Natural gas hydrate dissociation process full-coupling numerical simulation method and device

Abstract

The application relates to a natural gas hydrate decomposition process full-coupling numerical simulation method and device, wherein the method comprises the following steps: establishing a mass conservation model, an energy conservation model, a mechanical equilibrium model and a hydrate decomposition model of soil particles, hydrates, gas and water of natural gas hydrates in a decomposition process, constructing a heat-flow-force-chemistry full-coupling model of natural gas hydrates in the decomposition process, taking gas pressure, water pressure, temperature and displacement in different directions as basic unknown quantities of the model, and establishing a finite element weak integral form of the heat-flow-force-chemistry full-coupling model; performing numerical solution on the finite element weak integral form, and assembling a DEHydrate simulator based on a solution result to simulate an evolution trend of reservoir mechanical behavior of natural gas hydrates in the decomposition process. Therefore, the problems that existing hydrate decomposition simulators cannot realize complete coupling among seepage, hydrate phase change, heat transfer and geomechanics are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of deep-sea energy engineering, and particularly relates to a full-coupling numerical simulation method and device for a natural gas hydrate decomposition process. BACKGROUND

[0002] Natural gas hydrate (NGH) is widely distributed and has a huge reserve. The proven NGH reserve in the world is about 7.5 x 10 18 m 3 , in which the NGH reserve in China is about 8.41 x 10 14 m 3 . In addition, the energy density of NGH is high, and one cubic meter of NGH can release 160-180 m 3 of natural gas under normal temperature and pressure. If the commercial exploitation of NGH can be realized, the energy pressure of China and even the world can be effectively relieved.

[0003] If the commercial exploitation of NGH is to be realized, the gas production needs to reach 5 x 10 6 m 3 / d, but the existing trial production engineering only reaches 1 / 17 of the commercial requirement. Therefore, it is necessary to make a deeper research on the decomposition behavior of NGH, and increase the exploitation efficiency of NGH under the premise of ensuring the stability of the reservoir.

[0004] However, most of the existing simulators are commercial software, and most of them are from abroad. In China, the secondary development of mechanics is mainly based on foreign software, and there is no final software copyright. In addition, the full coupling between seepage, NGH phase change, heat transfer and geomechanics cannot be realized. Therefore, it is necessary to develop a full-coupling simulator for NGH decomposition heat-hole-force-chemistry, which has domestic independent intellectual property rights. SUMMARY

[0005] The present application provides a full-coupling numerical simulation method and device for a natural gas hydrate decomposition process, so as to solve the problem that the existing hydrate decomposition simulator cannot realize the full coupling between seepage, hydrate phase change, heat transfer and geomechanics.

[0006] The first aspect embodiment of the present application provides a natural gas hydrate decomposition process full coupling numerical simulation method, comprising the following steps: establishing a mass conservation model, an energy conservation model, a mechanical equilibrium model and a hydrate decomposition model of soil particles, hydrates, gas and water of natural gas hydrate in a decomposition process, and constructing a full coupling model of heat-flow-force-chemistry of the natural gas hydrate in the decomposition process; performing full coupling according to the full coupling model of heat-flow-force-chemistry, the mass conservation model, the energy conservation model, the mechanical equilibrium model and the hydrate decomposition model, taking gas pressure, water pressure, temperature and displacement in different directions as basic unknown quantities of the model, establishing a finite element weak integral form of the full coupling model of heat-flow-force-chemistry; and performing numerical solution on the finite element weak integral form, and based on the solution result, assembling a DEHydrate simulator, and simulating the evolution trend of reservoir mechanical behavior of the natural gas hydrate in the decomposition process based on the DEHydrate simulator.

[0007] Optionally, in an embodiment of the present application, the mass conservation equation of water is as follows:

[0008]

[0009] The gas mass conservation equation is as follows:

[0010]

[0011] The energy conservation equation is as follows:

[0012]

[0013] The mechanical equilibrium equation is as follows:

[0014]

[0015] wherein ρ i and S i (i=w, g, s, H) are the density and saturation of different components, is the porosity, t is the time, μ i (i=w, g) is the dynamic viscosity of fluid i, K ri (i=w, g) is the relative permeability of water and gas, which is related to the saturation of water and NGH, g is the gravity acceleration vector, that is, g=[0, 0, g]T(g=9.8 m / s 2 ), (kg / s) is the mass change rate of different components caused by decomposition, (kg / s) is the injection rate of gas or water, γ is the thermal expansion coefficient, T is the temperature (K), C pi(i=g, w, s, H) represent the specific heat capacity of gas, water, soil particles and NGH, respectively, λ c is the multi-component integrated thermal conductivity, Q in and Q H are the injected heat and the heat change caused by NGH decomposition, respectively, D is the stiffness matrix, δ is the Kronecker operator, P p is the average pore pressure, ρ c is the total density weighted by saturation.

[0016] Optionally, in an embodiment of the present application, the building of the thermal-fluid-mechanical fully coupled model of the decomposition process of the natural gas hydrate comprises: obtaining the thermal-fluid-mechanical fully coupled model based on the transient changes of the multiphase saturation, the capillary pressure, the permeability, the hydrate decomposition rate, the porosity and at least one other physical property of the porous medium.

[0017] Optionally, in an embodiment of the present application, the full coupling according to the thermal-fluid-mechanical fully coupled model, the mass conservation model, the energy conservation model, the mechanical equilibrium model and the hydrate decomposition model, and taking the gas pressure, the water pressure, the temperature and the displacement in different directions as the basic unknown quantities of the model, the building of the finite element weak integral form of the thermal-fluid-mechanical fully coupled model comprises: discretizing the time differential by using the backward Euler method, discretizing the space differential by using the first-order difference method, and in the finite element, calculating by using the Galerkin method and the weighted residual method to obtain the equation group of the finite element weak integral form, so as to obtain the finite element weak integral form of the thermal-fluid-mechanical fully coupled model.

[0018] Optionally, in an embodiment of the present application, the finite element weak integral form is:

[0019]

[0020] wherein u is the displacement, P g is the gas pressure, P w is the water pressure, and T is the temperature.

[0021] Optionally, in an embodiment of the present application, the finite element weak integral form is solved numerically, and a DEHydrate simulator is assembled based on the solving result, and the evolution trend of the reservoir mechanical behavior of the natural gas hydrate in the dissociation process is simulated based on the DEHydrate simulator, including: the low-order element is used to simulate the gas-liquid flow and heat transfer behavior, the high-order element and / or the low-order element is used to calculate the solid deformation, and the overall implicit finite element method is used for solving to obtain a model result; the stiffness matrix of the high-order element and / or the low-order element is obtained based on the model result and through spatial integration; the Newton iteration method is used to solve the nonlinear equation group meeting a preset condition to obtain a linear equation group, and the stiffness matrix is updated in each iteration; the Pardiso solver or the Gauss-Seidel method is used to solve the linear equation group.

[0022] The second aspect embodiment of the present application provides a full-coupling numerical simulation device for a natural gas hydrate dissociation process, including: a modeling module, configured to establish a mass conservation model, an energy conservation model, a mechanical equilibrium model and a hydrate dissociation model of soil particles, hydrates, gas and water of the natural gas hydrate in the dissociation process, and construct a full-coupling model of heat-flow-force-chemistry of the natural gas hydrate in the dissociation process; a full-coupling module, configured to perform full-coupling according to the full-coupling model of heat-flow-force-chemistry, the mass conservation model, the energy conservation model, the mechanical equilibrium model and the hydrate dissociation model, and establish a finite element weak integral form of the full-coupling model of heat-flow-force-chemistry by taking gas pressure, water pressure, temperature and displacement in different directions as basic unknown quantities of the model; and a simulation module, configured to solve the finite element weak integral form numerically, assemble a DEHydrate simulator based on a solving result, and simulate the evolution trend of the reservoir mechanical behavior of the natural gas hydrate in the dissociation process based on the DEHydrate simulator.

[0023] Optionally, in an embodiment of the present application, the mass conservation equation of the water is as follows:

[0024]

[0025] The mass conservation equation of the gas is as follows:

[0026]

[0027] The energy conservation equation is as follows:

[0028]

[0029] The mechanical equilibrium equation is as follows:

[0030]

[0031] where, p i and S i (i = w, g, s, H) are the density and saturation of different components, respectively, is the porosity, t is time, p i (i = w, g) is the dynamic viscosity of fluid i, K ri (i = w, g) is the relative permeability of water and gas, which is related to the saturation of water and NGH, g is the gravity acceleration vector, i.e. g = [0, 0, g]T(g = 9.8 m / s 2 ), (kg / s) is the mass change rate of different components caused by decomposition, (kg / s) is the injection rate of gas or water, g is the thermal expansion coefficient, T is temperature (K), c pi (i = g, w, s, H) represents the specific heat capacity of gas, water, soil particles and NGH, respectively, l c is the multi-component comprehensive thermal conductivity, Q in and Q H are the injected heat and the heat change caused by NGH decomposition, respectively, D is the stiffness matrix, d is the Kronecker operator, P p is the average pore pressure, p c is the total density weighted by saturation.

[0032] Optionally, in an embodiment of the present application, the modeling module comprises a processing unit configured to obtain the thermo-hydro-mechanical-chemical fully coupled model based on transient changes in multiphase saturation, capillary pressure, permeability, hydrate decomposition rate, porosity and at least one other physical property of the porous medium.

[0033] Optionally, in an embodiment of the present application, the fully coupled module comprises a second calculation unit configured to discretize the time differential using a backward Euler method and discretize the space differential using a first-order difference method, and in the finite element, calculate using a Galerkin method and a weighted residual method to obtain the finite element weak integral form of the equation set to obtain the finite element weak integral form of the thermo-hydro-mechanical-chemical fully coupled model.

[0034] Optionally, in an embodiment of the present application, the finite element weak integral form is:

[0035]

[0036] where, u is displacement, P g is gas pressure, P w is water pressure, and T is temperature.

[0037] Optionally, in an embodiment of the present application, the simulation module comprises: a first calculation unit for simulating gas-liquid flow and heat transfer behavior by using a low-order unit, calculating solid deformation by using a high-order unit and / or a low-order unit, and solving the model results by using a fully implicit finite element method as a whole; an integration unit for obtaining a stiffness matrix of the high-order unit and / or the low-order unit based on the model results and by spatial integration; an updating unit for solving a nonlinear equation group meeting a preset condition by using a Newton iteration method, obtaining a linear equation group, and updating the stiffness matrix in each iteration; and a solving unit for solving the linear equation group by using a Pardiso solver or a Gauss-Seidel method.

[0038] The third aspect of the present application provides an electronic device, comprising: 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 numerical simulation method for full coupling of the natural gas hydrate decomposition process as described in the above embodiments.

[0039] The fourth aspect of the present application provides a computer readable storage medium, which stores a computer program executable by a processor to implement the numerical simulation method for full coupling of the natural gas hydrate decomposition process as described above.

[0040] Therefore, the embodiments of the present application have the following beneficial effects:

[0041] The embodiments of the present application can establish a mass conservation model, an energy conservation model, a mechanical equilibrium model and a hydrate decomposition model of soil particles, hydrates, gas and water in the decomposition process of natural gas hydrate, construct a full coupling model of heat-flow-force-chemistry in the decomposition process of natural gas hydrate, take gas pressure, water pressure, temperature and displacement in different directions as basic unknown quantities of the model, and establish a finite element weak integral form of the full coupling model of heat-flow-force-chemistry; perform numerical solution on the finite element weak integral form, and based on the solution results, assemble a DEHydrate simulator to simulate the evolution trend of reservoir mechanical behavior in the decomposition process of natural gas hydrate. The present application provides an effective tool for predicting the evolution of reservoir mechanical behavior in the decomposition process of hydrate, which can simulate the transient law of reservoir pressure, temperature, displacement and stress in different directions, multiphase saturation, hydrate decomposition rate / amount, and gas production rate / amount in the decomposition process of hydrate. Thus, the problems that the existing hydrate decomposition simulator cannot realize full coupling between seepage, hydrate phase change, heat transfer and geomechanics are solved.

[0042] Additional aspects and advantages of the present application will be made apparent by the following description and the appended claims. Attached Figure Description

[0043] 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:

[0044] Figure 1 This is a flowchart of a fully coupled numerical simulation method for the decomposition process of natural gas hydrates provided in an embodiment of this application;

[0045] Figure 2 A schematic diagram of node distribution for describing different order elements of solid deformation and percolation heat transfer, provided as an embodiment of this application;

[0046] Figure 3 A simulator finite element program flowchart is provided for one embodiment of this application;

[0047] Figure 4 A schematic diagram of the radial distribution of saturation and displacement of a hydrate over two days is provided as an embodiment of this application.

[0048] Figure 5 A schematic diagram of an NGH mining model provided for one embodiment of this application;

[0049] Figure 6 A schematic diagram of the execution logic of a fully coupled numerical simulation method for the decomposition process of natural gas hydrates, provided as an embodiment of this application;

[0050] Figure 7 This is an example diagram of a fully coupled numerical simulation device for the natural gas hydrate decomposition process according to an embodiment of this application;

[0051] Figure 8 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application.

[0052] Among them, 10-fully coupled numerical simulation device for natural gas hydrate decomposition process, 100-modeling module, 200-fully coupled module, 300-simulation module, 801-memory, 802-processor, and 803-communication interface. Detailed Implementation

[0053] 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.

[0054] The following describes a fully coupled numerical simulation method and apparatus for the decomposition process of natural gas hydrate according to embodiments of this application, with reference to the accompanying drawings. Addressing the problems mentioned in the background art, this application provides a fully coupled numerical simulation method for the decomposition process of natural gas hydrate. In this method, mass conservation models, energy conservation models, mechanical equilibrium models, and hydrate decomposition models are established for soil particles, hydrates, gas, and water during the decomposition process, along with a fully coupled thermo-fluid-mechanical-chemical model. The thermo-fluid-mechanical-chemical model, mass conservation model, energy conservation model, mechanical equilibrium model, and hydrate decomposition model are fully coupled, and gas pressure, water pressure, temperature, and displacement in different directions are used as the basic unknowns of the model to establish a finite element weak integral form of the thermo-fluid-mechanical-chemical fully coupled model. The finite element weak integral form is numerically solved, and the solution results are aggregated into a DEHydrate simulator. The DEHydrate simulator is then used to simulate the evolution trend of reservoir mechanical behavior during the decomposition process of natural gas hydrate. This application establishes a multiphase flow, strongly nonlinear, large-scale fully coupled thermo-fluid-mechanical-chemical model for the hydrate decomposition process, and integrates the DEHydrate simulator. This provides an effective tool for predicting the evolution of reservoir mechanical behavior during hydrate decomposition, achieving simulation of multiple physical fields such as solid-liquid-gas multiphase flow, heat transfer, NGH phase transition, and solid deformation, as well as full coupling between multiphase seepage and geomechanical components. This makes the numerical simulation more consistent with actual NGH decomposition behavior. Therefore, it solves the problem that existing hydrate decomposition simulators cannot achieve complete coupling between seepage, hydrate phase transition, heat transfer, and geomechanics.

[0055] Specifically, Figure 1 This is a flowchart of a fully coupled numerical simulation method for the decomposition process of natural gas hydrates provided in an embodiment of this application.

[0056] like Figure 1 As shown, the fully coupled numerical simulation method for the natural gas hydrate decomposition process includes the following steps:

[0057] In step S101, a mass conservation model, an energy conservation model, a mechanical equilibrium model, and a hydrate decomposition model are established for soil particles, hydrates, gas, and water during the decomposition process of natural gas hydrates. A fully coupled thermo-fluid-mechanical-chemical model of natural gas hydrates during the decomposition process is also constructed.

[0058] The embodiments of this application can establish mass conservation models, energy conservation models, mechanical equilibrium models, and hydrate decomposition models for soil particles, hydrates, gas, and water during the decomposition of natural gas hydrates, based on the principles of mass conservation, energy conservation, and hydrostatic equilibrium. By establishing these models, a fully coupled thermo-fluid-mechanical-chemical model for the hydrate decomposition process is constructed.

[0059] Specifically, in the embodiments of this application, the mass conservation equation for soil particles in the reservoir is as follows:

[0060]

[0061] Where, ρ s (kg / m 3 ) and v s (m / s) represent the density and velocity of soil particles, respectively; t represents porosity, and t represents time.

[0062] Therefore, embodiments of this application can ignore the spatial gradient of soil particle density variation, assume that soil particles are incompressible, and base the data on soil particle velocity v. s With soil skeleton strain ε v From the relationship, we can obtain equation (2):

[0063]

[0064] Therefore, equation (1) can be simplified to:

[0065]

[0066] Secondly, during the decomposition of NGH, the mass conservation of NGH satisfies the following equation:

[0067]

[0068] Where, ρ H (kg / m 3 ), S H and v H (m / s) represent the density, saturation, and velocity of NGH, respectively. (kg / s) represents the rate of change in NGH mass caused by decomposition.

[0069] The mass conservation of methane gas in the pores satisfies the following equation:

[0070]

[0071] Where, ρg (kg / m 3 ) and S g These represent the density and saturation of methane gas, respectively. (kg / s) and (kg / s) represent the rate of change of gas mass produced by NGH decomposition and the gas injection rate, respectively. g denoted as ρ, where ρ is the absolute velocity of the gas.

[0072] The mass conservation of water in pores satisfies the following equation:

[0073]

[0074] Where, ρ w (kg / m 3 ) and S w These represent the density and saturation of water, respectively. (kg / s) and (kg / s) represent the rate of mass change of water produced by NGH decomposition and the water injection rate, respectively. w This is the absolute velocity of the water.

[0075] In the NGH decomposition process of this application embodiment, the energy conservation satisfies the following equation:

[0076]

[0077] Where γ is the coefficient of thermal expansion, T is the temperature (K), and C is the temperature (°C). pi (J / kg / K) (i = g, w, s, H represent gas, water, soil particles, and NGH, respectively) represent the specific heat capacity of different phases, λ c (W / m / K) is the combined thermal conductivity of a multi-component system, and can generally be expressed as:

[0078]

[0079] Where, λ i (W / m / K) represents the thermal conductivity of different phases, v rj (m / s)(j=g,w) is the relative velocity of gas or water to soil particles, Q in (J / (kg·s)) and Q H (J / (kg·s)) represent the heat changes caused by injected heat and NGH decomposition, respectively.

[0080] Based on the effective stress principle, NGH maintains a static mechanical equilibrium during decomposition, i.e.

[0081]

[0082] Where σ is the total stress vector, ρ cThe total density after saturation weighting is shown in equation (10):

[0083]

[0084] Therefore, the embodiments of this application establish mass conservation models, energy conservation models, mechanical equilibrium models, and hydrate decomposition models for soil particles, hydrates, gases, and water during the decomposition of natural gas hydrates, providing a theoretical basis for the subsequent realization of fully coupled numerical simulation of the natural gas hydrate decomposition process.

[0085] Optionally, in one embodiment of this application, a fully coupled thermo-fluid-mechanical-chemical model of natural gas hydrate decomposition process is constructed, including: obtaining a fully coupled thermo-fluid-mechanical-chemical model based on the transient changes of multiphase saturation, capillary pressure, permeability, hydrate decomposition rate, porosity and at least one other physical property of the porous medium.

[0086] It should be noted that the embodiments of this application can construct a fully coupled thermo-fluid-mechanical-chemical model of the hydrate decomposition process based on the multiphase flow of porous media and considering the transient changes in capillary pressure, permeability and other physical properties.

[0087] Those skilled in the art should understand that NGH is in equilibrium under certain temperature-pressure conditions. When the temperature or pressure within the reservoir changes, NGH may decompose, and the decomposition rate R... h (kmol / s) can be expressed by the Kim–Bishnoi equation:

[0088] R h =k d A s <f e -f>=k d A s <P e -P g >, (11)

[0089] Among them, f e Let f be the methane fugacity (Pa) at phase equilibrium, and f be the actual methane fugacity (Pa). Typically, f is taken as f. e -f=P e -P g k d A represents the decomposition kinetic constant of Arrhenius-type NGH. s To determine the effective surface area, it can be derived from the modified Kozeny-Carman relationship, P e The phase equilibrium pressure is directly related to the reservoir temperature. The specific expressions for the above parameters are as follows:

[0090]

[0091]

[0092] K = K0(1-S) H ) N (14)

[0093]

[0094] Where, k d0 The dynamic reaction coefficient for NGH decomposition is given by K, where K is the effective permeability of the reservoir (m). 2 K0 is the intrinsic permeability (m) of the porous medium without NGH. 2 N is the permeability reduction index caused by NGH in porous media, and A (Pa), B and C (K) are the regression coefficients of the equilibrium pressure of the NGH phase.

[0095] During the decomposition of NGH, the mass changes of water, methane, and NGH, as well as the heat changes in the pores, satisfy the following conditions:

[0096]

[0097]

[0098]

[0099] Q h =-ΔHR h (16)

[0100] Where, N H It is the number of hydrates, M α (α=H,w,g) represents the molar mass of different components, and ΔH represents the latent heat induced by the NGH phase transition, which can be obtained by fitting the Kamath equation shown in equation (17):

[0101] ΔH=c1+c2T, (17)

[0102] Where c1 and c2 are linear regression coefficients.

[0103] In porous media, the relationship between saturation and capillary pressure can be described by a soil-water characteristic curve. If NGH is present in the pores, the effective saturation needs to be corrected. The soil-water characteristic curve satisfied by the reservoir may differ for different geological conditions. In the DEHydrate simulator, selectable models include the Van Genuchten model and the Brooks-Corey model. Taking the Van Genuchten model as an example, its expression is:

[0104]

[0105] Among them, P c This is the capillary pressure, i.e., P. c =P g -P w P0 and n e For Van Genuchten coefficients and exponents, S e The effective saturation in the soil pores can be corrected based on the NGH saturation, as shown in the following formula:

[0106]

[0107] Among them, S rw and S rg Let be the residual saturation levels of water and methane gas in the pores, respectively. From this, we can obtain:

[0108]

[0109]

[0110]

[0111] Within the pores, the saturation of different components always satisfies S H +S g +S w =1, therefore, from equation (20), we can obtain the following equation:

[0112]

[0113] In Darcy's law, the relative permeability of water and gas can be calculated using the Stone modified model, as shown in the following equation:

[0114]

[0115] Where, n w and n g The index is calculated for relative penetration.

[0116] In the specific implementation process, the density and dynamic viscosity coefficient of different components are calculated using the same model in the TOUGH+HYDRATE simulator. The density of gas can be calculated using the Peng Robinson model, the Soave RedlichKwong model, and the standard Redlich Kwong model. The dynamic viscosity of gas is calculated using the Chung model. The density and dynamic viscosity of water are calculated using the IAPWS97 model and the Cooper-Dooley model, respectively. The density of NGH is calculated using the Ballard model.

[0117] At the same time, the above physical properties can also be directly fixed, that is, they do not change with parameters such as temperature, pressure, saturation and displacement.

[0118] In step S102, the thermo-fluid-mechanical-chemical fully coupled model, the mass conservation model, the energy conservation model, the mechanical equilibrium model, and the hydrate decomposition model are fully coupled, and the gas pressure, water pressure, temperature, and displacement in different directions are used as the basic unknowns of the model to establish the finite element weak integral form of the thermo-fluid-mechanical-chemical fully coupled model.

[0119] After constructing a fully coupled thermo-fluid-mechanical-chemical model of natural gas hydrate decomposition, the embodiments of this application can further, based on the fully coupled thermo-fluid-mechanical-chemical model of hydrate decomposition, use the mass conservation equation, energy conservation equation, and force balance equation of gas and water as the basic model for full coupling, and also consider the gas pressure P. g Water pressure P w Temperature T and displacement u in different directions are used as the basic unknowns of the model, thereby establishing the finite element weak integral form of the fully coupled thermo-fluid-mechanical-chemical model.

[0120] Optionally, in one embodiment of this application, a fully coupled thermo-fluid-mechanical-chemical model, a mass conservation model, an energy conservation model, a mechanical equilibrium model, and a hydrate decomposition model are fully coupled, and gas pressure, water pressure, temperature, and displacement in different directions are used as the basic unknowns of the model to establish the finite element weak integral form of the fully coupled thermo-fluid-mechanical-chemical model. This includes: discretizing the time differential using the backward Euler method and the spatial differential using the first-order finite difference method; and calculating in the finite element method using the Galerkin method and the weighted residual method to obtain the equation set of the finite element weak integral form, thereby obtaining the finite element weak integral form of the fully coupled thermo-fluid-mechanical-chemical model.

[0121] In the embodiments of this application, the DEHydrate simulator can be fully coupled with the mass conservation equation, energy conservation equation, and force balance equation of gas and water as the basic model, and the gas pressure P is also included. g Water pressure P w Temperature T and displacement u in different directions are used as the basic unknowns of the model. The entire model is solved using the finite element method, and the weighted residual method is selected to obtain the equations in the weak integral form of the finite element method.

[0122] Alternatively, in one embodiment of this application, the mass conservation equation for water is as follows:

[0123]

[0124] The gas mass conservation equation is shown below:

[0125]

[0126] The energy conservation equation is as follows:

[0127]

[0128] The mechanical equilibrium equations are as follows:

[0129]

[0130] Where, ρ i and S i (i = w, g, s, H) represent the density and saturation of different components, respectively. Porosity, t is time, μ i (i = w, g) is the dynamic viscosity of fluid i, K ri (i = w, g) represents the relative permeability of water and gas, which is related to the saturation of water and NGH, and g is the gravitational acceleration vector, i.e., g = [0, 0, g]T (g = 9.8 m / s²). 2 ), (kg / s) represents the rate of mass change of different components caused by decomposition. (kg / s) is the injection rate of gas or water, γ is the coefficient of thermal expansion, T is the temperature (K), and C is the temperature. pi (i = g, w, s, H) represent the specific heat capacities of gas, water, soil particles, and NGH, respectively, and λ c Q is the combined thermal conductivity of the multiple components. in and Q H These represent the heat changes caused by injected heat and NGH decomposition, respectively. D is the stiffness matrix, δ is the Kronecker operator, and P... p ρ is the average pore pressure. c This is the total density after saturation weighting.

[0131] Specifically, the mass conservation equation of NGH in this embodiment is shown in equation (4). Since NGH and soil particles are compositely linked, they flow together at the same velocity, i.e., v H =vs, therefore, we can obtain the following formula:

[0132]

[0133] In porous soil media, the mass conservation equation for water is shown in equation (6). By decomposing the time partial derivative, equation (24) can be obtained:

[0134]

[0135] Considering the relative velocity between water and soil particles generated after soil particle deformation, its mathematical expression is as follows:

[0136] v w =v s +v rw (25)

[0137] Among them, v ri (i = w, g) represents the relative velocity between fluid i and soil particles.

[0138] The flow of water in porous media follows Darcy's law, as shown in equation (26):

[0139]

[0140] Where, μ i (i = w, g) is the dynamic viscosity of fluid i, K ri (i = w, g) represents the relative permeability of water and gas, which is related to the saturation of water and NGH, as shown in equation (23). g is the gravitational acceleration vector, i.e., g = [0, 0, g]. T (g=9.8m / s 2 Combining equations (2) and (3), we obtain equation (27):

[0141]

[0142] Among them, the water saturation S w It is the capillary pressure P c The function, product strain, and displacement u need to satisfy geometric compatibility, by controlling the capillary pressure P. c Replace with basic variables (P) g -P w Therefore, based on equation (27), the mass conservation equation for water evolves into:

[0143]

[0144] in

[0145] ζ=[1 1 0](2D)=[1 1 1 0 0 0](3D)

[0146]

[0147] The embodiments of this application can be calculated using the weighted residual method to obtain the finite element weak integral, the specific expression of which is:

[0148]

[0149] Among them, W I (=N I ) is the weighting function.

[0150] Furthermore, in embodiments of this application, the divergence and gravity terms of equation (30) can be Gaussian transformed, and both the gradient and divergence can be converted into coordinate form, resulting in the weighted form of equation (30):

[0151]

[0152] Where, n i (i = 1, 2, 3) represent normal vectors in different directions.

[0153] Furthermore, embodiments of this application can discretize the time-domain partial derivative using the backward Euler method to obtain:

[0154]

[0155] Where the superscript n represents the current time step, m represents the current iteration step of the next time step, and m+1 represents the next iteration step of the next time step, the independent variable is chosen to be the value of the m+1 iteration step for fully implicit solution. Therefore, the water mass conservation equation is further derived as follows:

[0156]

[0157] By transforming the unknowns into nodal forms using shape functions, the finite element weak integral form of the water mass conservation equation is obtained, as shown in equation (34):

[0158]

[0159] in

[0160]

[0161]

[0162]

[0163]

[0164]

[0165]

[0166] in,

[0167] In the pores of soil particles, the mass conservation equation for the gas satisfies equation (5). In the embodiments of this application, the time term of this equation can first be decomposed to obtain:

[0168]

[0169] Assuming the gas flow in the pores follows Darcy's law, then the relative velocities of the gas satisfy:

[0170]

[0171]

[0172] In the embodiments of this application, the gas saturation is determined by the capillary pressure P. c and NGH saturation S H Since the density of water is related to its pressure and temperature, according to the NGH mass conservation equation, equation (36) can be modified as follows:

[0173]

[0174] Using the weighted residual method, the above formula can be transformed into:

[0175]

[0176] By performing a Gaussian transformation on the gravity and divergence terms of equation (39) and converting both the gradient and divergence terms into coordinate form, we obtain the finite element weighted form of equation (39)(C-5), as shown in equation (40):

[0177]

[0178] Furthermore, in embodiments of this application, the backward Euler method can be used to discretize the time-domain partial derivative form, and the basic variables are selected to be the values ​​of the m+1 iteration steps to satisfy the fully implicit requirement. Then, the mass conservation equation for the gas is:

[0179]

[0180] By transforming all the basic variables into nodal form using shape functions, the finite element weak integral form of the water mass conservation equation is obtained as follows:

[0181]

[0182] in

[0183]

[0184]

[0185]

[0186]

[0187]

[0188]

[0189] During the decomposition of NGH, energy conservation satisfies equation (7), and equation (7) can be simplified to:

[0190]

[0191] Where the subscript c represents the porous medium, i.e. the comprehensive average value, this equation, combined with Darcy's law (26) and (37), the energy conservation equation can be transformed into:

[0192]

[0193] When the second partial derivative of pressure is ignored, and the gradient and divergence are converted into coordinate form, the energy conservation equation is obtained as follows:

[0194]

[0195] Using the weighted residual method, the above formula can be transformed into:

[0196]

[0197] Taking a Gaussian transform of the heat conduction term in equation (47), we get:

[0198]

[0199] Discretizing the time-domain partial derivatives using the backward Euler method, and selecting the values ​​of the basic variables at iteration step m+1 to satisfy the fully implicit requirement, then the energy conservation is:

[0200]

[0201] Transforming the basic variables into nodal form, we obtain the finite element weak integral form of the energy conservation equation as shown below:

[0202]

[0203] in

[0204]

[0205]

[0206]

[0207]

[0208] During the NGH decomposition process, the mechanical equilibrium equation satisfies equation (8). When the compressive stress is defined as negative, according to the effective stress principle, we can obtain:

[0209] σ=σ'-αP p δ-(1-φ)γTδ(52)

[0210] Where δ is the Kronecker operator, P p The average pore pressure is expressed as follows:

[0211]

[0212] Therefore, equation (8) can be transformed into:

[0213]

[0214] Assume that the stress-strain relationship satisfies the linear elastic constitutive equation, that is:

[0215] σ′=Dε, (55)

[0216] Furthermore, in the embodiments of this application, equation (54) can be transformed into:

[0217]

[0218] Where D is the stiffness matrix.

[0219] Using the weighted residual method, the above formula can be transformed into:

[0220]

[0221] Among them, W u is the weighting function in the force equilibrium equation.

[0222] Through Gaussian transformation, the coordinate form of equation (57) is obtained as follows:

[0223]

[0224] In practical implementation, embodiments of this application can also employ the Galerkin method, where the shape function of the node is consistent with the weight function of the equation, resulting in:

[0225]

[0226] Transforming the basic variables into nodal form, the finite element weak integral form of the mechanical equilibrium equations is as follows:

[0227]

[0228] in

[0229]

[0230]

[0231]

[0232]

[0233]

[0234] and

[0235]

[0236] Optionally, in one embodiment of this application, the finite element weak integral form is:

[0237]

[0238] Where u is displacement, P g For gas pressure, P w Let T be the water pressure and T be the temperature.

[0239] It should be noted that the embodiments of this application above provide detailed finite element weak integral forms of the NGH mass conservation, water mass conservation, gas mass conservation, energy conservation, and force balance equations, resulting in large-scale nonlinear equations associated with the six fundamental unknowns:

[0240]

[0241] Where u is displacement, P g For gas pressure, P w Let T be the water pressure and T be the temperature.

[0242] Therefore, this embodiment of the application establishes a finite element weak integral form of a fully coupled thermo-fluid-mechanical-chemical model by using gas pressure, water pressure, temperature, and displacement in different directions as the basic unknowns of the model, which effectively ensures the realization of simulation of multiple physical fields such as solid-liquid-gas multiphase flow, heat transfer, NGH phase transition, and solid deformation.

[0243] In step S103, the finite element weak integral form is numerically solved, and the solution results are used to form a DEHydrate simulator. The evolution trend of reservoir mechanical behavior of natural gas hydrate during decomposition is simulated based on the DEHydrate simulator.

[0244] Furthermore, embodiments of this application can numerically solve the finite element weak integral form of the fully coupled thermo-fluid-mechanical-chemical model in the hydrate decomposition process derived above, and combine it into a DEHydrate simulator, thereby simulating and predicting the evolution trend of reservoir mechanical behavior in the natural gas hydrate decomposition process through the DEHydrate simulator.

[0245] Optionally, in one embodiment of this application, the finite element weak integral form is numerically solved, and the solution results are aggregated into a DEHydrate simulator. The DEHydrate simulator is then used to simulate the evolution trend of reservoir mechanical behavior during the decomposition of natural gas hydrates. This includes: simulating gas-liquid flow and heat transfer behavior using low-order elements, calculating solid deformation using high-order and / or low-order elements, and solving the entire model using the fully implicit finite element method to obtain model results; obtaining the stiffness matrix of high-order and / or low-order elements through spatial integration based on the model results; solving the nonlinear equation system that meets preset conditions using the Newton iteration method to obtain a linear equation system, and updating the stiffness matrix in each iteration; and solving the linear equation system using the Pardiso solver or the Gauss-Seidel method.

[0246] Specifically, in the embodiments of this application, the simulation size (coordinates) and mesh generation can be performed using the commercial software Gambit. DEHydrate can directly read the mesh file generated by Gambit software. When displacement u and gas pressure P are used... g Water pressure P w When temperature T is the fundamental variable, the shape function must satisfy Ladyzhenskaya- -Brezzi condition. In the DEHydrate simulator, gas-liquid flow and heat transfer behavior are simulated using low-order elements, while solid deformation can be calculated using either high-order or low-order elements. The model is solved using the fully implicit finite element method. According to equation (9), displacement is higher order than pressure. If the same low-order shape function is selected, numerical oscillation may occur.

[0247] Therefore, embodiments of this application can select elements of different orders in different equations. The mass conservation equation and the energy conservation equation use low-order elements, each element has four nodes, and the weight function W... I The function is linear, and in the force equilibrium equation, depending on the model, either higher-order or lower-order elements can be selected. Higher-order elements correspond to eight nodes, and the weight function W... u For example, it is a quadratic function. Figure 2 As shown, when choosing lower-order elements, the number of nodes and the selection of the weight function are consistent with the mass conservation principle. Therefore, the gas pressure P g Water pressure P w The shape function of temperature T is linear, while the shape function of displacement u can be a quadratic or linear function. Finally, the stiffness matrix of each element is obtained by spatial integration.

[0248] When the force equilibrium equations are calculated using second-order elements, for the stiffness of each element, A g1 A g2B g E g A w B w1 B w2 E w A t B T E T1 and E T3 All are 4×4 matrices, Ss is an 8×8×3 matrix, S j (i = g, w, T) is a 4×8×3 matrix, A s B s and E s The matrix is ​​8×4, as shown in equation (63). The physical properties of each element are obtained by weighting the physical properties of the nodes. Therefore, for physical properties related to displacement, such as elastic modulus E and Poisson's ratio v, the embodiments of this application can use quadratic shape function weighting, while for physical properties related to pressure and temperature, linear shape function weighting can be used, as shown in the following equation:

[0249] P w =P w1 N1+P w3 N3+P w5 N5+P w7 N7,

[0250] K rw =K rw1 N1+K rw3 N3+K rw5 N5+K rw7 N7,

[0251] u=u1N1+u2N2+u3N3+u4N4+u5N5+u6N6+u7N7+u8N8,

[0252] v=v1N1+v2N2+v3N3+v4N4+v5N5+v6N6+v7N7+v8N8. (64)

[0253] When the force equilibrium equations are calculated using first-order elements, the stiffness matrix and physical properties of each element related to displacement u can be compared with P. w ,P g It is obtained using a method similar to T.

[0254] Furthermore, in the embodiments of this application, the large-scale strongly nonlinear equation system is solved using the Newton-Raphson iteration method. In each iteration step, the left-hand stiffness matrix is ​​updated based on the result of the previous iteration step to meet the requirement of full implicitness. The linear equation system formed in each iteration step is solved using the Pardiso solver (LU decomposition). If the time step is too small, the Pardiso solver may not converge or may have a large error. In this case, the Gauss-Seidel method is selected for solving. The method for determining the time step is determined according to the user's settings.

[0255] It should be noted that, during the Newton iteration process at each time step, the embodiments of this application may adopt the following two convergence criteria:

[0256] 1) With F m The relative error between them is less than the error value 1, as shown in equation (65):

[0257]

[0258] Where i and j represent nodes, The gas mass conservation equation (gas pressure P) for node j in the m-th iteration step. g The right-hand side of the related terms, and the meanings of the other right-hand side terms are obtained similarly, N P and N u Representing P respectively w ,P g The total number of nodes related to T and the total number of nodes related to displacement u, u ii (ii = x, y, z) represent displacements in different directions;

[0259] 2) The relative error between the independent variable calculated in the (m+1)th iteration step and the mth iteration step is less than the error value 2, as shown in the following formula:

[0260]

[0261] If the iteration continues to fail to meet the convergence condition or produces unreasonable results due to matrix singularity, the step size is reduced and the iteration is repeated. The entire process is as follows: Figure 3 As shown. In the embodiments of this application, the DEHydrate simulator simulation program can be compiled on the Visual Studio platform, and its finite element code is implemented in the FORTRAN language.

[0262] The embodiments of this application analyze the evolution of the mechanical behavior of the reservoir during hydrate decomposition by referring to the following examples to illustrate the practicality of the DEHydrate simulator. Table 1 is the parameter table of the Masuda NGH decomposition test verification model.

[0263] Table 1

[0264]

[0265]

[0266] Furthermore, to verify the applicability of the DEHydrate simulator to large-scale practical problems, the embodiments of this application perform numerical simulations on benchmark case 2 (BP4-case2) from the Second International NGH Code Comparison Study (IGHCCS2). BP4-Case2 is an axisymmetric model with a total length of 5000m, a wellbore radius of 0.15m, and a wellbore thickness of 1m. The model mesh is relatively dense near the wellbore and gradually thins outwards, with the entire model divided into 2040 rectangular elements. Figure 4 The radial distribution of NGH saturation and radial displacement at t=10 days and t=30 days is shown. Figure 4 It can be seen that the results obtained by the DEHydrate simulator are in good agreement with the results of other simulators, and the positions of the decomposition fronts are almost the same.

[0267] In practice, those skilled in the art will need to select the initial and boundary conditions for the DEHydrate simulator based on different geological models, such as... Figure 5 As shown, a stable hydrate reservoir before drilling and production is generally selected as the initial condition. Considering the effects of gravity and the cryogenic gradient, the initial pressure of the entire reservoir follows a linear distribution based on seawater density, i.e. The initial temperature follows a linear distribution based on the geothermal gradient, i.e. Where A0 represents the geothermal gradient. The distribution of total stress within the reservoir is calculated based on a weighted average of the saturation and density of different phases and porosity, i.e. It is important to note that the stress calculated in this way will generally cause consolidation of the reservoir under initial conditions. Therefore, stress correction is required before simulation to ensure that the reservoir is in a stable state before drilling and production. The upper and lower boundaries of the simulation process can generally be regarded as constant temperature and pressure boundaries to simulate the sustainable mass and heat supply of seawater to the seabed reservoir. The stress or displacement boundaries, as well as the temperature and pressure on the sides, are determined according to the actual situation. The wellbore is considered to be formed instantaneously, and its boundary conditions are determined according to the wellbore design parameters.

[0268] It should be noted that, in actual implementation, the embodiments of this application can be applied to various mining conditions based on certain assumptions. Specifically, the aforementioned assumptions mainly include:

[0269] (1) The only gaseous component of NGH is methane;

[0270] (2) The flow of gas-liquid multiphase flow in pores satisfies Darcy's law;

[0271] (3) NGH is distributed on the surface of soil particles, and the two form a composite consolidation material;

[0272] (4) Composite solid materials adopt the small strain assumption, which can produce displacement, but cannot flow;

[0273] (5) Momentum changes caused by phase transitions are not considered;

[0274] (6) The dissolution of gases in water and the effect of inhibitors were ignored.

[0275] Therefore, the embodiments of this application can achieve full coupling of multiphase flow and geomechanics. The physical properties of the reservoir can be changed in real time according to pressure, temperature, displacement, etc. in each calculation, making the numerical simulation more consistent with the actual hydrate decomposition behavior, and thus more accurately predicting the evolution trend of reservoir mechanical behavior during hydrate decomposition.

[0276] The execution logic of the fully coupled numerical simulation method for the decomposition process of natural gas hydrates in this application will be described below with reference to the accompanying drawings.

[0277] Figure 6 This is a schematic diagram illustrating the execution logic of the fully coupled numerical simulation method for the natural gas hydrate decomposition process in this application. Figure 6 As shown, the execution logic of the fully coupled numerical simulation method for the natural gas hydrate decomposition process in this application is as follows:

[0278] S601: Based on the principles of mass conservation, energy conservation, and static equilibrium, mass conservation models, energy conservation models, mechanical equilibrium models, and hydrate decomposition models for soil particles, hydrates, gas, and water during the decomposition of natural gas hydrates were established. Furthermore, considering the multiphase flow of porous media and the transient changes in capillary pressure, permeability, and other physical properties, a fully coupled thermo-fluid-mechanical-chemical model for the hydrate decomposition process was constructed.

[0279] S602: Based on the fully coupled thermo-fluid-mechanical-chemical model of hydrate decomposition, the model uses the mass conservation equation, energy conservation equation, and force balance equation of gas and water as the basic model for full coupling, with gas pressure P as the reference. g Water pressure P w Temperature T and displacement u in different directions are used as the basic unknowns of the model to establish the finite element weak integral form of the fully coupled thermo-fluid-mechanical-chemical model.

[0280] S603: Numerical solution of the finite element weak integral form of the fully coupled thermo-fluid-mechanical-chemical model in the decomposition of hydrates, and assembles it into a DEHydrate simulator;

[0281] S604: Evolution trend of reservoir mechanical behavior during hydrate decomposition based on DEHydrate simulator.

[0282] According to the fully coupled numerical simulation method for the natural gas hydrate decomposition process proposed in this application, a multiphase flow, strongly nonlinear, large-scale thermo-fluid-mechanical-chemical fully coupled model is established for the hydrate decomposition process. A DEHydrate simulator is integrated to simulate multiple physical fields such as solid-liquid-gas multiphase flow, heat transfer, NGH phase transition, and solid deformation. Furthermore, the DEHydrate simulator provides an effective tool for predicting the evolution of reservoir mechanical behavior during hydrate decomposition, effectively simulating the transient laws governing reservoir pressure, temperature, displacement and stress in different directions, multiphase saturation, and hydrate decomposition rate / decomposition amount and gas production / production rate during hydrate decomposition. In this DEHydrate simulator, multiphase flow and geomechanical components are fully coupled, and the physical properties of the reservoir change in real time according to pressure, temperature, and displacement in each calculation, making the numerical simulation more consistent with actual NGH decomposition behavior.

[0283] Secondly, the fully coupled numerical simulation device for the decomposition process of natural gas hydrates proposed according to the embodiments of this application is described with reference to the accompanying drawings.

[0284] Figure 7 This is a block diagram of a fully coupled numerical simulation device for the decomposition process of natural gas hydrates according to an embodiment of this application.

[0285] like Figure 7 As shown, the fully coupled numerical simulation device 10 for the natural gas hydrate decomposition process includes: a modeling module 100, a fully coupled module 200, and a simulation module 300.

[0286] Among them, the modeling module 100 is used to establish the mass conservation model, energy conservation model, mechanical equilibrium model and hydrate decomposition model of soil particles, hydrate, gas and water in the decomposition process of natural gas hydrate, and to construct a fully coupled thermal-fluid-mechanical-chemical model of natural gas hydrate in the decomposition process.

[0287] The fully coupled module 200 is used to fully couple the thermo-fluid-mechanical-chemical fully coupled model, the mass conservation model, the energy conservation model, the mechanical equilibrium model, and the hydrate decomposition model. It uses gas pressure, water pressure, temperature, and displacement in different directions as the basic unknowns of the model to establish the finite element weak integral form of the thermo-fluid-mechanical-chemical fully coupled model.

[0288] The simulation module 300 is used to numerically solve the finite element weak integral form and to assemble the solution results into a DEHydrate simulator. The DEHydrate simulator is then used to simulate the evolution trend of reservoir mechanical behavior during the decomposition of natural gas hydrates.

[0289] Alternatively, in one embodiment of this application, the mass conservation equation for water is as follows:

[0290]

[0291] The gas mass conservation equation is shown below:

[0292]

[0293] The energy conservation equation is as follows:

[0294]

[0295] The mechanical equilibrium equations are as follows:

[0296]

[0297] Where, ρ i and S i (i = w, g, s, H) represent the density and saturation of different components, respectively. Porosity, t is time, μ i (i = w, g) is the dynamic viscosity of fluid i, K ri (i = w, g) represents the relative permeability of water and gas, which is related to the saturation of water and NGH, and g is the gravitational acceleration vector, i.e., g = [0, 0, g]T (g = 9.8 m / s²). 2 ), (kg / s) represents the rate of mass change of different components caused by decomposition. (kg / s) is the injection rate of gas or water, γ is the coefficient of thermal expansion, T is the temperature (K), and C is the temperature. pi (i = g, w, s, H) represent the specific heat capacities of gas, water, soil particles, and NGH, respectively, and λ c Q is the combined thermal conductivity of the multiple components. in and Q H These represent the heat changes caused by injected heat and NGH decomposition, respectively. D is the stiffness matrix, δ is the Kronecker operator, and P... p ρ is the average pore pressure. c This is the total density after saturation weighting.

[0298] Optionally, in one embodiment of this application, the modeling module 100 includes a processing unit for obtaining a fully coupled thermo-fluid-mechanical-chemical model based on the transient changes of the multiphase saturation, capillary pressure, permeability, hydrate decomposition rate, porosity, and at least one other physical property of the porous medium.

[0299] Optionally, in one embodiment of this application, the fully coupled module 200 includes: a second calculation unit, used to discretize the time differential using the backward Euler method and the spatial differential using the first-order finite difference method, and to calculate in the finite element method using the Galerkin method and the weighted residual method to obtain a set of equations in the weak integral form of the finite element method, so as to obtain the weak integral form of the thermo-fluid-mechanical-chemical fully coupled model.

[0300] Optionally, in one embodiment of this application, the finite element weak integral form is:

[0301]

[0302] Where u is displacement, P g For gas pressure, P w Let T be the water pressure and T be the temperature.

[0303] Optionally, in one embodiment of this application, the simulation module 300 includes: a first calculation unit, an integration unit, an update unit, and a solution unit.

[0304] The first calculation unit is used to simulate gas-liquid flow and heat transfer behavior using low-order elements, calculate solid deformation using high-order and / or low-order elements, and solve the model results using the fully implicit finite element method.

[0305] Integral elements are used to obtain the stiffness matrices of higher-order and / or lower-order elements based on model results and through spatial integration.

[0306] The update unit is used to solve the nonlinear equation system that meets the preset conditions using the Newton-Raphson iteration method to obtain the linear equation system, and to update the stiffness matrix in each iteration.

[0307] Solver unit, used to solve linear equation systems using the Pardiso solver or the Gauss-Seidel method.

[0308] It should be noted that the foregoing explanation of the fully coupled numerical simulation method for the natural gas hydrate decomposition process also applies to the fully coupled numerical simulation device for the natural gas hydrate decomposition process in this embodiment, and will not be repeated here.

[0309] According to the fully coupled numerical simulation device for the natural gas hydrate decomposition process proposed in this application, based on the principles of mass conservation, energy conservation, and hydrostatic equilibrium, mass conservation models, energy conservation models, mechanical equilibrium models, and hydrate decomposition models are established for soil particles, hydrates, gas, and water during the natural gas hydrate decomposition process. Furthermore, considering the multiphase flow of porous media and the transient changes in capillary pressure, permeability, and other physical properties, a fully coupled thermo-fluid-mechanical-chemical model for the hydrate decomposition process is constructed. Based on this fully coupled thermo-fluid-mechanical-chemical model, a fully coupled numerical simulation device for the gas and water decomposition process is established. The mass conservation equation, energy conservation equation, and force balance equation are used as the basic model for full coupling. Gas pressure, water pressure, temperature, and displacement in different directions are used as the basic unknowns of the model to establish the finite element weak integral form of the fully coupled thermo-fluid-mechanical-chemical model. Numerical solutions are performed on the finite element weak integral form of the fully coupled thermo-fluid-mechanical-chemical model in the hydrate decomposition process, and the results are integrated into the DEHydrate simulator. This enables the simulation of multi-physics fields such as solid-liquid-gas multiphase flow, heat transfer, NGH phase transition, and solid deformation, and can effectively predict the evolution trend of mechanical behavior in the NGH decomposition process.

[0310] Figure 8 A schematic diagram of the structure of an electronic device provided in an embodiment of this application. The electronic device may include:

[0311] The memory 801, the processor 802, and the computer program stored on the memory 801 and capable of running on the processor 802.

[0312] When the processor 802 executes the program, it implements the fully coupled numerical simulation method for the natural gas hydrate decomposition process provided in the above embodiments.

[0313] Furthermore, electronic devices also include:

[0314] Communication interface 803 is used for communication between memory 801 and processor 802.

[0315] The memory 801 is used to store computer programs that can run on the processor 802.

[0316] The memory 801 may include high-speed RAM memory, and may also include non-volatile memory, such as at least one disk storage device.

[0317] If the memory 801, processor 802, and communication interface 803 are implemented independently, then the communication interface 803, memory 801, and processor 802 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 8 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.

[0318] Optionally, in a specific implementation, if the memory 801, processor 802, and communication interface 803 are integrated on a single chip, then the memory 801, processor 802, and communication interface 803 can communicate with each other through an internal interface.

[0319] The processor 802 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.

[0320] This application also provides a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the above-described fully coupled numerical simulation method for the decomposition process of natural gas hydrates.

[0321] 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.

[0322] 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.

[0323] 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.

[0324] 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.

[0325] 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.

[0326] 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.

[0327] 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.

[0328] 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 fully coupled numerical simulation method for the decomposition process of natural gas hydrates, characterized in that, Includes the following steps: Establish mass conservation models, energy conservation models, mechanical equilibrium models, and decomposition models of soil particles, natural gas hydrate (NGH), gas, and water during the decomposition process of natural gas hydrate, and construct a fully coupled thermo-fluid-mechanical-chemical model of the decomposition process of the natural gas hydrate. The thermo-fluid-mechanical-chemical fully coupled model, the mass conservation model, the energy conservation model, the mechanical equilibrium model, and the natural gas hydrate decomposition model are fully coupled, and the gas pressure, water pressure, temperature, and displacement in different directions are used as the basic unknowns of the model to establish the finite element weak integral form of the thermo-fluid-mechanical-chemical fully coupled model. as well as The finite element weak integral form is numerically solved, and the solution results are used to form a DEHydrate simulator. The evolution trend of the reservoir mechanical behavior of the natural gas hydrate during the decomposition process is simulated based on the DEHydrate simulator. The mass conservation model for water is shown below: The gas mass conservation model is shown below: The energy conservation model is as follows: The mechanical equilibrium model is shown below: in, ρ i and S i (i=w, g, s, H) represent the density and saturation of different components, respectively. φ It is porosity. t For time, ( i =w, g) is a fluid i dynamic viscosity, (i=w, g) represents the relative permeability of water and gas, which is related to the saturation of water and NGH, and g is the gravitational acceleration vector, i.e., g = [0, 0, g]T (g=9.8 m / s²). 2 ), (kg / s) represents the rate of mass change of different components due to decomposition. (kg / s) represents the injection rate of gas or water. γ The coefficient of thermal expansion is... T Temperature (K) C pi ( i =g, w, s, H) represent the specific heat capacities of gas, water, soil particles, and NGH, respectively. λ c The combined thermal conductivity of the multiple components, Q in and Q H Let represent the heat injection and the heat change caused by NGH decomposition, respectively; D is the stiffness matrix; and δ is the Kronecker operator. P p The average pore pressure. ρ c Here, ρ is the total density after saturation weighting, and u is the displacement. P g This refers to gas pressure. P w The pressure of water; The construction of the fully coupled thermo-fluid-mechanical-chemical model of the natural gas hydrate decomposition process includes: The thermo-fluid-mechanical-chemical fully coupled model is obtained based on the transient changes in multiphase saturation, capillary pressure, permeability, natural gas hydrate decomposition rate, porosity, and at least one other physical property of the porous medium.

2. The method according to claim 1, characterized in that, The process involves fully coupling the thermo-fluid-mechanical-chemical fully coupled model, the mass conservation model, the energy conservation model, the mechanical equilibrium model, and the natural gas hydrate decomposition model, using gas pressure, water pressure, temperature, and displacement in different directions as the basic unknowns of the model. This process establishes the finite element weak integral form of the thermo-fluid-mechanical-chemical fully coupled model, including: The time differential is discretized using the backward Euler method, and the spatial differential is discretized using the first-order finite difference method. In the finite element method, the Galerkin method and the weighted residual method are used for calculation to obtain the finite element weak integral form of the equation system, thus obtaining the finite element weak integral form of the thermo-fluid-mechanical-chemical fully coupled model.

3. The method according to claim 2, characterized in that, The weak integral form of the finite element method is as follows: ， Where u is displacement, P g For gas pressure, P w water pressure 、T For temperature.

4. The method according to claim 1, characterized in that, The process of numerically solving the finite element weak integral form and assembling the solution results into a DEHydrate simulator, and then simulating the evolution trend of the reservoir mechanical behavior of the natural gas hydrate during the decomposition process using the DEHydrate simulator, includes: Low-order elements are used to simulate gas-liquid flow and heat transfer behavior, while high-order and / or low-order elements are used to calculate solid deformation. The entire model is solved using the fully implicit finite element method to obtain the model results. Based on the model results, the stiffness matrix of the higher-order and / or lower-order elements is obtained through spatial integration. The Newton-Raphson iteration method is used to solve the nonlinear equation system that meets the preset conditions to obtain the linear equation system, and the stiffness matrix is ​​updated in each iteration. The linear equations can be solved using the Pardiso solver or the Gauss-Seidel method.

5. A fully coupled numerical simulation device for the decomposition process of natural gas hydrates, characterized in that, The apparatus employing the fully coupled numerical simulation method for the decomposition process of natural gas hydrates as described in any one of claims 1-4 includes: The modeling module is used to establish mass conservation models, energy conservation models, mechanical equilibrium models, and natural gas hydrate decomposition models for soil particles, natural gas hydrate, gas, and water during the decomposition process, and to construct a fully coupled thermo-fluid-mechanical-chemical model of the natural gas hydrate decomposition process. The fully coupled module is used to fully couple the thermo-fluid-mechanical-chemical fully coupled model, the mass conservation model, the energy conservation model, the mechanical equilibrium model, and the natural gas hydrate decomposition model, and to establish the finite element weak integral form of the thermo-fluid-mechanical-chemical fully coupled model using gas pressure, water pressure, temperature, and displacement in different directions as the basic unknowns of the model; and The simulation module is used to numerically solve the finite element weak integral form, and based on the solution results, it sets up a DEHydrate simulator, and based on the DEHydrate simulator, it simulates the evolution trend of the reservoir mechanical behavior of the natural gas hydrate during the decomposition process.

6. The apparatus according to claim 5, characterized in that, The simulation module includes: The first calculation unit is used to simulate gas-liquid flow and heat transfer behavior using low-order elements, calculate solid deformation using high-order elements and / or low-order elements, and solve the whole using the fully implicit finite element method to obtain the model results. An integral unit is used to obtain the stiffness matrix of the higher-order and / or lower-order elements by spatial integration based on the model results. The update unit is used to solve the nonlinear equation system that meets the preset conditions using the Newton-Raphson iteration method to obtain the linear equation system, and to update the stiffness matrix in each iteration. The solver unit is used to solve the linear equations using the Pardiso solver or the Gauss-Seidel method.

7. An electronic device, characterized in that, include: 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 fully coupled numerical simulation method for the decomposition process of natural gas hydrates as described in any one of claims 1-4.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, The program is executed by a processor to implement the fully coupled numerical simulation method for the decomposition process of natural gas hydrates as described in any one of claims 1-4.

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