Device system and method for measuring minimum miscible pressure of oil gas through interface disappearance method

Abstract

The invention provides a device system and method for measuring the minimum miscible pressure of oil and gas through an interface disappearance method, the method can accurately simulate the oil and gas miscible condition of an underground oil reservoir, oil and gas miscible is conducted in a sand filling device through prepared stratum simulation oil and single-phase carbon dioxide obtained through treatment, and the oil and gas miscible pressure is measured through the interface disappearance method. The oil-gas minimum miscible pressure under the oil reservoir condition can be rapidly obtained, the testing time is short, and the accuracy of the obtained oil-gas minimum miscible pressure result is high.

Description

Technical Field

[0001] This invention relates to the field of petroleum extraction technology, and in particular to a device system and method for determining the minimum miscibility pressure of oil and gas using the interface disappearance method. Background Technology

[0002] In recent years, with the development of science and technology and the continuous improvement of extraction technology, the proportion of ultra-low permeability and tight oil reservoirs has been increasing. However, due to the poor reservoir properties, strong heterogeneity, and complex pore structure of ultra-low permeability and tight oil reservoirs, water injection development is difficult, ineffective, and results in low single-well production. CO2 can fully dissolve in crude oil, causing it to expand in volume and reduce viscosity, offering advantages such as reducing interfacial tension and improving crude oil flowability. When CO2 and crude oil reach a miscible state, interfacial tension disappears, seepage resistance is significantly reduced, and oil displacement efficiency is effectively improved. Therefore, CO2 huff and puff and CO2 drive are effective methods to improve the recovery rate of ultra-low permeability reservoirs. Minimum miscibility pressure is an important parameter for CO2 to improve reservoir recovery.

[0003] The existing methods for testing the lowest miscibility pressure are mainly (1) the thin tube method; (2) the interfacial tension disappearance method; and (3) the bubble-raising method.

[0004] (1) Thin-tube method: Injected gas displaces crude oil in the porous medium provided by the thin-tube model, eliminating the influence of factors such as mobility ratio, gravity differentiation, and heterogeneity to the greatest extent. For a given formation crude oil and reservoir temperature, the displacement pressure and the composition of the injected gas are the main factors affecting miscibility. By changing the displacement pressure or the composition of the injected gas, the relationship curve between the oil displacement efficiency and the displacement pressure (or the composition of the injected gas) under the same injection pore volume multiple is obtained. The pressure (or composition) corresponding to the inflection point of the curve is the minimum miscibility pressure (or minimum miscibility composition). Advantages: The measured minimum miscibility pressure is the lowest possible pressure after multiple contacts in the porous medium, and the difference in the oil-gas ratio is small. Disadvantages: It is necessary to measure 6 sets of different pressure values, each set of experiments requires 1 week, and a complete test of a sample requires about 50 days, which is too long.

[0005] (2) Disappearance of interfacial tension method: According to the definition of miscibility, when formation crude oil and injected gas are miscible, there is no interface between the oil phase and the gas phase. Therefore, the lowest pressure at which the oil-gas interfacial tension is zero is the minimum miscibility pressure. Based on the pendant drop experiment and the Bashforth-Adams equation, the oil-gas interfacial tension under reservoir temperature and different pressure (or composition) conditions is measured to obtain the relationship curve between interfacial tension and test pressure (or composition of injected gas). The curve is fitted and the pressure (or composition) corresponding to zero interfacial tension is inferred by curve extrapolation, which is the minimum miscibility pressure (or minimum miscibility composition). When the oil-gas interfacial tension is so low that pendant drops cannot be formed, after excluding the influence of equipment, the lowest pressure at which the pendant drop method cannot calculate the interfacial tension can also be used as the minimum miscibility pressure (or minimum miscibility composition). Advantages: Short test time; Disadvantages: The test environment is a non-porous medium, the measured result is the miscibility pressure of one phase, and after complete miscibility, the oil becomes flocculent, so the minimum miscibility pressure cannot be accurately determined, and the oil-gas ratio difference is too large.

[0006] (3) Bubble Injection Method: Bubbles are injected from the bottom of crude oil, and the shape and height of the bubbles as they rise in the crude oil are observed to determine the minimum miscibility pressure. In the immiscible state, the maximum height of the bubbles in the crude oil is high, and they cannot completely disappear or disappear slowly in the crude oil. Their volume gradually decreases due to diffusion, and their shape in the oil column is approximately spherical or nearly spherical at the top and flat at the bottom, with a clear outline. In the miscible state, after the bubbles come into contact with the crude oil, the bottom quickly forms a tail shape, which quickly disperses and disappears in the crude oil. The maximum height of the bubbles is low, and they can quickly disappear completely in the crude oil. By changing the experimental pressure or the composition of the injected gas, the relationship curve between the maximum height of the injected bubbles in the crude oil and the experimental pressure (or the composition of the injected gas) is obtained. The pressure (or composition) corresponding to the midpoint of the curve between the miscible and immiscible sections is the minimum miscibility pressure (or minimum miscibility composition). Advantages: Short test time, relatively accurate determination of the minimum miscibility pressure point; Disadvantages: The test environment is a non-porous medium, and the bubbles are easy to adhere to the wall, resulting in the miscibility pressure of a single miscible phase, with an excessively large difference in the oil-gas ratio.

[0007] All three methods have certain drawbacks. Therefore, it is of great significance to develop a method for determining the minimum miscibility pressure of oil and gas using the interface disappearance method, which is quick to measure and test, has a relatively small difference in oil-gas ratio, and has a small impact from emulsification effect. Summary of the Invention

[0008] In view of the problems existing in the prior art, the present invention provides a device system and method for determining the minimum miscibility pressure of oil and gas by the disappearance interface method. By accurately simulating the porous medium, temperature and pressure conditions of underground oil reservoirs, the minimum miscibility pressure of oil and gas can be tested. This provides key parameters for optimizing the development mode and economic and technical limits of oil reservoir gas drive, as well as for the design, optimization, dynamic tracking and adjustment of development schemes, in order to maximize the development benefits of gas drive oil reservoirs.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for determining the minimum miscibility pressure of oil and gas using the interface disappearance method, the method comprising the following steps:

[0011] (1) Prepare formation simulation oil;

[0012] (2) Evacuate the formation simulated oil storage device;

[0013] (3) After cleaning the sand filling device, the sand filling device is tested and evacuated in sequence, and then the filling medium is injected to the test temperature and test pressure.

[0014] (4) Keep the carbon dioxide in the carbon dioxide gas storage device at a constant temperature to the experimental temperature, pressurize the carbon dioxide to above the experimental pressure using a displacement pump, and stir thoroughly to obtain single-phase carbon dioxide.

[0015] (5) Under experimental temperature and pressure, the single-phase carbon dioxide was used to displace the filling medium in the sand-filled tube. When the components of the produced gas were all carbon dioxide, the displacement was stopped.

[0016] (6) The simulated oil in the formation is injected into the sand-filled pipe to achieve oil-gas miscibility. The injection is stopped when there is no obvious oil-gas interface, and the minimum oil-gas miscibility pressure is obtained.

[0017] The principle of this invention is as follows: According to the definition of miscibility, when formation crude oil and injected gas are miscible, there is no interface between the oil phase and the gas phase. Therefore, the lowest pressure at which the oil-gas interface disappears is the minimum miscibility pressure. For a given formation crude oil and reservoir temperature, the displacement pressure and the composition of the injected gas are the main factors affecting miscibility. By changing the displacement pressure or the composition of the injected gas, the relationship curve between the oil displacement time and the displacement pressure under the same injection pore volume multiple is obtained. The pressure corresponding to the inflection point of the curve is the minimum miscibility pressure.

[0018] The method for determining the minimum miscibility pressure of oil and gas using the interface disappearance method described in this invention can accurately simulate the miscibility conditions of underground oil reservoirs, such as porous media and temperature and pressure conditions. It uses prepared formation simulation oil and processed single-phase carbon dioxide to achieve oil and gas miscibility within a sand-filled device, thus obtaining the minimum miscibility pressure under reservoir conditions. This invention uses a sand-filled device as the miscibility generation container, which can maximize the reproduction of the spatial characteristics of the porous media in underground oil reservoirs; the method has a short testing time and yields highly accurate minimum miscibility pressure results.

[0019] Preferably, in step (2), after the vacuum degree reaches 133 Pa during the evacuation process of the formation simulated oil storage device, the evacuation continues for 2 to 5 hours. For example, it can be 2 hours, 2.2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours or 5 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Preferably, the solvent used for cleaning in step (3) includes any one or a combination of at least two of toluene, petroleum ether, or methanol, wherein typical but non-limiting combinations are a combination of toluene and petroleum ether, a combination of methanol and toluene, or a combination of petroleum ether and methanol.

[0021] Preferably, the cleaning is considered complete when the chromatographic analysis results of the product are the same as and stable as those of the solvent components.

[0022] Preferably, before the pressure test in step (3), the solvent in the sand filling device is dried with dry nitrogen.

[0023] Preferably, the qualified standard for the pressure test is that the pressure drop within 1 hour is less than 0.05 MPa, such as 0.049 MPa, 0.045 MPa, 0.043 MPa, 0.04 MPa, 0.03 MPa, 0.02 MPa or 0.01 MPa, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] Preferably, after the vacuum degree reaches 133 Pa, the evacuation is continued for 2 to 5 hours, for example, 2 hours, 2.2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours or 5 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] Preferably, the filling medium in step (3) includes nitrogen or aviation kerosene.

[0026] Preferably, the displacement velocity in step (5) is 60–90 cm. 3 / h, for example, could be 60cm 3 / h、62cm 3 / h、65cm 3 / h、70cm 3 / h、75cm 3 / h、80cm 3 / h or 90cm 3 / h, etc., but not limited to the listed values; other unlisted values ​​within this range also apply.

[0027] Preferably, after displacing 2 times the pore volume, the composition of the produced gas is analyzed every 0.1 to 0.2 times the pore volume. For example, it can be 0.1, 0.12, 0.15, 0.17, 0.19, or 0.2 times, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] Preferably, the pressure of the simulated formation oil injected in step (6) is 0.05 to 0.1 MPa higher than the experimental pressure. For example, it can be 0.05 MPa, 0.055 MPa, 0.06 MPa, 0.07 MPa, 0.08 MPa, 0.09 MPa or 0.01 MPa, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] Preferably, the injection rate of the formation simulated oil is 0.5 to 1 mL / min, for example, it can be 0.5 mL / min, 0.55 mL / min, 0.6 mL / min, 0.7 mL / min, 0.8 mL / min, 0.9 mL / min or 1 mL / min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] As a preferred technical solution of the present invention, the method includes the following steps:

[0031] (1) Prepare formation simulation oil;

[0032] (2) Evacuate the formation simulated oil storage device. After the vacuum degree reaches 133 Pa, continue evacuating for 2 to 5 hours.

[0033] (3) After cleaning the sand filling device, pressure test and evacuation are carried out in sequence, and then the filling medium is injected to maintain the experimental temperature and experimental pressure.

[0034] The solvent used for cleaning includes any one or a combination of at least two of toluene, petroleum ether, or methanol; the cleaning is considered complete when the chromatographic analysis of the product is consistent with and stable with the solvent composition; before the pressure test, the solvent in the sand-filling device is dried with dry nitrogen; the pass standard for the pressure test is a pressure drop of less than 0.05 MPa within 1 hour; after the vacuum reaches 133 Pa, the evacuation is continued for 2 to 5 hours; the filling medium includes nitrogen or aviation kerosene.

[0035] (4) Keep the carbon dioxide in the carbon dioxide gas storage device at a constant temperature to the experimental temperature, pressurize the carbon dioxide to above the experimental pressure using a displacement pump, and stir thoroughly to obtain single-phase carbon dioxide.

[0036] (5) Under experimental temperature and pressure, single-phase carbon dioxide was used at a rate of 60–90 cm⁻¹. 3 Displace the packing medium in the sand-filled tube at a rate of / h; after displacing 2 times the pore volume, analyze the composition of the produced gas every 0.1 to 0.2 times the pore volume; stop the displacement when the components of the produced sample are all carbon dioxide.

[0037] (6) Inject formation simulated oil into the sand-filled pipe at a rate of 0.5 to 1 mL / min to achieve oil-gas miscibility until there is no obvious interface between oil and gas, and then stop the injection to obtain the minimum oil-gas miscibility pressure; the pressure of the injected formation simulated oil is 0.05 to 0.1 MPa higher than the experimental pressure.

[0038] In a second aspect, the present invention also provides an apparatus system for determining the minimum miscibility pressure of oil and gas using the interface disappearance method, wherein the method for determining the minimum miscibility pressure of oil and gas using the interface disappearance method described in the first aspect is performed within the apparatus system.

[0039] The device system includes a displacement pump, a storage device, and a sand filling device connected in sequence; the storage device includes a cleaning device, a formation simulation oil storage device, and a carbon dioxide gas storage device arranged in parallel; the sand filling device is connected to a fluid collection device and a vacuum pump respectively; both the storage device and the sand filling device are located in a constant temperature device.

[0040] Preferably, the device system further includes a back pressure regulating device.

[0041] Preferably, the back pressure regulating device is located between the sand filling device and the fluid collection device.

[0042] Compared with the prior art, the present invention has at least the following beneficial effects:

[0043] (1) The method for determining the minimum miscibility pressure of oil and gas by the interface disappearance method provided by the present invention has a short test time, can accurately reflect the real miscibility state underground, and accurately calculate the minimum miscibility pressure.

[0044] (2) The device system for determining the minimum miscibility pressure of oil and gas by the interface disappearance method provided by the present invention uses a sand-filling device as a miscibility generation container, which can restore the spatial characteristics of porous media in underground oil reservoirs to the maximum extent. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the device system for determining the minimum miscibility pressure of oil and gas using the interface disappearance method in Embodiment 1 of the present invention.

[0046] Figure 2 This is a graph showing the experimental results of determining the minimum miscibility pressure of oil and gas using the interface disappearance method provided in Embodiment 1 of the present invention.

[0047] Figure 3 This is a graph showing the experimental results of determining the minimum miscibility pressure of oil and gas using the thin tube method in Comparative Example 1 of this invention.

[0048] In the diagram: 1-Displacement pump; 2-Cleaning device; 3-Formation simulation oil storage device; 4-Carbon dioxide gas storage device; 5-Sand filling device; 6-Back pressure regulating device; 7-Thermostatic device; 8-Fluid collection device; 9-Vacuum pump; 10-Valve. Detailed Implementation

[0049] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0050] The present invention will now be described in further detail. However, the examples described below are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0051] It should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "set," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0052] Those skilled in the art should understand that the present invention necessarily includes the necessary pipelines, conventional valves and general pump equipment for achieving process integrity, but the above content is not the main inventive point of the present invention. Those skilled in the art can add layouts based on process flow and equipment structure selection, and the present invention does not make any special requirements or specific limitations in this regard.

[0053] Example 1

[0054] This embodiment provides a method for determining the minimum miscibility pressure of oil and gas using the interface disappearance method, the method comprising the following steps:

[0055] (1) Prepare formation simulation oil using white oil;

[0056] (2) Evacuate the formation simulated oil storage device until the vacuum reaches 133 Pa, and then continue evacuating for 3 hours.

[0057] (3) After cleaning the sand filling device, pressure test and evacuation are carried out in sequence, and then the filling medium is injected to keep the temperature constant at 50℃ and the initial pressure at 6.8MPa. The sand filling device is a sand filling pipe with a length of 30cm and a radius of 2.54cm. The particle size of the quartz sand filled is 80-200 mesh.

[0058] The solvent used for cleaning is toluene; the cleaning is completed when the chromatographic analysis of the product is consistent with and stable with the solvent composition; before the pressure test, the solvent in the sand-filling device is dried with dry nitrogen; the qualified standard for the pressure test is a pressure drop of less than 0.05 MPa within 1 hour; after the vacuum degree reaches 133 Pa, the evacuation is carried out continuously for 4 hours; the filling medium is nitrogen.

[0059] (4) The carbon dioxide in the carbon dioxide gas storage device was kept at a constant temperature of 50°C, and the carbon dioxide was pressurized to above the experimental pressure using a displacement pump. After thorough stirring, single-phase carbon dioxide was obtained; the carbon dioxide concentration was 99.95 mol%.

[0060] (5) At an experimental temperature of 50℃ and an experimental pressure, single-phase carbon dioxide was used at a rate of 80 cm⁻¹. 3 Displace the packing medium in the sand-filled tube at a rate of / h; after displacing 2 times the pore volume, analyze the composition of the produced gas every 0.2 times the pore volume; stop displacement when the components of the produced sample are all carbon dioxide.

[0061] (6) Inject formation simulated oil into the sand-filled pipe at a rate of 0.5 mL / min to achieve oil-gas miscibility until there is no obvious interface between oil and gas, and then stop the injection to obtain the minimum oil-gas miscibility pressure; the pressure of the injected formation simulated oil is 0.05 MPa higher than the experimental pressure.

[0062] In this embodiment, after 2200s of displacement, the lowest miscibility pressure of the white oil was measured to be 10.6MPa.

[0063] This embodiment also provides an apparatus system for determining the minimum miscibility pressure of oil and gas using the interface disappearance method described above, as shown in the schematic diagram below. Figure 1 As shown.

[0064] The device system includes a displacement pump 1, a storage device, and a sand filling device 5 connected in sequence; the storage device includes a cleaning device 2, a formation simulation oil storage device 3, and a carbon dioxide gas storage device 4 arranged in parallel; the sand filling device 5 is connected to a fluid collection device 8 and a vacuum pump 9 respectively; both the storage device and the sand filling device 5 are located in a constant temperature device 7.

[0065] The device system also includes a back pressure regulating device 6; the back pressure regulating device 6 is disposed between the sand filling device 5 and the fluid collection device 8.

[0066] Valves 10 are installed at the inlet and outlet of the cleaning tank device 2, the formation simulation oil storage device 3, and the carbon dioxide gas storage device 4.

[0067] Both the fluid collection device 8 and the vacuum pump 9 are equipped with valves 10 at their inlets.

[0068] The experimental results of determining the minimum miscibility pressure of oil and gas using the interface disappearance method provided in this embodiment are shown in the figure below. Figure 2 As shown, from Figure 2 The minimum miscibility pressure of white oil can be determined to be 10.6 MPa.

[0069] Comparative Example 1

[0070] This comparative example provides a method for determining the minimum miscibility pressure of white oil and gas using a capillary tube method. The experimental conditions are as follows: formation crude oil: white oil; carbon dioxide concentration: 99.95 mol%; experimental temperature: 50℃; capillary tube length: 20 m, inner diameter: 3.86 mm, outer diameter: 3.35 mm; gas permeability: 4.43 D.

[0071] The method includes the following steps:

[0072] Saturated oil

[0073] a) After cleaning the thin tube model, inject aviation kerosene and maintain it at the experimental temperature and pressure. Set the back pressure to the required experimental pressure value.

[0074] b) Keep the formation crude oil sample at the experimental temperature for 4 hours, pressurize the sample to above the experimental pressure using a displacement pump, and stir thoroughly to make it a single phase.

[0075] c) Under experimental pressure and temperature, slowly open the outlet valve of the formation crude oil sample container and the inlet valve of the capillary model to displace the aviation kerosene in the capillary with the formation crude oil sample. Displacement rate: 60 cm⁻¹ 3 / h.

[0076] d) After displacing twice the pore volume, measure the produced oil and gas volume at the capillary outlet every 0.1 times the pore volume (in accordance with GB / T 26981), and take oil and gas samples to analyze their composition. Stop the displacement when the composition and gas-oil ratio of the produced sample are consistent with the formation crude oil sample.

[0077] Gas displacement

[0078] a) Keep the injected gas sample constant at the experimental temperature of 50°C.

[0079] b) Fill and flush the inlet valve line of the thin tube model with injection gas. Adjust the injection gas pressure to 0.1 MPa above the experimental pressure.

[0080] c) Under experimental temperature and pressure, and at a constant injection rate, displace the formation crude oil sample in the capillary model using injected gas. The displacement rate is 6 cm⁻¹. 3 / h.

[0081] d) During the displacement process, the displacement pressure difference between the injection pressure of the thin tube model and the experimental pressure set by the back pressure regulator is less than 0.5 MPa.

[0082] e) Stop displacement when the accumulated feed into the pump exceeds 1.20 times the pore volume.

[0083] The oil displacement efficiency was measured under six different pressures: 8MPa-62.52%, 9MPa-73.35%, 10MPa-83.67%, 11MPa-91.48%, 12MPa-93.22%, 13MPa-94.12%, and 1.2PV carbon dioxide displacement. The lowest miscibility pressure of white oil was measured to be 10.75MPa.

[0084] The experimental results of determining the minimum miscibility pressure of oil and gas using the capillary method in this comparative example are as follows: Figure 3 As shown, from Figure 3 The relationship between oil displacement efficiency and displacement pressure when 1.20 times the pore volume is injected in the thin tube experiment can be obtained. The pressure corresponding to the intersection of the immiscible section and the miscible section curves is the minimum miscible pressure, which is 10.75 MPa.

[0085] As can be seen from Example 1 and Comparative Example 1, the minimum miscibility pressure measured by the interface disappearance method provided by the present invention is similar to that measured by the existing mature capillary method for measuring the minimum miscibility pressure of white oil and gas, and can accurately reflect the true underground miscibility state.

[0086] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for determining the minimum miscibility pressure of oil and gas using the interface disappearance method, characterized in that, The method includes the following steps: (1) Prepare formation simulation oil; (2) Evacuate the formation simulated oil storage device; (3) After cleaning the sand filling device, the sand filling device is tested and evacuated in sequence, and then the filling medium is injected to the test temperature and test pressure. (4) Keep the carbon dioxide in the carbon dioxide gas storage device at a constant temperature to the experimental temperature, pressurize the carbon dioxide to above the experimental pressure using a displacement pump, and stir thoroughly to obtain single-phase carbon dioxide. (5) Under experimental temperature and pressure, the single-phase carbon dioxide was used to displace the filling medium in the sand-filled tube. When the components of the produced gas were all carbon dioxide, the displacement was stopped. (6) The simulated oil in the formation is injected into the sand-filled pipe to achieve oil-gas miscibility. The injection is stopped when there is no obvious oil-gas interface, and the minimum oil-gas miscibility pressure is obtained.

2. The method according to claim 1, characterized in that, In step (2), after the vacuum level reaches 133 Pa, the formation simulation oil storage device is continuously evacuated for 2 to 5 hours.

3. The method according to claim 1 or 2, characterized in that, The solvent used for cleaning in step (3) includes any one or a combination of at least two of toluene, petroleum ether, or methanol; Preferably, the cleaning is considered complete when the chromatographic analysis results of the product are the same as and stable as those of the solvent components.

4. The method according to any one of claims 1 to 3, characterized in that, Before the pressure test in step (3), the solvent in the sand filling device is dried with dry nitrogen. Preferably, the pass criterion for the pressure test is a pressure drop of less than 0.05 MPa within 1 hour; Preferably, after the vacuum level reaches 133 Pa, the evacuation continues for 2 to 5 hours.

5. The method according to any one of claims 1 to 4, characterized in that, The filling medium in step (3) includes nitrogen or aviation kerosene.

6. The method according to any one of claims 1 to 5, characterized in that, The displacement velocity in step (5) is 60-90 cm. 3 / h; Preferably, after displacing 2 times the pore volume, the composition of the produced gas is analyzed every 0.1 to 0.2 times the pore volume.

7. The method according to any one of claims 1 to 6, characterized in that, In step (6), the pressure of the injected formation simulated oil is 0.05–0.1 MPa higher than the experimental pressure; Preferably, the injection rate of the simulated formation oil is 0.5 to 1 mL / min.

8. The method according to any one of claims 1 to 7, characterized in that, The method includes the following steps: (1) Prepare formation simulation oil; (2) Evacuate the formation simulated oil storage device. After the vacuum degree reaches 133 Pa, continue evacuating for 2 to 5 hours. (3) After cleaning the sand filling device, pressure test and evacuation are carried out in sequence, and then the filling medium is injected to maintain the experimental temperature and experimental pressure. The solvent used for cleaning includes any one or a combination of at least two of toluene, petroleum ether, or methanol; the cleaning is considered complete when the chromatographic analysis of the product is consistent with and stable with the solvent composition; before the pressure test, the solvent in the sand-filling device is dried with dry nitrogen; the pass standard for the pressure test is a pressure drop of less than 0.05 MPa within 1 hour; after the vacuum reaches 133 Pa, the evacuation is continued for 2 to 5 hours; the filling medium includes nitrogen or aviation kerosene. (4) Keep the carbon dioxide in the carbon dioxide gas storage device at a constant temperature to the experimental temperature, pressurize the carbon dioxide to above the experimental pressure using a displacement pump, and stir thoroughly to obtain single-phase carbon dioxide. (5) Under experimental temperature and pressure, single-phase carbon dioxide was used at a rate of 60–90 cm⁻¹. 3 Displace the packing medium in the sand-filled tube at a rate of / h; after displacing 2 times the pore volume, analyze the composition of the produced gas every 0.1 to 0.2 times the pore volume; stop the displacement when the components of the produced sample are all carbon dioxide. (6) Inject formation simulated oil into the sand-filled pipe at a rate of 0.5 to 1 mL / min to achieve oil-gas miscibility until there is no obvious interface between oil and gas, and then stop the injection to obtain the minimum oil-gas miscibility pressure; the pressure of the injected formation simulated oil is 0.05 to 0.1 MPa higher than the experimental pressure.

9. A device system for determining the minimum miscibility pressure of oil and gas using the interface disappearance method, characterized in that, The device system performs a method for determining the minimum miscibility pressure of oil and gas using the interface disappearance method as described in any one of claims 1 to 8. The device system includes a displacement pump, a storage device, and a sand filling device connected in sequence; the storage device includes a cleaning device, a formation simulation oil storage device, and a carbon dioxide gas storage device arranged in parallel; the sand filling device is connected to a fluid collection device and a vacuum pump respectively; both the storage device and the sand filling device are located in a constant temperature device.

10. The apparatus system according to claim 9, characterized in that, The device system also includes a back pressure regulating device; Preferably, the back pressure regulating device is located between the sand filling device and the fluid collection device.

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