Calculation method for effective storage capacity of green methanol generated by h2 / co2 collaborative storage

Abstract

The application relates to a calculation method of an effective storage amount of green methanol generated by H2 / CO2 cooperative storage, which comprises the following steps: establishing an underground methanol flow control equation based on the mass conservation law of a porous medium and the Darcy flow law; performing numerical dispersion on the underground methanol flow control equation in a finite difference format; establishing an underground green methanol micro-compressible flow model to solve the distribution of liquid phase saturation S l and liquid phase fluid pressure P l ; analyzing the influence of capillary force action and relative permeability on the methanol flow based on the underground green methanol micro-compressible flow model; with the increase of the capillary force action and the relative permeability, the fluid pressure and the saturation diffusion also increase, and the capillary force action and the relative permeability are favorable factors for the methanol storage; quantitatively characterizing the influence of the capillary force action and the relative permeability factors on the methanol storage, and calculating the effective storage amount of the methanol. The application simulates the underground flow of the methanol and can calculate the effective storage amount of the methanol.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of underground energy storage H2 / CO2 collaborative sealing, in particular to an effective storage amount calculation method for green methanol generated by H2 / CO2 collaborative sealing. BACKGROUND

[0002] Underground energy storage is widely considered as a major strategy to achieve low carbon emissions, which can address energy supply and demand imbalance and global warming. Underground methanol storage is a potential renewable energy storage method. Under the background of extensive underground energy storage, the research on underground methanol storage is obviously insufficient compared with underground CO2 / H2. CO2 / H2 occurs catalytic reaction underground through a catalyst to generate green methanol, and at the same time, the methanol is converted into CO2 / H2 through a reverse catalyst for utilization, achieving hydrogen storage, carbon sealing, and realizing efficient energy utilization. SUMMARY

[0003] The purpose of the present application is to provide an effective storage amount calculation method for green methanol generated by H2 / CO2 collaborative sealing, which is used to solve the problem that the seepage mechanism of underground storage of green methanol is not clear and the storage amount of green methanol cannot be accurately calculated in the prior art.

[0004] The technical solution adopted by the present application to solve the technical problem is that the effective storage amount calculation method for green methanol generated by H2 / CO2 collaborative sealing comprises the following steps:

[0005] Step one, based on the mass conservation law of porous media and Darcy flow law, establish the underground methanol flow control equation;

[0006] Step two, based on the numerical method of implicit pressure solution and explicit saturation solution IMPES and five-point central difference discrete format, perform numerical dispersion of the finite difference format of the underground methanol flow control equation;

[0007] Step three, based on the underground methanol flow control equation, establish an underground green methanol micro-compressible flow model to solve the distribution of liquid phase saturation S l and liquid phase fluid pressure P l ;

[0008] Step four, based on the underground green methanol micro-compressible flow model, analyze the influence of capillary force action and relative permeability on methanol flow, and with the increase of capillary force action and relative permeability, the fluid pressure and saturation diffusion also increase, and capillary force action and relative permeability are favorable factors for methanol storage;

[0009] Step five, quantitatively characterize the influence of capillary force action and relative permeability factors on methanol storage, calculate the effective storage amount of methanol, and the calculation formula is as follows:

[0010]

[0011] wherein, is the buried amount of methanol, kg; p l is the liquid phase density; A is the methanol storage area, m 2 ; S1 is the liquid phase saturation; is the porosity; h is the reservoir thickness, h = 1 m.

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

[0013]

[0014] wherein:

[0015]

[0016] P c = P l - P g

[0017] P c = P c (S α )

[0018] k rα = k rα (S α )

[0019] wherein, represents the porosity, p α is the density, S α is the saturation, g is the gravitational acceleration, q α is the source term, k ra is the relative permeability, m α is the viscosity, is the absolute permeability, p α is the pressure, is the flow rate, t is the time, T is the total time, subscript a is l and g, subscript l represents the liquid phase, and subscript g represents the gas phase.

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

[0021]

[0022] wherein,

[0023] wherein, represents the porosity, p g is the gas phase density, p l is the liquid phase density, Sg is the gas phase saturation, S l is the liquid phase saturation, g is the gravitational acceleration, q l is the source term for the liquid phase, q g is the source term for the gas phase, q t is the total source term, λ l is the liquid phase mobility, λ g is the gas phase mobility, λ t is the total mobility, k rl is the liquid phase relative permeability, k rg is the gas phase relative permeability, μ l is the liquid phase viscosity, μ g is the gas phase viscosity, is the absolute permeability, p l is the liquid phase pressure, p c is the capillary pressure, c g is the gas phase compressibility, c l is the liquid phase compressibility.

[0024] The method for solving the distribution of the liquid phase saturation S l and the liquid phase fluid pressure P l in step three of the above scheme;

[0025] Based on the underground green methanol micro-compressible flow model, for micro-compressible fluid, 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 phase 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 fluid compressibility coefficient 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 -5Fig. 1 shows a schematic diagram of pressure distribution of micro-compressible fluid under different compressibility coefficients and a schematic diagram of liquid saturation distribution of micro-compressible fluid under different time steps; according to the two schematic diagrams, it is concluded that the diffusion of fluid pressure and saturation is more and more obvious with the decrease of fluid compressibility coefficient.

[0030] In step four of the above scheme, when analyzing the influence of capillary force action and relative permeability on the flow of methanol based on the underground green methanol micro-compressible flow model, different permeability models and capillary force action models are combined to analyze the influence of capillary force action and relative permeability on the flow of methanol:

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

[0032]

[0033]

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

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

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

[0037]

[0038]

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

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

[0041] Beneficial effects:

[0042] 1. According to the physicochemical properties of green methanol, the mass conservation law of porous media and Darcy flow law, the control equation of underground methanol flow is established.

[0043] 2. According to the physicochemical properties of green methanol, the numerical method of implicit solution pressure and explicit solution saturation (IMPES) and five-point central difference discrete format are used to carry out numerical dispersion of the established control equation of underground methanol flow.

[0044] 3. The present application establishes the underground green methanol micro-compressible flow model based on the control equation of green methanol flow, and determines the distribution of liquid phase saturation S l and liquid phase fluid pressure P l , which provides theoretical guidance for underground storage of green methanol.

[0045] 4. Based on the established green methanol micro-compressible flow mathematical model, the main control factors affecting fluid flow, capillary force action and relative permeability, in different time periods are analyzed. The research results show that higher capillary force action and relative permeability can increase the fluid pressure and saturation diffusion. Capillary force action and relative permeability are favorable factors for methanol storage, which can significantly improve the storage capacity.

[0046] 5. The present application establishes the mathematical model of green methanol micro-compressible flow, and considers the influence of capillary force action and relative permeability in the flow model, so as to quantitatively characterize the influence of these factors on methanol storage, further introduces the effective storage capacity of methanol, comprehensively analyzes the influence of various factors on methanol storage, and provides theoretical guidance for methanol storage in the future. DETAILED DESCRIPTION OF DRAWINGS

[0047] Figure 1 It is a micro-compressible fluid pressure distribution diagram under different compressibility coefficients;

[0048] Figure 2 It is a micro-compressible fluid liquid phase saturation distribution diagram under different time steps;

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

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

[0051] Figure 5Capillary pressure distribution for micro-compressible fluid for capillary pressure model 1 and model 2 (left side: 200 time steps, right side: 7600) at 200 and 7600 time steps;

[0052] Figure 6 Saturation distribution for micro-compressible fluid for capillary pressure model 1 and model 2 (left side: 200 time steps, right side: 7600) at 200 and 7600 time steps;

[0053] Figure 7 Effect of relative permeability and capillary pressure on effective storage of methanol for 7600 time steps. DETAILED DESCRIPTION:

[0054] The application will be further described below with reference to the drawings:

[0055] In combination Figures 1-7 As shown in the drawings, the effective storage calculation method of green methanol generated by H2 / CO2 cooperative storage includes the following steps:

[0056] S1, based on the mass conservation law of porous medium and Darcy flow law, the underground methanol flow control equation is established.

[0057] The control equation describing the flow of two-phase system in porous medium is based on the continuity assumption of partial differential equation form, in which the global variable is a continuous function in space and time. The system consists of two immiscible phases, liquid phase (l) and gas phase (g), and the flow of two phases is S α , α∈{l, g} is described by continuity equation and Darcy law. The control equation of two-phase flow in porous medium is given by the following formula:

[0058]

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

[0060]

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

[0062] Because the sum of saturations of all phases is 1, there is the following relationship:

[0063]

[0064] Further considering the capillary pressure effect, the calculation is as follows:

[0065] P c = P l -P g

[0066] The relative permeability and the capillary pressure effect are functions of the liquid phase 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 solution of pressure and explicit solution of saturation (IMPES) and five-point central difference discrete format, the established underground methanol flow control equation is numerically dispersed in finite difference format.

[0070] S3, based on the control equation of green methanol flow, a model for solving the distribution of liquid phase saturation S l and liquid phase fluid pressure P l of the underground green methanol micro-compressible flow is established.

[0071] The continuity equation of micro-compressible flow can be given by the following formula:

[0072]

[0073] For micro-compressible fluid, the fluid liquid phase density is a function related to the fluid pressure:

[0074] ρ l = ρ0[1 + c f (p l -p0)]

[0075] In the formula, ρ l is the liquid phase 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 summing over phases gives:

[0079]

[0080] Fluid compressibility:

[0081]

[0082]

[0083] Rock compressibility:

[0084]

[0085] where c l is the liquid phase compressibility, c g is the gas phase compressibility, and c r are the rock compressibilities, respectively.

[0086] So we have:

[0087]

[0088] Assume:

[0089] (1) Spatial density variations are negligible, i.e.

[0090] (2) Spatial absolute permeability variations are negligible, i.e.

[0091] (3) Rock compressibility is not considered,

[0092] (4) Capillary pressure variations in time are negligible, Finally, the green methanol micro-compressible flow model can be expressed as:

[0093]

[0094] where 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 rate; λ t is the total flow coefficient.

[0095] where the liquid phase saturation S l and the liquid phase fluid pressure P l are the unknowns to be solved for, and the relative permeability liquid / gas relative permeability k rl / krg and capillary force effect p c will affect the liquid saturation S l and liquid phase fluid pressure P l The results of the calculation, in step 4, we will analyze the two factors of influence and comparison.

[0096] Referring to Figures 1-2 , the methanol micro-compressible flow, the fluid compressibility coefficient is selected as c f = 1 x 10 -3 / MPa, c f = 1 x 10 -4 / MPa, c f = 1 x 10 -5 / MPa, c f = 5 x 10 -3 / MPa, c f = 5 x 10 -4 / MPa, c f = 5 x 10 -5 / MPa are studied, and the results show that with the decrease of fluid compressibility coefficient, the diffusion of fluid pressure and saturation becomes more obvious.

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

[0098] Corey model is adopted to calculate relative permeability:

[0099]

[0100]

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

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

[0103] J-function model is adopted to calculate capillary force effect:

[0104]

[0105]

[0106] where S lr represents the residual saturation of gas phase, λ is a parameter measured by experiment, S rl = 0.3, λ = 0.4; P E is the inlet pressure, where P E has different values for different rock types.

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

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

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

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

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

[0112] S5, quantitatively characterizing the influence of capillary force and relative permeability on the storage of methanol, calculating the effective storage amount of methanol, and the calculation formula is as follows:

[0113]

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

[0115] Referring to Figure 7 When the capillary force is not considered, the greater the relative permeability is, the easier the methanol flows, the larger the methanol swept area is, and therefore the greater the storage amount of methanol is. By using the same relative permeability model, the greater the capillary force is, the greater the pressure difference between gas and liquid phases is, the gas phase can displace the liquid phase, and the liquid phase is gathered, and finally a larger storage amount is obtained.

[0116] The present application is based on the catalytic reaction of CO2 / H2 to generate green methanol, and the feasibility of converting green methanol into CO2 / H2 through reverse catalysis, so as to store hydrogen and carbon and realize efficient utilization of energy. The present application aims to study the mechanism of underground methanol two-phase flow, and proposes a mathematical multiphase flow simulator using implicit pressure explicit saturation (IMPES) method for solving, which is used for simulating the pressure distribution and saturation distribution of underground methanol. The sensitivity analysis of capillary force and relative permeability is carried out. The research results show that the capillary force and the relative permeability are beneficial to the underground storage of methanol. The present application establishes a multiphase flow underground methanol slightly compressible flow model, and reveals the changes of saturation and pressure. The present application aims to study the influence of capillary force / relative permeability on the storage amount of methanol under the condition of green methanol slightly compressible flow, and provides theoretical guidance for underground storage of green methanol, at the same time, it is helpful to reduce atmospheric carbon emission, promote the utilization of underground resources, and promote global energy transformation.

[0117] The present application aims to study the mechanism of underground methanol two-phase flow, and proposes a mathematical multiphase flow simulator solved by implicit pressure explicit saturation (IMPES) method, which is used for simulating the pressure distribution and saturation distribution of underground methanol. In addition, the capillary force action and relative permeability are subjected to sensitivity analysis. The research results show that higher capillary pressure and relative permeability will lead to larger liquid phase pressure and saturation diffusion. Therefore, the capillary force action and relative permeability are favorable factors for methanol storage, which can significantly improve its storage capacity. The present application simulates the underground flow of methanol, reveals the changes of its saturation and pressure, helps to reduce atmospheric carbon emissions, promotes the utilization of underground resources, and promotes the global energy transformation. The present application calculates the methanol storage 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 amount of H2 / CO2 co- storage for generating green methanol, characterized in that Comprising the following steps: Step one, based on the mass conservation law of porous media and Darcy flow law, the underground methanol flow control equation is established; Wherein: P c = P l - P g P c = P c (S l ) k ra = k ra (S l ) wherein denotes the porosity, p a is the density, s a is the saturation, g is the gravitational acceleration, q a is the source term, k ra is the relative permeability, p a is the viscosity, is the absolute permeability, p α is the pressure, is the flow rate, t is the time, T is the total time, the index a is l and g, the index l denotes the liquid phase, the index g denotes the gas phase, P c is the capillary pressure; Step two, based on the numerical method of implicit solution pressure and explicit solution saturation IMPES and five-point central difference discrete format, the finite difference format numerical dispersion is carried out on the underground methanol flow control equation; Step three, based on the underground methanol flow control equation, establish the underground green methanol micro compressible flow model, solve the distribution of liquid phase saturation S l and liquid phase pressure p l ; The underground green methanol micro compressible flow model is: In the formula, q t = q l + q g , λ t = λ l + λ g . wherein denotes the porosity, p g is the gas phase density, p l is the liquid phase density, S g is the gas phase saturation, S l is the liquid phase saturation, g is the gravitational acceleration, q l is the source term for the liquid phase, q g is the source term for the gas phase, q t is the total source term, l l is the liquid phase mobility, l g is the gas phase mobility, l t is the total mobility, k rl is the liquid phase relative permeability, k rg is the gas phase relative permeability, m l is the liquid phase viscosity, m g is the gas phase viscosity, is the absolute permeability, p l is the liquid phase pressure, P c is the capillary pressure, c g is the gas phase compressibility, c l is the liquid phase compressibility; A method for solving the distribution of liquid saturation S l and liquid pressure p l in a porous medium. Based on the underground green methanol micro compressible flow model, for micro compressible fluid, the fluid liquid density is a function related to fluid pressure: σ l = σ0[1 + c f (p l -p0)] In the formula, ρ l ρ is the liquid phase density; ρ0 is the reference density; c f It is the fluid compressibility coefficient; p0 is the reference pressure; p l It is liquid phase pressure; The fluid compressibility coefficient in the above formula is selected as the following 6 values: c f = 1 x 10 -3 / MPa, c f = 1 x 10 -4 / MPa, c f = 1 x 10 -5 / MPa, c f = 5 x 10 -3 / MPa, c f = 5 x 10 -4 / MPa, c f = 5 x 10 -5 / MPa, respectively, the pressure distribution diagram of the micro-compressible fluid under different compressibility coefficients and the liquid saturation distribution diagram of the micro-compressible fluid under different time steps; according to the two distribution diagrams, it is concluded that the diffusion of the fluid pressure and saturation becomes more and more obvious with the decrease of the fluid compressibility coefficient; Step four, based on the underground green methanol micro compressible flow model, the influence of capillary force action and relative permeability on methanol flow is analyzed, different permeability models and capillary force action models are established, with the increase of capillary force action and relative permeability, the fluid pressure and saturation diffusion also increase, and capillary force action and relative permeability are the favorable factors for methanol storage: Corey model is adopted to calculate relative permeability: where S lr represents the residual saturation of the liquid phase, S gr represents the residual saturation of the gas phase, S lr = 0.3, S gr = 0.05; the indices a and β are parameters directly measured by steady-state experiments; Two sets of relative permeability models are adopted, wherein relative permeability model-1, α=7, β=3; relative permeability model-2, α=7, β=3; α=4, β=2; J-function model is adopted to calculate capillary force action: where λ is a parameter measured from experiments, S rl = 0.3, λ = 0.4; P E is the inlet pressure, where P E has different values for different rock types; Two sets of capillary pressure models were adopted, where the inlet pressure P E for capillary pressure model-2 was one third of the size of P E = 35 kPa for capillary pressure model-1. The relative permeability model-1 or relative permeability model-2 and capillary force action model-1 or capillary force action model-2 are brought into the green methanol micro-compressible flow model to obtain corresponding liquid phase saturation S l and liquid phase pressure p l , and then the influence of capillary force action and relative permeability on methanol flow is analyzed, and the subsequent analysis of the effective storage amount of methanol is prepared. Step five, the influence of capillary force action and relative permeability factors on methanol storage is quantitatively characterized, and the effective methanol storage amount is calculated, and the calculation formula is as follows: wherein Methanol storage volume, kg; p l A is the methanol storage area, m 2 ; S l S is the liquid saturation; h is the reservoir thickness, h = 1 m.

Images