A physical simulation device for CO2 / water alternating injection in a heterogeneous reservoir and a working method thereof

Abstract

The application discloses a kind of non-homogeneous reservoir CO2 / water alternate injection physical simulation device and working method, it is related to complex oil and gas reservoir development technical field, including injection system, displacement system, collection system.The core of different layer series is connected in parallel to carry out displacement experiment, and the influence of reservoir heterogeneity on water-gas alternating displacement is studied in depth;After displacement experiment, adjust six-way valve 2 valve, connect the pipeline before and after core holder, after pressure stabilizes, remove the pressure in pipeline by pressure relief valve, avoid secondary displacement of fluid to core in the process of unloading back pressure;Install check valve at the outlet end of intermediate container, avoid the fluid backflow phenomenon caused by pressure fluctuation in the process of water-gas alternating injection;Use electric conversion valve to replace traditional manual conversion valve to realize CO2 and water alternating injection, accurately control injection water-gas ratio and slug size;The outlet end of core holder is respectively connected with gas-liquid separation assembly and gas flowmeter, to realize accurate monitoring to different layer series of core.

Description

Technical Field

[0001] This invention relates to the field of complex oil and gas reservoir development technology, and in particular to a physical simulation device and working method for alternating CO2 / water injection in heterogeneous reservoirs. Background Technology

[0002] Heterogeneous oil and gas reservoirs exhibit significant differences in reservoir properties and permeability, resulting in low sweep efficiency from traditional water-drive and gas-drive methods, hindering efficient reservoir development. Alternating CO2 / water injection is a common method to improve reservoir sweep efficiency and the activation of low-permeability layers, representing a crucial means of enhancing oil recovery in heterogeneous and complex oil and gas reservoirs. Physical simulation experiments using alternating CO2 / water injection offer advantages such as low cost, short timeframe, and repeatability, making them a primary tool for studying reservoir enhancement mechanisms and guiding field practices.

[0003] Current physical simulation experimental setups for alternating CO2 / water injection still have shortcomings and problems: Traditional single-core displacement experiments are insufficient to reflect the actual reservoir conditions due to the strong heterogeneity between reservoir layers. Furthermore, traditional experimental setups cannot independently detect parameters such as recovery rate, gas production, and liquid production in each layer. During the experiment, the injection water-to-gas ratio and slug size in alternating CO2 / water injection are difficult to control precisely, hindering further in-depth exploration of the influencing factors of CO2 / water alternating injection oil production. Before displacement begins, the initial pressure in the pipeline between the core holder outlet and the backpressure valve is 0, which can cause premature core displacement using traditional displacement operations. During displacement, manually switching valves to achieve alternating CO2 and water injection makes it difficult to accurately control the experimental water-to-gas ratio and slug size. When displacement ends, traditional depressurization operations can lead to pressure imbalance at both ends of the core, causing secondary displacement and interfering with the experimental results.

[0004] Therefore, it is urgent to study a physical simulation device and method for alternating CO2 / water injection in heterogeneous reservoirs to overcome the above-mentioned technical defects. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention discloses a physical simulation device and working method for alternating CO2 / water injection in heterogeneous reservoirs, reducing experimental errors and exploring in depth the mechanism of enhanced oil recovery through alternating CO2 / water injection in heterogeneous reservoirs, providing theoretical guidance for the development of complex oil and gas reservoirs.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The first aspect of this invention provides a physical simulation device for alternating CO2 / water injection in heterogeneous reservoirs, comprising an injection system, a displacement system, a collection system, and a main pipeline connecting the injection system, the displacement system, and the collection system.

[0008] The main pipeline is equipped with a six-way valve No. 1, a six-way valve No. 2, and a four-way valve;

[0009] The injection system includes a first plunger pump, a second plunger pump, a first intermediate container for holding CO2, a second intermediate container for holding water, and a third intermediate container for holding oil. The first intermediate container is connected to the first plunger pump via pipeline 1. The second and third intermediate containers are connected to the second plunger pump via pipeline 2. A three-way valve is installed on pipeline 2. The first and second intermediate containers are connected via pipeline 3. An electrically operated three-way valve is installed on pipeline 3. The electrically operated three-way valve is connected to a six-way valve 1. The third intermediate container is connected to a six-way valve 1. A one-way valve 1 is installed on pipeline 3 near the first intermediate container. A one-way valve 2 is installed on pipeline 3 near the second intermediate container.

[0010] The displacement system includes a nuclear magnetic resonance spectrometer and a core holder scanned by the nuclear magnetic resonance spectrometer. The core holder includes a first core holder, a second core holder, and a third core holder connected in parallel. The inlet end of the core holder is connected to a six-way valve No. 1, and the outlet end of the core holder is connected to a back pressure valve via a pipeline. A four-way valve is provided on the pipeline. The back pressure valve is connected to a back pressure pump. The core holder is also connected to a confining pressure pump via a pipeline.

[0011] The collection system includes a connected gas-liquid separation component and a gas flow meter, with the other end of the gas-liquid separation component connected to a back pressure valve.

[0012] The outlets of the first and second intermediate containers in the injection system are equipped with one-way valves No. 1 and No. 2, respectively, to prevent backflow of fluid in the pipeline due to pressure fluctuations during the CO2 / water alternating injection process. The electric switching three-way valve can automatically switch the valve at regular intervals to achieve alternating injection of CO2 and water, ensuring one-way injection of CO2 and water during the displacement process and precise control of the injection water-gas ratio and slug size.

[0013] The displacement system consists of three parallel cores from three different strata. Alternating water-gas displacement of these parallel cores allows for a better investigation of the impact of reservoir heterogeneity on oil recovery, making the experiment more closely resemble actual reservoir conditions. The inlet and outlet pipelines of the three core holders are connected via a six-way valve (No. 2). Before the experiment, the pressure in the pipeline between the outlet of the core holder and the backpressure valve is zero. By opening the upper six-way valve (No. 2) to connect the pipelines before and after the core holder, the initial pressure of the entire experimental system is constructed using a plunger pump in constant pressure mode. This ensures that the pressure system of the experimental apparatus matches the actual reservoir, preventing premature core displacement caused by an initial pressure of zero in the outlet pipeline of the core holder. After the experiment, some high-pressure fluid remained in the inlet pipeline of the core holder. Depressurization of the backpressure valve would increase the pressure difference across the core holder. Opening the upper six-way valve (No. 2) connected the pipelines before and after the core holder, simultaneously releasing the pressure in these pipelines to prevent secondary displacement of the core due to backpressure valve depressurization. Nuclear magnetic resonance (NMR) technology was used to detect the residual oil saturation and its microscopic distribution in the experimental core, clarifying the mechanism by which alternating CO2 / water injection enhances oil recovery.

[0014] The collection system is equipped with a gas-liquid separation component and a gas flow meter at the outlet of the core holder, which can accurately measure the gas and liquid produced by each core.

[0015] Optionally, a six-way valve No. 3 is installed on the pipeline between the core holder and the confining pressure pump, and the first core holder, the second core holder and the third core holder are respectively connected to the six-way valve No. 3 via pipelines.

[0016] Optionally, the back pressure valves include back pressure valve 1, back pressure valve 2, and back pressure valve 3. The first core holder is connected to back pressure valve 1 via pipeline 4, and a four-way valve 1 is installed on pipeline 4. The second core holder is connected to back pressure valve 2 via pipeline 5, and a four-way valve 2 is installed on pipeline 5. The third core holder is connected to back pressure valve 3 via pipeline 6, and a four-way valve 3 is installed on pipeline 6. Four-way valves 1, 2, and 3 are all connected to six-way valve 2 via pipelines.

[0017] Optionally, back pressure valve 1, back pressure valve 2 and back pressure valve 3 are connected to a back pressure pump via pipeline 7, and a six-way valve 4 is installed on pipeline 7.

[0018] Optionally, the gas-liquid separation assembly includes a first gas-liquid separation assembly, a second gas-liquid separation assembly, and a third gas-liquid separation assembly; the gas flow meter includes a first gas flow meter, a second gas flow meter, and a third gas flow meter; back pressure valve 1 is connected to the first gas-liquid separation assembly via pipeline 8, and the first gas-liquid separation assembly is connected to the first gas flow meter; back pressure valve 2 is connected to the second gas-liquid separation assembly via pipeline 9, and the second gas-liquid separation assembly is connected to the second gas flow meter; back pressure valve 3 is connected to the third gas-liquid separation assembly via pipeline 10, and the third gas-liquid separation assembly is connected to the third gas flow meter.

[0019] A second aspect of the present invention provides a method of operation based on the above-described device, comprising the following steps:

[0020] S1. After saturating three different types of experimental cores with oil, place them into three core holders respectively.

[0021] S2, control the confining pressure pump and six-way valve No. 3 to apply confining pressure to the three core holders;

[0022] S3. Control the back pressure pump and six-way valve No. 4 to add back pressure to back pressure valves No. 1, No. 2 and No. 3;

[0023] S4. Control the valves of six-way valve 1 and six-way valve 2 to connect the front and rear pipelines of the core holder and set the initial pressure of the experimental device system in constant pressure mode of the second plunger pump.

[0024] S5. Adjust the electric conversion three-way valve and the three-way valve to achieve alternating injection of CO2 and water;

[0025] S6. After the core displacement is completed, control the valves of six-way valve 1 and six-way valve 2 to connect the front and rear pipelines of the core holder. After stabilization, discharge the high-pressure fluid in the pipeline from the pressure relief valve of six-way valve 2.

[0026] S7. The experimental core was scanned using a nuclear magnetic resonance spectrometer to determine the T2 spectrum and one-dimensional frequency coding of the experimental core.

[0027] S8. The liquid production and gas production are recorded by using the first gas-liquid separation component, the second gas-liquid separation component, the third gas-liquid separation component, the first gas flow meter, the second gas flow meter, and the third gas flow meter, respectively.

[0028] The beneficial effects of this invention are:

[0029] 1. Parallel displacement experiments were conducted using cores from different strata, which closely resembled the actual reservoir conditions and better reflected the heterogeneity of complex oil and gas reservoirs. This is conducive to in-depth research on the impact of reservoir heterogeneity on water-gas alternating displacement.

[0030] 2. Before the displacement experiment begins, adjust valve 2 of the six-way valve to connect the pipelines before and after the core holder, set the constant pressure mode of the high-precision plunger pump, and adjust the pressure at the outlet end of the core holder to make the pressure of the entire test system match the actual reservoir, thereby reducing experimental errors. After the displacement experiment is completed, adjust valve 2 of the six-way valve to connect the pipelines before and after the core holder. After the pressure stabilizes, release the pressure in the pipeline through the pressure relief valve of valve 2 of the six-way valve to avoid the pressure difference across the core holder increasing due to the pressure loss of the back pressure valve during the back pressure release process. This would prevent the fluid in the pipeline at the inlet end of the core holder from causing secondary displacement of the core, thereby reducing experimental errors.

[0031] 3. A one-way valve is installed at the outlet of the intermediate container to avoid backflow of fluid caused by pressure fluctuations during the alternating injection of water and air, thus ensuring unidirectional flow of fluid.

[0032] 4. Install an electric switching three-way valve at the outlet of the intermediate container to avoid the impact of traditional manual switching valves on the accuracy of the injection water-gas ratio and slug size, thus accurately controlling the injection water-gas ratio and slug size and reducing experimental errors.

[0033] 5. The outlet end of the core holder is connected to a gas-liquid separation component and a gas flow meter, respectively, to achieve accurate monitoring of cores of different layers and accurate measurement of the liquid production and gas production of each core, which is conducive to in-depth exploration of the mechanism of CO2 / water alternating flooding to enhance the recovery rate of heterogeneous reservoirs.

[0034] 6. The device of the present invention can realize CO2 / water alternating drive experiments with multiple cores in parallel, and can also realize gas drive experiments, water drive experiments, mixed gas drive experiments, etc. with a single core and multiple cores in parallel by adjusting the six-way valve No. 1 and the three-way valve at the inlet end of the core holder. It has a wide range of applications. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the physical simulation device for alternating CO2 / water injection in heterogeneous reservoirs according to the present invention.

[0036] Figure 2 This invention relates to the change in oil saturation during WAG flooding (water-to-gas ratio 2:1) based on NMR imaging.

[0037] Figure 3 These are the dynamic T2 spectra of three core samples from the WAG (water-air ratio 2:1) process of this invention.

[0038] Figure 4 This is a diagram showing the recovery degree of different core samples after WAG flooding according to the present invention.

[0039] In the diagram, 1. First plunger pump; 2. Second plunger pump; 3. First intermediate container; 4. Second intermediate container; 5. Third intermediate container; 6. Check valve 1; 7. Check valve 2; 8. Six-way valve 1; 9. Six-way valve 2; 13. Six-way valve 3; 21. Six-way valve 4; 10. First core holder; 11. Second core holder; 12. Third core holder; 14. Confining pressure pump; 22. Back pressure pump; 15. 16. Four-way valve No. 1; 17. Four-way valve No. 2; 18. Four-way valve No. 3; 19. First back pressure valve; 20. Second back pressure valve; 21. Third back pressure valve; 22. First gas-liquid separation assembly; 23. Second gas-liquid separation assembly; 24. Third gas-liquid separation assembly; 25. Electric conversion three-way valve; 26. Three-way valve; 27. First gas flow meter; 28. Second gas flow meter; 39. Third gas flow meter; 30. Nuclear magnetic resonance spectrometer. Detailed Implementation

[0040] 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.

[0041] A physical simulation device for alternating CO2 / water injection in heterogeneous reservoirs, such as Figure 1 As shown, it includes an injection system, a displacement system, a collection system, and a main pipeline connecting the injection system, the displacement system, and the collection system;

[0042] The main pipeline is equipped with six-way valves No. 1 and 8, six-way valves No. 2 and 9, and a four-way valve;

[0043] The injection system includes a first plunger pump 1, a second plunger pump 2, a first intermediate container 3 for holding CO2, a second intermediate container 4 for holding water, and a third intermediate container 5 for holding oil. The first intermediate container 3 is connected to the first plunger pump 1 via pipeline 1. The second intermediate container 4 and the third intermediate container 5 are connected to the second plunger pump 2 via pipeline 2. A three-way valve 27 is provided on pipeline 2. The first intermediate container 3 and the second intermediate container 4 are connected via pipeline 3. An electrically operated three-way valve 26 is provided on pipeline 3. The electrically operated three-way valve 26 is connected to a six-way valve 1 8. The third intermediate container 5 is connected to the six-way valve 1 8. A one-way valve 1 6 is provided on pipeline 3 near the first intermediate container 3. A one-way valve 2 7 is provided on pipeline 3 near the second intermediate container 4.

[0044] The displacement system includes a nuclear magnetic resonance spectrometer 31 and a core holder scanned by the nuclear magnetic resonance spectrometer 31. The core holder includes a first core holder 10, a second core holder 11, and a third core holder 12 connected in parallel. The inlet end of the core holder is connected to a six-way valve 18, and the outlet end of the core holder is connected to a back pressure valve via a pipeline. A four-way valve is provided on the pipeline. The back pressure valve is connected to a back pressure pump 22. The core holder is also connected to a confining pressure pump 14 via a pipeline.

[0045] The collection system includes a connected gas-liquid separation component and a gas flow meter, with the other end of the gas-liquid separation component connected to a back pressure valve.

[0046] A six-way valve 3 is installed on the pipeline between the core holder and the confining pressure pump 14. The first core holder 10, the second core holder 11 and the third core holder 12 are respectively connected to the six-way valve 3 via pipelines.

[0047] The back pressure valves include back pressure valve 1 (18), back pressure valve 2 (19), and back pressure valve 3 (20). The first core holder 10 is connected to back pressure valve 1 (18) via pipe 4, which is equipped with a four-way valve 1 (15). The second core holder 11 is connected to back pressure valve 2 (19) via pipe 5, which is equipped with a four-way valve 2 (16). The third core holder 12 is connected to back pressure valve 3 (20) via pipe 6, which is equipped with a four-way valve 3 (17). Four-way valves 1 (15), 2 (16), and 3 (17) are all connected to six-way valve 2 (9) via pipes. Back pressure valves 1 (18), 2 (19), and 3 (20) are connected to a back pressure pump 22 via pipe 7, which is equipped with a six-way valve 4 (21).

[0048] The gas-liquid separation assembly includes a first gas-liquid separation assembly 23, a second gas-liquid separation assembly 24, and a third gas-liquid separation assembly 25. The gas flow meter includes a first gas flow meter 28, a second gas flow meter 29, and a third gas flow meter 30. Back pressure valve 1 (18) is connected to the first gas-liquid separation assembly 23 via pipeline 8, and the first gas-liquid separation assembly 23 is connected to the first gas flow meter 28. Back pressure valve 2 (19) is connected to the second gas-liquid separation assembly 24 via pipeline 9, and the second gas-liquid separation assembly 24 is connected to the second gas flow meter 29. Back pressure valve 3 (20) is connected to the third gas-liquid separation assembly 25 via pipeline 10, and the third gas-liquid separation assembly 25 is connected to the third gas flow meter 30.

[0049] The working method includes the following steps:

[0050] S1. After saturating three different types of experimental cores with oil, place them into three core holders respectively.

[0051] S2, control the confining pressure pump 14 and the six-way valve 313 to apply confining pressure to the three core holders;

[0052] S3, control back pressure pump 22 and six-way valve 4 21 to apply back pressure to back pressure valve 1 18, back pressure valve 2 19, and back pressure valve 3 20;

[0053] S4. Control the valves of six-way valve 1 and 8 and six-way valve 2 and 9 to connect the front and rear pipelines of the core holder and set the initial pressure of the experimental device system in constant pressure mode of the second plunger pump 2.

[0054] S5. Adjust the electric conversion three-way valve 26 and three-way valve 27 to achieve alternating injection of CO2 and water;

[0055] S6. After the core displacement is completed, control the valves of six-way valve 1 (8) and six-way valve 2 (9) to connect the front and rear pipelines of the core holder. After stabilization, discharge the high-pressure fluid in the pipeline from the pressure relief valve of six-way valve 2 (9).

[0056] S7. The experimental core was scanned using a nuclear magnetic resonance spectrometer to determine the T2 spectrum and one-dimensional frequency coding of the experimental core.

[0057] S8. The liquid production volume and gas production volume are recorded by using the first gas-liquid separation component 23, the second gas-liquid separation component 24, the third gas-liquid separation component 25, the first gas flow meter 28, the second gas flow meter 29, and the third gas flow meter 30, respectively.

[0058] Application example:

[0059] A CO2 / water alternating flooding experiment was conducted in a heterogeneous reservoir. Three different types of cores from different strata of a heterogeneous oil reservoir were selected: Core No. 1, Core No. 2, and Core No. 3. The permeability of the three cores decreased sequentially. The permeability of Core No. 1 was about 100 mD, Core No. 2 was about 10 mD, and Core No. 3 was about 0.6 mD. The gas used in the experiment was high-purity CO2, the water used was 99.8% heavy water with a viscosity of 1.23 mPa·s at room temperature, and the oil used was crude oil from the field with a viscosity of 890.12 mPa·s at room temperature.

[0060] This experiment is a parallel water-gas alternating drive experiment using multiple core samples. The experimental setup diagram is shown below. Figure 1 As shown, the experimental steps are as follows:

[0061] S1. Wash the three types of cores with oil and measure the length and diameter of the cores. Determine the porosity and permeability of the experimental cores.

[0062] S2. After vacuuming the core, saturate it with water at a displacement rate of 0.05 ml / min, calculate the amount of saturated water, then saturate it with oil until no water is produced at the outlet. Calculate the amount of saturated oil to determine the degree of bound water saturation.

[0063] S3. Before the displacement begins, the core is scanned with a nuclear magnetic resonance scanner 31 to determine the initial T2 spectrum and one-dimensional frequency code of the core before displacement, and to observe its oil-water distribution.

[0064] S4. Place the No. 1, No. 2, and No. 3 cores selected for the experiment into the first core holder 10, the second core holder 11, and the third core holder 12, respectively. Control the confining pressure pump 14 and the six-way valve 3 13 to apply confining pressure to the three core holders. Control the back pressure pump 22 and the six-way valve 4 21 to apply back pressure to the back pressure valve 1 18, back pressure valve 2 19, and back pressure valve 3 20.

[0065] S5. Control the valves of six-way valve 1 and 8 and six-way valve 2 and 9 to connect the front and rear pipelines of the core holder and set the initial pressure of the experimental device system in constant pressure mode of the second plunger pump 2.

[0066] S6. Set the valve switching interval of the electric conversion three-way valve 26, set the plunger pump constant speed mode to 0.2ml / min, start the electric conversion three-way valve 26, and adjust the three-way valve 27 to achieve alternating injection of CO2 and water;

[0067] S7. During the experiment, when the volume of injected CO2 and water reaches 1, 3, 5, 7, 10 PV or when the core is broken, the displacement is stopped. The experimental core is scanned using an online NMR scanner to determine the T2 spectrum and one-dimensional frequency code of the experimental core. The liquid production and gas production at different times during the displacement process are recorded using the first gas-liquid separation component 23, the second gas-liquid separation component 24, the third gas-liquid separation component 25, the first gas flow meter 28, the second gas flow meter 29, and the third gas flow meter 30, respectively.

[0068] S8. After the core displacement is completed, control the valves of six-way valve 1 and six-way valve 2 to connect the front and rear pipelines of the core holder. After stabilization, discharge the high-pressure fluid in the pipeline from the pressure relief valve of six-way valve 2.

[0069] S9. After the experiment, the experimental core was scanned using an online nuclear magnetic resonance scanner 31 to obtain the T2 spectrum and one-dimensional frequency code of the core after the experiment. The total liquid production and gas production were obtained by three gas-liquid separation devices and a gas flow meter.

[0070] During the experiment, the high-permeability core No. 1 was the first to break through, followed by the medium-permeability core No. 2, and finally the low-permeability core No. 3. Figure 2 NMR imaging of three types of cores during the water-gas alternating displacement process is presented. It can be seen that as the number of injected PVs increases, the overall oil saturation of the cores gradually decreases, but large crude oil aggregates still exist, and the overall recovery effect is generally poor. Figure 3Dynamic T2 spectra during three core displacement processes were presented. It was observed that the microscopic oil displacement patterns were similar across different core layers, primarily utilizing oil from large pores, while oil from small and medium-sized pores was difficult to utilize due to higher capillary resistance. The real-time changes in produced fluid and gas during the displacement process were obtained experimentally. Figure 4 The recovery rates of different core samples after water-gas alternating flooding are given. The recovery rate of core sample 1 is about 20%, core sample 2 is about 25%, and core sample 3 is about 27%.

[0071] This experimental setup and method can accurately complete the physical simulation experiment of alternating CO2 / water injection in heterogeneous reservoirs. It can measure the recovery rate of core samples from each layer and the changes in residual oil in micropores during the displacement process, greatly reducing experimental errors. It is of great significance for in-depth exploration of the mechanism of enhanced oil recovery in CO2 / water trading zones of heterogeneous reservoirs and for providing theoretical guidance for the development of complex oil and gas reservoirs.

[0072] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A physical simulation device for alternating CO2 / water injection in heterogeneous reservoirs, characterized in that, It includes an injection system, a displacement system, a collection system, and main pipelines connecting the injection system, the displacement system, and the collection system; The main pipeline is equipped with a six-way valve No. 1, a six-way valve No. 2, and a four-way valve; The injection system includes a first plunger pump, a second plunger pump, a first intermediate container for holding CO2, a second intermediate container for holding water, and a third intermediate container for holding oil. The first intermediate container is connected to the first plunger pump via pipeline 1. The second and third intermediate containers are connected to the second plunger pump via pipeline 2. A three-way valve is installed on pipeline 2. The first and second intermediate containers are connected via pipeline 3. An electrically operated three-way valve is installed on pipeline 3. The electrically operated three-way valve is connected to a six-way valve 1. The third intermediate container is connected to a six-way valve 1. A one-way valve 1 is installed on pipeline 3 near the first intermediate container. A one-way valve 2 is installed on pipeline 3 near the second intermediate container. The displacement system includes a nuclear magnetic resonance spectrometer and a core holder scanned by the nuclear magnetic resonance spectrometer. The core holder includes a first core holder, a second core holder, and a third core holder connected in parallel. The inlet end of the core holder is connected to a six-way valve No. 1, and the outlet end of the core holder is connected to a back pressure valve via a pipeline. A four-way valve is provided on the pipeline. The back pressure valve is connected to a back pressure pump. The core holder is also connected to a confining pressure pump via a pipeline. The collection system includes a connected gas-liquid separation unit and a gas flow meter, with the other end of the gas-liquid separation unit connected to a back pressure valve; After the displacement experiment is completed, adjust valve No. 2 of the six-way valve to connect the pipelines before and after the core holder. After the pressure stabilizes, release the pressure in the pipeline through the pressure relief valve of valve No. 2 of the six-way valve.

2. The physical simulation device for alternating CO2 / water injection in heterogeneous reservoirs as described in claim 1, characterized in that, A six-way valve No. 3 is installed on the pipeline between the core holder and the confining pressure pump. The first core holder, the second core holder, and the third core holder are respectively connected to the six-way valve No. 3 via pipelines.

3. The physical simulation device for alternating CO2 / water injection in heterogeneous reservoirs as described in claim 2, characterized in that, The back pressure valves include back pressure valve 1, back pressure valve 2, and back pressure valve 3. The first core holder is connected to back pressure valve 1 via pipeline 4, and a four-way valve 1 is installed on pipeline 4. The second core holder is connected to back pressure valve 2 via pipeline 5, and a four-way valve 2 is installed on pipeline 5. The third core holder is connected to back pressure valve 3 via pipeline 6, and a four-way valve 3 is installed on pipeline 6. Four-way valves 1, 2, and 3 are all connected to six-way valve 2 via pipelines.

4. The physical simulation device for alternating CO2 / water injection in heterogeneous reservoirs as described in claim 3, characterized in that, Back pressure valves 1, 2, and 3 are connected to the back pressure pump via pipeline 7, and a six-way valve 4 is installed on pipeline 7.

5. The physical simulation device for alternating CO2 / water injection in heterogeneous reservoirs as described in claim 4, characterized in that, The gas-liquid separation assembly includes a first gas-liquid separation assembly, a second gas-liquid separation assembly, and a third gas-liquid separation assembly. The gas flow meter includes a first gas flow meter, a second gas flow meter, and a third gas flow meter. Back pressure valve 1 is connected to the first gas-liquid separation assembly via pipeline 8, and the first gas-liquid separation assembly is connected to the first gas flow meter. Back pressure valve 2 is connected to the second gas-liquid separation assembly via pipeline 9, and the second gas-liquid separation assembly is connected to the second gas flow meter. Back pressure valve 3 is connected to the third gas-liquid separation assembly via pipeline 10, and the third gas-liquid separation assembly is connected to the third gas flow meter.

6. A method of operating the device according to claim 5, characterized in that, Includes the following steps: S1. After saturating three different types of experimental cores with oil, place them into three core holders respectively. S2, control the confining pressure pump and six-way valve No. 3 to apply confining pressure to the three core holders; S3. Control the back pressure pump and six-way valve No. 4 to add back pressure to back pressure valves No. 1, No. 2 and No. 3; S4. Control the valves of six-way valve 1 and six-way valve 2 to connect the front and rear pipelines of the core holder and set the initial pressure of the experimental device system in constant pressure mode of the second plunger pump. S5, regulating three-way valve, electric switching three-way valve to achieve alternating injection of CO2 and water; S6. After the core displacement is completed, control the valves of six-way valve 1 and six-way valve 2 to connect the front and rear pipelines of the core holder. After stabilization, discharge the high-pressure fluid in the pipeline from the pressure relief valve of six-way valve 2. S7. The experimental core was scanned using a nuclear magnetic resonance spectrometer to determine the T2 spectrum and one-dimensional frequency coding of the experimental core. S8. The liquid production and gas production are recorded by using the first gas-liquid separation component, the second gas-liquid separation component, the third gas-liquid separation component, the first gas flow meter, the second gas flow meter, and the third gas flow meter, respectively.

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