Hydrate authigenic heat development process optimization method considering phase equilibrium relation evolution

Abstract

The invention discloses a hydrate self-heat-generation development process optimization method considering phase equilibrium relation evolution. The method comprises the following steps: constructing a hydrate reservoir self-heat-generation development physical model; matrix grid division is carried out; a set of hydrate reservoir self-heat-generation development process scheme is determined; initializing physical parameters of the hydrate reservoir spontaneous heat development physical model; constructing a two-phase seepage model and calculating pressure distribution and flow velocity distribution; constructing a chemical model and calculating a chemical reaction rate; constructing a heat transfer model and calculating temperature distribution; constructing a phase equilibrium relationship evolution model, and updating the equilibrium pressure and the equilibrium temperature of the current hydrate; judging whether the result converges; calculating a final temperature influence range of the current process scheme, and judging whether the final temperature influence range reaches a target range; otherwise, the current process scheme is the final process scheme. According to the method, the self-heat-generation development process of the hydrate reservoir can be optimized on the basis of considering the evolution of the phase equilibrium relationship of the hydrate.

Description

Technical Field

[0001] The invention relates to a method for optimizing a hydrate self-heat development process by taking into account the evolution of phase equilibrium relations, and belongs to the technical field of hydrate reservoir exploitation. Background Art

[0002] Hydrates are known as one of the most promising unconventional clean energy sources in the 21st century due to their huge reserves and clean combustion products. They also have high energy efficiency and broad market development prospects. However, the current hydrate mining technology is not mature enough, the mining environment is complex, and the mining is difficult. Hydrate autothermal development is a type of thermal stimulation method. By injecting an autothermal system into the reservoir, the liquid reaction generates heat to promote the decomposition of hydrates. It has been widely used.

[0003] In actual hydrate reservoirs, there are various inorganic salt ions, which have a certain influence on the phase equilibrium relationship of hydrates. With the injection of the self-heating system, the increase of inorganic salt ions will further cause the change of hydrate phase equilibrium. The existing hydrate phase equilibrium equations only consider the case of pure water, which is difficult to meet the high mineralization conditions in the actual production process. In addition, the current numerical simulation of hydrate self-heating exploitation often ignores the influence of inorganic salt ions on hydrate phase equilibrium. In order to be close to the actual situation on site, improve the efficiency of hydrate self-heating development, and further optimize the development process, it is necessary to propose a hydrate self-heating development process optimization method that considers the evolution of phase equilibrium relationship, so as to provide more effective guidance for the self-heating exploitation of hydrate reservoirs. Summary of the invention

[0004] The purpose of the present invention is to provide a method for optimizing the hydrate autothermal development process by taking into account the evolution of phase equilibrium relationships in order to address the problems existing in the prior art.

[0005] The technical solution provided by the present invention to solve the above technical problems is: a method for optimizing the hydrate self-heat development process considering the evolution of phase equilibrium relationship, comprising the following steps: S1. Construct a physical model for the self-heat development of hydrate reservoirs; S2. dividing the matrix grid of the hydrate reservoir autothermal development physical model and assigning physical parameters; S3. Determine a set of process schemes for the development of hydrate reservoir self-heat; S4, initializing or updating the physical parameters of the hydrate reservoir autothermal development physical model; S5. construct a two-phase seepage model and calculate the pressure distribution and flow velocity distribution; S6. Build chemical models and calculate chemical reaction rates; S7, construct a heat transfer model and calculate the temperature distribution; S8. construct a phase equilibrium relationship evolution model, calculate the mass percentage of inorganic salt ions, and then update the current equilibrium pressure and equilibrium temperature of the hydrate according to the mass percentage of inorganic salt ions; S9. Calculate the hydrate phase change decomposition rate at different salinities according to the current equilibrium pressure and equilibrium temperature of the hydrate; S10, calculating the gas production and liquid production rates caused by the hydrate phase change decomposition according to the hydrate phase change decomposition rate; S11, judging whether the result converges, if not, iterating the gas production and liquid production rates calculated in step S10 to step S5, and repeating steps S5-S11 until the result converges; S12. Calculate the final temperature influence range of the current process scheme, and determine whether it reaches the target temperature influence range; if not, optimize the process scheme of step S3, and repeat steps S3-S12 until the target temperature influence range is reached; if the target temperature influence range is reached, the current process scheme is the final optimized process scheme for self-heat development of hydrate reservoirs taking into account the evolution of phase equilibrium relationships.

[0006] A further technical solution is that the physical parameters include matrix porosity, matrix permeability, matrix pore compressibility, original hydrate saturation, burial depth, original hydrate reservoir temperature, original hydrate reservoir pressure, hydrate reservoir rock density, and hydrate density.

[0007] A further technical solution is to determine the injection rate of the hydrate reservoir self-heat development process in step S3.

[0008] A further technical solution is that the two-phase seepage model includes:

[0009]

[0010]

[0011]

[0012]

[0013]

[0014] Where: K rg , K rw are the relative permeabilities of gas and liquid phases, respectively; K is the proportionality coefficient; m g , m ware the flow viscosities of the gas phase and liquid phase respectively; p g , p w are the pressures of the gas phase and the liquid phase respectively; is the porosity; S w , S g are liquid phase saturation and gas phase saturation respectively; r w , r g are the liquid phase density and gas phase density respectively; t For time; R g , R w are the gas and liquid production rates caused by the phase change and decomposition of hydrates, respectively; r , z are the radial and axial coordinates in the cylindrical coordinate system respectively; v gr , v gz , v wr , v wz The gas phase r , z The seepage velocity and liquid phase in the direction r , z Direction of flow velocity.

[0015] A further technical solution is that the chemical model is:

[0016] Where: C is the mass concentration of the autothermal reactant; D is the reactant diffusion coefficient; is the Laplace operator; q c is the source term related to reactant injection; R act is the reaction consumption rate of the reactants; r w , r g are the liquid phase density and gas phase density respectively; t For time; v gr , v gz , v wr , v wz The gas phaser , z The seepage velocity and liquid phase in the direction r , z Direction of flow velocity.

[0017] A further technical solution is that the heat transfer model includes:

[0018] Where: Q hd , Q ac , Q loss They are the heat absorbed by hydrate decomposition, the heat generated by the autothermal reaction, and the heat loss; , are the porosity occupancy of porous media and the porosity occupancy of fluid respectively; is the reservoir thermal conductivity; r p , r h are the density of porous media and the density of hydrate respectively; T is the reservoir temperature; r w , r g are the liquid phase density and gas phase density respectively; is the enthalpy of hydrate formation; h p , h g , h w They are the thermal enthalpy of porous media, the thermal enthalpy of gas phase, and the thermal enthalpy of liquid phase respectively; R p is the porous medium reaction rate; R g , R w are the gas and liquid production rates caused by the phase change and decomposition of hydrates, respectively; S w , S g are liquid phase saturation and gas phase saturation respectively; r , z are the radial and axial coordinates in the cylindrical coordinate system respectively; v gr , v gz , v wr , v wz The gas phase r ,z The seepage velocity and liquid phase in the direction r , z Direction of flow velocity.

[0019] A further technical solution is that the phase equilibrium relationship evolution model includes:

[0020]

[0021]

[0022]

[0023]

[0024] Where: a w is the activity of the current liquid phase; , They are the turbidity of pure water and the turbidity of the current liquid phase respectively; n is the number of water molecules contained in the hydrate molecule; R is the universal gas constant; T e , T 0 are the hydrate equilibrium temperature after considering the evolution of hydrate phase equilibrium relationship and the hydrate equilibrium temperature without considering the evolution of hydrate phase equilibrium relationship; is the change in hydrate equilibrium temperature; t 1. t 2. t 3 are all correction factors; M is the molecular weight of dissolved salts; P e To balance the pressure; A , B , C , D All are regression coefficients; is the enthalpy of hydrate formation; X is the mass percentage of a certain salt ion.

[0025] A further technical solution is that the calculation formula for the hydrate phase change decomposition rate under different salinities is:

[0026] Where: is the intrinsic hydration reaction constant; is the Euler number e; is the hydration activation energy; M g Relative molecular mass of gas; Adec is the hydrate decomposition specific surface area; P g is the gas pressure; R is the universal gas constant; T is the reservoir temperature; P e To balance the pressure; R h is the hydrate phase change decomposition rate.

[0027] A further technical solution is that the convergence condition in step S9 is: the temperature difference in each time step is less than 2%.

[0028] A further technical solution is that the calculation formula in step S10 is:

[0029]

[0030] Where: M h is the relative molecular mass of the hydrate; M g is the relative molecular mass in the gas phase; M w is the relative molecular mass of the liquid phase; R h is the hydrate phase change decomposition rate; R g , R w They are respectively the gas production rate and liquid production rate caused by the phase change and decomposition of hydrate.

[0031] Beneficial effects of the present invention: Based on the evolution of the phase equilibrium relationship between inorganic salt ions and hydrates, the present invention can accurately simulate and evaluate the temperature influence range of the self-heating development of hydrate reservoirs, can optimize the self-heating development process of hydrate reservoirs, and has broad market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the process flow of the hydrate reservoir autothermal development process optimization method of the present invention; Figure 2 The radial temperature distribution of the reservoir under different mass percentages of sodium chloride in a specific embodiment; Figure 3 The influence curve of the mass percentage of sodium chloride on the temperature influence range and the maximum bottom temperature of a specific embodiment is shown; Figure 4 This is a diagram for optimizing the injection rate process for a specific embodiment. DETAILED DESCRIPTION

[0033] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] like Figure 1 As shown, the method for optimizing the hydrate self-heat development process considering the evolution of phase equilibrium relationship provided by the present invention comprises the following steps: S1. Construct a physical model for the self-heat development of hydrate reservoirs; S2. dividing the matrix grid of the hydrate reservoir autothermal development physical model and assigning physical parameters; The physical parameters include matrix porosity, matrix permeability, matrix pore compressibility, original hydrate saturation, burial depth, original hydrate reservoir temperature, original hydrate reservoir pressure, hydrate reservoir rock density, hydrate density and other parameters; S3. Determine a set of process schemes for the development of hydrate reservoir self-heat; S4, initializing or updating the physical parameters of the hydrate reservoir autothermal development physical model; S5. construct a two-phase seepage model and calculate the pressure distribution and flow velocity distribution; (1) (2) (3) (4) (5) (6) Where: K rg , K rw are the relative permeabilities of gas and liquid phases, respectively; K is the proportionality coefficient; m g , m w are the flow viscosities of the gas phase and liquid phase respectively; p g , p w are the pressures of the gas phase and the liquid phase respectively; is the porosity; S w , S g are liquid phase saturation and gas phase saturation respectively; rw , r g are the liquid phase density and gas phase density respectively; t For time; R g , R w are the gas and liquid production rates caused by the phase change and decomposition of hydrates, respectively; r , z are the radial and axial coordinates in the cylindrical coordinate system respectively; v gr , v gz , v wr , v wz The gas phase r , z The seepage velocity and liquid phase in the direction r , z Directional seepage velocity; S6. Build chemical models and calculate chemical reaction rates; (7) Where: C is the mass concentration of the autothermal reactant; D is the reactant diffusion coefficient; is the Laplace operator; q c is the source term related to reactant injection; R act is the reaction consumption rate of the reactants; r w , r g are the liquid phase density and gas phase density respectively; t For time; v gr , v gz , v wr , v wz The gas phase r , z The seepage velocity and liquid phase in the direction r , z Directional seepage velocity; S7, construct a heat transfer model and calculate the temperature distribution; (8) (9) Where: Q hd ,Q ac , Q loss They are the heat absorbed by hydrate decomposition, the heat generated by the autothermal reaction, and the heat loss; , are the porosity occupancy of porous media and the porosity occupancy of fluid respectively; is the reservoir thermal conductivity; r p , r h are the density of porous media and the density of hydrate respectively; T is the reservoir temperature; r w , r g are the liquid phase density and gas phase density respectively; is the enthalpy of hydrate formation; h p , h g , h w They are the thermal enthalpy of porous media, the thermal enthalpy of gas phase, and the thermal enthalpy of liquid phase respectively; R p is the porous medium reaction rate; R g , R w are the gas and liquid production rates caused by the phase change and decomposition of hydrates, respectively; S w , S g are liquid phase saturation and gas phase saturation respectively; r , z are the radial and axial coordinates in the cylindrical coordinate system respectively; v gr , v gz , v wr , v wz The gas phase r , z The seepage velocity and liquid phase in the direction r , z Directional seepage velocity; S8. construct a phase equilibrium relationship evolution model, calculate the mass percentage of inorganic salt ions, and then update the current equilibrium pressure and equilibrium temperature of the hydrate according to the mass percentage of inorganic salt ions; The calculation formula of the mass percentage of the inorganic salt ions is: (10) Where: Xis the mass percentage of a certain salt ion; , are the weight of the salt sample and the weight of water respectively; The phase equilibrium relationship evolution model includes: (11) (12) (13) (14) (15) Where: a w is the activity of the current liquid phase; , They are the turbidity of pure water and the turbidity of the current liquid phase respectively; n is the number of water molecules contained in the hydrate molecule; R is the universal gas constant; T e , T 0 are the hydrate equilibrium temperature after considering the evolution of hydrate phase equilibrium relationship and the hydrate equilibrium temperature without considering the evolution of hydrate phase equilibrium relationship; is the change in hydrate equilibrium temperature; t 1. t 2. t 3 are all correction factors; M is the molecular weight of dissolved salts; P e To balance the pressure; A , B , C , D All are regression coefficients; is the enthalpy of hydrate formation; X is the mass percentage of a certain salt ion; S9. Calculate the phase change decomposition rate of hydrate at different salinities according to the current equilibrium pressure and equilibrium temperature of the hydrate; (16) Where: is the intrinsic hydration reaction constant; is the Euler number e; is the hydration activation energy; M g Relative molecular mass of gas; A dec is the hydrate decomposition specific surface area; P g is the gas pressure; R is the universal gas constant; Tis the reservoir temperature; P e To balance the pressure; R h is the hydrate phase change decomposition rate; S10, calculating the gas production and liquid production rates caused by the hydrate phase change decomposition according to the hydrate phase change decomposition rate; (17) (18) Where: M h is the relative molecular mass of the hydrate; M g is the relative molecular mass in the gas phase; M w is the relative molecular mass of the liquid phase; R h is the hydrate phase change decomposition rate; R g , R w are the gas and liquid production rates caused by the phase change and decomposition of hydrates, respectively; S11, judging whether the result converges. If not, iterating the gas production and liquid production rates calculated in step S10 to step S5, and repeating steps S5-S11 until the result converges (i.e., the temperature difference in each time step is less than 2%). S12. Calculate the final temperature influence range of the current process scheme, and determine whether it reaches the target temperature influence range; if not, optimize the process scheme of step S3, and repeat steps S3-S12 until the target temperature influence range is reached; if the target temperature influence range is reached, the current process scheme is the final optimized process scheme for self-heat development of hydrate reservoirs taking into account the evolution of phase equilibrium relationships.

[0035] Example Taking a hydrate reservoir as an example, the present invention is used to optimize its self-heat development process, which specifically includes the following sub-steps: (1) constructing a physical model for the self-heat development of hydrate reservoirs, dividing the physical model into matrix grids, and assigning physical parameters; In this embodiment, the physical parameters are shown in Table 1: Table 1 Physical parameters of the physical model for hydrate reservoir autogenous heat development

[0036] (2) Determine a set of process solutions for the development of hydrate reservoir autothermal heat (3) initializing the physical parameters of the physical model of the hydrate reservoir autothermal development; (4) Using the two-phase seepage model shown in equations (1)-(6), simulate and calculate the pressure distribution; (5) Using the chemical model shown in formula (7), simulate the thermogenic chemical reaction and calculate the chemical reaction rate; (6) Using the heat transfer model shown in equations (8)-(9), simulate and calculate the temperature distribution; (7) Using the phase equilibrium relationship evolution model shown in equations (11)-(15), the mass percentage of inorganic salt ions is updated to calculate the current equilibrium temperature and equilibrium pressure of the hydrate; In this embodiment t 1. t 2. t The value of 3 is 0; In this embodiment A =0.005623, B =0.02169, C =0.6673, D =4.5113; The update of the mass percentage of inorganic salt ions is calculated based on the self-heating system reaction equation after a given reactant concentration. Taking the ammonium chloride-sodium nitrite system as an example, the reaction equation is as follows:

[0037] (8) Calculate the hydrate phase change rate according to the current equilibrium temperature and equilibrium pressure of the hydrate using equation (16); (9) Calculate the gas and liquid production rates caused by the hydrate phase change decomposition rate using equations (17)-(18); (10) Determine whether the result converges. If not, iterate the gas production and liquid production rates calculated in step (9) to step (4), and repeat steps (4) to (10) until the result converges. The convergence condition is that the temperature difference in each time step is less than 2%. (11) Calculate the final temperature influence range of the current process scheme. If the final temperature influence range of the current process scheme does not reach the target temperature influence range, optimize the injection efficiency of step (2) and repeat steps (2) to (11). Otherwise, the current process scheme is the final optimized hydrate reservoir self-heat development process scheme.

[0038] Taking different mass percentages of sodium chloride as an example, the radial temperature distribution of the reservoir under different mass percentages of sodium chloride is as follows: Figure 2 As shown; the influence curve of sodium chloride mass percentage on temperature influence range and maximum bottom hole temperature is shown in Figure 3As shown. It can be seen that sodium chloride will increase the temperature influence range. It is often used as a hydrate inhibitor to reduce the hydrate phase equilibrium temperature. During autothermal mining, hydrates are easier to decompose, thus increasing the temperature influence range. When the mass percentage is >8%, its influence effect is more obvious.

[0039] like Figure 4 As shown in the figure, in the process optimization part, by orthogonally decomposing different injection rates of 1080, 1260, 1440, 1620, and 1800 cubic meters per day with different mass percentages of sodium chloride, the injection rate can be optimized according to the actual level of inorganic salt ions (such as sodium ions) on site based on the conclusion.

[0040] In summary, the present invention can optimize the self-heating development process of hydrate reservoirs and provide technical support for hydrate reservoir exploitation. Compared with the prior art, the present invention has significant progress.

[0041] The above description is not intended to limit the present invention in any form. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for optimizing the hydrate self-heat development process by considering the evolution of phase equilibrium relations, characterized in that: The following steps are involved: S1. Construct a physical model for the self-heat development of hydrate reservoirs; S2. dividing the matrix grid of the hydrate reservoir autothermal development physical model and assigning physical parameters; S3. Determine a set of process schemes for the development of hydrate reservoir self-heat; S4, initializing or updating the physical parameters of the hydrate reservoir autothermal development physical model; S5. construct a two-phase seepage model and calculate the pressure distribution and flow velocity distribution; S6. Build chemical models and calculate chemical reaction rates; S7, construct a heat transfer model and calculate the temperature distribution; S8. construct a phase equilibrium relationship evolution model, calculate the mass percentage of inorganic salt ions, and then update the current equilibrium pressure and equilibrium temperature of the hydrate according to the mass percentage of inorganic salt ions; S9. Calculate the hydrate phase change decomposition rate at different salinities according to the current equilibrium pressure and equilibrium temperature of the hydrate; S10, calculating the gas production and liquid production rates caused by the hydrate phase change decomposition according to the hydrate phase change decomposition rate; S11, judging whether the result converges, if not, iterating the gas production and liquid production rates calculated in step S10 to step S5, and repeating steps S5-S11 until the result converges; S12. Calculate the final temperature influence range of the current process scheme, and determine whether it reaches the target temperature influence range; if not, optimize the process scheme of step S3, and repeat steps S3-S12 until the target temperature influence range is reached; if the target temperature influence range is reached, the current process scheme is the final optimized process scheme for self-heat development of hydrate reservoirs taking into account the evolution of phase equilibrium relationships.

2. The hydrate self-heat development process optimization method considering the evolution of phase equilibrium relationship according to claim 1 is characterized in that: The physical parameters include matrix porosity, matrix permeability, matrix pore compressibility, original hydrate saturation, burial depth, original temperature of hydrate reservoir, original pressure of hydrate reservoir, rock density of hydrate reservoir, and hydrate density.

3. The method for optimizing the hydrate self-heat development process considering the evolution of phase equilibrium relationship according to claim 1, characterized in that: In step S3, the injection rate of the hydrate reservoir autothermal development process is determined.

4. The method for optimizing the hydrate self-heat development process considering the evolution of phase equilibrium relationship according to claim 1, characterized in that: The two-phase seepage model includes: Where: K rg , K rw are the relative permeabilities of gas and liquid phases, respectively; K is the proportionality coefficient; μ g , μ w are the flow viscosities of the gas phase and liquid phase respectively; p g , p w are the pressures of the gas phase and the liquid phase respectively; is the porosity; S w , S g are liquid phase saturation and gas phase saturation respectively; ρ w , ρ g are the liquid phase density and gas phase density respectively; t For time; R g , R w are the gas and liquid production rates caused by the phase change and decomposition of hydrates, respectively; r , z are the radial and axial coordinates in the cylindrical coordinate system respectively; v gr , v gz , v wr , v wz The gas phase r , z The seepage velocity and liquid phase in the direction r , z Directional flow velocity.

5. The method for optimizing the hydrate self-heat development process considering the evolution of phase equilibrium relationship according to claim 1, characterized in that: The chemical model is: Where: C is the mass concentration of the autothermal reactant; D is the reactant diffusion coefficient; is the Laplace operator; q c is the source term related to reactant injection; R act is the reaction consumption rate of the reactants; ρ w , ρ g are the liquid phase density and gas phase density respectively; t For time; v gr , v gz , v wr , v wz The gas phase r , z The seepage velocity and liquid phase in the direction r , z Directional flow velocity.

6. The method for optimizing the hydrate self-heat development process considering the evolution of phase equilibrium relationship according to claim 1, characterized in that: The heat transfer model includes: Where: Q hd , Q ac , Q loss They are the heat absorbed by hydrate decomposition, the heat generated by the autothermal reaction, and the heat loss; , are the porosity occupancy of porous media and the porosity occupancy of fluid respectively; is the reservoir thermal conductivity; ρ p , ρ h are the density of porous media and the density of hydrate respectively; T is the reservoir temperature; ρ w , ρ g are the liquid phase density and gas phase density respectively; is the enthalpy of hydrate formation; h p , h g , h w They are the thermal enthalpy of porous media, the thermal enthalpy of gas phase, and the thermal enthalpy of liquid phase respectively; R p is the porous medium reaction rate; R g , R w are the gas and liquid production rates caused by the phase change and decomposition of hydrates, respectively; S w , S g are liquid phase saturation and gas phase saturation respectively; r , z are the radial and axial coordinates in the cylindrical coordinate system respectively; v gr , v gz , v wr , v wz The gas phase r , z The seepage velocity and liquid phase in the direction r , z Directional flow velocity.

7. The method for optimizing hydrate autothermal development process considering the evolution of phase equilibrium relationship according to claim 1, characterized in that: The phase equilibrium relationship evolution model includes: Where: a w is the activity of the current liquid phase; , They are the turbidity of pure water and the turbidity of the current liquid phase respectively; n is the number of water molecules contained in the hydrate molecule; R is the universal gas constant; T e , T 0 are the hydrate equilibrium temperature after considering the evolution of hydrate phase equilibrium relationship and the hydrate equilibrium temperature without considering the evolution of hydrate phase equilibrium relationship; is the change in hydrate equilibrium temperature; t 1. t 2. t 3 are all correction factors; M is the molecular weight of dissolved salts; P e To balance the pressure; A , B , C , D All are regression coefficients; is the enthalpy of hydrate formation; X is the mass percentage of a certain salt ion.

8. The method for optimizing hydrate autothermal development process considering the evolution of phase equilibrium relationship according to claim 1, characterized in that: The calculation formula of the hydrate phase change decomposition rate is: Where: is the intrinsic hydration reaction constant; is the Euler number e; is the hydration activation energy; M g Relative molecular mass of gas; A dec is the hydrate decomposition specific surface area; P g is the gas pressure; R is the universal gas constant; T is the reservoir temperature; P e To balance the pressure; R h is the hydrate phase change decomposition rate.

9. The method for optimizing hydrate autothermal development process considering the evolution of phase equilibrium relationship according to claim 1, characterized in that: The convergence condition in step S9 is: the temperature difference in each time step is less than 2%.

10. The method for optimizing hydrate autothermal development process considering the evolution of phase equilibrium relationship according to claim 1, characterized in that: The calculation formula in step S10 is: Where: M h is the relative molecular mass of the hydrate; M g is the relative molecular mass in the gas phase; M w is the relative molecular mass of the liquid phase; R h is the hydrate phase change decomposition rate; R g , R w They are respectively the gas production rate and liquid production rate caused by the phase change and decomposition of hydrate.

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