Shale oil reservoir flow simulation method based on limited fluid state equation

Abstract

The invention discloses a shale oil reservoir flow simulation method based on a limited fluid state equation, which belongs to the technical field of oil-gas field development and comprises the following steps of: establishing a limited fluid generalized state equation by considering a nano confinement effect; oil / gas phase balance is calculated based on the limited fluid generalized state equation; oil / gas two-phase physical property parameters are calculated; and establishing a multi-component multi-phase flow shale oil flow simulation formula. By adopting the method, the P-R state equation is corrected based on the nano confinement effect, phase equilibrium calculation is performed based on the corrected P-R state equation, the oil / gas two-phase physical property parameters are calculated, the parameters are substituted into the shale oil reservoir flow equation, the flow characteristics of the shale oil reservoir are defined, and the simulation efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field development, and particularly to a shale reservoir flow simulation method based on the equation of state for confined fluids. Background Art

[0002] Shale reservoirs are mainly composed of nano-pores, and the pore throat diameter tends to be 1 - 100 nm. When fluids are confined in these nano-scale pores, the fluid-wall interaction plays an important role. Since the interaction between fluid molecules and the pore wall attracts more fluid molecules to the region near the pore surface, forming an adsorbed phase, the fluid density is not uniformly distributed across the pore width. In shale reservoirs, a full understanding of fluid phase behavior is the key to efficient oil and gas production. The phase equilibrium of shale oil and gas is highly disturbed due to the adsorption of fluids in densely developed nano-pores. Accurately describing the adsorption of confined fluids in nano-pores and the resulting critical shift is crucial for a better understanding of the potential mechanisms of shale gas or shale oil storage, transportation, and recovery in shale reservoirs. At the same time, calculating the physical property parameters of the oil / gas phase and importing them into the established multi-component multi-phase flow calculation formula can better characterize the flow of fluids in shale reservoirs. Therefore, when calculating the flow development characteristics of shale reservoirs, the influence of nano-confinement effects on phase behavior and oil / gas property parameters needs to be considered. Summary of the Invention

[0003] The purpose of the present invention is to provide a shale reservoir flow simulation method based on the equation of state for confined fluids to solve the problems mentioned in the above background art.

[0004] To achieve the above purpose, the present invention provides a shale reservoir flow simulation method based on the equation of state for confined fluids, and the steps include: S1. Establish a generalized equation of state for confined fluids considering nano-confinement effects; S2. Calculate the oil / gas phase equilibrium based on the generalized equation of state for confined fluids; S3. Calculate the physical property parameters of the oil / gas phase equilibrium; S4. Establish a multi-component multi-phase flow shale oil flow simulation formula based on the physical property parameters of the oil / gas phase equilibrium.

[0005] Preferably, step S1 of establishing a generalized equation of state for confined fluids considering nano-confinement effects includes: S11. Calculate the adsorbed layer thickness, and the formula is: ; In the formula, represents the adsorbed layer thickness, represents the maximum adsorption amount of component , represents the mole fraction of component , Indicates components The isotherm parameters are P Indicates the balance pressure, represents the molar volume of the oil phase, N A represents Avogadro's constant; S22, according to the effective molecular volume coefficient of the adsorption area , Bulk Effective Molecular Volume Determine the reduced adsorption density , the formula is: ; ; ; In the formula, represents the effective volume of bulk fluid molecules, represents the effective volume of adsorbed fluid molecules, Indicates the true volume of fluid molecules; S33, determining the corrected molar volume based on the adsorption layer thickness and the converted adsorption layer density ; S34, according to the corrected molar volume Determine the modified PR state equation, the formula is: ; In the formula, P Indicates the balance pressure, R is the universal gas constant, represents the attraction parameter between molecules, represents the common volume parameter, T Indicates temperature; S35, calculating the critical property offset value according to the modified PR state equation; S36. Calculate the converted adsorption density according to the critical property offset value, and solve and verify the modified PR state equation.

[0006] Preferably, step S33 specifically includes: according to the adsorption volume and the effective volume of fluid molecules Determine the number of adsorbed fluid molecules , the formula is: ; In the formula, represents the effective radius, represents the true volume of the molecule, L Indicates length, represents the pore radius; According to the pore volume and the effective volume of free fluid molecules Determine the total number of fluid molecules , and the formula is: ; According to the pore volume , the total number of fluid molecules and Avogadro's number N A Determine the molar volume of the P-R equation of state , and the formula is: ; According to the number of adsorbed fluid molecules Determine the corrected molar volume , and the formula is: ; According to the number of adsorbed fluid molecules 、 The total number of fluid molecules and the molar volume Determine the relationship between the molar volume and the corrected molar volume , and the formula is: ; After simplification, it is: ; According to the pore radius and the adsorbed layer thickness Determine the effective pore radius , and the formula is: ; Substitute the formula of the effective pore radius into the corrected molar volume to get: ; According to the adsorbed layer thickness and the pore radius Define the parameter , and the formula is: ; Substitute the formula of the parameter into the simplified corrected molar volume to get: .

[0007] Preferably, the calculation of the oil / gas phase equilibrium based on the generalized equation of state of restricted fluids in step S2 includes: According to the molar fraction of the component , the gas phase molar fraction , Initial gas-liquid two-phase equilibrium constant Determine the gas-phase composition and the oil-phase composition , The formula is: ; ; In the formula, is given by the Wilson empirical formula, is calculated according to the Rachford-Rice formula; Adopt the modified P-R equation of state to calculate the gas-phase fugacity coefficient , the oil-phase fugacity coefficient , The formula is: ; ; In the formula, , represent the compressibility factors of the gas phase and the liquid phase, represents component 's covolume parameter, represents component 's interaction coefficient with component , represents component 's attraction parameter, represents the number of components in the mixture, , are calculated from the pressure P, temperature T , covolume parameter b , reduced adsorption density and parameter , , are calculated from the pressure P , temperature T , attraction parameter ; According to the gas-phase fugacity coefficient , the oil-phase fugacity coefficient , gas-phase composition and oil-phase composition , determine the gas-phase fugacity and oil-phase fugacity , The formula is: ; ; When the oil and gas two phases are in phase equilibrium, the gas-phase fugacity and the oil-phase fugacity are equal, then the convergence condition is satisfied, and the formula is: ; When the convergence condition is not met, the equilibrium constant needs to be recalculated. , and the equilibrium constant is determined according to the gas-phase composition and the oil-phase composition . The formula is: . ; The equilibrium constant is iterated using the successive substitution method. The formula is: ; The equilibrium constant calculated using the successive substitution method is used to recalculate the gas-phase mole fraction, and the gas-phase fugacity and the oil-phase fugacity are recalculated until the convergence condition is met. Finally, the compositions of the gas phase and the oil phase are output and .

[0008] Preferably, the calculation of the oil / gas phase equilibrium physical properties in step S3 includes: The gas-phase molecular weight and the oil-phase molecular weight are calculated according to the gas-phase composition , the oil-phase composition , and the molecular weight of the component . The formula is: . ; ; The gas-phase density and the oil-phase density are determined according to the gas-phase molecular weight and the oil-phase molecular weight . The formula is: ; ; In the formula, represents the oil-phase compressibility factor, represents the gas-phase compressibility factor; The gas viscosity and the oil-phase viscosity are calculated according to the gas-phase density and the oil-phase density . The formula is: ; ; In the formula, and According to the gas-phase molecular weight and temperature T Calculate represents the mixed viscosity parameter, according to the components molecular weight oil phase composition and components viscosity at lower pressure Calculated represents the reduced viscosity of the liquid, according to the components pseudo-critical temperature pseudo-critical pressure and molecular weight of the oil phase Calculated

[0009] Preferably, the multi-component and multi-phase flow shale oil flow simulation formula established based on the oil / gas phase equilibrium physical property parameters in step S5 includes: Use the multi-component and multi-phase flow shale oil flow simulation formula to calculate the transmission of shale oil and gas. According to the oil phase potential energy and gas phase potential energy oil phase saturation and gas phase saturation gas phase composition and oil phase composition Solve the mass balance equation of hydrocarbon components. The mass balance equation of hydrocarbon components is shown as follows: ; In the formula, represents the volume of the reservoir, represents the porosity, and are the relative mobilities of the oil phase and gas phase respectively, and are the production rates of the oil phase and gas phase respectively, is the transfer coefficient related to connectivity; According to the permeability k oil phase viscosity and gas phase viscosity oil phase relative permeability k ro and gas phase relative permeability k rg Determine the oil / gas phase mobility and , the formula is: ; .

[0010] Therefore, the present invention adopts the above-mentioned shale reservoir flow simulation method based on the restricted fluid state equation, modifies the P-R state equation based on the nano-confinement effect, performs phase equilibrium calculations based on the modified P-R state equation, calculates the physical property parameters of the oil / gas two-phase, substitutes the parameters into the shale reservoir flow equation, clarifies the flow characteristics of the shale reservoir, and improves the simulation efficiency.

[0011] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a schematic flow chart of the method according to an embodiment of the present invention; Figure 2 is a model diagram of a fractured shale reservoir provided by an embodiment of the present invention; Figure 3 is a graph showing the change of the critical temperature offset value with the pore size provided by an example of the present invention, where the symbols in the graph represent experimental data and the straight line is the data fitting value; Figure 4 is a flow chart for calculating the oil / gas phase equilibrium based on the modified P-R state equation provided by an embodiment of the present invention; Figure 5 is a phase diagram of Bakken shale oil calculated using the traditional P-R state equation and the modified P-R state equation provided by an embodiment of the present invention; Figure 6 is a graph showing the change of the oil / gas two-phase density with the pore size under different pressures provided by an embodiment of the present invention; Figure 7 is a graph showing the change of the oil / gas two-phase viscosity with the pore size under different pressures provided by an embodiment of the present invention; Figure 8 is the cumulative oil production under different conditions provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0013] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. The components of the embodiments of the present invention usually described and illustrated in the accompanying drawings here can be arranged and designed in various different configurations. In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is usually placed during use. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0014] Embodiment As Figure 1 shown, the present invention provides a shale oil reservoir flow simulation method based on a restricted fluid state equation, and the steps include: S1. Establish a generalized state equation of restricted fluid considering the nano-confinement effect; S2. Calculate the oil / gas phase equilibrium based on the generalized state equation of restricted fluid; S3. Calculate the physical property parameters of the oil / gas phase equilibrium; S4. Establish a multi-component and multi-phase flow shale oil flow simulation formula based on the physical property parameters of the oil / gas phase equilibrium.

[0015] In this embodiment, establishing the generalized state equation of restricted fluid considering the nano-confinement effect includes: S11. Calculate the adsorption layer thickness; In the shale reservoir, the adsorption effect is significant, and the number of fluid molecules in the free state is greatly reduced. The adsorption layer thickness can characterize the volume occupied by the adsorbed molecules, and the formula is: (1) Determine according to the equilibrium pressure P and the isotherm parameter b, and the formula is: (2) In the formula represents the mole fraction of component , represents the maximum adsorption amount of component .

[0016] Determine according to the molar volume of the oil phase and the Avogadro constant NA, and the formula is: (3) In the formula, represents the maximum adsorption thickness.

[0017] Substitute formula (2) and formula (3) into formula (1) to obtain the expression of the adsorption layer thickness, and the formula is: (1) In the formula, represents the isotherm parameter of component .

[0018] S22. Determine the reduced adsorption density; The reduced adsorption density can characterize the adsorption capacity of the fluid in the nanopore. According to the effective molecular volume coefficient of the adsorption zone and the effective molecular volume system of the bulk phase Determine the reduced adsorption density , the formula is: (5) Determine the bulk-phase effective molecular volume coefficient , the adsorbed-fluid effective molecular volume , and the true molecular volume of the fluid , the formula is: and the adsorbed-fluid effective molecular volume coefficient , the formula is: (6) (7) S33. Determine the corrected molar volume; Determine the number of adsorbed-fluid molecules from the adsorption volume and the effective molecular volume of the fluid , the formula is: (8) Substitute formula (5) into (8) and simplify to get: (9) In the formula, represents the effective radius, represents the true molecular volume, L represents the length, represents the pore radius; Determine the total number of fluid molecules from the pore volume and the effective molecular volume of the free fluid , the formula is: (10) Determine the molar volume of the P-R equation of state from the pore volume N A , the total number of fluid molecules , and the Avogadro number (11) Determine the corrected molar volume from the number of adsorbed-fluid molecules , the formula is: (12) Determine the relationship between the molar volume and the corrected molar volume from formulas (9) to (12), the formula is: ​​​​​​​​​​​​​​​​​​​(13) Substituting formulas (9) and (10) into formula (13) and simplifying gives: (14) According to the pore radius and the adsorption layer thickness determine the effective pore radius , the formula is: (15) Substitute the effective pore radius formula into the corrected molar volume to get: (16) According to the adsorption layer thickness and the pore radius define the parameter , the formula is: (17) Substitute the parameter formula into the simplified corrected molar volume to get: (18) S34. Determine the corrected P-R equation of state according to the corrected molar volume , the formula is: .

[0019] In the formula, P represents the equilibrium pressure, R represents the universal gas constant, represents the intermolecular attraction parameter, represents the co-volume parameter, T represents the temperature; S35. Calculate the critical property deviation value according to the corrected P-R equation of state; At a constant temperature, the first and second derivatives of pressure with respect to volume are equal to zero at the critical point. Differentiate formula (19), the formula is: (20) Calculate the corrected critical temperature and the corrected critical pressure according to formula (20), the formula is: (21) (22) The critical temperature T cand the critical pressure P c , the formula is: (23) (24) The critical temperature offset value is calculated according to formulas (21)-(24) and the critical pressure offset value , the formula is: (25) (26) S36. Calculate the reduced adsorption density according to the critical property offset value, and solve and verify the modified P-R equation of state.

[0020] Calculating the reduced adsorption density includes: Fitting the relationship between the critical temperature offset value and the pore size based on experimental data, the formula is: (27) According to the critical temperature T c and the critical pressure P c Determine , which represents the Lennard-Jone size parameter, the formula is: (28) According to the critical temperature offset value Determine the reduced adsorption density , the formula is: (29) In the formula, represents the pore radius.

[0021] In this embodiment, calculating the oil / gas phase equilibrium based on the generalized equation of state for restricted fluids in step S2 includes: Calculating the gas-phase mole fraction according to the Rachford-Rice formula , the formula is: (30) In the formula is the gas-liquid phase equilibrium constant, is the mole fraction of component .

[0022] The initial value is given by the wilson empirical formula, the formula is: (31) In the formula, is the acentric factor of component i, , are the critical temperature and critical pressure of component respectively.

[0023] According to the mole fraction of component , the gas-phase mole fraction , and the gas-liquid phase equilibrium constant , the gas-phase composition and the oil-phase composition are determined. The formula is: (32) (33) Using the modified P-R equation of state, the gas-phase fugacity coefficient and the oil-phase fugacity coefficient are calculated. The formula is: (34) (35) In the formula, , represent the compressibility factors of the gas phase and the liquid phase, represents the covolume parameter of component , represents the interaction coefficient between component and component , represents the attractive parameter of component , represents the number of components in the mixture. , are calculated from the pressure P , temperature T , covolume parameter b , reduced adsorption density and parameter . , are calculated from the pressure P , temperature T , attractive parameter . According to the gas-phase fugacity coefficient , the oil-phase fugacity coefficient , the gas-phase composition and the oil-phase composition , the gas-phase fugacity and the oil-phase fugacity are determined. The formula is: (36) (37) When the oil and gas are in phase equilibrium, the fugacity of the gas phase and the fugacity of the oil phase are equal, then the convergence condition is satisfied, and the formula is: (38) When the convergence condition is not satisfied, the equilibrium constant needs to be recalculated , and the equilibrium constant is determined according to the gas phase composition and the oil phase composition , and the formula is: (39) (40) The equilibrium constant is iterated using the successive substitution method, and the formula is: (41) The equilibrium constant obtained using formula (41) is used to recalculate formula (30), and formulas (32) to (41) are repeated until the convergence condition is satisfied, and finally the compositions of the gas phase and the oil phase are output 、 .

[0024] In this example, the calculation of the oil / gas phase equilibrium physical properties in step S3 includes: The relatively accurate compositions of the gas phase and the liquid phase calculated according to the modified P-R equation of state and can predict the property values of the oil and gas of some important formation fluids.

[0025] Calculation of the oil / gas phase molecular weight, including: Calculating the gas phase molecular weight and the oil phase molecular weight according to the gas phase composition , the oil phase composition and the molecular weight of the component , and the formula is: (42) (43) (44) Calculation of the oil / gas phase density, including: Determining the gas phase density and the oil phase density according to the gas phase molecular weight and the oil phase molecular weight , and the formula is: (45) (44) Wherein, represents the oil-phase compressibility factor, represents the gas-phase compressibility factor.

[0026] The calculation of oil / gas-phase viscosity includes: According to the gas-phase density and the oil-phase density calculate the gas viscosity and the oil-phase viscosity , and the formula is: (45) According to the gas-phase molecular weight and the temperature T determine , , and the formula is: (46) (47) According to calculate , and the formula is: (48) According to the viscosity of the oil phase at atmospheric pressure , the mixed viscosity parameter and the reduced viscosity of the liquid determine the oil-phase viscosity , and the formula is: (49) According to the component molecular weight , the oil-phase composition and the component viscosity at a lower pressure , determine the viscosity of the liquid at atmospheric pressure, and the viscosity of the liquid at atmospheric pressure is calculated as follows: (50) According to the pseudo-critical temperature of the component , the pseudo-critical pressure and the molecular weight of the oil phase determine the parameter related to the viscosity of the component , and the formula is: (51) In this embodiment, the multi-component and multi-phase flow shale oil flow simulation formula established based on the oil / gas-phase equilibrium physical property parameters includes: Using the multi-component and multi-phase flow shale oil flow simulation formula to calculate the transmission of shale oil and gas, according to the oil-phase potential energy and the gas-phase potential energy , the oil-phase saturation and the gas-phase saturation , the gas-phase composition and the oil-phase composition Solve the mass balance equation of hydrocarbon components, and the mass balance equation of hydrocarbon components is shown as the following formula: (52) In the formula, represents the volume of the reservoir, represents the porosity, and are the relative mobilities of the oil phase and the gas phase respectively, and are the production rates of the oil phase and the gas phase respectively, is the transfer coefficient related to connectivity; According to the permeability , the oil-phase viscosity and the gas-phase viscosity , the oil-phase relative permeability k ro and the gas-phase relative permeability k rg Determine the oil / gas phase mobility and , and the formula is: ; .

[0027] To verify the effectiveness of the method of the present invention, the application of a shale reservoir flow simulation method based on a restricted fluid state equation is as follows: Establish a shale reservoir model containing natural fractures, drill a horizontal well for production or injection, fracture 14 hydraulic fractures, the initial reservoir pressure is 2500 Psia, produce at a constant bottom-hole flowing pressure of 500 Psia for 15 years, and analyze the effects of depletion production and CO2 huff and puff on improving the recovery factor.

[0028] The specific reservoir parameters are shown in Table 1.

[0029] The fracture parameters are shown in Table 2.

[0030] The fractured shale reservoir model is as Figure 2 shown, the red line is the hydraulic fracture, and the blue line is the natural fracture connected to the hydraulic fracture.

[0031] Table 1 Specific reservoir parameters

[0032] Table 2 Fracture parameters

[0033] Step S1: Establish a generalized state equation for confined fluids considering the nano-confinement effect.

[0034] Shale reservoirs are mainly composed of nano-pores, and the pore throat diameter tends to be 1 - 100 nm. When fluids are confined in these nano-scale pores, the fluid-wall interaction plays an important role. Due to the interaction between fluid molecules and the pore wall, more fluid molecules are attracted to the region near the pore surface, forming an adsorbed phase. Therefore, the fluid density is not uniformly distributed across the pore width.

[0035] Traditional state equations have been widely used to describe the phase behavior of fluids in the bulk phase. However, considering the unique thermodynamic properties of confined fluids in nano-pores, the commonly used state equations are not applicable to the calculation of the phase behavior in confined spaces.

[0036] The parameters required for calculating the adsorbed layer thickness are shown in Table 3: Table 3 Adsorbed layer thickness parameters

[0037] The variation of the critical temperature offset value with the pore size is as Figure 3 shown, and formula (27) is obtained by fitting the experimental data.

[0038] Step S2: Calculate the oil / gas phase equilibrium based on the generalized state equation for confined fluids.

[0039] The phase equilibrium of shale oil and gas is highly disturbed due to the adsorption of fluids in densely developed nano-pores. Accurately describing the adsorption of confined fluids in nano-pores and the resulting critical displacement is crucial for better understanding the potential mechanisms of shale gas or shale oil storage, transportation, and recovery in shale reservoirs.

[0040] The flow chart for calculating the oil / gas phase equilibrium based on the modified P-R state equation is as Figure 4 shown.

[0041] Use the Bakken shale oil sample as the reservoir fluid, and the fluid components and parameters are shown in Table 4.

[0042] Table 4 Fluid components and parameters

[0043] The phase diagrams calculated using the traditional P-R state equation and the modified P-R state equation are as Figure 5 shown, and the entire phase envelope calculated using the modified P-R state equation is suppressed.

[0044] Step S3: Calculate the physical property parameters of the oil / gas two-phase.

[0045] The relatively accurate compositions of the gas phase and liquid phase calculated according to the modified P-R equation of state can predict the property values of oil and gas of some relatively important formation fluids.

[0046] The variations of the oil / gas two-phase density with the pore radius at different pressures calculated based on the modified P-R equation of state are as Figure 6 shown, and the variations of the oil / gas two-phase viscosity with the pore radius at different pressures are as Figure 7 shown. As the pore size decreases, the density and viscosity of the oil decrease, while the density and viscosity of the gas increase; at higher pressures, the density and viscosity of the oil / gas two-phase are both smaller, because at higher pressures, the interfacial tension between the oil phase and the gas phase is smaller, and the oil-gas capillary force weakens.

[0047] Step S4, establish a flow simulation formula for a multi-component and multi-phase shale oil reservoir.

[0048] Based on the modified P-R equation of state, perform phase equilibrium calculations, calculate the physical property parameters of the oil / gas two-phase, substitute the parameters into the shale oil reservoir flow equation, clarify the flow characteristics of the shale oil reservoir, clarify the recovery mechanism, and maximize the cumulative oil recovery rate.

[0049] The cumulative oil production in different cases is as Figure 8 shown. After using the modified P-R equation of state, the cumulative oil production increases; when using the traditional P-R equation of state for calculation, CO2 huff and puff can slightly improve the recovery rate; when using the modified P-R equation of state for calculation, CO2 huff and puff will reduce the methane production.

[0050] Therefore, the present invention adopts the above-mentioned shale oil reservoir flow simulation method based on the restricted fluid equation of state, modifies the P-R equation of state based on the nano-confinement effect, performs phase equilibrium calculations based on the modified P-R equation of state, calculates the physical property parameters of the oil / gas two-phase, substitutes the parameters into the shale oil reservoir flow equation, clarifies the flow characteristics of the shale oil reservoir, and improves the simulation efficiency.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A shale reservoir flow simulation method based on a restricted fluid state equation, characterized in that the steps include: S1. Considering the nanoconfinement effect, establish the generalized equation of state for confined fluid; S2, calculation of oil / gas phase equilibrium based on the generalized equation of state for confined fluids; S3. Calculate the physical property parameters of oil / gas phase equilibrium; S4. Establish a multi-component multi-phase shale oil flow simulation formula based on the oil / gas phase equilibrium physical property parameters.

2. A shale reservoir flow simulation method based on a confined fluid state equation according to claim 1, characterized in that: Step S1 considers the nanoconfinement effect to establish the generalized state equation of the confined fluid, including: S11. Calculate the thickness of the adsorption layer using the formula: ； In the formula, represents the adsorption layer thickness, Indicates components The maximum adsorption capacity, Indicates components The mole fraction of Indicates components The isotherm parameters are P Indicates the balance pressure, represents the molar volume of the oil phase, represents Avogadro's constant; S22, according to the effective molecular volume coefficient of the adsorption area , Bulk Effective Molecular Volume Determine the reduced adsorption density , the formula is: ； ； ； In the formula, represents the effective volume of bulk fluid molecules, represents the effective volume of adsorbed fluid molecules, Indicates the true volume of fluid molecules; S33, determining the corrected molar volume based on the adsorption layer thickness and the converted adsorption layer density ; S34, according to the corrected molar volume Determine the modified PR state equation, the formula is: ； In the formula, P Indicates the balance pressure, R is the universal gas constant, represents the attraction parameter between molecules, represents the common volume parameter, T Indicates temperature; S35, calculating the critical property offset value according to the modified PR state equation; S36. Calculate the converted adsorption density according to the critical property offset value, and solve and verify the modified PR state equation.

3. The shale reservoir flow simulation method based on the restricted fluid state equation according to claim 2, characterized in that: Step S33 specifically includes: according to the adsorption volume and the effective volume of fluid molecules Determine the number of adsorbed fluid molecules , the formula is: ； In the formula, represents the effective radius, represents the true volume of the molecule, L Indicates length, represents the pore radius; According to the pore volume and the effective volume of free fluid molecules Determine the total number of fluid molecules , the formula is: ； According to the pore volume , total number of fluid molecules and Avogadro's number N A Determine the molar volume of the PR equation of state , the formula is: ； According to the number of adsorbed fluid molecules Determine the Corrected Molar Volume , the formula is: ; According to the number of adsorbed fluid molecules 、 Total number of fluid molecules and molar volume Determining Molar Volume and the corrected molar volume The relationship between is: ； After simplification, we get: ； According to the pore radius and adsorption layer thickness Determine the effective pore radius , the formula is: ； The effective pore radius Substituting the corrected molar volume into the formula have to: ； According to the thickness of the adsorption layer and pore radius Defining parameters , the formula is: ； The parameters Substitute the formula and simplify to get the corrected molar volume Win: 。 4. The shale reservoir flow simulation method based on the constrained fluid state equation according to claim 3, characterized in that: Calculating the oil / gas phase equilibrium based on the generalized state equation of the confined fluid in step S2 includes: According to the components The mole fraction , gas phase mole fraction , initial gas-liquid two-phase equilibrium constant Determine the gas phase composition and oil phase composition , the formula is: ； ； In the formula, Given by Wilson's empirical formula, Calculated according to the Rachford-Rice formula; The gas phase fugacity coefficient is calculated using the modified PR state equation , oil phase fugacity coefficient , the formula is: ； ； In the formula, , represents the compressibility factor of the gas and liquid phases, Indicates components The co-volume parameter, Indicates components With components The interaction coefficient, Indicates components The attraction parameters represents the number of components in the mixture, , By pressure P ,temperature T , common volume parameter , converted adsorption density and parameters It is calculated that , By pressure P ,temperature T , attraction parameters Calculated; According to the gas phase fugacity coefficient , oil phase fugacity coefficient , gas phase composition and oil phase composition , determine the gas phase fugacity and oil phase fugacity , the formula is: ； ； When the oil and gas phases are in phase equilibrium, the gas phase fugacity and oil phase fugacity If they are equal, the convergence condition is met, and the formula is: ； When the convergence condition is not met, the equilibrium constant needs to be calculated again , according to the gas phase composition and oil phase composition Determine the equilibrium constant , the formula is: ； The equilibrium constant was calculated by the method of successive substitution. Iterate, the formula is: ； Equilibrium constant calculated using the successive substitution method Recalculate the gas phase mole fraction and repeat the calculation of the gas phase fugacity and oil phase fugacity , until the convergence condition is met, and finally the composition of the gas phase and the oil phase is output , .

5. The shale reservoir flow simulation method based on the restricted fluid state equation according to claim 4, characterized in that: The calculation of the oil / gas phase equilibrium physical property parameters in step S3 includes: According to the gas phase composition , oil phase composition and components Molecular weight Calculate gas phase molecular weight and oil phase molecular weight , the formula is: ； ； According to gas phase molecular weight and oil phase molecular weight Determine the gas phase density and oil phase density , the formula is: ； ； In the formula, represents the oil phase compressibility factor, represents the gas phase compressibility factor; According to the gas density and oil phase density Calculating gas viscosity and oil phase viscosity , the formula is: ； ； In the formula, and According to gas phase molecular weight and temperature T calculate, Indicates the mixed viscosity parameter, according to the components Molecular weight , oil phase composition and components Viscosity at lower pressure It is calculated that Indicates the relative viscosity of a liquid, according to its composition The pseudo-critical temperature T pc , pseudo critical pressure P pc and the molecular weight of the oil phase Calculated.

6. A shale reservoir flow simulation method based on a confined fluid state equation according to claim 5, characterized in that: In step S5, the multi-component multi-phase shale oil flow simulation formula is established based on the oil / gas phase equilibrium physical property parameters, including: The multi-component multi-phase shale oil flow simulation formula is used to calculate the transmission of shale oil and gas. and gas phase potential energy , oil phase saturation and gas phase saturation , gas phase composition and oil phase composition Solve the mass balance equation of the hydrocarbon components, which is shown in the following formula: ； In the formula, represents the volume of the reservoir, represents the porosity, and are the relative fluidity of the oil phase and the gas phase, and are the yields of oil phase and gas phase, respectively, is the transmission coefficient related to connectivity; According to the penetration rate , Oil phase viscosity and gas phase viscosity , oil phase relative permeability and gas phase relative permeability Determine oil / gas phase mobility and , the formula is: ； 。

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