Minimum miscible phase pressure calculation method considering trihydrocarbon phase in nanopore
By constructing nanopore impact characterization and three-phase phase equilibrium calculation algorithms in shale reservoirs, the problem of MMP in the existing technology cannot be accurately calculated when the coexistence of three hydrocarbon phases is achieved, and accurate MMP calculation is achieved, supporting efficient mining of shale oil and gas reservoirs.
Patent Information
- Application Number
- CN202510029064.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-08
- Publication Date
- 2025-04-08
AI Technical Summary
The prior art cannot accurately calculate the minimum mixed phase pressure (MMP) when the three hydrocarbon phases coexist during injection in shale reservoirs, and the predicted MMP value is relatively high due to the cross-train.
A minimum mixed-phase pressure calculation method for considering the triple hydrocarbon phase in nanopores was designed. By constructing a shale nanopore impact characterization and three-phase phase equilibrium calculation algorithm, the equilibrium state and tether length of the three hydrocarbon phases in nanopores were calculated, and then the MMP was determined.
Accurate MMP calculations when the three hydrocarbon phases coexist during injection in the shale reservoir are achieved, avoiding the problem of high prediction values and supporting efficient and economical exploitation of shale oil and gas reservoirs.
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Figure CN119785901A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of oil extraction, and in particular to a method for calculating the minimum miscible pressure in nanopores taking three hydrocarbon phases into consideration. Background Art
[0002] Carbon capture, utilization and storage (CCUS) is considered a key technology for mitigating climate change. Enhanced oil recovery The idea of storage in geological formations has become a widely accepted and viable CCUS approach, with shale formations becoming a potential candidate as unconventional oil and gas extraction gains more attention. Storage location, Flooding has been proven to be effective in improving oil and gas recovery in shale reservoirs. The minimum miscibility pressure (MMP) is The traditional MMP determination methods include empirical formula method, experimental test (such as capillary test) and theoretical calculation. Theoretical calculation is widely used due to its high efficiency and economy. The conventional MMP calculation method is affected by the nanopores in unconventional reservoirs, and the calculation results have certain errors. At the same time, when injecting at low temperature It can lead to three hydrocarbon phases (i.e. gas phase, oil-rich liquid phase and The coexistence of liquid phase and gas phase will also affect the final MMP calculation results. However, the existing model cannot accurately calculate the injection of gas into shale reservoirs. MMP when three hydrocarbon phases coexist.
[0003] The first prior art predicts MMP based on the interaction within a single unit and applies forward or backward contact according to the compatibility of the evaporation or condensation driver. This method is particularly effective for situations where oil and gas lines are dominant. Although this technology considers the prediction of MMP based on the unit contact method, it is often affected by the cross-line and the predicted MMP value is too high. The second prior art extrapolates the minimum critical line length to zero to determine the MMP without calculating the unit volume or mixed fluid. It is suitable for the prediction of MMP in unconventional reservoirs. It has been confirmed that this technology predicts that the MMP value in nanopores will be reduced. This technology takes into account the limitations of capillary forces and nanopores, but cannot accurately calculate the injection into shale reservoirs. MMP when three hydrocarbon phases coexist.
[0004] Therefore, due to the above-mentioned influence of cross-ties, the predicted MMP value is too high and the injection into the shale reservoir cannot be accurately calculated. In order to solve the problem of MMP when three hydrocarbon phases coexist, a method for calculating the minimum miscibility pressure considering three hydrocarbon phases in nanopores can be designed. Summary of the invention
[0005] In order to overcome the influence of cross-ties, the predicted MMP value is too high and the injection The problem of MMP when three hydrocarbon phases coexist.
[0006] The technical solution of the present invention is: a method for calculating the minimum miscible pressure in a nanopore considering three hydrocarbon phases, the steps of which are as follows: S1: Characterization of the impact of shale nanopores S11: Calculation of critical temperature and critical pressure of each component in the nanopore; S12: Construction of pressure balance model in phase equilibrium including capillary force; S2: In nanopores Construction of three-phase phase balance calculation algorithm S21: Input the known pressure P, temperature T, and mole fraction of each component in the mixture , the critical temperature and critical pressure of each component in the nanopore, the eccentricity factor, and the binary interaction coefficient BIP between the components; S22: Perform a stability test on a given mixture at a specified pressure and temperature. If the mixture is stable, the calculation is terminated and the molar fraction of each component of the initial mixture is output, and the molar fraction of the phase is set to 1. If the mixture is unstable, proceed to step S23. S23: Perform two-phase flash evaporation calculations and perform stability tests on the two equilibrium phases obtained by flash evaporation. If both are stable, output the fluid phase behavior characterization parameters such as the molar ratio of each phase of the two-phase fluid, the ratio of each component of the two phases, the two-phase pressure, and the capillary force. If any phase is unstable, proceed to step S24; S24: Three-phase Flash calculation; S3: Consideration in nanopores Construction of the MMP calculation algorithm for three phases S31: injecting gas G and crude oil O into two units respectively, and mixing the injected gas and crude oil in a ratio of 1:1 to obtain an oil-gas mixture; S32: Under given temperature and pressure conditions, the oil-gas mixture is subjected to nanopore Three-phase phase balance calculation, if the calculation result is two-phase or three-phase, then proceed to step S33; if it is found that the system is in single-phase balance, then negative phase two-phase flash calculation is performed to obtain two-phase balance; S33: Classify the calculated equilibrium phases. In the case of three phases, the phase with the closest composition to the injected gas is defined as the fast phase F, the phase closest to the crude oil is defined as the slow phase S, and the remaining phases are designated as the intermediate phases I. In the case of only two phases, the phase with the closest composition to the injected gas is defined as the fast phase F, and the phase closest to the crude oil is defined as the slow phase S; S34: Calculate the tie length. When the calculation result is three-phase, the tie length between the F and S phases needs to be calculated and recorded separately. , the tie length between phases F and I , the tie length between I and S phases When the calculation result is two phases, only the length of the tie wire between phases F and S needs to be calculated and recorded. ; S35: Determine the molar proportion of each component in the two phases required for the next contact and sort them. If the calculation result of step S32 is three phases, the S phase and the I phase are mixed in a ratio of 1:1 to obtain a new pseudo-liquid phase X; the F phase and the I phase are mixed in a ratio of 1:1 to obtain a new pseudo-gas phase Y. In the case of two phases, the S phase is set as the X phase, and the F phase is set as the Y phase. The positions shown in the second contact are sorted from left to right in the order of G, X, Y and O phases. The X phase is located in the unit close to the gas G injected at the rear end, and the Y phase is located in the unit close to the crude oil O at the front end. The phases in adjacent units are mixed in a ratio of 1:1 from left to right to obtain a new mixture; S36: Repeat steps S32 to S35, mix the phases multiple times and perform phase equilibrium calculation and tie length calculation. According to the process, perform the 3rd to 100th mixed phase calculations. There are 100 three-phase phase equilibrium calculations in the 100th contact. These phase equilibrium calculations are numbered from 1 to 100 from left to right, and the smallest phase equilibrium calculation in the 100th contact is recorded. , and ; S37: Repeat steps S31 to S36 at different pressures, and record the minimum value of the 100th contact at the pressure. , and ,when The pressure when the length becomes zero is MMP; S4: Consideration in nanopores Verification of the three-phase MMP calculation algorithm S41: Three-phase Stability testing and accuracy verification of balancing algorithms; S42: Considerations in Nanopores Verification of the accuracy of the three-phase MMP calculation algorithm Plot the cross plot of pressure and the minimum tie length calculated at that pressure, and compare it with the theoretically calculated high-efficiency oil displacement pressure If the pressure obtained from the experimental test and the pressure at the inflection point of the recovery factor curve are consistent, it means that the calculation result is accurate; S5: Nanopore And analysis of the miscibility of shale oil.
[0007] Preferably, S24 outputs the fluid phase behavior characterization parameters such as the molar ratio of each phase of the three-phase fluid, the ratio of each component of the three-phase, the three-phase pressure, and the capillary force.
[0008] Preferably, in S31, the unit containing gas is placed upstream, and the unit containing crude oil is placed downstream.
[0009] Preferably, the negative phase two-phase flash calculation performed in S32 is a known algorithm in the field of phase behavior.
[0010] Preferably, if no three phases appear at this pressure in S37, then there is no and .
[0011] As a preferred embodiment, the specific steps of S41 are: given a temperature, applying the three-phase Phase equilibrium calculation algorithm, calculates the phase behavior of the fluid when the pressure is very small and a certain component changes, such as setting The percentage change interval is 0.1mol% and the pressure change interval is 0.1bar to test the stability of the algorithm. When the molar percentage of a phase is zero, the corresponding P and x values are the points on the Px phase diagram envelope. The Px phase diagram is drawn according to the P and x values of each point on the Px phase diagram envelope. The agreement rate between the points on the phase diagram and the experimental test points is compared and adjusted. The binary interaction parameter (BIP) between the hydrocarbon components makes the agreement rate exceed 90%.
[0012] As a preferred embodiment, in S42 For the calculated and One of them is 0 pressure.
[0013] As a preferred embodiment, the specific steps of S5 are: calculating the volume phase and the nanopores with different pore sizes. The cross plot of the pressure of shale oil reverberation and the minimum tie length calculated at this pressure is used to analyze the efficient oil recovery pressure in the bulk phase and nanopores with different pore sizes. and the difference between MMP.
[0014] The beneficial effects of the present invention are as follows: by introducing the influence of shale nanopores and the three-hydrocarbon phase equilibrium calculation algorithm, a method for accurately calculating the injection of hydrocarbons into shale reservoirs is invented. The MMP calculation algorithm for the coexistence of three hydrocarbon phases was used to analyze the effect of the coexistence of three hydrocarbon phases in nanopores. and the miscibility of shale oil, which can be used to accurately calculate the injection During the period when the three hydrocarbon phases coexist The key parameter MMP of flooding supports the efficient and economical exploitation of shale oil and gas reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Figure 1 Shown is a schematic diagram of pressure balance in different phase equilibria when considering the presence of three hydrocarbon phases in a nanopore; Figure 2 The three phases in the nanopore are shown Schematic diagram of the phase contact method of the equilibrium MMP calculation method. G: injection gas; O: crude oil; X: pseudo-liquid phase; Y: pseudo-gas phase; S: slow phase; I: intermediate phase; F: fast phase;
[0016] Figure 3 Shown is a comparison of the calculated Px phase diagram and experimental data; Figure 4 Shown for The minimum tie line length for displacing crude oil varies with pressure; Figure 5 The results show that crude oil is transported in the bulk phase and in nanopores of different pore sizes at different pressures and 316.48 K. Comparison of the minimum tie length for displacement: (a) general view; (b) magnified view near the MMP. DETAILED DESCRIPTION
[0017] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.
[0018] See also Figure 1-Figure 5 The present invention provides an embodiment: a method for calculating the minimum miscible pressure in a nanopore considering three hydrocarbon phases, the steps of which are as follows: S1: Characterization of the impact of shale nanopores S11: Calculation of critical parameters of fluid components in nanopores According to the nanopore radius r and fluid size parameters , calculate the critical temperature in the nanopore and critical pressure Critical temperature of bulk fluid and critical pressure The relative error is then calculated based on the critical temperature and critical pressure of the bulk fluid. and , the calculation formula is as follows: =0.244 S12: Construction of pressure balance model in phase equilibrium with capillary forces When considering the presence of three hydrocarbon phases, the possible phase equilibriums in the phase equilibrium calculation include: gas phase and oil-rich liquid phase two-phase equilibrium ( equilibrium), gas phase and rich Liquid two-phase equilibrium ( balance), oil-rich liquid phase and rich Liquid two-phase equilibrium ( equilibrium) and gas phase, oil-rich liquid phase and rich Liquid three-phase equilibrium ( Balance), the pressure balance corresponding to the four phase balances is as follows Figure 1 As shown, the calculation formulas are: in, , and The gas phase, the oil-rich liquid phase and the The pressure of the liquid phase; , (or )and (or ) are respectively between the gas phase and the oil-rich liquid phase, and between the gas phase and the rich Between the liquid phase and the oil-rich liquid phase and the rich Capillary forces between liquid phases; The Young-Laplace equation is used to calculate the capillary force, and the formula is as follows: ,in represents interfacial tension (IFT); θ is the contact angle, θ is assumed to be zero. In order to characterize the effect of fluid composition on capillary force, the interfacial tension is calculated according to the following formula: in is the number of components; and are the densities of the wetting and non-wetting phases, respectively; and The wetting and non-wetting phases are represented by The mole fraction of each component; Indicates The Parachor constant of each component is calculated by the following formula: ,in It is The molecular mass of each component.
[0019] S2: Construction of the calculation algorithm for VL1L2 three-phase phase equilibrium in nanopores S21: Input the known pressure P, temperature T, and mole fraction of each component in the mixture , critical temperature, critical pressure, eccentricity factor, binary interaction coefficient BIP between components, wherein the critical temperature and critical pressure need to adopt the critical temperature and critical pressure in the nanopore calculated in step S1, and the BIP between hydrocarbon components is set to 0, The BIP between the hydrocarbon components is obtained by fitting the experimental points, as detailed in step S4.
[0020] S22: Perform stability test on a given mixture at specified pressure and temperature (this is a known algorithm in the field of phase behavior. To consider the influence of capillary forces, the compressibility factors of the test phase and the test phase must be compared in each iteration (which can be determined by the equation of state and is a well-known parameter in the field of phase behavior) to determine the test phase pressure and test phase pressure , if the compressibility factor of the test phase is low, then For a given pressure, equal Add capillary force between the two phases; otherwise, For a given pressure, equal Add capillary force between the two phases. ), if stable, end the calculation and output the molar fractions of each component of the initial mixture, and the molar fraction of the phase is set to 1; if unstable, proceed to step S23;
[0021] S23: Perform two-phase flash calculation (a known algorithm in the field of phase state, in order to consider the influence of nanopores, the pressure balance needs to be modified according to the first three pressure balance formulas corresponding to the four phase balances), and perform stability tests on the two balanced phases obtained by flash evaporation. If both are stable, output the fluid phase behavior characterization parameters such as the molar proportion of each phase of the two-phase fluid, the proportion of each component of the two phases, the two-phase pressure, and the capillary force. If any phase is unstable, proceed to step S24; S24: Three-phase Flash calculation (a known algorithm in the field of phase behavior. To consider the influence of nanopores, the pressure balance needs to be the last modification of the pressure balance formula corresponding to the four phase balances) outputs the molar proportion of each phase of the three-phase fluid, the proportion of each component in the three phases, the three-phase pressure, capillary force and other fluid phase behavior characterization parameters.
[0022] S3: Consideration in nanopores Construction of the MMP calculation algorithm for three phases S31: Inject gas G and crude oil O into two units respectively, place the unit containing gas upstream, and place the unit containing crude oil downstream, mix the injected gas and crude oil, and the composition of the resulting oil-gas mixture is determined by the following equation: in , and represent the molar proportion of each component in the obtained mixture, injected gas and crude oil, respectively, nc is the total number of components in the mixture, is the mole fraction of the gas phase, set to 0.5; S32: Under given temperature and pressure conditions, the oil-gas mixture is subjected to nanopore Three-phase phase equilibrium calculation, if the calculation result is two-phase or three-phase, then proceed to step S33, if it is found that the system is in single-phase equilibrium, then negative phase two-phase flash calculation (a known algorithm in the field of phase state) is performed to obtain two-phase equilibrium; S33: Classify the calculated equilibrium phases. In the case of three phases, the phase with the closest composition to the injected gas is defined as the fast phase F, the phase closest to the crude oil is defined as the slow phase S, and the remaining phases are designated as the intermediate phases I. In the case of only two phases, the phase with the closest composition to the injected gas is defined as the fast phase F, and the phase closest to the crude oil is defined as the slow phase S; S34: Calculate the tie length. When the calculation result is three-phase, the tie length between the F and S phases needs to be calculated and recorded separately. , the tie length between phases F and I , the tie length between I and S phases When the calculation result is two phases, only the length of the tie wire between phases F and S needs to be calculated and recorded. , the calculation formula of tie line length is as follows: in and represent the molar proportions of each component in the F, I, and S phases, respectively; S35: Determine the molar ratio of each component in the two phases required for the next contact and sort them. If the calculation result of step S32 is three phases, the S phase and the I phase are mixed in a ratio of 1:1 to obtain a new pseudo-liquid phase X; the F phase and the I phase are mixed in a ratio of 1:1 to obtain a new pseudo-gas phase Y. The molar ratio of each component in the X phase and the Y phase is calculated as follows: In the case of two phases, set the S phase to the X phase and the F phase to the Y phase. Figure 2 The positions shown in the second contact are arranged from left to right in the order of G, X, Y and O phases. The X phase is located in the unit close to the gas G injected at the rear end, while the Y phase is located in the unit close to the crude oil O at the front end. The phases in adjacent units are mixed in a 1:1 ratio from left to right to obtain a new mixture; S36: Repeat steps S32 to S35, mix the phases multiple times and perform phase equilibrium calculation and tie length calculation. Figure 2 The process shown in the figure is used to perform the 3rd to 100th miscible calculations. There are 100 three-phase phase equilibrium calculations in the 100th contact. These phase equilibrium calculations are numbered from 1 to 100 from left to right. The smallest phase equilibrium in the 100th contact is recorded. , and ; S37: Repeat steps S31 to S36 at different pressures, and record the minimum value of the 100th contact at the pressure. , and (If no three phases appear at this pressure, then there is no and ),when The pressure at which the length becomes zero is MMP.
[0023] S4: Consideration in nanopores Verification of the three-phase MMP calculation algorithm S41: Three-phase Stability testing and accuracy verification of the balancing algorithm Given a temperature, the three phases in the nanopore are applied Phase equilibrium calculation algorithm, calculates very small pressure and a certain component (such as ) changes (such as setting The change interval of the percentage is 0.1mol% and the change interval of the pressure is 0.1bar) to test the stability of the algorithm. When the molar percentage of a phase is zero, the corresponding values of P and x are the points on the envelope of the Px phase diagram. The Px phase diagram is drawn according to the values of P and x at each point on the envelope of the Px phase diagram. The agreement rate between the points on the phase diagram and the experimental test points is compared, and the adjustment is made. The binary interaction parameter BIP between the hydrocarbon components makes the agreement rate exceed 90% ( Figure 3 ); S42: Considerations in Nanopores Verification of the accuracy of the three-phase MMP calculation algorithm Plot the cross plot of pressure and the minimum tie length calculated at that pressure, and compare it with the theoretically calculated high-efficiency oil displacement pressure (Calculated and One of them is 0) and the pressure obtained by experimental test and the pressure of the inflection point of the recovery factor curve; if they are consistent, it means that the calculation result is accurate ( Figure 4 ); S5: Nanopore Analysis of the miscibility of shale oil Calculation of bulk and nanopores with different pore sizes The crossplot of the pressure of shale oil reverberation and the minimum tie length calculated under this pressure ( Figure 5 ), analyzing the efficient oil displacement pressure in bulk phase and nanopores with different pore sizes and the difference between MMP.
[0024] Through the above steps, by introducing the influence of shale nanopores and the three-phase phase equilibrium calculation algorithm, a method for accurately calculating the injection of hydrocarbons into shale reservoirs was invented. The MMP calculation algorithm for the coexistence of three hydrocarbon phases was used to analyze the effect of the coexistence of three hydrocarbon phases in nanopores. and the miscibility of shale oil, which can be used to accurately calculate the injection During the period when the three hydrocarbon phases coexist The key parameter MMP of flooding supports efficient and economical exploitation of shale oil and gas reservoirs to solve the problems of high predicted MMP values and inability to accurately calculate the injection pressure in shale reservoirs due to the influence of cross-ties. The problem of MMP when three hydrocarbon phases coexist.
[0025] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of those skilled in the art without departing from the spirit of the present invention.
Claims
1. A method for calculating the minimum miscible pressure in a nanopore considering three hydrocarbon phases, characterized in that: The steps are as follows: S1: Characterization of the impact of shale nanopores S11: Calculation of critical temperature and critical pressure of each component in the nanopore; S12: Construction of pressure balance model in phase equilibrium including capillary force; S2: In nanopores Construction of three-phase phase balance calculation algorithm S21: Input the known pressure P, temperature T, and mole fraction of each component in the mixture , the critical temperature and critical pressure of each component in the nanopore, the eccentricity factor, and the binary interaction coefficient BIP between the components; S22: Perform a stability test on a given mixture at a specified pressure and temperature. If the mixture is stable, the calculation is terminated and the molar fraction of each component of the initial mixture is output, and the molar fraction of the phase is set to 1. If the mixture is unstable, proceed to step S23. S23: Perform two-phase flash evaporation calculations and perform stability tests on the two equilibrium phases obtained by flash evaporation. If both are stable, output the fluid phase behavior characterization parameters such as the molar ratio of each phase of the two-phase fluid, the ratio of each component of the two phases, the two-phase pressure, and the capillary force. If any phase is unstable, proceed to step S24; S24: Three-phase Flash calculation; S3: Consideration in nanopores Construction of the MMP calculation algorithm for three phases S31: injecting gas G and crude oil O into two units respectively, and mixing the injected gas and crude oil in a ratio of 1:1 to obtain an oil-gas mixture; S32: Under given temperature and pressure conditions, the oil-gas mixture is subjected to nanopore Three-phase phase balance calculation, if the calculation result is two-phase or three-phase, proceed to step S33; If the system is found to be in single-phase equilibrium, a negative two-phase flash calculation is performed to obtain a two-phase equilibrium; S33: Classify the calculated equilibrium phases. In the case of three phases, the phase with the closest composition to the injected gas is defined as the fast phase F, the phase closest to the crude oil is defined as the slow phase S, and the remaining phases are designated as the intermediate phases I. In the case of only two phases, the phase with the closest composition to the injected gas is defined as the fast phase F, and the phase closest to the crude oil is defined as the slow phase S; S34: Calculate the tie length. When the calculation result is three-phase, the tie length between the F and S phases needs to be calculated and recorded separately. , the tie length between phases F and I , the tie length between I and S phases When the calculation result is two phases, only the length of the tie wire between phases F and S needs to be calculated and recorded. ; S35: Determine the molar proportion of each component in the two phases required for the next contact and sort them. If the calculation result of step S32 is three phases, the S phase and the I phase are mixed in a ratio of 1:1 to obtain a new pseudo-liquid phase X; the F phase and the I phase are mixed in a ratio of 1:1 to obtain a new pseudo-gas phase Y. In the case of two phases, the S phase is set as the X phase, and the F phase is set as the Y phase. The positions shown in the second contact are sorted from left to right in the order of G, X, Y and O phases. The X phase is located in the unit close to the gas G injected at the rear end, and the Y phase is located in the unit close to the crude oil O at the front end. The phases in adjacent units are mixed in a ratio of 1:1 from left to right to obtain a new mixture; S36: Repeat steps S32 to S35, mix the phases multiple times and perform phase equilibrium calculation and tie length calculation. According to the process, perform the 3rd to 100th mixed phase calculations. There are 100 three-phase phase equilibrium calculations in the 100th contact. These phase equilibrium calculations are numbered from 1 to 100 from left to right, and the smallest phase equilibrium calculation in the 100th contact is recorded. , and ; S37: Repeat steps S31 to S36 at different pressures, and record the minimum value of the 100th contact at the pressure. , and ,when The pressure when the length becomes zero is MMP; S4: Considerations in Nanopores Verification of the three-phase MMP calculation algorithm S41: Three-phase Stability testing and accuracy verification of balancing algorithms; S42: Considerations in Nanopores Verification of the accuracy of the three-phase MMP calculation algorithm Plot the cross plot of pressure and the minimum tie length calculated at that pressure, and compare it with the theoretically calculated high-efficiency oil displacement pressure If the pressure obtained from the experimental test and the pressure at the inflection point of the recovery factor curve are consistent, it means that the calculation result is accurate; S5: Nanopore And analysis of the miscibility of shale oil.
2. The method for calculating the minimum miscible pressure in nanopores considering three hydrocarbon phases according to claim 1, characterized in that: S24 outputs the fluid phase behavior characterization parameters such as the molar ratio of each phase of the three-phase fluid, the ratio of each component in the three-phase, the three-phase pressure, and the capillary force.
3. The method for calculating the minimum miscible pressure in nanopores considering three hydrocarbon phases according to claim 1, characterized in that: In S31, the unit containing gas is placed upstream, and the unit containing crude oil is placed downstream.
4. The method for calculating the minimum miscible pressure in nanopores considering three hydrocarbon phases according to claim 1, characterized in that: The negative two-phase flash calculation performed in S32 is a known algorithm in the field of phase behavior.
5. The method for calculating the minimum miscible pressure in nanopores considering three hydrocarbon phases according to claim 1, characterized in that: If no three phases appear at this pressure in S37, then it does not exist and .
6. The method for calculating the minimum miscible pressure in nanopores considering three hydrocarbon phases according to claim 1, characterized in that: The specific steps of S41 are: given temperature, applying the three phases in the nanopore Phase equilibrium calculation algorithm, calculates the phase behavior of the fluid when the pressure is very small and a certain component changes, such as setting The percentage change interval is 0.1mol% and the pressure change interval is 0.1bar to test the stability of the algorithm. When the molar percentage of a phase is zero, the corresponding P and x values are the points on the Px phase diagram envelope. The Px phase diagram is drawn according to the P and x values of each point on the Px phase diagram envelope. The agreement rate between the points on the phase diagram and the experimental test points is compared and adjusted. The binary interaction parameter (BIP) between the hydrocarbon components makes the agreement rate exceed 90%.
7. The method for calculating the minimum miscible pressure in a nanopore considering three hydrocarbon phases according to claim 1, characterized in that: S42 in For the calculated and One of them is 0 pressure.
8. The method for calculating the minimum miscible pressure in a nanopore considering three hydrocarbon phases according to claim 1, characterized in that: The specific steps of S5 are: calculate the volume phase and the nanopores with different pore sizes The cross plot of the pressure of shale oil reverberation and the minimum tie length calculated at this pressure is used to analyze the efficient oil recovery pressure in the bulk phase and nanopores with different pore sizes. and the difference between MMP.