An experimental device and method for studying interfacial mass transfer of dissolved CO2 in a crude oil system

Abstract

The application discloses a kind of dissolved CO2 interfacial mass transfer research experimental device and method in crude oil system, and relates to the technical field of oil and gas field development engineering.The experimental device includes fluid injection system, phase state reaction and observation system, pressure balance and control system, online sampling and component analysis system, the experimental device can realize the rapid energy compensation of two-component fluid, so as to inhibit the pressure disturbance caused by sampling, and the interfacial mass transfer process and degree of dissolved CO2 when contacting with light hydrocarbon gas are directly tested by experimental method.

Description

Technical Field

[0001] This invention relates to the field of oil and gas development engineering technology, specifically to an experimental apparatus and method for studying interphase mass transfer of dissolved CO2 in crude oil systems. Background Technology

[0002] CCUS-EOR technology creatively couples emission reduction costs with energy production benefits, providing a technological path for large-scale development to meet the huge emission reduction needs of high-carbon industries. Through CCUS-EOR technology, CO2 can be largely dissolved into the oil phase after contact with crude oil, changing the oil's volume, density, viscosity, and interfacial properties, thereby improving displacement efficiency.

[0003] However, field practice has revealed severe CO2 channeling in some miscible reservoirs employing this technology, posing an environmental threat. When the oil phase containing dissolved CO2 comes into contact with light hydrocarbons (such as CH4) in the formation, CO2 is re-released from the oil phase to form a free gas phase (i.e., inverse miscibility), causing the phase state and component distribution to continuously evolve over time. This process is coupled and controlled by phase equilibrium, interfacial mass transfer, and component replacement, and its kinetic characteristics directly affect the CO2 flooding effect, gas breakthrough, and injection-production optimization strategies.

[0004] Currently, it is difficult to monitor the phase evolution and component migration behavior of oil-gas two-phase under high temperature and high pressure conditions. Existing experimental methods mainly focus on final state or static characterization, which is difficult to provide phase dynamic information with high time resolution. At the same time, conventional sampling often relies on manual valve opening to release gas or direct sampling, which will cause significant system pressure fluctuations and mass loss, thereby disrupting the original equilibrium, causing subsequent evolution to be disturbed and difficult to be accurately corrected by quantitative methods.

[0005] For studies that require multiple time series and repeated sampling to repeatedly verify the light hydrocarbon-induced antimiscibility and mass transfer laws, there are few existing research cases, and there is currently a lack of experimental devices that can both meet the above technical requirements and be easy to routinely apply.

[0006] Based on the aforementioned shortcomings, there is an urgent need for an integrated, low-disturbance experimental setup: capable of high-frequency, low-disturbance constant-volume micro-sampling of the gas and liquid phases under high temperature and high pressure conditions; capable of real-time and controllable pressure and mass compensation of the system during each sampling or injection process to maintain near-constant pressure and mass conditions; and equipped with online component analysis methods and a systematic mass balance and correction process, thereby obtaining realistic and continuous displacement and mass transfer kinetic parameters of CO2 in the light hydrocarbon-crude oil contact process. The experimental conclusions are of great significance for formulating strategies such as CO2 exceedance concentration monitoring and early warning thresholds for target production wells, sampling frequency, and intermittent gas injection cycles. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides an experimental apparatus and method for studying interphase mass transfer of dissolved CO2 in crude oil systems. This apparatus enables high-frequency, low-disturbance gas / liquid phase constant-volume dynamic micro-sampling, and conducts experimental research on interphase mass transfer of dissolved CO2 in crude oil systems (antimiscible phase), providing key experimental data support for CO2 flooding followed by gas injection to enhance oil recovery technology.

[0008] To achieve the objectives of this invention, the invention is implemented through the following technical solutions:

[0009] In a first aspect, the present invention provides an experimental apparatus for studying interphase mass transfer of dissolved CO2 in a crude oil system, comprising:

[0010] Fluid injection system, phase reaction and observation system, pressure balance and control system, online sampling and component analysis system;

[0011] The fluid injection system is used to provide live oil and high-pressure CO2 and CH4 displacement fluids. The fluid injection system includes: a first intermediate container for storing high-pressure CO2; a second intermediate container for storing high-pressure CH4; and a third intermediate container for storing gas-bearing crude oil formulated according to formation parameters.

[0012] The phase reaction and observation system is used to visualize and observe fluid mixing, reaction, and phase changes. The system includes a high-temperature and high-pressure phase state analyzer, which is a high-pressure resistant reactor with an observation window. The reactor is equipped with a piston that can be controlled by an external displacement pump, and the pressure and volume inside the reactor are precisely regulated by the piston. A polarization camera is positioned directly opposite the observation window and is used to capture and record the dynamic evolution of the fluid phase state inside the reactor in real time.

[0013] The pressure balance and control system is used to maintain the pressure-substance balance inside the high-temperature and high-pressure phase phase instrument during fluid injection. The pressure balance and control system includes a high-pressure accumulator and a fourth high-pressure displacement pump. The high-pressure accumulator is pre-charged with fluid of the same target pressure as the high-temperature and high-pressure phase phase instrument as a pressure buffer source. The fourth high-pressure displacement pump is connected to the piston at the bottom of the high-temperature and high-pressure phase instrument. The fourth high-pressure displacement pump drives the piston to move to increase or decrease the pressure, thereby maintaining the dynamic pressure balance inside the high-temperature and high-pressure phase instrument.

[0014] The online sampling and component analysis system is used to sample the gas phase at the top and the liquid phase at the bottom of the high-temperature and high-pressure phase analyzer at different reaction time points without disrupting the system pressure and equilibrium, and to analyze their components. The online sampling and component analysis system includes a high-pressure constant-volume sampling ring, an oil-gas separation device, and a chromatograph. The high-pressure constant-volume sampling ring is connected to the gas phase outlet at the top of the high-temperature and high-pressure phase analyzer to accurately collect a constant volume of gas phase sample. The oil-gas separation device is connected to the liquid phase outlet of the high-temperature and high-pressure phase analyzer to perform oil-gas separation and metering on the collected liquid sample. The chromatograph is connected to the gas outlet of the high-pressure constant-volume sampling ring and the oil-gas separation device through pipelines and valves to analyze the component content in the gas phase and the gas extracted from the liquid sample.

[0015] Secondly, the present invention provides an experimental method for studying interphase mass transfer of dissolved CO2 in a crude oil system, using the aforementioned experimental apparatus, and the method includes the following steps:

[0016] S1. Simulate the first-state fluid formed by formation crude oil and injected gas CO2, and observe the phase characteristics of the first-state fluid;

[0017] S2. Simulate the process of the second injected gas entering the first-state fluid, generating an anti-miscible phenomenon, and observe the phase characteristics of the second-state fluid.

[0018] S3. Take a gas sample from the fluid in the second state and make a quantitative replenishment, test the composition of the sampled fluid, and obtain the molar percentage of CO2 contained in the fluid in the second state after sampling.

[0019] S4. Take a liquid sample of the fluid in the second state, test the composition of the sampled fluid, and obtain the molar percentage of CO2 contained in the fluid in the second state after sampling.

[0020] S5. After sampling, a new fluid system is obtained. After standing, repeat S3 and S4 to obtain the component parameters under multiple sampling conditions.

[0021] S6. Analyze the interphase mass transfer of dissolved CO2 in the second injected gas-crude oil system based on experimental observation data.

[0022] Preferably, step S1 includes:

[0023] Formation crude oil was prepared based on the results of on-site sampling and analysis of the target reservoir;

[0024] The experimental apparatus was evacuated, and the experimental temperature and pressure conditions were set. The prepared formation crude oil was then stored in the third intermediate container.

[0025] The crude oil in the third intermediate container is injected into the high-temperature and high-pressure phase state analyzer, and the piston movement is controlled by the fourth high-pressure displacement pump to maintain the pressure stability inside the high-temperature and high-pressure phase state analyzer.

[0026] CO2 in the first intermediate container is injected into a high-temperature and high-pressure phase analyzer to form a first-state fluid, and the phase characteristics of the first-state fluid are observed.

[0027] Preferably, when injecting fluid into the third intermediate container, the output pressure is preset to be 0.1 to 0.2 MPa higher than the formation pressure, and the fluid is injected at a constant rate.

[0028] Preferably, when fluid is injected into the third intermediate container, the fourth high-pressure displacement pump controls the piston movement at the same constant speed.

[0029] Preferably, the pressure of the fourth high-pressure displacement pump is maintained at the formation pressure when fluid is injected into the third intermediate container.

[0030] Preferably, the constant rate is 0.1 to 0.5 mL / min.

[0031] Preferably, step S2 includes:

[0032] The second injection gas in the second intermediate container is injected into a high-temperature and high-pressure phase state analyzer to observe the phase characteristics of the fluid in the second state.

[0033] Preferably, the second injected gas is CH4 or N2.

[0034] Preferably, step S3 includes:

[0035] The sample is transferred to the high-pressure accumulator for energy storage. Gas sampling of the second-state fluid is performed through the high-pressure constant-volume sampling ring. After sampling, the stored gas is injected into the high-temperature and high-pressure phase state meter through the high-pressure accumulator to maintain the material pressure balance in the high-temperature and high-pressure phase state meter.

[0036] Preferably, step S4 includes:

[0037] The sample is transferred to a high-pressure accumulator for energy storage. The high-temperature and high-pressure phase analyzer is rotated so that the liquid can flow out by its own weight and avoid entraining free gas phase. Liquid sampling of the second-state fluid is performed through a high-pressure buffer.

[0038] The beneficial effects of this invention are as follows:

[0039] (1) When conducting sampling research, the present invention can achieve dynamic pressure balance in the device by using the piston inside the high temperature and high pressure phase state instrument in conjunction with the high pressure accumulator, thereby achieving high frequency and low disturbance gas / liquid phase constant volume dynamic micro sampling, overcoming the defects of the existing phase state research experimental device that can only conduct static or final state research on phase state evolution and has pressure and mass disturbance.

[0040] (2) The present invention can simulate the dynamic process of CO2 “escaping” (anti-miscible) from crude oil and transferring mass to the gas phase when injected gas (such as CH4) comes into contact with crude oil that has been miscible with CO2 under reservoir conditions. It provides key experimental data support for the mechanism research and scheme optimization of CO2 flooding gas injection technology to enhance oil recovery. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the experimental apparatus of the present invention;

[0042] Figure 2 This is a schematic diagram of the method flow of the present invention;

[0043] Figure 3 The present invention provides a CO2 mass transfer curve over time in an embodiment;

[0044] Figure 4 The embodiment of the present invention provides a curve showing the transition from the mass transfer growth stage of CO2 to the asymptotic saturation stage.

[0045] Wherein: 101-First high-pressure displacement pump, 102-Second high-pressure displacement pump, 103-Third high-pressure displacement pump, 104-Fourth high-pressure displacement pump, 105-First valve, 106-Second valve, 107-First intermediate container, 108-Second intermediate container, 109-Third valve, 110-Fourth valve, 111-Third intermediate container, 112-Fifth valve, 113-Vacuum pump, 114-High-pressure five-way valve, 115-Temperature sensor, 116-Sixth valve, 117-Seventh valve, 118-High-pressure four-way valve, 119-Eighth valve, 120-High-pressure accumulator. 121-High-pressure constant-volume sampling ring, 122-Pressure gauge, 123-Ninth valve, 124-Tenth valve, 125-Oil-gas separator, 126-Gas flow meter, 127-Eleventh valve, 128-High-pressure buffer, 129-High-pressure sampler, 130-Chromatography analyzer, 131-Twelfth valve, 132-Programmable constant temperature chamber, 133-High-temperature and high-pressure phase analyzer, 134-Polarization camera, A-First valve port, B-Second valve port, C-Third valve port, D-Fourth valve port, E-Fifth valve port, a-Sixth valve port, b-Seventh valve port, c-Eighth valve port, d-Ninth valve port. Detailed Implementation

[0046] To enhance understanding of the present invention, the present invention will be further described in detail below with reference to embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0047] like Figure 1As shown, this invention provides an experimental apparatus for studying the interphase mass transfer of dissolved CO2 in a crude oil system, comprising: a first high-pressure displacement pump 101, a second high-pressure displacement pump 102, a third high-pressure displacement pump 103, a fourth high-pressure displacement pump 104, a first valve 105, a second valve 106, a first intermediate container 107, a second intermediate container 108, a third valve 109, a fourth valve 110, a third intermediate container 111, a fifth valve 112, a vacuum pump 113, a high-pressure five-way valve 114, and a temperature sensor 11. 5. Sixth valve 116, Seventh valve 117, High-pressure four-way valve 118, Eighth valve 119, High-pressure accumulator 120, High-pressure constant-volume sampling ring 121, Pressure gauge 122, Ninth valve 123, Tenth valve 124, Oil-gas separator 125, Gas flow meter 126, Eleventh valve 127, High-pressure buffer 128, High-pressure sampler 129, Chromatography analyzer 130, Twelfth valve 131, Programmable thermostat 132, High-temperature and high-pressure phase state analyzer 133, Polarization camera 134.

[0048] See Figure 1 The connection relationships are as follows: the first high-pressure displacement pump 101 is connected sequentially via pipeline to the first valve 105, the first intermediate container 107, the third valve 109, and the third valve port C of the high-pressure five-way valve 114; the first high-pressure displacement pump 101 is connected sequentially via pipeline to the second valve 106, the second intermediate container 108, the fourth valve 110, and the third valve port C of the high-pressure five-way valve 114; the second high-pressure displacement pump 102 is connected sequentially via pipeline to the fifth valve 112, the third intermediate container 111, and the first valve port A of the high-pressure five-way valve 114; the third high-pressure displacement pump 103 is connected sequentially via pipeline to the eighth valve 119, the high-pressure accumulator 120, the seventh valve 117, and the fourth valve port D of the high-pressure five-way valve 114; the fifth valve port E of the high-pressure five-way valve 114 is connected via pipeline to the first end of the high-temperature high-pressure phase state meter 133; the first end of the high-temperature high-pressure phase state meter 133 is also connected via pipeline... The line is connected in sequence to the sixth valve 116, the sixth valve port a of the high-pressure four-way valve 118, the ninth valve port d of the high-pressure four-way valve 118 is connected to the high-pressure accumulator 120, the seventh valve port b of the high-pressure four-way valve 118 is connected in sequence to the high-pressure sampler 129, the tenth valve 124, the oil-gas separator 125, the gas flow meter 126, the eleventh valve 127, and the chromatograph 130, and the eighth valve port c of the high-pressure four-way valve 118 is connected in sequence to the high-pressure constant volume sampling ring 121, the pressure gauge 122, the ninth valve 123, the high-pressure buffer 128, and the chromatograph 130, and the fourth high-pressure displacement pump 104 is connected in sequence to the twelfth valve 131 and the second end of the high-temperature and high-pressure phase analyzer 133, and the programmable constant temperature chamber 132 is set outside the high-temperature and high-pressure phase analyzer 133, and the vacuum pump 113 is connected in sequence to the second valve port B of the high-pressure five-way valve 114, and the vacuum pump 113 is connected in sequence to the second valve port B of the high-pressure five-way valve 114.

[0049] The programmable constant temperature chamber 132 is equipped with a temperature sensor 115, which can be programmed to stabilize the temperature inside the chamber at a set value, so as to maintain the temperature stability of the experiment.

[0050] The high-temperature and high-pressure phase state meter 133 has a cylindrical structure inside, and a piston is installed inside the cylindrical structure. The piston is controlled by an external displacement pump and can move linearly inside the cylindrical structure, thereby maintaining the fluid inside the high-temperature and high-pressure phase state meter 133 in a stable state and reducing disturbances caused by pressure and mass changes during sampling.

[0051] The high-temperature and high-pressure phase state analyzer 133 is made of stainless steel (e.g., 316L). The inner surface of the high-temperature and high-pressure phase state analyzer 133 is coated with an inert coating (e.g., PTFE) to reduce the adsorption of CO2 and light hydrocarbons and the reaction of materials.

[0052] The high-temperature and high-pressure phase analyzer 133 is fixed to the experimental platform, which can be adjusted to make an angle with the horizontal direction, with an adjustment range of 0~90°. By adjusting the angle, the high-temperature and high-pressure phase analyzer 133 can be driven to swing back and forth about a fixed axis in the horizontal direction by ±90° (i.e., a total swing amplitude of 180°). When the adjusted angle reaches the preset angle, a fixing device is provided to maintain the high-temperature and high-pressure phase analyzer 133 in an inclined state, which facilitates the sampling of samples with different flow states.

[0053] The high-temperature and high-pressure phase phase analyzer 133 is equipped with an observation window made of transparent material and reinforced glass or alloy sight glass. The polarization camera 134 is positioned directly facing the observation window. Through this setup, the operator can observe the fluid inside the high-temperature and high-pressure phase phase analyzer 133 via the observation window. The polarization camera 134 is used to capture and record the dynamic evolution of the fluid phase state (such as the gas-liquid interface, turbidity changes, etc.) within the tube in real time.

[0054] The maximum operating pressure of the first high-pressure displacement pump 101, the second high-pressure displacement pump 102, the third high-pressure displacement pump 103, and the fourth high-pressure displacement pump 104 in the experimental apparatus is 68.9 MPa, and the operating temperature range is room temperature to 165℃; the operating pressure range of the high-pressure accumulator 120 is 0 to 100 MPa, and the operating temperature range is room temperature to 200℃; the operating pressure range of the high-temperature and high-pressure phase state meter 133 is 0 to 100 MPa, and the operating temperature range is room temperature to 200℃; the operating pressure range of the first intermediate container 107, the second intermediate container 108, and the third intermediate container 111 is 0 to 70 MPa, and the operating temperature range is room temperature to 200℃.

[0055] During experimental testing, the first intermediate container 107 is used to store high-pressure CO2 gas, the second intermediate container 108 is used to store high-pressure injected gases (such as CH4, N2, etc.), and the third intermediate container 111 is used to store gas-bearing crude oil (i.e., live oil) prepared according to formation parameters. The high-temperature and high-pressure phase state analyzer 133 is the core of the experiment, used to complete the visual observation of fluid mixing, reaction, and phase changes. The high-temperature and high-pressure phase state analyzer 133 is a high-pressure resistant reactor with an observation window. The reactor has a cylindrical structure inside and is equipped with a piston that can be controlled by an external displacement pump for precise control of the internal pressure and volume.

[0056] The high-pressure accumulator 120 is pre-filled with a fluid (such as CH4 or a gas of the same composition as the target experiment) at the same pressure as the high-temperature high-pressure phase state instrument 133, serving as a pressure buffer source. The fourth high-pressure displacement pump 104 is connected to the piston at the bottom of the high-temperature high-pressure phase state instrument 133 and can increase or decrease the pressure by driving the piston in the forward or reverse direction, thereby cooperating with the high-pressure accumulator 120 to achieve dynamic pressure balance within the high-temperature high-pressure phase state instrument 133. The high-pressure accumulator 120 and the fourth high-pressure displacement pump 104 work together to achieve precise control of isobaric or micro-pressure difference within the high-temperature high-pressure phase state instrument 133, simulating constant formation pressure conditions.

[0057] To facilitate a better understanding of the method of using the device provided by this invention by those skilled in the art, such as Figure 2 As shown, the usage method is explained through the following specific steps. The experimental method is based on the above-mentioned device, and its core steps include: sample preparation and loading, CO2 injection and miscibility, isobaric CH4 injection and displacement, and multi-stage online sampling and analysis. The experimental method reveals the variation law of CO2 displacement and mass transfer with contact time through a cycle of pressure-compensated timed sampling and component analysis. This invention provides an experimental method for studying the interphase mass transfer of dissolved CO2 in a crude oil system, including the following steps:

[0058] S1. Simulate the first-state fluid formed by formation crude oil and injected gas CO2, and observe the phase characteristics of the first-state fluid;

[0059] S2. Simulate the process of the second injected gas entering the first-state fluid, generating an anti-miscible phenomenon, and observe the phase characteristics of the second-state fluid.

[0060] S3. Take a gas sample from the fluid in the second state and make a quantitative replenishment, test the composition of the sampled fluid, and obtain the molar percentage of CO2 contained in the fluid in the second state after sampling.

[0061] S4. Take a liquid sample of the fluid in the second state, test the composition of the sampled fluid, and obtain the molar percentage of CO2 contained in the fluid in the second state after sampling.

[0062] S5. After sampling, a new fluid system is obtained. After standing, repeat S3 and S4 to obtain the component parameters under multiple sampling conditions.

[0063] S6. Analyze the interphase mass transfer of dissolved CO2 in the second injected gas-crude oil system based on experimental observation data.

[0064] Specifically, step S1 includes the following steps:

[0065] (S11) Formation fluid preparation and injection volume calculation: Based on the field sampling and analysis results of the target reservoir, prepare the experimental formation fluid (i.e., "live oil") and conduct gas injection-expansion tests to obtain the bubble point curve of the high pressure properties of the oil phase fluid as a function of CO2 content; based on the expansion test and the target formation pressure, use the isothermal and isobaric property conversion method to calculate the amount of CO2 required to restore the bubble point pressure of the crude oil-CO2 mixture system to the original formation pressure, and convert it into an injection volume percentage as the basis for subsequent injection design;

[0066] (S12) System vacuuming and sealing preparation: Open the corresponding valve port of the high-pressure five-way valve 114 and the designated valve port of the high-pressure four-way valve 118 to connect the high-temperature high-pressure phase state meter 133, high-pressure constant volume sampling ring 121, high-pressure sampler 129 and vacuum pump 113; start vacuum pump 113 to evacuate for 30 minutes until the system reaches the predetermined negative pressure value, and then close the corresponding valves to maintain the vacuum environment; in this step, vacuuming is used to remove air and impurities in the system to ensure the representativeness of subsequent samples and the accuracy of measurements;

[0067] (S13) Temperature isothermal treatment: The high temperature and high pressure phase state instrument 133, which is in direct contact with the sample, is placed in the programmable constant temperature chamber 132. The temperature of the programmable constant temperature chamber 132 is set to the target formation temperature and the constant temperature control is started. After the temperature sensor 115 reading stabilizes to the set value, it is maintained for at least 8 hours to eliminate the influence of temperature gradient on phase state.

[0068] (S14) Live oil pretreatment and pressure balancing: The pretreated live oil is loaded into the third intermediate container 111, the fifth valve 112 connecting the third intermediate container 111 to the system is opened, and the second high-pressure displacement pump 102 is started to adjust and stabilize the internal pressure of the third intermediate container 111 at the target formation pressure. The balancing is maintained for no less than 8 hours to ensure that the live oil reaches the specified initial dissolution state.

[0069] (S15) Transfer of live oil sample into high-temperature and high-pressure phase analyzer 133: The output pressure of the second high-pressure displacement pump 102 is preset to be 0.1-0.2 MPa higher than the formation pressure to establish the injection driving pressure; the corresponding passages of the high-pressure five-way valve 114 are opened in sequence, and the propulsion rate of the second high-pressure displacement pump 102 is controlled at a constant low speed (selectable range of 0.1-0.5 mL / min) to transfer the live oil in the third intermediate container 111 to the high-temperature and high-pressure phase analyzer 133 at a constant rate. At the same time, the fourth high-pressure displacement pump 104 is controlled to draw liquid at a matching rate to ensure stable pressure and flow rate during the sample transfer process; when the high-temperature and high-pressure phase analyzer 133 has received approximately 40-50 mL of live oil sample, the sample transfer is stopped and the corresponding passages are closed;

[0070] (S16) Phase determination and precise calculation of required CO2 amount: Start the third high-pressure displacement pump 103 to implement fine-tuning pressure control of the high-temperature and high-pressure phase phase instrument 133, and accurately stabilize the system pressure within the formation pressure range; after the sample enters the high-temperature and high-pressure phase instrument 133 and reaches a steady state, use a polarization camera 134 and online spectroscopy to monitor the sample phase state and confirm that the sample is a homogeneous liquid phase; read and record parameters such as sample volume and density at steady state, and combine with the actual injection amount obtained in steps S11 and S15 to make the final confirmation and labeling of the required CO2 volume;

[0071] (S17) Injection preparation and differential pressure protection configuration: After determining the injection volume, first open the control valve for CO2 injection to establish the process path; set the pressure of the displacement pump that drives CO2 to be 0.1 to 0.2 MPa higher than the formation pressure to ensure that the injected gas has a stable driving potential and to prevent backflow of liquid in the high-temperature and high-pressure phase meter 133 during injection; at the same time, maintain the fourth high-pressure displacement pump 104 at the receiving end at the formation pressure to form a controlled pressure difference;

[0072] (S18) Constant-speed gas injection and constant-speed retraction to complete the injection: Open the injection passage valves in sequence according to the predetermined procedure, set the gas injection pump to discharge at a constant speed of 0.5 mL / min, set the fourth high-pressure displacement pump 104 to retract synchronously at the same speed, and always keep the injection pump pressure higher than the recovery pump by 0.1 to 0.2 MPa; monitor the cumulative discharge in real time during the injection process, and when the discharge count of the injection pump reaches the predetermined threshold (i.e. the injection volume determined in steps S11 and S16), stop the gas injection and close the injection passage valves in sequence to complete the quantitative addition of CO2 to the high-temperature and high-pressure phase state analyzer 133;

[0073] (S19) Steady-state dissolution and phase confirmation: After the injection is completed, the third high-pressure displacement pump 103 is activated to maintain the pressure of the high-temperature and high-pressure phase analyzer 133 at the formation pressure and keep it stable for at least 12 hours to ensure that CO2 is fully dissolved in the oil phase and reaches the steady-state liquid phase conditions.

[0074] During steady-state maintenance, a polarization camera 134 was used to continuously capture phase images. When the image characterization showed no free gas phase and the single-phase state tended to be stable, the final volume of the system was recorded. Based on this, the content of dissolved CO2 components in the crude oil system was calculated and the experimental data was archived.

[0075] Specifically, step S2 includes the following steps:

[0076] (S21) Pre-injection differential pressure protection and pressure preset: Before injection, the second valve 106 connected to the injection gas source is opened, and the output pressure of the injection displacement pump is preset to 0.1 to 0.2 MPa above the formation pressure to provide a continuous driving differential pressure for the injection section during the injection process and prevent the liquid in the high-temperature and high-pressure phase meter 133 from flowing back under the applied differential pressure; at the same time, the pressure of the fourth high-pressure displacement pump 104 used for receiving is constantly set to the formation pressure; the above pressure setting can be issued by the PLC controller and is fed back in real time by the pressure sensor in the pump;

[0077] (S22) Constant-rate constant-pressure gas injection and synchronous retraction: Open the injection passage (fourth valve 110) and the corresponding third valve port C and fifth valve port E of the high-pressure five-way valve 114 in sequence, start the injection pump and set its flow rate to 0.5 mL / min; at the same time, set the retraction pump to the same retraction rate (0.5 mL / min) as the injection pump, and ensure that the pressure of the injection pump is always 0.1 to 0.2 MPa higher than that of the retraction pump;

[0078] During the injection process, the cumulative discharge reading of the injection pump and the system pressure curve should be recorded in real time. When the cumulative discharge of the injection pump reaches the pre-calculated CH4 injection volume threshold, the gas injection should be stopped immediately, and the third valve port C, the fifth valve port E and the fourth valve 110 of the high-pressure five-way valve 114 should be closed in sequence to cut off the injection passage and complete the quantitative addition. The entire process requires smooth operation and slow valve opening and closing.

[0079] (S23) Post-injection pressure stabilization and short-term equilibrium: After injection is terminated, the third high-pressure displacement pump 103 is activated to maintain the high-temperature and high-pressure phase state analyzer 133 with fine pressure, so that the system pressure is stabilized at the formation pressure and the pressure fluctuation is controlled within ±0.05MPa; under this condition, it should be maintained for at least 0.5 hours (30 min) to allow the CO2-oil phase in the system to fully expand and dissolve; during the pressure stabilization period, the system volume change curve over time should be continuously recorded and the start and end times of steady state should be marked;

[0080] (S24) Phase dynamic monitoring: From the start of injection until the end of steady state, the polarization camera 134 is used to continuously record video and acquire key frames to track the evolution of gas-liquid interface, local bubble generation, swelling and precipitation phenomena in real time.

[0081] The timestamps acquired by the polarization camera 134 are recorded synchronously with the system volume and online chromatographic data to facilitate subsequent time-series correlation analysis of phase images and component changes. If abnormally rapid gas evolution or pressure exceeding the limit is observed, pressure maintenance operations should be stopped immediately according to safety procedures, and slow pressure return should be implemented. The abnormal event should be recorded, and relevant raw data should be saved.

[0082] Specifically, step S3 includes the following steps:

[0083] (S31) Transferring samples and storing energy to the high-pressure accumulator 120: 1) Opening the passage: Sequentially open the second valve 106, the fourth valve 110, the third valve port C and the fourth valve port D of the high-pressure five-way valve 114, and the seventh valve 117 to establish a connection passage from the first high-pressure displacement pump 101 to the high-pressure accumulator 120. 2) Constant-speed sample transfer: Set the flow rate of the first high-pressure displacement pump 101 to 0.5 mL / min, and transfer the displacement gas to the high-pressure accumulator 120 at this constant rate; at the same time, set the third high-pressure displacement pump 103 to maintain the pressure inside the high-pressure accumulator 120 at the formation pressure (pressure stabilizer), and at the same time, the third high-pressure displacement pump 103 retracts during the sample transfer to balance the flow rate. 3) Monitoring and Stopping: Monitor the "charged amount" of the high-pressure accumulator 120 in real time (which can be obtained from the pressure-volume relationship and the piston stroke gauge of the high-pressure accumulator 120); when the reading of the high-pressure accumulator 120 reaches the predetermined charge value required by the high-pressure constant volume sampling ring 121 (ensuring that the amount of available gas in the future meets the sampling and ensures equal replenishment), immediately stop the first high-pressure displacement pump 101 and sequentially close the second valve 106, the fourth valve 110, the third valve port C and the fourth valve port D of the high-pressure five-way valve 114 and the seventh valve 117 to complete the initial energy storage.

[0084] (S32) Filling the high-pressure constant-volume sampling ring 121: 1) Opening the sampling path: Open the sixth valve 116 at the top of the high-temperature and high-pressure phase phase meter 133 leading to the high-pressure constant-volume sampling ring 121, and open the sixth valve port a and the eighth valve port c of the high-pressure four-way valve 118 to establish a flow path from the top of the high-temperature and high-pressure phase phase meter 133 to the high-pressure constant-volume sampling ring 121. 2) Constant-volume filling and pressure equalization: Slowly open the passage to allow the free gas in the upper part of the high-temperature and high-pressure phase phase meter 133 to steadily fill the high-pressure constant-volume sampling ring 121, while monitoring the pressure inside the high-pressure constant-volume sampling ring 121 with the pressure gauge 122; when the pressure of the high-pressure constant-volume sampling ring 121 is basically equal to the internal pressure of the high-temperature and high-pressure phase phase meter 133, immediately close the eighth valve port c of the high-pressure four-way valve 118 to form a sealed constant-volume gas sample and record the pressure of the high-pressure constant-volume sampling ring 121.

[0085] (S33) Rapid energy replenishment from high-pressure accumulator 120 to high-temperature and high-pressure phase state analyzer 133: 1) Opening the energy replenishment path: Open the ninth valve port d of the high-pressure four-way valve 118 to ensure that the energy replenishment path between the high-pressure accumulator 120 and the high-temperature and high-pressure phase state analyzer 133 is connected; 2) Setting and rapid displacement: Preset the pressure of the third high-pressure displacement pump 103 to 0.5 MPa higher than the formation pressure (to provide energy replenishment driving force), and set the flow rate of the third high-pressure displacement pump 103 to 5 mL / min to quickly replenish the gas in the high-pressure accumulator 120 into the high-temperature and high-pressure phase state analyzer 133, realizing short-term pressure and volume replenishment. 3) End and shut down: After monitoring the pressure in the high-temperature and high-pressure phase state analyzer 133 to the target value and confirming stability during the energy replenishment process, stop the displacement operation of the third high-pressure displacement pump 103, and close the sixth valve port a, the ninth valve port d, and the sixth valve 116 of the high-pressure five-way valve 114 to complete the energy replenishment and maintain the pressure of the high-temperature and high-pressure phase state analyzer 133 at the target value.

[0086] (S34) High-pressure constant-volume sampling loop 121 gas sample transfer and analysis to chromatography: 1) Transfer path: Open the ninth valve 123 to slowly release the sealed gas in the high-pressure constant-volume sampling loop 121 through the high-pressure buffer 128, so that the gas enters the chromatographic injection system smoothly under controlled pressure. 2) Flow rate and injection control: Use the flow controller built into the chromatograph 130 to control the transfer rate to ensure the stability of the chromatographic injection volume and injection pressure. 3) Chromatographic analysis: Analyze according to the calibrated chromatographic conditions, obtain the peak area of ​​each component, and calculate the volume percentage or molar percentage of CH4, CO2 and other detectable components in the sample gas.

[0087] (S35) Calculate the CH4 and CO2 usage in the next high-pressure accumulator 120 based on the chromatographic results: 1) Component conversion: Based on the molar percentage (or volume percentage) obtained from the chromatographic analyzer 130 x CO2 x CH4 1) Combining the temperature T and pressure P of the high-pressure constant-volume sampling ring 121 during measurement and the constant-volume volume V of the high-pressure constant-volume sampling ring 121 (known), the mass of each component in the high-pressure constant-volume sampling ring 121 is calculated using the ideal gas approximation or the equation of state containing the compressibility factor. 2) Estimation of the number of samples transferred to the high-pressure accumulator 120: Based on the charging volume / molar mass of the sample transferred to the high-pressure accumulator 120 in step S31 and the volume balance before and after energy replenishment in step S33, the molar masses of CH4 and CO2 required for the high-pressure accumulator 120 to reach the target composition are calculated, and the calculation process and results are recorded (if the sample contains other components, their influence should be removed or corrected).

[0088] (S36) Supplement the high-pressure accumulator 120 with designated CO2 and CH4 according to the target components to complete the fixed-ratio energy storage: 1) Transfer CO2 to the high-pressure accumulator 120: Sequentially open the first valve 105, the third valve 109, the C and D channels of the high-pressure five-way valve 114, and the seventh valve 117 to establish the connection between the first high-pressure displacement pump 101 and the high-pressure accumulator 120; set the flow rate of the first high-pressure displacement pump 101 to 0.5 mL / min for constant displacement, and transfer the target molar mass of CO2 to the high-pressure accumulator 120. The third high-pressure displacement pump 103 maintains the formation pressure and retracts to balance. Monitor the charge level of the high-pressure accumulator 120 in real time. When the predetermined CO2 charge threshold is reached, stop the transfer and close the corresponding valves. 2) Transfer CH4 sample to high-pressure accumulator 120: Then, following the operating procedure in step S31, open the corresponding circuit and transfer CH4 sample from the first high-pressure displacement pump 101 to the high-pressure accumulator 120 at the same rate until the amount of CH4 required calculated in step S35 is reached in the high-pressure accumulator 120. Then, stop and close the circuit to complete the final energy storage. 3) Final verification: After completion, perform a short-term voltage stabilization and sampling (steps S32-S34 can be repeated) to verify that the gas composition in the high-pressure accumulator 120 is consistent with the target component ratio. If the deviation exceeds the allowable error range, fine-tune according to the supplementation / replacement strategy until the requirements are met.

[0089] Specifically, step S4 includes the following steps:

[0090] (S41) Tilting the high-temperature and high-pressure phase analyzer 133 to position the sampling port: Tilting the high-temperature and high-pressure phase analyzer 133 slowly in the predetermined direction through the experimental platform until the sampling passage (the port where the sixth valve 116 is located) is at the lowest point, ensuring that the liquid phase can flow out by its own weight and avoiding the entrainment of free gas phase; the tilting action must be smooth and slow to avoid generating violent gas-liquid disturbances or foam; the tilting angle and speed are recorded in the experimental log for repeatability.

[0091] (S42) Introduce the liquid phase into the high-pressure buffer 128 and stabilize the pressure: Sequentially open the sixth valve 116 and the sixth port a and the seventh port b of the high-pressure four-way valve 118 to establish a connection between the high-temperature high-pressure phase analyzer 133 and the high-pressure buffer 128; start and set the fourth high-pressure displacement pump 104 to maintain it at the target formation pressure (based on pressure sensor feedback, allowable deviation ±0.05MPa), and control the retraction rate to ensure the liquid smoothly enters the high-pressure buffer 128. It is recommended to control the flow rate within the range of 0.1-1.0 mL / min to reduce shearing and re-precipitation of dissolved gases. When the pressure inside the high-pressure buffer 128 is approximately equal to the pressure in the high-temperature high-pressure phase analyzer 133, and the fluid is stable with no signs of bubble escape, close the sixth valve 116 and the sixth port a and the seventh port b of the high-pressure four-way valve 118 to complete the safe transfer of the liquid and record the transfer volume, time, and pressure curves.

[0092] (S43) Quantitatively transfer the liquid in the high-pressure buffer 128 into the oil-gas separator 125: Slowly open the tenth valve 124, control the valve opening or the displacement pump rate, so that the liquid sample in the high-pressure buffer 128 flows smoothly into the oil-gas separator 125; the flow process should be slow to avoid violent agitation in the oil-gas separator 125; after the transfer is completed, close the tenth valve 124 and record the transfer volume and time from the high-pressure buffer 128 to the oil-gas separator 125.

[0093] (S44) The separated gas is smoothly fed into the chromatograph 130 for analysis: the eleventh valve 127 is opened, and the gas phase separated by the oil-gas separation device 125 is smoothly fed into the injection end of the chromatograph 130 through the pressure stabilizing and flow stabilizing device via the high-pressure buffer 128; during the sample delivery process, the instantaneous flow rate is monitored by the gas flow meter 126 and the cumulative volume is recorded; the analysis is performed according to the preset injection program of the chromatograph 130, and the calibration curve or standard gas of the day is used to correct the quantification of CO2 and CH4; the chromatographic peak area, retention time and analysis results are recorded.

[0094] (S45) Calculate the CO2 content in the oil sample from chromatographic and volumetric data: The following data can be obtained through experiments: V live : Live oil volume (i.e., the volume of the high-pressure sampler 129); V gas : Volume of gas obtained after separation; P gas T gas : Pressure (Pa) and temperature (K) of the separated gas; y CO2 y CH4 The molar percentages of CO2 and CH4 in the separated gas were determined by chromatography; ρ oil Oil sample density (kg / m³) 3 ).

[0095] Steps and formulas: First, calculate the total molar mass n of the separated gas. total

[0096] n total =(P gas ·V gas ) / (Z·R·T gas );

[0097] Calculate the molar mass of each component.

[0098] n CO2 =y CO2 ·n total；

[0099] n CH4 =y CH4 ·n total；

[0100] Molar concentration per unit volume of live oil (mol / L)

[0101] c CO2 (mol / L)=n CO2 / V live (L);

[0102] c CH4 (mol / L)=n CH4 / V live (L);

[0103] In the formula, Z is the gas deviation factor; R is the ideal gas constant; n CO2 n is the molar mass of CO2. CH4 c is the molar mass of CH4. CO2 c is the molar concentration of CO2; CH4 This represents the molar concentration of CH4.

[0104] Specifically, step S5 includes:

[0105] 1) Sampling and Settling Requirements: After completing one gas phase and oil phase sampling, perform equal compensation and pressure stabilization on the system again according to steps S3 and S4. Close unnecessary valves and maintain the pressure of the high-temperature and high-pressure phase analyzer 133 at the predetermined target value. Let the system settle for 0.5 hours. During the settling period, continuously record images from the polarization camera 134 to monitor phase changes. After settling for 0.5 hours, repeat the complete gas / oil sampling and analysis process in the order of steps S3 (gas phase constant volume sampling and chromatographic analysis) and S4 (oil sample collection → oil-gas separation → chromatographic analysis of precipitated gas). Use the sampling results of this time point as the data point for the next time point. After the sampling is completed, replenish the high-pressure accumulator 120 with gas based on the experimental data of the chromatograph 130 in this round. Continue to repeat the settling and sampling according to the predetermined time sequence until a total of 6 sets of valid samples are completed (using time points 0h (baseline), 2h, 6h, 18h, 30h, and 60h; the time points should be clearly defined in the experimental design and recorded in the experimental log). 2) Operational details and quality control for each repeated sampling: Before each sampling, confirm and record the instantaneous pressure of the system, the status of the high-pressure constant-volume sampling loop 121, and the high-pressure buffer 128; during sampling, record the pressure of the high-pressure constant-volume sampling loop 121, the sampling volume or the injection volume of the high-temperature high-pressure phase analyzer 133, the cumulative volume through the gas flow meter 126, and any compensation volume. Perform immediate pressure / volume compensation after each sampling and record the compensation molar mass, incorporating all compensation actions as part of the mass balance calculation. 3) Data recording and archiving: Compile and archive the original chromatograms, pressure / volume curves of the high-pressure constant-volume sampling loop 121, keyframes of the polarization camera 134 image, injection volume, and compensation records for each sampling, and archive them chronologically; each set of data must include metadata (operator, valve status, cumulative pump displacement, etc.).

[0106] Specifically, step S6 includes:

[0107] 1) Preliminary processing (preparing the dataset for plotting): Obtain the molar percentages (y) of CO2 and CH4 in the gas phase from each gas chromatography result. CO2 (t), y CH4 (t)); The molar percentages of CO2 and CH4 in the evolved gas were extracted from the oil sample by gas chromatography (y). CO2_oilgas (t), y CH4_oilgas (t)). The volume of the high-pressure constant-volume sampling ring 121 / high-pressure buffer 128 and the measured temperature and pressure data are used to convert the sampling volume into molar mass n. total (t), and calculate n CO2 (t)=y CO2 ·n total Similarly, calculate the molar mass of each component of the oil sample's precipitated gas and convert it to the molar mass per unit volume or mass of live oil (see the aforementioned conversion formula S45). Perform a mass balance check at each time point: cumulative CO2 injection ≈ cumulative CO2 in the gas phase + residual CO2 in the oil phase + system residue / measurement error; record and analyze the sources of error. 2) Graphical plotting: plot the curves of the percentage of CO2 moles in the gas phase versus contact time and the percentage of CO2 moles in the precipitated gas in the oil phase versus contact time, and simultaneously plot the curve of the percentage of CO2 moles dissolved in the oil phase versus time, so as to compare the evolution of phase state and dissolved amount.

[0108] Example 1

[0109] Taking a certain oil reservoir in Xinjiang as an example, the formation pressure of the reservoir is 35.68 MPa, the formation temperature is 72.61 degrees Celsius, the inner diameter of the cylinder of the high temperature and high pressure phase instrument 133 is 5 cm, and a total of 6 sets of tests were designed.

[0110] (S1) Formation fluid preparation and gas injection expansion experiment: The formation fluid for the experiment was prepared, and a portion was used to conduct gas injection-expansion tests. The solubility of CO2 in the formation fluid under formation pressure was measured to be 217 (m³). 3 / m 3 The solubility of CH4 is 61 (m). 3 / m 3 ).

[0111] System vacuuming and sealing: Open the corresponding valve ports of the high-pressure five-way valve 114 and the high-pressure four-way valve 118 to connect the high-temperature and high-pressure phase state meter 133, the high-pressure constant volume sampling ring 121, the high-pressure sampler 129 and the vacuum pump 113 passages. Start the vacuum pump 113 to evacuate to the predetermined negative pressure value and then close the valves to seal.

[0112] System temperature control: Place the high-temperature and high-pressure phase state instrument 133 in the programmable temperature control chamber 132, set and stabilize it to the target formation temperature, and maintain it for at least 8 hours.

[0113] Live oil pretreatment and pressure balancing: The live oil is loaded into the third intermediate container 111, and its pressure is adjusted to the target formation pressure and stabilized for no less than 8 hours.

[0114] Live oil sample transferred to high temperature and high pressure phase analyzer 133: The output pressure of the second high pressure displacement pump 102 is preset to be slightly higher than the formation pressure, and the live oil in the third intermediate container 111 is transferred to the high temperature and high pressure phase analyzer 133 at a constant low speed. At the same time, the fourth high pressure displacement pump 104 is controlled to aspirate liquid at a matching rate. The transfer is stopped after the sample volume reaches 40~50mL.

[0115] Phase determination and CO2 quantity calculation: The third high-pressure displacement pump 103 was started to precisely stabilize the pressure of the high-temperature and high-pressure phase analyzer 133 at the formation pressure. After confirming that the sample was a homogeneous liquid phase using a polarization camera 134 and online spectroscopy, the parameters were recorded and the CO2 injection volume was finally confirmed. The measured crude oil volume in the high-temperature and high-pressure phase analyzer 133 was 41.60 ml. The volume of CO2 dissolved in the live oil under standard conditions was calculated as follows:

[0116] V CO2-溶标准 =217×0.0416L=9.0272L.

[0117] The amount of CO2 injected in this experiment was determined to be:

[0118] n CO2 =9.0272 / 22.414=0.4030mol;

[0119] Setting the CH4 injection rate to be the same as that of CO2, the calculated volume of CO2 under reservoir pressure and temperature conditions is:

[0120] V CO2-溶地层 =n·R·T 地 / P 地

[0121] =0.4030×8.314×345.76 / (3.568×10 7 ) = 3.244 × 10 -5 m 3 =32.44mL.

[0122] CO2 injection preparation and differential pressure protection: Set the displacement pump pressure to drive CO2 slightly higher than the formation pressure, and maintain the back pressure pump at the formation pressure to form a driving differential pressure.

[0123] Constant-rate gas injection and synchronous retraction: The gas injection pump is set to discharge at a constant rate of 0.5 mL / min, and the recovery pump is set to retract synchronously at the same rate, while maintaining the pressure of the injection pump higher than that of the recovery pump, and stopping after the predetermined injection volume is reached.

[0124] Steady-state dissolution and phase confirmation: The third high-pressure displacement pump 103 was activated to maintain the pressure of the high-temperature and high-pressure phase analyzer 133 at the formation pressure for at least 12 hours. After confirming that the system had reached a homogeneous liquid phase using a polarization camera 134, the final volume of 57.32 ml was recorded. Based on the principle of conservation of mass, the molar percentage of CO2 in the system was calculated: the total mass m of the oil sample was calculated or weighed. oil The weight is 35.36g, and the average molecular weight M of the oil is calculated based on its components. avg =103.41 g / mol, calculate the molar mass n of the oil. oil =m oil / M avg =0.3418 mol, calculate the molar percentage of CO2 in the mixture, x. CO2 =100%·n CO2 / (n oil+ n CO2 =54.11%.

[0125] (S2) Pre-injection differential pressure protection and pressure preset: Open the second valve 106, preset the output pressure of the injection displacement pump to be slightly higher than the formation pressure, and set the pressure of the fourth high-pressure displacement pump 104 to be constant at the formation pressure.

[0126] Constant-rate, constant-pressure gas injection and synchronous retraction: Open the third port C and the fifth port E of the fourth valve 110 and the high-pressure five-way valve 114, and inject CH4 at a constant rate of 0.5 mL / min. The retraction pump retracts synchronously at the same rate, maintaining the injection pressure difference. Stop and close the passage after the predetermined CH4 injection volume is reached.

[0127] Post-injection pressure stabilization and short-term balancing: Activate the third high-pressure displacement pump 103 to stabilize the system pressure at the formation pressure and maintain it for at least 0.5 hours.

[0128] Phase dynamic monitoring: The entire process is continuously recorded using a polarization camera 134 to track the evolution of the gas-liquid interface, with data and images recorded synchronously.

[0129] (S3) Transferring samples to high-pressure accumulator 120 and storing energy: Open the second valve 106, the fourth valve 110, the third valve port C and the fourth valve port D of the high-pressure five-way valve 114 and the seventh valve 117, set the flow rate of the first high-pressure displacement pump 101 to 0.5 mL / min, transfer samples to the high-pressure accumulator 120 at a constant speed, and at the same time set the third high-pressure displacement pump 103 to maintain pressure and retract to balance, and stop after reaching the predetermined charging value.

[0130] High-pressure constant volume sampling ring 121 filling: Open the sixth valve 116, open the sixth valve port a and the eighth valve port c of the high-pressure four-way valve 118, so that the gas in the upper part of the high-temperature and high-pressure phase state meter 133 fills the high-pressure constant volume sampling ring 121. When the pressure is balanced with the internal pressure of the high-temperature and high-pressure phase state meter 133, close the eighth valve port c of the high-pressure four-way valve 118 to complete the constant volume sampling.

[0131] High-pressure accumulator 120 rapidly replenishes energy to high-temperature and high-pressure phase state meter 133: Open the ninth valve port d of high-pressure four-way valve 118, preset the pressure to a higher value, and rapidly replenish the gas in high-pressure accumulator 120 into high-temperature and high-pressure phase state meter 133 at 5mL / min, and stop replenishing energy after reaching the target pressure.

[0132] Gas sample chromatographic analysis using high-pressure constant-volume sampling loop 121: Open valve 123 to smoothly introduce the gas from high-pressure constant-volume sampling loop 121 into high-temperature high-pressure chromatograph 130 via high-pressure buffer 128 for analysis, obtaining the molar percentage of each component in the sample gas. The molar percentage of CO2 is calculated as y. CO2(0) =2.02%, n CO2(0) =2.552×10 -4 mol. Calculate the gas consumption for the next test: Based on the chromatographic analysis results, calculate the CH4 required to achieve the target composition in the high-pressure accumulator 120.

[0133] With respect to the molar mass of CO2 (this calculation is performed starting from the second round of experiments), V CO2（1） =0.02ml, V CH4（1） =0.98ml.

[0134] To replenish the high-voltage accumulator 120 with a fixed ratio of gas: sequentially open the corresponding passages and use the first high-voltage displacement pump 101 to quantitatively transfer CO2 and CH4 to the high-voltage accumulator 120 according to the calculated amount.

[0135] (S4) Tilting the high temperature and high pressure phase meter 133 to position the sampling port: Slowly tilt the high temperature and high pressure phase meter 133 so that the port where the sixth valve 116 is located is at the lowest point.

[0136] Introduce the liquid phase into the high-pressure buffer 128 and stabilize the pressure: Sequentially open the sixth valve 116 and the sixth valve port a and the seventh valve port b of the high-pressure four-way valve 118, start and set the fourth high-pressure displacement pump 104 to maintain the formation pressure, so that the liquid can smoothly enter the liquid high-pressure buffer 128.

[0137] The liquid in the high-pressure buffer 128 is quantitatively added to the oil-gas separator: the tenth valve 124 is slowly opened so that the liquid sample in the high-pressure buffer 128 flows smoothly into the oil-gas separator 125.

[0138] The separated gas is sent to the chromatograph 130 for analysis: the eleventh valve 127 is opened, and the gas phase separated by the oil-gas separation device 125 is smoothly sent to the chromatograph 130 for analysis through the high-pressure buffer 128.

[0139] Calculating CO2 content in the oil sample: Based on the volume, temperature and pressure data of the separated gas, and chromatographic analysis results, calculate the molar percentage of dissolved CO2 in a unit volume of live oil. Read the metering flow rate data and separator oil phase data to obtain a gas-oil ratio of 305.2. Then, using chromatographic test data, calculate the molar percentage of CO2 in the oil sample (x). CO2（t0） =54.09%.

[0140] (S5) Repeat Sampling Test: After completing the initial gas / liquid phase sampling and analysis, the system is compensated and stabilized with equal volume, and then allowed to stand for 0.5 hours. After standing, the complete sampling and analysis process of steps S3 and S4 is repeated. This process is repeated a total of 6 times, and the data is recorded. The test data is organized as shown in the table below.

[0141] Table 1 Experimental test data

[0142] ;

[0143] (S6) Data processing: Extract the molar percentage of CO2 from the gas phase and oil phase chromatogram results at each time point; convert the oil phase data into the molar mass of CO2 per unit volume of live oil; and perform mass balance verification.

[0144] Graphical Plotting and Analysis: Plot the CO2 mass transfer curve over time, such as... Figure 3 As shown, calculate and plot the transition point curve from the growth stage to the asymptotic saturation stage, as follows. Figure 4 As shown.

[0145] Therefore, the experimental apparatus and method provided by this invention can test the interphase mass transfer of dissolved CO2 in the injected gas-crude oil system, and explain the dynamic process of CO2 "escaping" (antimiscible) from the crude oil and transferring to the gas phase when injected natural gas (such as CH4) comes into contact with crude oil containing miscible CO2. It can be used to study the phase evolution of CO2 reservoirs under formation temperature and pressure conditions, the dissolution-precipitation kinetics of dissolved CO2, and the gas-liquid interphase mass transfer law, so as to correctly understand whether and when dissolved CO2 undergoes antimiscibility after contacting formation natural gas (such as CH4) and its evolution characteristics, clarify the component migration and mass transfer parameter change laws in different stages such as the initial rapid mass transfer stage, diffusion control stage, and quasi-steady-state stage, and provide reliable experimental basis and parameter support for engineering design schemes of CO2 injection to enhance recovery, such as injection pressure, injection rate, injection volume, and residence time.

[0146] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. An experimental apparatus for studying interphase mass transfer of dissolved CO2 in a crude oil system, characterized in that, include: Fluid injection system, phase reaction and observation system, pressure balance and control system, online sampling and component analysis system; The fluid injection system includes a first intermediate container (107) for storing high-pressure CO2. A second intermediate container (108) for storing high-pressure CH4; a third intermediate container (111) for storing gas-bearing crude oil formulated according to formation parameters. The phase reaction and observation system includes a high-temperature and high-pressure phase instrument (133), which is a high-pressure resistant reactor with an observation window. The reactor is equipped with a piston that can be controlled by an external displacement pump. The pressure and volume inside the reactor are regulated by the piston. A polarization camera (134) is set directly opposite the observation window. The pressure balance and control system includes a high-pressure accumulator (120), a third high-pressure displacement pump (103), a fourth high-pressure displacement pump (104), a high-pressure five-way valve (114), a high-pressure four-way valve (118), and a vacuum pump (113). The high-pressure accumulator (120) is pre-charged with fluid at the same pressure as the target pressure of the high-temperature and high-pressure phase meter (133). The fourth high-pressure displacement pump (104) is connected to the piston at the bottom of the high-temperature and high-pressure phase meter (133), and the fourth high-pressure displacement pump (104) drives the piston to move to achieve pressure increase or decrease. The third high-pressure displacement pump (103) is connected to the high-pressure accumulator (120) and the high-pressure five-way valve (114) via pipelines; the high-pressure five-way valve (114) is connected to the first end of the high-temperature and high-pressure phase analyzer (133) via pipelines; the first end of the high-temperature and high-pressure phase analyzer (133) is also connected to the high-pressure four-way valve (118) via pipelines; the high-pressure four-way valve (118) is connected to the high-pressure accumulator (120), the high-pressure sampler (129), and the chromatograph (130); the vacuum pump (113) is connected to the high-pressure five-way valve (114) via pipelines. The online sampling and component analysis system includes a high-pressure constant-volume sampling ring (121), an oil-gas separation device (125), and a chromatograph (130). The high-pressure constant-volume sampling ring (121) is connected to the gas phase outlet at the top of the high-temperature and high-pressure phase analyzer (133). The oil-gas separation device (125) is connected to the liquid phase outlet of the high-temperature and high-pressure phase analyzer (133). The chromatograph (130) is connected to the gas outlets of the high-pressure constant-volume sampling ring (121) and the oil-gas separation device (125) through pipelines and valves, respectively.

2. An experimental method for studying interphase mass transfer of dissolved CO2 in a crude oil system, using the experimental apparatus as described in claim 1, characterized in that, Includes the following steps: S1. Simulate the first-state fluid formed by formation crude oil and injected gas CO2, and observe the phase characteristics of the first-state fluid; S2. Simulate the process of the second injected gas entering the first-state fluid, generating an anti-miscible phenomenon, and observe the phase characteristics of the second-state fluid. S3. Take a gas sample from the fluid in the second state and make a quantitative replenishment, test the composition of the sampled fluid, and obtain the molar percentage of CO2 contained in the fluid in the second state after sampling. S4. Take a liquid sample of the fluid in the second state, test the composition of the sampled fluid, and obtain the molar percentage of CO2 contained in the fluid in the second state after sampling. S5. After sampling, a new fluid system is obtained. After standing, repeat S3 and S4 to obtain the component parameters under multiple sampling conditions. S6. Analyze the interphase mass transfer of dissolved CO2 in the second injected gas-crude oil system based on experimental observation data.

3. The experimental method for studying interphase mass transfer of dissolved CO2 in a crude oil system according to claim 2, characterized in that, Step S1 includes: Formation crude oil was prepared based on the results of on-site sampling and analysis of the target reservoir; The experimental apparatus was evacuated, and the experimental temperature and pressure conditions were set. The prepared formation crude oil was stored in the third intermediate container (111). The crude oil in the third intermediate container (111) is injected into the high temperature and high pressure phase instrument (133), and the piston movement is controlled by the fourth high pressure displacement pump (104) to maintain the pressure stability in the high temperature and high pressure phase instrument (133); CO2 in the first intermediate container (107) is injected into the high temperature and high pressure phase state instrument (133) to form a first state fluid, and the phase state characteristics of the first state fluid are observed.

4. The experimental method for studying interphase mass transfer of dissolved CO2 in a crude oil system according to claim 2, characterized in that, When injecting fluid into the third intermediate container (111), the output pressure is preset to be 0.1 to 0.2 MPa higher than the formation pressure, and the fluid is injected at a constant rate.

5. The experimental method for studying interphase mass transfer of dissolved CO2 in a crude oil system according to claim 2, characterized in that, When fluid is injected into the third intermediate container (111), the fourth high-pressure displacement pump (104) controls the piston movement at the same constant speed.

6. The experimental method for studying interphase mass transfer of dissolved CO2 in a crude oil system according to claim 2, characterized in that, When fluid is injected into the third intermediate container (111), the pressure of the fourth high-pressure displacement pump (104) is maintained at the formation pressure.

7. The experimental method for studying interphase mass transfer of dissolved CO2 in a crude oil system according to claim 4, characterized in that, The constant rate is 0.1–0.5 mL / min.

8. The experimental method for studying interphase mass transfer of dissolved CO2 in a crude oil system according to claim 2, characterized in that, Step S2 includes: The second injection gas in the second intermediate container (108) is injected into the high temperature and high pressure phase state instrument (133) to observe the phase state characteristics of the fluid in the second state.

9. The experimental method for studying interphase mass transfer of dissolved CO2 in a crude oil system according to claim 2, characterized in that, The second injected gas is CH4 or N2.

10. The experimental method for studying interphase mass transfer of dissolved CO2 in a crude oil system according to claim 2, characterized in that, Step S3 includes: The sample is transferred to the high-pressure accumulator (120) and stored. The second-state fluid is sampled by the high-pressure constant-volume sampling ring (121). After sampling, the stored gas is injected into the high-temperature high-pressure phase meter (133) through the high-pressure accumulator (120) to maintain the material pressure balance in the high-temperature high-pressure phase meter (133).

Images