element is used to determine the volume change results of the solid skeleton and pore space under ideal plastic conditions without hardening variables, and the state equation of the thermal porosity elasticity of unsaturated soil under isotropic conditions, which is as follows:

[0102]

[0103] In the formula, These represent plastic strain and changes in plastic porosity of water and gas, respectively.

[0104] The second analysis unit is used to obtain the yield trajectory of the ideal elastoplastic constitutive model based on the preset maximum plastic work principle. When the smoothness of the yield trajectory is zero, the yield trajectory is a convex function, and the yield trajectory is:

[0105] In the formula, λ represents the relative change in stress or porosity caused by strain or volume change under yielding conditions.

[0106] The third analysis unit is used when f <0 or f =0 and d f When <0, then =0, =0 and =0, where, f This is related to the plastic potential.

[0107] Optionally, in one embodiment of this application, the prediction module 300 includes: a third calculation unit, a fourth calculation unit, a fifth calculation unit, and a sixth calculation unit.

[0108] The third calculation unit is used to obtain the first hardening elastoplastic theory based on the correlated plastic potential energy. The first hardening elastoplastic theory is as follows:

[0109] in,

[0110] The fourth calculation unit is used to derive the second hardening elastoplastic theory based on the non-associated plastic potential energy. The second hardening elastoplastic theory is as follows:

[0111] in,

[0112] In the formula, H The hardening modulus is the plastic potential associated with hardening plasticity. The hardening modulus is the uncorrelated plastic potential. x J dλ is the hardening variable. E Let be the relative change in effective stress caused by strain under yield conditions, and be... , g J These are the hardening parameters.

[0113] The fifth calculation unit is used to calculate the hardening elastic-plastic modulus of the unassociated hardening elastic-plastic constitutive model based on the second hardening elastic-plastic theory:

[0114]

[0115] The sixth calculation unit is used to calculate the hardening elastic-plastic modulus of the associated hardening elastic-plastic constitutive model based on the first hardening elastic-plastic theory:

[0116] In the formula, D e Let σ be the elastic modulus matrix. E For effective stress, The hardening modulus parameter is used to characterize the effective stress.

[0117] It should be noted that the foregoing explanation of the embodiment of the method for constructing the stress-strain constitutive model of natural gas hydrate decomposition also applies to the apparatus for constructing the stress-strain constitutive model of natural gas hydrate decomposition in this embodiment, and will not be repeated here.

[0118] The stress-strain constitutive model construction device for natural gas hydrate decomposition proposed in this application includes a first modeling module for constructing a thermal porosity elastic constitutive model of the hydrate reservoir based on a preset Lagrange saturation theory and solid-liquid-gas interface interaction; a second modeling module for obtaining an ideal thermal porosity elastoplastic constitutive model of hydrates and soil particles based on the thermal porosity elastic constitutive model of the hydrate reservoir and the plastic strain characteristics of hydrates and soil particles; and a prediction module for establishing a generalized stiffness matrix of the hardening elastoplastic modulus based on the ideal thermal porosity elastoplastic constitutive model, the strain hardening characteristics of hydrates and soil particles, and correlated or uncorrelated plastic potential energy, and constructing a hardening elastoplastic constitutive model of the hydrate reservoir based on the generalized stiffness matrix, so as to predict the reservoir stability during the hydrate decomposition process through the hardening elastoplastic constitutive model of the hydrate reservoir. This application establishes a correct stress-strain constitutive relationship for the hydrate decomposition process to predict the reservoir stability during the hydrate decomposition process, thereby effectively ensuring the geomechanical stability of the hydrate reservoir and providing solid theoretical support for the stability analysis of hydrate reservoirs.

[0119] Figure 4 A schematic diagram of the structure of an electronic device provided in an embodiment of this application. The electronic device may include: The memory 401, the processor 402, and the computer program stored on the memory 401 and capable of running on the processor 402.

[0120] When the processor 402 executes the program, it implements the method for constructing the stress-strain constitutive model of natural gas hydrate decomposition provided in the above embodiments.

[0121] Furthermore, electronic devices also include: Communication interface 403 is used for communication between memory 401 and processor 402.

[0122] The memory 401 is used to store computer programs that can run on the processor 402.

[0123] The memory 401 may include high-speed RAM memory, and may also include non-volatile memory, such as at least one disk storage device.

[0124] 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 categorized as 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.

[0125] 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.

[0126] 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.

[0127] 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 constructing a stress-strain constitutive model of natural gas hydrate decomposition.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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 constructing a stress-strain constitutive model for the decomposition of natural gas hydrates, characterized in that, Includes the following steps: Based on the pre-defined Lagrange saturation theory and solid-liquid-gas interface interaction, a thermal porosity elastic constitutive model of hydrate reservoirs is constructed. Based on the thermoporous elastic constitutive model of the hydrate reservoir, and combined with the plastic strain characteristics of the hydrate and soil particles, an ideal thermoporous elastic-plastic constitutive model of the hydrate and the soil particles is obtained. Based on the ideal thermal elastoplastic constitutive model, the strain hardening characteristics of the hydrate and the soil particles, and combined with correlated or uncorrelated plastic potential energy, a generalized stiffness matrix of the hardening elastoplastic modulus is established. Based on the generalized stiffness matrix, a hardening elastoplastic constitutive model of the hydrate reservoir is constructed to predict the reservoir stability of the hydrate decomposition process.

2. The method according to claim 1, characterized in that, The aforementioned method, based on the pre-defined Lagrange saturation theory and solid-liquid-gas interface interaction, constructs a thermoporous elastic constitutive model for hydrate reservoirs, including: The volume changes of the solid framework and the pore space are analyzed to obtain the volume change results of the solid framework and the pore space; Calculate the state equation for the thermal porosity elasticity of unsaturated soil based on the volume change results; Based on the state equation of the unsaturated soil thermal porosity elasticity and the preset Legendre-Fenchel transformation strategy, the volume change results of the solid skeleton and the pore space under isotropic conditions and the state equation of the unsaturated soil thermal porosity elasticity under isotropic conditions are calculated. The volume changes of the solid framework and the pore space under isotropic conditions are as follows: The equation of state for the thermal porosity elasticity of the isotropic unsaturated soil is as follows: In the formula, σ ij For the component form of Cauchy stress σ, φ W This represents the change in the volume occupied by water. φ G θ represents the change in the volume occupied by the gas. m Let ε be the entropy of the solid matrix. kk For volumetric strain, K , G and α These represent the bulk modulus, shear modulus, and coefficient of thermal expansion of the solid skeleton, respectively. b G For the generalized Biot coefficient of gases, b W For water, the generalized Biot coefficient, N JK For the generalized Biot coupling modulus, C T ε is the specific heat capacity of the solid matrix. ij For strain tensor, α W The coefficient of thermal expansion of water is 1. α G is the coefficient of thermal expansion of the gas. T m Temperature under relative conditions In order to effectively transfer gas pressure to the solid framework, In order to effectively transfer the water pressure to the solid framework, This is the Kronecker matrix.

3. The method according to claim 2, characterized in that, The ideal thermal porosity elastic constitutive model of the hydrate reservoir, based on the thermal porosity elastic constitutive model of the hydrate and soil particles and combined with the plastic strain characteristics of the hydrate and soil particles, is obtained, including: Under ideal plasticity conditions where no hardening variables exist, the volume changes of the solid skeleton and the pore space under isotropic conditions, and the state equation for the thermal porosity elasticity of the unsaturated soil under isotropic conditions, are as follows: In the formula, These represent plastic strain and changes in plastic porosity of water and gas, respectively. The yield trajectory of the ideal elastoplastic constitutive model is obtained based on the preset maximum plastic work principle. When the smoothness of the yield trajectory is zero, the yield trajectory is a convex function, and the yield trajectory is as follows: In the formula, λ represents the relative change in stress or porosity caused by strain or volume change under yielding conditions; when f <0 or f =0 and d f When <0, then =0, =0 and =0, where, f This is related to the plastic potential.

4. The method according to claim 3, characterized in that, Based on the ideal thermal porosity elastoplastic constitutive model, the strain hardening characteristics of the hydrate and the soil particles, and combined with correlated or uncorrelated plastic potential energy, a generalized stiffness matrix of the hardening elastoplastic modulus is established. Based on this generalized stiffness matrix, a hardening elastoplastic constitutive model of the hydrate reservoir is constructed, including: The first hardening elastoplastic theory is derived based on the correlated plastic potential energy. The first hardening elastoplastic theory is as follows: in, The second hardening elastoplastic theory is derived based on the non-correlated plastic potential energy. The second hardening elastoplastic theory is as follows: in, In the formula, H The hardening modulus is the plastic potential associated with hardening plasticity. The hardening modulus is the uncorrelated plastic potential. χ J dλ is the hardening variable. E Let be the relative change in effective stress caused by strain under yield conditions, and be... , ζ J These are the hardening parameters; Based on the second hardening elastoplastic theory, the hardening elastoplastic modulus of the unassociated hardening elastoplastic constitutive model is calculated as follows: Based on the first hardening elastoplastic theory, the hardening elastoplastic modulus of the associated hardening elastoplastic constitutive model is calculated as follows: In the formula, D e Let σ be the elastic modulus matrix. E For effective stress, The hardening modulus parameter is used to characterize the effective stress.

5. A device for constructing a stress-strain constitutive model for the decomposition of natural gas hydrates, characterized in that, include: The first modeling module is used to construct a thermal porosity elastic constitutive model of hydrate reservoirs based on the preset Lagrange saturation theory and solid-liquid-gas interface interaction. The second modeling module is used to obtain the ideal thermal porosity elastic-plastic constitutive model of the hydrate and the soil particles based on the thermal porosity elastic constitutive model of the hydrate reservoir and the plastic strain characteristics of the hydrate and soil particles. The prediction module is used to establish a generalized stiffness matrix of the hardening elastic-plastic modulus based on the ideal thermal porosity elastoplastic constitutive model, the strain hardening characteristics of the hydrate and the soil particles, and the associated or unassociated plastic potential energy. Based on the generalized stiffness matrix, a hardening elastic-plastic constitutive model of the hydrate reservoir is constructed to predict the reservoir stability of the hydrate decomposition process through the hardening elastic-plastic constitutive model of the hydrate reservoir.

6. The apparatus according to claim 5, characterized in that, The first modeling module includes: The first analysis unit is used to analyze the volume changes of the solid skeleton and the pore space, and obtain the volume change results of the solid skeleton and the pore space. The first calculation unit is used to calculate the state equation of the thermal porosity elasticity of unsaturated soil based on the volume change results. The second calculation unit is used to calculate the volume change results of the solid skeleton and the pore space under isotropic conditions and the state equation of the thermal porosity elasticity of the unsaturated soil under isotropic conditions based on the state equation of the unsaturated soil thermal porosity elasticity and the preset Legendre-Fenchel transformation strategy. The volume changes of the solid framework and the pore space under isotropic conditions are as follows: The equation of state for the thermal porosity elasticity of the isotropic unsaturated soil is as follows: In the formula, σ ij For the component form of Cauchy stress σ, φ W This represents the change in the volume occupied by water. φ G θ represents the change in the volume occupied by the gas. m Let ε be the entropy of the solid matrix. kk For volumetric strain, K , G and α These represent the bulk modulus, shear modulus, and coefficient of thermal expansion of the solid skeleton, respectively. b G For the generalized Biot coefficient of gases, b W For water, the generalized Biot coefficient, N JK For the generalized Biot coupling modulus, C T ε is the specific heat capacity of the solid matrix. ij For strain tensor, α W The coefficient of thermal expansion of water is 1. α G is the coefficient of thermal expansion of the gas. T m Temperature under relative conditions In order to effectively transfer gas pressure to the solid framework, In order to effectively transfer the water pressure to the solid framework, This is the Kronecker matrix.

7. The apparatus according to claim 6, characterized in that, The second modeling module includes: The state determination unit is used to determine the volume changes of the solid skeleton and the pore space under ideal plasticity conditions without hardening variables, and the state equation of the thermal porosity elasticity of the unsaturated soil under isotropic conditions as follows: In the formula, These represent plastic strain and changes in plastic porosity of water and gas, respectively. The second analysis unit is used to obtain the yield trajectory of the ideal elastoplastic constitutive model according to the preset maximum plastic work principle, wherein when the smoothness of the yield trajectory is zero, the yield trajectory is a convex function, and the yield trajectory is: In the formula, λ represents the relative change in stress or porosity caused by strain or volume change under yielding conditions; The third analysis unit is used when f <0 or f =0 and d f When <0, then =0, =0 and =0, where, f This is related to the plastic potential.

8. The apparatus according to claim 7, characterized in that, The prediction module includes: The third calculation unit is used to obtain the first hardening elastoplastic theory based on the correlated plastic potential energy. The first hardening elastoplastic theory is as follows: in, The fourth calculation unit is used to derive the second hardening elastoplastic theory based on the non-correlated plastic potential energy. The second hardening elastoplastic theory is as follows: in, In the formula, H The hardening modulus is the plastic potential associated with hardening plasticity. The hardening modulus is the uncorrelated plastic potential. χ J dλ is the hardening variable. E Let be the relative change in effective stress caused by strain under yield conditions, and be... , ζ J These are the hardening parameters; The fifth calculation unit is used to calculate the hardening elastic-plastic modulus of the non-associated hardening elastic-plastic constitutive model based on the second hardening elastic-plastic theory: The sixth calculation unit is used to calculate the hardening elastic-plastic modulus of the associated hardening elastic-plastic constitutive model based on the first hardening elastic-plastic theory: In the formula, D e Let σ be the elastic modulus matrix. E For effective stress, The hardening modulus parameter is used to characterize the effective stress.

9. An electronic device, characterized in that, include: The memory, the processor, and the computer program stored in the memory and executable on the processor, the processor executing the program to implement the method for constructing a stress-strain constitutive model for the decomposition of natural gas hydrates as described in any one of claims 1-4.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, The program is executed by the processor to implement the method for constructing a stress-strain constitutive model for the decomposition of natural gas hydrates as described in any one of claims 1-4.

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