CN111256900B - Method and device for determining minimum miscible phase pressure of oil gas - Google Patents
Method and device for determining minimum miscible phase pressure of oil gas Download PDFInfo
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Abstract
The invention provides a method and a device for determining minimum miscible phase pressure of oil gas, wherein the method comprises the steps of determining initial gas phase fugacity and initial liquid phase fugacity of each component according to molar composition, an initial gas-liquid equilibrium constant, an initial capillary pressure value and fluid adsorption parameters in pores; updating gas-liquid equilibrium constants of all components of the crude oil sample after gas injection; determining the interfacial tension and capillary pressure of the gas-injected crude oil sample according to the updated gas-liquid equilibrium constant of each component of the gas-injected crude oil sample; and determining the minimum miscible pressure of the initial crude oil sample and the injected gas according to the interfacial tension and the capillary pressure. The method introduces fluid adsorption parameters in the pores in the calculation process, considers the influence of the fluid adsorption in the pores, and can be used for calculating the mole fraction of each component in the gas-liquid equilibrium of a gas-injected crude oil sample under the condition of nanometer pores, thereby being used for conventional oil reservoirs and determining the minimum miscible phase pressure of oil gas of unconventional oil reservoirs.
Description
Technical Field
The invention relates to the technical field of oil and gas field development and gas injection for improving recovery efficiency, in particular to a method and a device for determining minimum miscible phase pressure of oil and gas.
Background
Injecting gas (e.g. CO)2) The oil displacement has the advantages of wide application range, obvious effect of improving the recovery ratio and the like, and has huge application potential in oil exploitation, particularly in tight oil exploitation. The gas injection flooding is divided into miscible flooding and immiscible flooding, and the oil displacement efficiency of the miscible flooding is far higher than that of the immiscible flooding. Determining the Minimum Miscible Pressure (MMP) of the injected gas and the crude oil is an important research context in formulating gas injection enhanced recovery schemes and economic evaluations.
The existing methods for determining the minimum miscible pressure are divided into an experimental method, an empirical formula method and a state equation method. The experimental determination is the main method for obtaining the minimum miscible pressure, but the experimental determination has complex flow, large experimental workload and long consumption time, and the time is about 1-2 weeks. The minimum mixed phase pressure is calculated by an empirical formula, so that the method is simple and convenient, but the theoretical basis is not strong, the reliability is poor, the method can be used for pre-screening or rough feasibility research, and high-temperature and high-CH (channel) conditions are met4And N2The content, high gas-oil ratio and other special crude oil need to be further added with related parameters to improve the calculation accuracy. In addition, the mole fraction of each component in the gas and liquid equilibrium can be calculated by using a state equation and then substituted into a miscible rule function FmWhen F ismThe minimum miscible pressure is obtained when the pressure approaches zero or a negative value. However, this criterion is not ideal. First, different oil samples FmThe initial value difference is very large, and can reach several orders of magnitude, and F is uniformly combinedmThe values tend to be extremely small as a criterion, resulting in poor computational stability. Second, FmThe value tends to be extremely small, which is only a theoretical ideal condition, and in practical application, if the value is taken as a judgment standard, more mole fraction of injected gas is required to be added to reach a miscible state, so that an error occurs in a calculation result. Meanwhile, the method can not consider the influence of the nanopore confinement effect on the minimum miscible phase pressure of oil and gas, and can only be used for calculating the minimum miscible phase pressure of oil and gas in a conventional reservoir; due to the extremely strong fluid adsorption and the tubular force effect in the nanopores, the difference between the fluid phase state and the phase state condition in the nanopores is large, and the minimum miscible phase pressure of oil and gas also changes, so that the conventional equation of state method cannot be used for calculating the minimum miscible phase pressure of oil and gas in the process of increasing the recovery ratio of gas injection of an unconventional oil reservoir (a compact/shale oil reservoir).
Disclosure of Invention
The embodiment of the invention provides a method for determining minimum miscible phase pressure of oil and gas, which is used for providing a quick and accurate method for calculating the minimum miscible phase pressure of the oil and gas, can be used for conventional oil reservoirs and unconventional oil reservoirs, and comprises the following steps:
acquiring basic characteristic parameters of an initial crude oil sample and the molar composition of each component of the crude oil sample after gas injection, and determining an initial gas-liquid equilibrium constant of each component of the crude oil sample after gas injection;
determining the initial gas phase fugacity and the initial liquid phase fugacity of each component of the crude oil sample after gas injection according to the molar composition, the initial gas-liquid equilibrium constant, the initial capillary pressure value and the fluid adsorption parameters in the pores;
updating gas-liquid equilibrium constants of all components of the crude oil sample after gas injection according to the initial gas phase fugacity and the initial liquid phase fugacity;
determining the interfacial tension and capillary pressure of the gas-injected crude oil sample according to the updated gas-liquid equilibrium constant of each component of the gas-injected crude oil sample;
and determining the minimum miscible pressure of the initial crude oil sample and the injected gas according to the interfacial tension and the capillary pressure.
The embodiment of the invention also provides a device for determining the minimum miscible phase pressure of oil and gas, which is used for providing a quick and accurate method for calculating the minimum miscible phase pressure of oil and gas, can be used for both conventional oil reservoirs and unconventional oil reservoirs, and comprises the following steps:
the initial data acquisition module is used for acquiring basic characteristic parameters of an initial crude oil sample and the molar composition of each component of the crude oil sample after gas injection, and determining an initial gas-liquid equilibrium constant of each component of the crude oil sample after gas injection;
the initial fugacity determining module is used for determining the initial gas phase fugacity and the initial liquid phase fugacity of each component of the crude oil sample after gas injection according to the molar composition, the initial gas-liquid equilibrium constant and the initial capillary pressure value and the fluid adsorption parameters in the pores;
the gas-liquid equilibrium constant updating module is used for updating the gas-liquid equilibrium constant of each component of the crude oil sample after gas injection according to the initial gas phase fugacity and the initial liquid phase fugacity;
the interface tension and capillary tube pressure determining module is used for determining the interface tension and the capillary tube pressure of the gas-injected crude oil sample according to the updated gas-liquid equilibrium constant of each component of the gas-injected crude oil sample;
and the oil-gas minimum miscible pressure determining module is used for determining the minimum miscible pressure of the initial crude oil sample and the injected gas according to the interfacial tension and the capillary pressure.
The embodiment of the invention also provides computer equipment which comprises a memory, a processor and a computer program which is stored on the memory and can be run on the processor, wherein the processor realizes the oil-gas minimum miscible phase pressure determining method when executing the computer program.
The embodiment of the invention also provides a computer readable storage medium, and the computer readable storage medium stores a computer program for executing the oil-gas minimum miscible pressure determining method.
In the embodiment of the invention, the fluid adsorption parameters in the pores are introduced in the calculation process, the influence of the fluid adsorption in the pores is considered, and the method can be used for calculating the mole fraction of each component in the gas-liquid equilibrium state of a crude oil sample after gas injection under the condition of nanometer pores, thereby being used for conventional oil reservoirs and determining the minimum miscible phase pressure of oil gas of unconventional oil reservoirs; the minimum miscible pressure of the crude oil sample and the injected gas is determined according to the capillary pressure, and the influence of the capillary force on the phase balance is considered, so that the accuracy of the minimum miscible pressure result of the oil gas can be improved; the minimum miscible pressure of oil gas is determined according to the interfacial tension, and the miscible criterion function judgment in the prior art is replaced by an interfacial tension disappearance method, so that the convergence and the stability of calculation are improved. Therefore, compared with an experimental method, the method is more convenient and efficient; compared with an empirical formula method, the method is high in theoretical performance and universality, and is not limited to a single oil reservoir and a single oil field; compared with the traditional equation of state method, the method is used for conventional oil reservoirs, also considers the influence of the nano-pore confinement effect on the miscible phase pressure, and can be used for unconventional oil reservoirs.
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In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a schematic diagram of a method for determining minimum miscible pressure of oil and gas in an embodiment of the invention.
FIG. 2 is a schematic diagram of an oil-gas minimum miscible pressure determining device in the embodiment of the invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment of the invention provides a method for determining minimum miscible phase pressure of oil and gas, which is used for providing a quick and accurate method for calculating the minimum miscible phase pressure of oil and gas, and can be used for conventional oil reservoirs and unconventional oil reservoirs, as shown in figure 1, and the method comprises the following steps:
step 101: acquiring basic characteristic parameters of an initial crude oil sample and the molar composition of each component of the crude oil sample after gas injection, and determining an initial gas-liquid equilibrium constant of each component of the crude oil sample after gas injection;
step 102: determining the initial gas phase fugacity and the initial liquid phase fugacity of each component of the crude oil sample after gas injection according to the molar composition, the initial gas-liquid equilibrium constant, the initial capillary pressure value and the fluid adsorption parameters in the pores;
step 103: updating gas-liquid equilibrium constants of all components of the crude oil sample after gas injection according to the initial gas phase fugacity and the initial liquid phase fugacity;
step 104: determining the interfacial tension and capillary pressure of the gas-injected crude oil sample according to the updated gas-liquid equilibrium constant of each component of the gas-injected crude oil sample;
step 105: and determining the minimum miscible pressure of the initial crude oil sample and the injected gas according to the interfacial tension and the capillary pressure.
As can be known from the flow shown in fig. 1, in the embodiment of the present invention, by introducing the fluid adsorption parameters in the pores in the calculation process, the influence of the fluid adsorption in the pores is considered, and the method can be used for calculating the mole fraction of each component in the gas-liquid equilibrium state of the crude oil sample after gas injection under the condition of nano-pores, so that the method can be used for determining the minimum miscible phase pressure of the oil gas in the conventional oil reservoir and the unconventional oil reservoir; the minimum miscible phase pressure of the oil gas of the sample is determined according to the capillary pressure, and the influence of the capillary force on the phase balance is considered, so that the accuracy of the minimum miscible phase pressure result of the oil gas can be improved; the minimum miscible pressure of oil gas is determined according to the interfacial tension, and the miscible criterion function judgment in the prior art is replaced by an interfacial tension disappearance method, so that the convergence and the stability of calculation are improved. Therefore, compared with an experimental method, the method is more convenient and efficient; compared with an empirical formula method, the method is high in theoretical performance and universality, and is not limited to a single oil reservoir and a single oil field; compared with the traditional equation of state method, the method is used for conventional oil reservoirs, also considers the influence of the nano-pore confinement effect on the miscible phase pressure, and can be used for unconventional oil reservoirs.
In specific implementation, the basic characteristic parameters of an initial crude oil sample and the molar composition of each component of the crude oil sample after gas injection are firstly obtained. Wherein, the basic characteristic parameters at least comprise: crude oil composition, components of each composition, critical pressure P of each componentcCritical temperature TcOne or any combination of eccentricity factor omega, molecular weight MW and binary interaction coefficient BIP. Obtaining basic characteristic parameters and molar composition ziThen, determining the initial gas-liquid equilibrium constant K of each component of the crude oil sample after gas injection by using Wilson equationi：
In the formula, P0The initial pressure value of the crude oil sample after gas injection is represented, and a value can be initially given; i represents a component number.
And then, determining the initial gas phase fugacity and the initial liquid phase fugacity of each component of the crude oil sample after gas injection according to the molar composition, the initial gas-liquid equilibrium constant, the initial capillary pressure value and the fluid adsorption parameters in the pores. In an embodiment, the specific process includes:
obtaining initial gas phase composition and initial liquid phase composition of each component of the crude oil sample after gas injection according to the molar composition and the initial gas-liquid equilibrium constant;
and determining the initial gas phase fugacity and the initial liquid phase fugacity of each component of the crude oil sample after gas injection according to the initial capillary pressure value, the fluid adsorption parameters in the pores, the initial gas phase composition and the initial liquid phase composition.
Wherein the molar composition ziAnd initial gas-liquid equilibrium constant KiSubstituting into Rachford-Rice (RR) equation to calculate initial gas phase composition x of each component of the crude oil sample after gas injectioni(0)And initial liquid phase composition yi(0). The RR equation is as follows:
in the formula, NcRepresenting the total number of components in the crude oil sample; and is
zi＝(1-α)xi(0)+αyi(0)(ii) a Alpha represents the gas phase mole fraction.
Specifically, according to the initial capillary pressure value, fluid adsorption parameters in pores, initial gas phase composition and initial liquid phase composition, determining the initial gas phase fugacity and initial liquid phase fugacity of each component of the crude oil sample after gas injection, including:
substituting the initial capillary pressure value, fluid adsorption parameters in pores, initial gas phase composition and initial liquid phase composition into a modified state equation and an fugacity equation, and simultaneously solving to determine the initial gas phase fugacity and the initial liquid phase fugacity of each component of the crude oil sample after gas injection;
wherein, the above-mentioned modified equation of state is:
in the formula, P represents the pressure of the crude oil sample after gas injection, and the initial pressure value P is calculated in the calculation process0Substituting into P; t represents a thermodynamic temperature scale; vmRepresents a molar volume; r represents a universal gas constant; the constant a and the constant b represent action parameter units; gamma represents a dimensionless adsorption radius; beta represents the comparative adsorption density.
Compared with the Peng-Robinson (PR) equation of state in the prior art, the modified equation of state in the embodiment of the invention considers the influence of fluid adsorption in pores, can be used for calculating the mole fraction of each component in gas-liquid equilibrium in a gas injection sample under the condition of nano pores, and has enough large pore size (R)p1 μm) is equivalent to a conventional PR equation of state, and thus can be used for oil and gas minimum miscible pressure determination of a conventional reservoir and an unconventional reservoir.
The above-mentioned fugacity equations include:
gas phase fugacity equation:
liquid phase fugacity equation:
wherein:
ZLand ZVRespectively representing the compression factors of the liquid and gas phases; pcapIRepresents the initial capillary pressure; f. ofiLDenotes the initial liquid phase fugacity; f. ofiVIndicating the initial gas phase fugacity.
After confirming the initial gas phase fugacity and the initial liquid phase fugacity of each component of the crude oil sample, updating the gas-liquid equilibrium constant of each component of the crude oil sample after gas injection according to the initial gas phase fugacity and the initial liquid phase fugacity, and the specific process comprises the following steps:
if the initial gas phase fugacity and the initial liquid phase fugacity do not meet the first preset condition, updating the gas-liquid equilibrium constant of each component of the crude oil sample after gas injection according to the initial gas-liquid equilibrium constant, the initial gas phase fugacity and the initial liquid phase fugacity to obtain a first gas-liquid equilibrium constant K of each component of the crude oil sample after gas injectioni(new)；
If the initial gas phase fugacity and the initial liquid phase fugacity meet a first preset condition, taking the initial gas-liquid equilibrium constant as a first gas-liquid equilibrium constant K of each component of the updated gas-injected crude oil samplei(new)。
In an embodiment, the first preset condition may be, for example:
and updating the gas-liquid equilibrium constants of the components of the crude oil sample after gas injection according to the following formula to obtain first gas-liquid equilibrium constants of the components of the crude oil sample after gas injection:
wherein, Ki(new)Representing a first gas-liquid equilibrium constant of each component of the crude oil sample after gas injection; i represents a component number; f. ofiLDenotes the initial liquid phase fugacity; f. ofiVDenotes the initial gas phase fugacity; kiRepresenting the initial gas-liquid equilibrium constant.
Using the first gas-liquid equilibrium constant Ki(new)Replacing the initial gas-liquid equilibrium constant KiStep 102 is repeated a plurality of times until the obtained initial gas phase fugacity and initial liquid phase fugacity satisfy the first predetermined condition.
According to the updated gas-liquid equilibrium constant of each component of the crude oil sample after gas injection, namely the first gas-liquid equilibrium constant Ki(new)Determining the interfacial tension and capillary pressure of the crude oil sample after gas injection, and the specific process comprises the following steps:
determining a first gas phase composition and a first liquid phase composition of each component in the crude oil sample after gas injection according to the first gas-liquid equilibrium constant and the molar composition;
determining the interfacial tension of the crude oil sample after gas injection according to the first gas phase composition and the first liquid phase composition;
the capillary pressure of the crude oil sample after gas injection was determined from the interfacial tension and pore size.
In a specific example, the interfacial tension of a crude oil sample after gas injection was determined from the first gas phase composition and the first liquid phase composition according to the following formula:
wherein IFT represents the interfacial tension of the crude oil sample after gas injection; n is a radical ofcRepresenting the total parts of the components of the crude oil sample; chi shapeiRepresents the isospecific volume of each component; t represents a temperature; rhoL(T) represents the molar density of the first liquid phase of each component, pV(T) represents the molar density of the first gas phase of the components, consisting of the first gas phase xiAnd a firstComposition y of the liquid phaseiAnd calculating according to the corrected state equation.
In a specific example, the capillary pressure of a crude oil sample after gas injection was determined from the interfacial tension and pore size according to the following formula:
wherein, PcapRepresents the capillary pressure of the crude oil sample after gas injection; cos theta represents the cosine of the wetting angle between the crude oil sample and the pore wall surface after gas injection; rpIndicating the pore size.
After determining the interfacial tension and the capillary pressure, determining the minimum miscible pressure of the initial crude oil sample and the injected gas according to the interfacial tension and the capillary pressure, wherein the minimum miscible pressure comprises the following steps:
determining a second gas-liquid equilibrium constant of each component in the crude oil sample after gas injection according to the capillary pressure value and the initial capillary pressure value;
and determining the minimum miscible pressure of the initial crude oil sample and the injected gas according to the interfacial tension, the second gas-liquid equilibrium constant and the molar composition.
In the specific embodiment, according to the capillary pressure value and the initial capillary pressure value, determining a second gas-liquid equilibrium constant of each component in the crude oil sample after gas injection comprises:
if the difference value between the capillary pressure value and the initial capillary pressure value does not meet a second preset condition, circularly executing the following iteration steps until the difference value between the capillary pressure value and the initial capillary pressure value meets the second preset condition:
increasing the initial capillary pressure value;
determining the first gas phase fugacity and the first liquid phase fugacity of each component in the crude oil sample after gas injection according to the increased initial capillary pressure value, molar composition and the first gas-liquid equilibrium constant;
updating the first gas-liquid equilibrium constant of each component in the crude oil sample after gas injection according to the first gas-phase fugacity and the first liquid-phase fugacity to obtain a second gas-liquid equilibrium constant of each component in the crude oil sample after gas injection;
and determining the interfacial tension and the capillary pressure value of the crude oil sample after gas injection according to the second gas-liquid equilibrium constant, and setting the second gas-liquid equilibrium constant as the first gas-liquid equilibrium constant of the next iteration.
And if the difference value between the capillary pressure value and the initial capillary pressure value meets a second preset condition, determining the first gas-liquid equilibrium constant as a second gas-liquid equilibrium constant of each component in the crude oil sample after gas injection.
In a specific embodiment, the second preset condition may be, for example, less than 0.001, and it should be understood that the foregoing is only an example and is not intended to limit the scope of the present invention.
After the second gas-liquid equilibrium constant is obtained, determining the minimum miscible pressure of the initial crude oil sample and the injected gas according to the interfacial tension, the second gas-liquid equilibrium constant and the molar composition, wherein the minimum miscible pressure comprises the following steps:
and determining the pressure of the crude oil sample after gas injection as the minimum miscible phase pressure of the initial crude oil sample and the injected gas under the conditions that the second gas-liquid equilibrium constant and the molar composition meet a third preset condition and the interfacial tension meets a fourth preset condition.
The third preset condition may be, for example, |1- Σ ziKi|＜10-5The fourth preset condition may be, for example, that the interfacial tension value is less than 0.001. If the third preset condition is not met, increasing the initial pressure set value P of the crude oil sample after gas injection0Step 101-105 is repeated until the condition is satisfied. And after the third preset condition is met, if the fourth preset condition is not met, continuously adding more injected gas with mole fraction into the crude oil sample after gas injection, repeating the step 101 and the step 105 until the conditions are met, wherein the pressure value of the crude oil sample after gas injection is the minimum miscible phase pressure value of the oil gas.
It should be understood that the above formulas and preset conditions are only examples, and the formulas may be modified during the implementation, and the preset conditions may be changed.
Two specific examples are given below to illustrate how embodiments of the present invention determine minimum miscible pressure for hydrocarbons.
The method comprises the following specific operation steps:
s1: determining fundamental characteristic parameters of an initial crude oil sample, including crude oil composition, components of each composition, critical pressure P of each componentcCritical temperature TcEccentricity factor omega, molecular weight MW and binary interaction coefficient BIP;
s2: constructing a system: taking 1mol of crude oil with given initial components and temperature;
s3: and (3) reconstructing a system: mixing a certain amount of injected gas (e.g. 0.01mol) with the crude oil to make the components be 1, calculating the molar composition z of each component in the crude oil sample after gas injectioni；
S4: determination of bubble point pressure P by modified flash calculationb；
The modified flash calculation procedure is as follows:
s401: inputting basic characteristic parameters and pore size R of initial crude oil samplep；
S402: setting an initial pressure value P0And initial capillary pressure value PcapI(generally smaller values);
s403: initializing a gas-liquid equilibrium constant K by using a Wilson equationi；
S404: mixing the above KiSubstituting the value into RR equation, calculating initial gas phase composition xi(0)Initial liquid phase composition yi(0)；
S405: x is to bei(0)And yi(0)Respectively introducing the values into a correction state equation and an fugacity equation, and jointly solving to obtain the gas phase fugacity fiVAnd liquid phase fugacity fiL. If it satisfies
Carrying out the next step; if not, then according to
Updating KiRepeat S404 to S4Step 05, until the conditions are met;
s406: according to x obtained after updatingiAnd yiCalculating to obtain IFT;
s407: substituting the interfacial tension value into a formula to calculate the capillary pressure PcapIf Pcap-PcapI|＜10-3Carrying out the next step under MPa; if not, continuing to increase PcapIRepeating the steps S402 to S407 until the condition is met;
s408: if |1- Σ ziKi|＜10-5Bubble point pressure PbIs an initial pressure value P0(ii) a If not, continuing to increase the initial pressure value P0And repeating the steps S402 to S408 until the condition is met.
S5: calculation of bubble point pressure P with modified flash calculationbInterfacial tension of lower if IFT < 10-3mN/m, the minimum miscible pressure is the bubble point pressure; if not, continuously adding more mole fraction of injection gas into the crude oil sample, and repeating the steps from S3 to S5 until the conditions are met.
S6: the output bubble point pressure is the minimum miscible phase pressure value.
Example one
Step a, determining a basic characteristic parameter value as follows:
in a simulated oil system, the temperature T is 344K, and the injected gas is CO2And CH4Mixing the gases in equal proportion, and setting the radius R of the porep＝1μm。
Simulated oil components and component properties are shown in table 1:
TABLE 1 crude oil Components and component Properties
| Components | zi | Tc/K | Pc/MPa | ω | MW | χi |
| CO2 | 0 | 304.21 | 7.384 | 0.2250 | 44.010 | 82.00 |
| CH4 | 0.25 | 190.58 | 4.604 | 0.0104 | 16.043 | 74.05 |
| n-C4H10 | 0.50 | 425.18 | 3.797 | 0.2010 | 58.123 | 193.90 |
| n-C10H22 | 0.25 | 617.65 | 2.115 | 0.4900 | 142.290 | 440.69 |
The interaction coefficients of the components are shown in Table 2:
TABLE 2 interaction coefficients between the components of crude oil
| Components | CO2 | CH4 | n-C4H10 | n-C10H22 |
| CO2 | 0.0000 | 0.1000 | 0.1257 | 0.0942 |
| CH4 | 0.1000 | 0.0000 | 0.0270 | 0.0420 |
| n-C4H10 | 0.1257 | 0.0270 | 0.0000 | 0.0080 |
| n-C10H22 | 0.0942 | 0.0420 | 0.0080 | 0.0000 |
Step b, injecting 1.60mol of injection gas (0.8mol CO)2、0.8molCH4) Mixing with 1mol of crude oil, assigning the components to 1, calculating a new molar composition ziThe results are shown in Table 3:
TABLE 3 novel molar composition
| Components | CO2 | CH4 | n-C4H10 | n-C10H22 |
| zi | 0.3077 | 0.4038 | 0.1923 | 0.0962 |
Step c, calculating the bubble point pressure P by using a corrected flash evaporation calculation methodb＝15.7MPa。
D, calculating the interfacial tension IFT (equivalent to 7.36 multiplied by 10) under the bubble point pressure by using a corrected flash evaporation calculation method-4mN/m<10-3mN/m。
Step e, outputting the minimum miscible phase pressure MMP (P) of oil gas in the pore with the radius of 1 mu mb＝15.71MPa。
The calculated values are compared with the minimum miscible pressure measured by the bubble rising instrument method and are shown in table 4:
TABLE 4 comparison of the calculated values with the minimum miscible pressure by the bubble rising method
| Sample (I) | Measured value MPa by bubble rising instrument method | Calculated value MPa of the invention | Relative error (%) |
| Simulated oil | 15.35 | 15.71 | 2.35 |
Example two
Step a, determining parameter values according to the actual situation of a target reservoir, wherein the parameter values comprise the following steps:
in a certain shale oil reservoir, the temperature T is 388.7K, the pore radius is about 50nm mostly, and R is setp＝50nm。
The crude oil components and component properties are shown in table 5:
TABLE 5 crude oil Components and component Properties
| Components | zi | Pc/MPa | Tc/K | MW | Ω | χi |
| CO2 | 0.0 | 72.80 | 304.20 | 44.01 | 0.2250 | 78.0 |
| CH4 | 0.2506 | 45.40 | 190.60 | 16.04 | 0.0080 | 77.0 |
| C2-C4 | 0.22 | 42.54 | 363.30 | 42.82 | 0.1432 | 145.2 |
| C5-C7 | 0.20 | 33.76 | 511.56 | 83.74 | 0.2474 | 250.0 |
| C8-C9 | 0.13 | 30.91 | 579.34 | 105.91 | 0.2861 | 306.0 |
| C10+ | 0.1994 | 21.58 | 788.74 | 200.00 | 0.6869 | 686.3 |
The interaction coefficients of the components are shown in Table 6:
TABLE 6 interaction coefficients between the components of crude oils
| Components | CO2 | CH4 | C2-C4 | C5-C7 | C8-C9 | C10+ |
| CO2 | 0 | 0.1030 | 0.1327 | 0.1413 | 0.1500 | 0.1500 |
| CH4 | 0.1030 | 0 | 0.0078 | 0.0242 | 0.0324 | 0.0779 |
| C2-C4 | 0.1327 | 0.0078 | 0 | 0.0046 | 0.0087 | 0.0384 |
| C5-C7 | 0.1413 | 0.0242 | 0.0046 | 0 | 0.0006 | 0.0169 |
| C8-C9 | 0.1500 | 0.0324 | 0.0087 | 0.0006 | 0 | 0.0111 |
| C10+ | 0.1500 | 0.0779 | 0.0384 | 0.0169 | 0.0111 | 0 |
Step b, adding 2.25mol of CO2Mixing with 1mol of crude oil, assigning the components to 1, calculating a new molar composition ziSee table 7:
TABLE 7 novel molar composition
| Components | CO2 | CH4 | C2-C4 | C5-C7 | C8-C9 | C10+ |
| zi | 0.6923 | 0.0771 | 0.0677 | 0.0615 | 0.0400 | 0.0614 |
Step c, calculating the bubble point pressure P by using a corrected flash evaporation calculation methodb＝20.2MPa。
Step d, calculating bubble point pressure by using corrected flash evaporation calculation methodInterfacial tension under force IFT 5.72X 10-4mN/m<10-3mN/m。
Step e, outputting the minimum miscible phase pressure MMP (P) of oil gas in the pore with the radius of 50nmb＝20.2MPa
The implementation of the above specific application is only an example, and the rest of the embodiments are not described in detail.
Based on the same inventive concept, embodiments of the present invention further provide an oil-gas minimum miscible phase pressure determining device, and as the principle of the problem solved by the oil-gas minimum miscible phase pressure determining device is similar to the oil-gas minimum miscible phase pressure determining method, the implementation of the oil-gas minimum miscible phase pressure determining device may refer to the implementation of the oil-gas minimum miscible phase pressure determining method, and repeated parts are not repeated, and the specific structure is as shown in fig. 2:
the initial data acquisition module 201 is used for acquiring basic characteristic parameters of an initial crude oil sample and molar compositions of components of the crude oil sample after gas injection, and determining an initial gas-liquid equilibrium constant of each component of the crude oil sample after gas injection;
an initial fugacity determination module 202, configured to determine an initial gas phase fugacity and an initial liquid phase fugacity of each component of the crude oil sample after gas injection according to the molar composition, the initial gas-liquid equilibrium constant, the initial capillary pressure value, and the fluid adsorption parameter in the pore;
the gas-liquid equilibrium constant updating module 203 is used for updating the gas-liquid equilibrium constant of each component of the crude oil sample after gas injection according to the initial gas phase fugacity and the initial liquid phase fugacity;
the interface tension and capillary pressure determining module 204 is used for determining the interface tension and the capillary pressure of the gas-injected crude oil sample according to the updated gas-liquid equilibrium constant of each component of the gas-injected crude oil sample;
and the oil-gas minimum miscible pressure determining module 205 is used for determining the minimum miscible pressure of the initial crude oil sample and the injected gas according to the interfacial tension and the capillary pressure.
In a specific embodiment, the initial fugacity determination module 202 is specifically configured to:
obtaining initial gas phase composition and initial liquid phase composition of each component of the crude oil sample after gas injection according to the molar composition and the initial gas-liquid equilibrium constant;
and determining the initial gas phase fugacity and the initial liquid phase fugacity of each component of the crude oil sample after gas injection according to the initial capillary pressure value, the fluid adsorption parameters in the pores, the initial gas phase composition and the initial liquid phase composition.
In a specific embodiment, the gas-liquid equilibrium constant updating module 203 is specifically configured to:
if the initial gas phase fugacity and the initial liquid phase fugacity do not meet the first preset condition, updating the gas-liquid equilibrium constants of the components of the crude oil sample after gas injection according to the initial gas-liquid equilibrium constant, the initial gas phase fugacity and the initial liquid phase fugacity to obtain a first gas-liquid equilibrium constant of the components of the crude oil sample after gas injection;
and if the initial gas phase fugacity and the initial liquid phase fugacity meet a first preset condition, taking the initial gas-liquid equilibrium constant as the first gas-liquid equilibrium constant of each component of the updated gas-injected crude oil sample.
In particular implementation, the interfacial tension and capillary pressure determination module 204 is specifically configured to:
determining a first gas phase composition and a first liquid phase composition of each component in the crude oil sample after gas injection according to the first gas-liquid equilibrium constant and the molar composition;
determining the interfacial tension of the crude oil sample after gas injection according to the first gas phase composition and the first liquid phase composition;
the capillary pressure of the crude oil sample after gas injection was determined from the interfacial tension and pore size.
In an embodiment, the hydrocarbon minimum miscible pressure determination 205 module includes:
the second gas-liquid equilibrium constant determination unit is used for determining a second gas-liquid equilibrium constant of each component according to the capillary pressure value and the initial capillary pressure value;
and the oil-gas minimum miscible pressure determining unit is used for determining the minimum miscible pressure of the initial crude oil sample and the injected gas according to the interfacial tension, the second gas-liquid equilibrium constant and the molar composition.
Wherein the second gas-liquid equilibrium constant determination unit is specifically configured to:
if the difference value between the capillary pressure value and the initial capillary pressure value does not meet a second preset condition, circularly executing the following iteration steps until the difference value between the capillary pressure value and the initial capillary pressure value meets the second preset condition:
increasing the initial capillary pressure value;
determining the first gas phase fugacity and the first liquid phase fugacity of each component in the crude oil sample after gas injection according to the increased initial capillary pressure value, molar composition and the first gas-liquid equilibrium constant;
updating the first gas-liquid equilibrium constant of each component in the crude oil sample after gas injection according to the first gas-phase fugacity and the first liquid-phase fugacity to obtain a second gas-liquid equilibrium constant of each component in the crude oil sample after gas injection;
determining the interfacial tension and the capillary pressure value of the crude oil sample after gas injection according to the second gas-liquid equilibrium constant, and setting the second gas-liquid equilibrium constant as the first gas-liquid equilibrium constant of the next iteration;
and if the difference value between the capillary pressure value and the initial capillary pressure value meets a second preset condition, determining the first gas-liquid equilibrium constant as a second gas-liquid equilibrium constant of each component in the crude oil sample after gas injection.
Specifically, the oil-gas minimum miscible pressure determining unit is specifically configured to:
and determining the pressure of the crude oil sample after gas injection as the minimum miscible phase pressure of the initial crude oil sample and the injected gas under the conditions that the second gas-liquid equilibrium constant and the molar composition meet a third preset condition and the interfacial tension meets a fourth preset condition.
The embodiment of the invention also provides computer equipment which comprises a memory, a processor and a computer program which is stored on the memory and can be run on the processor, wherein the processor realizes the oil-gas minimum miscible phase pressure determining method when executing the computer program.
The embodiment of the invention also provides a computer readable storage medium, which stores a computer program for executing the oil-gas minimum miscible phase pressure determining method.
In summary, the method and the device for determining the minimum miscible phase pressure of oil gas provided by the embodiment of the invention have the following advantages:
the influence of fluid adsorption in the pores is considered by introducing fluid adsorption parameters in the pores in the calculation process, namely, the traditional PR state equation is replaced by the corrected state equation, the method can be used for calculating the mole fraction of each component in the gas-liquid equilibrium of a crude oil sample after gas injection under the condition of nanometer pores, can be used for conventional oil reservoirs, and can also be used for determining the minimum miscible phase pressure of oil gas of unconventional oil reservoirs; the minimum miscible phase pressure of the oil gas of the sample is determined according to the capillary pressure, and the influence of the capillary force on the phase balance is considered, so that the accuracy of the minimum miscible phase pressure result of the oil gas can be improved; the minimum miscible pressure of oil gas is determined according to the interfacial tension, and the miscible criterion function judgment in the prior art is replaced by an interfacial tension disappearance method, so that the convergence and the stability of the calculation are improved. Therefore, compared with an experimental method, the method is more convenient and efficient; compared with an empirical formula method, the method is high in theoretical performance and universality, and is not limited to a single oil reservoir and a single oil field; compared with the traditional equation of state method, the method is used for conventional oil reservoirs, also considers the influence of the nano-pore confinement effect on the miscible phase pressure, and can be used for unconventional oil reservoirs.
As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, apparatus, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes may be made to the embodiment of the present invention by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (2)
1. A method for determining minimum miscible pressure of oil and gas is characterized by comprising the following steps:
acquiring basic characteristic parameters of an initial crude oil sample and the molar composition of each component of the crude oil sample after gas injection, and determining an initial gas-liquid equilibrium constant of each component of the crude oil sample after gas injection;
determining the initial gas phase fugacity and the initial liquid phase fugacity of each component of the crude oil sample after gas injection according to the molar composition, the initial gas-liquid equilibrium constant, the initial capillary pressure value and the fluid adsorption parameters in the pores;
updating gas-liquid equilibrium constants of all components of the crude oil sample after gas injection according to the initial gas phase fugacity and the initial liquid phase fugacity;
determining the interfacial tension and capillary pressure of the gas-injected crude oil sample according to the updated gas-liquid equilibrium constant of each component of the gas-injected crude oil sample;
determining the minimum miscible pressure of the initial crude oil sample and the injected gas according to the interfacial tension and the capillary pressure;
determining the initial gas phase fugacity and the initial liquid phase fugacity of each component of the crude oil sample after gas injection according to the molar composition, the initial gas-liquid equilibrium constant, the initial capillary pressure value and the fluid adsorption parameters in the pores, and comprising the following steps:
obtaining initial gas phase composition and initial liquid phase composition of each component of the crude oil sample after gas injection according to the molar composition and the initial gas-liquid equilibrium constant;
and determining the initial gas phase fugacity and the initial liquid phase fugacity of each component of the crude oil sample after gas injection according to the initial capillary pressure value, the fluid adsorption parameters in the pores, the initial gas phase composition and the initial liquid phase composition. (ii) a
Determining the initial gas phase fugacity and the initial liquid phase fugacity of each component of the crude oil sample after gas injection according to the initial capillary pressure value, the fluid adsorption parameters in the pores, the initial gas phase composition and the initial liquid phase composition, and the method comprises the following steps:
determining the initial gas phase fugacity and the initial liquid phase fugacity of each component of the crude oil sample after gas injection according to the initial capillary pressure value, the fluid adsorption parameters in the pores, the initial gas phase composition and the initial liquid phase composition on the basis of a corrected state equation and an fugacity equation;
wherein the modified state equation is:
in the formula, P represents the pressure of the crude oil sample after gas injection; t represents a thermodynamic temperature scale; vmTo representMolar volume; r represents a universal gas constant; the constant a and the constant b represent action parameter units; gamma represents a dimensionless adsorption radius; β represents the comparative adsorption density;
wherein the fugacity equation comprises:
gas phase fugacity equation:
liquid phase fugacity equation:
wherein:
ZLand ZVRespectively representing the compression factors of the liquid and gas phases; pcapIRepresents the initial capillary pressure; f. ofiLDenotes the initial liquid phase fugacity; f. ofiVDenotes the initial gas phase fugacity;
updating gas-liquid equilibrium constants of each component of the crude oil sample after gas injection according to the initial gas phase fugacity and the initial liquid phase fugacity, wherein the gas-liquid equilibrium constants comprise:
if the initial gas phase fugacity and the initial liquid phase fugacity do not meet a first preset condition, updating the gas-liquid equilibrium constant of each component of the crude oil sample after gas injection according to the initial gas-liquid equilibrium constant, the initial gas phase fugacity and the initial liquid phase fugacity to obtain a first gas-liquid equilibrium constant of each component of the crude oil sample after gas injection;
if the initial gas phase fugacity and the initial liquid phase fugacity meet a first preset condition, taking the initial gas-liquid equilibrium constant as a first gas-liquid equilibrium constant of each component of the updated gas-injected crude oil sample;
updating the gas-liquid equilibrium constant of each component of the crude oil sample after gas injection according to the initial gas-liquid equilibrium constant, the initial gas-phase fugacity and the initial liquid-phase fugacity according to the following formula to obtain a first gas-liquid equilibrium constant of each component of the crude oil sample after gas injection:
wherein, Ki(new)Representing a first gas-liquid equilibrium constant of each component of the crude oil sample after gas injection; i represents a component number; f. ofiLDenotes the initial liquid phase fugacity; f. ofiVDenotes the initial gas phase fugacity; kiRepresents the initial gas-liquid equilibrium constant;
determining the interfacial tension and the capillary pressure of the gas-injected crude oil sample according to the updated gas-liquid equilibrium constant of each component of the gas-injected crude oil sample, and the method comprises the following steps:
determining a first gas phase composition and a first liquid phase composition of each component in the crude oil sample after gas injection according to the first gas-liquid equilibrium constant and the molar composition;
determining the interfacial tension of the crude oil sample after gas injection according to the first gas phase composition and the first liquid phase composition;
determining the capillary pressure of the crude oil sample after gas injection according to the interfacial tension and the pore size;
determining a minimum miscible pressure of the initial crude oil sample with the injected gas based on the interfacial tension and the capillary pressure, comprising:
determining a second gas-liquid equilibrium constant of each component in the crude oil sample after gas injection according to the capillary pressure value and the initial capillary pressure value;
determining the minimum miscible pressure of the initial crude oil sample and the injected gas according to the interfacial tension, the second gas-liquid equilibrium constant and the molar composition;
according to the capillary pressure value and the initial capillary pressure value, determining a second gas-liquid equilibrium constant of each component in the crude oil sample after gas injection, wherein the second gas-liquid equilibrium constant comprises the following steps:
if the difference value between the capillary pressure value and the initial capillary pressure value does not meet a second preset condition, circularly executing the following iteration steps until the difference value between the capillary pressure value and the initial capillary pressure value meets the second preset condition:
increasing the initial capillary pressure value;
determining the first gas phase fugacity and the first liquid phase fugacity of each component in the crude oil sample after gas injection according to the increased initial capillary pressure value, the molar composition and the first gas-liquid equilibrium constant;
updating the first gas-liquid equilibrium constant of each component in the crude oil sample after gas injection according to the first gas-phase fugacity and the first liquid-phase fugacity to obtain a second gas-liquid equilibrium constant of each component in the crude oil sample after gas injection;
determining the interfacial tension and the capillary pressure value of the crude oil sample after gas injection according to the second gas-liquid equilibrium constant, and setting the second gas-liquid equilibrium constant as the first gas-liquid equilibrium constant of the next iteration;
if the difference value between the capillary pressure value and the initial capillary pressure value meets a second preset condition, determining the first gas-liquid equilibrium constant as a second gas-liquid equilibrium constant of each component in the crude oil sample after gas injection;
determining the minimum miscible pressure of the initial crude oil sample and the injected gas according to the interfacial tension, the second gas-liquid equilibrium constant and the molar composition, wherein the minimum miscible pressure comprises the following steps:
and determining the pressure of the crude oil sample after gas injection as the minimum miscible pressure of the initial crude oil sample and the injected gas under the conditions that the second gas-liquid equilibrium constant and the molar composition meet a third preset condition and the interfacial tension meets a fourth preset condition.
2. An oil and gas minimum miscible pressure determining apparatus using the oil and gas minimum miscible pressure determining method according to claim 1, comprising:
the initial data acquisition module is used for acquiring basic characteristic parameters of an initial crude oil sample and the molar composition of each component of the crude oil sample after gas injection, and determining an initial gas-liquid equilibrium constant of each component of the crude oil sample after gas injection;
the initial fugacity determining module is used for determining the initial gas phase fugacity and the initial liquid phase fugacity of each component of the crude oil sample after gas injection according to the molar composition, the initial gas-liquid equilibrium constant and the initial capillary pressure value and the fluid adsorption parameters in the pores;
the gas-liquid equilibrium constant updating module is used for updating the gas-liquid equilibrium constant of each component of the crude oil sample after gas injection according to the initial gas phase fugacity and the initial liquid phase fugacity;
the interface tension and capillary tube pressure determining module is used for determining the interface tension and the capillary tube pressure of the gas-injected crude oil sample according to the updated gas-liquid equilibrium constant of each component of the gas-injected crude oil sample;
and the oil-gas minimum miscible pressure determining module is used for determining the minimum miscible pressure of the initial crude oil sample and the injected gas according to the interfacial tension and the capillary pressure.
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