Visual micro-fluidic hydrate simulation test device and depressurization decomposition method

Abstract

The invention discloses a visual micro-fluidic hydrate simulation test device and a depressurization decomposition method.The visual micro-fluidic hydrate simulation test device comprises a control module, a high-pressure clamp holder, a confining pressure maintaining unit, a micro-fluidic injection unit, a back pressure valve and a first plunger pump, and a micro-fluidic chip is installed in the high-pressure clamp holder; an outlet of the micro-fluidic chip extends to the outer side of the high-pressure clamping device through a discharging pipeline, a first pressure sensor and a back pressure valve are sequentially arranged on the discharging pipeline in the discharging direction, the back pressure valve is connected with the first plunger pump, and the control module is connected with the confining pressure maintaining unit, the micro-fluidic injection unit, the back pressure valve, the first plunger pump and the micro-fluidic chip. The pressure of the back pressure valve is regulated and controlled through the first plunger pump, in the hydrate pressure reduction process, the first plunger pump can be used for regulating and controlling the back pressure valve to control the reduction speed of the pore pressure in the micro-fluidic chip, and pressure reduction at a constant pressure reduction speed can be achieved; the influence on the decomposition of hydrates in the micro-fluidic chip due to difficulty in reducing and adjusting the pore pressure is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrate exploitation, and particularly to a visualization microfluidic controlled hydrate simulation test device and a pressure reduction decomposition method. Background Art

[0002] The high-pressure microfluidic visualization device can provide high-speed capture and visualization observation of the growth and decomposition processes of gas hydrate crystals in porous media. Therefore, this technology is widely used in the quantitative and qualitative analysis of the morphology of natural gas hydrates and the gas-water-hydrate three-phase saturation at the microscale. In the exploitation of natural gas hydrates, pressure reduction is the main method. In the existing pressure reduction methods, a single back-pressure valve is mostly used to control the pressure reduction. However, due to the small volume of the microfluidic chip (only about 2 mL), there is a problem of difficult control of pore pressure, and it is difficult to achieve a constant rate pressure reduction curve, which affects the gas and water production during the hydrate decomposition process and causes the problem that the gas-liquid interface changes too fast to be observed. At the same time, there is a lack of a quantitative detection function for the gas and liquid production of the microfluidic chip.

[0003] Therefore, there is an urgent need for a new visualization microfluidic controlled hydrate simulation test device and a pressure reduction decomposition method to solve the above technical problems. Summary of the Invention

[0004] The present invention aims to solve the above technical problems, that is, to solve the problem that in the existing pressure reduction methods, a single back-pressure valve is mostly used to control the pressure reduction. However, due to the small volume of the microfluidic chip (only about 2 mL), there is a problem of difficult control of pore pressure, and it is difficult to achieve a constant rate pressure reduction curve, which affects the gas and water production during the hydrate decomposition process and causes the problem that the gas-liquid interface changes too fast to be observed. At the same time, there is a lack of a quantitative detection function for the gas and liquid production of the microfluidic chip.

[0005] For this purpose, in a first aspect, the present invention provides a visualization microfluidic controlled hydrate simulation test device, including a control module, a high-pressure clamp, a confining pressure maintaining unit, a microfluidic injection unit, a back-pressure valve, and a first plunger pump. A microfluidic chip is installed in the high-pressure clamp. The confining pressure maintaining unit is configured to be able to adjust the pressure of the surrounding environment where the microfluidic chip is located in the high-pressure clamp. The microfluidic injection unit is connected to the inlet of the microfluidic chip for injecting the raw materials required for hydrate formation. The outlet of the microfluidic chip extends to the outside of the high-pressure clamp through a discharge pipeline. A first pressure sensor and a back-pressure valve are sequentially arranged on the discharge pipeline along the discharge direction. The back-pressure valve is connected to the first plunger pump. A camera is provided directly above the high-pressure clamp. The control module is communicatively connected to the confining pressure maintaining unit, the microfluidic injection unit, the back-pressure valve, the first plunger pump, the camera, and the microfluidic chip respectively.

[0006] In the specific implementation manner of the above-mentioned visualization microfluidic hydrate simulation test device, the visualization microfluidic hydrate simulation test device further includes a gas-liquid production quantification unit, which is installed at the end of the discharge pipeline. The gas-liquid production quantification unit can cooperate with the control module to quantify the liquid and gas generated during the hydrate decomposition process.

[0007] In the specific implementation manner of the above-mentioned visualization microfluidic hydrate simulation test device, the gas-liquid production quantification unit includes a gas-liquid separator, an electronic scale, a second pressure sensor, and a first temperature sensor. The end of the discharge pipeline is connected to the gas-liquid separator, the gas-liquid separator is placed on the electronic scale, and the second pressure sensor and the first temperature sensor are installed at the gas outlet of the gas-liquid separator. The electronic scale, the second pressure sensor, and the first temperature sensor are all communicatively connected to the control module.

[0008] In the specific implementation manner of the above-mentioned visualization microfluidic hydrate simulation test device, the microfluidic injection unit includes a liquid injection unit and a gas injection unit. The liquid injection unit includes a first peristaltic pump and a first piston container. The first peristaltic pump is connected to the first piston container to cooperate with each other to transport liquid to the inlet of the microfluidic chip. The gas injection unit includes a second peristaltic pump, a second piston container, and a gas cylinder. The gas cylinder is connected to the second piston container to inject gas into it. The second peristaltic pump is connected to the second piston container to cooperate with each other to transport gas to the inlet of the microfluidic chip. The first peristaltic pump and the second peristaltic pump are both communicatively connected to the control module.

[0009] In the specific implementation manner of the above-mentioned visualization microfluidic hydrate simulation test device, the liquid outlet of the first piston container is connected to the inlet of the microfluidic chip through a first pipeline. A first valve and a second valve are installed on the first pipeline. The first valve is arranged close to the first piston container, and a third pressure sensor is installed on the first pipeline.

[0010] In the specific implementation manner of the above-mentioned visualization microfluidic hydrate simulation test device, the gas outlet of the gas cylinder is connected to the inlet and outlet of the second piston container through a second pipeline. The inlet and outlet of the second piston container are connected to the first pipeline between the first valve and the second valve through a third pipeline. A fourth pressure sensor is installed at the inlet and outlet part of the second piston container.

[0011] In the specific implementation manner of the above-mentioned visualization microfluidic hydrate simulation test device, the confining pressure maintaining unit includes a second plunger pump and a fifth pressure sensor. The second plunger pump is internally connected to the high-pressure holder through a fourth pipeline, and the fifth pressure sensor is installed on the fourth pipeline.

[0012] In a second aspect, the present invention further provides a method for depressurizing and decomposing visual microfluidic hydrates, which is carried out based on the visual microfluidic hydrate simulation test device described in any one of the first aspects. The depressurization and decomposition method includes the following steps: Control the generation of hydrates inside the microfluidic chip; After the hydrates are generated in the microfluidic chip, the control module controls the internal temperature of the high-pressure holder to rise to the hydrate production temperature, and turns on the camera for shooting; The control module controls the first plunger pump to adjust the pressure of the back pressure valve to reach the same pressure value as the current pore pressure of the microfluidic chip, and then controls the first plunger pump to adjust the pressure of the back pressure valve at a set linear depressurization rate until it drops to the bottom hole flowing pressure, and maintains a constant pressure until the hydrate decomposition is completed, and then turns off the camera.

[0013] In a specific embodiment of the above method for depressurizing and decomposing visual microfluidic hydrates, when the visual microfluidic hydrate simulation test device includes a gas-liquid production quantification unit, the depressurization and decomposition method further includes: Control the gas-liquid production quantification unit to obtain the water production information and gas production information during the depressurization and decomposition process of hydrates in real time; Calculate the water production volume during the depressurization and decomposition process of hydrates according to the water production information, and calculate the gas production volume during the depressurization and decomposition process of hydrates according to the gas production information.

[0014] In a specific embodiment of the above method for depressurizing and decomposing visual microfluidic hydrates, the visual microfluidic hydrate simulation test device includes a gas-liquid separator and an electronic scale. The end of the discharge pipeline is connected to the gas-liquid separator, and the gas-liquid separator is placed on the electronic scale. The step of "controlling the generation of hydrates inside the microfluidic chip" specifically includes: The control module controls the confining pressure maintaining unit to inject water into the high-pressure holder. When the water is full, the microfluidic injection unit is controlled to inject water into the microfluidic chip. During this process, the confining pressure maintaining unit is controlled to maintain the confining pressure value in the high-pressure holder and the pore pressure value in the microfluidic chip to differ by a first set difference until the water production volume can be detected on the electronic scale, and then the injection of water into the microfluidic chip is stopped; The control module controls the first plunger pump to adjust the pressure of the back pressure valve so that its pressure differs from the pore pressure of the microfluidic chip by a second set difference, and then controls the microfluidic injection unit to inject gas into the microfluidic chip to achieve gas displacement of water until the injection of gas stops when the target pressure value is reached. During this process, the confining pressure value in the high-pressure holder and the pore pressure value in the microfluidic chip are maintained to differ by a first set difference; The control module controls the internal temperature of the high-pressure clamp to drop to the hydrate formation temperature to generate hydrates, and controls the camera to take intermittent pictures of the microfluidic chip during the generation process until the pore pressure value in the microfluidic chip is lower than the set pressure value, at which point the picture taking stops.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention regulates the pressure of the back pressure valve through the first piston pump. During the pressure reduction process of hydrates, the first piston pump can be used to regulate the back pressure valve to control the rate of decrease of the pore pressure in the microfluidic chip, enabling pressure reduction at a constant rate of pressure reduction, that is, enabling controllable pressure reduction of the microfluidic chip (pressure reduction rate, bottom hole flowing pressure), avoiding the influence on the decomposition of hydrates in the microfluidic chip due to difficult adjustment of pore pressure reduction, and thus improving the accuracy of analysis of information such as the gas-liquid interface during the hydrate decomposition process.

[0016] 2. The present invention installs a gas-liquid separator at the end of the discharge pipeline, which can separate the produced gas and liquid. The water production volume during the hydrate decomposition process can be calculated based on the weight detected by the electronic scale, and the gas production volume during the hydrate decomposition process can be calculated based on the detection information of the second pressure sensor and the first temperature sensor, that is, realizing the function of quantitatively measuring the gas and water produced by the decomposition of hydrates. Description of the Drawings

[0017] The preferred embodiments of the present invention will be described below with reference to the drawings. In the drawings: Figure 1 is the overall structural schematic diagram of the visual microfluidic hydrate simulation test device provided by the present invention; Figure 2 is the step flow chart of the pressure reduction decomposition method of the visual microfluidic hydrate provided by the present invention; Figure 3 is Figure 2 the specific step flow chart of step S1 in

[0018] List of Reference Numerals in the Drawings: 1. Data collector; 2. Computer; 3. Fourth pressure sensor; 4. Third pressure sensor; 5.; 6. Third valve; 7. Gas cylinder; 8. Second peristaltic pump; 9. First peristaltic pump; 10. Second piston container; 11. First piston container; 12. Water bath; 13. Fourth valve; 14. First valve; 15. Second valve; 16. Second temperature sensor; 17. Circulating water bath driver; 18. Second piston pump; 19. Camera; 20. Microfluidic chip; 21. Light source; 22. First pressure sensor; 23. High-pressure clamp; 24. First piston pump; 25. Back pressure valve; 26. Second pressure sensor; 27. First temperature sensor; 28. Gas-liquid separator; 29. Electronic scale. Detailed implementation mode

[0019] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Apparently, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0020] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the system or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation to the present invention. In addition, the use of terms such as "first" and "second" to define components is only for the convenience of distinguishing the above components. Without further declaration, the above terms have no special meaning and cannot be construed as indicating or implying relative importance.

[0021] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "set", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0022] The present invention relates to the technical field of hydrate exploitation, and particularly to a visualization microfluidic controlled hydrate simulation test device and a pressure reduction decomposition method. The purpose is to solve the problems in the existing pressure reduction methods. In the existing methods, a single back pressure valve is mostly used to control the pressure reduction. However, due to the small volume of the microfluidic chip (only about 2 mL), it is difficult to control the pore pressure. It is difficult to achieve a constant rate pressure reduction curve, which affects the gas and water production during the hydrate decomposition process and causes the gas-liquid interface to change too fast to be observed. At the same time, there is a lack of a quantitative detection function for the gas and liquid production of the microfluidic chip. For this purpose, the visualization microfluidic controlled hydrate simulation test device provided by the present invention includes a control module, a high-pressure holder, a confining pressure maintaining unit, a microfluidic injection unit, a back pressure valve, and a first plunger pump. A microfluidic chip is installed in the high-pressure holder. The confining pressure maintaining unit is configured to be able to adjust the pressure of the surrounding environment where the microfluidic chip is located in the high-pressure holder. The microfluidic injection unit is connected to the inlet of the microfluidic chip for injecting the raw materials required for hydrate formation. The outlet of the microfluidic chip extends to the outside of the high-pressure holder through a discharge pipeline. A first pressure sensor and a back pressure valve are sequentially arranged on the discharge pipeline along the discharge direction. The back pressure valve is connected to the first plunger pump. A camera is provided directly above the high-pressure holder. The control module is communicatively connected to the confining pressure maintaining unit, the microfluidic injection unit, the back pressure valve, the first plunger pump, the camera, and the microfluidic chip. The present invention regulates the pressure of the back pressure valve through the first plunger pump. During the pressure reduction process of the hydrate, the first plunger pump can be used to regulate the back pressure valve to control the pressure reduction rate of the pore pressure in the microfluidic chip, and a constant pressure reduction rate can be achieved, that is, pressure-controlled pressure reduction of the microfluidic chip (pressure reduction rate, bottom hole flowing pressure) can be realized.

[0023] Next, the visualization microfluidic controlled hydrate simulation test device and the pressure reduction decomposition method provided by the embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0024] Refer to Figure 1 , the present invention provides a visualization microfluidic controlled hydrate simulation test device, including a control module, a high-pressure holder, a confining pressure maintaining unit, a microfluidic injection unit, a back pressure valve, and a first plunger pump. A microfluidic chip is installed in the high-pressure holder. The confining pressure maintaining unit is configured to be able to adjust the pressure of the surrounding environment where the microfluidic chip is located in the high-pressure holder. The microfluidic injection unit is connected to the inlet of the microfluidic chip for injecting the raw materials required for hydrate formation. The outlet of the microfluidic chip extends to the outside of the high-pressure holder through a discharge pipeline. A first pressure sensor and a back pressure valve are sequentially arranged on the discharge pipeline along the discharge direction. The back pressure valve is connected to the first plunger pump. A camera is provided directly above the high-pressure holder. The control module is communicatively connected to the confining pressure maintaining unit, the microfluidic injection unit, the back pressure valve, the first plunger pump, the camera, and the microfluidic chip.

[0025] Specifically, the control module includes a data collector and a computer that are interconnected. The data collector transfers relevant data to the computer, and the computer controls the actions of corresponding components. Regarding the specific structure of the control module, it is prior art known to those skilled in the art and will not be elaborated in detail here. The present invention further includes a light source for providing sufficient brightness when the camera takes pictures.

[0026] The high-pressure gripper is connected to the circulating water bath driver, and the circulating water bath driver is connected to the water bath tank. The high-pressure gripper can heat or cool the water injected into the high-pressure gripper through the circulating water bath driver and the water bath tank to provide the temperature conditions for hydrate formation in the microfluidic chip. A second temperature sensor is provided on the high-pressure gripper for detecting the temperature of the confining pressure liquid inside the high-pressure gripper. The circulating water bath driver is connected to the control module, and the temperature regulation of the confining pressure liquid (i.e., water) inside the high-pressure gripper is controlled by collecting the temperature information detected by the second temperature sensor.

[0027] In one embodiment, the confining pressure maintaining unit includes a second plunger pump and a fifth pressure sensor. The second plunger pump is internally connected to the high-pressure gripper through a fourth pipeline, and the fifth pressure sensor is installed on the fourth pipeline. Water is injected into the high-pressure gripper through the second plunger pump to increase the pressure. The adjustment of the pressure inside the high-pressure gripper by the second plunger pump is controlled according to the pore pressure information of the microfluidic chip to continuously maintain a pressure difference of 1 MPa with the microfluidic chip at all times, providing confining pressure for the microfluidic chip.

[0028] In one embodiment, the visual microfluidic hydrate simulation test device further includes a gas-liquid production quantification unit. The gas-liquid production quantification unit is installed at the end of the discharge pipeline and can cooperate with the control module to quantify the liquid and gas generated during the hydrate decomposition process.

[0029] In the above embodiment, preferably, the gas-liquid production quantification unit includes a gas-liquid separator, an electronic scale, a second pressure sensor, and a first temperature sensor. The end of the discharge pipeline is connected to the gas-liquid separator, the gas-liquid separator is placed on the electronic scale, and the gas outlet of the gas-liquid separator is equipped with a second pressure sensor and a first temperature sensor. The electronic scale, the second pressure sensor, and the first temperature sensor are all communicatively connected to the control module.

[0030] In one embodiment, the microfluidic injection unit includes a liquid injection unit and a gas injection unit. The liquid injection unit includes a first peristaltic pump and a first piston container. The first peristaltic pump is connected to the first piston container to cooperate with each other to transport liquid to the inlet of the microfluidic chip. The gas injection unit includes a second peristaltic pump, a second piston container and a gas cylinder. The gas cylinder is connected to the second piston container to inject gas into it. The second peristaltic pump is connected to the second piston container to cooperate with each other to transport gas to the inlet of the microfluidic chip. Both the first peristaltic pump and the second peristaltic pump are communicatively connected to the control module.

[0031] Specifically, the liquid outlet of the first piston container is connected to the inlet of the microfluidic chip through a first pipeline. A first valve and a second valve are installed on the first pipeline. The first valve is arranged close to the first piston container. A third pressure sensor is installed on the first pipeline. The gas outlet of the gas cylinder is connected to the inlet and outlet of the second piston container through a second pipeline. The inlet and outlet of the second piston container are connected to the first pipeline between the first valve and the second valve through a third pipeline. A fourth pressure sensor is installed at the inlet and outlet of the second piston container.

[0032] More specifically, a third valve is installed at the gas outlet of the gas cylinder. A fourth valve is arranged on the second pipeline between the second piston container and the first pipeline.

[0033] The usage method of the microfluidic injection unit is as follows: Water is injected (into the microfluidic chip) at a constant rate of a set rate (0.01 mL / min) through the first peristaltic pump and the first piston container. The gas-liquid distribution in the pores of the microfluidic chip is photographed in real time by a camera until the entire microfluidic chip is filled with water and linear water production is observed by an electronic scale, then the entire microfluidic system is filled with water. Then, the third valve is opened by the gas cylinder to inject gas into the second piston container until the gas cylinder pressure, and the back pressure valve is pressurized by the first plunger pump to be 0.1 MPa less than the gas cylinder pressure. Gas displacement of water is carried out by the second peristaltic pump at 0.001 mL / min and the second piston container. The weight of the electronic scale is recorded during the displacement process to quantify the initial gas saturation and water saturation in the microfluidic chip, so as to quantify the initial gas-liquid ratio before hydrate formation.

[0034] In another embodiment, referring to Figure 2 , the present invention also provides a method for depressurization decomposition of visual microfluidic hydrates, which is carried out based on the visual microfluidic hydrate simulation test device described in any one of the above embodiments. The depressurization decomposition method includes the following steps: S1, controlling the generation of hydrates inside the microfluidic chip; S2, after the hydrates are generated in the microfluidic chip, the control module controls the temperature inside the high-pressure clamp to rise to the hydrate production temperature, and the camera is turned on for shooting; S3. The control module controls the first plunger pump to regulate the pressure of the backpressure valve until it reaches the same pressure value as the pore pressure of the current microfluidic chip. Then, the control module controls the first plunger pump to regulate the pressure of the backpressure valve at a set linear pressure reduction rate until it drops to the bottom-hole flowing pressure and maintains a constant pressure until the hydrate decomposition is completed, and then the camera is turned off. During the hydrate decomposition process, the camera continuously takes pictures of the microfluidic chip to obtain the gas-liquid interface information during the hydrate decomposition process. It should be noted that the value of the set linear pressure reduction rate is set according to the actual situation, and this application does not make specific limitations.

[0035] In step S3, the specific judgment steps for maintaining a constant pressure until the hydrate decomposition is completed are divided into two methods. The first method is: to judge according to whether the gas-liquid separation interface of the hydrate photographed by the camera changes. If the gas-liquid separation interface does not change, it means that the hydrate decomposition is completed. The second method is: to judge according to the pressure data detected by the second pressure sensor. If no gas production is judged based on the pressure value, it means that the hydrate decomposition is completed. One of these two judgment methods is selected for use.

[0036] In the above embodiment, preferably, refer to Figure 3 , the visual microfluidic hydrate simulation test device includes a gas-liquid separator and an electronic scale. The end of the discharge pipeline is connected to the gas-liquid separator, and the gas-liquid separator is placed on the electronic scale. The step S1 of "controlling the generation of hydrate inside the microfluidic chip" specifically includes: S11. The control module controls the confining pressure maintaining unit to inject water into the high-pressure holder. When the water is filled, the control module controls the microfluidic injection unit to inject water into the microfluidic chip. During this process, the control module controls the confining pressure maintaining unit to maintain the confining pressure value in the high-pressure holder and the pore pressure value in the microfluidic chip to differ by a first set difference until the water production can be detected on the electronic scale, and then stop injecting water into the microfluidic chip; S12. The control module controls the first plunger pump to regulate the pressure of the backpressure valve so that its pressure differs from the pore pressure of the microfluidic chip by a second set difference. At this time, this pressure is less than the pore pressure, so that gas can displace water. Then, the control module controls the microfluidic injection unit to inject gas into the microfluidic chip to achieve gas displacement of water until the injection of gas stops when the target pressure value is reached. During this process, the confining pressure value in the high-pressure holder and the pore pressure value in the microfluidic chip are maintained to differ by a first set difference; at this time, the confining pressure value is greater than the pore pressure value to ensure that the microfluidic chip is not damaged; S13. The control module controls the temperature inside the high-pressure holder to drop to the hydrate formation temperature to generate hydrates. During the generation process, the control module controls the camera to take intermittent pictures of the microfluidic chip until the pore pressure value in the microfluidic chip is lower than the set pressure value and then stop taking pictures.

[0037] In the above embodiments, the specific values of the first set difference and the second set difference are not specifically limited. Exemplarily, the first set difference is 1 MPa and the second set difference is 0.1 MPa. Regarding the value of the target pressure, the present application is not specifically limited, and it is selected and set according to the actual situation on the premise of not deviating from the basic principle of the present invention.

[0038] Step S12 is specifically as follows: Water is injected (into the microfluidic chip) at a constant rate (such as 0.01 mL / min) through the first peristaltic pump and the first piston container. The gas-liquid distribution in the pores of the microfluidic chip is photographed in real time by a camera until the microfluidic chip is completely filled with water and linear water production is observed by the electronic scale, then the entire microfluidic system is completely filled with water; then, the third valve is opened by the gas cylinder to inject gas into the second piston container until the gas cylinder pressure, and the back pressure valve is pressurized by the first plunger pump to be 0.1 MPa less than the gas cylinder pressure. The second peristaltic pump is used to perform gas displacement of water with the second piston container at a set rate (such as 0.01 mL / min). During the displacement process, the weight of the electronic scale is recorded to quantify the initial gas saturation and water saturation in the microfluidic chip, so as to quantify the initial gas-liquid ratio before hydrate formation. The pressure in the microfluidic chip can be detected by the first pressure sensor, so as to control the pressure in the high-pressure holder by the second plunger pump according to this pressure, and regulate the pressure of the back pressure valve according to this pressure.

[0039] According to the weight of the discharged water m w Calculate the initial water saturation of the microfluidic chip S A0 And the initial gas saturation S G0 .

[0040] The specific calculation formula is: ; . Wherein, is the volume of the microfluidic chip.

[0041] Step S13 is specifically as follows: The control module controls the circulating water bath to cool the confining liquid in the high-pressure holder to 2 °C at a cooling rate of 5 K / h for the formation of natural gas hydrates. During the experiment, the computer controls the camera to continuously take pictures of the entire microfluidic chip at a fixed frequency of 2 s / picture. When the change of the first pressure sensor is lower than 10 KPa / hr, the computer considers that the formation of natural gas hydrates is over and closes the camera.

[0042] In one embodiment, when the visual microfluidic hydrate simulation test device includes a gas-liquid production quantification unit, the pressure reduction decomposition method further includes: Controlling the gas-liquid production quantification unit to obtain the water production information and gas production information during the pressure reduction decomposition process of the hydrate in real time; Calculate the water production during the hydrate depressurization decomposition process based on the produced water information, and calculate the gas production during the hydrate depressurization decomposition process based on the produced gas information.

[0043] When the hydrate is formed and not yet decomposed, control the value of the electronic scale to zero, which is convenient for measuring the water production.

[0044] Specifically, obtain the water production information separated by the gas-liquid separator in real time through the electronic scale, calculate the water production during the hydrate depressurization decomposition process based on this water production information, obtain the pressure and temperature of the gas discharged from the gas-liquid separator in real time through the second pressure sensor and the first temperature sensor, and calculate the gas production during the hydrate depressurization decomposition process based on the pressure and temperature, these produced gas information.

[0045] The specific calculation is: Recorded by the electronic scale m w Continuously record the water production, and measure the pressure through the second pressure sensor P c and measure the temperature through the first temperature sensor T c Continuously calculate the gas production.

[0046] The molar amount of water production is: n w = m w / M w Among them, m w is the water production recorded by the electronic scale from the start to the completion of decomposition, M w is the molar mass of water, 18 g / mol.

[0047] The molar amount of gas production is: n g = P c V c / Z / R / T c Among them, P c is the pressure of the gas separated by the gas-liquid separator, V c is the volume of the gas-liquid separator, Z is the compressibility factor, R is the gas constant, T c is the temperature of the gas separated by the gas-liquid separator.

[0048] The decomposition and pressure reduction method designed by the present invention can also be applied to the generation and decomposition characteristics of natural hydrates, the microscopic changes in the morphology of hydrates, the gas-liquid interface changes in unconventional gas reservoirs such as coalbed methane and shale gas, relative permeability testing, and can also be used for the sequestration of carbon dioxide hydrates on the deep-sea seabed, etc.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the protection scope of the technical solutions of the embodiments of the present invention.

Claims

1. A visual microfluidic hydrate simulation test device, characterized in that: It comprises a control module, a high-pressure clamp, a confining pressure maintaining unit, a microfluidic injection unit, a back pressure valve and a first plunger pump, wherein a microfluidic chip is installed in the high-pressure clamp, and the confining pressure maintaining unit is configured to be able to adjust the pressure of the surrounding environment of the microfluidic chip in the high-pressure clamp, the microfluidic injection unit is connected to the inlet of the microfluidic chip for injecting raw materials required for hydrate generation, the outlet of the microfluidic chip extends to the outside of the high-pressure clamp through a discharge pipeline, a first pressure sensor and a back pressure valve are sequentially arranged on the discharge pipeline along the discharge direction, the back pressure valve is connected to the first plunger pump, a camera is arranged directly above the high-pressure clamp, and the control module is respectively connected to the confining pressure maintaining unit, the microfluidic injection unit, the back pressure valve, the first plunger pump, the camera and the microfluidic chip.

2. The visualized microfluidic hydrate simulation test device according to claim 1, characterized in that: The visualized microfluidic hydrate simulation test device also includes a gas-liquid output quantitative unit, which is installed at the end of the discharge pipeline. The gas-liquid output quantitative unit cooperates with the control module to quantify the liquid and gas generated during the hydrate decomposition process.

3. The visualized microfluidic hydrate simulation test device according to claim 2, characterized in that: The gas-liquid output quantitative unit includes a gas-liquid separator, an electronic scale, a second pressure sensor and a first temperature sensor. The end of the discharge pipeline is connected to the gas-liquid separator, and the gas-liquid separator is placed on the electronic scale. The gas outlet of the gas-liquid separator is installed with the second pressure sensor and the first temperature sensor. The electronic scale, the second pressure sensor and the first temperature sensor are all communicatively connected to the control module.

4. The visualized microfluidic hydrate simulation test device according to claim 1, characterized in that: The microfluidic injection unit includes a liquid injection unit and a gas injection unit, the liquid injection unit includes a first horizontal flow pump and a first piston container, the first horizontal flow pump is connected to the first piston container to cooperate with each other to transport liquid to the inlet of the microfluidic chip, the gas injection unit includes a second horizontal flow pump, a second piston container and a gas cylinder, the gas cylinder is connected to the second piston container to inject gas into the interior, the second horizontal flow pump is connected to the second piston container to cooperate with each other to transport gas to the inlet of the microfluidic chip, and the first horizontal flow pump and the second horizontal flow pump are both communicatively connected to the control module.

5. The visualized microfluidic hydrate simulation test device according to claim 4, characterized in that: The liquid outlet of the first piston container is connected to the inlet of the microfluidic chip through a first pipeline, a first valve and a second valve are installed on the first pipeline, the first valve is arranged close to the first piston container, and a third pressure sensor is installed on the first pipeline.

6. The visualized microfluidic hydrate simulation test device according to claim 5, characterized in that: The gas outlet of the gas cylinder is connected to the inlet and outlet of the second piston container through a second pipeline, the inlet and outlet of the second piston container are connected to the first pipeline between the first valve and the second valve through a third pipeline, and a fourth pressure sensor is installed at the inlet and outlet of the second piston container.

7. The visualized microfluidic hydrate simulation test device according to claim 1, characterized in that: The confining pressure maintaining unit includes a second plunger pump and a fifth pressure sensor. The second plunger pump is connected to the interior of the high-pressure clamp through a fourth pipeline. The fifth pressure sensor is installed on the fourth pipeline.

8. A visual microfluidic hydrate decomposition method, characterized in that: Based on the visualized microfluidic hydrate simulation test device according to any one of claims 1 to 7, the decompression decomposition method comprises the following steps: Controlling the generation of hydrates inside the microfluidic chip; After hydrates are generated in the microfluidic chip, the control module controls the internal temperature of the high-pressure holder to rise to the hydrate mining temperature, and turns on the camera to take pictures; The control module controls the first plunger pump to adjust the pressure of the back pressure valve to reach a pressure value that is the same as the current pore pressure of the microfluidic chip, and then controls the first plunger pump to adjust the pressure of the back pressure valve at a set linear pressure reduction rate until it drops to the bottom hole flow pressure, and maintains a constant pressure until the hydrate decomposition is completed, and then turns off the camera.

9. The visualized microfluidic hydrate decomposition method according to claim 8, characterized in that: When the visualized microfluidic hydrate simulation test device includes a gas-liquid output quantitative unit, the decompression decomposition method further includes: Controlling the gas-liquid production quantitative unit to obtain water production information and gas production information in the hydrate decomposition process in real time; The water production amount of the hydrate decomposition process during decompression is calculated according to the water production information, and the gas production amount of the hydrate decomposition process during decompression is calculated according to the gas production information.

10. The visualized microfluidic hydrate decomposition method according to claim 8 or 9, characterized in that: The visualized microfluidic hydrate simulation test device comprises a gas-liquid separator and an electronic scale, the end of the discharge pipeline is connected to the gas-liquid separator, and the gas-liquid separator is placed on the electronic scale. The step of "controlling the generation of hydrates inside the microfluidic chip" specifically comprises: The control module controls the confining pressure maintaining unit to inject water into the high-pressure clamp, and controls the microfluidic injection unit to inject water into the microfluidic chip when the high-pressure clamp is full of water. In the process, the confining pressure maintaining unit is controlled to maintain a confining pressure value in the high-pressure clamp and a pore pressure value in the microfluidic chip with a first set difference value until the water production can be detected on the electronic scale, and then stops injecting water into the microfluidic chip; The control module controls the first plunger pump to adjust the pressure of the back pressure valve so that the pressure thereof differs from the pore pressure of the microfluidic chip by a second set difference, and then controls the microfluidic injection unit to inject gas into the microfluidic chip to achieve gas-driven water displacement, and stops injecting gas when a target pressure value is reached, and in this process, the confining pressure value in the high-pressure clamp and the pore pressure value in the microfluidic chip are maintained to differ by the first set difference; The control module controls the internal temperature of the high-pressure clamp to drop to the hydrate formation temperature to generate hydrates, and controls the camera to take pictures of the microfluidic chip at intervals during the generation process until the pore pressure value in the microfluidic chip is lower than the set pressure value and stops taking pictures.

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