A system and method for determining a multi-criteria displacement phase diagram for nanopores

Abstract

The present invention belongs to the technical field of shale oil and gas development, and discloses a system and method for determining a multi-criteria displacement phase diagram for nanopores, which can solve the problem that the multi-criteria displacement phase diagram of nanopores cannot be determined in the prior art. The nanofluidic chip in the system has a nanoporous medium, and the visualization imaging component is used to record the image of the invading phase fluid displacing the displaced phase fluid in the nanoporous medium. The calculation component is used to obtain the displacement mode and average flow rate under different displacement pressure difference conditions, and obtain the viscosity ratio and capillary number, which are mapped to a double logarithmic coordinate system in the form of data points, and the multi-criteria displacement phase diagram is obtained by fitting. The system can effectively control and monitor fluid flow for the nanofluidic chip, assist in observing the displacement mode in the two-phase flow process, and obtain the multi-criteria displacement phase diagram of nanopores. The method for determining the multi-criteria displacement phase diagram for nanopores disclosed by the present invention has the same advantages as the above-mentioned system.

Description

Technical Field

[0001] The invention belongs to the technical field of shale oil and gas development, and in particular relates to a system and method for determining a multi-criteria displacement phase diagram for nanopores. Background Art

[0002] In the field of oil and gas extraction, the displacement process of two-phase fluids in porous media is closely related to many underground and industrial activities, such as carbon capture, geological carbon storage, enhanced oil and gas recovery, and groundwater pollution remediation. There are more micron-sized pores in conventional reservoirs, while there are usually a large number of nano-sized pores in shale reservoirs. The specific surface area of ​​these nano-sized pores increases exponentially compared to micron-sized pores, which greatly increases the instability of the fluid interface, which manifests itself as different displacement modes on a macro scale, resulting in low fluid displacement efficiency.

[0003] Without considering gravity, a multi-criteria displacement phase diagram is generally used to describe the competitive effect of viscosity and capillary force in the displacement process of immiscible fluids. The relationship between capillary number, viscosity ratio and displacement mode is established based on the phase diagram. This method allows people to intuitively distinguish the boundary conditions for transitions between different displacement modes.

[0004] However, existing visualization studies on immiscible two-phase flow patterns and multi-criteria displacement phase diagrams are mainly concentrated at the micrometer scale, while it is difficult to conduct fluid experiments at the nanometer scale. As a result, a large number of theoretical studies lack the support of experimental data. At the same time, due to the limitations of processing methods, the microscopic models used in conventional two-phase displacement experiments generally use rectangular pores and pore throats. This structure is not nanoscale pores, which makes the detection results prone to deviations.

[0005] Therefore, there is an urgent need for a system that can effectively identify fluid seepage in nanopores to assist in observing the flow details in the two-phase displacement process at the nanoscale, so as to determine the multi-criteria displacement phase diagram for nanopores. Summary of the invention

[0006] To solve the above problems, the present invention provides a system and method for determining a multi-criteria displacement phase diagram for nanopores, which can effectively control and monitor fluid flow for a nanofluidic chip, assist in observing the displacement pattern in the two-phase flow process, calculate the viscosity ratio and capillary number corresponding to different displacement pressure differences, and obtain the multi-criteria displacement phase diagram of nanopores, filling the gap in displacement research in the nanoscale field, and assisting in revealing the physical laws of how the non-mixable displacement characteristics in nanoporous media are affected by nanopore parameters.

[0007] The present invention provides a system for determining a multi-criteria displacement phase diagram for nanopores, comprising a nanofluidic chip, a fluid injection component, a visualization imaging component and a calculation component;

[0008] The fluid injection assembly comprises a first fluid injection device for injecting a displaced phase fluid and a second fluid injection device for injecting an invading phase fluid;

[0009] The nanofluidic chip is provided with a displaced phase fluid injection port and an invading phase fluid injection port and a nanoporous medium connected to the two;

[0010] The visualization imaging component is used to record an image of the invading phase fluid displacing the displaced phase fluid in the nanoporous medium;

[0011] The calculation component is used to obtain the displacement mode and average flow rate under different displacement pressure difference conditions according to the image, obtain the viscosity ratio and capillary number according to the physical parameters of the two-phase fluid and the average flow rate, map the viscosity ratio and the capillary number in the form of data points to a double logarithmic coordinate system, and obtain a multi-criteria displacement phase diagram by fitting.

[0012] Preferably, in the above-mentioned system for determining the multi-criteria displacement phase diagram for nanopores, the first fluid injection device includes a first constant pressure and constant speed pump and a first intermediate container, the first intermediate container is used to hold the displaced phase fluid, the first intermediate container is connected to the displaced phase fluid injection port through a first valve, a first joint and a second valve in sequence, and the first joint is also connected to a first vent valve.

[0013] Preferably, in the above-mentioned system for determining the multi-criteria displacement phase diagram for nanopores, the second fluid injection device includes a second constant pressure and constant speed pump and a second intermediate container, the second intermediate container is used to hold the invading phase fluid, the second intermediate container is connected to the invading phase fluid injection port through a third valve, a second joint and a fourth valve in sequence, and the second joint is also connected to a second vent valve.

[0014] Preferably, the above-mentioned system for determining the multi-criteria displacement phase diagram for nanopores further includes a vacuum pump, which is connected to the second joint through a fifth valve to evacuate the nanoporous medium to a vacuum state when only the fifth valve and the fourth valve are opened.

[0015] Preferably, in the above-mentioned system for determining the multi-criteria displacement phase diagram for nanopores, the displaced phase fluid injection port is connected to the nanoporous medium via a first microchannel, and the invading phase fluid injection port is connected to the nanoporous medium via a second microchannel.

[0016] Preferably, in the above-mentioned system for determining the multi-criteria displacement phase diagram for nanopores, the visualization imaging component includes a microscope and a camera with a lens facing the microscope, the camera is connected to the computing component, and the camera is used to record the image in the microscope and transmit the image to the computing component.

[0017] Preferably, in the above-mentioned system for determining the multi-criteria displacement phase diagram for nanopores, the computing component includes a computer device and a display device, the computer device is used to obtain the multi-criteria displacement phase diagram according to the image fitting, and the display device is used to display the multi-criteria displacement phase diagram.

[0018] Preferably, the above-mentioned system for determining the multi-criteria displacement phase diagram for nanopores further comprises a constant temperature heating box, and the constant temperature heating box is used to control the temperature of the nanofluidic chip by using a heating jacket.

[0019] The present invention provides a method for determining a multi-criteria displacement phase diagram for nanopores, using a system for determining a multi-criteria displacement phase diagram for nanopores as described in any one of the above, comprising the following steps:

[0020] Under a first pressure, injecting a displaced phase fluid into the nanoporous medium through the displaced phase fluid injection port using the first fluid injection device until the flow channel is completely saturated;

[0021] At a second pressure higher than the first pressure by a first displacement pressure difference, injecting an invading phase fluid into the nanoporous medium through the invading phase fluid injection port using the second fluid injection device to displace the displaced phase fluid;

[0022] Using the visualization imaging component to record an image of the invading phase fluid displacing the displaced phase fluid in the nanoporous medium, and transmitting the image to the computing component;

[0023] The value of the first displacement pressure difference is changed, and the above steps are repeated. The displacement mode and the average flow rate under different displacement pressure difference conditions are obtained by using the calculation component. The viscosity ratio and the capillary number are obtained according to the physical parameters of the two-phase fluid and the average flow rate. The viscosity ratio and the capillary number are mapped to a double logarithmic coordinate system in the form of data points, and a multi-criteria displacement phase diagram is obtained by fitting.

[0024] Preferably, in the above-mentioned method for determining the multi-criteria displacement phase diagram for nanopores, the use of the calculation component to obtain the displacement mode and the average flow rate under different displacement pressure difference conditions, the viscosity ratio and the capillary number are obtained according to the average flow rate, the viscosity ratio and the capillary number are mapped to a double logarithmic coordinate system in the form of data points, and the multi-criteria displacement phase diagram is obtained by fitting, including:

[0025] The image is segmented and processed by the computing component at preset time intervals to obtain two-phase distribution images corresponding to different time nodes, the intrusion phase fluid regions corresponding to different time nodes are extracted based on threshold filtering and processed to obtain binary images, the binary images corresponding to adjacent time nodes are subtracted to obtain displacement values ​​of the intrusion phase fluid fronts at adjacent time nodes, the displacement values ​​are divided by the preset time interval to obtain the instantaneous rate, all instantaneous rates in the entire displacement process are averaged to obtain the average flow rate of the fluid under the displacement pressure difference condition, and the step is repeated after changing the value of the first displacement pressure difference to determine the average flow rate of the fluid under different displacement pressure difference conditions;

[0026] Based on the two-phase distribution image at the breakthrough moment of the invading phase fluid, determine whether the displacement mode corresponding to different displacement pressure differences is capillary fingering, viscous fingering or cross-region;

[0027] Using the formula The viscosity ratio is calculated, where is the dynamic viscosity of the invading phase fluid, is the dynamic viscosity of the displaced phase fluid, using the formula The capillary number is calculated, where represents the interfacial tension between two phase fluids, is the average flow velocity;

[0028] The experimental data points are mapped into a double logarithmic coordinate system with the viscosity ratio as the abscissa and the capillary number as the ordinate;

[0029] The data point range is divided according to the three displacement modes identified, and the data points in the intersection area are calculated by the formula The parameter range corresponding to the boundary of the cross region is obtained by fitting, where represents the number of capillaries in the intersection area, represents the viscosity ratio of the crossover region, represents the slope of the boundary, C represents a constant related to fluid properties and pore structure, and the range corresponding to each region is obtained based on the displacement mode and the cross-region boundary division, and the multi-criteria displacement phase diagram is drawn.

[0030] From the above description, it can be seen that the above-mentioned system for determining the multi-criteria displacement phase diagram for nanopores provided by the present invention has a displaced phase fluid injection port and an invading phase fluid injection port and a nanoporous medium connected to the two on the nanofluidic chip; the visualization imaging component is used to record the image of the invading phase fluid displacing the displaced phase fluid in the nanoporous medium; the calculation component is used to obtain the displacement mode and average flow rate under different displacement pressure difference conditions according to the image, obtain the viscosity ratio and the capillary number according to the physical parameters of the two-phase fluid and the average flow rate, map the viscosity ratio and the capillary number in the form of data points to a double logarithmic coordinate system, and fit to obtain the multi-criteria displacement phase diagram. Therefore, the beneficial effect of the system is that it can effectively control and monitor the fluid flow for the nanofluidic chip, assist in observing the displacement mode in the two-phase flow process, calculate the viscosity ratio and the capillary number corresponding to different displacement pressure differences, and obtain the multi-criteria displacement phase diagram of the nanopores, fill the gap in the displacement research in the nanoscale field, and assist in revealing the physical law that the non-mixed displacement characteristics in the nanoporous medium are affected by the nanopore parameters. The method for determining the multi-criteria displacement phase diagram for nanopores provided by the present invention has the same advantages as the above system. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0032] Figure 1 A schematic diagram of the overall composition of an embodiment of a system for determining a multi-criteria displacement phase diagram for nanopores provided by the present invention;

[0033] Figure 2 Schematic diagram of the composition of a uniformly distributed nanofluidic chip;

[0034] Figure 3 Schematic diagram of the composition of a nanofluidic chip with dual-porous media;

[0035] Figure 4 Schematic diagram of the composition of the cross-scale micro-nanofluidic chip;

[0036] Figure 5 A schematic diagram of an embodiment of a method for determining a multi-criteria displacement phase diagram for nanopores provided by the present invention;

[0037] Figure 6 Schematic diagram of two-phase distribution under different pressure differences during gas-liquid two-phase displacement;

[0038] Figure 7 This is the multi-criteria displacement phase diagram obtained in 100nm porous media. DETAILED DESCRIPTION

[0039] The core of the present invention is to provide a system and method for determining a multi-criteria displacement phase diagram for nanopores, which can effectively control and monitor fluid flow for nanofluidic chips, assist in observing the displacement pattern in the two-phase flow process, calculate the viscosity ratio and capillary number corresponding to different displacement pressure differences, and obtain the multi-criteria displacement phase diagram of nanopores, filling the gap in displacement research in the nanoscale field, and assisting in revealing the physical laws of how the non-mixable displacement characteristics in nanoporous media are affected by nanopore parameters.

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] The present invention provides a method for determining a multi-criteria displacement phase diagram for nanopores. Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown, Figure 1 The overall composition diagram of an embodiment of a system for determining a multi-criteria displacement phase diagram for nanopores provided by the present invention is shown in FIG. Figure 2 Schematic diagram of the composition of a uniformly distributed nanofluidic chip. Figure 3 Schematic diagram of the composition of the nanofluidic chip with dual-pore media. Figure 4 The schematic diagram of the composition of the cross-scale micro-nanofluidic chip is shown in Figure 1. Figure 2 , Figure 3 and Figure 4 These are three forms of nanofluidic chips that can be used in the embodiments of the present invention. The specific form of the nanofluidic chip can be selected according to the actual research needs. The determination system of the multi-criteria displacement phase diagram for nanopores can include a nanofluidic chip 1, a fluid injection component 2, a visualization imaging component 3 and a calculation component 4;

[0042] The fluid injection assembly 2 may include a first fluid injection device 21 for injecting a displaced phase fluid and a second fluid injection device 22 for injecting an invading phase fluid. The displaced phase fluid may be, but not limited to, octane, and the invading phase fluid may be, but not limited to, nitrogen.

[0043] from Figure 2 , Figure 3 and Figure 4It can be seen that the nanofluidic chip 1 has a displaced phase fluid injection port 11 and an invading phase fluid injection port 12 and a nanoporous medium 13 connected to the two. Specifically, the nanofluidic chip 1 can be processed by a process combining chemical vapor deposition and wet etching to obtain a nanoscale flow channel. For the completeness of the regularity exploration, several nanofluidic chips with different structures can be prepared. The differences between different nanofluidic chips are mainly reflected in the structure of the nanoporous medium 13, for example Figure 2 The flow control structure is all nano-scale pores, and each black part represents a flow channel, which can be composed of equal-diameter cylinders arranged in an equilateral triangle array. The depth can be preferably 100nm, and of course other depths can be selected according to actual needs. This is the main target area for observing and measuring the two-phase seepage characteristics in nanoporous media. Figure 3 and Figure 4 The structure of Figure 3 It is a fluidic structure with dual-pore media coupling at the 100nm and 500nm levels. Figure 4 It is a micro-nanofluidic structure with cross-scale coupling of 100nm and 3μm.

[0044] The visualization imaging component 3 is used to record the image of the invading phase fluid displacing the displaced phase fluid in the nanoporous medium. Specifically, such an image can be recorded throughout the process to provide a basis for subsequent calculations.

[0045] The calculation component 4 is used to obtain the displacement pattern and average flow rate under different displacement pressure difference conditions according to the image, obtain the viscosity ratio and capillary number according to the physical parameters and average flow rate of the two-phase fluid, map the viscosity ratio and capillary number in the form of data points to the double logarithmic coordinate system, and fit to obtain the multi-criteria displacement phase diagram.

[0046] The nanofluidic chip used in this embodiment has a high degree of freedom and can effectively identify the interface morphology of two-phase seepage under the synergistic influence of capillary effect, two-phase viscosity difference and displacement pressure difference, realizes the visual observation of the displacement mode under the joint action of capillary force, viscous force and driving force in the nano-confined space, and calculates the boundary conditions of the transformation of the non-mixed displacement interface morphology in the nanoscale in combination with the visual information, filling the gap of the multi-criteria displacement phase diagram at the nanoscale, and also has the advantages of easy operation and strong repeatability, breaking through the limitations of traditional experimental methods such as core experiments in the oil and gas field, and providing an effective experimental means for studying nanoscale fluid problems.

[0047] It can be seen from the above description that in the embodiment of the above-mentioned system for determining the multi-criteria displacement phase diagram for nanopores provided by the present invention, since the nanofluidic chip has a displaced phase fluid injection port and an invading phase fluid injection port and a nanoporous medium connected to the two; the visualization imaging component is used to record the image of the invading phase fluid displacing the displaced phase fluid in the nanoporous medium; the calculation component is used to obtain the displacement mode and average flow rate under different displacement pressure difference conditions according to the image, and obtain the viscosity ratio and capillary number according to the physical parameters and average flow rate of the two-phase fluid, and map the viscosity ratio and capillary number in the form of data points to a double logarithmic coordinate system, and fit to obtain the multi-criteria displacement phase diagram. Therefore, the system can effectively control and monitor the fluid flow for the nanofluidic chip, assist in observing the displacement mode in the two-phase flow process, calculate the viscosity ratio and capillary number corresponding to different displacement pressure differences, and obtain the multi-criteria displacement phase diagram of the nanopores, fill the gap in the displacement research in the nanoscale field, and assist in revealing the physical law that the non-mixed displacement characteristics in the nanoporous medium are affected by the nanopore parameters.

[0048] In a specific embodiment of the above-mentioned system for determining the multi-criteria displacement phase diagram for nanopores, continue to refer to Figure 1 The first fluid injection device 21 may include a first constant pressure and constant speed pump 211 and a first intermediate container 212. The first intermediate container 212 is used to hold the displaced phase fluid. The first intermediate container 212 is connected to the displaced phase fluid injection port 11 through the first valve 213, the first connector 214 and the second valve 215 in sequence. The first connector 214 is also connected to the first vent valve 216. The first connector 214 may be a three-way connector. The piston in the first intermediate container 212 is driven by the first constant pressure and constant speed pump 211. The first valve 213 and the second valve 215 are opened to inject the displaced phase fluid into the nanofluidic chip 1. When the nanofluidic chip 1 is observed to be full of the displaced phase fluid, saturation is completed. In addition, the first vent valve 216 may be opened when it is necessary to vent. It can be seen that this facilitates various operations.

[0049] In a further embodiment, the second fluid injection device 22 may include a second constant pressure and constant speed pump 221 and a second intermediate container 222, the second intermediate container 222 is used to hold the intrusion phase fluid, the second intermediate container 222 is connected to the intrusion phase fluid injection port 12 through the third valve 223, the second connector 224 and the fourth valve 225 in sequence, and the second connector 224 is also connected to the second vent valve 226. It should be noted that after the nanofluidic chip 1 is observed to be saturated, the piston in the second intermediate container 222 is driven by the second constant pressure and constant speed pump 221 in time, and the third valve 223 and the fourth valve 225 are opened, so that the intrusion phase fluid can be injected into the nanofluidic chip 1. When the front edge of the intrusion phase fluid is observed to reach the junction of the first microchannel 14 and the nanoporous medium 13, the displacement process is completed, the pressure is balanced in time, and the third valve 223 is closed. In addition, the second vent valve 226 can be opened when it is necessary to vent, which can be seen that this facilitates various operations.

[0050] In a further embodiment, a vacuum pump 227 may be further included, and the vacuum pump 227 is connected to the second connector 224 through the fifth valve 228 to evacuate the nanoporous medium 13 to a vacuum state when only the fifth valve 228 and the fourth valve 225 are opened. It should be noted that the second connector 224 may be a four-way connector. In this case, after the entire system is built, pretreatment may be performed to check the air tightness of the entire system, and then the vacuum pump 227 may be used to evacuate the nanofluidic chip and the connecting pipeline to eliminate the adverse effects of the air therein on the final measurement result.

[0051] In another specific embodiment of the above-mentioned system for determining the multi-criteria displacement phase diagram for nanopores, the above-mentioned displaced phase fluid injection port 11 and the nanoporous medium 13 can be connected by a first microchannel 14, and the invading phase fluid injection port 12 and the nanoporous medium 13 can be connected by a second microchannel 15. The width of the first microchannel 14 and the second microchannel 15 can both be 200μm and the depth can both be 3μm. The use of the first microchannel and the second microchannel has the following advantages: first, it is easy to visualize and observe, and it is convenient to control the position and speed of the fluid entering the nanofluidic chip to prevent the fluid from being injected too fast or too slow; second, it is to cache the fluid to ensure that the fluid can enter the nanoporous medium at the same speed at the inlet, avoiding the influence of uneven inlet speed on subsequent experimental results.

[0052] In another specific embodiment of the above-mentioned system for determining the multi-criteria displacement phase diagram for nanopores, continue to refer to Figure 1The above-mentioned visualization imaging component 3 may include a microscope 31 and a camera 32 with a lens facing the microscope 31. The camera 32 is connected to the computing component, and the camera is used to record the image in the microscope and transmit the image to the computing component. Specifically, the microscope 31 is used to visualize the displacement characteristics of the fluid in the nanofluidic chip after magnification. The camera 32 can transmit the obtained video to the computing component in real time for storage and calculation. During operation, the magnification and related parameters of the microscope need to be adjusted to ensure that the entire nanoporous medium field of view can be clearly observed.

[0053] For further information, please refer to Figure 1 The computing component 4 may include a computer device 41 and a display device 42. The computer device 41 is used to obtain a multi-criteria displacement phase diagram according to image fitting, and the display device 42 is used to display the multi-criteria displacement phase diagram. Specifically, the computer device 41 may control the working state of the camera, realize automatic data collection, storage and processing, and determine the average flow rate and displacement mode under different displacement pressure difference conditions according to the image information, so as to determine the range and boundary corresponding to different displacement modes in the multi-criteria displacement phase diagram. In addition, in order to ensure the stability of the optical microscope, the optical microscope may be fixed on a shockproof platform.

[0054] In a preferred embodiment of the above-mentioned system for determining the multi-criteria displacement phase diagram for nanopores, continue to refer to Figure 1 , and may also include a constant temperature heating box 5, which is used to control the temperature of the nanofluidic chip 1 using a heating jacket. In addition, Figure 1 A clamp 6 for clamping the nanofluidic chip 1 is also shown. The constant temperature heating box 5 can simultaneously control the temperature of the clamp 6 to avoid the influence of temperature on the experimental results.

[0055] The implementation example of the method for determining a multi-criteria displacement phase diagram for nanopores provided by the present invention is as follows: Figure 5 As shown, Figure 5 A schematic diagram of an embodiment of a method for determining a multi-criteria displacement phase diagram for nanopores provided by the present invention, the method uses a system for determining a multi-criteria displacement phase diagram for nanopores as described in any of the above items, and after the system is built, an airtightness test is performed, and a vacuum treatment is performed, which may include the following steps:

[0056] S1: Under a first pressure, injecting a displaced phase fluid into the nanoporous medium through a displaced phase fluid injection port using a first fluid injection device until the flow channel is completely saturated;

[0057] It should be noted that, in a specific example, the first pressure can be kept constant at 3 MPa, and the displaced phase fluid can be but is not limited to octane. Of course, it can also be adjusted according to actual needs, and there is no limitation here. At this time, the fluid in the chip can be preheated for 20 minutes to stabilize the temperature of the nanofluidic chip at 25°C to unify the temperature parameters of the experimental environment and avoid different experimental results due to different temperatures. Specifically, the temperature can be controlled by but is not limited to a constant temperature heating box.

[0058] S2: injecting an invading phase fluid into the nanoporous medium through an invading phase fluid injection port using a second fluid injection device at a second pressure higher than the first pressure by a first displacement pressure difference to displace the displaced phase fluid;

[0059] Specifically, in a specific example, the first displacement pressure difference can be 0.3 MPa. In this case, the second pressure is 3.3 MPa. The invading phase fluid can be nitrogen. Of course, this can be adjusted according to actual needs. When the second fluid breaks through the connection between the nanoporous medium and the microchannel and flows stably, it is necessary to reduce the pressure to the first pressure in time to balance the pressure of the two-phase fluid.

[0060] S3: using a visualization imaging component to record an image of the invading phase fluid displacing the displaced phase fluid in the nanoporous medium, and transmitting the image to a computing component;

[0061] Specifically, during the entire experiment, the nanoporous medium can be selected as the main recording area, the optical microscope magnification is adjusted to 1 times, to ensure that the lens can observe the entire nanoporous medium area, and the camera is turned on, and the phase distribution morphology of the two-phase seepage in the nanofluidic chip is imaged in real time through the optical microscope connected to the computing component, and the entire displacement process is recorded, and the recording is terminated after the pressure is balanced and the two-phase interface morphology is stable. After the operation is completed, the first valve 213 and the third valve 223 need to be closed in time, and the fifth valve 228 needs to be opened, and the nanofluidic chip and the connecting pipelines need to be evacuated again by the vacuum pump to carry out the two-phase displacement experiment under the remaining displacement pressure difference conditions.

[0062] S4: Change the value of the first displacement pressure difference, repeat the above steps, use the calculation component to obtain the displacement mode and average flow rate under different displacement pressure difference conditions, obtain the viscosity ratio and capillary number according to the physical parameters and average flow rate of the two-phase fluid, map the viscosity ratio and capillary number in the form of data points to the double logarithmic coordinate system, and obtain the multi-criteria displacement phase diagram by fitting.

[0063] Specifically, after the previous step, after the vacuuming is completed, the above steps are repeated. The only difference is that the value of the first displacement pressure difference, that is, the value of the second pressure is different in each experiment. The second pressure can be 3.30MPa, 3.50MPa, 3.70MPa, 3.90MPa, 4.28MPa, 4.60MPa, 4.92MPa and 5.24MPa. A total of 8 groups of experiments are carried out. Of course, these can be selected according to actual needs and are not limited here. Each group of displacement experiments starts from the time when the invading phase fluid is about to enter the nanoporous medium and ends at the breakthrough moment. The entire displacement process is recorded to obtain visual image information of the two-phase displacement under different pressure difference conditions.

[0064] In a specific embodiment of the method for determining the multi-criteria displacement phase diagram for nanopores, the displacement mode and average flow rate under different displacement pressure difference conditions are obtained by using a calculation component, the viscosity ratio and the capillary number are obtained according to the average flow rate, the viscosity ratio and the capillary number are mapped to a double logarithmic coordinate system in the form of data points, and the multi-criteria displacement phase diagram is obtained by fitting, which may specifically include the following specific steps:

[0065] S41: using a computing component to segment and process an image at a preset time interval to obtain two-phase distribution images corresponding to different time nodes. The preset time interval can be, but is not limited to, 5% of the total time length, which can be selected according to actual needs and is not limited here. Based on threshold filtering, the intrusion phase fluid regions corresponding to different time nodes are extracted and processed to obtain binary images. The binary images corresponding to adjacent time nodes are subtracted to obtain displacement values ​​of the intrusion phase fluid fronts at adjacent time nodes. The displacement values ​​are divided by the preset time interval to obtain the instantaneous rate of the intrusion phase front. The average of all instantaneous rates in the entire displacement process is taken to obtain the average flow rate of the fluid under the displacement pressure difference condition. When the preset time interval is 5% of the total time length, the average flow rate is calculated by the average value of 20 sampling rates. This can better characterize the characteristic rate of the intrusion phase front in the entire process, making it universally applicable to different displacement modes. After changing the value of the first displacement pressure difference, repeat this step to determine the average flow rate of the fluid under different displacement pressure difference conditions.

[0066] In a specific example, the displacement pressure differences used are 0.30 MPa, 0.50 MPa, 0.70 MPa, 0.90 MPa, 1.28 MPa, 1.60 MPa, 1.92 MPa and 2.24 MPa, and the corresponding average flow velocities are calculated to be 0.08 m / s, 0.31 m / s, 0.47 m / s, 0.57 m / s, 0.72 m / s, 0.89 m / s, 1.06 m / s and 1.19 m / s. The parameters obtained are shown in Table 1. Table 1 shows the average flow velocity, capillary number and The calculation results summary table.

[0067] Table 1 Average flow rate, capillary number and Summary table of calculation results

[0068]

[0069] S42: Based on the two-phase distribution image at the moment of breakthrough of the invading phase fluid, determine whether the displacement mode corresponding to different displacement pressure differences is capillary fingering, viscous fingering or cross-region. Specifically, during capillary fingering, the fluid flow is relatively stable and has good continuity. A large amount of lateral fingering will occur during the forward movement, and it may even move in the opposite direction of the forward movement. During viscous fingering, the fluid will move rapidly toward the outlet, the interface instability will increase, and a large number of dispersed and discontinuous pathways will exist. The area between these two displacement modes is the cross-region. The two-phase distribution when nitrogen breaks through the nanoporous medium and the second microchannel is used as the main reference node. The two-phase distribution diagrams under different displacement pressure differences are obtained respectively. The displacement mode of the fluid is identified according to the distribution state of the two-phase fluid, such as Figure 6 As shown, Figure 6 The diagram is a schematic diagram of the two-phase distribution under different pressure differences during the gas-liquid two-phase displacement process. It can be seen that the displacement mode corresponding to 0.30MPa is capillary fingering, 0.50MPa to 0.90MPa corresponds to the cross region, and 1.28MPa to 2.24MPa corresponds to the viscous fingering;

[0070] S43: Using formula Calculate the viscosity ratio, where is the dynamic viscosity of the intruding phase fluid, in units of , is the dynamic viscosity of the displaced phase fluid, in units of , using the formula Calculate the capillary number, where Ca is a dimensionless number, It represents the interfacial tension of two-phase fluids, in N / m. is the average flow velocity in m·s -1 ;

[0071] Specifically, the dynamic viscosity of nitrogen is 0.0177m The dynamic viscosity of octane is 0.544m The interfacial tension between nitrogen and octane is 18.24 mN / m. The calculated capillary number is shown in Table 1.

[0072] S44: Map the experimental data points into a double logarithmic coordinate system with the viscosity ratio as the abscissa and the capillary number as the ordinate;

[0073] That is to say, the viscosity ratio is taken as the horizontal coordinate after taking the logarithm, and the capillary number is taken as the vertical coordinate after taking the logarithm, and the experimental data points are plotted in a double logarithmic coordinate system.

[0074] S45: Divide the data point range according to the three displacement modes identified, and use the formula based on the data points in the intersection area The parameter range corresponding to the boundary of the cross region is obtained by fitting, where represents the number of capillaries in the intersection region, which is a dimensionless number. represents the viscosity ratio of the crossover region, which is also a dimensionless number, represents the slope of the boundary, which can be taken as 1 here. C represents a constant related to fluid properties and pore structure, which is also a dimensionless number. In this example, it can be taken as -3.848 to -3.263. Based on the displacement mode and the boundary of the cross region, the corresponding range of each region is obtained, and the multi-criteria displacement phase diagram is drawn, such as Figure 7 As shown, Figure 7 This is the multi-criteria displacement phase diagram obtained in 100nm porous media.

[0075] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A system for determining a multi-criteria displacement phase diagram for nanopores, characterized in that: Including nanofluidic chip, fluid injection component, visualization imaging component and computing component; The fluid injection assembly comprises a first fluid injection device for injecting a displaced phase fluid and a second fluid injection device for injecting an invading phase fluid; The nanofluidic chip is provided with a displaced phase fluid injection port and an invading phase fluid injection port and a nanoporous medium connected to the two; The visualization imaging component is used to record an image of the invading phase fluid displacing the displaced phase fluid in the nanoporous medium; The calculation component is used to obtain the displacement mode and average flow rate under different displacement pressure difference conditions according to the image, obtain the viscosity ratio and the capillary number according to the physical parameters of the two-phase fluid and the average flow rate, map the viscosity ratio and the capillary number in the form of data points to a double logarithmic coordinate system, and obtain a multi-criteria displacement phase diagram by fitting. The multi-criteria displacement phase diagram is obtained in the following manner: based on the two-phase distribution image at the breakthrough moment of the invading phase fluid, determine whether the displacement mode corresponding to the different displacement pressure difference is capillary fingering, viscous fingering or cross-region; Using the formula The viscosity ratio is calculated, where is the dynamic viscosity of the invading phase fluid, is the dynamic viscosity of the displaced phase fluid, using the formula The capillary number is calculated, where represents the interfacial tension between two phase fluids, is the average flow velocity; The experimental data points are mapped into a double logarithmic coordinate system with the viscosity ratio as the abscissa and the capillary number as the ordinate; The data point range is divided according to the three displacement modes identified, and the data points in the intersection area are calculated by the formula The parameter range corresponding to the boundary of the cross region is obtained by fitting, where represents the number of capillaries in the intersection area, represents the viscosity ratio of the crossover region, represents the slope of the boundary, C represents a constant related to fluid properties and pore structure, and the range corresponding to each region is obtained based on the displacement mode and the cross-region boundary division, and the multi-criteria displacement phase diagram is drawn.

2. The system for determining a multi-criteria displacement phase diagram for nanopores according to claim 1, characterized in that: The first fluid injection device includes a first constant pressure and constant speed pump and a first intermediate container. The first intermediate container is used to hold the displaced phase fluid. The first intermediate container is connected to the displaced phase fluid injection port through a first valve, a first joint and a second valve in sequence. The first joint is also connected to a first vent valve.

3. The system for determining a multi-criteria displacement phase diagram for nanopores according to claim 2, characterized in that: The second fluid injection device includes a second constant pressure and constant speed pump and a second intermediate container. The second intermediate container is used to hold the invading phase fluid. The second intermediate container is connected to the invading phase fluid injection port through a third valve, a second joint and a fourth valve in sequence. The second joint is also connected to a second vent valve.

4. The system for determining a multi-criteria displacement phase diagram for nanopores according to claim 3, characterized in that: A vacuum pump is also included, and the vacuum pump is connected to the second joint through a fifth valve so as to evacuate the nanoporous medium to a vacuum state when only the fifth valve and the fourth valve are opened.

5. The system for determining a multi-criteria displacement phase diagram for nanopores according to claim 4, characterized in that: The displaced phase fluid injection port is connected to the nanoporous medium via a first microchannel, and the invading phase fluid injection port is connected to the nanoporous medium via a second microchannel.

6. The system for determining a multi-criteria displacement phase diagram for nanopores according to claim 5, characterized in that: The visualization imaging component includes a microscope and a camera with a lens facing the microscope, the camera is connected to the computing component, and the camera is used to record images in the microscope and transmit the images to the computing component.

7. The system for determining a multi-criteria displacement phase diagram for nanopores according to claim 6, characterized in that: The computing component includes a computer device and a display device. The computer device is used to obtain a multi-criteria displacement phase diagram according to the image fitting, and the display device is used to display the multi-criteria displacement phase diagram.

8. The system for determining a multi-criteria displacement phase diagram for nanopores according to any one of claims 1 to 7, characterized in that: It also includes a constant temperature heating box, which is used to control the temperature of the nanofluidic chip using a heating jacket.

9. A method for determining a multi-criteria displacement phase diagram for nanopores, characterized in that: The system for determining a multi-criteria displacement phase diagram for nanopores according to any one of claims 1 to 8 comprises the following steps: Under a first pressure, injecting a displaced phase fluid into the nanoporous medium through the displaced phase fluid injection port using the first fluid injection device until the flow channel is completely saturated; At a second pressure higher than the first pressure by a first displacement pressure difference, injecting an invading phase fluid into the nanoporous medium through the invading phase fluid injection port using the second fluid injection device to displace the displaced phase fluid; Using the visualization imaging component to record an image of the invading phase fluid displacing the displaced phase fluid in the nanoporous medium, and transmitting the image to the computing component; The value of the first displacement pressure difference is changed, and the above steps are repeated. The displacement mode and the average flow rate under different displacement pressure difference conditions are obtained by using the calculation component. The viscosity ratio and the capillary number are obtained according to the physical parameters of the two-phase fluid and the average flow rate. The viscosity ratio and the capillary number are mapped to a double logarithmic coordinate system in the form of data points, and a multi-criteria displacement phase diagram is obtained by fitting.

10. The method for determining a multi-criteria displacement phase diagram for nanopores according to claim 9, characterized in that: The method of using the calculation component to obtain the displacement mode and average flow rate under different displacement pressure difference conditions, obtaining the viscosity ratio and the capillary number according to the average flow rate, mapping the viscosity ratio and the capillary number in the form of data points to a double logarithmic coordinate system, and fitting to obtain a multi-criteria displacement phase diagram includes: The image is segmented and processed by the computing component at preset time intervals to obtain two-phase distribution images corresponding to different time nodes, the intrusion phase fluid regions corresponding to different time nodes are extracted based on threshold filtering and processed to obtain binary images, the binary images corresponding to adjacent time nodes are subtracted to obtain displacement values ​​of the intrusion phase fluid fronts at adjacent time nodes, the displacement values ​​are divided by the preset time interval to obtain the instantaneous rate, all instantaneous rates in the entire displacement process are averaged to obtain the average flow rate of the fluid under the displacement pressure difference condition, and the step is repeated after changing the value of the first displacement pressure difference to determine the average flow rate of the fluid under different displacement pressure difference conditions; Based on the two-phase distribution image at the breakthrough moment of the invading phase fluid, determine whether the displacement mode corresponding to different displacement pressure differences is capillary fingering, viscous fingering or cross-region; Using the formula The viscosity ratio is calculated, where is the dynamic viscosity of the invading phase fluid, is the dynamic viscosity of the displaced phase fluid, using the formula The capillary number is calculated, where represents the interfacial tension between two phase fluids, is the average flow velocity; The experimental data points are mapped into a double logarithmic coordinate system with the viscosity ratio as the abscissa and the capillary number as the ordinate; The data point range is divided according to the three displacement modes identified, and the data points in the intersection area are calculated by the formula The parameter range corresponding to the boundary of the cross region is obtained by fitting, where represents the number of capillaries in the intersection area, represents the viscosity ratio of the crossover region, represents the slope of the boundary, C represents a constant related to fluid properties and pore structure, and the range corresponding to each region is obtained based on the displacement mode and the cross-region boundary division, and the multi-criteria displacement phase diagram is drawn.

Images