System and method for determining minimum miscible pressure and diffusion coefficient of flue gas displacement crude oil

Abstract

The invention provides a system and method for determining the minimum miscible pressure and the diffusion coefficient of flue gas displacement crude oil, and relates to the technical field of oil and gas development, and a micro-fluidic chip in the determining system comprises one path of observation flow channel and at least one path of pressure protection flow channel; the crude oil injection assembly is used for injecting crude oil into the observation runner; the flue gas injection assembly is used for injecting flue gas into the observation flow channel and the pressure protection flow channel; the image acquisition and processing assembly is used for acquiring an image of the displacement and diffusion process of the observation flow channel and obtaining the minimum miscible pressure and diffusion coefficient of the flue gas displacement crude oil according to the acquired image, the flue gas is obtained by mixing CO2 and N2, and the minimum miscible pressure and diffusion coefficient of the flue gas displacement crude oil can be synchronously measured, so that the measurement accuracy of the flue gas displacement crude oil is improved. The problems that pure gas is taken as an object in most of the prior art, a coupling action mechanism of each component on a displacement behavior in a flue gas mixing system is difficult to reveal effectively, and core parameters cannot be measured synchronously are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas development, and particularly relates to a system and method for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil. Background Art

[0002] As one of the most important basic energy sources in modern industry, petroleum occupies an irreplaceable core position in the global energy system. Statistical data shows that petroleum still accounts for more than 30% in the current global primary energy consumption structure, especially in fields such as transportation and chemical raw materials, where there is a rigid demand.

[0003] However, with the continuous deepening of the development of global oil and gas fields, most oil fields have entered the middle and late stages of development. The average recovery rate of conventional primary and secondary oil recovery technologies (such as water flooding) is generally less than 40%, which means that more than 60% of the original geological reserves still remain underground. In this context, the research and development of enhanced oil recovery (EOR) technologies have important strategic significance and economic value.

[0004] Among many EOR technologies, the flue gas flooding technology has attracted much attention due to its dual benefits of improving oil recovery and greenhouse gas sequestration. In the process of implementing the present invention, the inventor has found that currently, in the process of carrying out relevant research and extracting key parameters, most of them take pure gas as the object, which is difficult to effectively reveal the coupling mechanism of each component in the flue gas mixture system on the displacement behavior, and it is also impossible to synchronously measure the core parameters. Summary of the Invention

[0005] In view of this, the present application provides a system and method for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil, so as to solve the problem that most of the existing ones take pure gas as the object, which is difficult to effectively reveal the coupling mechanism of each component in the flue gas mixture system on the displacement behavior, and it is also impossible to synchronously measure the core parameters.

[0006] To achieve the above object, the embodiments of the present invention provide the following technical solutions:

[0007] The first aspect of the present application discloses a system for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil, including: a microfluidic chip, a crude oil injection component, a flue gas injection component, a confining pressure control component, a pressure detection component, a temperature control component, a vacuum pumping component, and an image acquisition and processing component;

[0008] The microfluidic chip is clamped by a chip holder and placed in a pressure chamber, and the microfluidic chip includes 1 observation flow channel and at least 1 pressure protection flow channel;

[0009] The crude oil injection component is used to inject the crude oil into the observation flow channel;

[0010] The flue gas injection component is used to inject the flue gas into the observation flow channel and the pressure protection flow channel;

[0011] The confining pressure control component is used to control the pressure of the pressure chamber;

[0012] The pressure detection component is used to detect the pressure of the crude oil and the flue gas injected into the observation flow channel;

[0013] The temperature control component is used to control the temperature inside the microfluidic chip;

[0014] The vacuum pumping component is used to pump vacuum for the connecting pipelines between the microfluidic chip, the crude oil injection component and the flue gas injection component;

[0015] The image acquisition and processing component is used to acquire the images of the process of the flue gas displacing the crude oil in the observation flow channel, and obtain the minimum miscibility pressure and diffusion coefficient of the flue gas displacing the crude oil according to the acquired images.

[0016] Optionally, in the above-mentioned system for determining the minimum miscibility pressure and diffusion coefficient of the flue gas displacing the crude oil, the crude oil injection component includes: a first fluid pump, a first intermediate container, a first valve, a second valve and a third valve;

[0017] The first fluid pump is connected to one end of the first intermediate container through the first valve;

[0018] The other end of the first intermediate container is sequentially connected to the crude oil injection end of the observation flow channel through the second valve and the third valve;

[0019] The first intermediate container stores the crude oil;

[0020] The first fluid pump is used to control the pressure of the crude oil at the crude oil injection end.

[0021] Optionally, in the above-mentioned system for determining the minimum miscibility pressure and diffusion coefficient of the flue gas displacing the crude oil, the vacuum pumping component includes: a vacuum pump, a fourth valve and a first three-way interface;

[0022] The vacuum pump is sequentially connected to the main pipeline interface of the first three-way interface through the fourth valve;

[0023] The first branch interface and the second branch interface of the first three-way interface are respectively connected to the pipeline between the second valve and the third valve;

[0024] The vacuum pump is used to pump vacuum.

[0025] Optionally, in the above-mentioned system for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil, the number of pressure protection flow channels is 2, and the flue gas injection assembly includes: a second fluid pump, a second intermediate container, a fifth valve, a sixth valve, a seventh valve, an eighth valve, a second three-way interface, a third three-way interface, a fourth three-way interface, and a fifth three-way interface;

[0026] The second fluid pump is connected to one end of the second intermediate container through the fifth valve;

[0027] The other end of the second intermediate container is connected to the flue gas injection end of the observation flow channel through the sixth valve, the second three-way interface, and the seventh valve in sequence, and is connected to the flue gas injection end on one side of the pressure protection flow channel through the sixth valve, the second three-way interface, the eighth valve, the third three-way interface, and the fourth three-way interface in sequence, and is connected to the flue gas injection end on the other side of the pressure protection flow channel through the sixth valve, the second three-way interface, the eighth valve, the third three-way interface, and the fifth three-way interface in sequence;

[0028] The second intermediate container stores the flue gas;

[0029] The second fluid pump is used to control the flue gas pressure at the flue gas injection end.

[0030] Optionally, in the above-mentioned system for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil, the pressure detection assembly includes: a first pressure detection assembly and a second pressure detection assembly;

[0031] The first pressure detection assembly includes a sixth three-way interface and a first pressure sensor. The first pressure sensor is connected to the main pipeline interface of the sixth three-way, and the first branch interface and the second branch interface of the sixth three-way interface are respectively connected to the crude oil output pipeline of the crude oil injection assembly;

[0032] The second pressure detection assembly includes a seventh three-way interface and a second pressure sensor. The second sensor is connected to the main pipeline interface of the seventh three-way interface, and the first branch interface and the second branch interface of the seventh three-way interface are respectively connected to the flue gas output pipeline of the flue gas injection assembly.

[0033] Optionally, in the above-mentioned system for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil, the confining pressure control assembly includes: a third fluid pump, a third intermediate container, a ninth valve, and a tenth valve;

[0034] The third fluid pump is connected to one end of the third intermediate container through the ninth valve;

[0035] The other end of the third intermediate container is connected to the pressure chamber through the tenth valve;

[0036] The third intermediate container contains ethylene glycol solution;

[0037] The third fluid pump is used to control the pressure of the ethylene glycol solution injected into the pressure chamber;

[0038] The temperature control component includes: a heating box and a temperature measuring probe, and the heating box and the temperature measuring probe are connected to the pressure chamber;

[0039] The image acquisition and processing component includes: a microscope, a camera and a host computer;

[0040] The lens of the camera faces the microscope, the camera is connected to the host computer, and the camera is used to record the image inside the microscope and transmit the image to the host computer;

[0041] The host computer is used to perform calculations based on the image to obtain the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil.

[0042] The second aspect of the present application discloses a method for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil, which is applied to the system for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil as described in any one of the first aspect. The method includes:

[0043] Determine the mixing ratio of CO2 and N2 required for the experiment, and prepare flue gas according to the mixing ratio;

[0044] After the system for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil meets the experimental conditions, determine the displacement pressure adjustment step of the flue gas displacing crude oil;

[0045] According to the displacement pressure adjustment step, perform the flue gas displacing crude oil experiment for each displacement pressure in sequence, and obtain the image of the diffusion process of flue gas displacing crude oil corresponding to each displacement pressure until the efficiency of the flue gas displacing crude oil reaches 100%;

[0046] Calculate the images of the diffusion process of flue gas displacing crude oil corresponding to each displacement pressure respectively, obtain the efficiency of the flue gas displacing crude oil and the diffusion coefficient of the flue gas displacing crude oil at each displacement pressure, and use the displacement pressure corresponding to the efficiency of 100% as the minimum miscibility pressure of the flue gas displacing crude oil.

[0047] Optionally, in the above determination method, determining the mixing ratio of CO2 and N2 required for the experiment and preparing flue gas according to the mixing ratio includes:

[0048] Determine the volume of the mixing tank for mixing the CO2 and the N2, and the target pressure after the mixing of the CO2 and the N2;

[0049] According to the volume of the mixing tank, the target pressure, and the mixing ratio, respectively determine the gas pressures and the number of moles of the CO2 and the N2;

[0050] According to the magnitude relationship between the gas pressure of the CO2 and the gas pressure of the N2, successively send the determined CO2 and N2 with the number of moles into the mixing tank for mixing to obtain the flue gas.

[0051] Optionally, in the above determination method, calculate the images of the flue gas displacing crude oil diffusion process corresponding to each displacement pressure to obtain the efficiency of the flue gas displacing crude oil at each displacement pressure, including:

[0052] In the images of the flue gas displacing crude oil diffusion process corresponding to each displacement pressure, determine the oil-phase saturation state image and the stable state image of the oil-gas distribution;

[0053] Determine the average gray value of the oil-phase saturation state image and the average gray value of the stable image of the oil-gas distribution;

[0054] Perform calculations based on the background gray value of the completely oil-free state image, the average gray value of the oil-phase saturation state image, and the average gray value of the stable image of the oil-gas distribution to obtain the efficiency of the flue gas displacing crude oil at each displacement pressure;

[0055] Calculate the images of the flue gas displacing crude oil diffusion process corresponding to each displacement pressure to obtain the diffusion coefficient of the flue gas displacing crude oil at each displacement pressure, including:

[0056] According to the gray value change of the image of the flue gas displacing crude oil diffusion process corresponding to each displacement pressure, determine the boundary position of the flue gas displacing crude oil;

[0057] According to the boundary position, determine the diffusion distance and diffusion time of the flue gas displacing crude oil;

[0058] Perform calculations based on the diffusion distance and the diffusion time to obtain the diffusion coefficient of the flue gas displacing crude oil at each displacement pressure.

[0059] Optionally, in the above determination method, it further includes:

[0060] Establish a corrected diffusion coefficient model;

[0061] Use the corrected diffusion coefficient model to correct the diffusion coefficient of the flue gas displacing crude oil at each displacement pressure.

[0062] The present invention provides a system for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil, comprising: a microfluidic chip, a crude oil injection component, a flue gas injection component, a confining pressure control component, a pressure detection component, a temperature control component, a vacuum pumping component, and an image acquisition and processing component; the microfluidic chip is clamped by a chip holder and placed in a pressure chamber, and the microfluidic chip includes 1 observation flow channel and at least 1 pressure protection flow channel; the crude oil injection component is used to inject crude oil into the observation flow channel; the flue gas injection component is used to inject flue gas into the observation flow channel and the pressure protection flow channel; the confining pressure control component is used to control the pressure of the pressure chamber; the pressure detection component is used to detect the pressure of the crude oil and the flue gas injected into the observation flow channel; the temperature control component is used to control the temperature inside the microfluidic chip; the vacuum pumping component is used to pump the connecting pipelines between the microfluidic chip, the crude oil injection component, and the flue gas injection component; the image acquisition and processing component is used to acquire the images of the displacement and diffusion process of the observation flow channel, and obtain the minimum miscibility pressure and diffusion coefficient of the flue gas displacing crude oil according to the acquired images. Since the flue gas in this application is obtained by mixing CO2 and N2, and can synchronously measure the minimum miscibility pressure and diffusion coefficient of the flue gas displacing crude oil, it solves the problem that most of the existing ones take pure gas as the object, it is difficult to effectively reveal the coupling action mechanism of each component in the flue gas mixing system on the displacement behavior, and it is also impossible to synchronously measure the core parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0064] Figure 1 It is a schematic structural diagram of a system for determining the minimum miscibility pressure and diffusion coefficient of two kinds of flue gas displacing crude oil provided by this application;

[0065] Figure 2 It is a physical diagram of a microfluidic chip provided by an embodiment of this application;

[0066] Figure 3 It is a flowchart of a method for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil provided by an embodiment of this application;

[0067] Figure 4 It is a flowchart of another method for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil provided by an embodiment of this application;

[0068] Figure 5A displacement efficiency curve graph of flue gas (70% N2 + 30% CO2) under different displacement pressures at 140°C provided by an embodiment of the present application;

[0069] Figure 6 A corrected curve graph of the gas diffusion coefficient of flue gas (70% N2 + 30% CO2) under different displacement pressures at 140°C provided by an embodiment of the present application. Detailed implementation manners

[0070] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0071] An embodiment of the present application provides a system for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil to solve the problems that most existing ones take pure gas as the object, it is difficult to effectively reveal the coupling action mechanism of each component in the flue gas mixing system on the displacement behavior, and it is also impossible to synchronously measure the core parameters.

[0072] Please refer to Figure 1 , the system for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil mainly includes: a microfluidic chip 1n, a crude oil injection assembly, a flue gas injection assembly, a confining pressure control assembly, a pressure detection assembly, a temperature control assembly, a vacuum pumping assembly, and an image acquisition and processing assembly.

[0073] The microfluidic chip 1n is clamped by a chip holder and placed in a pressure chamber. The microfluidic chip 1n includes 1 observation flow channel and at least 1 pressure protection flow channel. Figure 1 The flow channel at the bottommost in [[ ]] is the observation flow channel, and the 2 flow channels at the upper part are the pressure protection flow channels.

[0074] Since the microfluidic chip 1n includes 1 observation flow channel and at least 1 pressure protection flow channel, the number of flow channels of the microfluidic chip 1n is at least 2.

[0075] The microfluidic chip 1n can adopt a silicon-glass composite structure. The microfluidic chip 1n contains a fluid injection port with a width of 200 μm and a microchannel array with a spacing of 1 μm. Through a serpentine flow channel design, such as a total length of 18 cm; it realizes the full development of the fluid in a limited space, ensures the injection stability and significantly strengthens the interphase mass transfer process, effectively simulates the complex environment of the oil reservoir and promotes the observation of two-phase miscible behavior.

[0076] Exemplarily, the physical diagram of the microfluidic chip 1n in the present application can be as Figure 2As shown, the microfluidic chip 1n is provided with a total of 3 flow channels.

[0077] It should be noted that, as Figure 1 shown, the chip holder and the pressure chamber can form a chip fixture 1g. Among them, the pressure holder is precision machined from 316 stainless steel and surface polished, and is used to fix the microfluidic chip 1n and connect the fluid pipeline; ethylene glycol is injected into the pressure chamber, and pressure loading is achieved through an external constant pressure and constant speed pump. A sapphire glass observation window is provided at the top for experimental observation. The combination of the liquid pressure in the chip holder and the pressure chamber applies pressure to the chip together to ensure the realization of a high-pressure environment during the experiment.

[0078] The crude oil injection assembly is used to inject crude oil into the observation flow channel.

[0079] In some embodiments, as Figure 1 shown, the crude oil injection assembly may include: a first fluid pump 1a, a first intermediate container 1p, a first valve 1b, a second valve 2b, and a third valve 3b.

[0080] The first fluid pump 1a is connected to one end of the first intermediate container 1p through the first valve 1b; the other end of the first intermediate container 1p is sequentially connected to the crude oil injection end of the observation flow channel through the second valve 2b and the third valve 3b; the first intermediate container 1p contains crude oil; the first fluid pump 1a is used to control the crude oil pressure at the crude oil injection end.

[0081] In practical applications, the first fluid pump 1p can be a constant pressure and constant speed pump; specifically, it can be an ISCO high-pressure injection pump, with a working pressure range of 0~60 MPa, a flow rate range of 0.001~60 ml / min, and an accuracy range of ±0.5%. It has two working modes of constant pressure and constant flow, and can control the crude oil flow rate and pressure at the crude oil injection end of the observation flow channel by controlling the first fluid pump 1p.

[0082] When the first valve 1b is in the open state, the pipeline between the first fluid pump 1a and the first intermediate container 1p is in a conducting state; when the second valve 2b and the third valve 3b are both in the open state, the pipeline between the first intermediate container 1p and the crude oil injection end of the observation flow channel is in a conducting state.

[0083] The crude oil can be an alkane, which is the main component of petroleum; of course, it is not limited to this, and it can also be determined according to the application environment and user needs, and all are within the protection scope of this application.

[0084] The flue gas injection assembly is used to inject flue gas into the observation flow channel and the pressure protection flow channel.

[0085] Among them, the injected flue gas is obtained by mixing CO2 and N2. The mixing ratio of CO2 and N2 can be determined according to the application environment and user requirements, and all are within the protection scope of this application.

[0086] In some embodiments, as Figure 1 shown, the number of pressure protection channels is 2. The flue gas injection assembly may include: a second fluid pump 2a, a second intermediate container 2p, a fifth valve 5b, a sixth valve 6b, a seventh valve 7b, an eighth valve 8b, a second tee joint 2c, a third tee joint 3c, a fourth tee joint 4c, and a fifth tee joint 5c.

[0087] The second fluid pump 2a is connected to one end of the second intermediate container 2p through the fifth valve 5b; the other end of the second intermediate container 2p is connected to the flue gas injection end of the observation channel through the sixth valve 6b, the second tee joint 2c, and the seventh valve 7b in sequence, and is connected to the flue gas injection end on one side of the pressure protection channel through the sixth valve 6b, the second tee joint 2c, the eighth valve 8b, the third tee joint 3c, and the fourth tee joint 4c in sequence, and is connected to the flue gas injection end on the other side of the pressure protection channel through the sixth valve 6b, the second tee joint 2c, the eighth valve 8b, the third tee joint 3c, and the fifth tee joint 5c in sequence; the second intermediate container 2p stores flue gas; the second fluid pump 2a is used to control the flue gas pressure at the flue gas injection end.

[0088] When the fifth valve 5b is in the open state, the pipeline between the second fluid pump 2a and the second intermediate container 2p is in the conducting state; when the sixth valve 6b and the seventh valve 7b are in the open state, the pipeline between the second intermediate container 2p and the flue gas injection end of the observation channel is in the conducting state; when the sixth valve 6b and the eighth valve 8b are in the open state, the pipeline between the second intermediate container 2p and the flue gas injection end of the pressure protection channel is in the conducting state.

[0089] In practical applications, in order to ensure the pressure stability of the microfluidic chip 1n, the pressure protection channels of the microfluidic chip 1n are generally set to 2 paths, that is, as Figure 1 shown. In practice, considering the cost, the more the number of pressure protection channels, the higher the corresponding cost. Considering the cost issue, the pressure protection channels can be set to 2 paths. Of course, without considering the cost, the more the number of pressure protection channels, the more stable the chip is in a high-pressure environment.

[0090] It should be noted that the second fluid pump 2a can be a constant pressure and constant speed pump; specifically, it can be an ISCO high-pressure injection pump, with a working pressure range of 0 to 60 MPa, a flow rate range of 0.001 to 60 ml / min, and an accuracy range of ±0.5%. It has two working modes of constant pressure and constant flow, and the flue gas flow rate and pressure at the injection end of the observation flow channel and the pressure protection flow channel can be controlled by controlling the second fluid pump 2a.

[0091] The confining pressure control assembly is used to control the pressure in the pressure chamber.

[0092] In some embodiments, as Figure 1 shown, the confining pressure control assembly may include: a third fluid pump 3a, a third intermediate container 3p, a ninth valve 9b, and a tenth valve 10b.

[0093] The third fluid pump 3a is connected to one end of the third intermediate container 3p through the ninth valve 9b; the other end of the third intermediate container 3p is connected to the pressure chamber through the tenth valve 9b; the third intermediate container 3p contains ethylene glycol solution; the third fluid pump 3a is used to control the pressure of the ethylene glycol solution injected into the pressure chamber.

[0094] When the ninth valve 9b is in the conducting state, the pipeline between the third fluid pump 3a and the third intermediate container 3p is in the conducting state; when the tenth valve 10b is in the conducting state, the pipeline between the third intermediate container 3p and the pressure chamber is in the conducting state.

[0095] In practical applications, the third fluid pump 3a can be a constant pressure and constant speed pump; specifically, it can be an ISCO high-pressure injection pump, with a working pressure range of 0 to 60 MPa, a flow rate range of 0.001 to 60 ml / min, and an accuracy range of ±0.5%. It has two working modes of constant pressure and constant flow, and the ethylene glycol flow rate and pressure flowing into the pressure chamber can be controlled by controlling the third fluid pump 3a.

[0096] Ethylene glycol is injected into the pressure chamber through the confining pressure control assembly as the confining pressure solution. Since ethylene glycol has a relatively high boiling point, it can effectively prevent shaking and is beneficial to ensuring the observation effect.

[0097] In order to ensure the confining pressure effect of the confining pressure control assembly, a circumferential confining pressure clamp can also be set around the pressure chamber.

[0098] The pressure detection assembly is used to detect the crude oil pressure and flue gas pressure injected into the observation flow channel.

[0099] In some embodiments, the pressure detection assembly includes: a first pressure detection assembly and a second pressure detection assembly;

[0100] As Figure 1As shown, the first pressure detection component includes a sixth three-way interface 6c and a first pressure sensor 1d. The first pressure sensor 1d is connected to the main pipeline interface of the sixth three-way 6c. The first branch interface and the second branch interface of the sixth three-way interface 6c are respectively connected to the crude oil output pipeline of the crude oil injection component.

[0101] Specifically, the sixth three-way interface 6c can be connected to the pipeline between the second valve 2b and the third valve 3b. The first pressure sensor 1d is used to detect the crude oil pressure injected into the observation flow channel.

[0102] As Figure 1 shown, the second pressure detection component includes a seventh three-way interface 7c and a second pressure sensor 2d. The second sensor 2d is connected to the main pipeline interface of the seventh three-way interface 7c. The first branch interface and the second branch interface of the seventh three-way interface 7c are respectively connected to the flue gas output pipeline of the flue gas injection component.

[0103] Specifically, the seventh three-way interface 7c can be connected to the pipeline between the second three-way interface 2c and the seventh valve 7b. The second pressure sensor 2d is used to detect the flue gas pressure injected into the observation flow channel.

[0104] In practical applications, the first pressure sensor 1d and the second pressure sensor 2d can be high-pressure sensors, with a maximum pressure resistance of 100 MPa, an instantaneous pressure of 10 MPa, and a pressure accuracy range of ±0.1%.

[0105] The temperature control component is used to control the temperature inside the microfluidic chip 1n.

[0106] In some embodiments, as Figure 1 shown, the temperature control component can include: a heating box and a temperature measurement probe 1h. The heating box and the temperature measurement probe 1h are connected to the pressure chamber.

[0107] The heating box adopts a three-zone independent PID temperature control system, with a temperature control range of room temperature to 300 °C, a temperature control accuracy of ±0.5 °C, and an average heating rate of 4 °C / min, capable of realizing experimental conditions in a high-temperature environment.

[0108] The temperature measurement probe can be a platinum resistance temperature sensor, with a measurement range of -50 to 300 °C, an accuracy of ±0.1 °C, and a response time of less than 1 s, used to accurately measure the temperature of the microfluidic chip 1n inside the holder.

[0109] The vacuum pumping component is used to pump the connecting pipelines between the microfluidic chip 1n, the crude oil injection component, and the flue gas injection component to avoid the influence of air.

[0110] In some embodiments, as Figure 1 shown, the vacuum pumping component can include: a vacuum pump 1f, a fourth valve 4b, and a first three-way interface 1c.

[0111] The vacuum pump 1f is sequentially connected to the main pipeline interface of the first three-way interface 1c through the fourth valve 4b; the first branch interface and the second branch interface of the first three-way interface 1c are respectively connected to the pipeline between the second valve 2b and the third valve 3b; the vacuum pump 1f is used for vacuum pumping.

[0112] In practical applications, since the vacuum pump 1f is connected to the common pipeline of the pressure injection system, the flue gas injection component and the microfluidic chip 1n through the fourth valve 4b, therefore, controlling the operation of the vacuum pump 1f can evacuate the connecting pipeline between the microfluidic chip 1n, the crude oil injection component and the flue gas injection component to ensure the tightness of the system for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil.

[0113] It should be noted that after connecting the pipelines according to the experimental process, a high-temperature and high-pressure microfluidic experimental platform is built, and the tightness test is carried out through the vacuum pumping component to ensure the safety and tightness of the experimental process. Specifically, the three-stage vacuum pumping treatment can be sequentially carried out on the flue gas end, the crude oil end and the confining pressure end.

[0114] The image acquisition and processing component is used to acquire the images of the process of flue gas displacing crude oil in the observation flow channel, and obtain the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil according to the acquired images.

[0115] In some embodiments, as Figure 1 shown, the image acquisition and processing component may include: a microscope 1e, a camera 2e and a host computer 3e.

[0116] The lens of the camera 2e faces the microscope 1e, the camera 2e is connected to the host computer 3e, and the camera 2e is used to record the images in the microscope 1e and transmit the images to the host computer 3e; the host computer 3e is used to calculate according to the images to obtain the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil.

[0117] As Figure 1 shown, the host computer 2e generally consists of a computer and a display. The lens of the camera 2e faces the microscope 1e. The microscope 1e is a high-temperature and high-pressure long-focus microscope, and the working magnification can be adjusted in the wide range of 0-10 times. The optical system is equipped with a high-temperature-resistant multi-layer coated lens group, and is equipped with a high-transmittance quartz observation window to ensure clear imaging quality under high-temperature and high-pressure conditions. The camera 2e is a high-speed CMOS camera matching the microscope 1e, with a maximum resolution of 1024×1024 pixels, and can realize real-time observation under high-temperature and high-pressure conditions.

[0118] The image acquisition and processing component is used to record the images of the process of flue gas displacing crude oil in the observation flow channel, and specifically can record such images throughout the process to provide a basis for subsequent calculations. Specifically, the specific process of calculating the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil based on the images can be seen in the following method, which will not be elaborated here.

[0119] Based on the above principle, the system for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil provided in this embodiment includes: a microfluidic chip 1n, a crude oil injection component, a flue gas injection component, a confining pressure control component, a pressure detection component, a temperature control component, a vacuum pumping component, and an image acquisition and processing component; the microfluidic chip 1n is clamped by a chip holder and placed in a pressure chamber, and the microfluidic chip 1n includes 1 observation flow channel and at least 1 pressure protection flow channel; the crude oil injection component is used to inject crude oil into the observation flow channel; the flue gas injection component is used to inject flue gas into the observation flow channel and the pressure protection flow channel; the confining pressure control component is used to control the pressure of the pressure chamber; the pressure detection component is used to detect the pressure of the crude oil and flue gas injected into the observation flow channel; the temperature control component is used to control the temperature inside the microfluidic chip 1n; the vacuum pumping component is used to pump the connecting pipelines between the microfluidic chip 1n, the crude oil injection component, and the flue gas injection component; the image acquisition and processing component is used to acquire the images of the process of flue gas displacing crude oil in the observation flow channel, and obtain the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil according to the acquired images. Since the flue gas in this application is obtained by mixing CO2 and N2, and can synchronously measure the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil, it solves the problem that most of the existing ones are based on pure gases, which is difficult to effectively reveal the coupling mechanism of each component in the flue gas mixture system on the displacement behavior, and also cannot synchronously measure the core parameters.

[0120] Optionally, another embodiment of this application also provides a method for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil, which can be applied to the system for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil as described in any of the above, please refer to Figure 3 , and this method mainly includes:

[0121] S101. Determine the mixing ratio of CO2 and N2 required for the experiment, and prepare flue gas according to the mixing ratio.

[0122] The flue gas is prepared by mixing CO2 and N2 according to a certain mixing ratio. The specific mixing ratio can be determined according to the application environment and user requirements. Exemplarily, such as the mixing ratio of CO2 and N2 being 7:3, the mixing ratio of CO2 and N2 being 3:7, etc., are all within the protection scope of this application.

[0123] In some embodiments, the specific process of step S101, determining the mixing ratio of CO2 and N2 required for the experiment and preparing the flue gas according to the mixing ratio, mainly includes steps S201 to S203 as follows:

[0124] S201. Determine the volume of the mixing tank for mixing CO2 and N2, and the target pressure after the mixing of CO2 and N2.

[0125] The mixing tank is a container for mixing CO2 and N2, and its specific volume can be determined according to the application environment and user requirements. Exemplarily, the volume of the mixing tank can be 1L.

[0126] The target pressure can be determined according to the pressure resistance of the microfluidic chip, generally not exceeding the maximum pressure-bearing value of the microfluidic chip, the minimum miscibility pressure for displacing crude oil with flue gas, and the maximum instantaneous pressure measurement limit of the pressure sensor in the determination system of the diffusion coefficient.

[0127] Exemplarily, the target pressure is generally any value within 0 - 5 MPa.

[0128] S202. According to the volume of the mixing tank, the target pressure, and the mixing ratio, respectively determine the gas pressures and molar amounts of CO2 and N2.

[0129] After determining the volume of the mixing tank, the target pressure, and the mixing ratio, use the NIST database to obtain the molar volume of a certain gas at the target pressure, convert the molar amount that needs to enter the mixing tank according to the obtained molar volume, then calculate the molar amount required for the other gas according to the mixing ratio, and inversely calculate the molar volume of the other gas from the volume and obtain the corresponding pressure.

[0130] S203. According to the magnitude relationship between the gas pressure of CO2 and the gas pressure of N2, sequentially send the determined molar amounts of CO2 and N2 into the mixing tank for mixing to obtain the flue gas.

[0131] When using the mixing tank to mix CO2 and N2, according to the magnitude relationship between the gas pressure of CO2 and the gas pressure of N2, first inject the low-pressure gas into the mixing tank, and then inject the high-pressure gas to avoid mixing backflow, so as to obtain the flue gas composed of CO2 and N2 with a certain ratio.

[0132] Exemplarily, assume that the volume of the mixing tank for mixing CO2 and N2 is 1L, the target pressure after mixing CO2 and N2 is 3.5 MPa, and the mixing ratio of N2 and CO2 (N2:CO2 = 7:3) is 7:3. Then the specific process of preparing the flue gas according to the mixing ratio can be as follows:

[0133] Using the NIST database, the molar volume of N2 at the target pressure of 3.5 MPa was found to be 0.64082 l / mol. The number of moles of N2 in the container was converted to 1.56 mol, and the required number of moles of CO2 was calculated to be 0.67 mol, with a molar volume of 1.5 l / mol. By back-calculating the molar volume of CO2 and looking it up in NIST, the pressure was found to be 1.35 MPa. When inflating, low-pressure gas is injected first, followed by high-pressure gas to avoid reverse flow mixing, resulting in flue gas composed of CO2 and N2 with a ratio of 7:3.

[0134] S102. After the system for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil meets the experimental conditions, determine the displacement pressure adjustment step of the flue gas displacing crude oil.

[0135] The conditions for the system for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil to meet the experimental conditions are as follows: The system for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil has passed the pressure resistance test and the sealing test, meets the pressure resistance requirements and the sealing requirements, and the confining pressure is stable; Exemplarily, the highest pressure resistance requirement is 100 MPa.

[0136] Specifically, after the system for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil meets the experimental conditions, the crude oil can be injected into the microfluidic chip at a constant pressure using the first fluid pump, adjust the oil-gas pressure difference at both ends of the observation flow channel to 0.02 MPa, observe the oil-phase saturation state through a high-temperature and high-pressure microscope, wait for 30 minutes to ensure that the oil phase reaches the saturation state, and then introduce the displacement gas.

[0137] It should be noted that 0.02 MPa is the minimum pressure to overcome the capillary force, that is, the minimum pressure for the flue gas to displace the crude oil to flow. If the displacement pressure difference is too high, it may lead to an imbalance in the flow between the gas and the liquid. The gas may break through the liquid phase too quickly, resulting in an incomplete and uneven displacement process; too high a displacement pressure difference may also cause instability at the displacement front, affecting the uniformity and efficiency of the displacement, and may even cause the gas to break through prematurely in some areas of the reservoir, thus affecting the accuracy of parameter determination.

[0138] The displacement pressure adjustment step of the flue gas displacing crude oil is the difference between the displacement pressure of each flue gas displacing crude oil experiment and the displacement pressure of the previous flue gas displacing crude oil experiment. Exemplarily, the displacement pressure of the first flue gas displacing crude oil experiment is 15 MPa, the displacement pressure of the second flue gas displacing crude oil experiment is 20 MPa, the displacement pressure of the third flue gas displacing crude oil experiment is 25 MPa... and so on. The displacement pressure adjustment step is 5 MPa / time.

[0139] It should be noted that the specific value of the displacement pressure adjustment step for displacing crude oil with flue gas can be determined according to the application environment and user requirements, and this application does not make specific limitations, all within the protection scope of this application.

[0140] S103. According to the displacement pressure adjustment step, perform the flue gas displacing crude oil experiment on each displacement pressure in turn, and obtain the flue gas displacing crude oil diffusion process image corresponding to each displacement pressure until the efficiency of the flue gas displacing crude oil reaches 100%.

[0141] After determining the displacement pressure adjustment step, the flue gas displacing crude oil experiment can be performed on each displacement pressure in turn. By using the image acquisition and processing component in the system for determining the minimum miscibility pressure and diffusion coefficient of the flue gas displacing crude oil, obtain the flue gas displacing crude oil diffusion process image corresponding to each displacement pressure until the efficiency of the flue gas displacing crude oil reaches 100%.

[0142] Since the minimum miscibility pressure of the flue gas displacing crude oil can be obtained when the efficiency of the flue gas displacing crude oil reaches 100%, the efficiency of the flue gas displacing crude oil reaching 100% can be used as the end condition for performing the flue gas displacing crude oil experiment.

[0143] S104. Calculate the flue gas displacing crude oil diffusion process images corresponding to each displacement pressure respectively, obtain the efficiency of the flue gas displacing crude oil and the diffusion coefficient of the flue gas displacing crude oil at each displacement pressure, and use the displacement pressure corresponding to the efficiency of 100% as the minimum miscibility pressure of the flue gas displacing crude oil.

[0144] In some embodiments, the specific process of calculating the flue gas displacing crude oil diffusion process images corresponding to each displacement pressure in step S104 to obtain the efficiency of the flue gas displacing crude oil at each displacement pressure is as follows, mainly including steps S301 to S303:

[0145] S301. In the flue gas displacing crude oil diffusion process image corresponding to each displacement pressure, determine the oil phase saturation state image and the stable oil-gas distribution state image.

[0146] The oil phase saturation state is the state when the crude oil fills the entire observation flow channel, and the oil phase saturation state image is the corresponding image when the crude oil fills the entire observation flow channel, which can be collected by the image acquisition and processing component in the system for determining the minimum miscibility pressure and diffusion coefficient of the flue gas displacing crude oil.

[0147] The stable state of oil-gas distribution is the state when, during the displacement experiment, after the breakthrough of flue gas, the distribution state of flue gas and crude oil in the observation flow path no longer changes. The image of the stable state of oil-gas distribution is the corresponding image when the distribution state of flue gas and crude oil in the observation flow path no longer changes during the displacement experiment. Similarly, it can be obtained through the image acquisition and processing component in the system for determining the minimum miscibility pressure and diffusion coefficient of displacing crude oil with flue gas.

[0148] S302. Determine the average gray value of the oil-phase saturation state image and the average gray value of the stable oil-gas distribution image.

[0149] In practice, the specific process for determining the average gray value of the oil-phase saturation state image is as follows: perform gray-scale processing on the oil-phase saturation state image to obtain the gray value of each pixel point in the oil-phase saturation state image, and then average the gray values of all pixel points in the oil-phase saturation state image to obtain the average gray value of the oil-phase saturation state image.

[0150] Similarly, the specific process for determining the average gray value of the stable oil-gas distribution image is as follows: perform gray-scale processing on the stable oil-gas distribution image to obtain the gray value of each pixel point in the stable oil-gas distribution image, and then average the gray values of all pixel points in the stable oil-gas distribution image to obtain the average gray value of the stable oil-gas distribution image.

[0151] S303. Calculate based on the background gray value of the completely oil-free state image, the average gray value of the oil-phase saturation state image, and the average gray value of the stable oil-gas distribution image to obtain the efficiency of displacing crude oil with flue gas at each displacement pressure.

[0152] The completely oil-free state image is the image when no crude oil is injected into the observation flow path and no flue gas is injected either, and there is no any flowing liquid or gas in the observation flow path. It can be obtained through the image acquisition and processing component in the system for determining the minimum miscibility pressure and diffusion coefficient of displacing crude oil with flue gas.

[0153] In practice, the gray value of a certain pixel in the background of the completely oil-free state image can be used as the background gray value of the completely oil-free state image; of course, the average value of the gray values of multiple or all pixels in the background of the completely oil-free state image can also be used as the background gray value of the completely oil-free state image.

[0154] The efficiency η of displacing crude oil with flue gas can be calculated according to the following formula:

[0155] η = [(Ginitial - Gfinal) / (Ginitial - Gbackground)]*100%;

[0156] Among them, Ginitial represents the average gray value of the oil-phase saturation state image, Gfinal represents the average gray value of the stable oil-gas distribution image, and Gbackground represents the background gray value of the completely oil-free state image.

[0157] It should be noted that calculating the efficiency of flue gas displacing crude oil by means of gray values can avoid the subjectivity of traditional threshold segmentation.

[0158] It should be noted that after obtaining the efficiency of flue gas displacing crude oil at each displacement pressure, an image of displacement efficiency and displacement pressure can be plotted. Combining the image, the displacement pressure corresponding to 100% efficiency of flue gas displacing crude oil is taken as the minimum miscibility pressure of flue gas displacing crude oil.

[0159] In some embodiments, the specific process of calculating the diffusion coefficient of flue gas displacing crude oil for the image of the diffusion process of flue gas displacing crude oil corresponding to each displacement pressure in step S104 is as follows, mainly including steps S401 to S403:

[0160] S401. Determine the boundary position of flue gas displacing crude oil according to the gray value change of the image of the diffusion process of flue gas displacing crude oil corresponding to each displacement pressure.

[0161] In practice, relevant algorithms are used to grayscale and denoise the displacement diffusion process image to improve the accuracy of analysis.

[0162] The frame difference method is used to calculate the gray value change between consecutive frames in the image of the diffusion process of flue gas displacing crude oil, extract the position of the gas-liquid interface in the displacement process, accurately identify the gas-liquid two-phase interface, and thus determine the boundary position of flue gas displacing crude oil.

[0163] It should be noted that in practice, a microscope camera in the determination system of the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil can be used to shoot high-resolution experimental videos, and each frame in the video is used as an image of the diffusion process of flue gas displacing crude oil.

[0164] S402. Determine the diffusion distance and diffusion time of flue gas displacing crude oil according to the boundary position.

[0165] Based on the boundary position, the frame difference method is also used to identify the position of the gas front in the boundary position. By tracking the position of the gas front, the diffusion distance and diffusion time of flue gas displacing crude oil are obtained.

[0166] Among them, the diffusion distance is the distance of the moving path of the gas front position.

[0167] S403. Calculate based on the diffusion distance and diffusion time to obtain the diffusion coefficient of flue gas displacing crude oil under each displacement pressure.

[0168] The diffusion coefficient D of flue gas displacing crude oil under each displacement pressure can be calculated through a formula. eff :

[0169] D eff = l 2 / 4t diff ;

[0170] where l represents the diffusion distance and t diff represents the diffusion time.

[0171] Based on the above, the method for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil provided in this embodiment is applied to the system for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil as described in any of the above embodiments. By calculating the images of the flue gas displacing crude oil diffusion process corresponding to each displacement pressure respectively, the efficiency of flue gas displacing crude oil and the diffusion coefficient of flue gas displacing crude oil under each displacement pressure are obtained, so as to simultaneously obtain the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil, and solve the problem that the prior art cannot synchronously measure the core parameters in the process of flue gas displacing oil.

[0172] Optionally, in another embodiment provided in this application, please refer to Figure 4 , the method for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil further includes steps S501 and S502:

[0173] S501. Establish a corrected diffusion coefficient model.

[0174] In practical applications, the corrected diffusion coefficient model can be expressed as:

[0175] D P = D0(1 + k(P - P0));

[0176] D P represents the corrected diffusion coefficient of flue gas displacing crude oil, D0 represents the diffusion coefficient corresponding to the minimum miscibility pressure of flue gas displacing crude oil, P0 represents the minimum miscibility pressure of flue gas displacing crude oil, P represents the current displacement pressure of the diffusion coefficient to be corrected, and k is the pressure sensitivity coefficient calibrated through multiple groups of pressure experiments.

[0177] S502. Use the corrected diffusion coefficient model to correct the diffusion coefficient of flue gas displacing crude oil under each displacement pressure.

[0178] In practical applications, the diffusion coefficient of flue gas displacing crude oil at each displacement pressure can be corrected using the above-mentioned modified diffusion coefficient model.

[0179] The method for determining the minimum miscibility pressure and diffusion coefficient for flue gas displacement of crude oil provided in this embodiment further improves the accuracy of the diffusion coefficient during flue gas displacement by establishing a modified diffusion coefficient model to correct the diffusion coefficient of the flue gas displacement of crude oil at each displacement pressure.

[0180] Based on the system and method for determining the minimum miscible pressure and diffusion coefficient of flue gas displacing crude oil provided in the above embodiments, in practice, the experimental temperature is 140°C and the flue gas is (70% N2 + 30% CO2) as an example, combined with Figure 1 、 Figure 5 and Figure 6 The specific process of determining the minimum miscibility pressure and diffusion coefficient of flue gas displacement of crude oil can be as follows:

[0181] ① Configure a specific ratio of flue gas (N2:CO2=7:3), use a 1L pressure-resistant container as the mixing tank, use the NIST database to find the N2 molar volume at the target pressure of 3.5MPa to be 0.64082 l / mol, convert the N2 molar number (mol) in the container to 1.56 mol, calculate the required CO2 molar number (mol) to be 0.67 mol, and its molar volume is 1.5 l / mol. The CO2 molar volume is calculated by reverse calculation and the pressure is 1.35 MPa from NIST. When charging, inject low-pressure gas first and then high-pressure gas to avoid backflow mixing, so as to obtain a flue gas composed of CO2 and N2 with a ratio of 7:3.

[0182] ② Connect the pipelines according to the experimental flow chart and build a system to determine the minimum miscible pressure and diffusion coefficient of flue gas displacement of crude oil. First, conduct a sealing test on the system to ensure the safety and sealing of the experimental process. Then, perform a three-stage vacuum treatment (20 minutes per stage) on the gas end, oil end, and confining pressure chamber.

[0183] ③ After completing the third-stage vacuuming, the confining pressure chamber is saturated by opening the ninth valve 9b and the tenth valve 10b and running the third fluid pump 3a to saturate and empty the confining pressure chamber.

[0184] ④ Saturate the oil sample. Pressurize the crude oil to 2 MPa below the confining pressure and inject it into the microfluidic chip 1n through the third valve 3b. Observe the oil phase saturation state through the microscope 1e. After the oil sample is saturated, open the seventh valve 7b to introduce gas.

[0185] ⑤Perform system pressure boosting. Synchronously boost the confining pressure, oil pressure, and gas pressure to 22 MPa and 20 MPa through the first fluid pump 1a, the second fluid pump 2a, and the third fluid pump 3a. During the pressure boosting process, always maintain the confining pressure 2 MPa higher than the internal pressure.

[0186] ⑥Start the temperature control component and set the target temperature to 140 °C.

[0187] ⑦After the temperature and pressure are stable, adjust the oil pressure to 19.98 MPa to start displacement. When the displacement interface enters the matrix, start video recording, record the displacement time, and observe the displacement mode; after the displacement ends, increase the oil pressure to re-saturate. After the saturation ends, adjust the gas pressure so that the displacement pressure difference is always 0.02 MPa.

[0188] ⑧After completing a set of displacement experiments, gradually increase the gas injection pressure at an experimental interval of 2 MPa, and repeat step ⑦. When the gas pressure rises to 33 MPa, piston displacement is observed and there is no residual oil, and the experiment ends.

[0189] ⑨Analyze the experimental data (calculate the oil displacement efficiency based on the change in gray value). Quantitatively calculate the oil displacement efficiency by analyzing the gray value change of the experimental images. First, calculate its average gray value (Ginitial) through the high-resolution image of the initial oil phase saturation state, and then calculate the final average gray value (Gfinal) after each group of displacements (after the oil and gas distribution is stable). At the same time, complete the calibration of the background gray value (Gbackground) when there is completely no oil. The oil displacement efficiency (η) is calculated by the formula η = [(Ginitial - Gfinal) / (Ginitial - Gbackground)] * 100%. This method avoids the subjectivity of traditional threshold segmentation. Plot the displacement efficiency - displacement pressure image. When the displacement efficiency reaches 100%, it is determined as the minimum miscibility pressure of flue gas and crude oil.

[0190] ⑩Use multi-scale image technology to obtain the diffusion time of the original experiment: First, use relevant algorithms to grayscale and denoise each frame of the high-resolution experimental video to improve the accuracy of analysis. Then, use the frame difference method to calculate the gray value change between consecutive frames, extract the position of the gas-liquid interface during the displacement process, and accurately identify the gas-liquid two-phase interface. According to the leading edge position identified by the frame difference method, use the leading edge tracking algorithm to further accurately identify and locate the specific position of the gas-liquid interface (i.e., the leading edge position). By tracking the leading edge position of the gas, accurately obtain the diffusion path and time of the gas in the medium.

[0191] Based on the obtained experimental data diffusion time tdiff and diffusion distance l above, through the formula: D eff = l 2 / 4tdiff to determine the diffusion coefficient of the gas under different pressures, and then establish a corrected diffusion coefficient model: D P = D0(1 + k(P - P0)); where k is the pressure sensitivity coefficient calibrated through multiple pressure experiments, P0 is the minimum miscibility pressure determined above, and D0 is the diffusion coefficient corresponding to the minimum miscibility pressure, so as to obtain the diffusion coefficient considering pressure correction. By organizing the experimental data, the corrected diffusion coefficient model at this temperature is: D P = D0(1 + 0.007(P - P0)).

[0192] It should be noted that the above is only a specific example of the present application in actual application. In addition, it can be deformed according to the application environment and user needs. As long as the principle is the same as that of the present application, it is within the protection scope of the present application.

[0193] The features described in each embodiment in this specification can be replaced or combined with each other. For the same or similar parts between the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple. For the relevant parts, reference can be made to the partial description of the method embodiment. The systems and system embodiments described above are only illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art can understand and implement it without creative work. Professionals can further realize that the units and algorithm steps of each example described in combination with the embodiments disclosed in this article can be implemented by electronic hardware, computer software, or a combination of the two. To clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described according to functions in the above description. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Professionals can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0194] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily 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 is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

[0195] It should also be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or device comprising the element.

Claims

1. A system for determining the minimum miscibility pressure and diffusion coefficient of crude oil displaced by flue gas, characterized in that, Comprising: A microfluidic chip, a crude oil injection assembly, a flue gas injection assembly, a confining pressure control assembly, a pressure detection assembly, a temperature control assembly, a vacuum pumping assembly, and an image acquisition and processing assembly; The microfluidic chip is clamped by a chip holder and placed in a pressure chamber. The microfluidic chip includes 1 observation flow channel and at least 1 pressure protection flow channel; The crude oil injection assembly is used to inject the crude oil into the observation flow channel; The flue gas injection assembly is used to inject the flue gas into the observation flow channel and the pressure protection flow channel; The confining pressure control assembly is used to control the pressure of the pressure chamber; The pressure detection assembly is used to detect the crude oil pressure and the flue gas pressure injected into the observation flow channel; The temperature control assembly is used to control the temperature inside the microfluidic chip; The vacuum pumping assembly is used to pump vacuum for the connecting pipelines between the microfluidic chip, the crude oil injection assembly, and the flue gas injection assembly; The image acquisition and processing assembly is used to acquire images of the process of flue gas displacing crude oil diffusion in the observation flow channel, and obtain the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil based on the acquired images.

2. The determination system of the minimum miscibility pressure and diffusion coefficient for displacing crude oil with flue gas according to claim 1, wherein The crude oil injection assembly includes: a first fluid pump, a first intermediate container, a first valve, a second valve, and a third valve; The first fluid pump is connected to one end of the first intermediate container through the first valve; The other end of the first intermediate container is sequentially connected to the crude oil injection end of the observation flow channel through the second valve and the third valve; The first intermediate container stores the crude oil; The first fluid pump is used to control the crude oil pressure at the crude oil injection end.

3. The determination system of the minimum miscibility pressure and diffusion coefficient for displacing crude oil with flue gas according to claim 2, wherein The vacuum pumping assembly includes: a vacuum pump, a fourth valve, and a first three-way interface; The vacuum pump is sequentially connected to the main pipeline interface of the first three-way interface through the fourth valve; The first branch interface and the second branch interface of the first three-way interface are respectively connected to the pipeline between the second valve and the third valve; The vacuum pump is used to pump vacuum.

4. The determination system of the minimum miscibility pressure and diffusion coefficient for displacing crude oil with flue gas according to claim 1, wherein The number of the pressure protection flow channels is 2. The flue gas injection assembly includes: a second fluid pump, a second intermediate container, a fifth valve, a sixth valve, a seventh valve, an eighth valve, a second three-way interface, a third three-way interface, a fourth three-way interface, and a fifth three-way interface; The second fluid pump is connected to one end of the second intermediate container through the fifth valve; The other end of the second intermediate container is sequentially connected to the flue gas injection end of the observation flow channel through the sixth valve, the second three-way interface, and the seventh valve, sequentially connected to the flue gas injection end on one side of the pressure protection flow channel through the sixth valve, the second three-way interface, the eighth valve, the third three-way interface, and the fourth three-way interface, and sequentially connected to the flue gas injection end on the other side of the pressure protection flow channel through the sixth valve, the second three-way interface, the eighth valve, the third three-way interface, and the fifth three-way interface; The second intermediate container stores the flue gas; The second fluid pump is used to control the flue gas pressure at the flue gas injection end.

5. The system for determining the minimum miscibility pressure and diffusion coefficient of displacing crude oil with flue gas according to claim 1, characterized in that The pressure detection component includes: a first pressure detection component and a second pressure detection component; The first pressure detection component includes a sixth three-way interface and a first pressure sensor. The first pressure sensor is connected to the main pipeline interface of the sixth three-way. The first branch interface and the second branch interface of the sixth three-way interface are respectively connected to the crude oil output pipeline of the crude oil injection component; The second pressure detection component includes a seventh three-way interface and a second pressure sensor. The second sensor is connected to the main pipeline interface of the seventh three-way. The first branch interface and the second branch interface of the seventh three-way interface are respectively connected to the flue gas output pipeline of the flue gas injection component.

6. The determination system for the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil according to claim 1, characterized in that The confining pressure control component includes: a third fluid pump, a third intermediate container, a ninth valve and a tenth valve; The third fluid pump is connected to one end of the third intermediate container through the ninth valve; The other end of the third intermediate container is connected to the pressure chamber through the tenth valve; The third intermediate container stores ethylene glycol solution; The third fluid pump is used to control the pressure of the ethylene glycol solution injected into the pressure chamber; The temperature control component includes: a heating box and a temperature measuring probe. The heating box and the temperature measuring probe are connected to the pressure chamber; The image acquisition and processing component includes: a microscope, a camera and a host computer; The lens of the camera faces the microscope. The camera is connected to the host computer. The camera is used to record the image inside the microscope and transmit the image to the host computer; The host computer is used to calculate according to the image to obtain the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil.

7. A method for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil, characterized in that Applied to the system for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil according to any one of claims 1-6, the method includes: Determine the mixing ratio of CO2 and N2 required for the experiment, and prepare flue gas according to the mixing ratio; After the system for determining the minimum miscibility pressure and diffusion coefficient of flue gas displacing crude oil meets the experimental conditions, determine the displacement pressure adjustment step of the flue gas displacing crude oil; According to the displacement pressure adjustment step, perform the flue gas displacing crude oil experiment on each displacement pressure in turn, and obtain the image of the diffusion process of flue gas displacing crude oil corresponding to each displacement pressure until the efficiency of the flue gas displacing crude oil reaches 100%; Calculate the images of the diffusion process of flue gas displacing crude oil corresponding to each displacement pressure respectively, obtain the efficiency of the flue gas displacing crude oil and the diffusion coefficient of the flue gas displacing crude oil at each displacement pressure, and use the displacement pressure corresponding to the efficiency of 100% as the minimum miscibility pressure of the flue gas displacing crude oil.

8. The determination method according to claim 7, characterized in that Determine the mixing ratio of CO2 and N2 required for the experiment, and prepare flue gas according to the mixing ratio, including: Determine the volume of the mixing tank for mixing CO2 and N2, and the target pressure after mixing CO2 and N2; According to the volume of the mixing tank, the target pressure and the mixing ratio, determine the gas pressure and mole number of CO2 and N2 respectively; According to the magnitude relationship between the gas pressure of the CO2 and the gas pressure of the N2, the determined moles of the CO2 and the N2 are sequentially fed into the mixing tank for mixing to obtain the flue gas.

9. The determination method according to claim 7, wherein Calculating the flue gas displacement efficiency of crude oil at each displacement pressure for each image of the flue gas displacement of crude oil diffusion process, including: Determining the oil-phase saturation state image and the stable state image of oil-gas distribution in each image of the flue gas displacement of crude oil diffusion process corresponding to each displacement pressure; Determining the average gray value of the oil-phase saturation state image and the average gray value of the stable oil-gas distribution image; Calculating based on the background gray value of the completely oil-free state image, the average gray value of the oil-phase saturation state image, and the average gray value of the stable oil-gas distribution image to obtain the flue gas displacement efficiency of crude oil at each displacement pressure; Calculating the diffusion coefficient of the flue gas displacement of crude oil at each displacement pressure for each image of the flue gas displacement of crude oil diffusion process, including: Determining the boundary position of the flue gas displacement of crude oil according to the gray value change of each image of the flue gas displacement of crude oil diffusion process corresponding to each displacement pressure; Determining the diffusion distance and diffusion time of the flue gas displacement of crude oil according to the boundary position; Calculating based on the diffusion distance and the diffusion time to obtain the diffusion coefficient of the flue gas displacement of crude oil at each displacement pressure.

10. The determination method according to claim 7, wherein It further includes: Establishing a corrected diffusion coefficient model; Using the corrected diffusion coefficient model to correct the diffusion coefficient of the flue gas displacement of crude oil at each displacement pressure.

Images