CN-115586110-B - Experimental method for testing gas-liquid diffusion distance and diffusion coefficient based on micro-flow control

Abstract

The invention relates to an experimental method for testing gas-liquid diffusion distance and diffusion coefficient based on micro-flow control. The experimental device consists of a microfluidic chip, a microfluidic chip holder, a 4-opening high-temperature and high-pressure resistant microscopic reaction kettle, a micro displacement pump, a back pressure constant pressure pump, a back pressure valve, an intermediate container, a temperature control box, an image acquisition device and the like. The method comprises the steps of (1) establishing a corresponding simulated porous medium model, (2) configuring a sample, (3) connecting an experimental device and detecting leakage, (4) presaturating crude oil, (5) adjusting the temperature to the stratum temperature, (6) establishing system pressure to stratum pressure, (7) simulating a microscopic diffusion experiment, recording diffusion conditions in real time, (8) unloading the pressure after the experiment is finished, (9) measuring the diffusion distance by observing the color change of the crude oil by using image processing software, and (10) calculating the diffusion coefficient by using the diffusion distance. The invention has the advantages of convenient and quick test, accurate and reliable result and provides theoretical guidance and technical support for improving the recovery ratio.

Inventors

• HU YISHENG
• SHI CHENHUI
• PANG KANG
• PU LEI

Assignees

• 西南石油大学

Dates

Publication Date

20260508

Application Date

20221109

Claims (5)

1. 1. The experimental method for testing the gas-liquid diffusion distance and the diffusion coefficient based on the microfluidics technology is characterized in that the visual experimental device comprises a high-power electron microscope (1), an image collector (2), a deionized water intermediate container (3), a gas intermediate container (4), a crude oil intermediate container (5), a micro displacement pump (6), a three-way valve (7, 8, 9,10, 11, 12, 13, 14, 15), an N 2 intermediate container (16), a 4-opening high-temperature high-pressure resistant micro reaction kettle (17), a microfluidic chip (18), a microfluidic chip holder (19), a heating jacket (20), a temperature control box (39), a back pressure constant pressure pump (21), a back pressure valve (22), a test tube (23), pressure sensors (24, 25, 26, 27, 28, 29), valves (30, 31, 32, 33, 34, 35, 36, 37, 38), an illumination device (40), a micro diffusion chamber (41), a fluid channel (42), a first inlet and outlet (43), a second inlet (45), a third outlet (47) and a fourth outlet (47); A first inlet and a second inlet (44) and a second inlet (47) which are respectively connected with the rectangular micro diffusion chambers in the micro-fluidic chip (18) form a fluid channel (42) through which fluid passes, 4 pairs of rectangular micro diffusion chambers (41) with the same length and the same width are longitudinally arranged in the fluid channel (42), and blind end parts (43) which are respectively connected with a third outlet (45) and a fourth outlet (46) are arranged in pairs; The method comprises the steps that an inlet end and an outlet end of a microfluidic chip (18) are embedded with corresponding positions of grooves of a microfluidic chip holder (19) in a 4-opening high-temperature and high-pressure resistant micro-reaction kettle (17), the inlet end of the microfluidic chip holder (19) is connected with a gas intermediate container (4), a crude oil intermediate container (5) and a micro displacement pump (6) through three-way valves (10, 11, 12 and 13), the outlet end of the microfluidic chip holder is connected with a back pressure valve (22), an N 2 intermediate container (16) and a back pressure constant pressure pump (21) through three-way valves (10, 11, 12 and 13), pressure sensors (24, 25, 26, 27, 28 and 29) are arranged at the inlet end and the outlet end of the microfluidic chip holder (19), the whole microfluidic chip (18) and the microfluidic chip holder (19) are arranged in the 4-opening high-temperature and high-pressure resistant micro-reaction kettle (17), an observation window is arranged at the upper end of the 4-opening high-temperature and high-pressure resistant micro-reaction kettle (17), a high-power electron microscope (1) and an image collector (2) are arranged on the window, and an illumination device (40) is arranged at the lower end of the 4-opening high-temperature and high-pressure resistant micro-reaction kettle (17); the experimental method for testing the gas-liquid diffusion distance and the diffusion coefficient comprises the following steps: (1) Based on optimization and combination of plunger rock sample two-dimensional CT scanning images, establishing a corresponding simulated porous medium model; (2) Configuring crude oil according to the research content requirements and performing representative inspection; (3) The glass sheet is embedded in a clamp holder and is connected with the whole experiment system, an outlet valve is closed, a pump and an intermediate container are used for injecting air into the system for pressurization, an inlet valve is closed, whether the air tightness of the whole experiment system is good or not is checked, and the experiment device is restored to an initial state after the leak detection is finished; (4) Presaturation of crude oil is carried out in a micro diffusion chamber in a microfluidic chip at a speed of 0.0001mL/min, and when the stable outflow of crude oil from a liquid outlet is observed, presaturation is completed; (5) According to an experimental scheme, the temperature of the 4-opening high-temperature-resistant high-pressure-resistant microscopic reaction kettle is regulated to the simulated stratum temperature by utilizing a heating sleeve; (6) According to an experimental scheme, the confining pressure and the internal pressure of the microfluidic chip are simultaneously established from an inlet end to the formation pressure at a speed of 0.001mL/min, and a back pressure which is higher than the confining pressure and the internal pressure by about 3MPa is simultaneously applied to an outlet end; (7) Injecting gas into a micro diffusion chamber in a micro-fluidic chip at a limit pressure by using a micro displacement pump at a rate of 0.001mL/min to simulate a micro diffusion experiment, recording the diffusion conditions of an initial moment and an effective oil extraction moment in real time by using a high-power electron microscope (1) and an image collector (2), and ending the gas injection diffusion experiment when the pressure is no longer changed and the pump speed is 0; (8) After the experiment is finished, the pressure of the whole system is removed, the intermediate container and the pipeline are removed, and data are analyzed; (9) According to the high-power electron microscope (1) and the image collector (2), capturing images at each moment in real time, and determining the diffusion distance at the corresponding moment by observing the color change of crude oil by utilizing image processing software; (10) Calculating the gas-liquid diffusion coefficient of the pore scale in the porous medium through the diffusion distance obtained through experiments; The equation for calculating the pore scale gas-liquid diffusion coefficient in the porous medium in the step (9) is as follows: Wherein the intermediate variable e=a (1/V)/L; Wherein D j is the diffusion coefficient of the gas j component in the porous medium under the pore scale, cm 2 /s; The diffusion distance of the gas j component at the moment H i -i under the pore scale in the porous medium is cm; a is the sectional area of the micro-fluidic chip, cm 2 ; l-length of microfluidic chip, cm; v-is the volume of the microscopic diffusion chamber, cm 3 ; t i -effective oil extraction time, s; t o -initial time, s; And (b) deforming the (a) to obtain that ln (H ij )＝D j (t i -t o ),lnH ij ) and t i are in a linear relation, and applying least square fitting to obtain a slope S j , wherein the diffusion coefficient can be obtained according to D j ＝S j /E.
2. 2. The experimental method based on the microfluidic test of the gas-liquid diffusion distance and the diffusion coefficient according to claim 1 is characterized in that the appearance of the 4-opening high-temperature-resistant high-pressure-resistant micro reaction kettle (17) is a cylinder, the 4-opening high-temperature-resistant high-pressure-resistant micro reaction kettle (17) consists of an upper end cover and a lower end kettle body, the upper end cover of the reaction kettle and the lower end kettle body of the reaction kettle are sealed by 10 special screws, four microfluidic chip holders (19) are embedded in the 4-opening high-temperature-resistant high-pressure-resistant micro reaction kettle (17), the microfluidic chip (18) is embedded in the corresponding position in the microfluidic chip holder (19) and sealed by a rubber ring, an illumination device (40) is placed under the microfluidic chip (18), an image acquisition device is placed right above the microfluidic chip (18), and the experimental process is observed.
3. 3. The experimental method based on the microfluidic test of the gas-liquid diffusion distance and the diffusion coefficient according to claim 1, wherein the microfluidic chip (18) is provided with 4 outlets, and the waste liquid in the pre-saturation stage is discharged from the third outlet (45) and the fourth outlet (46).
4. 4. The experimental method based on the microfluidic test of the gas-liquid diffusion distance and the diffusion coefficient according to claim 1, wherein the third outlet (45) and the fourth outlet (46) are respectively connected with the pressure sensor (29), and the internal pressure of the microfluidic chip (18) is monitored in real time to ensure the safe performance of the experiment.
5. 5. The experimental method based on the microfluidic test of the gas-liquid diffusion distance and the diffusion coefficient according to claim 1, wherein in the steps (6) and (7), the internal pressure of the microfluidic chip is monitored in real time through pressure sensors connected with the upper end and the lower end of the microfluidic chip in the process of simultaneously establishing the confining pressure and the internal pressure of the microfluidic chip to the formation pressure, and the pressure difference between the confining pressure and the internal pressure is kept to be not more than about 0.2MPa, so that the microfluidic chip is not damaged.

Description

Experimental method for testing gas-liquid diffusion distance and diffusion coefficient based on micro-flow control Technical Field The invention relates to an experimental method for testing gas-liquid diffusion distance and diffusion coefficient based on micro-flow control, and belongs to the technical field of oil-gas field development engineering. Background Gas injection recovery is one of the most important methods for improving recovery efficiency at present, and common injection gases mainly comprise hydrocarbon gases, nitrogen, flue gases, carbon dioxide and the like. In the gas injection process of the oil reservoir, the dynamic state of gas injection driving is affected to a certain extent by different fluidity ratio, gravity viscous force and diffusion mixing action between the injected gas and crude oil. At present, molecular diffusion is considered to be a very important oil displacement mechanism, especially for matrix rock blocks with small pore throat size, low permeability and high capillary pressure, the gas gravity drainage is limited, and the molecular diffusion is the main mechanism. In particular, in recent years, after primary oil extraction, a large amount of crude oil remains in pores as residual oil, so that the research of the gas-liquid diffusion coefficient of microscopic pore scale has very practical guiding significance for improving the recovery ratio. In the prior art, experimental methods for determining the gas-liquid diffusion coefficient can be divided into two types, namely a direct method and an indirect method. The direct method is to sample the fluid at different time and different diffusion distance, then analyze the samples to obtain the concentration data of the gas, and combine the corresponding mathematical model to deduce the diffusion coefficient, the indirect method is to test a system variation parameter caused by diffusion, such as the system pressure, the fluid density and the like caused by mass transfer, and finally determine the diffusion coefficient by adopting the corresponding mathematical model. Because the sampling process of the direct method is easy to be interfered by subjective factors, the experiment is error, and along with the development of modern testing technology, the indirect method becomes a main means for testing the molecular diffusion coefficient, and the most widely applied methods at present are as follows: (1) NMR (Nuclear magnetic resonance) method the diffusion coefficient is determined based on the principle that the change in physical properties of the mixture during diffusion causes a change in NMR spectrum. NMR methods are expensive and costly. Representative results are that in 2005 Wen and Kantzas (JCPT), the change in mobility of hydrogen-containing molecules of the solvent and the oil when the solvent is brought into contact with a heavy oil or bitumen sample is detected by the change in NMR relaxation characteristics, and then the concentration-independent diffusion coefficients are calculated for three oils and six solvents according to the feik's second law. (2) PVT (pressure-volume-temperature) method the principle of testing is that gas molecules diffuse from the gas phase to the liquid phase until equilibrium is reached, during which the gas pressure is constantly changing over time. The PVT method is widely applied due to the convenience, simplicity and accuracy. Representative results include Riazi in 1996, a constant volume diffusion experimental test method established by M.R. (SPEJ), and a method for determining a molecular diffusion coefficient of a high-temperature and high-pressure multi-component oil-gas system in a PVT barrel based on Riazi principle in volume 3 of the natural gas industry, which is recorded in a section of computation of multi-component gas-gas diffusion coefficient published by Guo Ping et al, but the influence of a porous medium is not considered by the results. At present, the related research of a gas-liquid diffusion experiment method in a porous medium is also in exploration, wherein representative results are that the invention patent relates to a testing device and a testing method (CN 111239176A) for determining the diffusion distance of injected gas in the gas injection oil extraction process, which can utilize nuclear magnetic resonance test analysis to determine the diffusion position of the injected gas in crude oil, and the invention patent relates to a testing device and a testing method (CN 102644459B) for measuring the molecular diffusion coefficient of a multi-component gas-liquid system in a rock core, which can be used for measuring the molecular diffusion coefficient of each component in a gas phase and an oil phase of a real rock core under different oil reservoir temperature and pressure conditions. However, the research of the gas-liquid diffusion experimental method in the porous medium is carried out on the core scale, the research on the gas-liquid diffusion