A shale reservoir flow simulation method based on a restricted fluid state equation

Abstract

The application discloses a shale oil reservoir flow simulation method based on a restricted fluid state equation, and belongs to the technical field of oil and gas field development, and comprises the following steps: establishing a generalized state equation of a restricted fluid by considering nano-restriction effect; calculating oil / gas phase balance based on the generalized state equation of the restricted fluid; calculating oil / gas two-phase physical property parameters; and establishing a shale oil flow simulation formula of multi-component and multi-phase flow. By using the method, the P-R state equation is corrected based on nano-restriction effect, phase balance calculation is carried out based on the corrected P-R state equation, oil / gas two-phase physical property parameters are calculated, the parameters are substituted into a shale oil reservoir flow equation, the flow characteristics of the shale oil reservoir are determined, and the simulation efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, and in particular to a method for simulating shale reservoir flow based on confined fluid state equations. Background Technology

[0002] Shale reservoirs are predominantly composed of nanopores, with throat diameters ranging from 1 to 100 nm. When fluids are confined within these nanopores, fluid-wall interactions play a crucial role. The interaction between fluid molecules and the pore walls attracts more fluid molecules to the vicinity of the pore surface, forming an adsorbed phase. Consequently, fluid density is not uniformly distributed across the pore width. A thorough understanding of the fluid phase state is key to efficient oil and gas extraction in shale reservoirs. The phase equilibrium of shale oil and gas is highly disturbed by fluid adsorption within densely developed nanopores. Accurately describing the adsorption of confined fluids within nanopores and the resulting critical shift is essential for a better understanding of the potential mechanisms of shale gas or shale oil storage, transport, and recovery in shale reservoirs. Simultaneously calculating the petrophysical parameters of the oil / gas phases and incorporating them into established multi-component multiphase flow calculation formulas can better characterize fluid flow in shale reservoirs. Therefore, when calculating the flow development characteristics of shale oil reservoirs, the influence of the nanoconfinement effect on phase state and oil / gas property parameters must be considered. Summary of the Invention

[0003] The purpose of this invention is to provide a method for simulating shale reservoir flow based on confined fluid state equations, in order to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, this invention provides a method for simulating shale reservoir flow based on confined fluid state equations, comprising the following steps:

[0005] S1. Establish the generalized equation of state for confined fluids considering the nanoconfining effect;

[0006] S2. Calculation of oil / gas phase equilibrium based on the generalized equation of state for confined fluids;

[0007] S3. Calculate the equilibrium physical properties of the oil / gas phase;

[0008] S4. Establish a multi-component multiphase flow shale oil flow simulation formula based on oil / gas phase equilibrium physical property parameters.

[0009] Preferably, step S1, which considers the nanoconfining effect to establish the generalized equation of state for the confined fluid, includes:

[0010] S11. Calculate the thickness of the adsorption layer using the following formula:

[0011] ;

[0012] In the formula, represents the thickness of the adsorbed layer, represents the component , represents the component , represents the component , P represents the equilibrium pressure, represents the molar volume of the oil phase, represents the Avogadro constant;

[0013] S22, determining the effective molecular volume coefficient of the adsorbed zone according to the adsorbed volume , determining the reduced adsorbed density , the formula is:

[0014] ;

[0015] ;

[0016] ;

[0017] In the formula, represents the effective volume of the fluid molecules in the bulk phase, represents the effective volume of the fluid molecules in the adsorbed phase, represents the real volume of the fluid molecules;

[0018] S33, determining the corrected molar volume based on the thickness of the adsorbed layer and the reduced adsorbed layer density ;

[0019] S34, determining the corrected P-R state equation according to the corrected molar volume , the formula is:

[0020] ;

[0021] In the formula, P represents the equilibrium pressure, R represents the universal gas constant, represents the attraction parameter between molecules, represents the co-volume parameter, T represents the temperature;

[0022] S35, calculating the critical property offset value according to the corrected P-R state equation;

[0023] S36, calculating the reduced adsorbed density according to the critical property offset value, and solving the corrected P-R state equation for verification.

[0024] Preferably, step S33 specifically comprises: determining the effective molecular volume coefficient of the adsorbed zone according to the adsorbed volume and the effective volume of fluid molecules determining the number of adsorbed fluid molecules , the formula is:

[0025] ;

[0026] wherein, represents the effective radius, represents the real volume of molecules, L represents the length, represents the pore radius;

[0027] determining the total number of fluid molecules according to the pore volume and the effective volume of free fluid molecules , the formula is:

[0028] ;

[0029] determining the P-R state equation molar volume according to the pore volume , the total number of fluid molecules and the Avogadro number , the formula is:

[0030] ;

[0031] determining the corrected molar volume according to the number of adsorbed fluid molecules , the formula is: ;

[0032] determining the relationship between the molar volume 、 the total number of fluid molecules n and the corrected molar volume , the formula is:

[0033] ;

[0034] After simplifying, we get:

[0035] ;

[0036] determining the effective radius of the pore according to the pore radius and the thickness of the adsorption layer , the formula is:

[0037] ; ​​​​​​

[0038] The effective pore radius r is defined as The modified molar volume Vm is obtained by substituting the modified molar volume Vm into the formula The formula is simplified to obtain the modified molar volume Vm

[0039] ;

[0040] According to the thickness of the adsorbed layer and the pore radius The parameter is defined as The formula is

[0041] ;

[0042] The parameter is substituted into the formula to simplify and obtain the modified molar volume Vm The formula is The formula is

[0043] .

[0044] Preferably, the oil / gas phase equilibrium based on the restricted fluid generalized state equation in step S2 comprises:

[0045] According to the molar fraction of the component , the gas phase molar fraction , the initial gas-liquid two-phase equilibrium constant , the gas phase composition and the oil phase composition are determined, and the formula is

[0046] ;

[0047] ;

[0048] In the formula, is given by the Wilson empirical formula, is calculated according to the Rachford-Rice formula;

[0049] Using the modified P-R state equation, the gas phase fugacity coefficient , the oil phase fugacity coefficient are calculated, and the formula is

[0050] ; ;

[0051] In the formula, , represent the compressibility factors of the gas phase and the liquid phase, represents the common volume parameter of the component , and represents the common volume parameter of the component ​Interaction coefficient of component , Attractive parameter of component , Number of components in mixture, , Calculated from pressure P, temperature T , common volume parameter , reduced adsorption density and parameter , , Calculated from pressure P , temperature T , attractive parameter ;

[0052] According to gas phase fugacity coefficient , oil phase fugacity coefficient , gas phase composition and oil phase composition , determine gas phase fugacity and oil phase fugacity , formula is:

[0053] ;

[0054] ;

[0055] When oil and gas two phases are in phase equilibrium, gas phase fugacity and oil phase fugacity are equal, then meet convergence condition, formula is:

[0056] ;

[0057] When not meet convergence condition, need to calculate equilibrium constant again, according to gas phase composition and oil phase composition determine equilibrium constant , formula is:

[0058] ;

[0059] Use continuous replacement method to iterate equilibrium constant , formula is:

[0060] ;

[0061] Use equilibrium constant calculated by continuous replacement method to recalculate gas phase mole fraction, repeat to calculate gas phase fugacity and oil phase fugacity until the convergence condition is satisfied, and finally output the compositions of the gas phase and the oil phase 、 .

[0062] Preferably, the calculation of the oil / gas phase equilibrium property parameters in step S3 comprises:

[0063] According to the gas phase composition , the oil phase composition and the components molecular weight , the gas phase molecular weight and the oil phase molecular weight are calculated, and the formula is:

[0064] ;

[0065] ;

[0066] According to the gas phase molecular weight and the oil phase molecular weight , the gas phase density and the oil phase density are determined, and the formula is:

[0067] ;

[0068] ;

[0069] In the formula, represents the oil phase compressibility factor, represents the gas phase compressibility factor;

[0070] According to the gas phase density and the oil phase density , the gas viscosity and the oil phase viscosity are calculated, and the formula is:

[0071] ;

[0072] ;

[0073] In the formula, and are calculated according to the gas phase molecular weight and the temperature T , represents the mixing viscosity parameter, which is calculated according to the molecular weight of the components , the oil phase composition and the viscosity of the components under lower gas pressure, The contrast viscosity of the liquid is calculated according to the components of the pseudo critical temperature , the pseudo critical pressure and the molecular weight of the oil phase .

[0074] Preferably, the step S5 of establishing the shale oil flow simulation formula of multi-component and multi-phase flow based on the oil / gas phase equilibrium property parameters comprises:

[0075] The shale oil and gas transmission is calculated by using the shale oil flow simulation formula of multi-component and multi-phase flow, and the mass balance equation of hydrocarbon components is solved 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 , and the mass balance equation of hydrocarbon components is as follows:

[0076] ;

[0077] In the formula, V represents the volume of the reservoir, porosity, and are the relative flowabilities 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 the connectivity; The oil / gas phase mobility

[0078] and k are determined according to the permeability , the oil phase viscosity and the gas phase viscosity , the oil phase relative permeability and the gas phase relative permeability , and the formula is as follows:

[0079] ;

[0080] .

[0081] Therefore, the shale reservoir flow simulation method based on the limited fluid state equation is used in the present application, the P-R state equation is corrected based on the nano limited effect, the phase equilibrium calculation is performed based on the corrected P-R state equation, the oil / gas two-phase property parameters are calculated, the parameters are substituted into the shale reservoir flow equation, the flow characteristics of the shale reservoir are determined, and the simulation efficiency is improved.

[0082] ​The technical solutions of the present application are described in further detail below with reference to the accompanying drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0083] Figure 1 is a method flowchart of an embodiment of the present application;

[0084] Figure 2 is a fracture-type shale reservoir model diagram provided by an embodiment of the present application;

[0085] Figure 3 is a graph of the variation of the critical temperature offset value with pore size provided by an example of the present application, in which the symbols represent experimental data and the straight line is a data fitting value;

[0086] Figure 4 is a flowchart of the calculation of oil / gas phase equilibrium based on a modified P-R state equation provided by an embodiment of the present application;

[0087] Figure 5 is a phase diagram of the Bakken shale oil calculated using a conventional P-R state equation and a modified P-R state equation provided by an embodiment of the present application;

[0088] Figure 6 is a graph of the variation of the oil / gas two-phase density with pore size under different pressures provided by an embodiment of the present application;

[0089] Figure 7 is a graph of the variation of the oil / gas two-phase viscosity with pore size under different pressures provided by an embodiment of the present application;

[0090] Figure 8 is the cumulative oil production under different conditions provided by an embodiment of the present application. DETAILED DESCRIPTION

[0091] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described in detail below with reference to the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. The components of the embodiments of the present application described and shown in the accompanying drawings can be arranged and designed in various different configurations. In the description of the present application, it should be noted that the terms "upper", "lower", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the present application is usually placed, and are only used to facilitate the description of the present application and simplify the description, and therefore cannot be understood as indicating or implying that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0092] EMBODIMENT

[0093] AsFigure 1 As shown, the present application provides a shale oil reservoir flow simulation method based on a restricted fluid state equation, steps including:

[0094] S1, considering the nano confinement effect, a generalized state equation of restricted fluid is established;

[0095] S2, calculating oil / gas phase equilibrium based on the generalized state equation of restricted fluid;

[0096] S3, calculating oil / gas phase equilibrium physical parameters;

[0097] S4, establishing a multi-component and multi-phase flow shale oil flow simulation formula based on oil / gas phase equilibrium physical parameters.

[0098] In this embodiment, the generalized state equation of restricted fluid considering the nano confinement effect includes:

[0099] S11, calculating the thickness of the adsorption layer;

[0100] In shale reservoirs, adsorption is significant, and greatly reduces the number of fluid molecules in a free state, and the thickness of the adsorption layer can represent the volume occupied by adsorbed molecules, the formula is:

[0101] (1)

[0102] According to the equilibrium pressure P and the isotherm parameter b, determine , the formula is:

[0103] (2)

[0104] In the formula, represents the mole fraction of component , and represents the maximum adsorption amount of component .

[0105] According to the oil phase molar volume and Avogadro's constant NA, determine , the formula is:

[0106] (3)

[0107] In the formula, represents the maximum adsorption thickness.

[0108] Substitute formula (2) and formula (3) into formula (1) to obtain the expression of the thickness of the adsorption layer, the formula is:

[0109] (1)

[0110] In the formula, isotherm parameters of the component .

[0111] S22, determining the reduced adsorption density;

[0112] The reduced adsorption density can represent the adsorption capacity of the fluid in the nanopore, according to the effective molecular volume coefficient of the adsorption zone , the effective molecular volume coefficient of the bulk phase determining the reduced adsorption density , the formula is:

[0113] (5)

[0114] According to the effective volume of the bulk phase fluid molecule , the effective volume of the adsorbed fluid molecule , the real volume of the fluid molecule determining the effective molecular volume coefficient of the bulk phase and the effective volume coefficient of the adsorbed fluid molecule , the formula is:

[0115] (6)

[0116] (7)

[0117] S33, determining the corrected molar volume;

[0118] According to the adsorption volume and the effective volume of the fluid molecule determining the number of adsorbed fluid molecules , the formula is:

[0119] (8)

[0120] Substitute formula (5) into (8) to get:

[0121] (9)

[0122] In the formula, represents the effective radius, represents the real volume of the molecule, L represents the length, represents the pore radius;

[0123] According to the pore volume and the effective volume of the free fluid molecule determining the total number of fluid molecules , the formula is:

[0124] (10)

[0125] According to the pore volume , the total fluid molecule number and the Avogadro number , the P-R state equation molar volume is determined, and the formula is:

[0126] (11)

[0127] According to the adsorbed fluid molecule number , the corrected molar volume is determined, and the formula is: (12)

[0128] According to the formula (9)~formula (12), the relationship between the molar volume and the corrected molar volume is determined, and the formula is:

[0129] (13)

[0130] The formula (9) and the formula (10) are brought into the formula (13) and simplified to obtain:

[0131] (14)

[0132] According to the pore radius and the adsorption layer thickness , the pore effective radius is determined, and the formula is:

[0133] (15)

[0134] The pore effective radius formula is substituted into the corrected molar volume to obtain:

[0135] (16)

[0136] According to the adsorption layer thickness and the pore radius , the parameter is defined, and the formula is:

[0137] (17)

[0138] The parameter formula is substituted into the simplified corrected molar volume to obtain:

[0139] (18)

[0140] S34, according to the corrected molar volume The modified P-R equation of state is determined, and the formula is:

[0141] .

[0142] In the formula, P represents the equilibrium pressure, R represents the universal gas constant, represents the attraction parameter between molecules, represents the co-volume parameter, T represents the temperature;

[0143] S35, calculating the critical property offset value according to the modified P-R equation of state;

[0144] At constant temperature, the first and second derivatives of pressure with respect to volume at the critical point are equal to zero, and the formula (19) is derived, which is:

[0145] (2)

[0146] The modified critical temperature and the modified critical pressure are calculated according to formula (20), which is:

[0147] (3)

[0148] (22)

[0149] The critical temperature and the critical pressure are derived by deriving the traditional P-R equation of state, which is:

[0150] (23)

[0151] (24)

[0152] The critical temperature offset value and the critical pressure offset value are calculated according to formulas (21)-(24), which are:

[0153] (25)

[0154] (26)

[0155] S36, calculating the reduced adsorption density according to the critical property offset value, and verifying the modified P-R equation of state.

[0156] The calculation of the reduced adsorption density includes:

[0157] The relationship between the critical temperature shift and the pore size is fitted according to the experimental data, and the formula is:

[0158] (27)

[0159] According to the critical temperature and the critical pressure , , represents the Lennard-Jone size parameter, and the formula is:

[0160] (28)

[0161] According to the critical temperature shift , ,

[0162] (29)

[0163] In the formula, represents the pore radius.

[0164] In this embodiment, the oil / gas phase equilibrium calculated based on the restricted fluid generalized state equation in step S2 includes:

[0165] According to the Rachford-Rice formula, the gas phase mole fraction is calculated, and the formula is:

[0166] (30)

[0167] In the formula , K is the gas-liquid two-phase equilibrium constant, is the mole fraction of component .

[0168] The initial value is given by the wilson empirical formula, and the formula is:

[0169] (31)

[0170] In the formula, is the eccentric factor of component i, , are the critical temperature and critical pressure of component , respectively.

[0171] According to the mole fraction i of component , the gas phase mole fraction , and the gas-liquid two-phase equilibrium constant , the gas phase composition and oil phase composition , where

[0172] (32)

[0173] (33)

[0174] The fugacity coefficient of gas phase is calculated by using the modified P-R equation of state , and the fugacity coefficient of oil phase is calculated by using the modified P-R equation of state , where

[0175] (34)

[0176] (35)

[0177] where , Zg and Zo represent the compressibility factor of gas phase and oil phase, Zg and Zo represent the compressibility factor of gas phase and oil phase, Zg and Zo represent the compressibility factor of gas phase and oil phase, Zg and Zo represent the compressibility factor of gas phase and oil phase, Zg and Zo represent the compressibility factor of gas phase and oil phase, Zg and Zo represent the compressibility factor of gas phase and oil phase, Zg and Zo represent the compressibility factor of gas phase and oil phase, Zg and Zo represent the compressibility factor of gas phase and oil phase, Zg and Zo represent the compressibility factor of gas phase and oil phase, , Zg and Zo represent the compressibility factor of gas phase and oil phase, P Zg and Zo represent the compressibility factor of gas phase and oil phase, T Zg and Zo represent the compressibility factor of gas phase and oil phase, Zg and Zo represent the compressibility factor of gas phase and oil phase, Zg and Zo represent the compressibility factor of gas phase and oil phase, Zg and Zo represent the compressibility factor of gas phase and oil phase, , Zg and Zo represent the compressibility factor of gas phase and oil phase, P Zg and Zo represent the compressibility factor of gas phase and oil phase, T Zg and Zo represent the compressibility factor of gas phase and oil phase, Zg and Zo represent the compressibility factor of gas phase and oil phase,

[0178] The fugacity of gas phase and the fugacity of oil phase are determined by using the fugacity coefficient of gas phase , the fugacity coefficient of oil phase , the composition of gas phase , and the composition of oil phase , where

[0179] (36)

[0180] (37)

[0181] When the oil and gas phases are in phase equilibrium, the fugacity of gas phase and the fugacity of oil phase​​ If equal, the convergence condition is satisfied, and the formula is:

[0182] (38)

[0183] When the convergence condition is not satisfied, the equilibrium constant needs to be calculated again , according to the gas phase composition and the oil phase composition to determine the equilibrium constant , the formula is:

[0184] (39)

[0185] The continuous replacement method is used to iterate the equilibrium constant , the formula is:

[0186] (40)

[0187] The equilibrium constant obtained by using formula (40) k i Recalculate formula (30), repeat formula (32) to formula (40), until the convergence condition is satisfied, and finally output the composition of the gas phase and the oil phase , .

[0188] In this example, the calculation of the oil / gas phase equilibrium property parameters in step S3 includes:

[0189] The relatively accurate gas phase and liquid phase compositions calculated according to the modified P-R state equation and can predict some important oil and gas properties of formation fluids.

[0190] Oil / gas phase molecular weight calculation includes:

[0191] According to the gas phase composition , the oil phase composition and the molecular weight of the component , the gas phase molecular weight and the oil phase molecular weight are calculated, the formula is:

[0192] (41)

[0193] (42)

[0194] Oil / gas phase density calculation includes:

[0195] According to the gas phase molecular weight and the oil phase molecular weight​ Determine gas phase density and oil phase density , where:

[0196] (43)

[0197] (44)

[0198] where: Zg represents the gas phase compressibility factor, Zo represents the oil phase compressibility factor.

[0199] Oil / gas phase viscosity calculations include:

[0200] Determine gas viscosity and oil phase viscosity from gas phase density and oil phase density , where:

[0201] (45)

[0202] Determine gas viscosity from gas phase molecular weight T and temperature , , where:

[0203] (46)

[0204] (47)

[0205] Determine from , where:

[0206] (48)

[0207] Determine oil phase viscosity from viscosity of oil phase at atmospheric pressure , mixing viscosity parameter and contrast viscosity of liquid, where:

[0208] (49)

[0209] Determine viscosity of liquid at atmospheric pressure from component molecular weights , oil phase composition and viscosity of components at lower pressure, where viscosity of liquid at atmospheric pressure is calculated as follows:

[0210] ​​​ (50)

[0211] According to the component Pseudo-critical temperature , pseudo-critical pressure and the molecular weight of the oil phase Determine the component The parameter related to viscosity , the formula is:

[0212] (51)

[0213] In this embodiment, the shale oil flow simulation formula of multi-component and multi-phase flow is established based on the oil / gas phase equilibrium property parameters, which includes:

[0214] The multi-component and multi-phase flow shale oil flow simulation formula is used to calculate the transmission of shale oil and gas, and according to the oil phase potential energy And the 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, which is shown in the following formula:

[0215] (52)

[0216] In the formula, Indicates the volume of the reservoir, Indicates the porosity, And The relative mobility of the oil phase and the gas phase respectively, And The yield of the oil phase and the gas phase respectively, The transfer coefficient related to the connectivity;

[0217] According to the permeability , oil phase viscosity And the gas phase viscosity , oil phase relative permeability And the gas phase relative permeability Determine the oil / gas phase mobility And , the formula is:

[0218] ;

[0219] .

[0220] To verify the effectiveness of the method of the present application, the application of a shale oil reservoir flow simulation method based on a restricted fluid state equation is as follows:

[0221] A shale reservoir model containing natural fractures is established, a horizontal well is drilled for production or injection, 14 hydraulic fractures are fractured, the initial reservoir pressure is 2500 Psia, the well bottom hole pressure is 500 Psia for 15 years, the effects of depletion production and CO2 huff and puff on enhanced recovery are analyzed.

[0222] The reservoir specific parameters are shown in Table 1.

[0223] The fracture parameters are shown in Table 2.

[0224] The fracture type shale reservoir model is shown in Figure 2 , the red line is the hydraulic fracture, and the blue line is the natural fracture connected with the hydraulic fracture.

[0225] Table 1 Reservoir specific parameters

[0226]

[0227] Table 2 Fracture parameters

[0228]

[0229] Step S1, considering the nano confinement effect, a generalized state equation of confined fluid is established.

[0230] Shale reservoirs are mainly nano-porous, with pore throat diameters tending to 1-100 nm. When the fluid is confined in these nano-scale pores, the fluid-wall interaction plays an important role, because the interaction between fluid molecules and pore walls will attract more fluid molecules to the area near the pore surface, forming an adsorbed phase, so the fluid density is not uniformly distributed over the pore width.

[0231] 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 suitable for the calculation of phase behavior in confined space.

[0232] The parameters required for the calculation of the thickness of the adsorbed layer are shown in Table 3:

[0233] Table 3 Parameters for calculating the thickness of the adsorbed layer

[0234]

[0235] The change of critical temperature offset value with pore size is shown in Figure 3 , and formula (27) is obtained by fitting the experimental data.

[0236] Step S2, based on the generalized state equation of confined fluid, the oil / gas phase equilibrium is calculated.

[0237] The phase equilibrium of shale oil and gas is highly disturbed by the adsorption of fluids in the densely developed nanopores. Accurate description of the adsorption of confined fluids in nanopores and the critical displacement caused thereby is essential for better understanding of the potential mechanisms of storage, transportation and recovery of shale gas or shale oil in shale reservoirs.

[0238] The flow chart for calculating oil / gas phase equilibrium based on the modified P-R state equation is shown in Figure 4

[0239] The Bakken shale oil sample was used as the reservoir fluid, and the fluid components and parameters are shown in Table 4.

[0240] Table 4 Fluid components and parameters

[0241]

[0242] The phase diagrams calculated using the conventional P-R state equation and the modified P-R state equation are shown in Figure 5 The entire phase envelope calculated using the modified P-R state equation is suppressed.

[0243] Step S3, calculating the oil / gas two-phase physical property parameters.

[0244] The more accurate gas and liquid phase compositions calculated according to the modified P-R state equation can predict some important oil and gas property values of the formation fluid.

[0245] The changes of oil / gas two-phase density with pore radius at different pressures calculated based on the modified P-R state equation are shown in Figure 6 The changes of oil / gas two-phase viscosity with pore radius at different pressures are shown in Figure 7 With the decrease of pore size, the density and viscosity of oil decrease, and the density and viscosity of gas increase; at a higher pressure, the density and viscosity of the oil / gas two-phase are smaller, because the interfacial tension between the oil phase and the gas phase is smaller at a higher pressure, and the oil and gas capillary force is weakened.

[0246] Step S4, establishing a multi-component and multi-phase shale oil reservoir flow simulation formula.

[0247] Based on the modified P-R state equation for phase equilibrium calculation, 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 determined, the recovery mechanism is determined, and the cumulative oil recovery is maximized.

[0248] The cumulative oil production under different conditions is shown in Figure 8 ​As shown, the cumulative oil production is increased after using the modified P-R state equation; the CO2 huff and puff can slightly increase the recovery rate when using the traditional P-R state equation; the CO2 huff and puff can reduce the methane production when using the modified P-R state equation.

[0249] Therefore, the shale oil reservoir flow simulation method based on the limited fluid state equation is adopted, the P-R state equation is modified based on the nano limited effect, the phase equilibrium calculation is performed based on the modified P-R state equation, the oil / gas two-phase property parameters are calculated, the parameters are substituted into the shale oil reservoir flow equation, the flow characteristics of the shale oil reservoir are determined, and the simulation efficiency is improved.

[0250] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application but not to limit it, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that: the technical solutions of the present application can still be modified or replaced by the equivalent, 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 application.

Claims

1. A method for shale reservoir flow simulation based on a restricted fluid state equation, characterized by the steps of The method comprises the following steps: S1, considering the nano confinement effect, a generalized state equation of confined fluid is established, which comprises: S11, the thickness of the adsorption layer is calculated, and the formula is: where δ ad represents the adsorbed layer thickness, V m,i represents the maximum adsorption capacity of component i, z i represents the mole fraction of component i, b i represents the isotherm parameter of component i, P represents the equilibrium pressure, v M represents the molar volume of the oil phase, N A represents the Avogadro constant; S12、According to the effective molecular volume coefficient ε of adsorption zone a , the effective molecular volume coefficient ε of bulk phase t The conversion adsorption density β is determined, and the formula is: β = ε t / ε a ; e a = V e-a / V real ; e t = V e-t / V real ; where V e-t represents the effective volume of the fluid molecules in the bulk phase, V e-a represents the effective volume of the fluid molecules in the adsorbed phase, V real represents the real volume of the fluid molecules; S13, determine the corrected molar volume V based on the adsorption layer thickness and the converted adsorption layer density m '; S14. The corrected molar volume V m The corrected P-R equation of state is determined as In the formula, P represents the equilibrium pressure, R represents the universal gas constant, a represents the attraction parameter between molecules, b represents the common volume parameter, and T represents the temperature; S15, the critical property offset value is calculated according to the modified P-R state equation; S16, the converted adsorption density is calculated according to the critical property offset value, and the modified P-R state equation is solved and verified; S2, oil / gas phase equilibrium is calculated based on the generalized state equation of the confined fluid; S3, oil / gas phase equilibrium property parameters are calculated; S4, multi-component and multi-phase flow shale oil flow simulation formula is established based on the oil / gas phase equilibrium property parameters.

2. The shale reservoir flow simulation method based on a restricted fluid state equation according to claim 1, characterized in that, Step S33 specifically includes: determining the number n of adsorbed fluid molecules according to the adsorption volume V a and the effective volume V e-a of the fluid molecules, i.e. a ​ where r e represents the effective radius, V real represents the real volume of the molecule, L represents the length, r p represents the pore radius; According to the pore volume V p and the effective volume of free fluid molecules V e-t The total number of fluid molecules n is determined t , the formula is: According to the pore volume V p , the total number of fluid molecules n t , and the Avogadro number N A , the P-R equation of state molar volume V m is determined, and the formula is: According to the number of adsorbed fluid molecules n a Determination of the corrected molar volume V m The formula is: According to the number of adsorbed fluid molecules n a , the total number of fluid molecules n and the molar volume V m Determine the relationship between the molar volume V m And the corrected molar volume V m The formula is: After simplification, we have: According to the pore radius r p and the adsorption layer thickness δ ad The effective pore radius r e is determined, which is given by the formula r e = r p - δ ad ; The effective pore radius r e The formula is substituted with the corrected molar volume V m Result: According to the thickness δ of the adsorption layer ad and the pore radius r p The parameter γ is defined by the formula: Substitute the parameter γ into the formula to simplify and get the corrected molar volume V m The result is:

3. The shale reservoir flow simulation method based on a restricted fluid state equation of claim 2, wherein: The oil / gas phase equilibrium based on the generalized state equation of the confined fluid in step S2 comprises: According to the mole fraction z of component i i , the gas phase mole fraction f v , the initial gas-liquid two-phase equilibrium constant k i Determine the gas phase composition x i and the oil phase composition y i , the formula is: where k i Given by Wilson's empirical equation, f v Calculated according to the Rachford-Rice equation; The gas fugacity coefficient is calculated using the modified P-R equation of state The oil fugacity coefficient The formula is: where Z V , Z L represents the compressibility factor of gas and liquid phase, b i represents the co-volume parameter of component i, δ ij represents the interaction coefficient of component i and component j, a i represents the attractive force parameter of component i, nc represents the number of components in the mixture, B V , B L calculated from pressure P, temperature T, co-volume parameter b, reduced adsorption density β and parameter γ, A V , A L calculated from pressure P, temperature T, attractive force parameter a; According to the gas phase fugacity coefficient Oil phase fugacity coefficient Gas phase composition x i And oil phase composition y i , determining the gas phase fugacity f i V And oil phase fugacity f i L , the formula is: When oil and gas phases are in phase equilibrium, the gas phase fugacity f i V and the oil phase fugacity f i L are equal, then the convergence condition is satisfied, and the formula is: When the convergence condition is not satisfied, the equilibrium constant k needs to be calculated again i , the equilibrium constant k is determined according to the gas phase composition x i and the oil phase composition y i , and the formula is: i ​ The equilibrium constant k was determined by the continuous substitution method i The iteration was performed with the formula: The equilibrium constant k is calculated using the successive substitution method i The gas phase mole fraction is recalculated and the gas phase fugacity f is recalculated i V and the oil phase fugacity f i L until the convergence condition is met, and the compositions x i , y i of the gas and oil phases are finally output.

4. The shale reservoir flow simulation method based on a restricted fluid state equation of claim 3, wherein, The calculation of the oil / gas phase equilibrium property parameters in step S3 comprises: According to the gas phase composition x i , the oil phase composition y i and the component i molecular weight MW i The gas phase molecular weight MW g and the oil phase molecular weight MW o are calculated, the formula is: According to the gas phase molecular weight MW g and the oil phase molecular weight MW o The gas phase density p is determined g and the oil phase density p o with the formula: wherein Z o represents the oil phase compressibility factor, Z g represents the gas phase compressibility factor; The gas density p is calculated from the gas composition g and the oil phase density p o The gas viscosity m is calculated from the gas composition g and the oil phase viscosity m o The formula is: where k v and x v are calculated from the gas phase molecular weight MW g and the temperature T, μ * represents the mixing viscosity parameter and is calculated from the molecular weight MW i of the components i, the oil phase composition y i and the viscosity of the components i at lower gas pressure ρ r represents the relative viscosity of the liquid and is calculated from the pseudo critical temperature T pc , the pseudo critical pressure P pc and the molecular weight MW o of the oil phase.

5. The shale reservoir flow simulation method based on a restricted fluid state equation of claim 4, wherein: The establishment of the multi-component and multi-phase flow shale oil flow simulation formula based on the oil / gas phase equilibrium property parameters in step S5 comprises: The transport of shale oil and gas is calculated using a multi-component, multi-phase flow shale oil flow simulation formula, and the mass balance equation of hydrocarbon components is solved according to oil phase potential energy Φ o and gas phase potential energy Φ g , oil phase saturation S o and gas phase saturation S g , gas phase composition x i and oil phase composition y i , which is shown in the following formula: where V j represents the volume of the reservoir, φ represents the porosity, λ ro and λ rg are the relative mobilities of the oil and gas phases, respectively, and are the oil and gas phase production rates, respectively, and T is a transfer coefficient related to the connectivity. According to the permeability k, the oil phase viscosity μ o and the gas phase viscosity μ g , the oil phase relative permeability k ro and the gas phase relative permeability k rg Determination of the oil / gas phase mobility λ ro and λ rg , formula:

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