Method and system for characterizing the miscibility state of co2 and crude oil after interaction based on interfacial tension

Abstract

The application discloses a CO2 and crude oil mixed phase state characterization method and system based on interfacial tension, relates to the technical field of CO2 flooding development of oil reservoirs, and comprises the following steps: S1, obtaining the oil displacement efficiency and displacement pressure relationship curve and determining the minimum miscibility pressure through numerical simulation of a tubular experiment; S2, obtaining the interfacial tension and displacement pressure relationship curve and determining the critical interfacial tension through numerical simulation of a tubular experiment; S3, determining the key parameter for characterizing the mixed phase state based on the minimum miscibility pressure and the critical interfacial tension; and S4, performing engineering characterization of the mixed phase state after the action of CO2 and crude oil based on the key parameter for characterizing the mixed phase state. The application divides the mixed phase state in combination with the size of the interfacial tension, further refines the mixed phase state in the CO2 flooding process, reduces the error caused by the change of the minimum miscibility pressure with the mining time on the judgment of the mixed phase state, and makes the mixed phase state in the CO2 flooding development process more finely characterized.

Description

Technical Field

[0001] This invention relates to the field of CO2 flooding development technology for oil reservoirs, and in particular to a method and system for characterizing the miscible state of CO2 and crude oil after interaction based on interfacial tension. Background Technology

[0002] Conventional waterflooding is costly and slow to take effect. When the formation water and injected water are incompatible, problems such as injection difficulties and severe pressure build-up in injection wells can occur. Currently, after half a century of waterflooding development, most oilfields worldwide have achieved an overall water cut exceeding 90%, with some blocks reaching as high as 95%, leading to increasingly poor waterflooding performance. According to Hall curves, gas injection capacity is generally 2 to 6 times that of water. Therefore, for reservoirs where conventional waterflooding yields low recovery rates and is difficult to develop economically, gas injection development can be considered. Gas-driven recovery technology is a widely recognized tertiary oil recovery technology that rivals chemical flooding and thermal recovery in recent years. It has a wide range of applications, does not have overly complex requirements on reservoir properties, and has a very broad development prospect.

[0003] Both indoor and field tests have shown that CO2 is a highly ideal oil displacement agent compared to other injected gases. Besides the displacement mechanisms inherent in general gas drive, it also possesses unique displacement mechanisms due to its high solubility in oil and water: under certain temperature and pressure conditions, after CO2 injection comes into contact with crude oil, the lighter components in the crude oil are extracted, enriching the CO2. The difference in composition between the two phases decreases, and the interfacial tension between the two phases gradually decreases until it reaches zero, thus forming a miscible phase and achieving optimal oil displacement. Both theoretical and field practice indicate that CO2 miscible flooding has significantly higher oil displacement efficiency than immiscible flooding. In the United States, CO2 gas drive projects are primarily based on miscible flooding, with as many as 128 projects, accounting for 94.7% of the total. In terms of enhanced oil recovery, CO2 miscible flooding yields 1264 × 10⁻⁶ tons. 4 t / a, accounting for 92.2% of the total enhanced oil recovery production from CO2 flooding.

[0004] Traditional classification standards divide CO2 flooding into two types: miscible flooding and immiscible flooding. There are three main approaches to this distinction: one is based on the minimum miscibility pressure between the oil and gas phases; when the formation pressure is greater than the minimum miscibility pressure, miscible flooding is considered feasible, while when the formation pressure is less than or equal to the minimum miscibility pressure, it is considered immiscible or near-miscible. Another approach is based on the interfacial tension between the oil and gas; theoretically, a zero interfacial tension defines miscibility, while a greater than zero interfacial tension defines immiscibility. The last approach is based on the principle that injected CO2 needs to undergo multi-stage contact with crude oil to achieve miscibility, defining a minimum enrichment concentration for the injected gas; that is, when the injected gas content reaches this specific value, it can achieve miscibility with the crude oil (minimum enrichment level). Currently, the most commonly used method in engineering is the first minimum miscibility pressure method, while the second interfacial tension method is mainly used in laboratory settings to determine miscibility.

[0005] In actual oil reservoirs, pressure and fluid composition exhibit far more complex spatiotemporal variations. Simply classifying reservoirs into miscible and immiscible flooding cannot accurately describe the gas injection and development process. Some scholars use interfacial tension to study gas-driven oil recovery, but they haven't provided a clear standard or reasonable basis for classifying different miscibility states based on interfacial tension. Therefore, a more explicit and detailed characterization method is needed for the miscibility state of oil and gas during gas-driven processes. Summary of the Invention

[0006] The purpose of this invention is to provide a method and system for characterizing the miscibility of crude oil after the interaction of CO2 and crude oil based on interfacial tension, in order to solve the problem that existing methods are not clear enough in determining the miscibility of oil reservoirs developed by CO2 flooding. To achieve the above objective, this invention provides the following technical solution:

[0007] This invention provides a method for characterizing the miscibility state of CO2 and crude oil after interaction based on interfacial tension. The method includes the following steps:

[0008] Step S1: Obtain the relationship curve between oil displacement efficiency and displacement pressure through numerical simulation of capillary experiments, and determine the minimum miscibility pressure;

[0009] Step S2: Obtain the relationship curve between interfacial tension and displacement pressure through numerical simulation of the thin tube experiment, and determine the critical interfacial tension;

[0010] Step S3: Based on the minimum miscibility pressure and critical interfacial tension, determine the key parameters characterizing the miscibility state;

[0011] Step S4: Based on the key parameters characterizing the miscibility state, perform engineering characterization of the miscibility state after the interaction of CO2 and crude oil.

[0012] Further, step S1: determining the relationship curve between oil displacement efficiency and displacement pressure through numerical simulation of capillary experiments, and obtaining the minimum miscibility pressure, includes:

[0013] Step S11: Sample the formation fluid of the target oil reservoir and conduct high-pressure physical property tests to obtain PVT data;

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

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

[0016] Step S14: Based on the high-pressure critical parameters, obtain the relationship curve between oil displacement efficiency and displacement pressure through numerical simulation of the thin tube experiment, and determine the minimum miscibility pressure.

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

[0018] Further, step S2: obtaining the relationship curve between interfacial tension and displacement pressure through numerical simulation of a thin tube experiment, and determining the critical interfacial tension, includes:

[0019] Step S21: Determine the relative permeability curve of oil and gas through a relative permeability experiment, and calculate the maximum oil displacement efficiency of immiscible flooding based on the residual oil saturation determined by the relative permeability curve of oil and gas.

[0020] Step S22: Based on the results of the numerical simulation capillary experiment, determine the oil displacement efficiency at the inflection point of the displacement pressure curve and obtain the maximum oil displacement efficiency when the oil is in a near-miscible state.

[0021] Step S23: Establish the variation curves of interfacial tension and oil displacement efficiency with displacement pressure, and determine the corresponding critical interfacial tension based on the maximum oil displacement efficiency of immiscible and near-miscible oil 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 This indicates the original oil saturation.

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

[0026] Further, step S4: based on key parameters characterizing the miscibility state, engineering characterization of the miscibility state after the interaction of CO2 and crude oil is performed, including:

[0027] Based on the key parameters characterizing the miscible state, the miscible state is further 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 miscibility pressure is called the critical interfacial tension, which is the interfacial tension corresponding to the maximum oil displacement efficiency during near-miscible oil displacement; σ imm This represents the interfacial tension corresponding to the maximum oil displacement efficiency of immiscible displacement.

[0030] This invention also provides a characterization system for the miscibility of CO2 and crude oil after interaction based on interfacial tension. The system includes: a first determining module, a second determining module, a third determining module, and a characterization module; wherein,

[0031] The first determining module is used to obtain the relationship curve between oil displacement efficiency and displacement pressure through numerical simulation of capillary experiments, and to determine the minimum miscibility pressure;

[0032] The second determining module is used to obtain the relationship between interfacial tension and displacement pressure through numerical simulation of a thin tube experiment, and to determine the critical interfacial tension;

[0033] The third determining module is used to determine key parameters characterizing the miscibility state based on the minimum miscibility pressure and critical interfacial tension.

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

[0035] Further, the first determining module includes: a first acquiring unit, a second acquiring unit, a third acquiring unit, and a first determining unit; wherein,

[0036] The first acquisition unit is used to sample the formation fluid of the target oil reservoir and conduct 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, and reassemble the split components according to the principle of similar properties to obtain pseudo-components that represent the formation fluid properties of the target reservoir.

[0038] The third acquisition unit is used to acquire high-pressure critical parameters from the pseudo-components representing the formation fluid properties of the target oil reservoir.

[0039] The first determining unit is used to obtain the relationship curve between oil displacement efficiency and displacement pressure by numerical simulation of a thin tube experiment based on the high-pressure critical parameters, and to determine the minimum miscibility pressure.

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

[0041] The calculation unit is used to determine the relative permeability curve of oil and gas through a relative permeability experiment, and to calculate the maximum oil displacement efficiency of the immiscible flooding based on the residual oil saturation determined by the relative permeability curve of oil and gas.

[0042] The fourth acquisition unit is used to determine the oil displacement efficiency at the inflection point of the curve relating oil displacement efficiency and displacement pressure based on the results of the numerical simulation capillary experiment, and to obtain the maximum oil displacement efficiency when oil is driven in a near-miscible state.

[0043] The second determining unit is used to establish the variation curves of interfacial tension and oil displacement efficiency with displacement pressure, and to determine the corresponding critical interfacial tension based on the maximum oil displacement efficiency of immiscible and near-miscible flooding.

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

[0045]

[0046] In the formula, σ mis The interfacial tension corresponding to the minimum miscibility pressure is called the critical interfacial tension, which is the interfacial tension corresponding to the maximum oil displacement efficiency during near-miscible oil displacement; σ imm This represents the interfacial tension corresponding to the maximum oil displacement efficiency of immiscible displacement.

[0047] The technical effects and advantages of this invention are as follows:

[0048] This invention first obtains PVT (Pressure Volume Temperature) data by sampling formation fluids and conducting high-pressure physical property experiments, and then performs fluid phase fitting. The minimum miscibility pressure is determined through numerical simulation and capillary experiments. Next, the interfacial tensions corresponding to immiscible and miscible flooding are determined using the relative permeability curves of oil and gas and the minimum miscibility pressure. The miscibility state is then divided into four states using the interfacial tensions of fully miscible, miscible, near-miscible, and immiscible interfaces: fully miscible, miscible, near-miscible, and immiscible. Compared to existing technologies, this invention proposes classifying the miscibility state based on the magnitude of interfacial tension, further refining the miscibility state during CO2 flooding, reducing errors caused by the change in minimum miscibility pressure with production time, and enabling a more precise characterization of the miscibility state during CO2 flooding development.

[0049] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description and the drawings. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used 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 those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 This is an exemplary flowchart of a method for characterizing the miscible state of CO2 and crude oil after interaction based on interfacial tension, according to the present invention.

[0052] Figure 2 This is a schematic diagram of an exemplary numerical model of a simulated capillary tube experiment according to the present invention;

[0053] Figure 3 This is an exemplary engineering characterization diagram of the mixed-phase state of the present invention;

[0054] Figure 4 The graph shows the relationship between oil displacement efficiency and displacement pressure in a numerical simulation capillary experiment exemplified by this invention.

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

[0056] Figure 6 This is an exemplary schematic diagram of the engineering characterization of the mixed-phase state in the study area of ​​this invention;

[0057] Figure 7 This is a schematic diagram of a system for characterizing the miscible state of CO2 and crude oil after interaction, based on interfacial tension, as exemplified by the present invention. Detailed Implementation

[0058] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0059] To address the shortcomings of existing technologies, this invention discloses a method for characterizing the miscibility state of CO2 and crude oil after interaction based on interfacial tension. Figure 1 This is a flowchart illustrating an exemplary method for characterizing the miscible state of CO2 and crude oil after interaction based on interfacial tension, as described in the present invention. Figure 1 As shown, the method includes the following steps:

[0060] Step S1: Obtain the relationship curve between oil displacement efficiency and displacement pressure through numerical simulation of capillary experiments, and determine the minimum miscibility pressure;

[0061] Currently, the most commonly used method for determining minimum miscibility pressure in engineering is the capillary tube test method. However, this method is time-consuming, expensive, and easily affected by the dispersion of sand within the capillary tube, leading to misleading results. To overcome these drawbacks, a method combining numerical simulation and capillary tube testing is employed. Based on fluid phase fitting, a fluid model of the capillary tube test is constructed to quickly obtain the minimum miscibility pressure. The specific steps include the following:

[0062] Step S11: Obtain PVT data through high-pressure property experiments.

[0063] Oil and gas samples were taken from separators of typical well groups in the target reservoir block under one trial production regime. The quality of the samples was checked, and to ensure representativeness, the sampling pressure was confirmed to be higher than the fluid saturation pressure. Oil and gas volume were calculated based on the production gas-oil ratio, and gas chromatography was used to determine the original well fluid composition and the required oil and gas quantities for sample preparation. Laboratory samples were then prepared based on the calculation results. Using these samples as a basis, constant-mass expansion experiments at formation temperature, multiple degassing experiments, and viscosity measurements were conducted. The experimental data were compiled, and their consistency with conventional understanding was checked. The sum of the mole fractions of each component was verified to be equal to one. Before using the data for fitting, unit conversions were ensured to be consistent.

[0064] Step S12: Splitting and Recombination of Components

[0065] Due to limitations in experimental methods, some high-carbon-number hydrocarbon compounds are difficult to separate and are often combined into a single component. The composition of this component is determined through normalization analysis. The components of these high-carbon-number hydrocarbon mixtures are referred to as "C". n+ "Components. In fluid characterization, "C" n+ "The influence of components is quite significant, but their thermodynamic properties are difficult to determine accurately. To more accurately characterize fluids, it is necessary to..." n+ "The process of further subdividing the components into narrow fractions with higher carbon numbers and determining the high-pressure critical parameters for each narrow fraction is called 'C'." n+ "Component splitting." C n+ "The splitting process of recombinant components requires extensive computation, often relying on commercial software. After extension, the recombinant components are divided into several single-carbon array components. However, the number of single-carbon array components after extension is too large, necessitating appropriate merging and recombining. This reduces the number of components, thereby lowering the computational complexity, while still accurately representing the characteristics of the fluid. As the number of pseudo-components increases, the phase diagram becomes closer to the actual phase diagram. However, simply increasing the number of pseudo-components does not improve accuracy. During the recombining process, it is essential to consider whether the physical properties of the components are similar and whether the difference between the phase diagrams before and after recombining is significant."

[0066] Step S13: Fluid phase fitting

[0067] Fluid phase fitting involves continuously adjusting fitting parameters to ensure a good match between the fitted results and experimental data, thereby obtaining high-pressure critical parameters that accurately characterize the fluid. Specialized phase fitting software is typically used for fluid phase fitting. One of the most commonly used software programs is the PVTi module in Eclipse, a reservoir numerical simulation software developed by Schlumberger. This module is used to fit PVT data obtained from high-pressure physical property experiments on reservoir fluids. These experiments include constant mass expansion experiments, multi-stage degassing experiments, and viscosity testing experiments. By repeatedly adjusting the fitting parameters and continuously performing regression parameter selection, sensitivity analysis, and regression analysis, a satisfactory set of high-pressure critical parameters is finally obtained. This set of high-pressure critical parameters will be used for subsequent numerical simulation model calculations.

[0068] Step S14: Determine the minimum miscibility pressure using a capillary tube experiment using numerical simulation.

[0069] Traditional thin-tube physical model devices are filled with quartz sand to simulate porous media and meet the seepage laws of experiments. The standard for determining miscibility is that the oil displacement efficiency reaches 90% after injecting 1.2PV of gas. In general, multiple displacement experiments with different pressures are set up during the measurement process, and the minimum miscibility pressure is determined according to the inflection point of the oil displacement efficiency with pressure.

[0070] The numerical simulation experiment of the capillary tube was based on a traditional capillary tube physical model, which established a component numerical simulation model. The parameters of this numerical simulation model include: model size of 200*1*1, grid step size of 5cm in the X direction, 1cm in the Y direction, 1cm in the Z direction, average porosity of 0.1, average permeability of 5430mD, and pore volume of 100cm³. 3 In the numerical simulation model, the fluid data uses high-pressure critical parameters obtained through fluid fitting. An injection well and a production well are set at each end of the constructed capillary tube. Similar to traditional capillary physics experiments, the injection rate is assumed to be 1.2 PV. By changing the displacement pressure in the numerical simulation model, a set of displacement pressure versus oil displacement efficiency relationship curves are obtained. The pressure corresponding to the inflection point of this curve is the minimum miscibility pressure. Specifically, the minimum miscibility pressure is determined using the linear intersection method, by finding the abrupt change point of the slope on the oil displacement efficiency versus displacement pressure relationship curve. The numerical model for the capillary tube experiment is as follows: Figure 2 As shown.

[0071] Step S2: Obtain the relationship curve between interfacial tension and displacement pressure through numerical simulation of the thin tube experiment, and determine the critical interfacial tension;

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

[0073] Step S21: Determine the relative permeability curve of oil and gas through a relative permeability experiment, and calculate the maximum oil displacement efficiency of immiscible flooding based on the residual oil saturation determined by the relative permeability curve. The maximum oil displacement efficiency in the immiscible state can be calculated from the residual oil saturation in that state, and the residual oil saturation can be determined through a relative permeability experiment, as shown in the following formula.

[0074]

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

[0076] Step S22: Based on the results of the numerical simulation capillary experiment, determine the oil displacement efficiency at the inflection point of the curve relating oil displacement efficiency and displacement pressure, which is the maximum oil displacement efficiency of near-miscible displacement.

[0077] Step S23: Establish the variation curves of interfacial tension and oil displacement efficiency with displacement pressure, and determine the corresponding critical interfacial tension based on the maximum oil displacement efficiency of immiscible and near-miscible flooding.

[0078] Step S3: Based on the minimum miscibility pressure and critical interfacial tension, determine the key parameters characterizing the miscibility state;

[0079] The critical interfacial tension is used to describe the miscibility of oil and gas in porous media in more detail. The range affected by the injected fluid in the reservoir is subdivided into four states: fully miscible, miscible, nearly miscible and immiscible. The key points for the division are the fully miscible characterization parameter, the miscible characterization parameter and the nearly miscible characterization parameter, respectively.

[0080] Step S31: Parameters for characterizing fully miscible phases

[0081] We define the point where the interfacial tension equals 0 as the point of complete miscibility between the oil and gas phases. At this point, the oil-gas interface disappears, and the oil displacement efficiency is theoretically 100%. However, this state is difficult to achieve in oil reservoirs due to the complex and variable nature of fluid composition and pressure distribution. When complete miscibility cannot be achieved in an oil reservoir, and the interfacial tension is greater than zero, the corresponding oil displacement effect varies significantly depending on the range of interfacial tension values.

[0082] Step S32: Miscibility Characterization Parameters

[0083] The minimum miscibility pressure is used to classify the effectiveness of gas-driven oil displacement from a macroscopic average perspective. When the displacement pressure is higher than the minimum miscibility pressure, the entire displacement process is considered to be a well-performing miscible displacement, while when the displacement pressure is lower than the minimum miscibility pressure, the entire displacement process is considered to be a poorly perishable displacement. Here, we use the interfacial tension corresponding to the minimum miscibility pressure as the critical interfacial tension, that is, the interfacial tension corresponding to the maximum oil displacement efficiency in near-miscible state oil displacement, denoted by σ. mis express.

[0084] Step S33: Near-Mixturbinates Characterization Parameters

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

[0086] Step S4: Based on the key parameters characterizing the miscibility state, perform engineering characterization of the miscibility state after the interaction of CO2 and crude oil;

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

[0088]

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

[0090] Example:

[0091] Step S1: Sampling and high-pressure physical property experiments were conducted on the formation fluids to obtain PVT data. Then, fluid phase fitting was performed, and the minimum miscibility pressure was determined through numerical simulation of capillary experiments. Table 1 shows the high-pressure physical property experimental data of the formation fluids, and Table 2 shows the composition of the formation crude oil. Figure 4 The curve showing the relationship between oil displacement efficiency and displacement pressure in the numerical simulation capillary experiment of this invention is an example of the present invention. The minimum miscibility pressure of the formation fluid obtained through step S11 is 16.44 MPa.

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

[0093]

[0094]

[0095] Table 2 Composition of Crude Oil in Formations

[0096] Components Moles (%) <![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 using numerical simulation capillary experiments. Then, determine the critical interfacial tension corresponding to immiscible and near-immiscible flooding using the relative permeability curves of oil and gas and the minimum miscibility pressure. Figure 5 The relative permeability curve of oil and gas in the study area is an example of the present invention. The maximum oil displacement efficiency under immiscible conditions is 57.8% obtained by calculation formula.

[0098] Step S3: Determine the key parameters characterizing the miscibility state. By changing the displacement pressure of the model, the minimum miscibility pressure of the formation fluid is obtained as 16.44 MPa, at which point the corresponding interfacial tension is 0.11 mN / m. Based on the residual oil saturation of the oil-gas phase permeability curve in the study area, the maximum oil displacement efficiency under the immiscible state is calculated to be 57.8%, with a corresponding interfacial tension of 0.96 mN / m.

[0099] Step S4: Describe the miscibility of CO2 and crude oil after their interaction using engineering characterization methods. Figure 6 This is an exemplary schematic diagram of the engineering characterization of the miscible state in the study area of ​​this invention, as shown below. Figure 6 As shown, the critical interfacial tension parameters determined through the above steps indicate that the oil and gas phases in the study area are in a completely miscible state when the interfacial tension is 0, in a miscible state when the interfacial tension is between 0 and 0.11 mN / m, in a near-miscible state when the interfacial tension is between 0.11 and 0.96 mN / m, and in an immiscible state when the interfacial tension is greater than 0.96 mN / m.

[0100] This invention also discloses a system for characterizing the miscible state of CO2 and crude oil after interaction based on interfacial tension. Figure 7 This is a schematic diagram of an exemplary system for characterizing the miscible state of CO2 and crude oil after interaction, based on interfacial tension, according to the present invention. Figure 7 As shown, the system includes: a first determining module 11, a second determining module 12, a third determining module 13, and a characterization module 14; wherein, the first determining module 11 is used to obtain the relationship curve between oil displacement efficiency and displacement pressure through numerical simulation of capillary experiments, and determine the minimum miscibility pressure; the second determining module 12 is used to obtain the relationship between interfacial tension and displacement pressure through numerical simulation of capillary experiments, and determine the critical interfacial tension; the third determining 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 interaction of CO2 and crude oil based on the key parameters characterizing the miscibility state.

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

[0102] Further, the second determining module 12 includes: a calculation unit, a fourth acquisition unit, and a second determining unit; wherein, the calculation unit is used to determine the relative permeability curve of oil and gas through relative permeability experiments, and calculate the maximum oil displacement efficiency of immiscible flooding based on the residual oil saturation determined by the relative permeability curve of oil and gas; the fourth acquisition unit is used to determine the oil displacement efficiency at the inflection point of the oil displacement efficiency versus displacement pressure curve based on the results of numerical simulation capillary experiments, and obtain the maximum oil displacement efficiency when flooding in near-miscible state; the second determining unit is used to establish the variation curves of interfacial tension and oil displacement efficiency versus displacement pressure, and determine the corresponding critical interfacial tension based on the maximum oil displacement efficiency of immiscible flooding and near-miscible flooding.

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

[0104]

[0105] In the formula, σ mis The interfacial tension corresponding to the minimum miscibility pressure is called the critical interfacial tension, which is the interfacial tension corresponding to the maximum oil displacement efficiency during near-miscible oil displacement; σ imm This represents the interfacial tension corresponding to the maximum oil displacement efficiency of immiscible displacement.

[0106] Finally, it should be noted that the above description 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 foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for characterizing the miscible state of CO2 and crude oil after interaction based on interfacial tension, characterized in that, The method includes the following steps: Step S1: Obtain the relationship curve between oil displacement efficiency and displacement pressure through numerical simulation of capillary experiments, and determine the minimum miscibility pressure; Step S2: Obtain the relationship curve between interfacial tension and displacement pressure through numerical simulation of the thin tube experiment, and determine the critical interfacial tension; Step S3: Based on the minimum miscibility pressure and critical interfacial tension, determine the key parameters characterizing the miscibility state; Step S4: Based on the key parameters characterizing the miscibility state, perform engineering characterization of the miscibility state after the interaction of CO2 and crude oil; In step S3, the miscibility state includes: fully miscible, miscible, nearly miscible and immiscible states; the key parameters include: fully miscible characterization parameters, miscible characterization parameters and nearly miscible characterization parameters; Step S4: Based on key parameters characterizing the miscibility of the phase, perform engineering characterization of the miscibility of the phase after the reaction of CO2 and crude oil, including: Based on the key parameters characterizing the miscible state, the miscible state is further subdivided into four states according to two critical interfacial tensions, as follows: ； In the formula, The interfacial tension corresponding to the minimum miscibility pressure is called the critical interfacial tension, which is the interfacial tension corresponding to the maximum oil displacement efficiency when oil is discharged in a near-miscible state. This represents the interfacial tension corresponding to the maximum oil displacement efficiency of immiscible displacement.

2. The method for characterizing the miscibility state of CO2 and crude oil after interaction based on interfacial tension according to claim 1, characterized in that, Step S1: Determine the relationship curve between oil displacement efficiency and displacement pressure through numerical simulation of capillary experiments, and obtain the minimum miscibility pressure, including: Step S11: Sample the formation fluid of the target oil reservoir and conduct high-pressure physical property tests to obtain PVT data; Step S12: Check the component content of the PVT data, split the heavy components, and reassemble the split components according to the principle of similar properties to obtain pseudo-components that represent the formation fluid properties of the target reservoir. Step S13: Perform fluid phase fitting on the pseudo-components representing the fluid properties of the target reservoir formation to obtain high-pressure critical parameters; Step S14: Based on the high-pressure critical parameters, obtain the relationship curve between oil displacement efficiency and displacement pressure through numerical simulation of the thin tube experiment, and determine the minimum miscibility pressure.

3. The method for characterizing the miscibility of CO2 and crude oil after interaction based on interfacial tension according to claim 2, characterized in that, The high-pressure physical property experiments include: constant composition expansion experiment, multiple degassing experiment and viscosity measurement experiment.

4. The method for characterizing the miscibility state of CO2 and crude oil after interaction based on interfacial tension according to claim 1, characterized in that, Step S2: Obtain the relationship curve between interfacial tension and displacement pressure through numerical simulation of a thin tube experiment, and determine the critical interfacial tension, including: Step S21: Determine the relative permeability curve of oil and gas through a relative permeability experiment, and calculate the maximum oil displacement efficiency of immiscible flooding based on the residual oil saturation determined by the relative permeability curve of oil and gas. Step S22: Based on the results of the numerical simulation capillary experiment, determine the oil displacement efficiency at the inflection point of the displacement pressure curve and obtain the maximum oil displacement efficiency when the oil is in a near-miscible state. Step S23: Establish the variation curves of interfacial tension and oil displacement efficiency with displacement pressure, and determine the corresponding critical interfacial tension based on the maximum oil displacement efficiency of immiscible and near-miscible oil displacement.

5. The method for characterizing the miscibility state of CO2 and crude oil after interaction based on interfacial tension according to claim 4, characterized in that, The maximum oil 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 This indicates the original oil saturation.

6. A system for characterizing the miscible state of CO2 after interaction with crude oil based on interfacial tension, characterized in that, The system includes: a first determining module, a second determining module, a third determining module, and a characterization module; wherein, The first determining module is used to obtain the relationship curve between oil displacement efficiency and displacement pressure through numerical simulation of capillary experiments, and to determine the minimum miscibility pressure; The second determining module is used to obtain the relationship between interfacial tension and displacement pressure through numerical simulation of a thin tube experiment, and to determine the critical interfacial tension; The third determining module is used to determine key parameters characterizing the miscibility state based on the minimum miscibility pressure and critical interfacial tension. The characterization module is used to perform engineering characterization of the miscibility state after the reaction of CO2 and crude oil based on key parameters characterizing the miscibility state. The characterization module is specifically used to subdivide the miscible state into four states based on key parameters characterizing the miscible state and according to two critical interfacial tensions, as follows: ； In the formula, The interfacial tension corresponding to the minimum miscibility pressure is called the critical interfacial tension, which is the interfacial tension corresponding to the maximum oil displacement efficiency when oil is discharged in a near-miscible state. This represents the interfacial tension corresponding to the maximum oil displacement efficiency of immiscible displacement.

7. The system for characterizing the miscibility of CO2 and crude oil after interaction based on interfacial tension according to claim 6, characterized in that, The first determining module includes: a first acquiring unit, a second acquiring unit, a third acquiring unit, and a first determining unit; wherein, The first acquisition unit is used to sample the formation fluid of the target oil reservoir and conduct 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, and reassemble the split components according to the principle of similar properties to obtain pseudo-components that represent the formation fluid properties of the target reservoir. The third acquisition unit is used to acquire high-pressure critical parameters from the pseudo-components representing the formation fluid properties of the target oil reservoir. The first determining unit is used to obtain the relationship curve between oil displacement efficiency and displacement pressure by numerical simulation of a thin tube experiment based on the high-pressure critical parameters, and to determine the minimum miscibility pressure.

8. The system for characterizing the miscible state of CO2 and crude oil based on interfacial tension according to claim 6, characterized in that, The second determining module includes: a calculation unit, a fourth acquisition unit, and a second determining unit; wherein, The calculation unit is used to determine the relative permeability curve of oil and gas through a relative permeability experiment, and to calculate the maximum oil displacement efficiency of the immiscible flooding based on the residual oil saturation determined by the relative permeability curve of oil and gas. The fourth acquisition unit is used to determine the oil displacement efficiency at the inflection point of the curve relating oil displacement efficiency and displacement pressure based on the results of the numerical simulation capillary experiment, and to obtain the maximum oil displacement efficiency when oil is driven in a near-miscible state. The second determining unit is used to establish the variation curves of interfacial tension and oil displacement efficiency with displacement pressure, and to determine the corresponding critical interfacial tension based on the maximum oil displacement efficiency of immiscible and near-miscible flooding.

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