Microfluidic displacement system and method for simulating low-permeability reservoir CO2 displacement

Abstract

The invention discloses a microfluidic displacement system for simulating CO2 displacement of a low-permeability reservoir. Comprising a microfluidic model, a high-temperature and high-pressure kettle, a microscope, a high-speed camera, a control and data processing computer, a plurality of liquid displacement pumps, a plurality of liquid containers, a drying oven, a back pressure controller, a buffer container, an annular pressure control pump, a CO2 pressurization module, a pressure monitoring safety module and a temperature control module. The device is suitable for the technical field of petroleum development, traditional back pressure valve control is upgraded to a mode that a back pressure controller, a pressure monitoring sensor and a buffer container are combined and a proportional-integral-differential algorithm is added to achieve efficient and accurate pressure control, and the CO2 displacement process of the low-permeability reservoir can be well simulated; and the method has important significance for deeply researching the CO2 flooding mechanism of the low-permeability reservoir.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil development, and specifically relates to a microfluidic displacement system and method for simulating CO 2 flooding in low-permeability oil reservoirs. Background Technique

[0002] Microfluidic technology is widely used in fields such as biochemical analysis, pharmaceutical screening, and environmental monitoring. With the in-depth research on oil reservoir development technology, microfluidic technology has been applied to the oil and gas field development field, mainly through equipment such as microfluidic models, microscopes, high-speed cameras, and image processing software to observe experimental phenomena and process data.

[0003] Zhang Yan et al. (authorized announcement number: CN109441414A) proposed a microscopic oil displacement experiment method and liquid injection method for simulating oil reservoir conditions, which can achieve precise control of the displacement medium water or chemical agent during displacement. Zhu Weiyao et al. (authorized announcement number: CN106437637A) proposed a visual microscopic experiment device and method for carbon dioxide flooding of ultra-heavy oil under high temperature and high pressure, which can realize the analysis of the visual carbon dioxide microscopic oil displacement process and the precipitation process of asphaltene by carbon dioxide under high temperature and high pressure conditions. Long Yunqian et al. (authorized announcement number: CN107939362B) proposed a microscopic oil displacement device for polymer particle dispersion system under high temperature and high pressure, which can simulate the formation high temperature and high pressure environment, and can observe and analyze the migration characteristics of polymer microspheres in the formation and the remaining oil distribution characteristics under conditions close to actual displacement conditions.

[0004] Currently, most of the microfluidic displacement systems for water flooding and chemical flooding are atmospheric pressure displacement systems. For example, the maximum pressure resistance of the microscopic model used by Liu Liping in the research of "Water Flooding Characteristics and Influencing Factors of Oil Displacement Efficiency in Chang 8 Reservoir of Baibao Oilfield in Ordos Basin" is 0.2 MPa; in the research of "Research on the Migration Law of Microscopic Remaining Oil and Oil Displacement Effect of Polymer Flooding" by Tan Chang, the microscopic model is directly connected to the atmosphere through the discharge port. These devices cannot achieve the high temperature and high pressure CO 1 displacement process. 2

[0005] In addition, water flooding and chemical flooding are more applied to medium-high permeability oil reservoirs. The pore throats of the reservoirs are relatively large, and the magnification requirements are low. For example, in the Chinese patent with the authorized announcement number of CN109441414A, the microscopic model is fixed by multiple clamping heads with different structures, which will greatly increase the inner cavity volume of the autoclave. If this design is applied under high pressure conditions, the thickness of the high-pressure observation window increases, resulting in an increase in the object distance of the microscope and limited magnification, and it is impossible to obtain high-magnification images of the displacement process in low-permeability models.

[0006] Although the two Chinese patents with the authorized announcement numbers of CN106437637A and CN107939362B involve CO 2 ​For enhanced oil recovery or low-permeability reservoirs, a backpressure valve is used to control the backpressure in both cases. However, this control method is easily affected in micro-displacement. In the microfluidic experiment of CO 2 In the enhanced oil recovery microfluidic experiment, the backpressure valve must inject a certain volume of fluid to open. At this time, the injected fluid cannot be discharged, easily causing the injected fluid to flow back, and unable to reflect the real displacement process, thus leading to the failure of the experiment. Summary of the Invention

[0007] The purpose of the present invention is to overcome the defects of the prior art and provide a microfluidic displacement system and method for simulating CO2 enhanced oil recovery in low-permeability reservoirs.

[0008] To achieve the above purpose, the present invention adopts the following technical solutions:

[0009] In the first aspect, a microfluidic displacement system for simulating CO 2 enhanced oil recovery in low-permeability reservoirs includes: a microfluidic model, a high-temperature and high-pressure autoclave, a microscope and a high-speed camera, a control and data processing computer, several displacement pumps, several liquid storage containers, an oven, a backpressure controller, a buffer container, an annular pressure control pump, a CO 2 boosting module, a pressure monitoring and safety module, and a temperature control module.

[0010] Preferably, it includes: a first displacement pump and a second displacement pump. The outlet of the first displacement pump is connected to the inlet of the first liquid storage container through a valve, and the outlet of the second displacement pump is connected to the inlets of the second liquid storage container, the third liquid storage container, and the fourth liquid storage container through valves.

[0011] Preferably, pistons are provided inside several of the liquid storage containers, and the outlets of several liquid storage containers are merged through independent valves and then connected to the inlet of the microfluidic model through a valve.

[0012] Preferably, the outlet of the fourth liquid storage container is connected to the reserved outlet end of the boosting system integration box. Drain valves are provided at the front end and the outlet end of the inlet valves of several liquid storage containers, and several liquid storage containers are arranged in the oven.

[0013] Preferably, the backpressure controller is connected to the bottom of the buffer container, and the upper part of the buffer container is connected to the outlet of the microfluidic model through a valve.

[0014] Preferably, a pressure regulating valve, a CO 2 intermediate container, and a boosting pump are provided inside the boosting system integration box. The boosting pump is connected to the CO 2 intermediate container through a valve, and an external gas source inlet is reserved for the boosting pump. Another outlet of the CO 2 intermediate container is connected to the pressure regulating valve through a valve, and the pressure regulating valve is connected to the reserved outlet end. The external gas source inlet reserved for the boosting pump is connected to an air compressor.

[0015] Preferably, the annular pressure control pump is connected to the annular pressure inlet of the high-temperature and high-pressure autoclave via a valve.

[0016] Preferably, the microscope, high-speed camera and high-temperature autoclave are all arranged on a fixed seat, the fixed seat is connected to a rotatable bearing, and the microscope and high-speed camera are connected to a control and data processing computer.

[0017] Preferably, the high-temperature autoclave comprises an end cover and a high-temperature autoclave body, which are sealed by a combined sealing structure, and a square groove is opened inside the high-temperature autoclave to form a microfluidic model fixing seat.

[0018] Preferably, the microfluidic model has conducting grooves on two opposite sides, and the injection port, the drain port and the high-precision inlet all adopt a three-way structure, wherein the injection port and the drain port are directly connected.

[0019] Preferably, the drilled hole on the side wall of the high-temperature and high-pressure autoclave body and the drilled hole connected to the inlet of the microfluidic model in the vertical direction form a through hole for connecting the inlet of the high-temperature and high-pressure autoclave with the inlet of the microfluidic model.

[0020] Preferably, the horizontal distance of the through hole is shortened by optimizing the valve needle length of the valve, and the channel volume between the high-temperature and high-pressure autoclave inlet and the microfluidic model inlet is 0.08 mL.

[0021] Second, it is used to simulate low permeability reservoir CO 2 The microfluidic displacement method comprises the following steps:

[0022] S1 After assembling the inner cavity of the high-temperature autoclave and the microfluidic model, the inner cavity of the high-temperature autoclave and the microfluidic model are evacuated, and the microfluidic model is filled with water;

[0023] S2 controls the ring pressure control pump to pump a certain amount of distilled water into the inner cavity of the high-temperature autoclave and then closes the drain valve. After reaching a certain pressure, the ring pressure control pump maintains a constant pressure mode; turn on the control and data processing computer to set the experimental temperature; connect the outlet of the high-temperature autoclave with the inlet of the back pressure control part, and gradually increase the pressure of the back pressure controller after the pressure is balanced until the back pressure and temperature required by the experiment are reached;

[0024] S3 pressurizes the crude oil in the No. 4 liquid container 7 by the No. 2 liquid displacement pump, and at the same time pressurizes the high-concentration oil-soluble red simulated oil in the No. 1 liquid container by the No. 1 liquid displacement pump. After the pressure is increased to the experimental design pressure, the valve is opened to inject saturated oil; adjust the relevant parameters of the microscope and the high-speed camera to obtain a clear image; by adjusting the displacement speed of the liquid displacement pump, the injection ratio of the high-concentration oil-soluble red simulated oil and the crude oil is changed to make the red color of the crude oil clearly visible; after the back pressure controller is returned to more than twice the pore volume of the microfluidic model, the displacement of the saturated oil is completed; take photos and videos with a microscope and a high-speed camera to save the experimental process information;

[0025] Preferably, before switching the displacement fluid, close the valve, switch the displacement fluid in the second liquid container to the model injection pipeline, open the drain port. At this time, the new displacement fluid displaces the previous displacement fluid in the liquid container to the valve pipeline until the new displacement fluid is produced, and then close the drain port; when the monitoring values of the pressure monitoring sensors are equal, open the valve, and the displacement fluid enters the microfluidic model inlet through the high-precision inlet structure. During the displacement process, take pictures and videos through a microscope and a high-speed camera to save the experimental process information.

[0026] Preferably, after the displacement is completed, gradually reduce the back pressure of the high-temperature and high-pressure autoclave through the back pressure controller, and at the same time open the drain valve to synchronously relieve the annular pressure and the back pressure as much as possible until the normal pressure is reached.

[0027] Preferably, use professional image processing software to process the images obtained during the experiment to obtain information on microscopic oil displacement efficiency, displacement front, and target trajectory analysis, providing basic data for relevant research.

[0028] Preferably, in step S1, it specifically includes:

[0029] S11 Fix the heterogeneous microfluidic model in the high-temperature and high-pressure autoclave, install a combined sealing structure on the end cover and then connect and fix it to the high-temperature and high-pressure autoclave body, and install the high-temperature and high-pressure autoclave heating and insulation jacket;

[0030] S12 Place the end cover of the assembled high-temperature and high-pressure autoclave at the bottom, install it on the fixed seat of the rotatable high-temperature and high-pressure autoclave fixing device, and at the same time install the microscope and the high-speed camera on the fixed seat; adjust the position of the fixed seat around the rotatable bearing to make the heterogeneous microfluidic model perpendicular to the ground, and connect all pipelines, control lines, data lines and power lines.

[0031] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are:

[0032] In the present invention, the traditional back pressure valve control is upgraded to a combination of a back pressure controller, a pressure monitoring sensor, a buffer container and a proportional-integral-derivative algorithm to achieve efficient and accurate pressure control, and it will not cause the backflow of the fluid in the model, eliminating the defects of using the back pressure valve control, greatly increasing the magnification of the microscope, and thus being able to obtain high-magnification and clear microscopic images of the tiny pore throats of the low-permeability microfluidic model; for the low-permeability microfluidic model with a small pore volume, it can well simulate the CO 2 displacement process, which is of great significance for deeply studying the mechanism of CO 2 displacement in low-permeability reservoirs. Description of the Drawings

[0033] Figure 1Schematic diagram of the system connection of the present invention;

[0034] Figure 2 Schematic diagram of the fixing device for the rotatable high-temperature and high-pressure autoclave in the present invention;

[0035] Figure 3 Schematic diagram of the structure of the microfluidic high-temperature and high-pressure autoclave in the present invention.

[0036] Reference numerals: 1, oven; 2, first drain valve; 3, second drain valve; 4, first liquid storage container; 5, second liquid storage container; 6, third liquid storage container; 7, fourth liquid storage container; 8, first liquid displacement pump; 9, second liquid displacement pump; 10, first pressure gauge; 11, pressure regulating valve; 12, external gas source inlet; 13, second pressure gauge; 14, third drain valve; 15, CO 2 intermediate container; 16, booster pump; 17, booster system integration box; 18, air compressor; 19, first pressure monitoring sensor; 20, fourth drain valve; 21, microscope and high-speed camera; 22, control and data processing computer; 23, high-temperature and high-pressure autoclave heating and insulation jacket; 24, high-temperature and high-pressure autoclave; 25, microfluidic model; 26, temperature sensor; 27, second pressure monitoring sensor; 28, fifth drain valve; 29, annular pressure control pump; 30, sixth drain valve; 31, third pressure monitoring sensor; 32, fourth pressure monitoring sensor; 33, buffer container; 34, back pressure controller; 35, rotatable bearing; 36, fixed seat; 37, fixed bracket; 38, wheel; 39, end cover; 40, high-temperature and high-pressure autoclave body; 41, combined seal structure; 42, microfluidic model fixed seat; 43, high-precision inlet; 44, injection port; 45, valve; 46, drain port. Detailed implementation manners

[0037] The following further describes the detailed implementation manners of the microfluidic displacement system and method for simulating CO Figures 1-3 flooding in low-permeability reservoirs of the present invention in conjunction with the attached 2 drawings. The microfluidic displacement system and method for simulating CO 2 flooding in low-permeability reservoirs of the present invention are not limited to the descriptions of the following embodiments.

[0038] Embodiment 1:

[0039] A microfluidic displacement system for simulating CO 2 flooding in low-permeability reservoirs, as Figures 1-3 shown, includes: a microfluidic model 25, a high-temperature and high-pressure autoclave 24, a microscope and a high-speed camera 21, a control and data processing computer 22, a plurality of liquid displacement pumps, a plurality of liquid storage containers, an oven 1, a back pressure controller 34, a buffer container 33, an annular pressure control pump 29, a CO 2 booster module, a pressure monitoring and safety module, and a temperature control module.

[0040] Further, it includes: a first liquid displacement pump 8 and a second liquid displacement pump 9. The outlet of the first liquid displacement pump 8 is connected to the inlet of the first liquid storage container 4 through a valve, and the outlet of the second liquid displacement pump 9 is connected to the inlets of the second liquid storage container 5, the third liquid storage container 6, and the fourth liquid storage container 7 through valves.

[0041] Further, pistons are provided inside several liquid storage containers, and the outlets of several liquid storage containers are joined together through independent valves and then connected to the inlet of the microfluidic model 25 through a valve.

[0042] Further, the outlet of the fourth liquid storage container 7 is connected to the reserved outlet end of the booster system integration tank 17. Emptying valves are provided at the front ends and outlet ends of the inlet valves of several liquid storage containers, and several liquid storage containers are all arranged in the oven 1.

[0043] Further, the backpressure controller 34 is connected to the bottom of the buffer container 33, and the upper part of the buffer container 33 is connected to the outlet of the microfluidic model 25 through a valve.

[0044] Further, a pressure regulating valve 11, a CO 2 intermediate container 15, and a booster pump 16 are provided inside the booster system integration tank 17. The booster pump 16 is connected to the CO 2 intermediate container 15 through a valve, wherein the booster pump 16 has a reserved external air source inlet, and the CO 2 intermediate container 15 has another outlet connected to the pressure regulating valve 11 through a valve. The pressure regulating valve 11 is connected to the reserved outlet end, and the reserved external air source inlet of the booster pump 16 is connected to an air compressor 18.

[0045] Further, the annular pressure control pump 29 is connected to the annular pressure inlet of the autoclave 23 through a valve.

[0046] Further, the microscope and high-speed camera 21 and the autoclave 24 are both arranged on the fixed seat 36. The fixed seat 36 is connected to the rotatable bearing 35, and the microscope and high-speed camera 21 are connected to the control and data processing computer 22.

[0047] Further, the drill hole on the side wall of the autoclave body 40 and the drill hole connecting the inlet of the microfluidic model 25 in the vertical direction form a through hole for connecting the inlet of the autoclave 24 and the inlet of the microfluidic model 25.

[0048] Example 2:

[0049] A microfluidic displacement system for simulating CO 2 displacement in a low-permeability oil reservoir, as Figures 1-3 shown. Other steps are similar to those in Example 1. Further, in the horizontal direction, the horizontal distance is shortened by optimizing the needle length of the valve of the through hole, and the channel volume between the inlet of the autoclave 24 and the inlet of the microfluidic model 25 is 0.08 mL.

[0050] Example 3:

[0051] A microfluidic displacement system for simulating CO 2 flooding in low-permeability reservoirs, as Figures 1-3 shown. Other steps are similar to those in Example 1. Further, the autoclave 24 includes an end cap 39 and an autoclave body 40, which are sealed by a combined sealing structure 41. A square groove is formed inside the autoclave 24 to form a microfluidic model fixing seat 42. At this time, with the model size fixed, the cross-sectional area of the autoclave body is the smallest. Under the condition of meeting the safety pressure requirements, the sapphire window takes into account both thickness and safety, so that the vertical distance between the microfluidic model fixing seat 42 and the sapphire window on one side of the autoclave body 40 is 39 mm;

[0052] Further, two opposite sides of the microfluidic model 25 are provided with conduction grooves, and the injection port 44, the evacuation port 46 and the high-precision inlet 43 all adopt a tee structure, wherein the injection port 44 and the evacuation port 46 are directly connected.

[0053] Example 4:

[0054] A microfluidic displacement system for simulating CO 2 flooding in low-permeability reservoirs, as Figure 1 shown, consists of a microfluidic model 25, an autoclave 24, a microscope and a high-speed camera 21, a control and data processing computer 22, displacement pumps 8 and 9, liquid storage containers 4-7, an oven 1, a backpressure controller 34, a buffer container 33, an annular pressure control pump 29, a CO 2 boosting section, a pressure monitoring and safety section, and a temperature control section;

[0055] The liquid storage containers 4, 5, 6, and 7 are respectively filled with high-concentration oil-soluble red simulated oil, simulated oil, simulated formation water, and CO 2 ; When saturating the oil, the displacement pumps 8 and 9 are used to displace the liquid storage containers 4 and 5 respectively to dye the simulated oil. At the same time, by adjusting the displacement speed of the displacement pump 8, the depth of the color of the dyed simulated oil is adjusted to make the shooting effect clear and the contrast good.

[0056] The pressure monitoring sensor 31, the buffer container 33, and the backpressure controller 34 constitute a backpressure control system, and the buffer container is filled with pure water. When used for backpressure control, the backpressure controller maintains a constant backpressure, and the pressure monitoring sensor 31 monitors the outlet pressure of the model, compares the set pressure with the outlet pressure of the model, and guides the backpressure controller to perform a pressure response through a proportional-integral-derivative algorithm to achieve efficient and accurate pressure control. In addition, after the outlet pressure rises or falls, since the proportional-integral-derivative algorithm is adopted, the backpressure controller can quickly track, so there will be no backflow of the fluid in the model, eliminating the defect of using a backpressure valve for control.

[0057] Example 5:

[0058] A microfluidic displacement system for simulating CO 2 flooding in low-permeability reservoirs, as Figure 2 shown. The high-temperature and high-pressure autoclave 24, microscope, and high-speed camera 21 are installed on the fixed seat 36. The fixed seat is connected to the fixed bracket 37 through a rotatable bearing 35. The entire fixed seat and the equipment installed thereon can be rotated 90 degrees through the rotatable bearing. By rotation, the microfluidic model can simulate the planar and longitudinal heterogeneity of the actual reservoir.

[0059] Example 6:

[0060] A microfluidic displacement system for simulating CO 2 flooding in low-permeability reservoirs, as Figure 3 shown. The fixed seat 42 of the microfluidic model and the autoclave structure adopt an integrated design. By opening a square groove inside the autoclave to fix the model, and opening conduction grooves on two opposite sides of the model to facilitate the up and down flow of the annular pressure fluid, it is also convenient for model installation and removal. This design eliminates the dedicated model fixed seat commonly used in other designs. With the model size fixed, the cross-sectional area of the autoclave is minimized. Under the condition of meeting the same safety pressure requirements, the thickness of the sapphire window becomes smaller, making the vertical distance between the fixed seat 42 of the microfluidic model and the sapphire window on one side of the high-temperature and high-pressure autoclave body 40 39 mm. This enables the selection range of the microscope objective lens to be extended from 0.5 times and 1 time to using a 2-fold microscope objective lens, greatly increasing the magnification of the microscope, thereby obtaining high-magnification and clear microscopic images of the tiny pore throats of the low-permeability microfluidic model.

[0061] Example 7:

[0062] A microfluidic displacement system for simulating CO 2 flooding in low-permeability reservoirs, as Figure 3 shown. The injection port 44, the drain port 46, and the ultra-low dead volume inlet structure 43 are of a tee structure, where the injection port 44 and the drain port 46 are directly connected. By controlling the on-off of the valve 45 and the drain port 46, the displacement fluid in the liquid storage containers 4, 5, 6, and 7 and the pipeline up to the valve 45 can be drained, improving the accuracy of the fluid injected into the microfluidic model and ensuring the consistency between the experiment and the actual displacement process.

[0063] Example 8:

[0064] A microfluidic displacement system for simulating CO 2 flooding in low-permeability reservoirs, as Figure 3As shown, the ultra-low invalid volume inlet structure 43 and the kettle body structure adopt an integrated design, and a through hole is formed by drilling a hole on the side wall of the high-temperature and high-pressure kettle body 40 and connecting the microfluidic model inlet in the vertical direction to form a through hole to achieve high-precision injection of the injected fluid medium. The vertical distance is shortened as much as possible while meeting the ring pressure control and safety requirements. In the horizontal direction, the valve needle length and other structures are optimized to shorten the horizontal distance as much as possible. This design minimizes the residual amount of the last displacement medium when switching the displacement medium, and can make the error between the later injected medium and the actual injection amount less than 0.08mL, meeting the injection accuracy requirements of the low-permeability microfluidic model with a smaller pore volume, thereby greatly improving the accuracy of the experiment and obtaining experimental results that meet the actual situation.

[0065] Embodiment 9:

[0066] For simulation of low permeability reservoir CO 2 The microfluidic displacement method comprises the following steps:

[0067] S1 After assembling the inner cavity of the high-temperature autoclave 24 and the microfluidic model 25, the inner cavity of the high-temperature autoclave 24 and the microfluidic model 25 are evacuated, and the microfluidic model 25 is filled with water;

[0068] S2 controls the ring pressure control pump 29 to pump a certain amount of distilled water into the inner cavity of the high-temperature autoclave 24, and then closes the drain valve 28. After a certain pressure is reached, the ring pressure control pump 29 maintains a constant pressure mode; turns on the control and data processing computer 22 to set the experimental temperature; connects the outlet of the high-temperature autoclave 24 to the inlet of the back pressure control part, and gradually increases the pressure of the back pressure controller 34 after the pressure is balanced until the back pressure and temperature required by the experiment are reached;

[0069] S3 pressurizes the crude oil in the No. 4 liquid container 7 by the No. 2 liquid displacement pump 9, and at the same time pressurizes the high-concentration oil-soluble red simulated oil in the No. 1 liquid container 4 by the No. 1 liquid displacement pump 8. After the pressure is increased to the experimental design pressure, the valve 45 is opened to inject saturated oil; adjust the relevant parameters of the microscope and the high-speed camera 21 to obtain a clear image; by adjusting the displacement speed of the liquid displacement pump 8, the injection ratio of the high-concentration oil-soluble red simulated oil and the crude oil is changed, so that the red color of the crude oil is clearly visible; after the back pressure controller 34 is returned to more than twice the pore volume of the microfluidic model, the displacement of the saturated oil is completed; take photos and videos through the microscope and the high-speed camera 21 to save the experimental process information;

[0070] Further, before switching the displacement fluid, close valve 45, switch the displacement fluid in the second liquid container 5 to the model injection pipeline, open the drain port 46. At this time, the new displacement fluid flushes out the last displacement fluid in the liquid container 6 to the pipeline of valve 45 until the new displacement fluid is produced, then close the drain port 46; when the monitored values of the pressure monitoring sensors 19 and 31 are equal, open valve 5. The displacement fluid enters the microfluidic model inlet through the high-precision inlet structure. During the displacement process, take pictures and videos through the microscope and the high-speed camera 21 to save the information of the experimental process.

[0071] Further, after the displacement is completed, gradually reduce the back pressure of the high-temperature and high-pressure autoclave 24 through the back pressure controller 34, and at the same time open the drain valve 28 to try to achieve synchronous pressure relief of the annulus pressure and the back pressure until the normal pressure is reached.

[0072] Further, use professional image processing software to process the images obtained during the experiment to obtain information on microscopic oil displacement efficiency, displacement front, and target trajectory analysis, providing basic data for related research.

[0073] Further, in step S1, it specifically includes:

[0074] S11 Fix the heterogeneous microfluidic model 25 in the high-temperature and high-pressure autoclave 24. After installing the combined sealing structure 41 on the end cover 39, connect and fix it to the high-temperature and high-pressure autoclave body 40, and install the high-temperature and high-pressure autoclave heating and insulation jacket 23.

[0075] S12 Place the end cover 39 of the assembled high-temperature and high-pressure autoclave at the bottom, install it on the fixed seat 36 of the rotatable high-temperature and high-pressure autoclave fixing device, and at the same time install the microscope and the high-speed camera 21 on the fixed seat 36; adjust the position of the fixed seat 36 around the rotatable bearing 35 to make the heterogeneous microfluidic model 25 in a vertical position with respect to the ground, and connect all pipelines, control lines, data lines and power lines.

[0076] Example 10:

[0077] A microfluidic displacement method for simulating CO 2 displacement in low-permeability oil reservoirs, including the following steps:

[0078] Step 1: Fix the heterogeneous microfluidic model 25 in the high-temperature and high-pressure autoclave 24. After installing the combined sealing structure 41 on the end cover 39, connect and fix it to the high-temperature and high-pressure autoclave body 40, and install the high-temperature and high-pressure autoclave heating and insulation jacket 23.

[0079] Step 2: Place the end cover 39 of the assembled autoclave at the bottom and install it on the fixed seat 36 of the rotatable autoclave fixture, and install the microscope and the high-speed camera 21 on the fixed seat 36; adjust the position of the fixed seat 36 around the rotatable bearing 35 so that the heterogeneous microfluidic model 25 is in a vertical position with the ground, so that the longitudinal heterogeneity of the reservoir can be simulated; connect various pipelines, control lines, data lines and power lines.

[0080] Step 3: Evacuate the inner cavity of the high-temperature and high-pressure autoclave 24 and the microfluidic model 25 at the same time; use the self-priming method to fill the inner cavity with distilled water and then close the drain valve 28; the liquid displacement pump 9 saturates the microfluidic model 25 with water by displacing the simulated formation water in the liquid container 7 until liquid is discharged from the outlet of the high-temperature and high-pressure autoclave 24, and then stop the liquid displacement pump 9.

[0081] Step 4: After the annular pressure control pump 29 pumps a certain amount of distilled water into the inner cavity of the high-temperature and high-pressure autoclave 24, the drain valve 28 is closed. After a certain pressure is reached, the annular pressure control pump 29 maintains a constant pressure mode; the control and data processing computer 22 is turned on to set the experimental temperature, and the high-temperature and high-pressure autoclave 24 begins to heat up; the outlet of the high-temperature and high-pressure autoclave 24 is connected to the inlet of the back pressure control part, and after the pressure is balanced, the pressure of the back pressure controller 34 is gradually increased until the back pressure and temperature required by the experiment are reached.

[0082] Step 5: Use the liquid displacement pump 9 to pressurize the crude oil (simulated oil) in the liquid container 7, and use the liquid displacement pump 8 to pressurize the high-concentration oil-soluble red simulated oil in the liquid container 4. After the pressure is increased to the experimental design pressure, open the valve 45 to start oil saturation; adjust the object distance and magnification of the microscope and the high-speed camera 21 and other related parameters to obtain a clear image; by adjusting the displacement speed of the liquid displacement pump 8, change the injection ratio of the high-concentration oil-soluble red simulated oil and the crude oil (simulated oil) to make the red color of the crude oil (simulated oil) clearly visible; after the back pressure controller 34 retreats to more than twice the pore volume of the microfluidic model, the oil saturation is completed; take photos and videos with the microscope and the high-speed camera 21 to save the experimental process information.

[0083] Step 6: Before switching the displacement fluid, close valve 45, switch the displacement fluid in the liquid container 5 to the model injection pipeline, open the drain port 46, at this time, the new displacement fluid can empty the last displacement fluid in the pipeline from the liquid container 6 to the valve 45, until the new displacement fluid is produced, and close the drain port 46; when the monitoring values ​​of the pressure monitoring sensor 19 and the pressure monitoring sensor 31 are equal, open valve 5, and the displacement fluid enters the microfluidic model inlet through the high-precision inlet structure. During the displacement process, take pictures and videos through a microscope and a high-speed camera 21 to save the experimental process information.

[0084] Step 7: After the displacement is completed, gradually reduce the back pressure of the autoclave 24 through the back pressure controller 34. At the same time, open the drain valve 28 to achieve synchronous pressure relief of the annulus pressure and the back pressure as much as possible until the normal pressure is reached.

[0085] Step 8: Use professional image processing software to process the images obtained during the experiment, so as to obtain information such as microscopic oil displacement efficiency, displacement front, and target trajectory analysis, providing basic data for relevant research.

[0086] By adopting the above technical solutions:

[0087] Regarding the characteristics of the low-permeability microfluidic model and CO 2 displacement, the traditional back pressure valve control is upgraded to a combination of a back pressure controller, a pressure monitoring sensor, a buffer container, and a proportional-integral-derivative algorithm to achieve efficient and accurate pressure control, and it will not cause the backflow of the fluid in the model, eliminating the defects of using the back pressure valve control. Through the integrated design of the autoclave and the microfluidic model base, the vertical distance between the microfluidic model fixing seat and the sapphire window is 39 mm, and the selection range of the microscope objective lens is extended from 0.5 times and 1 time to using a 2 times microscope objective lens, greatly increasing the magnification of the microscope, so as to obtain high-magnification and clear microscopic images of the tiny pore throats of the low-permeability microfluidic model. Considering the small pore volume of the low-permeability microfluidic model, an ultra-low dead volume inlet structure with an actual injection volume error of less than 0.08 mL is designed, greatly improving the authenticity of the experiment. The formed experimental method can well simulate the CO 2 displacement process in the low-permeability reservoir, which is of great significance for deepening the study of the mechanism of CO 2 displacement in the low-permeability reservoir.

[0088] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, several simple deductions or substitutions can be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A microfluidic displacement system for simulating CO 2 flooding in low-permeability reservoirs It is characterized in that including: Microfluidic model (25), high-temperature and high-pressure autoclave (24), microscope and high-speed camera (21), control and data processing computer (22), several liquid driving pumps, several liquid containers, oven (1), backpressure controller (34), buffer container (33), annular pressure control pump (29), CO 2 pressure boosting module, pressure monitoring and safety module, and temperature control module.

2. The microfluidic displacement system for simulating CO 2 flooding in low-permeability reservoirs as claimed in claim 1, It is characterized in that including: A first liquid displacement pump (8) and a second liquid displacement pump (9), the outlet of the first liquid displacement pump (8) is connected to the inlet of a first liquid storage container (4) through a valve, and the outlet of the second liquid displacement pump (9) is connected to the inlets of a second liquid storage container (5), a third liquid storage container (6) and a fourth liquid storage container (7) through valves.

3. The microfluidic displacement system for simulating CO 2 flooding in low-permeability reservoirs as claimed in claim 2, It is characterized in that Pistons are provided inside several of the liquid storage containers, and the outlets of several liquid storage containers are joined together after passing through independent valves and then connected to the inlet of a microfluidic model (25) through a valve.

4. The microfluidic displacement system for simulating CO 2 flooding in low-permeability reservoirs as claimed in claim 2, It is characterized in that: The outlet of the fourth liquid storage container (7) is connected to the reserved outlet end of a pressure boosting system integration tank (17) through a valve. Drain valves are provided at the front ends and outlet ends of the inlet valves of several liquid storage containers, and several liquid storage containers are arranged in an oven (1).

5. The microfluidic displacement system for simulating CO 2 flooding in low-permeability reservoirs as claimed in claim 2, It is characterized in that: The back pressure controller (34) is connected to the bottom of a buffer container (33), and the upper part of the buffer container (33) is connected to the outlet of the microfluidic model (25) through a valve.

6. The microfluidic displacement system for simulating CO 2 flooding in low-permeability reservoirs as claimed in claim 4, It is characterized in that: The pressure boosting system integration box (17) is provided with a pressure regulating valve (11), a CO 2 intermediate container (15), and a pressure boosting pump (16). The pressure boosting pump (16) is connected to the CO 2 intermediate container (15) through a valve. The pressure boosting pump (16) has a reserved external air source inlet, and the CO 2 intermediate container (15) is connected to the pressure regulating valve (11) through another valve at its outlet. The pressure regulating valve (11) is connected to the reserved outlet end. The reserved external air source inlet of the pressure boosting pump (16) is connected to an air compressor (18).

7. The microfluidic displacement system for simulating CO 2 flooding in low-permeability oil reservoirs as claimed in claim 1, It is characterized in that: The annular pressure control pump (29) is connected to the annular pressure inlet of an autoclave (23) through a valve.

8. The microfluidic displacement system for simulating CO 2 flooding in low-permeability reservoirs as claimed in claim 1, It is characterized in that: The microscope and high-speed camera (21) and the autoclave (24) are both arranged on a fixing seat (36), the fixing seat (36) is connected to a rotatable bearing (35), and the microscope and high-speed camera (21) are connected to a control and data processing computer (22).

9. The microfluidic displacement system for simulating CO 2 flooding in low-permeability reservoirs as claimed in claim 8, It is characterized in that: The autoclave (24) includes an end cover (39) and an autoclave body (40), and the two are sealed through a combined sealing structure (41). A square groove is formed inside the autoclave (24) to form a microfluidic model fixing seat (42).

10. The microfluidic displacement system for simulating CO 2 flooding in low-permeability reservoirs as claimed in claim 9, It is characterized in that: Two opposite sides of the microfluidic model (25) are provided with conduction grooves, and the injection port (44), the evacuation port (46) and the high-precision inlet (43) all adopt a tee structure, wherein the injection port (44) and the evacuation port (46) are directly connected.

11. The microfluidic displacement system for simulating CO 2 flooding in low-permeability reservoirs as claimed in claim 9, It is characterized in that: The drill hole on the side wall of the autoclave body (40) and the drill hole vertically connecting the inlet of the microfluidic model (25) form a through hole for connecting the inlet of the autoclave (24) and the inlet of the microfluidic model (25).

12. The microfluidic displacement system for simulating CO 2 flooding in low-permeability reservoirs as claimed in claim 11, It is characterized in that: The horizontal distance is shortened by optimizing the valve needle length in the horizontal direction of the through hole, and the channel volume between the inlet of the autoclave (24) and the inlet of the microfluidic model (25) is 0.08 mL.

13. A microfluidic displacement method for simulating CO 2 flooding in low-permeability reservoirs It is characterized in that including the following steps: S1 After assembling the inner cavity of the autoclave (24) and the microfluidic model (25), evacuate the inner cavity of the autoclave (24) and the microfluidic model (25), and fill the microfluidic model (25) with water. The S2 control loop pressure control pump (29) pumps a certain amount of distilled water into the inner cavity of the high-temperature and high-pressure autoclave (24), then closes the drain valve (28). After reaching a certain pressure, the loop pressure control pump (29) maintains a constant pressure mode; turns on the control and data processing computer (22) to set the experimental temperature; connects the outlet of the high-temperature and high-pressure autoclave (24) to the inlet of the back pressure control section. After the pressure is balanced, gradually increase the pressure of the back pressure controller (34) until the required back pressure and temperature for the experiment are reached. In S3, the No. 2 displacement pump (9) is used to boost the pressure of the crude oil in the No. 4 liquid container 7, and at the same time, the No. 1 displacement pump (8) is used to boost the pressure of the high-concentration oil-soluble red simulated oil in the No. 1 liquid container (4). After boosting to the experimental design pressure, open the valve (45) to inject saturated oil; adjust the relevant parameters of the microscope and high-speed camera (21) to obtain clear images; by adjusting the displacement speed of the displacement pump (8), change the injection ratio of the high-concentration oil-soluble red simulated oil to the crude oil so that the red color of the crude oil is clearly visible; after the back pressure controller (34) is retracted to a value greater than twice the pore volume of the microfluidic model, complete the displacement of the saturated oil; take pictures and videos through the microscope and high-speed camera (21) to save the experimental process information.

14. The microfluidic displacement method for simulating CO 2 flooding in a low-permeability reservoir as claimed in claim 13, It is characterized in that: Before switching the displacement fluid, close the valve (45), switch the displacement fluid in the No. 2 liquid container (5) to the model injection pipeline, and open the drain port (46). At this time, the new displacement fluid drains the previous displacement fluid in the liquid container (6) to the pipeline of the valve (45) until the new displacement fluid is produced, and then close the drain port (46); when the monitoring values of the pressure monitoring sensors (19) and (31) are equal, open the valve (5), and the displacement fluid enters the inlet of the microfluidic model through the high-precision inlet structure. During the displacement process, take pictures and videos through the microscope and high-speed camera (21) to save the experimental process information.

15. The microfluidic displacement method for simulating CO 2 flooding in low-permeability reservoirs as claimed in claim 13, It is characterized in that: After the displacement is completed, gradually reduce the back pressure of the high-temperature and high-pressure autoclave (24) through the back pressure controller (34), and at the same time open the drain valve (28), and try to achieve synchronous pressure relief of the loop pressure and back pressure until normal pressure is reached.

16. The microfluidic displacement method for simulating CO 2 flooding in low-permeability reservoirs as claimed in claim 13, It is characterized in that: Use professional image processing software to process the images obtained during the experiment to obtain information on microscopic oil displacement efficiency, displacement front, and target trajectory analysis, providing basic data for relevant research.

17. The microfluidic displacement method for simulating CO 2 flooding in a low-permeability reservoir as claimed in claim 13, It is characterized in that: In the step S1, it specifically includes: S11 Place the heterogeneous microfluidic model (25) in the high-temperature and high-pressure autoclave (24) for fixation. After installing the combined sealing structure (41) on the end cover (39), connect and fix it to the high-temperature and high-pressure autoclave body (40), and install the high-temperature and high-pressure autoclave heating and insulation jacket (23). S12 Place the end cover (39) of the assembled high-temperature and high-pressure autoclave at the bottom and install it on the fixed seat (36) of the rotatable high-temperature and high-pressure autoclave fixing device. At the same time, install the microscope and high-speed camera (21) on the fixed seat (36); adjust the position of the fixed seat (36) around the rotatable bearing (35) so that the heterogeneous microfluidic model (25) is in a vertical position with respect to the ground, and connect all pipelines, control lines, data lines, and power lines.

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