Method and system for characterizing miscible state after action of CO2 and crude oil based on interfacial tension

Abstract

The invention discloses a method and a system for characterizing a miscible state after action of CO2 and crude oil based on interfacial tension, and relates to the technical field of oil reservoir CO2 flooding development, the method comprises the following steps: S1, obtaining a relation curve of oil displacement efficiency and displacement pressure through a numerical simulation tubule experiment, and determining the minimum miscible pressure; s2, obtaining a relation curve of interfacial tension and displacement pressure through a numerical simulation tubule experiment, and determining critical interfacial tension; s3, on the basis of the minimum miscible pressure and the critical interfacial tension, key parameters representing the miscible state are determined; and S4, carrying out engineering characterization on the miscible state after the CO2 and the crude oil act on the basis of the key parameters for characterizing the miscible state. According to the method, the miscible state is divided according to the interfacial tension, the miscible state in the CO2 flooding process is further refined, errors caused by the fact that the miscible state is judged due to the fact that the minimum miscible pressure changes along with mining time are reduced, and the miscible state in the CO2 flooding development process is represented more finely.

Description

Technical Field

[0001] The present invention relates to the technical field of CO2 flooding development of oil reservoirs, and in particular to a method and system for characterizing the miscible state of CO2 and crude oil based on interfacial tension. Background Art

[0002] Conventional water flooding is costly and slow to take effect. When formation water and injected water are incompatible, a series of problems will arise, such as difficulty in water injection and severe pressure buildup in injection wells. At present, after half a century of water injection development, the comprehensive water content of most oil fields in the world has exceeded 90%, and the comprehensive water content of some blocks has reached 95%, and the effect of water flooding development is getting worse and worse. According to the Hall curve, the injection capacity of gas is generally 2 to 6 times that of water. Therefore, gas injection development can be considered for oil reservoirs with low recovery rates in conventional water injection and difficult to achieve effective development within the economic range. In recent years, gas drive extraction technology has been recognized as a tertiary oil recovery technology that is on par with chemical drive and thermal recovery. It has a wide range of applications and does not have overly complex requirements for reservoir physical properties. It has a very broad development prospect.

[0003] Both indoor and field tests have shown that CO2 is a very ideal oil displacement agent compared with other injected gases. In addition to the displacement mechanism of general gas drive, it also has some special displacement mechanisms due to the high solubility of CO2 in oil and water: after the injected CO2 and crude oil come into contact under certain temperature and pressure conditions, the light components in the crude oil are extracted to enrich the CO2, the difference between the two components becomes smaller, and the interfacial tension between the two phases gradually decreases until it reaches 0, thus forming a miscible phase, and the oil displacement effect is optimal. Both theory and mine practice have shown that the oil displacement efficiency of CO2 miscible drive is significantly higher than that of immiscible drive. The US CO2 gas injection drive projects are also mainly based on miscible drives, with the number of projects reaching 128, accounting for 94.7% of the total; in terms of enhanced oil recovery, the output of CO2 miscible drive is 1264×10 4 t / a, accounting for 92.2% of the total enhanced oil recovery output of CO2 flooding.

[0004] The traditional classification standard divides CO2 flooding into two types of displacement methods: miscible flooding and immiscible flooding. There are three main ways of distinguishing: one is based on the minimum miscible pressure between the oil and gas phases. When the formation pressure is greater than the minimum miscible pressure, it is considered that miscible flooding can be implemented. When the formation pressure is less than or equal to the minimum miscible pressure, it is considered that it is not miscible or nearly miscible; one is based on the interfacial tension between oil and gas. In theory, the case where the interfacial tension is 0 is defined as miscible, and the case where the interfacial tension is greater than 0 is defined as immiscible; the last one is based on the principle that injected CO2 needs to be in multi-stage contact with crude oil to achieve miscibility, and defines the minimum enrichment concentration of the injected gas, that is, it is considered that when the injected gas content reaches this certain value, it can achieve miscibility with crude oil (minimum enrichment degree). The first minimum miscible pressure judgment method is commonly used in engineering, and the second interfacial tension method is mainly a laboratory miscible method.

[0005] In actual reservoirs, pressure and fluid composition have more complex temporal and spatial variations. Simply dividing them into miscible drive and immiscible drive cannot accurately describe the reservoir gas injection development process. Some scholars use interfacial tension to study the gas-to-oil process, but they do not provide a standard or reasonable basis for dividing different miscible states by interfacial tension. Therefore, it is necessary to establish a more clear and detailed characterization method for the miscible state of oil and gas in the gas drive process. Summary of the invention

[0006] The purpose of the present invention is to provide a method and system for characterizing the miscible state of CO2 and crude oil based on interfacial tension, so as to solve the problem that the existing methods are not clear enough in judging the miscible state of CO2 flooding reservoir development. To achieve the above purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a method for characterizing the miscible state of CO2 after the reaction with crude oil based on interfacial tension, the method comprising the following steps:

[0008] Step S1: by numerically simulating a capillary experiment, a curve of relationship between oil displacement efficiency and displacement pressure is obtained, and the minimum miscible pressure is determined;

[0009] Step S2: by numerically simulating the capillary experiment, a relationship curve between the interfacial tension and the displacement pressure is obtained, and the critical interfacial tension is determined;

[0010] Step S3: determining key parameters characterizing the miscible state based on the minimum miscible pressure and the critical interfacial tension;

[0011] Step S4: Based on the key parameters characterizing the miscible state, engineering characterization of the miscible state after the reaction of CO2 and crude oil is performed.

[0012] Furthermore, the step S1: determining the relationship curve between oil displacement efficiency and displacement pressure by numerically simulating a capillary experiment to obtain the minimum miscible pressure includes:

[0013] Step S11: sampling the target reservoir formation fluid and performing high pressure physical property experiments to obtain PVT data;

[0014] Step S12: Check the component content of the PVT data, split the heavy components, reorganize the split components according to the principle of similar properties, and obtain pseudo-components representing the properties of the target reservoir formation fluid;

[0015] Step S13: performing fluid phase fitting on the pseudo-component representing the target reservoir formation fluid properties to obtain high-pressure critical parameters;

[0016] Step S14: Based on the high pressure critical parameters, a curve of relationship between oil displacement efficiency and displacement pressure is obtained through numerical simulation of a capillary tube experiment, and a minimum miscible pressure is determined.

[0017] Furthermore, the high-pressure physical property experiment includes: a constant composition expansion experiment, multiple degassing experiments and a viscosity measurement experiment.

[0018] Furthermore, the step S2: obtaining the relationship curve between the interfacial tension and the displacement pressure by numerically simulating the capillary experiment and determining the critical interfacial tension includes:

[0019] Step S21: determining the oil-gas relative permeability curve through a phase permeability experiment, and calculating the maximum oil displacement efficiency of the immiscible flooding according to the residual oil saturation determined by the oil-gas relative permeability curve;

[0020] Step S22: according to the results of the numerical simulation capillary tube experiment, determine the oil displacement efficiency and the oil displacement efficiency at the inflection point of the displacement pressure curve, and obtain the maximum oil displacement efficiency when displacing oil in a near-miscible state;

[0021] Step S23: establishing a variation curve of interfacial tension, oil displacement efficiency and displacement pressure, and determining the corresponding critical interfacial tension according to the maximum oil displacement efficiency of immiscible displacement and near-miscible displacement.

[0022] Furthermore, the maximum oil displacement efficiency of the immiscible flooding is calculated by the following formula:

[0023]

[0024] In the formula, E D Indicates oil displacement efficiency; S or Indicates residual oil saturation; S oi Indicates the original oil saturation.

[0025] Furthermore, in step S3, the miscible state includes: completely miscible, miscible, nearly miscible and immiscible states; the key parameters include: completely miscible characterization parameters, miscible characterization parameters and nearly miscible characterization parameters.

[0026] Furthermore, the step S4: based on the key parameters characterizing the miscible state, engineering characterization of the miscible state after the reaction of CO2 and crude oil is performed includes:

[0027] Based on the key parameters characterizing the miscible state, the miscible state is subdivided into four states according to two critical interfacial tensions, as follows:

[0028]

[0029] In the formula, σ mis The interfacial tension corresponding to the minimum miscible pressure is taken as the critical interfacial tension of miscible phase, that is, the interfacial tension corresponding to the maximum oil recovery efficiency in the near-miscible state; σ imm It represents the interfacial tension corresponding to the maximum oil displacement efficiency of immiscible displacement.

[0030] The present invention also provides a system for characterizing the miscible state of CO2 after the reaction of crude oil based on interfacial tension, the system comprising: a first determination module, a second determination module, a third determination module and a characterization module; wherein,

[0031] The first determination module is used to obtain a relationship curve between oil displacement efficiency and displacement pressure by numerically simulating a capillary experiment, and determine the minimum miscible pressure;

[0032] The second determination module is used to obtain the relationship between the interfacial tension and the displacement pressure through numerical simulation of the capillary experiment and determine the critical interfacial tension;

[0033] The third determination module is used to determine key parameters characterizing the miscible state based on the minimum miscible pressure and the critical interfacial tension;

[0034] The characterization module is used to perform engineering characterization of the miscible state after the reaction of CO2 and crude oil based on key parameters characterizing the miscible state.

[0035] Furthermore, the first determination module includes: a first acquisition unit, a second acquisition unit, a third acquisition unit and a first determination unit; wherein,

[0036] The first acquisition unit is used to sample the target reservoir formation fluid and perform high-pressure physical property experiments to obtain PVT data;

[0037] The second acquisition unit is used to check the component content of the PVT data, split the heavy components therein, reorganize the split components according to the principle of similar properties, and obtain pseudo-components representing the properties of the target reservoir formation fluid;

[0038] The third acquisition unit is used to acquire high pressure critical parameters for the pseudo-component representing the target reservoir formation fluid property;

[0039] The first determination unit is used to obtain a relationship curve between oil displacement efficiency and displacement pressure and determine a minimum miscible pressure based on the high-pressure critical parameter through a numerical simulation of a capillary tube experiment.

[0040] Furthermore, the second determination module includes: a calculation unit, a fourth acquisition unit and a second determination unit; wherein,

[0041] The calculation unit is used to determine the oil-gas relative permeability curve through phase permeability experiment, and calculate the maximum oil displacement efficiency of the immiscible flooding according to the residual oil saturation determined by the oil-gas relative permeability curve;

[0042] The fourth acquisition unit is used to determine the oil displacement efficiency at the inflection point of the relationship curve between oil displacement efficiency and displacement pressure according to the numerical simulation capillary test results, and to obtain the maximum oil displacement efficiency in the near-miscible state oil displacement;

[0043] The second determination unit is used to establish a variation curve of interfacial tension, oil displacement efficiency and displacement pressure, and determine the corresponding critical interfacial tension according to the maximum oil displacement efficiency of immiscible flooding and near-miscible flooding.

[0044] Furthermore, the characterization module is specifically used to subdivide the miscible state into four states according to two critical interfacial tensions based on the key parameters characterizing the miscible state, as follows:

[0045]

[0046] In the formula, σ mis The interfacial tension corresponding to the minimum miscible pressure is taken as the critical interfacial tension of miscible phase, that is, the interfacial tension corresponding to the maximum oil recovery efficiency in the near-miscible state; σ imm It represents the interfacial tension corresponding to the maximum oil displacement efficiency of immiscible displacement.

[0047] Technical effects and advantages of the present invention:

[0048] The present invention firstly samples the formation fluid and conducts high-pressure physical property experiments to obtain PVT (Pressure Volume Temperature) data, and performs fluid phase fitting, and determines the minimum miscible pressure through numerical simulation of capillary experiments; then the interface tension corresponding to immiscible drive and miscible drive is determined through the oil and gas relative permeability curve and the minimum miscible pressure, and the miscible state is divided into four states using the complete miscible interface tension, the miscible interface tension and the immiscible interface tension, namely: complete miscible, miscible, nearly miscible and immiscible. Compared with the prior art, the present invention proposes to divide the miscible state in combination with the size of the interface tension, further refine the miscible state in the CO2 drive process, reduce the error caused by the change of the minimum miscible pressure with the production time in the judgment of the miscible state, and make the miscible state in the CO2 drive development process more refined.

[0049] Other features and advantages of the present invention will be described in the following description, and partly become obvious from the description, or be understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0051] Figure 1 This is a flow chart of a method for characterizing the miscible state of CO2 and crude oil based on interfacial tension according to the present invention;

[0052] Figure 2 Schematic diagram of an exemplary numerical model of a simulated capillary experiment of the present invention;

[0053] Figure 3 It is a schematic diagram of an exemplary miscible state engineering characterization of the present invention;

[0054] Figure 4 is a curve diagram showing the relationship between oil displacement efficiency and displacement pressure of an exemplary numerical simulation slim tube experiment of the present invention;

[0055] Figure 5 This is an exemplary graph of oil and gas relative permeability in the study area of ​​the present invention;

[0056] Figure 6 This is a schematic diagram of an exemplary engineering characterization of the miscible state in the research area of ​​the present invention;

[0057] Figure 7 This is a schematic diagram of an exemplary system for characterizing the miscible state of CO2 and crude oil based on interfacial tension according to the present invention. DETAILED DESCRIPTION

[0058] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0059] In order to solve the deficiencies of the prior art, the present invention discloses a method for characterizing the miscible state of CO2 and crude oil based on interfacial tension. Figure 1 The following is a flow chart of a method for characterizing the miscible state of CO2 and crude oil based on interfacial tension according to the present invention. Figure 1 As shown, the method comprises the following steps:

[0060] Step S1: by numerically simulating a capillary experiment, a curve of relationship between oil displacement efficiency and displacement pressure is obtained, and the minimum miscible pressure is determined;

[0061] At present, the most commonly used method for determining the minimum miscible pressure in engineering is the capillary test method, which is time-consuming and expensive to implement in practice, and is easily affected by the dispersion of the sand filled in the capillary tube, resulting in misleading results. In order to eliminate these unfavorable factors, a method combined with numerical simulation is now used to construct a fluid model of the capillary test based on the fluid phase state fitting, so as to quickly obtain the minimum miscible pressure, which specifically includes the following steps:

[0062] Step S11: Obtain PVT data through high-voltage physical property experiments

[0063] The oil and gas samples of the separators of the typical well groups in the target reservoir block under a trial production system were sampled and the quality of the samples was checked. To make the samples representative, the sampling pressure was confirmed to be higher than the saturation pressure of the fluid. The oil and gas volume was calculated according to the production gas-oil ratio, and the original well flow composition and the amount of sampled oil and gas were obtained by gas chromatography experiments. The laboratory samples were prepared according to the calculation results. Based on this sample, constant quality expansion experiments, multiple degassing experiments and viscosity measurement experiments were carried out at formation temperature. The experimental data obtained were sorted out to check whether the experimental data conformed to the conventional knowledge, and whether the molar fractions of each component content added up to one. Before using it for fitting, it was noted that the units were converted uniformly.

[0064] Step S12: Splitting and reorganization of components

[0065] Due to the limitation of experimental methods, some high carbon number hydrocarbon compounds are difficult to separate and are combined into one component. The component content is determined by normalization analysis. The components composed of these high carbon number hydrocarbon mixtures are called "C n+ "Component. In fluid characterization, "C n+ The influence of the "C" component is more significant, but its thermodynamic properties are difficult to measure accurately. In order to characterize the fluid more accurately, it is necessary to n+ The components are subdivided into narrow fractions with higher carbon numbers and the high pressure critical parameters of each narrow fraction are determined. This process is called "C n+ "Split of components." n+ "The splitting process of the heavy component requires a lot of calculations, which are often achieved with the help of commercial software. After extension, the recombinant components are differentiated into several single carbon group components, but the number of single carbon group components after extension is too large, so they need to be properly merged and reorganized, which not only reduces the number of components and thus reduces the complexity of the calculation, but also accurately expresses the characteristics of the fluid. As the number of pseudo-components increases, the phase diagram is closer to the actual phase diagram. However, simply increasing the number of pseudo-components cannot improve the accuracy. In the process of recombination, it is necessary to consider whether the physical properties of the components are similar and whether the gap between the phase diagrams before and after the recombination is obvious.

[0066] Step S13: Fluid phase fitting

[0067] Fluid phase fitting is a process of constantly adjusting fitting parameters so that the fitting results and experimental data can be well matched, and obtaining high-pressure critical parameters that can accurately characterize the fluid characteristics. Generally, professional phase fitting software is used to complete the phase fitting of fluids. One of the most commonly used fitting software is the PVTi module in the reservoir numerical simulation software Eclipse developed by Schlumberger. This module is used to fit the PVT data obtained from the high-pressure physical property experiment of the reservoir formation fluid. The high-pressure physical property experiment includes: constant mass expansion experiment, multi-stage degassing experiment and viscosity test experiment. By repeatedly adjusting the fitting parameters, continuously performing regression parameter selection, sensitivity analysis, and regression analysis, a relatively satisfactory set of high-pressure critical parameters is finally obtained. This set of high-pressure critical parameters will be used for the subsequent numerical simulation model calculation.

[0068] Step S14: Numerical simulation of capillary experiment to determine minimum miscible pressure

[0069] The traditional capillary physical model device is filled with quartz sand to simulate porous media to meet the experimental seepage law. The criterion for determining miscibility is that the oil displacement efficiency reaches 90% after injecting 1.2PV of gas. Generally, multiple groups of displacement experiments with different pressures are set up during the measurement process, and the minimum miscibility pressure is determined based on the inflection point where the oil displacement efficiency changes with pressure.

[0070] The numerical simulation capillary experiment is to establish a component numerical simulation model based on the traditional capillary physical model. The parameters of the numerical simulation model include: the numerical simulation model size is 200*1*1, the grid step size in the X direction is 5cm, the grid step size in the Y direction is 1cm, the grid step size in the Z direction is 1cm, the average porosity is 0.1, the average permeability is 5430mD, and the pore volume is 100cm 3 , the fluid data in the numerical simulation model adopts the high-pressure critical parameters obtained by fluid fitting. An injection well and a production well are set at both ends of the constructed slim tube. As in the traditional slim tube physical experiment, the injection volume is assumed to be 1.2PV. By changing the displacement pressure of the numerical simulation model, a set of displacement pressure and oil recovery efficiency relationship curves are obtained. The pressure corresponding to the inflection point of the curve is the minimum miscibility pressure. Specifically, the minimum miscibility pressure is determined by the linear intersection method. The minimum miscibility pressure is determined by finding the mutation point of the slope on the relationship curve between oil recovery efficiency and displacement pressure. The numerical model of the simulated slim tube experiment is as follows: Figure 2 shown.

[0071] Step S2: by numerically simulating the capillary experiment, a relationship curve between the interfacial tension and the displacement pressure is obtained, and the critical interfacial tension is determined;

[0072] The interfacial tension curves under different displacement pressures are obtained by numerical simulation of capillary experiments. The critical interfacial tensions that need to be determined include: the interfacial tension when the near-miscible flooding oil displacement efficiency reaches the maximum and the interfacial tension when the immiscible flooding oil displacement efficiency reaches the maximum. The specific steps are as follows:

[0073] Step S21: Determine the oil-gas relative permeability curve through the phase permeability experiment, and calculate the maximum oil displacement efficiency of the immiscible flooding according to the residual oil saturation determined by the oil-gas relative permeability curve. The maximum oil displacement efficiency of the immiscible state can be calculated by the residual oil saturation in this state, and the residual oil saturation can be determined by the phase permeability experiment, and the calculation formula is as follows.

[0074]

[0075] In the formula, E D Indicates oil displacement efficiency; S or Indicates residual oil saturation; S oi Indicates the original oil saturation.

[0076] Step S22: According to the results of the numerical simulation capillary tube experiment, the oil displacement efficiency at the inflection point of the relationship curve between oil displacement efficiency and displacement pressure is determined, which is the maximum oil displacement efficiency of the near-miscible displacement.

[0077] Step S23: establishing a curve of interfacial tension, oil displacement efficiency and displacement pressure, and determining the corresponding critical interfacial tension according to the maximum oil displacement efficiency of immiscible flooding and near-miscible flooding.

[0078] Step S3: determining key parameters characterizing the miscible state based on the minimum miscible pressure and the critical interfacial tension;

[0079] The miscible state of oil and gas in porous media is described in more detail through critical interfacial tension. The range affected by the injected fluid in the reservoir is subdivided into four states: complete miscibility, miscibility, near-miscibility and immiscibility. The key points of the division are complete miscibility characterization parameters, miscibility characterization parameters and near-miscibility characterization parameters, respectively.

[0080] Step S31: Completely miscible characterization parameters

[0081] We define the point where the interfacial tension is equal to 0 as the point where the oil and gas phases are completely miscible. At this point, the oil-gas interface disappears and the oil recovery efficiency is theoretically 100%. However, this state is difficult to achieve in the reservoir due to the complex and variable nature of the fluid composition and pressure distribution. When the reservoir cannot be completely miscible and the interfacial tension is greater than zero, the oil recovery effect corresponding to the interfacial tension value in different ranges is also significantly different.

[0082] Step S32: Mixed phase characterization parameters

[0083] The minimum miscible pressure is used to divide the gas-to-oil displacement effect from a macroscopic average perspective. When the displacement pressure is higher than the minimum miscible pressure, the entire displacement process is considered to be a miscible displacement with a better oil displacement effect, while when the displacement pressure is lower than the minimum miscible pressure, the entire displacement process is considered to be a near-miscible displacement with a poor oil displacement effect. Here, we use the interfacial tension corresponding to the minimum miscible pressure as the critical interfacial tension of the miscible phase, that is, the interfacial tension corresponding to the maximum oil displacement efficiency in the near-miscible state, and use σ mis express.

[0084] Step S33: Near-miscible characterization parameters

[0085] The maximum oil displacement efficiency of immiscible displacement is calculated by the oil-gas relative permeability curve. The corresponding interfacial tension is the immiscible critical interfacial tension (i.e., the near miscible starting point), expressed as σ imm express.

[0086] Step S4: Based on the key parameters characterizing the miscible state, engineering characterization of the miscible state after the reaction of CO2 and crude oil is performed;

[0087] Based on the key parameters characterizing the miscible state, the miscible state is subdivided into four states according to two critical interfacial tensions, as follows:

[0088]

[0089] The addition of fully miscible regions and near-miscible regions to the traditional miscible characterization method is helpful to further understand the relationship between miscible phases and recovery rate on site and to select appropriate mining methods. Figure 3 Schematic diagram of an exemplary miscible state engineering characterization of the present invention, such as Figure 3 As shown in the figure, when the interfacial tension is 0, the oil displacement efficiency theoretically reaches 100%. At this time, the corresponding point is the key point of complete miscibility, and the corresponding area is the complete miscibility area. When the interfacial tension is greater than 0 but does not exceed σ mis The corresponding region is the miscible region, σ mis The corresponding pressure is the minimum miscible pressure, which is the miscible critical point commonly used in engineering. When the interfacial tension increases further until it reaches σ imm When , the corresponding area is the near-miscible area. The recovery factor of this area is slightly lower than that of the miscible and fully miscible areas but much higher than that of the immiscible area. imm It can be calculated through the phase permeability curve, which is the interfacial tension at the maximum recovery rate corresponding to the immiscible phase; when the interfacial tension is greater than σ imm When the displacement mode is immiscible displacement, the recovery factor decreases rapidly.

[0090] Example:

[0091] Step S1: Sampling of formation fluid and high-pressure physical property experiments are performed to obtain PVT data, and then fluid phase state fitting is performed. The minimum miscibility pressure is determined by numerical simulation of capillary experiments. Table 1 shows the high-pressure physical property experimental data of formation fluids, and Table 2 shows the composition of formation crude oil. Figure 4 This is a curve diagram showing the relationship between oil displacement efficiency and displacement pressure of an exemplary numerical simulation capillary tube experiment of the present invention. The minimum miscible pressure of the formation fluid obtained by step S11 is 16.44 MPa.

[0092] Table 1 Experimental data of high pressure physical properties of formation fluids

[0093]

[0094]

[0095] Table 2 Formation crude oil composition

[0096] Components Mole (%) <![CDATA[N2]]> 1 <![CDATA[CO2]]> 0.68 <![CDATA[H2S]]> 1.78 <![CDATA[CH4]]> 47 <![CDATA[C2H6]]> 6.95 <![CDATA[C3H8]]> 5.52 <![CDATA[i-C4H 10 ]]> 1.15 <![CDATA[n-C4H 10 ]]> 2.58 <![CDATA[i-C5H 12 ]]> 1.49 <![CDATA[n-C5H 12 ]]> 1.37 <![CDATA[pC6]]> 2.58 <![CDATA[pC7]]> 3.82 <![CDATA[pC8]]> 2.81 <![CDATA[pC9]]> 2.12 <![CDATA[pC 10+ ]]> 19.15 total 100

[0097] Step S2: Determine the relationship curve between interfacial tension and displacement pressure by numerical simulation capillary experiment method, and determine the critical interfacial tension corresponding to immiscible flooding and near-miscible flooding by using oil-gas relative permeability curve and minimum miscible pressure. Figure 5 This is an exemplary oil and gas relative permeability curve of the study area of ​​the present invention. The maximum oil recovery efficiency under the immiscible state is 57.8% obtained through the calculation formula.

[0098] Step S3: Determine the key parameters that characterize the miscible state. By changing the displacement pressure of the model, the minimum miscible pressure of the formation fluid is obtained to be 16.44 MPa, and the corresponding interfacial tension is 0.11 mN / m. According to the residual oil saturation of the oil and gas permeability curve in the study area, the maximum oil recovery efficiency under the immiscible state is calculated to be 57.8%, and the corresponding interfacial tension is 0.96 mN / m.

[0099] Step S4: Describe the engineering characterization method for the miscible state after the reaction of CO2 and crude oil. Figure 6 Schematic diagram of the engineering characterization of the miscible state in the research area of ​​the present invention. Figure 6 As shown in the figure, the critical interfacial tension parameters determined by the above steps are: when the interfacial tension of the oil and gas phases in the study area is 0, it is in a completely miscible state; when the interfacial tension is 0-0.11mN / m, it is in a miscible state; when the interfacial tension is 0.11-0.96mN / m, it is in a near-miscible state; when the interfacial tension is greater than 0.96mN / m, it is in an immiscible state.

[0100] The present invention also discloses a system for characterizing the miscible state of CO2 and crude oil based on interfacial tension. Figure 7 FIG. 1 is a schematic diagram of a system for characterizing the miscible state of CO2 and crude oil based on interfacial tension according to an exemplary embodiment of the present invention. Figure 7 As shown, the system includes: a first determination module 11, a second determination module 12, a third determination module 13 and a characterization module 14; wherein the first determination module 11 is used to obtain a curve of the relationship between oil recovery efficiency and displacement pressure and determine the minimum miscibility pressure by numerically simulating a capillary experiment; the second determination module 12 is used to obtain a relationship between interfacial tension and displacement pressure and determine the critical interfacial tension by numerically simulating a capillary experiment; the third determination module 13 is used to determine key parameters characterizing the miscibility state based on the minimum miscibility pressure and the critical interfacial tension; the characterization module 14 is used to perform engineering characterization of the miscibility state after the action of CO2 and crude oil based on the key parameters characterizing the miscibility state.

[0101] Furthermore, the first determination module 11 includes: a first acquisition unit, a second acquisition unit, a third acquisition unit and a first determination unit; wherein the first acquisition unit is used to sample the target reservoir formation fluid and perform high-pressure physical property experiments to obtain PVT data; the second acquisition unit is used to check the component content of the PVT data, split and reorganize the heavy components therein, and obtain pseudo-components representing the properties of the target reservoir formation fluid; the third acquisition unit is used to obtain high-pressure critical parameters for the pseudo-components representing the properties of the target reservoir formation fluid; the first determination unit is used to obtain the relationship curve between oil recovery efficiency and displacement pressure and determine the minimum miscibility pressure based on the high-pressure critical parameters through numerical simulation of capillary experiments.

[0102] Furthermore, the second determination module 12 includes: a calculation unit, a fourth acquisition unit and a second determination unit; wherein the calculation unit is used to determine the oil-gas relative permeability curve through a phase permeability experiment, and calculate the maximum oil recovery efficiency of the immiscible drive according to the residual oil saturation determined by the oil-gas relative permeability curve; the fourth acquisition unit is used to determine the oil recovery efficiency at the inflection point of the curve of the relationship between the oil recovery efficiency and the displacement pressure according to the results of the numerical simulation capillary experiment, and obtain the maximum oil recovery efficiency when the oil is recovered in a near-miscible state; the second determination unit is used to establish a curve of the change of the interfacial tension and the oil recovery efficiency and the displacement pressure, and determine the corresponding critical interfacial tension according to the maximum oil recovery efficiencies of the immiscible drive and the near-miscible drive.

[0103] Furthermore, the characterization module 14 is specifically used to subdivide the miscible state into four states according to two critical interfacial tensions based on the key parameters characterizing the miscible state, as follows:

[0104]

[0105] In the formula, σ mis The interfacial tension corresponding to the minimum miscible pressure is taken as the critical interfacial tension of miscible phase, that is, the interfacial tension corresponding to the maximum oil recovery efficiency in the near-miscible state; σ imm It represents the interfacial tension corresponding to the maximum oil displacement efficiency of immiscible displacement.

[0106] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for characterizing the miscible state of CO2 and crude oil based on interfacial tension, characterized in that: The method comprises the following steps: Step S1: by numerically simulating a capillary experiment, a curve of relationship between oil displacement efficiency and displacement pressure is obtained, and the minimum miscible pressure is determined; Step S2: by numerically simulating the capillary experiment, a relationship curve between the interfacial tension and the displacement pressure is obtained, and the critical interfacial tension is determined; Step S3: determining key parameters characterizing the miscible state based on the minimum miscible pressure and the critical interfacial tension; Step S4: Based on the key parameters characterizing the miscible state, engineering characterization of the miscible state after the reaction of CO2 and crude oil is performed.

2. The method for characterizing the miscible state of CO2 and crude oil based on interfacial tension according to claim 1, characterized in that: The step S1: determining the relationship curve between oil displacement efficiency and displacement pressure through numerical simulation of capillary tube experiment, and obtaining the minimum miscible pressure, comprises: Step S11: sampling the target reservoir formation fluid and performing high pressure physical property experiments to obtain PVT data; Step S12: Check the component content of the PVT data, split the heavy components, reorganize the split components according to the principle of similar properties, and obtain pseudo-components representing the properties of the target reservoir formation fluid; Step S13: performing fluid phase fitting on the pseudo-component representing the target reservoir formation fluid properties to obtain high-pressure critical parameters; Step S14: Based on the high pressure critical parameters, a curve of relationship between oil displacement efficiency and displacement pressure is obtained through numerical simulation of a capillary tube experiment, and a minimum miscible pressure is determined.

3. A method for characterizing the miscible state of CO2 and crude oil based on interfacial tension according to claim 1 or 2, characterized in that: The high-pressure physical property experiment includes: a constant composition expansion experiment, a multiple degassing experiment and a viscosity measurement experiment.

4. The method for characterizing the miscible state of CO2 and crude oil based on interfacial tension according to claim 1, characterized in that: The step S2: obtaining the relationship curve between the interfacial tension and the displacement pressure by numerically simulating the capillary experiment and determining the critical interfacial tension comprises: Step S21: determining the oil-gas relative permeability curve through a phase permeability experiment, and calculating the maximum oil displacement efficiency of the immiscible flooding according to the residual oil saturation determined by the oil-gas relative permeability curve; Step S22: according to the results of the numerical simulation capillary tube experiment, determine the oil displacement efficiency and the oil displacement efficiency at the inflection point of the displacement pressure curve, and obtain the maximum oil displacement efficiency when displacing oil in a near-miscible state; Step S23: establishing a variation curve of interfacial tension, oil displacement efficiency and displacement pressure, and determining the corresponding critical interfacial tension according to the maximum oil displacement efficiency of immiscible displacement and near-miscible displacement.

5. The method for characterizing the miscible state of CO2 and crude oil based on interfacial tension according to claim 4, characterized in that: The maximum displacement efficiency of the immiscible flooding is calculated by the following formula: In the formula, E D Indicates oil displacement efficiency; S or Indicates residual oil saturation; S oi Indicates the original oil saturation.

6. The method for characterizing the miscible state of CO2 and crude oil based on interfacial tension according to claim 1, characterized in that: In step S3, the miscible state includes: completely miscible, miscible, nearly miscible and immiscible states; the key parameters include: completely miscible characterization parameters, miscible characterization parameters and nearly miscible characterization parameters.

7. The method for characterizing the miscible state of CO2 and crude oil based on interfacial tension according to claim 1, characterized in that: The step S4: based on the key parameters characterizing the miscible state, engineering characterization of the miscible state after the reaction of CO2 and crude oil is performed, includes: Based on the key parameters characterizing the miscible state, the miscible state is subdivided into four states according to two critical interfacial tensions, as follows: In the formula, σ mis The interfacial tension corresponding to the minimum miscible pressure is taken as the critical interfacial tension of miscible phase, that is, the interfacial tension corresponding to the maximum oil recovery efficiency in the near-miscible state; σ imm It represents the interfacial tension corresponding to the maximum oil displacement efficiency of immiscible displacement.

8. A system for characterizing the miscible state of CO2 and crude oil based on interfacial tension, characterized in that: The system comprises: a first determination module, a second determination module, a third determination module and a characterization module; wherein, The first determination module is used to obtain a relationship curve between oil displacement efficiency and displacement pressure by numerically simulating a capillary experiment, and determine the minimum miscible pressure; The second determination module is used to obtain the relationship between the interfacial tension and the displacement pressure through numerical simulation of the capillary experiment and determine the critical interfacial tension; The third determination module is used to determine key parameters characterizing the miscible state based on the minimum miscible pressure and the critical interfacial tension; The characterization module is used to perform engineering characterization of the miscible state after the reaction of CO2 and crude oil based on key parameters characterizing the miscible state.

9. The system for characterizing the miscible state of CO2 and crude oil after the interaction based on interfacial tension according to claim 8 is characterized in that: The first determination module includes: a first acquisition unit, a second acquisition unit, a third acquisition unit and a first determination unit; wherein, The first acquisition unit is used to sample the target reservoir formation fluid and perform high-pressure physical property experiments to obtain PVT data; The second acquisition unit is used to check the component content of the PVT data, split the heavy components therein, reorganize the split components according to the principle of similar properties, and obtain pseudo-components representing the properties of the target reservoir formation fluid; The third acquisition unit is used to acquire high pressure critical parameters for the pseudo-component representing the target reservoir formation fluid property; The first determination unit is used to obtain a relationship curve between oil displacement efficiency and displacement pressure and determine a minimum miscible pressure based on the high pressure critical parameter through numerical simulation of a capillary tube experiment.

10. The system for characterizing the miscible state of CO2 and crude oil after the interaction based on interfacial tension according to claim 8, characterized in that: The second determination module includes: a calculation unit, a fourth acquisition unit and a second determination unit; wherein, The calculation unit is used to determine the oil-gas relative permeability curve through phase permeability experiment, and calculate the maximum oil displacement efficiency of the immiscible flooding according to the residual oil saturation determined by the oil-gas relative permeability curve; The fourth acquisition unit is used to determine the oil displacement efficiency at the inflection point of the relationship curve between oil displacement efficiency and displacement pressure according to the numerical simulation capillary test results, and to obtain the maximum oil displacement efficiency in the near-miscible state oil displacement; The second determination unit is used to establish a variation curve of interfacial tension, oil displacement efficiency and displacement pressure, and determine the corresponding critical interfacial tension according to the maximum oil displacement efficiency of immiscible flooding and near-miscible flooding.

11. The system for characterizing the miscible state of CO2 and crude oil based on interfacial tension according to claim 8, characterized in that: The characterization module is specifically used to subdivide the miscible state into four states based on the key parameters characterizing the miscible state and two critical interfacial tensions, as follows: In the formula, σ mis The interfacial tension corresponding to the minimum miscible pressure is taken as the critical interfacial tension of miscible phase, that is, the interfacial tension corresponding to the maximum oil recovery efficiency in the near-miscible state; σ imm It represents the interfacial tension corresponding to the maximum oil displacement efficiency of immiscible displacement.

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