Experimental apparatus and method for enhancing tight oil production based on mixed fluid displacement

Abstract

This invention provides an experimental apparatus and method for improving tight oil production based on mixed fluid displacement, specifically relating to the field of oil and gas field development technology. The apparatus includes a booster pump, a carbon dioxide storage tank, a hydrocarbon storage tank, a chemical additive storage tank, a pressure regulating valve, a core holder, and a confining pressure pump. One end of the booster pump is connected to the storage tank, and the other end is connected via an injection pipe to the inlet of the carbon dioxide, hydrocarbon, and chemical additive storage tanks respectively. The outlet of each storage tank is connected to the inlet of the core holder via an outlet pipe. A pressure regulating valve is installed on the outlet pipe to adjust the internal pressure. The confining pressure application chamber inside the core holder is connected via a confining pressure application pipe to a confining pressure application device for providing confining pressure to the core. The outlet of the core holder is connected to a waste liquid recovery tank. This invention is based on a CO2-C2H6-DME composite gas displacement strategy, combining the advantages of CO2 displacement, hydrocarbon gas displacement, and chemical displacement, thus improving the oil displacement effect and facilitating the efficient development of tight oil.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, and specifically to an experimental apparatus and method for improving tight oil production based on mixed fluid displacement. Background Technology

[0002] With the accelerating pace of global economic development and the continuous advancement of industrial technology, oil and gas consumption is gradually increasing. Conventional oil and gas resources can no longer fully meet the energy needs of the entire society, making tight oil resources a promising area for exploration and development.

[0003] Compared to conventional oil reservoirs, tight oil reservoirs contain a large number of nanoscale pores with complex pore structures, high capillary resistance, and difficult crude oil flow. When using depletion-based extraction, the pressure decay rate is too rapid, resulting in short reservoir development cycles, low recovery rates, and high residual oil content. Therefore, reasonable production enhancement measures are needed after flexible extraction. Furthermore, tight oil reservoirs are generally highly water-sensitive, making water injection difficult and prone to causing irreversible damage to the formation. Therefore, gas injection development in tight oil reservoirs is gradually attracting attention.

[0004] Currently, gases commonly used to enhance oil recovery in tight oil reservoirs include CO2, N2, natural gas, flue gas, and air. Among these, CO2 is the most studied and the most effective, as it more easily achieves miscibility under reservoir conditions. However, due to the interweaving of natural and artificial fractures in tight reservoirs, cross-flow problems often occur during gas injection, significantly limiting the sweep range and oil displacement efficiency of the injected gas. Further research into the miscibility of different injection media with crude oil has revealed that C2H6-dimethyl ether gas can achieve the minimum miscibility pressure of crude oil, and the reduction is greater than that of pure CO2.

[0005] Therefore, there is an urgent need to propose an experimental device and method for improving tight oil production based on mixed fluid displacement. This method utilizes a mixed fluid composed of CO2, hydrocarbon gas, and chemical additives to enhance the recovery rate of tight oil, fully leveraging the advantages of CO2 displacement, hydrocarbon gas displacement, and chemical displacement to increase crude oil production in tight oil reservoirs. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes an experimental apparatus and method for improving tight oil production based on mixed fluid displacement. By experimentally evaluating the displacement effect under different gas ratios, displacement pressures, and gas conditions, the advantages of combining CO2 displacement, hydrocarbon gas displacement, and chemical displacement are verified, providing a basis for the efficient development of pointed tight oil.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] An experimental apparatus for improving tight oil production based on mixed fluid displacement is placed in a constant temperature chamber and includes a booster pump, a carbon dioxide storage tank, a hydrocarbon storage tank, a chemical additive storage tank, a pressure regulating valve, a core holder, and a confining pressure pump.

[0009] The inflow end of the booster pump is connected to the storage tank, and the outflow end of the booster pump is connected to the inflow end of the injection pipe. The outflow end of the injection pipe is divided into three branches, including a first injection branch, a second injection branch, and a third injection branch. The first injection branch is connected to the air inlet of the carbon dioxide storage tank, the second injection branch is connected to the air inlet of the hydrocarbon storage tank, and the third injection branch is connected to the air inlet of the chemical auxiliary agent storage tank.

[0010] The outlet of the carbon dioxide storage tank is connected to the inlet of the outflow pipe via a first exhaust branch pipe; the outlet of the hydrocarbon storage tank is connected to the inlet of the outflow pipe via a second exhaust branch pipe; and the chemical additive storage tank is connected to the inlet of the outflow pipe via a third exhaust branch pipe. A pressure regulating valve is installed on the outflow pipe, and the outflow end of the outflow pipe is connected to one end of the core holder. The other end of the core holder is connected to the waste liquid recovery tank via a waste liquid pipe.

[0011] The core holder has a confining pressure injection hole on its side wall. The confining pressure injection hole is connected to the confining pressure application chamber inside the core holder. It is connected to a hydraulic oil storage tank through a confining pressure application pipe. A confining pressure pump is installed on the confining pressure application pipe to inject hydraulic oil into the confining pressure application chamber inside the core holder to provide confining pressure.

[0012] Preferably, the carbon dioxide storage tank is connected to a carbon dioxide gas tank, the hydrocarbon storage tank is connected to a hydrocarbon gas tank, and the chemical auxiliaries storage tank is connected to a chemical auxiliaries gas tank; the hydrocarbon gas tank stores ethane gas, and the chemical auxiliaries gas tank stores dimethyl ether gas.

[0013] Preferably, a carbon dioxide storage tank control valve is provided on both the first injection branch pipe and the first exhaust branch pipe, a hydrocarbon storage tank control valve is provided on both the second injection branch pipe and the second exhaust branch pipe, and a chemical auxiliary agent storage tank control valve is provided on both the third injection branch pipe and the third exhaust branch pipe.

[0014] The outflow pipe is equipped with a first pressure gauge and a first control valve. The first pressure gauge is located near the outflow end of the pressure regulating valve, and the first control valve is located near the inlet end of the core holder.

[0015] The waste liquid pipeline is equipped with a second control valve and a gas flow meter.

[0016] Preferably, the confining pressure application pipeline is equipped with a confining pressure control valve and a second pressure gauge on the side near the confining pressure pump.

[0017] A method for improving tight oil production based on mixed fluid displacement, employing the experimental apparatus described above for improving tight oil production based on mixed fluid displacement, and based on a CO2-C2H6-DME composite gas displacement strategy, specifically includes the following steps:

[0018] Step 1: Obtain the dried core, measure the dry weight, length and diameter of the core, saturate the core with simulated oil, measure the wet weight of the core, obtain the amount of saturated oil in the core, and then place the core saturated with simulated oil in a nuclear magnetic resonance spectrometer for nuclear magnetic resonance measurement to obtain the distribution of simulated oil in the core.

[0019] Step 2: Place the core of saturated simulated oil in the core holder, adjust the temperature of the constant temperature chamber to the preset temperature, and then perform vacuum treatment on the experimental device for improving tight oil production based on mixed fluid displacement.

[0020] Step 3: After opening the carbon dioxide storage tank control valve on the first exhaust branch pipe, the hydrocarbon storage tank control valve on the second exhaust branch pipe, the chemical auxiliary agent storage tank control valve on the third exhaust branch pipe, as well as the first control valve and the second control valve, first open the chemical auxiliary agent gas tank and inject dimethyl ether gas into the chemical auxiliary agent storage tank, then open the carbon dioxide gas tank and inject carbon dioxide gas into the carbon dioxide storage tank, and finally open the hydrocarbon gas tank and inject ethane gas into the hydrocarbon storage tank. Observe the reading of the first pressure gauge and adjust the pressure regulating valve so that the reading of the first pressure gauge shows the preset container gas pressure. At this time, the pressure of the mixed fluid flowing out of the pipe is the preset container gas pressure.

[0021] Step 4: Turn on the confining pressure pump and the confining pressure control valve. Combined with the preset confining pressure value, use the confining pressure pump to inject the hydraulic oil in the hydraulic oil storage tank into the core holder to apply confining pressure to the core. Observe the reading of the second pressure gauge and control the confining pressure pump so that the reading of the second pressure gauge is always the preset confining pressure value.

[0022] Step 5: Open the carbon dioxide storage tank control valve on the first injection branch pipe, the hydrocarbon storage tank control valve on the second injection branch pipe, the chemical auxiliary agent storage tank control valve on the third injection branch pipe, and the booster pump. Use the booster pump to input the pre-prepared water vapor into the core holder. Observe the reading of the first pressure gauge. Adjust the pressure regulating valve to keep the reading of the first pressure gauge at the preset pressure value. After stabilization, proceed to the displacement experiment and use the gas flow meter to record the volume of the injected mixed fluid.

[0023] Step 6: Turn off the booster pump, confining pressure pump, chemical additive gas tank, carbon dioxide gas tank and hydrocarbon gas tank to end the displacement experiment. Take the core out of the core holder and weigh it. Use the mass ratio of the core before and after the displacement experiment to obtain the core recovery rate. Place the core in the nuclear magnetic resonance spectrometer again for nuclear magnetic resonance measurement to obtain the distribution of simulated oil in the core after the displacement experiment.

[0024] Preferably, in step 3, the preset container gas pressure is calculated based on the ideal gas law as follows:

[0025] PV = ZnRT (1)

[0026] In the formula, P is the gas pressure in the container, in Pa; V is the gas volume, in m³. 3 Z is the gas deviation coefficient; n is the amount of substance of the gas, in mol; R is the molar gas constant, in J / (mol·K); T is the temperature, in K.

[0027] Preferably, in step 5, the preset pressure value is set according to the formation pressure to be simulated.

[0028] Preferably, in the CO2-C2H6-DME composite gas displacement strategy, CO2, C2H6, and DME form a mixed fluid with a volume ratio of 7:2:1. The mixed fluid achieves optimal oil recovery within a pore size of 0.01μm to 1μm.

[0029] The beneficial technical effects of this invention are as follows:

[0030] 1. This invention proposes an experimental apparatus and method for improving tight oil production based on mixed fluid displacement. By experimentally evaluating the displacement effect of mixed fluid on core samples under different gas ratios, displacement pressures, and gas conditions, the displacement effect of CO2-hydrocarbon gas-chemical additive mixed fluid is analyzed, filling the gap in the development and application of CO2-hydrocarbon gas-chemical additive mixed fluid in tight oil displacement.

[0031] 2. This invention fully replicates the displacement effect of a mixed fluid composed of carbon dioxide gas, hydrocarbon gas, and chemical additives under real formation conditions by simulating the high temperature and high pressure environment of the formation. Through experiments, the displacement effect of the CO2-hydrocarbon gas-chemical additive mixed fluid was verified, and it was found that it can significantly reduce crude oil viscosity, reduce the minimum miscibility pressure of oil and gas, improve crude oil flowability, and increase the sweep efficiency, thus achieving a good oil displacement effect and providing a basis for promoting the efficient development of tight oil. Attached Figure Description

[0032] Figure 1This is a schematic diagram of the experimental apparatus for improving tight oil production based on mixed fluid displacement according to the present invention. In the figure, 1-storage tank, 2-boost pump, 3-carbon dioxide storage tank, 4-hydrocarbon storage tank, 5-chemical additive storage tank, 6-carbon dioxide storage tank control valve, 7-hydrocarbon storage tank control valve, 8-chemical additive storage tank control valve, 9-pressure regulating valve, 10-first pressure gauge, 11-first control valve, 12-core holder, 13-containment pressure pump, 14-hydraulic oil storage tank, 15-containment pressure control valve, 16-second pressure gauge, 17-second control valve, 18-gas flow meter, 19-waste liquid recovery tank.

[0033] Figure 2 The characteristics of improved recovery when CO2 displacement is used for different core types.

[0034] Figure 3 The characteristics of improved oil recovery when CO2-C2H6 displacement is used for different core types.

[0035] Figure 4 The characteristics of improved oil recovery when using a CO2-C2H6-DME composite gas displacement strategy to replace different core types.

[0036] Figure 5 The T2 NMR spectra of cores under different displacement pressures when CO2 displacement is employed.

[0037] Figure 6 The T2 NMR spectra of cores under different displacement pressures when CO2-C2H6 displacement is employed.

[0038] Figure 7 The T2 NMR spectra of cores under different displacement pressures during displacement using a CO2-C2H6-DME composite displacement strategy. Detailed Implementation

[0039] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0040] This invention proposes an experimental apparatus for improving tight oil production based on mixed fluid displacement, placed in a constant temperature chamber, such as... Figure 1 As shown, it includes a booster pump 2, a carbon dioxide storage tank 3, a hydrocarbon storage tank 4, a chemical additive storage tank 5, a pressure regulating valve 9, a core holder 12, and a confining pressure pump 13.

[0041] The carbon dioxide storage tank is connected to the carbon dioxide gas tank, the hydrocarbon storage tank is connected to the hydrocarbon gas tank storing ethane gas, and the chemical auxiliaries storage tank is connected to the chemical auxiliaries gas tank storing dimethyl ether.

[0042] The inflow end of the booster pump 2 is connected to the storage tank 1, and the outflow end of the booster pump is connected to the inflow end of the injection pipe. The outflow end of the injection pipe is divided into three branches, including a first injection branch, a second injection branch, and a third injection branch. The first injection branch is connected to the air inlet of the carbon dioxide storage tank, the second injection branch is connected to the air inlet of the hydrocarbon storage tank, and the third injection branch is connected to the air inlet of the chemical auxiliary agent storage tank.

[0043] The outlet of the carbon dioxide storage tank is connected to the inlet of the outflow pipe through a first exhaust branch pipe, the outlet of the hydrocarbon storage tank is connected to the inlet of the outflow pipe through a second exhaust branch pipe, and the chemical auxiliary agent storage tank is connected to the inlet of the outflow pipe through a third exhaust branch pipe.

[0044] A carbon dioxide storage tank control valve 6 is installed on both the first injection branch pipe and the first exhaust branch pipe; a hydrocarbon storage tank control valve 7 is installed on both the second injection branch pipe and the second exhaust branch pipe; and a chemical auxiliary agent storage tank control valve 8 is installed on both the third injection branch pipe and the third exhaust branch pipe.

[0045] The outflow pipe is equipped with a pressure regulating valve 9, a first pressure gauge 10, and a first control valve 11. The outflow end of the outflow pipe is connected to one end of the core holder 12. The first pressure gauge is located near the outflow end of the pressure regulating valve, and the first control valve is located near the inlet end of the core holder. The other end of the core holder 12 is connected to the waste liquid recovery tank 19 through a waste liquid pipe for recovering the waste liquid flowing out of the core holder. The waste liquid pipe is equipped with a second control valve 17 and a gas flow meter 18.

[0046] The core holder 12 has a confining pressure injection hole on its side wall, which is connected to the confining pressure application chamber inside the core holder. It is connected to a hydraulic oil storage tank 14 via a confining pressure application pipe. A confining pressure pump 13 is installed on the confining pressure application pipe to inject hydraulic oil into the confining pressure application chamber inside the core holder to provide confining pressure. A confining pressure control valve 15 and a second pressure gauge 16 are also installed on the side of the confining pressure application pipe near the confining pressure pump.

[0047] This invention also proposes a method for improving tight oil production based on mixed fluid displacement, employing the experimental apparatus described above for improving tight oil production based on mixed fluid displacement, and based on a CO2-C2H6-DME composite gas displacement strategy, specifically including the following steps:

[0048] Step 1: Obtain the dried core, measure the dry weight, length and diameter of the core, saturate the core with simulated oil, measure the wet weight of the core, obtain the amount of saturated oil in the core, and then place the core saturated with simulated oil in a nuclear magnetic resonance spectrometer for nuclear magnetic resonance measurement to obtain the distribution of simulated oil in the core.

[0049] Step 2: Place the core of saturated simulated oil in the core holder, adjust the temperature of the constant temperature chamber to 80°C, and then perform vacuum treatment on the experimental device for improving tight oil production based on mixed fluid displacement, so that all pipelines and tanks of the entire experimental device are in a vacuum state.

[0050] Step 3: Open the carbon dioxide storage tank control valve on the first exhaust branch pipe, the hydrocarbon storage tank control valve on the second exhaust branch pipe, the chemical auxiliary agent storage tank control valve on the third exhaust branch pipe, as well as the first control valve and the second control valve.

[0051] Based on the ideal gas law, the preset container gas pressure is calculated according to formula (1) and the volume ratio between carbon dioxide, ethane and dimethyl ether in the mixed fluid.

[0052] To begin preparing the mixed fluid, first open the chemical additive gas tank and inject dimethyl ether gas into it. Then, open the carbon dioxide gas tank and inject carbon dioxide gas into it. Finally, open the hydrocarbon gas tank and inject ethane gas into it. Observe the reading of the first pressure gauge and adjust the pressure regulating valve so that the reading of the first pressure gauge shows the preset container gas pressure. At this time, the pressure of the mixed fluid flowing out of the pipeline is the preset container gas pressure.

[0053] Step 4: Turn on the confining pressure pump and the confining pressure control valve. Combined with the preset confining pressure value, use the confining pressure pump to inject hydraulic oil from the hydraulic oil storage tank into the core holder to apply confining pressure to the core. Observe the reading of the second pressure gauge and control the confining pressure pump so that the reading of the second pressure gauge is always the preset confining pressure value.

[0054] Step 5: Open the control valves of the carbon dioxide storage tank on the first injection branch pipe, the hydrocarbon storage tank on the second injection branch pipe, the chemical additive storage tank on the third injection branch pipe, and the booster pump. Use the booster pump to input the pre-prepared water vapor into the core holder. Observe the reading of the first pressure gauge. Adjust the pressure regulating valve to keep the reading of the first pressure gauge at the preset pressure value that is equal to the pressure of the formation to be simulated. Continue this for a period of time until it stabilizes. Then, proceed with the displacement experiment and use a gas flow meter to record the volume of the injected mixed fluid.

[0055] Step 6: Turn off the booster pump, confining pressure pump, chemical additive gas tank, carbon dioxide gas tank and hydrocarbon gas tank to end the displacement experiment. Take the core out of the core holder and weigh it. Use the mass ratio of the core before and after the displacement experiment to obtain the core recovery rate. Place the core in the nuclear magnetic resonance spectrometer again for nuclear magnetic resonance measurement to obtain the distribution of simulated oil in the core after the displacement experiment.

[0056] To further verify the effect of the CO2-C2H6-DME composite gas displacement strategy on the recovery rate of tight oil cores, displacement experiments were conducted using the aforementioned experimental apparatus and method for improving tight oil production based on mixed fluid displacement. The recovery rates of different core types using CO2 displacement, CO2-C2H6 displacement, and the CO2-C2H6-DME composite gas displacement strategy were obtained. The characteristics of the recovery rate improvement achieved by using these three strategies were compared, such as... Figures 2-4 As shown.

[0057] Displacement experiments were then conducted using the aforementioned experimental apparatus and method for improving tight oil production based on mixed fluid displacement. Nuclear magnetic resonance (NMR) T2 spectra of cores under different displacement pressures were obtained. The NMR T2 spectra of cores under CO2 displacement, CO2-C2H6 displacement, and CO2-C2H6-DME composite gas displacement strategies were compared. Figures 5-7 As shown, considering the degree of recovery improvement under different pore size conditions, it was found that the CO2-C2H6-DME composite gas displacement strategy has the best effect on improving the recovery of tight oil cores.

[0058] Compared to CO2 displacement, the mixed fluid composed of CO2 and C2H6 reaches its peak oil recovery rate in the pore size range of 0.0001μm to 0.001μm, while the mixed fluid containing CO2, C2H6 and DME reaches the optimal oil recovery rate in the range of 0.01μm to 1μm. This verifies that the CO2-C2H6-DME composite gas displacement strategy can effectively improve the production of tight cores and is conducive to improving the recovery rate of tight reservoirs.

[0059] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," "link," and "fix" 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 communication between two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0060] 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. An experimental apparatus for improving tight oil production based on mixed fluid displacement, placed in a constant temperature chamber, characterized in that, This includes booster pumps, carbon dioxide storage tanks, hydrocarbon storage tanks, chemical additive storage tanks, pressure regulating valves, core holders, and confining pressure pumps; The inflow end of the booster pump is connected to the storage tank, and the outflow end of the booster pump is connected to the inflow end of the injection pipe. The outflow end of the injection pipe is divided into three branches, including a first injection branch, a second injection branch, and a third injection branch. The first injection branch is connected to the air inlet of the carbon dioxide storage tank, the second injection branch is connected to the air inlet of the hydrocarbon storage tank, and the third injection branch is connected to the air inlet of the chemical auxiliary agent storage tank. The outlet of the carbon dioxide storage tank is connected to the inlet of the outflow pipe via a first exhaust branch pipe; the outlet of the hydrocarbon storage tank is connected to the inlet of the outflow pipe via a second exhaust branch pipe; and the chemical additive storage tank is connected to the inlet of the outflow pipe via a third exhaust branch pipe. A pressure regulating valve is installed on the outflow pipe, and the outflow end of the outflow pipe is connected to one end of the core holder. The other end of the core holder is connected to the waste liquid recovery tank via a waste liquid pipe. The core holder is provided with a confining pressure injection hole on its side wall. The confining pressure injection hole is connected to the confining pressure application chamber inside the core holder. The confining pressure injection hole is connected to a hydraulic oil storage tank through a confining pressure application pipe. A confining pressure pump is provided on the confining pressure application pipe to inject hydraulic oil into the confining pressure application chamber inside the core holder to provide confining pressure. The carbon dioxide storage tank is connected to the carbon dioxide gas tank, the hydrocarbon storage tank is connected to the hydrocarbon gas tank, and the chemical auxiliary agent storage tank is connected to the chemical auxiliary agent gas tank; the hydrocarbon gas tank stores ethane gas, and the chemical auxiliary agent gas tank stores dimethyl ether gas. A carbon dioxide storage tank control valve is installed on both the first injection branch pipe and the first exhaust branch pipe; a hydrocarbon storage tank control valve is installed on both the second injection branch pipe and the second exhaust branch pipe; and a chemical auxiliary agent storage tank control valve is installed on both the third injection branch pipe and the third exhaust branch pipe. The outflow pipe is equipped with a first pressure gauge and a first control valve. The first pressure gauge is located near the outflow end of the pressure regulating valve, and the first control valve is located near the inlet end of the core holder. The waste liquid pipeline is equipped with a second control valve and a gas flow meter; The confining pressure application pipeline is equipped with a confining pressure control valve and a second pressure gauge on the side near the confining pressure pump.

2. A method for increasing tight oil production based on mixed fluid displacement, characterized in that, The experimental apparatus for improving tight oil production based on mixed fluid displacement as described in claim 1, based on a CO2-C2H6-DME composite gas displacement strategy, specifically includes the following steps: Step 1: Obtain the dried core, measure the dry weight, length and diameter of the core, saturate the core with simulated oil, measure the wet weight of the core, obtain the amount of saturated oil in the core, and then place the core saturated with simulated oil in a nuclear magnetic resonance spectrometer for nuclear magnetic resonance measurement to obtain the distribution of simulated oil in the core. Step 2: Place the core of saturated simulated oil in the core holder, adjust the temperature of the constant temperature chamber to the preset temperature, and then perform vacuum treatment on the experimental device for improving tight oil production based on mixed fluid displacement. Step 3: After opening the carbon dioxide storage tank control valve on the first exhaust branch pipe, the hydrocarbon storage tank control valve on the second exhaust branch pipe, the chemical auxiliary agent storage tank control valve on the third exhaust branch pipe, as well as the first control valve and the second control valve, first open the chemical auxiliary agent gas tank and inject dimethyl ether gas into the chemical auxiliary agent storage tank, then open the carbon dioxide gas tank and inject carbon dioxide gas into the carbon dioxide storage tank, and finally open the hydrocarbon gas tank and inject ethane gas into the hydrocarbon storage tank. Observe the reading of the first pressure gauge and adjust the pressure regulating valve so that the reading of the first pressure gauge shows the preset container gas pressure. At this time, the pressure of the mixed fluid flowing out of the pipe is the preset container gas pressure. Step 4: Turn on the confining pressure pump and the confining pressure control valve. Combined with the preset confining pressure value, use the confining pressure pump to inject the hydraulic oil in the hydraulic oil storage tank into the core holder to apply confining pressure to the core. Observe the reading of the second pressure gauge and control the confining pressure pump so that the reading of the second pressure gauge is always the preset confining pressure value. Step 5: Open the carbon dioxide storage tank control valve on the first injection branch pipe, the hydrocarbon storage tank control valve on the second injection branch pipe, the chemical auxiliary agent storage tank control valve on the third injection branch pipe, and the booster pump. Use the booster pump to input the pre-prepared water vapor into the core holder. Observe the reading of the first pressure gauge. Adjust the pressure regulating valve to keep the reading of the first pressure gauge at the preset pressure value. After stabilization, proceed to the displacement experiment and use the gas flow meter to record the volume of the injected mixed fluid. Step 6: Turn off the booster pump, confining pressure pump, chemical additive gas tank, carbon dioxide gas tank and hydrocarbon gas tank to end the displacement experiment. Take the core out of the core holder and weigh it. Use the mass ratio of the core before and after the displacement experiment to obtain the core recovery rate. Place the core in the nuclear magnetic resonance spectrometer again for nuclear magnetic resonance measurement to obtain the distribution of simulated oil in the core after the displacement experiment.

3. The method for improving tight oil production based on mixed fluid displacement according to claim 2, characterized in that, In step 3, based on the ideal gas law, the preset container gas pressure is calculated as follows: PV=ZnRT (1) In the formula, P is the gas pressure in the container, in Pa; V is the gas volume, in m³. 3 Z is the gas deviation coefficient; n is the amount of substance of the gas, in mol; R is the molar gas constant, in J / (mol·K); T is the temperature, in K.

4. The method for improving tight oil production based on mixed fluid displacement according to claim 2, characterized in that, In step 5, the preset pressure value is set according to the formation pressure to be simulated.

5. The method for improving tight oil production based on mixed fluid displacement according to claim 2, characterized in that, In the CO2-C2H6-DME composite gas displacement strategy, CO2, C2H6, and DME form a mixed fluid with a volume ratio of 7:2:

1. The mixed fluid achieves the optimal oil recovery rate within a pore size of 0.01μm to 1μm.

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