Method for determining minimum miscible pressure of compact / shale oil and gas based on inter-unit simulation model

Abstract

According to the method for determining the minimum miscible pressure of the compact / shale oil and gas based on the inter-unit simulation model, the movement strategy of flash evaporation calculation and balance of the redundant volume of the mixture is adopted, and the calculation precision of the fluid volume is improved; meanwhile, the purpose of improving the accuracy of determining the minimum miscible pressure of the compact / shale oil and gas is achieved by adopting the double standards that the oil recovery rate is 97% and the minimum key line length is zero as the minimum miscible pressure of the oil and gas.

Description

Technical Field

[0001] This invention relates to a method for determining minimum miscibility pressure, and more particularly to a method for determining the minimum miscibility pressure of tight / shale oil and gas based on an inter-unit simulation model. Background Technology

[0002] Injecting carbon dioxide into oil reservoirs can both improve oil recovery and bury the greenhouse gas carbon dioxide within depleted reservoirs. Minimum miscibility pressure (MINOP) is one of the key parameters in the design and implementation of carbon dioxide injection projects. Accurate prediction of MINOP is crucial for parameter optimization, scheme design, and production forecasting in carbon dioxide injection projects.

[0003] In existing technologies, there are many methods for determining minimum miscibility pressure, such as experimental methods, empirical formula methods, and numerical simulations. Experimental methods can accurately predict the minimum miscibility pressure of oil and gas, but they suffer from drawbacks such as high cost and time consumption. Empirical formula methods are simple, fast, and low-cost. However, since empirical formulas are fitted based on specific reservoir or fluid properties, their applicability is narrow and their accuracy is not high. Due to the inherent shortcomings of experimental and empirical correlation methods, numerical simulation has become the most popular method for predicting minimum miscibility pressure of oil and gas, and it has a certain degree of accuracy. In the past few decades, researchers have attempted to develop numerical simulation methods based on equations of state to determine minimum miscibility pressure. The capillary simulation method is a direct calculation method that estimates minimum miscibility pressure by simulating capillary experiments using a one-dimensional component model. Due to the influence of numerical dispersion, the accuracy of the minimum miscibility pressure predicted by the capillary simulation method is not high. In addition, the simulation process of the capillary simulation method is cumbersome and time-consuming. By simplifying the mesh elements to mixing elements, the capillary simulation method can be further simplified into an inter-element simulation method. In the inter-unit simulation model, only the isobaric-isothermal phase equilibrium of the oil-gas mixture is considered, simulating the physical one-dimensional gas displacement process, and providing results for the final oil recovery and the minimum miscibility pressure. The method uses two criteria to determine the minimum miscibility pressure: 1. Tracking the final recovery at different pressures until the oil recovery reaches 97%; 2. Tracking the minimum critical line length at different pressures until it reaches zero.

[0004] The methods described above for determining minimum miscibility pressure are all applicable to predicting the minimum miscibility pressure of hydrocarbons in conventional reservoirs. However, due to the strong capillary pressure and confinement effect caused by the nanopores commonly found in tight / shale reservoirs, these aspects often lose accuracy when applied to tight / shale reservoirs. Summary of the Invention

[0005] To address the technical problems raised in the background section, it is necessary to provide a method for determining the minimum miscibility pressure of tight / shale oil and gas based on an inter-unit simulation model, which can improve the accuracy of determining the minimum miscibility pressure of tight / shale oil and gas.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for determining the minimum miscibility pressure of tight / shale oil and gas based on an inter-unit simulation model includes the following steps:

[0008] S1, Inter-cell simulation model initialization: Determine the basic characteristic parameters of crude oil and injected gas, and the model parameters of the inter-cell simulation model. The model parameters must include at least the total number of cells. The total number of batches of injected gas was calculated based on the fundamental characteristic parameters of crude oil and injected gas, and the model parameters of the inter-unit simulation model. ;

[0009] S2, will Each batch of injection gas is sequentially injected into the first unit. Inter-unit simulation models are used to perform calculations between each unit to obtain the minimum critical system length and the final oil recovery rate under different pressures. This includes the following steps:

[0010] S21, the i-th batch of injected gas and the initial oil in the first unit are first contacted and mixed to obtain an equilibrium gas-liquid phase. The feed composition of the first unit is calculated using the volumes of the injected gas and the initial oil.

[0011] S22, under a set pressure, flash evaporation calculations are performed using the feed composition to obtain the mole fraction, gas phase volume, liquid phase volume, and gas phase fraction of each component in the equilibrium mixture. And calculate the length of the critical tie line in contact between the injected gas and the fluid in the unit;

[0012] S23, Strategy for moving excess volume of the mixture to balance it: If If the resulting equilibrium mixture is a liquid phase, the liquid phase exceeding the volume of that unit is directly transferred to the next unit; if If the resulting equilibrium mixture exhibits two phases and the liquid phase volume is smaller than the unit volume, then the gas phase exceeding that unit volume is transferred to the next unit; if If the resulting equilibrium mixture is two-phase and the liquid phase volume is greater than the unit volume, then all the gas phase and the liquid phase exceeding the unit volume are transferred to the next unit.

[0013] S24, calculate the feed composition of the fluid in the next unit, then return to step S22 and repeat steps S22-S24 until the liquid phase exceeding the excess volume of the last unit is output from the last unit.

[0014] S25, Repeat steps S21-S24 until completion. The injection of each batch of gas was recorded, and the volume of liquid phase output from the last unit was used to calculate the final oil recovery rate. The minimum critical line length is selected from the critical line lengths of the initial injection gas contact with the initial oil.

[0015] S26. Based on the set initial pressure, increase the pressure according to the preset step size. If the set initial pressure is less than the minimum miscibility pressure, repeat the above steps S21-S25 and record the minimum critical system length and final oil recovery rate at each pressure.

[0016] S3. Based on the minimum critical line length under different pressures, the minimum critical line length relationship curves under different pressures are obtained. Based on the final oil recovery rate under different pressures, the oil recovery rate relationship curves under different pressures are obtained. Based on the minimum critical line length relationship curves and the oil recovery rate relationship curves under different pressures, the minimum miscibility pressure of oil and gas is determined by the line length method and the oil recovery rate method.

[0017] Furthermore, the fundamental characteristic parameters of crude oil and injected gas include: the composition of crude oil and injected gas, the components of each component, and the critical pressure of each component. Critical temperature Eccentricity factor Model parameters include: reservoir temperature. Initial pressure Unit volume Gas-oil ratio Total number of units and pore radius .

[0018] Furthermore, the total batches of injected gas Calculate according to the following formula:

[0019] ;

[0020] In the formula, This refers to the total batch of injected gas; This represents the total number of units; The gas-oil ratio is 1.2; the total injected gas volume is 1.2 times the pore volume, which is also the standard injected gas volume recognized in the capillary experiment, ensuring the best displacement efficiency of the injected gas.

[0021] Furthermore, in step S22, the critical line length for each batch of injected gas in contact with the initial oil is calculated according to the following formula:

[0022] ;

[0023] In the formula, The critical tie length for each batch of injected gas in contact with the initial oil. In the liquid phase Mole fraction of the component; In the middle of the gas phase Mole fraction of the component; To balance the total number of components in the gas and liquid phases.

[0024] Furthermore, the flash calculation includes the following steps:

[0025] A1, Set the initial capillary pressure to zero. =0;

[0026] A2, Calculation of mole fraction of gas and liquid phases: The mole fraction of gas and liquid phases is calculated using the Rachford-Rice equation. , and :

[0027]

[0028] In the formula: for The gas phase fraction of the components; for Total mole fraction of the components; This is the initial gas-liquid equilibrium constant;

[0029] A3, Fugacity Calculation of Gas and Liquid Phases: The fugacity coefficients of the gas and liquid phases are calculated using the Peng-Robinson equation of state with volume shift, as shown in the following equation:

[0030]

[0031]

[0032] In the formula: and is the constant of the equation of state for the gas phase. and B L The constant of the equation of state for the liquid phase; It is the liquid phase compressibility factor; It is the gas phase compressibility factor; In the liquid phase Mole fraction of the component; In the middle of the gas phase Mole fraction of the component; To balance the total number of components in the gas and liquid phases; In the middle of the gas phase Fugacity of components; In the liquid phase Fugacity of components; In the liquid phase Fugacity coefficient of the component; In the middle of the gas phase The fugacity coefficient of the component; P L P is the liquid phase pressure; V This refers to the gas phase pressure. Components The repulsive constant, Components With components The gravitational constant between them;

[0033] A4. Substituting the obtained mole fractions of the gas and liquid phases and the fugacity of the gas and liquid phases into the gas-liquid equilibrium criterion in the following formula, the error is: :

[0034]

[0035] The relationship between capillary pressure and gas-liquid phase pressure in nanopores is given by the following equation:

[0036]

[0037] In the formula, For capillary pressure; set =Initial pressure;

[0038] A5. If the liquid phase equilibrium criterion is met, stop the flash evaporation calculation; if the gas-liquid phase equilibrium criterion is not met, update the calculation using the following equation. Repeat steps A2-A4 above until the gas-liquid equilibrium criterion is met:

[0039]

[0040] In the formula: for The gas-liquid equilibrium constant of the components; This represents the number of iterations.

[0041] A6, Capillary pressure calculation: Calculate the gas phase molar density of each component. and liquid phase molar density V v V is the molar volume of the gas phase. L The liquid phase molar volume is given; the gas phase molar volume and liquid phase molar volume are calculated using the Peng-Robinson equation of state with volume shift, as shown in the following equation:

[0042]

[0043]

[0044] In the formula: c is the volume translation; This refers to the gas phase pressure. This refers to the gas phase pressure. This is the universal gas constant, typically taken as 8.314 J / (mol·K). -1 ; For reservoir temperature; This represents the molar volume of the gas phase. This is the molar volume of the liquid phase; and The parameters describing intermolecular interactions and occupied volume are expressed as follows:

[0045]

[0046]

[0047]

[0048]

[0049]

[0050] In the formula: For temperature comparison, ; It is the eccentricity factor; This is the critical temperature of the pores. The critical pore pressure is then determined, and the capillary pressure is calculated. ;

[0051] A7, Substitute the calculated capillary pressure into the capillary pressure criterion in the following formula, the error is... :

[0052] ;

[0053] If the capillary pressure criterion is not met, replace the old capillary pressure with the new capillary pressure, and then update according to step A5. Repeat steps A2-A7 above until the capillary pressure criterion is met.

[0054] Furthermore, the method for calculating capillary pressure in step A6 includes:

[0055] The gas phase molar density of each component in the gas-liquid phase was calculated. and liquid phase molar density Then, the gas-liquid interfacial tension is calculated according to the following Macleod-Sugden equation. :

[0056]

[0057] In the formula, for Parachor constant of the component; The liquid phase molar density; The gas phase molar density;

[0058] The capillary pressure is calculated using the Young-Laplace equation, as shown below:

[0059]

[0060] In the formula, Gas-liquid interfacial tension; Let be the gas-liquid phase contact angle; based on experimental results in the literature, assume... It is 30°; Where is the pore radius.

[0061] Furthermore, the gas-liquid equilibrium constants of each component are initialized using the Wilson equation as follows. :

[0062]

[0063] In the formula, The initial pressure is set. For reservoir temperature; For the first Critical temperature of the component; For the first Critical pressure of the component; For the first The eccentricity factor of the component.

[0064] Furthermore, the critical temperature and critical pressure of each component in the gas-liquid phase are calculated using the critical property migration model, as shown in the following equation:

[0065]

[0066]

[0067]

[0068]

[0069] In the formula, The bulk critical temperature, also known as the first... Critical temperature of the component; This is the critical temperature within the pores. This is the bulk critical pressure, which is also the critical pressure of the i-th component; The critical pressure within the pores; For Lennard-Jones dimensional parameters; Where is the pore radius.

[0070] Furthermore, the final oil recovery rate is calculated using the following formula:

[0071]

[0072] In the formula, The final oil recovery rate after 1.2 PV gas injection; The initial oil volume at 1 atm and 298 K; The volume of oil extracted from the last unit at 1 atm and 298 K.

[0073] Furthermore, in step S3, when determining the minimum miscibility pressure of oil and gas using the tie-line length method, the minimum miscibility pressure of oil and gas is determined by extrapolating the minimum critical tie-line length using a polynomial at the last 5 pressures. The polynomial is shown in the following equation:

[0074] ;

[0075] In the formula, and It is a constant; for The intercept of the axis, For pressure; The minimum critical tie length for each batch of injected gas to come into contact with the fluid in the unit.

[0076] By adopting the above technical solution, the present invention has the following beneficial effects:

[0077] The present invention provides a method for determining the minimum miscibility pressure of tight / shale oil and gas based on an inter-unit simulation model. This method employs a flash calculation plus a strategy of moving excess volume of the equilibrium mixture, which improves the accuracy of fluid volume calculation. At the same time, it uses a dual standard of 97% oil recovery rate and zero minimum critical line length to determine the minimum miscibility pressure of oil and gas, thereby improving the accuracy of determining the minimum miscibility pressure of tight / shale oil and gas. Attached Figure Description

[0078] Figure 1 The flowchart illustrates a preferred embodiment of the present invention for determining the minimum miscibility pressure of tight / shale oil and gas based on an inter-unit simulation model.

[0079] Figure 2 This is a flowchart of flash evaporation calculation in a preferred embodiment of the present invention.

[0080] Figure 3 This is a schematic diagram of the inter-unit simulation model for the method of determining the minimum miscibility pressure of tight / shale oil and gas based on the inter-unit simulation model, which is a preferred embodiment of the present invention.

[0081] Figure 4 This is a schematic diagram illustrating the transfer of excess volume from one unit to the next in the method for determining the minimum miscibility pressure of tight / shale oil and gas based on an inter-unit simulation model, which is a preferred embodiment of the present invention.

[0082] Figure 5 This is the curve showing the relationship between the minimum critical line length and pressure.

[0083] Figure 6 A schematic diagram for extrapolating the minimum miscibility pressure using the minimum critical line length.

[0084] Figure 7 This is a curve showing the relationship between oil recovery rate and pressure. Detailed Implementation

[0085] Please see Figure 1 A preferred embodiment of the present invention provides a method for determining the minimum miscibility pressure of tight / shale oil and gas based on an inter-unit simulation model, comprising the following steps:

[0086] S1, Inter-cell simulation model initialization: Determine the basic characteristic parameters of crude oil and injected gas, and the model parameters of the inter-cell simulation model. The model parameters must include at least the total number of cells. The total number of batches of injected gas was calculated based on the fundamental characteristic parameters of crude oil and injected gas, and the model parameters of the inter-unit simulation model. .

[0087] In this embodiment, the basic characteristic parameters of crude oil and injected gas include at least: the composition of crude oil and injected gas, the components of each component, and the critical pressure of each component. Critical temperature reservoir temperature Initial pressure ( (less than minimum miscibility pressure), pressure increase step size (e.g., 0.1 MP), eccentricity factor .

[0088] The model parameters should include at least: cell volume ( ), gas-oil ratio ( ), Total number of units ( ) and pore radius ( ).

[0089] Total number of batches of injected gas N b Calculate according to the following formula:

[0090] (1);

[0091] In the formula, This refers to the total batch of injected gas; This represents the total number of units; The gas-oil ratio is 1.2; the total injected gas volume is 1.2 times the pore volume (PV), which is also the standard injected gas volume recognized in capillary experiments, ensuring the best displacement efficiency of the injected gas.

[0092] S2, will Each batch of injection gas is sequentially injected into the first unit. Inter-unit simulation models are used to perform calculations between each unit to obtain the minimum critical system length and the final oil recovery rate under different pressures. This includes the following steps:

[0093] S21, the i-th batch of injected gas and the initial oil in the first unit are first contacted and mixed to obtain an equilibrium gas-liquid phase. The feed composition of the first unit is calculated using the volumes of the injected gas and the initial oil.

[0094] The volume of the i-th batch of injected gas is calculated as follows: Assume all cells are initially filled with initial oil and achieve complete mixing at each contact. Therefore, the feed composition can be calculated using the volume of injected gas and the fluid in the cells. Specifically, In the formula, This represents the total mole fraction of component j in the feed. This represents the total mole fraction of fluid component j in the unit. , This represents the total mole fraction of component j in the injected gas. This is the ratio of the number of moles of injected gas to the number of moles of fluid in the unit. Number of moles of injected gas = GOR × Gas molar volume, number of fluid moles in the unit = Fluid molar volume, therefore, =GOR × fluid molar volume / gas molar volume.

[0095] S22, under a set pressure, flash evaporation calculations are performed using the feed composition to obtain the mole fraction, gas phase volume, liquid phase volume, and gas phase fraction of each component in the equilibrium mixture. The critical tie length between the injected gas and the fluid in the unit is calculated. Step S22 specifically includes the following steps:

[0096] A1, Set the initial capillary pressure to zero ( );

[0097] A2, Calculation of mole fraction of gas and liquid phases: The mole fraction of gas and liquid phases is calculated using the Rachford-Rice equation. , and :

[0098] ;

[0099] In the formula: for The gas phase fraction of the components; for Total mole fraction of the components; In the liquid phase Mole fraction of the component; In the middle of the gas phase Mole fraction of the component; To initialize the initial gas-liquid equilibrium constants, the Wilson equation is used to initialize the gas-liquid equilibrium constants of each component. :

[0100]

[0101] In the formula, For the set initial pressure, 10 -1 MPa; Let K be the reservoir temperature. For the first Critical temperature of the component, K; For the first Critical pressure of the component, 10 -1 MPa; For the first The eccentricity factor of the component.

[0102] In this embodiment, the critical temperature and critical pressure of each component in the gas-liquid phase are calculated using the critical property shift model, as shown in the following formula:

[0103]

[0104]

[0105]

[0106]

[0107] In the formula, The bulk critical temperature, also known as the first... Critical temperature of the component, K; The critical temperature within the pores, in K; The critical pressure of the bulk phase, also known as the first Critical pressure of the component, 10 -1 MPa; The critical pressure within the pores, 10 -1 MPa; The Lennard-Jones dimension parameter (collision diameter, obtained through experimental fitting), in nm; Where is the pore radius, in nm.

[0108] A3, Calculation of fugacity in gas and liquid phases: The fugacity coefficients of the gas and liquid phases are calculated using the Peng-Robinson equation of state with volume shift, as shown in formulas (8) and (9) below:

[0109]

[0110]

[0111] In the formula: and B v is the constant of the equation of state for the gas phase. and B L Z is the constant of the equation of state for the liquid phase; L It is the liquid phase compressibility factor; It is the gas phase compressibility factor; In the liquid phase Mole fraction of the component; In the middle of the gas phase Mole fraction of the component; To balance the total number of components in the gas and liquid phases; In the middle of the gas phase Fugacity of components; In the liquid phase Fugacity of components; In the liquid phase Fugacity coefficient of the component; In the middle of the gas phase Fugacity coefficient of the component; For liquid phase pressure, 10 - 1 MPa; For gas phase pressure, 10 -1 MPa; Components The repulsive constant, Components With components The gravitational constant between them.

[0112] A4, substituting the obtained mole fractions of the gas and liquid phases and the fugacity of the gas and liquid phases into the gas-liquid equilibrium criterion (10), the error is... :

[0113]

[0114] The relationship between capillary pressure and gas-liquid phase pressure in nanopores is given by the following equation:

[0115]

[0116] In the formula, For capillary pressure, 10 -1 MPa; setting Initial pressure;

[0117] A5. If the liquid phase equilibrium criterion is met, stop the flash evaporation calculation; if the gas-liquid phase equilibrium criterion is not met, update equation (12). Repeat steps A2-A4 above until the gas-liquid equilibrium standard is met, then proceed to step A6:

[0118]

[0119] In the formula: for The gas-liquid equilibrium constant of the components; This represents the number of iterations.

[0120] A6, Capillary pressure calculation: Calculate the gas phase molar density of each component. and liquid phase molar density V v V is the molar volume of the gas phase. L Let be the liquid phase molar volume. The gas phase molar volume and liquid phase molar volume are calculated using the Peng-Robinson equation of state with volume shift, as shown in the following equation:

[0121]

[0122]

[0123] In the formula: c is the volume translation; The pressure is the gas phase pressure, in Pa. The pressure is the gas phase pressure, in Pa. This is the universal gas constant, typically taken as 8.314 J / (mol·K). -1 ; Let K be the reservoir temperature. m is the molar volume of the gas phase. 3 .mol -1 ; m is the molar volume of the liquid phase. 3 .mol -1 ; and The parameters describing intermolecular interactions and occupied volume are expressed as follows:

[0124]

[0125]

[0126]

[0127]

[0128]

[0129] In the formula: For temperature comparison, ; This is the critical temperature of the pores. This is the critical pressure of the pores.

[0130] Then calculate the capillary pressure. Specifically, capillary pressure The calculation methods include:

[0131] The gas phase molar density of each component in the gas-liquid phase was calculated. and liquid phase molar density Then, the gas-liquid interfacial tension was calculated according to the Macleod-Sugden equation (13). :

[0132]

[0133] In the formula, for Parachor constant of the component; The liquid phase molar density is expressed in mol / cm³. 3 ; The gas phase molar density is expressed in mol / cm³. 3 ;

[0134] The capillary pressure is calculated using the Young-Laplace equation, as shown below:

[0135]

[0136] In the formula, Gas-liquid interfacial tension, mN / m; Let be the gas-liquid phase contact angle; based on experimental results in the literature, assume... It is 30°.

[0137] A7, Substitute the calculated capillary pressure into the capillary pressure criterion (15), the error is :

[0138]

[0139] If the capillary pressure criterion is not met, the old capillary pressure is updated with the new capillary pressure, and then updated using equation (12). Repeat steps A2-A7 above until the capillary pressure criterion is met.

[0140] The critical tie length between each batch of injected gas and the initial oil is calculated using the following formula:

[0141] ;

[0142] In the formula, The critical tie length for each batch of injected gas in contact with the initial oil. In the liquid phase Mole fraction of the component; In the middle of the gas phase Mole fraction of the component.

[0143] S23, Strategy for moving excess volume of the equilibrium mixture: Strategy for moving excess volume of the equilibrium mixture: If If the resulting equilibrium mixture is a liquid phase, the liquid phase exceeding the volume of that unit is directly transferred to the next unit; if If the resulting equilibrium mixture exhibits two phases and the liquid phase volume is smaller than the unit volume, then the gas phase exceeding that unit volume is transferred to the next unit; if If the resulting equilibrium mixture exhibits two phases and the liquid phase volume is greater than the unit volume, then all the gas phase and the liquid phase exceeding the unit volume are transferred to the next unit.

[0144] S24, calculate the feed composition of the fluid in the next unit, then return to step S22, repeat steps S22-S24 until the liquid phase exceeding the excess volume of the last unit is output from the last unit.

[0145] S25, Repeat steps S21-S24 until completion. Each batch of injected gas (i.e., 1.2 PV of gas is injected) is used to record the volume of liquid phase output from the last unit for calculating the final oil recovery rate. The calculated value is then used to... The minimum critical line length is selected from the line lengths of the injected gas in contact with the initial oil.

[0146] In this embodiment, the final oil recovery rate is calculated using the following formula:

[0147]

[0148] In the formula, The final oil recovery rate after 1.2 PV gas injection; The initial oil volume at 1 atm and 298 K; The volume of oil extracted from the last unit at 1 atm and 298 K.

[0149] S26. Based on the set initial pressure, increase the pressure according to the preset step size. If the set initial pressure is less than the minimum miscibility pressure, repeat the above steps S21-S25 and record the minimum critical system length and final oil recovery rate at each pressure.

[0150] S3. Based on the minimum critical line length under different pressures, the minimum critical line length relationship curves under different pressures are obtained. Based on the final oil recovery rate under different pressures, the oil recovery rate relationship curves under different pressures are obtained. Based on the minimum critical line length relationship curves and the oil recovery rate relationship curves under different pressures, the minimum miscibility pressure MMP of oil and gas is determined by the line length method and the oil recovery rate method.

[0151] When using the tie-line length method to determine the minimum miscibility pressure (MMP) of oil and gas, theoretically, the pressure corresponding to the minimum critical tie-line length reaching zero is the minimum miscibility pressure (MMP). However, when the pressure approaches MMP, the calculation is difficult to converge. To effectively solve this problem, in this embodiment, the minimum critical tie-line length is extrapolated using a polynomial for the last five pressures. The polynomial is shown in formula (18):

[0152]

[0153] In the formula, and It is a constant; for The intercept of the axis, For pressure; The minimum critical tie length for each batch of injected gas to come into contact with the fluid in the unit.

[0154] Determine parameters , , When calculating the numerical values, pressure is used as the x-axis and the minimum critical line length as the y-axis. The curve is obtained by fitting the curve using the last 5 pressure data points. The correlation coefficient is closer to 1, indicating a better curve fit. It is recommended to determine the parameters. , and hour, .

[0155] Theoretically, the pressure corresponding to the minimum critical line length reaching zero is the minimum miscibility pressure (MMP). Since the algorithm has difficulty converging near the critical point, the calculation stops when the minimum critical line length is close to zero. To obtain the minimum miscibility pressure, the last five pressure points are taken, and the fitted curve is extrapolated to the pressure value corresponding to the minimum critical line length being zero; this is the minimum miscibility pressure.

[0156] In this embodiment, the oil and gas MMP determined using the tether length method and the oil recovery rate method are used to cross-verify the accuracy of the MMP. Generally, calculations are performed at constant temperature under different pressures. If the MMP determined by the tie length method is close to the inflection point of oil recovery, then the determined MMP value is considered reasonable.

[0157] The method for determining the minimum miscibility pressure of tight / shale oil and gas based on an inter-unit simulation model according to the present invention will be described below with specific embodiments.

[0158] Implementation Case 1

[0159] At a reservoir temperature of 71.1℃, pure CO2 displaced a three-component simulated oil (23% CH4+, 30% n-C4+, 45% nC4+). 10 ), set pore radius =20 nm.

[0160] Inter-unit simulation model initialization: Input the basic characteristic parameters of crude oil and injected gas, reservoir temperature T (71.1℃), initial pressure P0 (less than the minimum miscibility pressure), and pressure increment step size. (e.g., 0.1 MPa), as shown in Table 1. Model parameters: Set the total number of elements. pore radius ( =20 nm) and gas-oil ratio ( ), unit volume The value is 1 mL. The total batch size of injected gas is calculated using formula (1). =4000).

[0161] Table 1. Simulated oil and gas composition, component properties, and binary interaction parameters

[0162]

[0163] In Table 1, is the molecular weight.

[0164] Through steps S2-S6, inter-unit simulation models are used to perform calculations on a unit-by-unit basis, obtaining the minimum critical line length relationship curves and oil recovery rate relationship curves under different pressures. The minimum critical line length relationship curves under different pressures are as follows: Figure 5 As shown, from Figure 5 The last 5 data points were selected and polynomial extrapolation was performed until the minimum critical line length was zero (as follows). Figure 6 As shown in the figure, the minimum miscibility pressure was found to be 11.72 MPa. The oil recovery curves obtained under different pressures are shown in the figure. Figure 7 As shown, the inflection point of the oil recovery rate curve under different pressures corresponds to a pressure of 11.65 MPa. The two are close (for example, the relative error between the two does not exceed 2%). The average of the minimum miscibility pressure determined by the two methods is taken as the final determined MMP, that is, (11.72+11.65) / 2=11.685 MPa.

[0165] Implementation Case 2

[0166] At a reservoir temperature of 115.6 ℃, pure CO2 was used to displace Bakken shale oil, with the pore radius set... =100 nm.

[0167] Inter-unit simulation model initialization: Input the basic characteristic parameters of crude oil and injected gas, reservoir temperature (T=115.6 ℃), initial pressure P0 (less than the minimum miscibility pressure), and pressure increment step size. (e.g., 0.1 MPa), as shown in Table 2. Model parameters: Set the total number of elements. Unit volume ( pore radius The ratio of gasoline to oil ( The total number of injected gas batches is calculated using formula (1). =4000).

[0168] Table 2 Composition and physical properties of Bakken shale oil

[0169]

[0170] Through steps S2-S6, inter-unit simulation models are used to perform calculations on an inter-unit basis to obtain the minimum critical line length relationship curves and oil recovery rate relationship curves under different pressures. Then, the last 5 data points are selected for polynomial extrapolation until the minimum critical line length is zero, yielding a minimum miscibility pressure of 23.10 MPa. The obtained oil recovery rate relationship curves under different pressures show an inflection point at a pressure of 22.87 MPa. Since these two methods are close, the average of the minimum miscibility pressures determined by both methods is used as the final determined MMPa.

[0171] The above description is a detailed description of the preferred embodiments of the present invention. However, the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modifications made under the technical spirit of the present invention should fall within the patent scope covered by the present invention.

Claims

1. A method for determining the minimum miscibility pressure of tight / shale oil and gas based on an inter-unit simulation model, characterized in that, Includes the following steps: S1, Inter-cell simulation model initialization: Determine the basic characteristic parameters of crude oil and injected gas, and the model parameters of the inter-cell simulation model. The model parameters must include at least the total number of cells. The total number of batches of injected gas was calculated based on the fundamental characteristic parameters of crude oil and injected gas, and the model parameters of the inter-unit simulation model. ; S2, will Each batch of injection gas is sequentially injected into the first unit. Inter-unit simulation models are used to perform calculations between each unit to obtain the minimum critical system length and the final oil recovery rate under different pressures. This includes the following steps: S21, the i-th batch of injected gas and the initial oil in the first unit are first contacted and mixed to obtain an equilibrium gas-liquid phase. The feed composition of the first unit is calculated using the volumes of the injected gas and the initial oil. S22, under a set pressure, flash evaporation calculations are performed using the feed composition to obtain the mole fraction, gas phase volume, liquid phase volume, and gas phase fraction of each component in the equilibrium mixture. And calculate the length of the critical tie line in contact between the injected gas and the fluid in the unit; S23, Strategy for moving excess volume of the mixture to balance it: If If the resulting equilibrium mixture is a liquid phase, the liquid phase exceeding the volume of that unit is directly transferred to the next unit; if If the resulting equilibrium mixture exhibits two phases and the liquid phase volume is smaller than the unit volume, then the gas phase exceeding the unit volume will be transferred to the next unit; for example... If the resulting equilibrium mixture is two-phase with the liquid phase volume greater than the unit volume, then all the gas phase and the liquid phase exceeding the unit volume are transferred to the next unit. S24, calculate the feed composition of the fluid in the next unit, then return to step S22 and repeat steps S22-S24 until the liquid phase exceeding the excess volume of the last unit is output from the last unit. S25, Repeat steps S21-S24 until completion. The injection of each batch of gas was recorded, and the volume of liquid phase output from the last unit was used to calculate the final oil recovery rate. The minimum critical line length is selected from the critical line lengths of the initial injection gas contact with the initial oil. S26. Based on the set initial pressure, increase the pressure according to the preset step size. If the set initial pressure is less than the minimum miscibility pressure, repeat the above steps S21-S25 and record the minimum critical system length and final oil recovery rate at each pressure. S3. Based on the minimum critical line length under different pressures, the minimum critical line length relationship curves under different pressures are obtained. Based on the final oil recovery rate under different pressures, the oil recovery rate relationship curves under different pressures are obtained. Based on the minimum critical line length relationship curves and the oil recovery rate relationship curves under different pressures, the minimum miscibility pressure of oil and gas is determined by the line length method and the oil recovery rate method.

2. The method for determining the minimum miscibility pressure of tight / shale oil and gas based on an inter-unit simulation model as described in claim 1, characterized in that, The fundamental characteristic parameters of crude oil and injected gas include: the composition of crude oil and injected gas, the components of each component, and the critical pressure of each component. Critical temperature Eccentricity factor Model parameters include: reservoir temperature. Initial pressure Unit volume Gas-oil ratio Total number of units and pore radius .

3. The method for determining the minimum miscibility pressure of tight / shale oil and gas based on an inter-unit simulation model as described in claim 2, characterized in that, Total batches of injected gas Calculate according to the following formula: ； In the formula, This refers to the total batch of injected gas; This represents the total number of units; The gas-oil ratio; 1.2 means that the total volume of injected gas is 1.2 times the pore volume, which is also the standard volume of injected gas recognized in capillary experiments, ensuring the best displacement efficiency of the injected gas.

4. The method for determining the minimum miscibility pressure of tight / shale oil and gas based on an inter-unit simulation model as described in claim 1, characterized in that, In step S22, the critical line length for each batch of injected gas in contact with the initial oil is calculated according to the following formula: ； In the formula, The critical tie length for each batch of injected gas in contact with the initial oil. In the liquid phase Mole fraction of the component; In the middle of the gas phase Mole fraction of the component; To balance the total number of components in the gas and liquid phases.

5. The method for determining the minimum miscibility pressure of tight / shale oil and gas based on an inter-unit simulation model as described in claim 2, characterized in that, Flash evaporation calculations include the following steps: A1, Set the initial capillary pressure to zero. ; A2, Calculation of mole fraction of gas and liquid phases: The mole fraction of gas and liquid phases is calculated using the Rachford-Rice equation. , and : In the formula: for The gas phase fraction of the components; for Total mole fraction of the components; This is the initial gas-liquid equilibrium constant; A3, Fugacity Calculation of Gas and Liquid Phases: The fugacity coefficients of the gas and liquid phases are calculated using the Peng-Robinson equation of state with volume shift, as shown in the following equation: In the formula: and is the constant of the equation of state for the gas phase. and B L Z is the constant of the equation of state for the liquid phase; L It is the liquid phase compressibility factor; It is the gas phase compressibility factor; In the liquid phase Mole fraction of the component; In the middle of the gas phase Mole fraction of the component; To balance the total number of components in the gas and liquid phases; In the middle of the gas phase Fugacity of components; In the liquid phase Fugacity of components; In the liquid phase Fugacity coefficient of the component; In the middle of the gas phase Fugacity coefficient of the component; Liquid phase pressure; This refers to the gas phase pressure. Components The repulsive constant, Components With components The gravitational constant between them; A4. Substituting the obtained mole fractions of the gas and liquid phases and the fugacity of the gas and liquid phases into the gas-liquid equilibrium criterion in the following formula, the error is: : The relationship between capillary pressure and gas-liquid phase pressure in nanopores is given by the following equation: In the formula, For capillary pressure; set =Initial pressure; A5. If the liquid phase equilibrium criterion is met, stop the flash evaporation calculation; if the gas-liquid phase equilibrium criterion is not met, update using the following equation. Repeat steps A2-A4 above until the gas-liquid equilibrium criterion is met: In the formula: for The gas-liquid equilibrium constant of the components; This represents the number of iterations. A6, Capillary pressure calculation: Calculate the gas phase molar density of each component. and liquid phase molar density V V This represents the molar volume of the gas phase. The liquid phase molar volume, gas phase molar volume, and liquid phase molar volume are calculated using the Peng-Robinson equation of state with volume shift, as shown in the following equation: In the formula: c is the volume translation; This refers to the gas phase pressure. Liquid phase pressure; This is the universal gas constant, typically taken as 8.314 J / (mol·K). -1 ; For reservoir temperature; and The parameters describing intermolecular interactions and occupied volume are expressed as follows: In the formula: For temperature comparison, ; It is the eccentricity factor; This is the critical temperature of the pores. The critical pore pressure is then determined, and the capillary pressure is calculated. ; A7, Substitute the calculated capillary pressure into the capillary pressure criterion in the following formula, the error is... : ； If the capillary pressure criterion is not met, replace the old capillary pressure with the new capillary pressure, and then update according to step A5. Repeat steps A2-A7 above until the capillary pressure criterion is met.

6. The method for determining the minimum miscibility pressure of tight / shale oil and gas based on an inter-unit simulation model as described in claim 5, characterized in that, The method for calculating capillary pressure in step A6 includes: The gas phase molar density of each component in the gas-liquid phase was calculated. and liquid phase molar density Then, the gas-liquid interfacial tension is calculated according to the following Macleod-Sugden equation. : In the formula, for Parachor constant of the component; The liquid phase molar density; The gas phase molar density; The capillary pressure is calculated using the Young-Laplace equation, as shown below: In the formula, For gas-liquid interfacial tension; Let be the gas-liquid phase contact angle. Based on experimental results in the literature, assume... It is 30°; Where is the pore radius.

7. The method for determining the minimum miscibility pressure of tight / shale oil and gas based on an inter-unit simulation model as described in claim 5, characterized in that, The gas-liquid equilibrium constants of each component are initialized using the Wilson equation as follows. : In the formula, The initial pressure is set. For reservoir temperature; For the first Critical temperature of the component; For the first Critical pressure of the component; For the first The eccentricity factor of the component.

8. The method for determining the minimum miscibility pressure of tight / shale oil and gas based on an inter-unit simulation model as described in claim 7, characterized in that, The critical temperature and critical pressure of each component in the gas-liquid phase are calculated using the critical property migration model, as shown in the following equation: In the formula, The bulk critical temperature, also known as the first... Critical temperature of the component; This is the critical temperature within the pores. The critical pressure of the bulk phase, also known as the first Critical pressure of the component; The critical pressure within the pores; For Lennard-Jones dimensional parameters; Where is the pore radius.

9. The method for determining the minimum miscibility pressure of tight / shale oil and gas based on an inter-unit simulation model as described in claim 1, characterized in that, The final oil recovery rate is calculated using the following formula: In the formula, The final oil recovery rate after 1.2 PV gas injection; The initial oil volume at 1 atm and 298 K; The volume of oil extracted from the last unit at 1 atm and 298 K.

10. The method for determining the minimum miscibility pressure of tight / shale oil and gas based on an inter-unit simulation model as described in claim 7, characterized in that, In step S3, when determining the minimum miscibility pressure of oil and gas using the tie-line length method, the minimum miscibility pressure is determined by extrapolating the minimum critical tie-line length using a polynomial at the last five pressures. The polynomial is shown in the following equation: ； In the formula, and It is a constant; for The intercept of the axis, For pressure; The minimum critical tie length for each batch of injected gas to come into contact with the fluid in the unit.

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