Method for determining saturation pressure of multi-component fluid within nanopores of porous medium

Abstract

The invention discloses a method for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium, aiming at the nanopores of any size of the porous medium, the method comprises the following steps: aiming at each preset pressure, determining the volume phase molar density of the multi-component fluid and a first state equation parameter corresponding to each fluid component; determining the first fugacity of each fluid component according to the volume phase molar density and the first state equation parameter corresponding to each fluid component, and determining the first fugacity of each fluid component according to the molecular diameter of each fluid component, the first state equation parameter and the pore diameter of the nanopores; determining a second state equation parameter of a preset position in the nanopore under a preset pressure; establishing a target equation corresponding to each fluid component according to the second state equation parameter and the first fugacity; determining the target fluid density of the multi-component fluid at the preset position according to all the target equations; and determining the saturation pressure of the multi-component fluid in the nanopores according to all the target fluid densities.

Description

Technical Field

[0001] The present application relates to the technical field of oil and gas field development, and in particular to a method, device, and storage medium for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium. Background Art

[0002] Under conventional large-scale conditions, condensate gas undergoes a phase transition from a gaseous state to a gas-liquid two-phase state (reverse condensation) during constant temperature and pressure reduction from high pressure to low pressure. This transition point is called the dew point pressure (upper dew point). Similarly, crude oil undergoes a phase transition from a liquid state to a vapor-liquid two-phase state during constant temperature and pressure reduction from high pressure to low pressure. This transition point is called the bubble point pressure. Dew point and bubble point pressures are collectively referred to as saturation pressure. Saturation pressure is the key point at which a fluid undergoes a vapor-liquid two-phase transition and has a significant impact on its phase state. Under conditions of known fluid composition, mature and accurate methods are currently available for calculating the saturation pressure of multicomponent fluids under large-scale conditions, such as the conventional cubic equation of state (PR / SRK equations). However, in nanopores, due to the interaction between wall molecules and fluid molecules, the fluid phase state differs from that under conventional large-scale conditions, and the saturation pressure also shifts. Existing methods for calculating the saturation pressure of multicomponent fluids do not account for the influence of nanopore confinement and are therefore unsuitable for nanopores. At present, the use of visualized nanotube microfluidics experiments has observed that the saturation pressure of the fluid inside the nanotube is significantly different from that under conventional conditions. However, the experiment is time-consuming and labor-intensive, and has high requirements for instruments and equipment. Summary of the Invention

[0003] The purpose of the embodiments of the present application is to provide a method, device and storage medium for determining the saturation pressure of a multi-component fluid in the nanopores of a porous medium, so as to solve the technical problems in the prior art that experiments are time-consuming and labor-intensive and have high requirements for instruments and equipment.

[0004] To achieve the above objectives, the present application provides, in a first aspect, a method for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium, wherein the porous medium includes a plurality of nanopores. For any nanopore size of the porous medium, the method comprises:

[0005] Determining the bulk molar density of the multi-component fluid at each preset pressure and a first state equation parameter corresponding to each fluid component included in the multi-component fluid;

[0006] For each preset pressure, determining a first fugacity of each fluid component at the preset pressure based on the bulk molar density at the preset pressure and a first state equation parameter corresponding to each fluid component;

[0007] Obtain the pore diameter of the nanopores and the molecular diameter of each fluid component;

[0008] For each preset pressure, determining a second state equation parameter of each fluid component at a preset position within the nanopore at the preset pressure based on the molecular diameter of each fluid component, the first state equation parameter, and the pore diameter;

[0009] For each preset pressure, establishing a target equation corresponding to each fluid component at the preset pressure according to the second state equation parameter and the first fugacity corresponding to each fluid component at the preset pressure;

[0010] For each preset pressure, determining a target fluid density of the multi-component fluid at a preset position at the preset pressure according to all target equations at the preset pressure;

[0011] The saturation pressure of the multi-component fluid in the nanopores is determined according to the total target fluid density of the multi-component fluid.

[0012] In an embodiment of the present application, the target fluid density is the molar density of the target fluid, and determining the saturation pressure of the multi-component fluid in the nanopore according to the total target fluid density of the multi-component fluid includes: based on the total target fluid density of the multi-component fluid, determining the preset pressure corresponding to the occurrence of a step-like density jump phenomenon as the saturation pressure of the multi-component fluid in the nanopore.

[0013] In an embodiment of the present application, the preset position is the middle of the nanopore, and the spacing distance between the middle of the nanopore and the wall is the pore radius of the nanopore. For each preset pressure, according to the molecular diameter, the first state equation parameter and the pore diameter of each fluid component, determining the second state equation parameter of each fluid component at the preset position in the nanopore under the preset pressure includes: determining a first ratio of the pore diameter to the molecular diameter of each fluid component, and a second ratio of the pore radius to the molecular diameter of each fluid component; for each preset pressure, determining the second state equation parameter of each fluid component at the preset position under the preset pressure according to the first ratio, the second ratio and the first state equation parameter corresponding to each fluid component.

[0014] In an embodiment of the present application, for each preset pressure, a target equation corresponding to each fluid component at the preset pressure is established based on the second state equation parameters and the first fugacity corresponding to each fluid component at the preset pressure, including: for each preset pressure, determining the third state equation parameters corresponding to the multi-component fluid at the preset pressure based on the second state equation parameters of all fluid components at the preset pressure; for each preset pressure, determining the second fugacity of each fluid component at the preset position at the preset pressure based on the first fugacity of each fluid component at the preset pressure; for each preset pressure, establishing the target equation corresponding to each fluid component at the preset pressure based on the third state equation parameters corresponding to the multi-component fluid at the preset pressure and the second fugacity of each fluid component.

[0015] In an embodiment of the present application, for each preset pressure, a target equation corresponding to each fluid component at the preset pressure is established based on the third state equation parameter corresponding to the multi-component fluid at the preset pressure and the second fugacity of each fluid component. The function expression of the target equation is shown in formula (1):

[0016]

[0017] in, i refers to the i-th fluid component included in the multi-component fluid, z refers to the preset position z of the nano-medium, F i It refers to the target equation corresponding to the i-th fluid component at the preset position z under the preset pressure, f i ff (z) refers to the second fugacity of the i-th fluid component at the preset position z at each preset pressure, y i (z) is the mole fraction of the adsorbed phase of the i-th fluid component at the preset position z, R is the ideal gas constant, T is the preset temperature of the given multi-component fluid, P local (z) refers to the actual pressure of the multi-component fluid at the preset position, ρ local (z) refers to the target fluid molar density of the multicomponent fluid at each preset pressure, b and b i Refers to the fixed state equation parameter corresponding to the i-th fluid component, a ff (z) refers to the third state equation parameter corresponding to the preset position z at each preset pressure, y i It refers to the mole fraction of the i-th fluid component in the bulk multi-component fluid.

[0018] In an embodiment of the present application, for each preset pressure, determining the second fugacity of each fluid component at the preset position at the preset pressure according to the first fugacity of each fluid component at the preset pressure includes calculating the second fugacity according to the following formula (2):

[0019]

[0020]

[0021]

[0022] Wherein, i refers to the i-th fluid component included in the multi-component fluid, z refers to the preset position z of the nano-medium, It refers to the second fugacity of each fluid component at the preset position z at each preset pressure, The first fugacity of each fluid component at each preset pressure, Refers to the calculation of the second fugacity The intermediate parameter, N A is Avogadro's constant, L is the pore diameter of the nanomaterial, z0 is the pore radius of the nanomaterial, ρ atoms refers to the number of atoms per unit area of ​​the wall, ε fsi is the interaction energy between the fluid and the wall, σ ss refers to the interlayer distance of solid molecules, σ fsi It refers to the average value of the fluid molecular diameter and the solid molecular diameter of the i-th fluid component.

[0023] In an embodiment of the present application, for each preset pressure, determining the third state equation parameters corresponding to the multi-component fluid at the preset pressure based on the second state equation parameters of all fluid components at the preset pressure includes determining the third state equation parameters according to the following formula (5):

[0024]

[0025]

[0026] Among them, a ff (z) refers to the third state equation parameter corresponding to the preset position z at each preset pressure, i refers to the i-th fluid component included in the multi-component fluid, j refers to the j-th fluid component, a ffi (z) refers to the second state equation parameter corresponding to the i-th fluid component, a ffj (z) refers to the second state equation parameter corresponding to the jth fluid component, a ffij Refers to the second state equation parameter corresponding to the i-th fluid component and the j-th fluid component, x i refers to the mole fraction of the i-th fluid component in the bulk multi-component fluid, x j It refers to the mole fraction of the jth fluid component in a multi-component fluid in the bulk phase.

[0027] In an embodiment of the present application, for each preset pressure, determining the first fugacity of each fluid component at the preset pressure according to the first state equation parameters and the bulk molar density corresponding to each fluid component at the preset pressure includes determining the first fugacity according to the following formula (7):

[0028]

[0029] Where i refers to the i-th fluid component included in the multi-component fluid, f i bulk Refers to the first fugacity of the i-th fluid component at each preset pressure, x iis the mole fraction of the i-th fluid component in the bulk multicomponent fluid, R is the ideal gas constant, T is the preset temperature of the given multicomponent fluid, P is the preset pressure, and ρ bulk refers to the bulk molar density of the multicomponent fluid, b and b i Refers to the fixed state equation parameters corresponding to the i-th fluid component, a, a ij They respectively refer to the first state equation parameters corresponding to each preset pressure and the i-th fluid component.

[0030] A second aspect of the present application provides a device for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium, comprising:

[0031] a memory configured to store instructions; and

[0032] The processor is configured to call instructions from the memory and implement the above-mentioned method for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium when executing the instructions.

[0033] A third aspect of the present application provides a machine-readable storage medium, characterized in that the machine-readable storage medium stores instructions for enabling a machine to execute the method for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium according to the above-mentioned method.

[0034] This technical solution, based on nanovoids of varying sizes and fluid component types, can simulate and calculate the saturation pressure of a multicomponent fluid within a specific nanovoid of a porous medium under any given temperature and bulk composition conditions. This solution, without requiring time-consuming and labor-intensive experiments and sophisticated instrumentation, establishes a method for calculating the saturation pressure of multicomponent fluids within nanopores for different fluid compositions, wall materials, pore sizes, and temperature conditions. This method provides fundamental data and technical support for clarifying the behavior of fluid phases of varying compositions within nanopores of varying sizes, demonstrating its high practicality. Furthermore, this simulation reduces time and labor costs, and is of great significance for reservoir physics calculations in oil and gas field development.

[0035] Other features and advantages of the embodiments of the present application will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings are used to provide a further understanding of the embodiments of the present application and constitute a part of the specification. Together with the following detailed description, they are used to explain the embodiments of the present application but do not constitute a limitation on the embodiments of the present application. In the accompanying drawings:

[0037] Figure 1A schematic flow chart of a method for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium according to an embodiment of the present application is shown;

[0038] Figure 2 Schematic diagram showing a step-by-step increase in fluid density in the middle of the nanopore during the isothermal decompression process according to an embodiment of the present application;

[0039] Figure 3 Schematic diagram showing the density of the methane-n-butane fluid mixture in the middle of the nanopore during the isothermal decompression process at 70° C. according to an embodiment of the present application;

[0040] Figure 4 Schematic diagram showing the density of the methane-n-butane fluid mixture in the middle of the nanopores during the isothermal decompression process at 110° C. according to an embodiment of the present application;

[0041] Figure 5 A block diagram schematically illustrates a structure of a device for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium according to an embodiment of the present application;

[0042] Figure 6 The schematic diagram shows the structure of a computer device according to an embodiment of the present application. DETAILED DESCRIPTION

[0043] To make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. It should be understood that the specific implementation methods described herein are only used to illustrate and explain the embodiments of the present application and are not used to limit the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0044] It should be noted that if the embodiments of the present application involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indications will also change accordingly.

[0045] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present application, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of such features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the fact that they can be implemented by ordinary technicians in this field. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0046] Figure 1 The following schematically shows a flow chart of a method for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium according to an embodiment of the present application. Figure 1 As shown, an embodiment of the present application provides a method for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium. The porous medium includes multiple nanopores. For any size of nanopores in the porous medium, the method may include the following steps.

[0047] S102, determining the bulk molar density of the multi-component fluid at each preset pressure, and a first state equation parameter corresponding to each fluid component included in the multi-component fluid.

[0048] It can be understood that the main physical characteristics of porous media are very small pore size and large specific surface area. The tiny pores in porous media may be interconnected, or they may be partially connected and partially disconnected. Nanopores refer to pore structures with nanoscale dimensions in materials. Nanopores have a great influence on the transmission properties of materials. In the fields of adsorption materials and membrane separation materials, nanopore structures can provide a high surface area, thereby increasing the adsorption and separation efficiency of substances. There are abundant nanopore structures in reservoir rocks such as coalbed methane and shale oil and gas. Bulk molar density refers to the molar density of a multi-component fluid in the fluid phase. The first state equation parameter refers to the parameter of the state equation when the influence of nanopores on the multi-component fluid is not considered. The preset pressure is the pre-set ambient pressure.

[0049] In one embodiment, the bulk molar density of a multi-component fluid at different preset pressures is calculated while also being given a fixed preset temperature, i.e., the temperature condition remains constant. Thus, the bulk molar density of the multi-component fluid at each preset pressure can be calculated according to the following formula (8):

[0050]

[0051] Among them, ρ bulkIt refers to the bulk molar density of the multicomponent fluid at each preset pressure, P refers to the given preset pressure, T refers to the given preset temperature, Z refers to the compressibility factor (dimensionless) at the preset temperature and preset pressure, and R refers to the ideal gas constant, R = 8.314472 cm 3 MPa / (K.mol).

[0052] Specifically, the compression factor can be obtained by consulting the compression factor chart or by calculation. The compression factor can be calculated according to the following formula (9):

[0053] Z 3 -(1-B)Z 2 +(A-2B-3B 2 )Z-(AB-B 2 -B 3 )=0(9)

[0054] Where Z is the compressibility factor at the preset temperature and pressure, and A and B are also parameters of the equation of state. In the above formula (9), Z has at least one real root and at most three real roots. One of these real roots is determined as the target compressibility factor based on the minimum Gibbs free energy condition to calculate the bulk molar density of the multicomponent fluid.

[0055] The state equation parameters include a, b, a i 、a ij 、b i , A, B, etc. Specifically, different state equation parameters can be calculated according to the following formula:

[0056]

[0057]

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[0064] Where i refers to the i-th fluid component, j refers to the j-th fluid component, a, b, a i 、a ij 、b i , A, B are all parameters of the state equation, Tci is the critical temperature of the i-th fluid component, p ci is the critical pressure of the i-th fluid component, ω i is the eccentricity factor (dimensionless) of the i-th fluid component, T is the given preset temperature, R is the ideal gas constant, m i It means calculating a i The intermediate parameter, N c Refers to the total number of fluid components in a multi-component fluid, x i refers to the mole fraction of the i-th fluid component in the multi-component fluid of the bulk phase, x j refers to the mole fraction of the jth fluid component in the multi-component fluid in the bulk phase, p refers to a given preset pressure, k ij It refers to the binary interaction coefficient between the i-th fluid component and the j-th fluid component.

[0065] S104 , for each preset pressure, determining a first fugacity of each fluid component at the preset pressure according to the bulk molar density at the preset pressure and a first state equation parameter corresponding to each fluid component.

[0066] The first fugacity refers to the fugacity of each fluid component at a preset pressure, ignoring the effect of nanovoids on the multi-component fluid. The first fugacity is the fugacity of each fluid component in the bulk phase of the multi-component fluid. It is understood that the temperature conditions remain constant under different preset pressure conditions.

[0067] In an embodiment of the present application, for each preset pressure, determining the first fugacity of each fluid component at the preset pressure according to the first state equation parameters and the bulk molar density corresponding to each fluid component at the preset pressure includes determining the first fugacity according to the following formula (7):

[0068]

[0069] Where i refers to the i-th fluid component included in the multi-component fluid, The first fugacity of each fluid component at each preset pressure, x i is the mole fraction of the i-th fluid component in the bulk multicomponent fluid, R is the ideal gas constant, T is the preset temperature of the given multicomponent fluid, P is the preset pressure, and ρ bulk refers to the bulk molar density of the multicomponent fluid, b and b i They refer to the fixed state equation parameters of the i-th fluid component at each preset pressure, a, a ij Refers to the first state equation parameter corresponding to each preset pressure.

[0070] S106 , obtaining the pore diameter of the nanopore and the molecular diameter of each fluid component.

[0071] S108 , for each preset pressure, determining a second state equation parameter of each fluid component at a preset position in the nanopore at the preset pressure according to the molecular diameter of each fluid component, the first state equation parameter, and the pore diameter.

[0072] Considering that factors such as fluid composition, wall material, pore size, temperature, and pressure all have an important influence on the fluid phase state in nanopores. Nanopores may hinder the flow of fluid components due to their very small pore diameter. Moreover, in nanopores, due to the interaction between wall molecules and fluid molecules, the fluid phase state is different from that in conventional large space conditions. Therefore, for each preset pressure, according to the molecular diameter of each fluid component, the first state equation parameters and the pore diameter, the original first state equation parameters corresponding to each fluid component can be corrected to determine the second state equation parameters of each fluid component at the preset position in the nanopore at the preset pressure. The second state equation parameters refer to the parameters corresponding to each fluid component in the state equation when considering the influence of nanovoids on multi-component fluids.

[0073] In an embodiment of the present application, the preset position is the middle of the nanopore, and the spacing distance between the middle of the nanopore and the wall is the pore radius of the nanopore. For each preset pressure, according to the molecular diameter, the first state equation parameter and the pore diameter of each fluid component, determining the second state equation parameter of each fluid component at the preset position in the nanopore under the preset pressure includes: determining a first ratio of the pore diameter to the molecular diameter of each fluid component, and a second ratio of the pore radius to the molecular diameter of each fluid component; for each preset pressure, determining the second state equation parameter of each fluid component at the preset position under the preset pressure according to the first ratio, the second ratio and the first state equation parameter corresponding to each fluid component.

[0074] Taking into account the interaction between wall molecules and fluid molecules in nanopores, the first ratio of the pore diameter to the molecular diameter of each fluid component and the second ratio of the pore radius to the molecular diameter of each fluid component are determined through the molecular diameter of each fluid component. The size relationship between the first ratio and the second ratio corresponding to each fluid component, as well as the range of the first ratio and the second ratio are compared to correct the first state equation parameters to accurately determine the second state equation parameters when the nanopore sizes are different and the fluid molecule sizes are different.

[0075] Specifically, the preset position is the middle position in the nanopore When the first ratio When , the second state equation parameters are calculated according to the following formula (18):

[0076]

[0077] When the first ratio is When , the second state equation parameters are calculated according to the following formula (19):

[0078]

[0079] When the first ratio is When , the second state equation parameters are calculated according to the following formula (20):

[0080]

[0081] When the first ratio is When , the second state equation parameters are calculated according to the following formula (21):

[0082]

[0083] In the above formulas (18)(19)(20)(21), a ffi (z) refers to the second state equation parameter of the i-th fluid component at the preset position z under the preset pressure, σ ffi refers to the molecular diameter of the i-th fluid component, L refers to the pore diameter, and z refers to the pore radius, that is, the distance between the middle of the pore and the pore wall. When the first ratio is In this case, it can be understood that theoretically there are no fluid molecules in the pore, so the fluid density in this case is 0.

[0084] S110 , for each preset pressure, establishing a target equation corresponding to each fluid component at the preset pressure according to the second state equation parameter and the first fugacity corresponding to each fluid component at the preset pressure.

[0085] The target equation is a nonlinear equation established at a preset pressure based on the second equation of state parameters and the first fugacity for each fluid component. It can be understood that given different preset pressure conditions, a fixed preset temperature is also given (i.e., the temperature condition remains constant). As many target equations as there are fluid components at a given preset pressure and temperature, we can establish as many target equations as there are fluid components.

[0086] In an embodiment of the present application, for each preset pressure, a target equation corresponding to each fluid component at the preset pressure is established based on the second state equation parameters and the first fugacity corresponding to each fluid component at the preset pressure, including: for each preset pressure, determining the third state equation parameters corresponding to the multi-component fluid at the preset pressure based on the second state equation parameters of all fluid components at the preset pressure; for each preset pressure, determining the second fugacity of each fluid component at the preset position at the preset pressure based on the first fugacity of each fluid component at the preset pressure; for each preset pressure, establishing the target equation corresponding to each fluid component at the preset pressure based on the third state equation parameters corresponding to the multi-component fluid at the preset pressure and the second fugacity of each fluid component.

[0087] The third state equation parameter refers to the parameter of the state equation corresponding to the multi-component fluid when considering the effect of nanopores on the multi-component fluid. The third state equation parameter can be calculated using the second state equation parameter. The second fugacity refers to the fugacity of each fluid component at different preset locations at a preset pressure when considering the adsorption effect of nanopores on the multi-component fluid. That is, the second fugacity is the fugacity of the adsorbed phase of each fluid component within the nanopores. The second fugacity can be calculated using the first fugacity. Furthermore, based on the third state equation parameter corresponding to the multi-component fluid at the preset pressure and the second fugacity of each fluid component, a target equation corresponding to each fluid component at the preset pressure is established.

[0088] Specifically, in an embodiment of the present application, for each preset pressure, determining the second fugacity of each fluid component at the preset position at the preset pressure according to the first fugacity of each fluid component at the preset pressure includes calculating the second fugacity according to the following formula (2):

[0089]

[0090]

[0091]

[0092] Wherein, i refers to the i-th fluid component included in the multi-component fluid, z refers to the preset position z of the nano-medium, It refers to the second fugacity of the i-th fluid component at the preset position z at each preset pressure, It refers to the first fugacity of the i-th fluid component at each preset pressure, Refers to the calculation of the second fugacity The intermediate parameter, N A is Avogadro's constant, L is the pore diameter of the nanomaterial, z0 is the pore radius of the nanomaterial, ρ atoms refers to the number of atoms per unit area of ​​the wall, εfsi is the interaction energy between the fluid and the wall, σ ss refers to the interlayer distance of solid molecules, σ fsi It refers to the average value of the fluid molecular diameter and solid molecular diameter of the i-th fluid component. fsi =(σ ffi +σ ss ) / 2, σ ffi is the fluid molecular diameter of the i-th fluid component, σ ss refers to the solid molecular diameter of the i-th fluid component, ε ffi It refers to the interaction energy between the i-th fluid component fluid and fluid, ε ss It refers to the interaction energy between the solid and the i-th fluid component.

[0093] In an embodiment of the present application, for each preset pressure, determining the third state equation parameters corresponding to the multi-component fluid at the preset pressure based on the second state equation parameters of all fluid components at the preset pressure includes determining the third state equation parameters according to the following formula (5):

[0094]

[0095]

[0096] Among them, a ff (z) refers to the third state equation parameter corresponding to the preset position z at each preset pressure, i refers to the i-th fluid component included in the multi-component fluid, j refers to the j-th fluid component, a ffi (z) refers to the second state equation parameter corresponding to the i-th fluid component, a ffj (z) refers to the second state equation parameter corresponding to the jth fluid component, a ffij Refers to the second state equation parameter corresponding to the i-th fluid component and the j-th fluid component, x i refers to the mole fraction of the i-th fluid component in the multi-component fluid of the bulk phase, x j refers to the mole fraction of the jth fluid component in the multi-component fluid of the bulk phase, k ij It refers to the binary interaction coefficient between the i-th fluid component and the j-th fluid component.

[0097] In one embodiment, for each preset pressure, a target equation corresponding to each fluid component at the preset pressure is established based on the third state equation parameter corresponding to the multi-component fluid at the preset pressure and the second fugacity of each fluid component. The function expression of the target equation is shown in formula (1):

[0098]

[0099]

[0100] Where i refers to the i-th fluid component included in the multi-component fluid, z refers to the preset position z of the nano-medium, F i It refers to the target equation corresponding to the i-th fluid component at the preset position z under the preset pressure, f i ff (z) refers to the second fugacity of each fluid component at a preset position z at each preset pressure, y i (z) refers to the mole fraction of the adsorbed phase of the i-th fluid component at the preset position z, y i refers to the mole fraction of the i-th fluid component in the bulk multi-component fluid, R refers to the ideal gas constant, T refers to the preset temperature of the given multi-component fluid, P local (z) refers to the actual pressure of the multi-component fluid at the preset position, ρ local (z) refers to the target fluid molar density of the multicomponent fluid at each preset pressure, b and b i It refers to the fixed state equation parameter corresponding to each preset pressure and preset position z of the i-th fluid component, a ff (z) refers to the third state equation parameter corresponding to the preset position z at each preset pressure. b and b i The value calculated in formula (9) can be used, that is, calculated according to formula (15)(19).

[0101] S112 , for each preset pressure, determining a target fluid density of the multi-component fluid at a preset position under the preset pressure according to all target equations under the preset pressure.

[0102] It is understandable that due to the interaction between the wall molecules and the fluid molecules, the actual pressure of the multi-fluid components in the nanovoid is different from the preset pressure. And, referring to the above formula (8), it can be seen that, Then you can Substituting into the target equation (1), the unknown number of the target equation (1) is the actual pressure P at the preset position z under the preset pressure P local (z), and the mole fraction y of the adsorbed phase of the i-th fluid component at the preset position z i (z). The nonlinear equations consisting of the target equations of multiple fluid components, combined with formula (24), give i+1 nonlinear equations. The number of unknowns is equal to the number of equations, which satisfies the solution condition. The trust region method can be used for numerical solution to obtain the actual pressure P local (z) and mole fraction y i (z). Further, according to It can be concluded that the middle of the pore Target fluid density

[0103] S114: Determine the saturation pressure of the multi-component fluid within the nanopores based on the total target fluid density of the multi-component fluid. The dew point pressure and bubble point pressure are collectively referred to as the saturation pressure. The saturation pressure is the key point at which the fluid undergoes a vapor-liquid two-phase transition.

[0104] In an embodiment of the present application, the target fluid density is the molar density of the target fluid, and determining the saturation pressure of the multi-component fluid in the nanopore according to the total target fluid density of the multi-component fluid includes: based on the total target fluid density of the multi-component fluid, determining the preset pressure corresponding to the occurrence of a step-like density jump phenomenon as the saturation pressure of the multi-component fluid in the nanopore.

[0105] Figure 2 The schematic diagram shows the step-by-step increase in fluid density in the middle of the nanopore during the isothermal decompression process according to the embodiment of the present application. Figure 2 Comparing the fluid density in the middle of the nanopore during isothermal decompression, if a step-like density jump occurs at point M, the corresponding preset pressure can be determined as the saturation pressure of the multi-component fluid within the nanopore. It is understood that simulation calculations are generally performed using a pressure reduction method from high to low pressure. The pressure interval determines the calculation accuracy, and a pressure interval of 0.001 MPa is recommended.

[0106] This technical solution, based on nanovoids of varying sizes and fluid component types, can simulate and calculate the saturation pressure of a multicomponent fluid within a specific nanovoid of a porous medium under any given temperature and bulk composition conditions. This solution, without requiring time-consuming and labor-intensive experiments and sophisticated instrumentation, establishes a method for calculating the saturation pressure of multicomponent fluids within nanopores for different fluid compositions, wall materials, pore sizes, and temperature conditions. This method provides fundamental data and technical support for clarifying the behavior of fluid phases of varying compositions within nanopores of varying sizes, demonstrating its high practicality. Furthermore, this simulation reduces time and labor costs, and is of great significance for reservoir physics calculations in oil and gas field development.

[0107] The specific embodiments of the present invention are as follows:

[0108] Example 1: Calculate the saturation pressure of the methane-n-butane binary system in graphite nanopores at 70° C. The pore diameter (width) of the nanopores is 5 nm, and other basic parameters are shown in Table 1.

[0109] Table 1 Basic parameters of Case 1

[0110]

[0111]

[0112] According to the above method for determining the saturation pressure of the multi-component fluid in the nanopores of the porous medium, the fluid density in the middle of the nanopores when the pressure drops from 15 MPa to 10 MPa at a temperature of 70°C is calculated.

[0113] Specifically, taking the middle of the pore (z = 2.5 nm position) under 15 MPa as an example, the calculation steps are as follows:

[0114] Step 1: Given a mixture with two components, calculate the bulk phase molar density at 70°C and 15 MPa to be 0.0080 mol / cm3 using formula (8) and (9). Calculate the first fugacity of each fluid component in the bulk phase fluid under given temperature, pressure, and composition conditions using formula (7): The first fugacity of methane is The first fugacity of n-butane is

[0115] Step 2: Given the pore diameter (width) as L = 5 nm; σ ff1 is 0.2338, σ ff2 is 0.3257nm; the middle position of the channel is selected and recorded as z = 2.5nm.

[0116] Step 3: Due to Therefore, the parameter a in the conventional state equation is replaced by formula (18) for the i-th fluid component at position z = 2.5 nm in the nanopore. i Corrected to a ffi (z). Therefore, the state equation parameter corresponding to methane is a ff1 (z=2.5nm)=1.867×10 5 , the state equation parameter of n-butane is a ff2 (z=2.5nm)=1.7150×10 6 . And according to formula (6) to calculate the corrected

[0117] Step 4: Calculate the second fugacity of each component of the fluid at z = 2.5 nm in the nanochannel by combining formulas (2), (3), and (4):

[0118] Step 5: Solve the nonlinear equations (1) to calculate the molar density of the target fluid at the position z = 2.5 nm in the nanopore: ρ local (z=2.5nm)=0.0083mol / cm3.

[0119] Step 6. Repeat steps 2 to 5 to calculate the change in fluid density in the middle of the nanochannel under the conditions of a given temperature of 70°C and a pressure drop from 15 MPa to 10 MPa, setting the pressure interval to 0.001 MPa. Figure 3 As shown, it can be seen that when the pressure drops from 10.683 MPa to 10.682 MPa, the fluid density in the middle of the nanopore changes, thereby judging that the saturation pressure of the fluid in the nanopore under the current conditions is 10.682 MPa.

[0120] Example 2: Calculate the saturation pressure of the methane-n-butane binary system in graphite nanopores at a temperature of 110° C. The nanopore width is 8 nm, and other basic parameters are shown in Table 2.

[0121] Table 2 Basic parameters of Case 2

[0122]

[0123] According to the above method for determining the saturation pressure of the multi-component fluid in the nanopores of the porous medium, the density of the fluid in the middle of the nanopores at a temperature of 110° C. when the pressure drops from 10 MPa to 8 MPa is calculated.

[0124] Specifically, taking the middle of the pore (z = 4 nm position) under 10 MPa as an example, the calculation steps are as follows:

[0125] Step 1: Given a mixture with two components, use equations (8) and (9) to calculate the bulk phase molar density at 110°C and 10 MPa, which is 0.0058 mol / cm3. Use equation (7) to calculate the fugacity of each component of the bulk fluid under given temperature, pressure, and composition conditions: the first fugacity of methane is The first fugacity of n-butane is

[0126] Step 2: Given the pore diameter (width) L = 8 nm, select the middle position of the pore, denoted as z = 4 nm.

[0127] Step 3: Due to Therefore, the parameter a in the conventional state equation is replaced by Equation (18) for each component i at position z = 4 nm in the nanopore. i Corrected to a ffi (z). Therefore, the state equation parameter corresponding to methane is a ff1 (z = 4 nm) = 1.741 × 10 5 , the state equation parameter of n-butane is a ff2 (z=4nm)=1.6079×10 6 . And according to formula (6) to calculate the corrected

[0128] Step 4: Calculate the fugacity of each fluid component at z = 4 nm in the nanochannel according to formulas (2), (3), and (4):

[0129] (5) Solve the nonlinear equations (1) and calculate the molar density of the target fluid at position z = 4 nm in the nanochannel: ρ local (z=4nm)=0.0060mol / cm3.

[0130] (6) Repeat steps 2 to 5 to calculate the change in fluid density in the middle of the nanopore under the condition of a given temperature of 110°C and a pressure drop from 10 MPa to 8 MPa, setting the pressure interval to 0.001 MPa. Figure 4 As shown, it can be seen that when the bulk pressure decreases from 8.654 MPa to 8.653 MPa, the fluid density in the middle of the nanopore changes, and it is judged that the saturation pressure of the fluid in the nanopore under the current conditions is 8.653 MPa.

[0131] Figure 5 The following schematically shows a structural block diagram of a device for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium according to an embodiment of the present application. Figure 5 As shown, an embodiment of the present application provides a controller, which may include:

[0132] Memory 510 configured to store instructions; and

[0133] The processor 520 is configured to call instructions from the memory 510 and implement the above-mentioned apparatus for determining the saturation pressure of the multi-component fluid in the nanopores of the porous medium when executing the instructions.

[0134] Specifically, in the embodiment of the present application, the processor 520 may be configured to:

[0135] Determining the bulk molar density of the multi-component fluid at each preset pressure and a first state equation parameter corresponding to each fluid component included in the multi-component fluid;

[0136] For each preset pressure, determining a first fugacity of each fluid component at the preset pressure based on the bulk molar density at the preset pressure and a first state equation parameter corresponding to each fluid component;

[0137] Obtain the pore diameter of the nanopores and the molecular diameter of each fluid component;

[0138] For each preset pressure, determining a second state equation parameter of each fluid component at a preset position within the nanopore at the preset pressure based on the molecular diameter of each fluid component, the first state equation parameter, and the pore diameter;

[0139] For each preset pressure, a target equation corresponding to each fluid component at the preset pressure is established based on the second state equation parameter and the first fugacity corresponding to each fluid component at the preset pressure;

[0140] For each preset pressure, determining a target fluid density of the multi-component fluid at a preset position at the preset pressure according to all target equations at the preset pressure;

[0141] The saturation pressure of the multi-component fluid in the nanopores is determined according to the total target fluid density of the multi-component fluid.

[0142] In the embodiment of the present application, the processor 520 may also be configured to:

[0143] The target fluid density is the molar density of the target fluid. Determining the saturation pressure of the multi-component fluid in the nanopore based on the total target fluid density of the multi-component fluid includes: based on the total target fluid density of the multi-component fluid, determining a preset pressure corresponding to a density step-like jump phenomenon as the saturation pressure of the multi-component fluid in the nanopore.

[0144] In the embodiment of the present application, the processor 520 may also be configured to:

[0145] The preset position is the middle of the nanopore, and the spacing distance between the middle of the nanopore and the wall is the pore radius of the nanopore. For each preset pressure, according to the molecular diameter, the first state equation parameter and the pore diameter of each fluid component, the second state equation parameter of each fluid component at the preset position in the nanopore under the preset pressure is determined, including: determining a first ratio of the pore diameter to the molecular diameter of each fluid component, and a second ratio of the pore radius to the molecular diameter of each fluid component; for each preset pressure, determining the second state equation parameter of each fluid component at the preset position under the preset pressure according to the first ratio, the second ratio and the first state equation parameter corresponding to each fluid component.

[0146] In the embodiment of the present application, the processor 520 may also be configured to:

[0147] For each preset pressure, a target equation corresponding to each fluid component at the preset pressure is established based on the second state equation parameters and the first fugacity corresponding to each fluid component at the preset pressure, including: for each preset pressure, determining the third state equation parameters corresponding to the multi-component fluid at the preset pressure based on the second state equation parameters of all fluid components at the preset pressure; for each preset pressure, determining the second fugacity of each fluid component at the preset position at the preset pressure based on the first fugacity of each fluid component at the preset pressure; for each preset pressure, establishing the target equation corresponding to each fluid component at the preset pressure based on the third state equation parameters corresponding to the multi-component fluid at the preset pressure and the second fugacity of each fluid component.

[0148] In the embodiment of the present application, the processor 520 may also be configured to:

[0149] For each preset pressure, a target equation corresponding to each fluid component at the preset pressure is established based on the third state equation parameters corresponding to the multi-component fluid at the preset pressure and the second fugacity of each fluid component. The function expression of the target equation is shown in formula (1):

[0150]

[0151] in, i refers to the i-th fluid component included in the multi-component fluid, z refers to the preset position z of the nano-medium, F i It refers to the target equation corresponding to the i-th fluid component at the preset position z under the preset pressure, f i ff (z) refers to the second fugacity of each fluid component at a preset position z at each preset pressure, y i (z) is the mole fraction of the adsorbed phase of the i-th fluid component at the preset position z, R is the ideal gas constant, T is the preset temperature of the given multi-component fluid, P local (z) refers to the actual pressure of the multi-component fluid at the preset position, ρ local (z) refers to the target fluid molar density of the multicomponent fluid at each preset pressure, b and b i Refers to the fixed state equation parameter corresponding to the i-th fluid component, a ff (z) refers to the third state equation parameter corresponding to the preset position z at each preset pressure, y i It refers to the mole fraction of the i-th fluid component in the bulk multi-component fluid.

[0152] In the embodiment of the present application, the processor 520 may also be configured to:

[0153] For each preset pressure, determining a second fugacity of each fluid component at the preset pressure at the preset position based on the first fugacity of each fluid component at the preset pressure includes calculating the second fugacity according to the following formula (2):

[0154]

[0155]

[0156]

[0157] Wherein, i refers to the i-th fluid component included in the multi-component fluid, z refers to the preset position z of the nano-medium, It refers to the second fugacity of each fluid component at the preset position z at each preset pressure, The first fugacity of each fluid component at each preset pressure, Refers to the calculation of the second fugacity The intermediate parameter, N A is Avogadro's constant, L is the pore diameter of the nanomaterial, z0 is the pore radius of the nanomaterial, ρ atoms refers to the number of atoms per unit area of ​​the wall, ε fsi is the interaction energy between the fluid and the wall, σ ss refers to the interlayer distance of solid molecules, σ fsi It refers to the average value of the fluid molecular diameter and the solid molecular diameter of the i-th fluid component.

[0158] In the embodiment of the present application, the processor 520 may also be configured to:

[0159] For each preset pressure, determining the third state equation parameters corresponding to the multi-component fluid at the preset pressure based on the second state equation parameters of all fluid components at the preset pressure includes determining the third state equation parameters according to the following formula (5):

[0160]

[0161]

[0162] Among them, a ff (z) refers to the third state equation parameter corresponding to the preset position z at each preset pressure, i refers to the i-th fluid component included in the multi-component fluid, j refers to the j-th fluid component, a ffi (z) refers to the second state equation parameter corresponding to the i-th fluid component, a ffj (z) refers to the second state equation parameter corresponding to the jth fluid component, a ffijRefers to the second state equation parameter corresponding to the i-th fluid component and the j-th fluid component, x i refers to the mole fraction of the i-th fluid component in the bulk multi-component fluid, x j refers to the mole fraction of the jth fluid component in the bulk multicomponent fluid, k ij It refers to the binary interaction coefficient between the i-th fluid component and the j-th fluid component.

[0163] In the embodiment of the present application, the processor 520 may also be configured to:

[0164] For each preset pressure, determining the first fugacity of each fluid component at the preset pressure according to the first state equation parameters and the bulk molar density corresponding to each fluid component at the preset pressure includes determining the first fugacity according to the following formula (7):

[0165]

[0166] Where i refers to the i-th fluid component included in the multi-component fluid, The first fugacity of each fluid component at each preset pressure, x i is the mole fraction of the i-th fluid component in the bulk multicomponent fluid, R is the ideal gas constant, T is the preset temperature of the given multicomponent fluid, P is the preset pressure, and ρ bulk refers to the bulk molar density of the multicomponent fluid, b and b i Refers to the fixed state equation parameters corresponding to the i-th fluid component, a, a ij They respectively refer to the first state equation parameters corresponding to each preset pressure and the i-th fluid component.

[0167] Through this technical solution, based on different pore minerals and fluid component types, the PR equation of state is used to calculate the fugacity of each component in the bulk phase. Based on the relationship between the bulk phase fugacity and the adsorbed phase fugacity and the simplified local density theory (SLD), the density distribution and fluid composition distribution of multi-component fluid molecules within nanopores are simulated under given conditions of temperature, pressure, and composition. By further calculating the density distribution of the multi-component fluid within a specific nanopore at a given temperature and different pressures, the saturation pressure of the fluid within the nanopore is determined based on the change in fluid density within the nanopore. This solution establishes a method for calculating the saturation pressure of multi-component fluids within nanopores for different fluid compositions, wall materials, pore sizes, and temperature conditions, without the need for time-consuming and labor-intensive experiments and sophisticated instrumentation. This method is of great significance for reservoir physics calculations in oil and gas field development. This solution provides basic data and technical support for clarifying the behavior of fluid phases of different compositions within nanopores of different sizes.

[0168] An embodiment of the present application further provides a machine-readable storage medium having stored thereon instructions for causing a machine to execute the above-mentioned method for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium.

[0169] In one embodiment, a computer device is provided. The computer device may be a server, and its internal structure diagram may be as follows: Figure 6 As shown. The computer device includes a processor A01, a network interface A02, a memory (not shown in the figure) and a database (not shown in the figure) connected via a system bus. Among them, the processor A01 of the computer device is used to provide computing and control capabilities. The memory of the computer device includes an internal memory A03 and a non-volatile storage medium A04. The non-volatile storage medium A04 stores an operating system B01, a computer program B02 and a database (not shown in the figure). The internal memory A03 provides an environment for the operation of the operating system B01 and the computer program B02 in the non-volatile storage medium A04. The database of the computer device is used to store data on a method for determining the saturation pressure of a multi-component fluid in the nanopores of a porous medium. The network interface A02 of the computer device is used to communicate with an external terminal via a network connection. When the computer program B02 is executed by the processor A01, a method for determining the saturation pressure of a multi-component fluid in the nanopores of a porous medium is implemented.

[0170] Those skilled in the art will understand that Figure 6 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than shown in the figure, or combine certain components, or have a different component arrangement.

[0171] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0172] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0173] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0174] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0175] In a typical configuration, a computing device includes one or more processors (CPUs), input / output interfaces, network interfaces, and memory.

[0176] The memory may include non-permanent memory in a computer-readable medium, random access memory (RAM) and / or non-volatile memory in the form of read-only memory (ROM) or flash RAM. The memory is an example of a computer-readable medium.

[0177] Computer-readable media includes permanent and non-permanent, removable and non-removable media that can be implemented by any method or technology to store information. The information can be computer-readable instructions, data structures, program modules or other data. Examples of computer storage media include, but are not limited to, phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disc read-only memory (CD-ROM), digital versatile disc (DVD) or other optical storage, magnetic cassettes, magnetic disk storage or other magnetic storage devices or any other non-transmission media that can be used to store information that can be accessed by a computing device. As defined herein, computer-readable media does not include transitory computer-readable media (transitory media), such as modulated data signals and carrier waves.

[0178] It should also be noted that the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, commodity, or apparatus that includes a series of elements includes not only those elements but also other elements not explicitly listed, or includes elements inherent to such process, method, commodity, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a ..." does not exclude the presence of other identical elements in the process, method, commodity, or apparatus that includes the element.

[0179] The above are merely embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should all be included within the scope of the claims of the present application.

Claims

1. A method for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium, characterized in that: The porous medium includes a plurality of nanopores. For any size of the nanopores in the porous medium, the method includes: Determining the bulk molar density of the multi-component fluid at each preset pressure and a first state equation parameter corresponding to each fluid component included in the multi-component fluid; For each preset pressure, determining a first fugacity of each fluid component at the preset pressure according to the bulk molar density at the preset pressure and a first state equation parameter corresponding to each fluid component; obtaining the pore diameter of the nanopore and the molecular diameter of each fluid component; For each preset pressure, determining a second state equation parameter of each fluid component at a preset position in the nanopore at the preset pressure based on the molecular diameter of each fluid component, the first state equation parameter, and the pore diameter; For each preset pressure, establishing a target equation corresponding to each fluid component at the preset pressure according to the second state equation parameter and the first fugacity corresponding to each fluid component at the preset pressure; For each preset pressure, determining a target fluid density of the multi-component fluid at the preset position at the preset pressure according to all target equations at the preset pressure; The saturation pressure of the multi-component fluid in the nanopore is determined according to the total target fluid density of the multi-component fluid.

2. The method for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium according to claim 1, characterized in that: The target fluid density is a target fluid molar density, and determining the saturation pressure of the multi-component fluid in the nanopore according to the total target fluid density of the multi-component fluid includes: Based on the total target fluid density of the multi-component fluid, a preset pressure corresponding to a step-like density jump phenomenon is determined as the saturation pressure of the multi-component fluid in the nanopores.

3. The method for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium according to claim 1, characterized in that: The preset position is the middle of the nanopore, and the distance between the middle of the nanopore and the wall is the pore radius of the nanopore. For each preset pressure, determining the second state equation parameter of each fluid component at the preset position in the nanopore at the preset pressure according to the molecular diameter of each fluid component, the first state equation parameter, and the pore diameter includes: determining a first ratio of the pore diameter to a molecular diameter of each fluid component and a second ratio of the pore radius to a molecular diameter of each fluid component; For each preset pressure, the second state equation parameter of each fluid component at the preset position under the preset pressure is determined according to the first ratio, the second ratio and the first state equation parameter corresponding to each fluid component.

4. The method for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium according to claim 1, characterized in that: For each preset pressure, establishing a target equation corresponding to each fluid component at the preset pressure according to the second state equation parameter and the first fugacity corresponding to each fluid component at the preset pressure includes: For each preset pressure, determining a third state equation parameter corresponding to the multi-component fluid at the preset pressure according to the second state equation parameters of all fluid components at the preset pressure; For each preset pressure, determining a second fugacity of each fluid component at the preset position at the preset pressure according to the first fugacity of each fluid component at the preset pressure; For each preset pressure, a target equation corresponding to each fluid component at the preset pressure is established based on the third state equation parameters corresponding to the multi-component fluid at the preset pressure and the second fugacity of each fluid component.

5. The method for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium according to claim 4, characterized in that: For each preset pressure, establishing a target equation corresponding to each fluid component at the preset pressure according to the third state equation parameter corresponding to the multi-component fluid at the preset pressure and the second fugacity of each fluid component includes: a function expression of the target equation is shown in formula (1): in, i refers to the i-th fluid component included in the multi-component fluid, z refers to the preset position z of the nano-medium, F i It refers to the target equation corresponding to the i-th fluid component at the preset position z under the preset pressure, f i ff (z) refers to the second fugacity of each fluid component at a preset position z at each preset pressure, y i (z) refers to the mole fraction of the adsorbed phase of the i-th fluid component at the preset position z, R refers to the ideal gas constant, T refers to the preset temperature of the given multi-component fluid, P local (z) refers to the actual pressure of the multi-component fluid at the preset position, ρ local (z) refers to the target fluid molar density of the multi-component fluid at each preset pressure, b and b i Refers to the fixed state equation parameter corresponding to the i-th fluid component, a ff (z) refers to the third state equation parameter corresponding to the preset position z at each preset pressure, y i refers to the mole fraction of the i-th fluid component in the multi-component fluid in the bulk phase.

6. The method for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium according to claim 4, characterized in that: The step of determining, for each preset pressure, the second fugacity of each fluid component at the preset position at the preset pressure based on the first fugacity of each fluid component at the preset pressure includes calculating the second fugacity according to the following formula (2): Wherein, i refers to the i-th fluid component included in the multi-component fluid, z refers to the preset position z of the nano-medium, and f i ff (z) refers to the second fugacity of the i-th fluid component at the preset position z at each preset pressure, f i bulk It refers to the first fugacity of the i-th fluid component at each preset pressure, Ψ i fs (z) refers to the calculation of the second fugacity f i ff (z) intermediate parameter, N A is Avogadro's constant, L is the pore diameter of the nano-medium, z0 is the pore radius of the nano-medium, ρ atoms refers to the number of atoms per unit area of ​​the wall, ε fsi is the interaction energy between the fluid and the wall, σ ss refers to the interlayer distance of solid molecules, σ fsi It refers to the average value of the fluid molecular diameter and the solid molecular diameter of the i-th fluid component.

7. The method for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium according to claim 4, wherein for each preset pressure, determining a third state equation parameter corresponding to the multi-component fluid at the preset pressure based on the second state equation parameters of all fluid components at the preset pressure comprises determining the third state equation parameter according to the following formula (5): in, a ff (z) refers to the third state equation parameter corresponding to the preset position z at each preset pressure, i refers to the i-th fluid component included in the multi-component fluid, j refers to the j-th fluid component, a ffi (z) refers to the second state equation parameter corresponding to the i-th fluid component, a ffj (z) refers to the second state equation parameter corresponding to the jth fluid component, a ffij Refers to the second state equation parameter corresponding to the i-th fluid component and the j-th fluid component, x i refers to the mole fraction of the i-th fluid component in the multi-component fluid of the bulk phase, x j refers to the mole fraction of the jth fluid component in the multi-component fluid of the bulk phase, k ij It refers to the binary interaction coefficient between the i-th fluid component and the j-th fluid component.

8. The method for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium according to claim 1, characterized in that: The step of determining, for each preset pressure, a first fugacity of each fluid component at the preset pressure based on the first state equation parameter corresponding to each fluid component at the preset pressure and the bulk molar density includes determining the first fugacity according to the following formula (7): Wherein, i refers to the i-th fluid component included in the multi-component fluid, f i bulk Refers to the first fugacity of the i-th fluid component at each preset pressure, x i is the mole fraction of the i-th fluid component in the multi-component fluid in the bulk phase, R is the ideal gas constant, T is the preset temperature of the multi-component fluid, P is the preset pressure, and ρ bulk refers to the bulk molar density of the multicomponent fluid, b and b i Refers to the fixed state equation parameters corresponding to the i-th fluid component at each preset pressure, a, a ij They respectively refer to the first state equation parameters corresponding to each preset pressure and the i-th fluid component.

9. A device for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium, characterized in that: include: a memory configured to store instructions; as well as A processor is configured to call the instructions from the memory and implement the method for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium according to any one of claims 1 to 8 when executing the instructions.

10. A machine-readable storage medium, characterized in that The machine-readable storage medium stores instructions for causing a machine to execute the method for determining the saturation pressure of a multi-component fluid in nanopores of a porous medium according to any one of claims 1 to 8.

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