Method for optimizing pore-enlarging and permeation-enhancing working solution injection process of hydrate reservoir

Abstract

The invention discloses a hydrate reservoir reaming and permeability-enhancing working fluid injection process optimization method which comprises the following steps: S1, constructing a hydrate reservoir reaming and permeability-enhancing working fluid injection physical model, and performing matrix grid division and physical parameter endowing on the physical model; s2, based on a finite volume method, constructing a hydrate reservoir reaming and permeability-increasing working fluid injection numerical calculation model; s3, determining an injection process scheme of the reaming and permeability-increasing working fluid, loading boundary conditions, and performing numerical simulation according to the numerical calculation model of the reaming and permeability-increasing working fluid injection of the hydrate reservoir; and S4, a numerical simulation result of the current process scheme is obtained, whether the numerical simulation result meets the reaming and permeation increasing requirements or not is judged, if not, the process scheme is changed, and S3 to S4 are repeated till the current process scheme meets the reaming and permeation increasing requirements. According to the method, the process and construction parameters of the pore-enlarging and permeation-increasing measures of the hydrate reservoir can be optimized, the optimized process is obtained, and technical support is provided for hydrate exploitation.

Description

Technical Field

[0001] The invention relates to the technical field of hydrate reservoir exploitation, and in particular to a method for optimizing the injection process of a hydrate reservoir pore expansion and permeability enhancement working fluid. Background Art

[0002] As a substitute for oil and coal, natural gas hydrates have gradually attracted worldwide attention, and their mining value has also been increasingly valued. Moreover, the mining of hydrates can increase energy supply, reduce dependence on traditional fossil fuels, and promote the diversification of energy. However, in the current hydrate mining process, due to the low initial permeability of natural gas hydrates and strong porosity and permeability heterogeneity, as mining proceeds, secondary hydrate generation is prone to occur in the near-well area, blocking the channel and causing a decrease in permeability around the well. Therefore, in order to improve this problem, the porosity and permeability of the reservoir is improved by injecting pore expansion and permeability increasing working fluid into the pore and permeability space of natural gas hydrates, thereby improving the gas-liquid development efficiency in the reservoir and achieving pore expansion and permeability increasing of the hydrate reservoir.

[0003] Pore ​​expansion and permeability enhancement is a complex multi-physics field coupling problem. The reaction between the pore expansion and permeability enhancement working fluid and the matrix rock releases heat, which promotes the decomposition of natural gas hydrates. The decomposition of hydrates causes the flow to become a gas-liquid two-phase flow. At the same time, the pore permeability properties of the matrix change as the working fluid is injected. Therefore, how to clarify the effect of pore expansion and permeability enhancement and ensure the applicability and efficiency of the process plan is a technical problem that needs to be solved urgently. Summary of the invention

[0004] In view of the above problems, the present invention aims to provide a method for optimizing the injection process of working fluid for hydrate reservoir pore expansion and permeability enhancement.

[0005] The technical solution of the present invention is as follows:

[0006] A method for optimizing the injection process of a hydrate reservoir pore expansion and permeability enhancement working fluid comprises the following steps:

[0007] S1: constructing a physical model for hydrate reservoir pore expansion and permeability enhancement working fluid injection, and performing matrix grid division and physical parameter assignment on the physical model;

[0008] S2: constructing a numerical calculation model for hydrate reservoir pore expansion and permeability enhancement working fluid injection based on the finite volume method, wherein the numerical calculation model for hydrate reservoir pore expansion and permeability enhancement working fluid injection includes a hydrate phase change decomposition model, a gas-liquid two-phase seepage model, a temperature field calculation model, a chemical reaction model, and a pore permeability evolution model;

[0009] S3: determining a process scheme for injecting the pore-expanding and permeability-enhancing working fluid, loading boundary conditions, and performing numerical simulation according to the numerical calculation model for injecting the pore-expanding and permeability-enhancing working fluid into the hydrate reservoir;

[0010] S4: Obtain the numerical simulation results of the current process scheme, and determine whether the numerical simulation results meet the requirements of pore expansion and permeability increase. If not, change the process scheme and repeat S3-S4 until the current process scheme meets the requirements of pore expansion and permeability increase.

[0011] Preferably, in step S1, the physical parameters include initial flow porosity, absolute permeability, reservoir temperature and reservoir pressure of the formation.

[0012] Preferably, the hydrate phase change decomposition model is:

[0013]

[0014] Where: are respectively the gas phase, water phase generation rate and hydrate dissociation rate, kg / (m 3 ·s); M g 、M w 、M h are the molar masses of gas, water and hydrate, kg / mol, respectively; n is the number of water molecules in a hydrate molecule; is the hydration reaction constant; E d is the hydration activation energy, J / mol; R is the universal gas constant, 8.314 J / (mol·K); T is the reservoir temperature, K; A dec is the hydrate decomposition specific surface area, m 2 / m 3 ;P e , P are the pressure of the hydrate reservoir under equilibrium conditions and the actual pressure at any time, Pa, respectively.

[0015] Preferably, the gas-liquid two-phase seepage model is:

[0016]

[0017] Where: · is the divergence operator; K is the absolute permeability, D; k rw , k rg are the relative permeability of water phase and gas phase, D; ρ w , g , h are the densities of water phase, gas phase and hydrate, kg / m 3 ;μ w , μ g are the water phase viscosity and gas phase viscosity, mPa·s, respectively; is the gradient operator; P is the pressure, Pa / m; are respectively the gas phase, water phase consumption rate and hydrate formation rate, kg / (m 3 ·s);φ ffis the flow porosity; S w , S g , S h are the saturations of water phase, gas phase and hydrate respectively; t is time, s.

[0018] Preferably, the temperature field calculation model is:

[0019] (6)

[0021] Where: H w , H g , H h , H c are the enthalpy changes of water, gas, hydrate formation or decomposition, and chemical reaction between working fluid and minerals; P w , P g are water phase pressure and gas phase pressure, Pa / m, respectively; is the average apparent thermal conductivity of the hydrate reservoir, J / (m·K); T is the temperature, K; u c is the working fluid consumption rate during mineral dissolution, kmol / (m 3 ·s); U w , U g , U h , U r are the internal energies of water phase, gas phase, hydrate and rock, J / mol, respectively.

[0022] Preferably, the chemical reaction model includes a mass conservation equation for the working fluid and a mass conservation equation for salt generated by mineral dissolution;

[0023] The working fluid mass conservation equation is:

[0024]

[0025] Where: C c is the concentration of the working fluid chemical, kg / kg; D c is the diffusion coefficient of the working fluid chemical in the water phase, m 2 / s; R c is the chemical consumption rate, kg / (m 2 ·s); β 100 The dissolving power of 100% chemical agent, kg / kg; M m is the average molar mass of dissolved minerals, kg / kmol; N mine is the stoichiometric coefficient of dissolved minerals;

[0026] The mass conservation equation for the salt generated by mineral dissolution is:

[0027]

[0028] Where: is the average concentration of salts generated by mineral dissolution, kg / kg; is the average diffusion coefficient of the generated salt in the aqueous phase, m 2 / s;ρ s is the rock density, kg / m 3 .

[0029] Preferably, the porosity and permeability evolution model is:

[0030]

[0031]

[0032] Where: is the updated flow porosity; φ0 is the initial flow porosity; Δt is a time step, s; K0 is the initial absolute permeability, D; β is an empirical constant; r and r0 are the pore radius and the initial pore radius, cm, respectively; A dec，0 is the initial specific surface area, m 2 / m 3 .

[0033] Preferably, in step S3, the pore expansion and permeability enhancement working fluid injection process scheme includes any one or more of injection displacement, injection fluid volume, working fluid formula and pore expansion and permeability enhancement chemical agent concentration.

[0034] The beneficial effects of the present invention are:

[0035] The present invention combines the finite volume method to construct a numerical calculation model for the injection of hydrate reservoir pore expansion and permeability enhancement working fluid, which takes into account the hydrate phase change decomposition, gas-liquid two-phase seepage, temperature field influence, chemical reaction and pore permeability evolution influence. This can accurately simulate and evaluate the pore permeability changes of the hydrate reservoir pore expansion and permeability enhancement working fluid after injection, and can optimize the hydrate reservoir pore expansion and permeability enhancement working fluid injection process, which has broad market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0037] Figure 1 It is a schematic flow chart of a method for optimizing the process of injecting a hydrate reservoir pore expansion and permeability enhancement working fluid according to the present invention;

[0038] Figure 2A schematic diagram of a physical model for injecting working fluid to expand the pores and increase the permeability of a hydrate reservoir in a specific implementation;

[0039] Figure 3 It is a schematic diagram of the pore expansion and permeability enhancement effect when the mass fraction of the working fluid is 0.15 in a specific implementation;

[0040] Figure 4 It is a schematic diagram of the pore expansion and permeability enhancement effect when the mass fraction of the working fluid is 0.2 in a specific implementation;

[0041] Figure 5 It is a schematic diagram of the pore expansion and permeability enhancement effect when the mass fraction of the working fluid is 0.25 in a specific implementation;

[0042] Figure 6 For a specific implementation, the injection strength is 0.5m 3 Schematic diagram of the pore expansion and permeability enhancement effect of / m;

[0043] Figure 7 For a specific implementation, the injection strength is 1.5m 3 Schematic diagram of pore expansion and permeability enhancement effect of / m;

[0044] Figure 8 For a specific implementation, the injection strength is 3.0m 3 / m schematic diagram of the pore expansion and permeability enhancement effect. DETAILED DESCRIPTION

[0045] The present invention is further described below in conjunction with the accompanying drawings and embodiments. It should be noted that, in the absence of conflict, the embodiments in this application and the technical features in the embodiments can be combined with each other. It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meanings as those generally understood by those of ordinary skill in the art to which this application belongs. The words "including" or "comprising" and the like used in the disclosure of the present invention mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0046] like Figure 1 As shown, the present invention provides a method for optimizing the injection process of a hydrate reservoir pore expansion and permeability enhancement working fluid, comprising the following steps:

[0047] S1: construct a physical model for the injection of hydrate reservoir pore expansion and permeability enhancement working fluid, and divide the matrix grid and assign physical parameters to the physical model.

[0048] In a specific embodiment, the physical model includes a hydrate phase change decomposition physical model, a gas-liquid two-phase seepage physical model, a temperature field calculation physical model, a chemical reaction physical model, and a porosity and permeability evolution physical model.

[0049] It should be noted that the physical models of the above embodiments have the same structure and are used for numerical simulation calculations in subsequent steps. Five identical physical models can be established, or only one physical model can be constructed and simulated five times.

[0050] In a specific embodiment, the physical parameters include initial flow porosity, absolute permeability, reservoir temperature and reservoir pressure of the formation.

[0051] S2: A numerical calculation model for the injection of pore expansion and permeability enhancement working fluid for hydrate reservoirs is constructed based on the finite volume method. The numerical calculation model for the injection of pore expansion and permeability enhancement working fluid for hydrate reservoirs includes a hydrate phase change decomposition model, a gas-liquid two-phase seepage model, a temperature field calculation model, a chemical reaction model, and a pore permeability evolution model.

[0052] In a specific embodiment, the hydrate phase change decomposition model is:

[0053]

[0054] Where: are respectively the gas phase, water phase generation rate and hydrate dissociation rate, kg / (m 3 ·s); M g 、M w 、M h are the molar masses of gas, water and hydrate, kg / mol, respectively; n is the number of water molecules in a hydrate molecule; is the hydration reaction constant; E d is the hydration activation energy, J / mol; R is the universal gas constant, 8.314 J / (mol·K); T is the reservoir temperature, K; A dec is the hydrate decomposition specific surface area, m 2 / m 3 ;P e , P are the pressure of the hydrate reservoir under equilibrium conditions and the actual pressure at any time, Pa, respectively.

[0055] The gas-liquid two-phase percolation model is:

[0056]

[0057]

[0058] Where: is the divergence operator; K is the absolute permeability, D; k rw , k rg are the relative permeability of water phase and gas phase, D; ρ w , g , h are the densities of water phase, gas phase and hydrate, kg / m3 ;μ w , μ g are the water phase viscosity and gas phase viscosity, mPa·s, respectively; is the gradient operator; P is the pressure, Pa / m; are respectively the gas phase, water phase consumption rate and hydrate formation rate, kg / (m 3 ·s);φ ff is the flow porosity; S w , S g , S h are the saturations of water phase, gas phase and hydrate respectively; t is time, s.

[0059] The temperature field calculation model is:

[0060]

[0061] Where: H w , H g , H h , H c are the enthalpy changes of water, gas, hydrate formation or decomposition, and chemical reaction between working fluid and minerals; P w , P g are water phase pressure and gas phase pressure, Pa / m, respectively; is the average apparent thermal conductivity of the hydrate reservoir, J / (m·K); T is the temperature, K; u c is the working fluid consumption rate during mineral dissolution, kmol / (m 3 ·s); U w , U g , U h , U r are the internal energies of water phase, gas phase, hydrate and rock, J / mol, respectively.

[0062] The chemical reaction model includes a mass conservation equation for the working fluid and a mass conservation equation for salt generated by mineral dissolution;

[0063] The working fluid mass conservation equation is:

[0064]

[0065] Where: C c is the concentration of the working fluid chemical (defined as the mass of the working fluid chemical per unit mass of water), kg / kg; D c is the diffusion coefficient of the working fluid chemical in the water phase, m 2 / s; R c is the chemical consumption rate, kg / (m 2 ·s); β 100M is the dissolving power of 100% chemical agent (defined as the ratio of the mass of dissolved mineral to the mass of 100% chemical agent reaction), kg / kg; m is the average molar mass of dissolved minerals, kg / kmol; N mine is the stoichiometric coefficient of dissolved minerals;

[0066] The mass conservation equation for the salt generated by mineral dissolution is:

[0067]

[0068] Where: is the average concentration of salts generated by mineral dissolution (defined as the average mass of salts generated by mineral dissolution), kg / kg; is the average diffusion coefficient of the generated salt in the aqueous phase, m 2 / s;ρ s is the rock density, kg / m 3 .

[0069] The porosity evolution model is:

[0070]

[0071] Where: is the updated flow porosity; φ0 is the initial flow porosity; Δt is a time step, s; K0 is the initial absolute permeability, D; β is an empirical constant; r and r0 are the pore radius and the initial pore radius, cm, respectively; A dec，0 is the initial specific surface area, m 2 / m 3 .

[0072] In the above porosity and permeability evolution model, the matrix porosity and absolute permeability are updated by equations (11)-(12), and equations (13)-(14) are expressions of the pore radius and specific surface area and their corresponding initial values.

[0073] S3: Determine a process plan for injecting the pore expansion and permeability enhancement working fluid, load boundary conditions, and perform numerical simulation according to the numerical calculation model for injecting the pore expansion and permeability enhancement working fluid into the hydrate reservoir.

[0074] In a specific embodiment, the pore expansion and permeability enhancement working fluid injection process scheme includes any one or more of injection displacement, injection fluid volume, working fluid formula, and pore expansion and permeability enhancement chemical agent concentration.

[0075] When performing numerical simulation, the relative permeability, chemical reaction rate and other parameter data are calculated and updated according to the grid unit; the multi-field coupled linear equation group in the hydrate reservoir expansion and permeability increasing working fluid injection numerical calculation model is used to solve the pressure, temperature, saturation and the like; the iteration error is calculated to determine whether the iteration converges at the current time step, and optionally, the difference in the pressure, temperature and saturation distribution between the previous and next iterations is calculated to determine whether the iteration converges, and if not, the iterative calculation is repeated until the current time step converges; the matrix porosity and absolute permeability are calculated and updated; it is determined whether the numerical simulation of the current process scheme is completed, and if not, the numerical simulation is repeated until all time step simulations are completed.

[0076] S4: Obtain the numerical simulation results of the current process scheme, and determine whether the numerical simulation results meet the requirements of pore expansion and permeability increase. If not, change the process scheme and repeat S3-S4 until the current process scheme meets the requirements of pore expansion and permeability increase.

[0077] It should be noted that the pore expansion and permeability increase requirements are generally determined according to the actual reservoir, and whether the pore expansion and permeability increase requirements are met is mainly determined by whether the pore permeability change reaches the change threshold. In addition, it is also judged by the distance of the impact of the increase in pore permeability on its range. This is a prior art, and the specific requirements are not repeated here.

[0078] In a specific embodiment, taking a hydrate reservoir as an example, the present invention is used to optimize the pore expansion and permeability enhancement working fluid injection process, which specifically includes the following sub-steps:

[0079] (1) Constructing a physical model for hydrate reservoir pore expansion and permeability enhancement working fluid injection, and performing matrix grid division and physical parameter assignment on the physical model. In this embodiment, the physical model constructed is as follows: Figure 2 As shown;

[0080] (2) Determine a set of hydrate reservoir pore expansion and permeability enhancement working fluid injection process scheme. In this embodiment, the main focus is on optimizing the mass fraction of the working fluid and the injection intensity in the pore expansion and permeability enhancement working fluid injection process scheme. The mass fractions of the working fluid studied are 0.150, 0.200, and 0.250, respectively, and the injection intensity studied is 0.5m 3 / m、1.5m 3 / m, 3.0m 3 / m;

[0081] (3) initializing or updating the physical parameters of the physical model for injection of the hydrate reservoir pore expansion and permeability enhancement working fluid;

[0082] (4) using the hydrate phase change decomposition model shown in equations (1)-(2) to simulate and calculate the hydrate dissociation rate and the gas phase and water phase generation rates;

[0083] (5) Using the gas-liquid two-phase seepage model shown in equations (3)-(5), simulate and calculate the gas-liquid two-phase flow velocity distribution;

[0084] (6) Using the chemical reaction model shown in equations (7)-(10), simulate and calculate the working fluid concentration, consumption rate and dissolved mineral concentration;

[0085] (7) Using the temperature field calculation model shown in formula (6), simulate and calculate the temperature distribution;

[0086] (8) using the porosity and permeability evolution model shown in equations (11)-(14) to calculate and update the changes in porosity and absolute permeability;

[0087] (9) Repeat steps (4) to (8) in one time step until the calculation converges. After convergence, determine whether the simulation is complete;

[0088] (10) Repeat steps (4)-(9) to simulate the next time step until all time step simulations are completed, calculate the changes in the final porosity and permeability of the current process solution, and determine whether the current process solution meets the requirements of pore expansion and permeability increase. If it does not meet the requirements, repeat steps (2)-(10) until the optimization obtains a process solution that meets the requirements of pore expansion and permeability increase.

[0089] In this embodiment, the pore expansion and permeability enhancement effects under different working fluid mass fractions are as follows: Figure 3-Figure 5 As shown. Figure 3-Figure 5 It can be seen that the larger the mass fraction of the working fluid, the larger the pore expansion and permeation radius. However, when the mass fraction increases to a certain value, the pore expansion and permeation radius will not continue to increase. Therefore, the mass fraction of the working fluid can be optimized to be between 0.2-0.25.

[0090] The pore expansion and permeability enhancement effects under different injection intensities are as follows Figure 6-Figure 8 As shown. Figure 6-Figure 8 It can be seen that increasing the injection intensity is beneficial to increasing the depth of pore expansion and permeability increase, so the injection intensity of 3m can be optimized. 3 / m.

[0091] In summary, the present invention can optimize the injection process of the working fluid for hydrate reservoir expansion and permeability enhancement, and provide technical support for the chemical agent exploitation of the working fluid in the hydrate reservoir. Compared with the prior art, the present invention has significant progress.

[0092] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modify the technical contents disclosed above into equivalent embodiments 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 according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for optimizing the injection process of a hydrate reservoir pore expansion and permeability enhancement working fluid, characterized in that: The following steps are involved: S1: constructing a physical model for hydrate reservoir pore expansion and permeability enhancement working fluid injection, and performing matrix grid division and physical parameter assignment on the physical model; S2: constructing a numerical calculation model for hydrate reservoir pore expansion and permeability enhancement working fluid injection based on the finite volume method, wherein the numerical calculation model for hydrate reservoir pore expansion and permeability enhancement working fluid injection includes a hydrate phase change decomposition model, a gas-liquid two-phase seepage model, a temperature field calculation model, a chemical reaction model, and a pore permeability evolution model; S3: determining a process scheme for injecting the pore-expanding and permeability-enhancing working fluid, loading boundary conditions, and performing numerical simulation according to the numerical calculation model for injecting the pore-expanding and permeability-enhancing working fluid into the hydrate reservoir; S4: Obtain the numerical simulation results of the current process scheme, and determine whether the numerical simulation results meet the requirements of pore expansion and permeability increase. If not, change the process scheme and repeat S3-S4 until the current process scheme meets the requirements of pore expansion and permeability increase.

2. The method for optimizing the injection process of hydrate reservoir pore expansion and permeability enhancement working fluid according to claim 1, characterized in that: In step S1, the physical parameters include initial flow porosity, absolute permeability, reservoir temperature and reservoir pressure of the formation.

3. The method for optimizing the injection process of hydrate reservoir pore expansion and permeability enhancement working fluid according to claim 1, characterized in that: The hydrate phase change decomposition model is: Where: are respectively the gas phase, water phase generation rate and hydrate dissociation rate, kg / (m 3 ·s); M g 、M w 、M h are the molar masses of gas, water and hydrate, kg / mol, respectively; n is the number of water molecules in a hydrate molecule; is the hydration reaction constant; E d is the hydration activation energy, J / mol; R is the universal gas constant, 8.314 J / (mol·K); T is the reservoir temperature, K; A dec is the hydrate decomposition specific surface area, m 2 / m 3 ; P e , P are the pressure of the hydrate reservoir under equilibrium conditions and the actual pressure at any time, Pa, respectively.

4. The method for optimizing the injection process of hydrate reservoir pore expansion and permeability enhancement working fluid according to claim 3, characterized in that: The gas-liquid two-phase percolation model is: Where: is the divergence operator; K is the absolute permeability, D; k rw , k rg are the relative permeability of water phase and gas phase, D; ρ w , g , h are the densities of water phase, gas phase and hydrate, kg / m 3 ;μ w , μ g are the water phase viscosity and gas phase viscosity, mPa·s, respectively; is the gradient operator; P is the pressure, Pa / m; are respectively the gas phase, water phase consumption rate and hydrate formation rate, kg / (m 3 ·s);φ ff is the flow porosity; S w , S g , S h are the saturations of water phase, gas phase and hydrate respectively; t is time, s.

5. The method for optimizing the injection process of hydrate reservoir pore expansion and permeability enhancement working fluid according to claim 4, characterized in that: The temperature field calculation model is: Where: H w , H g , H h , H c are the enthalpy changes of water, gas, hydrate formation or decomposition, and chemical reaction between working fluid and minerals; P w , P g are water phase pressure and gas phase pressure, Pa / m, respectively; is the average apparent thermal conductivity of the hydrate reservoir, J / (m·K); T is the temperature, K; u c is the working fluid consumption rate during mineral dissolution, kmol / (m 3 ·s); U w , U g , U h , U r are the internal energies of water phase, gas phase, hydrate and rock, J / mol, respectively.

6. The method for optimizing the injection process of hydrate reservoir pore expansion and permeability enhancement working fluid according to claim 5, characterized in that: The chemical reaction model includes a mass conservation equation for the working fluid and a mass conservation equation for salt generated by mineral dissolution; The working fluid mass conservation equation is: Where: C c is the concentration of the working fluid chemical, kg / kg; D c is the diffusion coefficient of the working fluid chemical in the water phase, m 2 / s; R c is the chemical consumption rate, kg / (m 2 ·s); β 100 The dissolving power of 100% chemical agent, kg / kg; M m is the average molar mass of dissolved minerals, kg / kmol; N mine is the stoichiometric coefficient of dissolved minerals; The mass conservation equation for the salt generated by mineral dissolution is: Where: is the average concentration of salts generated by mineral dissolution, kg / kg; is the average diffusion coefficient of the generated salt in the aqueous phase, m 2 / s;ρ s is the rock density, kg / m 3 .

7. The method for optimizing the injection process of hydrate reservoir pore expansion and permeability enhancement working fluid according to claim 6, characterized in that: The porosity evolution model is: Where: is the updated flow porosity; φ0 is the initial flow porosity; Δt is a time step, s; K0 is the initial absolute permeability, D; β is an empirical constant; r and r0 are the pore radius and the initial pore radius, cm, respectively; A dec,0 is the initial specific surface area, m 2 / m 3 .

8. The method for optimizing the injection process of hydrate reservoir pore expansion and permeability enhancement working fluid according to any one of claims 1 to 7, characterized in that: In step S3, the pore expansion and permeability enhancement working fluid injection process scheme includes any one or more of injection displacement, injection fluid volume, working fluid formula, and pore expansion and permeability enhancement chemical agent concentration.

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