Effective burying amount calculation method for green methanol generated by H2 / CO2 collaborative storage

Abstract

The invention relates to a method for calculating the effective burying amount of green methanol generated by H2 / CO2 collaborative storage, which comprises the following steps of: establishing an underground methanol flow control equation based on the mass conservation law of a porous medium and the Darcy flow law; carrying out numerical discretization of a finite difference format on the underground methanol flow control equation; establishing an underground green methanol micro-compressible flow model, and solving distribution of liquid phase saturation S1 and liquid phase fluid pressure P1; based on an underground green methanol micro-compressible flow model, the influence of the capillary force effect and the relative permeability on methanol flow is analyzed, along with the increase of the capillary force effect and the relative permeability, the fluid pressure and saturation diffusion are also increased, and the capillary force effect and the relative permeability are favorable factors for methanol storage; and quantitatively characterizing the influence of capillary force action and relative permeability factors on methanol burying, and calculating the effective burying amount of methanol. According to the invention, underground flow of methanol is simulated, and the effective burying amount of methanol can be calculated.

Description

Technical field:

[0001] The present invention relates to the technical field of underground energy storage H2 / CO2 synergistic sequestration, and in particular to a method for calculating the effective storage volume of green methanol generated by H2 / CO2 synergistic sequestration. Background technology:

[0002] Underground energy storage is widely considered to be a major strategy for achieving low carbon emissions and can address energy supply and demand imbalances and global warming. Underground methanol storage is a promising way to store renewable energy. In the context of extensive underground energy storage, research on underground methanol energy storage is significantly insufficient compared to underground CO2 / H2 storage. CO2 / H2 undergoes a catalytic reaction underground through a catalyst to produce green methanol. At the same time, methanol is converted into CO2 / H2 through reverse catalysis for utilization, achieving hydrogen storage, carbon sealing, and efficient energy utilization. Summary of the invention:

[0003] The purpose of the present invention is to provide a method for calculating the effective storage capacity of green methanol generated by H2 / CO2 synergistic storage. This method for calculating the effective storage capacity of green methanol generated by H2 / CO2 synergistic storage is used to solve the problem in the prior art that the seepage mechanism of underground storage of green methanol is unclear and the storage capacity of green methanol cannot be accurately calculated.

[0004] The technical solution adopted by the present invention to solve the technical problem is: the effective storage volume calculation method of the H2 / CO2 synergistic storage to generate green methanol includes the following steps:

[0005] Step 1: Based on the law of conservation of mass in porous media and Darcy's flow law, establish the underground methanol flow control equation;

[0006] Step 2: Based on the numerical method IMPES for implicit pressure solution and explicit saturation solution and the five-point central difference discretization format, the underground methanol flow control equation is numerically discretized in the finite difference format;

[0007] Step 3: Based on the underground methanol flow control equation, establish the underground green methanol micro-compressible flow model and solve the liquid phase saturation S l and the liquid phase fluid pressure P l Distribution of

[0008] Step 4: Based on the underground green methanol micro-compressible flow model, the effects of capillary force and relative permeability on methanol flow are analyzed. As the capillary force and relative permeability increase, the fluid pressure and saturation diffusion also increase. Capillary force and relative permeability are favorable factors for methanol storage.

[0009] Step 5: Quantitatively characterize the effects of capillary force and relative permeability on methanol storage, and calculate the effective storage capacity of methanol. The calculation formula is as follows:

[0010]

[0011] In the formula, is the methanol storage capacity, kg; ρ l is the liquid phase density; A is the methanol storage area, m 2 ; Sl is the liquid phase saturation; is the porosity; h is the reservoir thickness, h=1m.

[0012] The underground methanol flow control equation in step 1 of the above scheme is:

[0013]

[0014] in:

[0015]

[0016] P c =P l -P g

[0017] P c =P c (S α )

[0018] k rα =k rα (S α )

[0019] In the formula, represents the porosity, ρ α is the density, S α is the saturation, g is the acceleration due to gravity, q α is the source term, k ra is the relative permeability, μ α is the viscosity, is the absolute permeability, p α It's pressure. is the flow rate, t is the time, T is the total time, and the subscript α is l and g, with the subscript l representing the liquid phase and the subscript g representing the gas phase.

[0020] The underground green methanol micro-compressible flow model in step 3 of the above scheme is:

[0021]

[0022] In the formula,

[0023] In the formula, represents the porosity, ρ g is the gas phase density, ρ l is the liquid density, Sg is the gas phase saturation, S l is the liquid saturation, g is the gravitational acceleration, q l is the source term of the liquid phase, q g is the source term of the gas phase, q t is the total source term, λ l is the liquid phase flow coefficient, λ g is the gas phase flow coefficient, λ t is the total flow coefficient, k rl is the liquid relative permeability, k rg is the relative permeability of gas, μ l is the liquid viscosity, μ g is the gas phase viscosity, is the absolute permeability, p l is the liquid phase pressure, p c is the capillary force, c g is the gas phase compressibility coefficient, c l is the liquid phase compressibility.

[0024] In step 3 of the above scheme, the liquid phase saturation S is solved l and the liquid phase fluid pressure P l The distribution method of

[0025] Based on the underground green methanol micro-compressible flow model, for micro-compressible fluids, the fluid liquid phase density is a function related to the fluid pressure:

[0026] ρ l =ρ0[1+c f (p l -p0)]

[0027] In the formula, ρ l is the liquid density; ρ0 is the reference density; c f is the fluid compressibility coefficient; p0 is the reference pressure; pl is the fluid pressure;

[0028] The compressibility coefficient of the fluid in the above formula is selected as the following 6 values:

[0029] c f =1×10 -3 / MPa,c f =1×10 -4 / MPa,c f =1×10 -5 / MPa,c f =5×10 -3 / MPa,c f =5×10 -4 / MPa,c f =5×10 -5 / MPa, and make schematic diagrams of the pressure distribution of micro-compressible fluids under different compressibility coefficients and the liquid phase saturation distribution of micro-compressible fluids under different time steps. According to the two distribution schematic diagrams, it is concluded that with the decrease of the fluid compressibility coefficient, the diffusion of fluid pressure and saturation becomes more and more obvious.

[0030] In step 4 of the above scheme, based on the underground green methanol micro-compressible flow model, the effects of capillary force and relative permeability on methanol flow are analyzed by combining different permeability models and capillary force models:

[0031] The Corey model is used to calculate the relative permeability:

[0032]

[0033]

[0034] Among them, S lr Represents the residual saturation of the gas phase, S gr Indicates the residual saturation of the liquid phase, S lr =0.3,S gr = 0.05; exponents α and β are parameters directly measured by steady-state experiments;

[0035] Two sets of relative permeability models are adopted, including relative permeability model-1, α=7, β=3; relative permeability model-2, α=7, β=3; α=4, β=2;

[0036] The J-function model is used to calculate the capillary force:

[0037]

[0038]

[0039] Among them, S lr represents the residual saturation of the gas phase, λ is a parameter measured experimentally, S rl =0.3, λ=0.4.; P E is the inlet pressure, where for different rock types, P The value of E is different;

[0040] Two sets of capillary force models are adopted, where the inlet pressure P of capillary force model-2 is E It is one third of the capillary force -1, P E =35kPa.

[0041] Beneficial effects:

[0042] 1. According to the physical and chemical properties of green methanol, the control equation of underground methanol flow is established based on the law of conservation of mass in porous media and Darcy's flow law.

[0043] 2. Aiming at the physicochemical properties of green methanol, the present invention numerically discretizes the established control equations for underground methanol flow in a finite difference format based on the numerical method of implicit pressure solution and explicit saturation solution (IMPES) and a five-point central difference discretization format.

[0044] 3. The present invention relies on the control equation of green methanol flow to establish an underground green methanol micro-compressible flow model and clarify the liquid phase saturation S l and the liquid phase fluid pressure P l The distribution of methanol provides theoretical guidance for underground storage of green methanol.

[0045] 4. Based on the established mathematical model of green methanol micro-compressible flow, the present invention analyzes the main controlling factors affecting fluid flow in different time periods: capillary force and relative permeability. The research results show that higher capillary force and relative permeability will increase fluid pressure and saturation diffusion. Capillary force and relative permeability are favorable factors for methanol storage and can significantly increase its storage capacity.

[0046] 5. The present invention establishes a mathematical model of green methanol micro-compressible flow, and considers the effects of capillary force and relative permeability in the flow model. In order to quantitatively characterize the effects of these factors on methanol storage, the effective storage capacity of methanol is further introduced, and the effects of various factors on methanol storage are comprehensively analyzed, providing theoretical guidance for subsequent methanol storage. Description of the drawings:

[0047] Figure 1 Schematic diagram of pressure distribution of micro-compressible fluid under different compressibility coefficients;

[0048] Figure 2 Schematic diagram of liquid saturation distribution of micro-compressible fluid at different time steps;

[0049] Figure 3 The micro-compressible fluid pressure distribution at the time steps of 200 and 7600 for relative permeability model 1 and model 2 (the left side is 200 time steps and the right side is 7600);

[0050] Figure 4 The micro-compressible fluid saturation distribution at the time steps of 200 and 7600 for relative permeability model 1 and model 2 (the left side is 200 time steps and the right side is 7600);

[0051] Figure 5Pressure distribution of micro-compressible fluid under the capillary force model 1 and model 2 (200 time steps on the left and 7600 on the right) at the time steps of 200 and 7600;

[0052] Figure 6 The saturation distribution of micro-compressible fluid under the time steps of 200 and 7600 for the capillary force model 1 and model 2 (the left side is 200 time steps and the right side is 7600);

[0053] Figure 7 The effect of relative permeability and capillary force on the effective storage capacity of methanol at 7600 time steps. Specific implementation method:

[0054] The present invention will be further described below in conjunction with the accompanying drawings:

[0055] Combination Figure 1-Figure 7 As shown in the figure, the calculation method of the effective storage volume of green methanol generated by H2 / CO2 synergistic storage includes the following steps:

[0056] S1. Based on the law of conservation of mass in porous media and Darcy's flow law, the underground methanol flow control equation was established.

[0057] The governing equations describing the flow of a two-phase system in a porous medium are based on the continuity assumption in the form of partial differential equations, where global variables are continuous functions in space and time. The system consists of two immiscible phases, liquid (l) and gas (g), and the flow of the two phases, i.e., S α , α∈{l,g} is described by the continuity equation and Darcy's law. The governing equation for two-phase flow in porous media is given by:

[0058]

[0059] in, is the Darcy seepage velocity of each phase, and the calculation equation is as follows:

[0060]

[0061] In the formula, represents the porosity, ρ α is the density, S a is the saturation, q a is the source term, k ra is the relative permeability, μ a is the viscosity, is the absolute permeability, p a It's pressure. is the flow rate, and the subscripts l and g denote the liquid phase and the gas phase, respectively.

[0062] Since the sum of the saturations of all phases is 1, the following relationship holds:

[0063]

[0064] The calculation considering the capillary force is as follows:

[0065] P c =P l -P g

[0066] Relative permeability and capillary force are functions of liquid saturation. This functional relationship is usually obtained through experiments, so there is the following relationship:

[0067] P c =P c (S α )

[0068] k rα =k rα (S α )

[0069] S2. Based on the implicit pressure and explicit saturation solution numerical method (IMPES) and the five-point central difference discretization format, the established underground methanol flow control equation is numerically discretized in finite difference format.

[0070] S3. Based on the control equation of green methanol flow, an underground green methanol micro-compressible flow model is established to solve the liquid phase saturation S l and the liquid phase fluid pressure P l distribution.

[0071] The continuity equation for slightly compressible flow can be given by:

[0072]

[0073] For slightly compressible fluids, the density of the fluid phase is a function of the fluid pressure:

[0074] ρ l =ρ0[1+c f (p l -p0)]

[0075] In the formula, ρ l is the liquid density; ρ0 is the reference density; c f is the fluid compressibility coefficient; p0 is the reference pressure; pl is the fluid pressure.

[0076] Solve the differential equation for each phase:

[0077]

[0078] And because ∑S α=1, so the sum of each phase is:

[0079]

[0080] Fluid compressibility:

[0081]

[0082]

[0083] Rock compressibility:

[0084]

[0085] In the formula, c l represents the liquid compressibility coefficient, c g represents the gas phase compressibility coefficient, c r They represent the rock compressibility coefficient respectively.

[0086] So we have:

[0087]

[0088] Assumptions:

[0089] (1) The density variation in space is negligible, that is,

[0090] (2) The absolute permeability variation in space is negligible, that is,

[0091] (3) The compressibility of rock is not considered.

[0092] (4) The change of capillary force over time is negligible. Finally, the green methanol micro-compressible flow model can be expressed as:

[0093]

[0094] In the formula, λ l is the liquid phase flow coefficient; λ g is the gas phase flow coefficient; q l is the liquid phase flow rate; q g is the gas phase flow rate; q t is the total flow; t is the total flow coefficient.

[0095] The liquid saturation S l and the liquid phase fluid pressure P l is the unknown quantity to be solved, and the relative permeability liquid phase / gas phase relative permeability k rl / krg and capillary force p c Will affect the liquid saturation S l and the liquid phase fluid pressure P l In step 4, we will analyze and compare these two influencing factors.

[0096] See also Figure 1-2 , methanol slightly compressible flow, select the fluid compressibility coefficient as c f =1×10 -3 / MPa,c f =1×10 -4 / MPa,c f =1×10 -5 / MPa,c f =5×10 -3 / MPa,c f =5×10 -4 / MPa,c f =5×10 -5 / MPa, the results show that with the decrease of fluid compressibility, the diffusion of fluid pressure and saturation becomes more obvious.

[0097] S4. Based on the methanol micro-compressible flow model, the effects of capillary force and relative permeability on methanol flow are analyzed. The results show that higher capillary force and relative permeability will increase fluid pressure and saturation diffusion. Capillary force and relative permeability are favorable factors for methanol storage and can significantly increase its storage capacity.

[0098] The Corey model is used to calculate the relative permeability:

[0099]

[0100]

[0101] Among them, S lr Represents the residual saturation of the gas phase, S gr Indicates the residual saturation of the liquid phase, S lr =0.3, S gr = 0.05; exponents α and β are parameters directly measured by steady-state experiments.

[0102] Two sets of relative permeability models are used, including relative permeability model-1, α=7, β=3; relative permeability model-2, α=7, β=3; α=4, β=2.

[0103] The J-function model is used to calculate the capillary force:

[0104]

[0105]

[0106] Among them, S lr represents the residual saturation of the gas phase, λ is a parameter measured experimentally, S rl =0.3, λ=0.4.; P E is the inlet pressure, where for different rock types, P E The value of is different.

[0107] Two sets of capillary force models are used, in which the capillary force model-2 inlet pressure P E The value of is one third of the capillary force model-1, P E =35kPa.

[0108] The relative permeability-1 or relative permeability-2 and the capillary force-1 or capillary force-2 are introduced into the methanol micro-compressible flow model to obtain the corresponding liquid phase saturation S l and the liquid phase fluid pressure P l , and then analyze the effects of capillary force and relative permeability on methanol flow, and at the same time, lay the foundation for the subsequent analysis of the effective storage capacity of methanol.

[0109] See also Figure 3 , using different permeabilities (relative permeability model-2 is greater than relative permeability model-1), and selecting time steps of 200 and 7600 for simulation respectively. The increase in relative permeability makes it easier for the methanol fluid to flow, so the pressure is less likely to accumulate, resulting in a less obvious pressure diffusion. Overall, the methanol fluid pressure in relative permeability model 2 is less than that in model 1.

[0110] See also Figure 4 , similar to fluid pressure, Figure 6 The distribution of methanol fluid saturation is shown. The methanol liquid phase saturation at relative permeability 2 is significantly higher than that at relative permeability 1, because the higher the relative permeability, the more favorable the migration of methanol. The wider the distribution range of methanol, the higher the saturation. The greater the relative permeability, the more favorable the underground storage of methanol.

[0111] See also Figure 5-6 , in order to clearly demonstrate the effect of capillary force on methane fluid pressure and liquid saturation, different capillary forces are used, relative permeability-1 and time step are 200 and 7600 respectively. The increase of capillary force will lead to an increase in the pressure difference between the gas phase and the liquid phase of the fluid. The rich gas phase will replace the liquid phase and dissolve in it, promoting the migration and accumulation of liquid methanol. As a result, the pressure and saturation of the liquid phase fluid will increase. Since capillary force-1 is greater than capillary force-2, the capillary force-2 is compared and analyzed respectively. Figure 7It can be seen that the stronger the capillary force, the greater the pressure and saturation of the methanol liquid phase, and the capillary force effect is conducive to the underground storage of methanol.

[0112] S5. Quantitatively characterize the effects of capillary force and relative permeability on methanol storage, and calculate the effective storage capacity of methanol. The calculation formula is as follows:

[0113]

[0114] In the formula, is the effective storage capacity of methanol, kg; A is the methanol storage area, m 2 ρ l is the liquid phase density; h is the reservoir thickness, m, and this patent takes h=1m.

[0115] See also Figure 7 , when the capillary force is not considered, the greater the relative permeability, the easier it is for methanol to flow, the larger the methanol coverage, and therefore the greater the storage capacity of methanol. Using the same relative permeability model, the greater the capillary force, the greater the pressure difference between the gas and liquid phases, the gas phase will displace the liquid phase and cause it to aggregate, and ultimately a larger storage capacity will be obtained.

[0116] The present invention generates green methanol based on the catalytic reaction of CO2 / H2. Correspondingly, the feasibility of converting green methanol into CO2 / H2 through reverse catalysis is achieved to achieve hydrogen storage and carbon storage, and realize efficient utilization of energy. The present invention aims to study the mechanism of underground two-phase flow of methanol, and proposes a mathematical multiphase flow simulator solved by implicit pressure explicit saturation (IMPES) method, which is used to simulate the pressure distribution and saturation distribution of underground methanol. Sensitivity analysis of the two influencing factors of capillary force and relative permeability was carried out. The research results show that capillary force and relative permeability are conducive to the underground storage of methanol. The present invention establishes an underground methanol micro-compressible flow model considering multiphase flow, and reveals the changes in its saturation and pressure. The present invention aims to study the influence of capillary force / relative permeability on the storage of methanol under micro-compressible flow of green methanol, provide theoretical guidance for underground storage of green methanol, and at the same time, help reduce atmospheric carbon emissions, promote the utilization of underground resources, and promote global energy transformation.

[0117] The present invention aims to study the mechanism of underground two-phase flow of methanol, and proposes a mathematical multiphase flow simulator solved by the implicit pressure explicit saturation (IMPES) method to simulate the pressure distribution and saturation distribution of underground methanol. In addition, a sensitivity analysis of capillary force and relative permeability is performed. The results show that higher capillary pressure and relative permeability will lead to greater liquid phase pressure and saturation diffusion. Therefore, capillary force and relative permeability are favorable factors for methanol storage and can significantly improve its storage capacity. The present invention simulates the underground flow of methanol and reveals the changes in its saturation and pressure, which helps to reduce atmospheric carbon emissions, promote the utilization of underground resources, and promote global energy transformation. The present invention calculates the methanol storage capacity under the influence of various factors and provides theoretical guidance for underground storage of green methanol.

Claims

1. A method for calculating the effective storage volume of green methanol generated by H2 / CO2 synergistic storage, characterized in that The steps include: Step 1: Based on the mass conservation law of porous media and Darcy's flow law, establish the underground methanol flow control equation; Step 2: Based on the numerical method IMPES for implicit pressure solution and explicit saturation solution and the five-point central difference discretization format, the underground methanol flow control equation is numerically discretized in the finite difference format; Step 3: Based on the underground methanol flow control equation, establish the underground green methanol micro-compressible flow model and solve the liquid phase saturation S l and the liquid phase fluid pressure P l Distribution of Step 4: Based on the underground green methanol micro-compressible flow model, the effects of capillary force and relative permeability on methanol flow are analyzed. As the capillary force and relative permeability increase, the fluid pressure and saturation diffusion also increase. Capillary force and relative permeability are favorable factors for methanol storage. Step 5: Quantitatively characterize the effects of capillary force and relative permeability on methanol storage, and calculate the effective storage capacity of methanol. The calculation formula is as follows: In the formula, is the methanol storage capacity, kg; ρ l is the liquid phase density; A is the methanol storage area, m 2 ; Sl is the liquid phase saturation; is the porosity; h is the reservoir thickness, h=1m.

2. The method for calculating the effective storage volume of green methanol generated by H2 / CO2 synergistic storage according to claim 1 is characterized by: The underground methanol flow control equation in step 1 is: in: P c =P l -P g P c =P c (S α ) k rα =k rα (S α ) In the formula, represents the porosity, ρ α is the density, S α is the saturation, g is the acceleration due to gravity, q α is the source term, k rα is the relative permeability, μ α is the viscosity, is the absolute permeability, p α It's pressure. is the flow rate, t is the time, T is the total time, the subscripts α and g are, the subscript , indicates the liquid phase, and the subscript g indicates the gas phase.

3. The method for calculating the effective storage volume of green methanol generated by H2 / CO2 synergistic storage according to claim 2 is characterized by: The underground green methanol micro-compressible flow model in step 3 is: In the formula, In the formula, represents the porosity, ρ g is the gas phase density, ρ l is the liquid density, S g is the gas phase saturation, S l is the liquid saturation, g is the gravitational acceleration, q l is the source term of the liquid phase, q g is the source term of the gas phase, q t is the total source term, λ l is the liquid phase flow coefficient, λ g is the gas phase flow coefficient, λ t is the total flow coefficient, k rl is the liquid relative permeability, k rg is the relative permeability of gas, μ l is the liquid viscosity, μ g is the gas phase viscosity, is the absolute permeability, p l is the liquid phase pressure, p c is the capillary force, c g is the gas phase compressibility coefficient, c l is the liquid phase compressibility.

4. The method for calculating the effective storage volume of green methanol generated by H2 / CO2 synergistic storage according to claim 3 is characterized by: In step 3, the liquid phase saturation S is solved l and the liquid phase fluid pressure P l The distribution method of Based on the underground green methanol micro-compressible flow model, for micro-compressible fluids, the fluid liquid phase density is a function related to the fluid pressure: r l =ρ0[1+c f (p l -p0)] In the formula, ρ l is the liquid density; ρ0 is the reference density; c f is the fluid compressibility coefficient; p o Reference pressure; p l is the fluid pressure; The fluid compressibility coefficient in the above formula is selected as the following 6 values: c f =1×10 -3 / MPa,c f =1×10 -4 / MPa,c f =1×10 -5 / MPa,c f =5×10 -3 / MPa,c f =5×10 -4 / MPa,c f =5×10 -5 / MPa, respectively, the schematic diagram of the pressure distribution of the micro-compressible fluid under different compressibility coefficients and the schematic diagram of the liquid phase saturation distribution of the micro-compressible fluid under different time steps; According to the two distribution diagrams, it can be concluded that as the fluid compressibility decreases, the diffusion of fluid pressure and saturation becomes more and more obvious.

5. The method for calculating the effective storage volume of green methanol generated by H2 / CO2 synergistic storage according to claim 4 is characterized in that: In the fourth step, based on the underground green methanol micro-compressible flow model, the influence of capillary force and relative permeability on methanol flow is analyzed by combining different permeability models and capillary force models: The Corey model is used to calculate the relative permeability: Among them, S lr Represents the residual saturation of the gas phase, S gr Indicates the residual saturation of the liquid phase, S lr =0.3, S gr = 0.05; exponents α and β are parameters directly measured by steady-state experiments; Two sets of relative permeability models are adopted, in which relative permeability model-1, α=7, β=3; relative permeability model-2, a=7, β=3; α=4, β=2; The J-function model is used to calculate the capillary force: Among them, S lr represents the residual saturation of the gas phase, λ is a parameter measured experimentally, S rl =0.3, λ=0.4.; P E is the inlet pressure, where for different rock types, P E The value of is different; Two sets of capillary force models are adopted, where the inlet pressure P of capillary force model-2 is E P is one third of the capillary force -1. E =35kPa.

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