A method for studying hydrate secondary phase transition behavior and a pressure decoupling microfluidic device used thereby

Abstract

The application relates to a method for studying hydrate secondary phase transition behavior and a pressure-decoupling microfluidic device used in the method, and the pressure-decoupling microfluidic device comprises a reaction unit, a fluid conveying and control unit, an online detection and characterization unit and a data acquisition and control unit; the reaction unit comprises a reaction kettle, a microfluidic chip arranged in the reaction kettle and a pressure limiting structure arranged in the microfluidic chip; the fluid conveying and control unit is connected with the reaction unit; the online detection and characterization unit is connected with the reaction unit; and the data acquisition and control unit is connected with the reaction unit, the fluid conveying and control unit and the online detection and characterization unit respectively. The microfluidic device of the application arranges the microfluidic chip in the reaction kettle, realizes decoupling control of the internal pressure of the microfluidic chip and the external pressure through the pressure limiting structure, realizes independent control of the background pressure and the displacement pressure difference, and breaks through the technical bottleneck that high pressure and high resolution cannot be compatible.

Description

Technical Field

[0001] This invention relates to the field of basic research and experimental technology for natural gas hydrate extraction, and in particular to a research method for the secondary phase transition behavior of hydrates and the pressure decoupling microfluidic device used therein. Background Technology

[0002] Natural gas hydrates, as a vast and promising clean energy source, have made their safe and efficient extraction a key research focus in the energy field. During extraction, fluids (such as thermal fluids, CO2, or inhibitors) are often injected to induce hydrate decomposition and release methane. However, fluid intrusion easily triggers a "secondary phase transition" behavior in hydrates, where local decomposition is followed by regeneration in adjacent areas. This process significantly alters reservoir flow characteristics, leading to channel blockage, increased sand production, and reservoir instability. Therefore, revealing the microscopic dynamics of hydrates during fluid intrusion is crucial for achieving safe and controllable extraction.

[0003] Various visualization experimental techniques exist for understanding the phase transition and seepage mechanisms of hydrates at the pore scale. One mainstream approach is a confined pressure clamp-type high-pressure microfluidic system. For example, CN115753773A discloses a simulation test method and apparatus for gas hydrates, including: a high-pressure reaction unit comprising a reaction vessel and a microfluidic chip disposed within the reaction vessel, the reaction vessel including a first visualization window; and an image capturing unit comprising an adjustable support, a movable component movably connected to the adjustable support, and an image capturing element fixed to the movable component. The image capturing element is disposed above and facing the first visualization window. The movable component is used to move the image capturing element along a first direction and a second direction. The adjustable support is used to move the movable component and the image capturing element along a third direction, such that the imaging range of the image capturing element encompasses the entire first visualization window, thereby capturing images in real time showing the changes in the gas-liquid-hydrate three-phase interface within the entire microfluidic chip. The first direction, the second direction, and the third direction are perpendicular to each other, and the third direction is parallel to the central axis of the reaction vessel. The simulation experimental device further includes a microfluidic injection unit, a data acquisition unit, and a processing unit. The microfluidic injection unit is used to inject gas and water into the microfluidic chip. The data acquisition unit is used to acquire signals within the microfluidic chip, including pressure and temperature signals during the reaction of gas and water to form gas hydrates and during the decomposition of the gas hydrates. The processing unit is used to receive the signals acquired by the data acquisition unit and adjust the pressure and / or temperature during the formation or decomposition of the gas hydrates according to the signals. The data acquisition unit includes a pressure sensor and a temperature sensor. The pressure sensor is used to detect the pressure within the microfluidic chip and also to detect the pressure within the reaction vessel. The processing unit also controls the microfluidic chip and the reaction vessel to maintain a constant pressure difference based on the pressure sensed by the pressure sensor. The temperature sensor is used to detect the temperature within the microfluidic chip. The high-pressure reaction unit also includes a confining pressure pump, which is connected to the reaction vessel and is used to adjust the pressure inside the reaction vessel. The confining pressure pump is electrically connected to the pressure sensor, and the processing unit controls the operation of the confining pressure pump based on the pressure signal sensed by the pressure sensor.

[0004] CN113818843A discloses a microfluidic experimental apparatus and method for consolidating natural gas hydrate reservoirs, comprising: a microfluidic chip on which a reaction chamber is formed; a deep-sea natural gas hydrate reservoir construction device having a first grouting channel connecting the reaction chamber, the deep-sea natural gas hydrate reservoir construction device being used to construct a deep-sea natural gas hydrate reservoir within the reaction chamber; and a MICP slurry injection device having a second grouting channel connecting the reaction chamber, for injecting MICP slurry into the deep-sea natural gas hydrate reservoir within the reaction chamber.

[0005] Although the above techniques have made significant progress in observing hydrate phase transitions under high pressure, they all share a significant common drawback: (1) The background pressure is coupled with the displacement pressure difference, making it impossible to simulate continuous micro-intrusion. In confined pressure clamp-type systems, the internal pressure of the chip must follow changes in the confined pressure. To inject fluid into the chip, the injection pump pressure must be higher than the confined pressure to drive the fluid, resulting in the displacement pressure differential being superimposed on the background pressure. Experiments show that when the background pressure is ≥5MPa, even with an extremely low injection rate of 1μL / min, the pressure fluctuations of the injection pump are amplified, leading to localized instantaneous overpressure inside the chip, which can easily cause chip rupture or seal failure. Therefore, existing technologies can only use intermittent "inject-stop-inject" injection, which cannot simulate the slow, continuous intrusion process of fluid in the reservoir over hours or even days. In integrated high-pressure chips, the internal pressure of the chip is directly equal to the system pressure, and the problem of the displacement pressure differential being inseparable from the background pressure is still faced during injection. Although this approach avoids the confined pressure medium, the chip itself bears the entire pressure differential, requiring extremely high material strength and sealing, and the flow rate control accuracy of the injected fluid is limited by the pump pulses.

[0006] (2) It is impossible to independently control the background pressure and displacement velocity, making it difficult to quantitatively trigger secondary nucleation. The conditions for the secondary phase transition (decomposition followed by regeneration) of hydrates are extremely sensitive: the CH4 released from the decomposition front needs to reach local supersaturation, but cannot be washed away too quickly. This requires that the background pressure (which determines CH4 solubility) and the displacement flow rate (which determines the transport rate of CH4) can vary independently during the experiment. In existing technologies, the two are highly coupled: changing the background pressure will inevitably affect the pressure balance inside the chip, and changing the flow rate will inevitably cause fluctuations in the injection pressure, making it impossible to establish a quantitative calibration experiment with "fixed background pressure and gradient increase in flow rate".

[0007] (3) Lack of macro-micro cross-scale correlation capability Existing microfluidic devices only obtain image information at the pore scale and cannot simultaneously record macroscopic responses such as pressure, temperature, and gas production volume of the entire system. While conventional high-pressure reactors have macroscopic monitoring capabilities, their resolution is insufficient to identify microscopic mechanisms. This disconnect makes it impossible to establish a quantitative relationship between "secondary nucleation within pores" and "reservoir permeability reduction."

[0008] (4) Poor experimental repeatability and expensive equipment The seals of the confining pressure holder are prone to aging and leakage after repeated pressurization, and the confining pressure medium may seep into the chip and contaminate the sample. Integrated high-voltage chips require extremely high processing precision, with a single chip costing thousands of yuan, and are difficult to clean and reuse after experiments. Although methods such as large-scale synchrotron radiation CT can provide three-dimensional imaging, their low temporal resolution (minute-level) and extremely high equipment costs prevent their widespread adoption in conventional laboratories.

[0009] Therefore, existing technologies generally face the core contradiction of "the incompatibility between high pressure and high resolution," lacking an integrated experimental platform that can simultaneously meet the requirements of high-pressure environment, micron-level real-time imaging, continuous micro-injection, and multi-physics field coordinated control. Therefore, there is an urgent need to develop a novel device and research method for studying the secondary phase transition behavior of hydrates to overcome the aforementioned technological bottlenecks. Summary of the Invention

[0010] To address the aforementioned technical problems, this invention provides a method for studying the secondary phase transition behavior of hydrates and the pressure-decoupled microfluidic device used therein. The pressure-decoupled microfluidic device of this invention places a microfluidic chip inside a reactor and achieves decoupled control of the internal and external pressures of the chip through a pressure-limiting structure, thereby enabling independent control of the background pressure and the displacement pressure difference, breaking through the technical bottleneck that high pressure and high resolution cannot be achieved simultaneously.

[0011] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a pressure-decoupled microfluidic device, which includes a reaction unit, a fluid delivery and control unit, an online detection and characterization unit, and a data acquisition and control unit; The reaction unit includes a reaction vessel, a microfluidic chip disposed inside the reaction vessel, and a pressure limiting structure disposed inside the microfluidic chip; The fluid delivery and control unit is connected to the reaction unit; The online detection and characterization unit is connected to the reaction unit; The data acquisition and control unit is connected to the reaction unit, the fluid transport and control unit, and the online detection and characterization unit, respectively.

[0012] In this invention, within the reaction unit, the internal chamber of the reactor is used to contain the pressure medium and form a first pressure field. A microfluidic chip is detachably disposed within the internal chamber of the reactor, forming a second pressure field independent of the first pressure field inside the microfluidic chip. The pressure-limiting structure has flow-limiting characteristics, used to dynamically limit the real-time pressure difference between the inside and outside of the microfluidic chip to a preset safety threshold (less than 1 MPa), thereby enabling independent control of the first pressure field and the displacement pressure difference. Simultaneously, this invention uses a fluid delivery and control unit to inject working fluid into the microfluidic chip at a certain flow rate, forming a displacement pressure difference distinct from the first pressure field. An online detection and characterization unit is used to collect images and spectral data of the hydrate phase change within the microfluidic chip in real time, and a data acquisition and control unit is used to achieve synchronous acquisition and closed-loop control of multiple parameters.

[0013] It should be noted that the data acquisition and control unit is based on the LabVIEW or Python platform, and synchronously acquires the pressure and temperature inside the reactor, the pressure at the inlet and outlet of the microfluidic chip, the injection flow rate, image data and spectral data, and automatically adjusts the device in the fluid delivery and control unit according to the set program.

[0014] The pressure-decoupled microfluidic device of the present invention has two modes of use: one is to synthesize hydrates inside the microfluidic chip and inject fluid through the fluid delivery and control unit to observe local seepage and phase change behavior; the other is to synthesize hydrates in a reactor and embed the microfluidic chip as a seepage probe into a local area, inject fluid through the fluid delivery and control unit, and monitor the correlation between the overall device response and local seepage.

[0015] For the pressure limiting structure of the present invention, if the pressure decoupled microfluidic device experiences an instantaneous pressure increase in the microfluidic chip due to pump pulses or blockages during use, the pressure limiting structure will allow a small amount of fluid to leak from the inside of the microfluidic chip into the reaction vessel chamber (or in the reverse direction), rapidly releasing the pressure difference to a safe threshold (<1MPa), thereby preventing the microfluidic chip from rupturing.

[0016] As a preferred embodiment of the present invention, the reactor has a slotted structure inside.

[0017] Preferably, the microfluidic chip is disposed within the card slot structure.

[0018] Preferably, the pressure limiting structure is disposed on the side of the microfluidic chip near the card slot.

[0019] As a preferred embodiment of the present invention, the pressure limiting structure includes a microchannel array.

[0020] Preferably, the microchannel array includes any one or a combination of at least two of the following: trapezoidal microchannel array, rectangular microchannel array, V-shaped microchannel array, or U-shaped microchannel array. Typical but non-limiting combinations include: a combination of trapezoidal and rectangular microchannel arrays, a combination of trapezoidal and V-shaped microchannel arrays, a combination of V-shaped and U-shaped microchannel arrays, a combination of trapezoidal, V-shaped, and U-shaped microchannel arrays, and preferably a trapezoidal microchannel array.

[0021] It should be noted that the cross-sectional shape of the microchannel array in this invention is mainly determined by the processing technology. The processing technologies used in this invention include focused ion beam (FIB) etching, reactive ion etching (RIE), or laser micromachining. Specifically, the trapezoidal microchannel array has the following cross-sectional characteristics: the opening width (lower base) on the side near the slot is 5-20 μm, the opening width (upper base) on the side away from the slot is 0.6-0.8 times the lower base, and the depth is 5-15 μm. This is the natural cross-sectional shape of wet-etched quartz glass, the processing technology is mature, the sidewalls are smooth, gas permeation is uniform, and it balances flow resistance and response speed, making it the optimal solution. The rectangular microchannel array has the following cross-sectional characteristics: width 5-20 μm, depth 5-15 μm. Its advantages are simple flow resistance calculation, clear equivalent hydraulic diameter, and suitability for theoretical modeling and numerical simulation verification. Deep reactive ion etching (RIE) is typically used. Etching (DRIE) or laser micromachining; the cross-sectional characteristics of V-shaped microchannel arrays are: an inverted triangular cross-section, an opening width of 5~20μm, and a depth of 5~15μm. It is a natural cross-section formed by anisotropic etching, and under the same opening width conditions, it has a smaller flow cross-sectional area, higher flow resistance, and lower leakage rate than trapezoidal and rectangular arrays, making it suitable for ultra-low leakage requirements (<10 μm). -5 The application scenarios of SCCM have the disadvantage that the sharp corner structure may have stress concentration under high pressure. It is usually processed by anisotropic wet etching (such as KOH solution etching of silicon or quartz). The cross-sectional characteristics of U-shaped microchannel array are: the side near the slot has a rounded transition, the opening width is 5~20μm, the depth is 5~15μm, and the radius of the arc is 0.3~0.5 times the opening width. It is a typical cross-section formed by laser micromachining, with no stress concentration points and high mechanical strength.

[0022] This invention allows for the combined use of multiple microchannels of different shapes on the same microfluidic chip. For example, a rectangular microchannel (with lower flow resistance, facilitating rapid pressure balance establishment) can be used near the inlet of the microfluidic chip, while a V-shaped microchannel (with higher flow resistance, preventing pressure fluctuations from being transmitted) can be used near the outlet. This combined design can optimize the uniformity of pressure distribution on the side of the microfluidic chip near the slot.

[0023] Preferably, the microchannel array includes 4 to 20 channels, for example, 4, 8, 12, 16 or 20 channels, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0024] Preferably, the channels of the microchannel array are parallel to each other.

[0025] Preferably, the width of the channels in the microchannel array is 5~20μm, for example, it can be 5μm, 8μm, 10μm, 15μm or 20μm, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0026] Preferably, the depth of the channels in the microchannel array is 5~15μm, for example, it can be 5μm, 8μm, 10μm, 12μm or 15μm, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0027] Preferably, the length of the channels in the microchannel array is comparable to the width of the microfluidic chip.

[0028] Preferably, the spacing between adjacent channels in the microchannel array is 200~1000μm, for example, it can be 200μm, 400μm, 600μm, 800μm or 1000μm, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0029] The microchannel array in this invention allows the pressure medium (gas or liquid) inside the reactor to permeate to the outer surface of the chip at extremely low flow rates, keeping the pressure on the outer surface of the microfluidic chip in constant equilibrium with the background pressure inside the reactor, without causing significant mass exchange (permeability < 10). -15 m 2 ).

[0030] Meanwhile, the microchannel array in this invention has a very small channel size, which greatly reduces the flow resistance to gas, resulting in an extremely low leakage rate (<0.01 sccm). During the experimental time (several hours), it will not significantly change the total amount of gas in the reactor or interfere with the synthesis of hydrates.

[0031] As a preferred embodiment of the present invention, the pressure-limiting structure includes a porous spacer layer.

[0032] It should be noted that in the pressure decoupling microfluidic device of the present invention, the porous spacer layer needs to work stably for a long time under high pressure of 5~15MPa, temperature change of -10~50℃, and in the presence of saline and CH4 / CO2 media.

[0033] Preferably, the material of the porous spacer layer includes any one or a combination of at least two of ceramics, sintered metals, or porous glass; wherein typical but non-limiting combinations include: a combination of ceramics and sintered metals, a combination of ceramics and porous glass, a combination of sintered metals and porous glass, and a combination of ceramics, sintered metals, and porous glass.

[0034] Among them, porous ceramics are the most preferred material type for the pressure limiting structure of high-pressure microfluidic devices, with advantages such as high temperature and high pressure resistance, corrosion resistance, uniform pore size and high mechanical strength.

[0035] Preferably, the ceramic comprises any one or a combination of at least two of alumina ceramics (Al2O3-995), silicon carbide ceramics (SiC-98), zirconia ceramics (ZrO2-3Y), or silicon nitride ceramics.

[0036] Preferably, the sintered metal includes stainless steel powder (316L stainless steel) sintered material and / or titanium powder sintered material.

[0037] Preferably, the porous glass comprises high-silica porous glass (brand name: Vycor).

[0038] Preferably, the pore size of the porous structure in the porous spacer layer is 0.1~1μm, for example, it can be 0.1μm, 0.2μm, 0.4μm, 0.6μm, 0.8μm or 1μm, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0039] Preferably, the porosity of the porous structure in the porous spacer layer is 30-50%, for example, it can be 30%, 35%, 40%, 45% or 50%, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0040] As a preferred embodiment of the present invention, the microfluidic chip includes an inlet and an outlet.

[0041] It should be noted that in this invention, the direction of the channels in the microchannel array is perpendicular to the axis of the inlet and outlet of the microfluidic chip.

[0042] Preferably, the microfluidic chip has a biomimetic porous structure inside.

[0043] In this invention, a biomimetic porous structure inside a microfluidic chip is used to simulate the pore network of hydrate formations.

[0044] Preferably, the biomimetic porous structure of the microfluidic chip includes a main channel, branch capillary channels connected to the main channel, and dead-end pores disposed at one end of the main channel.

[0045] Preferably, the dead-end aperture is located near the outlet of the microfluidic chip.

[0046] The dead-end pores in this invention are used to simulate the retention zone.

[0047] Preferably, the microfluidic chip further includes an electrode array connected to the branched capillary channels.

[0048] The electrode array is positioned on the inner surface of the cover plate of the microfluidic chip (i.e., the inner side of the upper cover plate opposite to the side of the microfluidic chip etched with microchannels), and is formed by depositing metal patterns via magnetron sputtering or electron beam evaporation. The electrode array achieves in-situ, real-time, and non-destructive monitoring of hydrate saturation by measuring the impedance (impedance spectrum or impedance modulus and phase angle at a fixed frequency) of the fluid / hydrate mixture. Principle: Hydrates are poor conductors of electricity (high resistivity), aqueous solutions have high conductivity (due to dissolved ions), and gases are almost non-conductive. Signal response: Hydrate formation / generation: Conductive aqueous phase is replaced by insulating hydrate → overall resistance increases (impedance modulus |Z|↑); Hydrate decomposition: Insulator decreases, conductive aqueous phase increases → overall resistance decreases (impedance modulus |Z|↓). Secondary nucleation may initially occur outside the focal plane of the optical microscope (e.g., on the sidewalls or deep within the channel), and the impedance signal begins to change before obvious changes are observed in the optical image. Impedance changes can serve as an early warning signal of secondary nucleation, prompting the operator to focus on the Raman spectrum and microscopic image of that area. By observing the changing trends of the impedance modulus |Z| and phase angle θ, the proportions of hydrates, water, and gas can be quickly distinguished. When an inhibitor or CO2 solution is injected, the impedance can quickly reflect the starting point and rate of hydrate decomposition, and is more continuous than Raman spectroscopy (which involves discrete point sampling).

[0049] Preferably, the width of the main channel is 180~220μm, for example, it can be 180μm, 190μm, 200μm, 210μm or 220μm, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0050] Preferably, the length of the main channel is 10-20mm, for example, it can be 10mm, 12mm, 15mm, 18mm or 20mm, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0051] Preferably, the width of the branch capillary channel is 50~100μm, for example, it can be 50μm, 60μm, 70μm, 80μm, 90μm or 100μm, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0052] Preferably, the length of the branch capillary channel is 5 to 8 mm, for example, it can be 5 mm, 5.5 mm, 6 mm, 7 mm or 8 mm, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0053] Preferably, the diameter of the dead-end pore is 50~100μm, for example, it can be 50μm, 60μm, 70μm, 80μm, 90μm or 100μm, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0054] Preferably, the depths of the main channel, the branch capillary channel, and the dead-end pore are each independently 80~120μm, for example, 80μm, 90μm, 100μm, 110μm or 120μm, but are not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0055] Preferably, the microfluidic chip also contains a slice of natural rock core.

[0056] Preferably, the length of the natural core slice is 5 to 10 mm, for example, it can be 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0057] Preferably, the width of the natural core slice is 5 to 10 mm, for example, it can be 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0058] Preferably, the depth of the natural rock core slice is 0.5~1mm, for example, it can be 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm or 1mm, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0059] The natural core slice embedding zone is a replaceable functional module of the microfluidic chip, with the following specific characteristics: Location: Located in one corner or on one side of the microfluidic chip, independent of the biomimetic porous network; Function: Used to embed real reservoir core slices (such as sediment cores from the Shenhu area of ​​the South China Sea) to observe hydrate phase transition behavior in real pore structures, study the influence of natural mineral composition (such as clay minerals) on hydrate nucleation / decomposition, and bridge the gap between the "idealized pore model" and the "real reservoir complexity". This embedding zone is a replaceable design, and whether to use it and what kind of core slice to use can be selected according to experimental needs to enhance the geological representativeness of the experiment.

[0060] As a preferred embodiment of the present invention, the reaction vessel has an observation window on the outlet side of the microfluidic chip.

[0061] In this invention, the working pressure of the reactor is 0.1~15MPa, for example, it can be 0.1MPa, 0.5MPa, 1MPa, 5MPa, 10MPa or 15MPa, and the reaction temperature in the reactor is -10~50℃, for example, it can be -10℃, 0℃, 10℃, 20℃, 30℃, 40℃ or 50℃, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0062] Preferably, the observation window is made of sapphire and / or quartz glass.

[0063] It should be noted that the light transmittance of the observation window is >90% and the pressure resistance is >15MPa.

[0064] Preferably, the material of the microfluidic chip includes any one or a combination of at least two of quartz glass, sapphire, stainless steel or ceramic, wherein typical but non-limiting combinations include: a combination of quartz glass and sapphire, a combination of quartz glass and stainless steel, a combination of sapphire and stainless steel, and a combination of sapphire, stainless steel and ceramic.

[0065] Preferably, the fluid delivery and control unit includes a liquid storage device, a constant flow pump, a mass flow meter, and a back pressure valve that are sequentially connected to the outlet of the microfluidic chip; the back pressure valve is connected to the inlet of the microfluidic chip.

[0066] The back pressure valve is used to control the outlet pressure of the microfluidic chip and maintain the displacement pressure difference (set range is 0~1MPa).

[0067] It should be noted that the flow rate of the constant flow pump is 0.1~100μL / min, for example, it can be 0.1μL / min, 1μL / min, 10μL / min, 50μL / min or 100μL / min, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0068] The pressure adjustment range of the back pressure valve is 0~15MPa, for example, it can be 0MPa, 2MPa, 5MPa, 10MPa or 15MPa, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0069] The microfluidic chip is connected to the external pipeline through a titanium alloy high-pressure connector. The contact surface between the connector and the microfluidic chip is sealed with a metal-sapphire-elastomer composite seal, such as a copper gasket-sapphire flat gasket-fluororubber O-ring.

[0070] Preferably, the fluid delivery and control unit further includes a temperature control device connected to the reactor.

[0071] Preferably, the online detection and characterization unit includes an image detection device and a spectral detection device.

[0072] Preferably, the image detection device includes any one or a combination of at least two of the following: an inverted microscope, a high-speed camera, or a micro-CT imaging device. Typical but non-limiting combinations include: a combination of an inverted microscope and a high-speed camera, a combination of an inverted microscope and a micro-CT imaging device, a combination of a high-speed camera and a micro-CT imaging device, and a combination of an inverted microscope, a high-speed camera, and a micro-CT imaging device.

[0073] The inverted microscope has a spatial resolution better than 1 μm, and the high-speed camera has a temporal resolution of up to 1 ms.

[0074] Preferably, the spectral detection device includes a confocal Raman spectrometer.

[0075] The confocal Raman spectrometer (Horiba LabRAM HR Evolution) in this invention emits a 532 nm laser with a spectral resolution of 1 cm⁻¹. -1 Used to identify hydrate types (CH4 characteristic peak 2904 cm⁻¹) -1 CO2 characteristic peak at 1275 cm⁻¹ -1 ).

[0076] It should be noted that this invention does not rely on scarce facilities such as large synchrotron radiation sources or neutron sources; all components used (reaction vessel, constant flow pump, microscope or Raman spectrometer) are readily available equipment in conventional laboratories. The microfluidic chip can be mass-produced using standard photolithography or 3D printing techniques, with a unit cost far lower than that of a monolithic high-voltage chip. The overall cost of the pressure-decoupled microfluidic device is approximately one-tenth of that of a synchrotron radiation CT experiment, and it is easy to operate and maintain, making it suitable for large-scale application.

[0077] Meanwhile, the device of the present invention adopts a modular design and can be flexibly expanded according to research needs. The device is not only applicable to CH4 hydrate, but also to various systems such as CO2 hydrate or THF hydrate, and can simulate various mining processes such as depressurization method, thermal shock method, chemical inhibitor method or CO2 replacement method, and has strong versatility.

[0078] Secondly, the present invention provides a method for studying the secondary phase transition behavior of hydrates, wherein the method is performed using the pressure-decoupled microfluidic device described in the first aspect.

[0079] The pressure-decoupled microfluidic device of this invention can achieve independent control of background pressure and displacement pressure difference, breaking through the technical bottleneck that high pressure and high resolution cannot be achieved simultaneously, and enabling the pressure-decoupled microfluidic device to quantitatively study the critical conditions of secondary phase transition of hydrates.

[0080] As a preferred technical solution of the present invention, the research method includes the following steps: (1) Establishing background pressure: Applying a first pressure to the outside of the microfluidic chip using a reaction vessel; (2) Displacement injection: Under the condition of maintaining the first pressure unchanged, working fluid is injected into the interior of the microfluidic chip using the fluid delivery and control unit to form a displacement pressure difference; (3) Dynamic observation: The data acquisition and control unit is used to acquire images and spectral data of hydrate phase transition in the microfluidic chip in real time; and the secondary phase transition behavior data of hydrate is obtained through the images and spectral data; The hydrate secondary phase transition behavior data includes any one or a combination of at least two of the following: hydrate decomposition rate, secondary nucleation frequency, decomposition front propagation speed, hydrate saturation evolution curve, or critical triggering conditions.

[0081] This invention first applies a first pressure to the outside of a microfluidic chip using a reaction vessel to ensure that the environment in which the microfluidic chip is located meets the thermodynamic stability conditions of hydrates. The first pressure is uniformly applied to the outer surface of the microfluidic chip and the pore space inside the microfluidic chip that has not yet been occupied by the working fluid. At this time, the pressure inside and outside the microfluidic chip reaches dynamic equilibrium (pressure difference < 0.1 MPa). Then, the working fluid is injected into the inside of the microfluidic chip to form a displacement pressure difference. At this time, the pressure limiting structure dynamically limits the real-time pressure difference inside and outside the microfluidic chip within a preset safety threshold range, so that the first pressure and the displacement pressure difference are independently controlled. That is, when the working fluid is injected, the injection pump only needs to overcome the flow resistance of the flow channel of the microfluidic chip, without having to resist the background pressure. Therefore, the working pressure of the injection pump is much lower than the requirement without decoupling. Furthermore, the data acquisition and control unit collects images and spectral data of the hydrate phase transition inside the microfluidic chip in real time, and then analyzes them using image processing software to obtain the hydrate decomposition rate, secondary nucleation frequency, the propagation speed of the decomposition front, the hydrate saturation evolution curve, or the critical triggering condition.

[0082] By using image processing software to perform threshold segmentation and area calculation on the microscopic image sequence, and fitting the slopes of the descending and ascending segments respectively, the hydrate decomposition rate and secondary nucleation rate can be obtained. It should be noted that the analysis methods for hydrate decomposition rate, secondary nucleation frequency, decomposition front advancement speed and hydrate saturation evolution curve are well known to those skilled in the art and will not be elaborated here.

[0083] As a preferred technical solution of the present invention, the first pressure is 0.1~15MPa, for example, it can be 0.1MPa, 1MPa, 2MPa, 5MPa, 10MPa or 15MPa, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0084] Preferably, the injection rate of the working fluid is 0.1~10μL / min, for example, it can be 0.1μL / min, 0.5μL / min, 1μL / min, 2μL / min, 5μL / min or 10μL / min, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0085] This invention enables continuous, controllable injection of fluid into the chip at extremely low flow rates (0.1~10μL / min) under the high background pressure (≥5MPa) required to maintain hydrate stability, without damaging the chip during the injection process.

[0086] Preferably, the injection time of the working fluid is ≥120 min, for example, it can be 120 min, 140 min, 160 min, 180 min or 200 min, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0087] Preferably, the working fluid includes any one or a combination of at least two of water, a hot fluid, a CO2 saturated aqueous solution, a methanol solution, an ethylene glycol solution, or a tetrahydrofuran solution, wherein typical but non-limiting combinations include: a combination of water and a hot fluid, a combination of a hot fluid and a CO2 saturated aqueous solution, a combination of a methanol solution and an ethylene glycol solution, and a combination of a methanol solution, an ethylene glycol solution, and a tetrahydrofuran solution.

[0088] Preferably, the temperature of the hot fluid is 30~100℃, for example, it can be 30℃, 60℃, 90℃ or 100℃, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0089] Preferably, the hydrate includes CH4 hydrate and / or CO2 hydrate.

[0090] Preferably, the displacement pressure difference is 0.1~1MPa, for example, it can be 0.1MPa, 0.2MPa, 0.4MPa, 0.6MPa, 0.8MPa or 1MPa, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0091] As a preferred technical solution of the present invention, the research method further includes using a data acquisition and control unit to collect the first pressure and reaction temperature inside the reactor in real time.

[0092] It should be noted that the first pressure and reaction temperature are macroscopic data. This invention can align macroscopic data with microscopic images and spectral data on the same time coordinate system, establishing a micro-macroscale cross-scale correlation model to quantitatively determine the extent to which secondary nucleation within pores leads to a decrease in overall permeability, overcoming the defect of existing microfluidic devices that suffer from "microscopic-macroscopic disconnection". This cross-scale correlation capability provides valuable experimental verification data for numerical simulation of hydrate extraction.

[0093] This invention can also increase the reaction temperature, simulate the combined effect of hot fluid intrusion and pressure reduction, and observe the correlation between changes in macroscopic thermodynamic parameters and microscopic secondary nucleation in real time.

[0094] Preferably, the critical triggering condition includes any one of the following: critical flow rate, critical supersaturation, and critical temperature gradient.

[0095] It should be noted that, with the pressure-decoupled microfluidic device provided by this invention, the operator can independently adjust the injection flow rate, fluid composition, and temperature while maintaining a constant background pressure in the reactor (simulating reservoir static pressure) to simulate the slow, continuous intrusion process of fluid in the reservoir (flow rate can be as low as 0.1 μL / min, with continuous injection for several hours). In contrast, existing technologies can only perform intermittent or high-flow-rate injections, and cannot realistically reproduce the physical process of the slow propagation of the fluid front.

[0096] Preferably, under the condition of keeping the first pressure and reaction temperature constant, the injection flow rate of the working fluid is changed in a gradient increasing manner, and the injection flow rate corresponding to the first observation of the secondary nucleation phenomenon in the dynamic observation step is the critical flow rate.

[0097] Preferably, under the condition of keeping the first pressure and reaction temperature constant, the injection flow rate of the working fluid is changed in a gradient increasing manner, and the difference between the actual gas concentration and the equilibrium gas concentration when the secondary nucleation phenomenon is first observed in the dynamic observation step is the critical supersaturation.

[0098] Preferably, under the condition of keeping the first pressure and the injection flow rate of the working fluid constant, the temperature difference between the inlet and outlet of the microfluidic chip is changed in a gradient increasing manner. When the secondary nucleation phenomenon is first observed in the dynamic observation step, the change in temperature difference per unit length of the microfluidic chip is calculated, which is the critical temperature gradient.

[0099] Preferably, under the condition of keeping the first pressure, reaction temperature and injection flow rate constant, the concentration of the inhibitor in the working fluid is changed in a gradient increasing manner, and the concentration corresponding to the first complete suppression of secondary nucleation phenomenon in the dynamic observation step is the critical inhibitor concentration under this condition.

[0100] This invention, by gradually changing the injection flow rate, inhibitor concentration, or fluid temperature under initial pressure and reaction temperature, and by monitoring the hydrate phase transition state in real time, can systematically and repeatably determine key parameters such as the critical flow rate or critical inhibitor concentration for triggering secondary nucleation. This data has direct guiding value for preventing hydrate blockage and optimizing extraction processes.

[0101] The present invention can also simultaneously adjust the first pressure or reaction temperature while the displacement injection step is being performed, so as to simulate the synergistic effect of depressurization mining or thermal shock mining and fluid intrusion, and extract the kinetic parameter spectrum of the secondary phase transition behavior of hydrate under dual-field coupling conditions.

[0102] This invention also allows for the uninterrupted switching of the type of injected working fluid during the displacement injection step. By observing the phase transition dynamics within seconds to minutes before and after the switch, the inhibitory or promoting effects of different working fluids on secondary nucleation, as well as the competitive mechanisms during fluid replacement, can be quantitatively evaluated. This provides a convenient experimental method for rapidly screening efficient inhibitors and optimizing the replacement process.

[0103] The working principle of the microfluidic device pressure decoupling of the present invention is as follows: During normal operation, the reaction vessel is filled with high-pressure gas (background pressure P). bg Gas seeps into the tiny gap between the outer surface of the microfluidic chip and the reactor body, causing the pressure on the outer surface of the microfluidic chip to equal the background pressure P. bg The internal fluid channels of the microfluidic chip are filled with water or gas, and their pressure is controlled by an injection pump and a back pressure valve. When no gas is injected, the internal pressure is also close to P. bg (Due to initial equilibrium). The net pressure difference ΔP between the inside and outside of the microfluidic chip is < 0.1 MPa, indicating that the microfluidic chip is in a safe state. When the working fluid is injected (dynamic displacement), the injection pump is started to deliver the working fluid to the inlet of the microfluidic chip at a set flow rate. The pump needs to overcome the flow resistance of the microfluidic chip's channels (typically 0.1~1 MPa), therefore the pressure at the inlet of the microfluidic chip is slightly higher than the pressure at the outlet. Because the outer surface of the microfluidic chip is constantly under pressure from the background pressure P inside the reactor through a pressure-limiting structure... bg To maintain connectivity, the pressure at all points on the outer surface of the microfluidic chip remains approximately equal to P. bg The pressure distribution within the flow channels of a microfluidic chip originates from the inlet (P). bg +flow resistance) to the outlet (P) bg (Back pressure valve set to P) bg Therefore, the maximum pressure difference between the inside of the microfluidic chip and the external pressure is less than 1 MPa. The injection pump only needs to provide the displacement pressure difference (flow resistance) and does not need to counteract the background pressure.

[0104] When pressure is abnormal, suppose that a sudden pressure surge occurs inside the microfluidic chip due to some reason (such as bubble blockage or pump malfunction). At this time, the pressure difference between the inside and outside of the microfluidic chip increases, and gas will flow in the opposite direction from the outer surface of the microfluidic chip to the inner chamber of the reactor through the pressure-limiting structure (because the external pressure is lower and the internal pressure surges, the internal pressure is greater than the external pressure, causing the gas to flow in the opposite direction). Due to the extremely high flow resistance of the pressure-limiting structure, the reverse gas flow will also quickly release the pressure difference. More importantly, the microfluidic chip itself has high compressive strength but low tensile strength. When the internal pressure is too high, the microfluidic chip will undergo slight bending deformation, which will increase the flow cross-sectional area of ​​the pressure-limiting structure, thereby accelerating pressure release. Therefore, this structure has an adaptive pressure clamping function, ensuring that the pressure difference between the inside and outside of the microfluidic chip is always <1 MPa.

[0105] Compared with the prior art, the present invention has at least the following beneficial effects: (1) In the present invention, in the reaction unit, the internal chamber of the reactor is used to contain the pressure medium and form a first pressure field. The microfluidic chip is detachably disposed in the internal chamber of the reactor and a second pressure field independent of the first pressure field is formed inside the microfluidic chip. The pressure limiting structure has a flow limiting characteristic and is used to dynamically limit the real-time pressure difference inside and outside the microfluidic chip within a preset safety threshold (less than 1 MPa), so that the first pressure field and the displacement pressure difference are independently controlled. (2) The pressure decoupled microfluidic device in this invention can achieve independent control of background pressure and displacement pressure difference, breaking through the technical bottleneck that high pressure and high resolution cannot be achieved at the same time, so that the pressure decoupled microfluidic device can quantitatively study the critical conditions of secondary phase transition of hydrates. Attached Figure Description

[0106] Figure 1 This is a schematic diagram of the pressure decoupling microfluidic device provided in Embodiment 1 of the present invention.

[0107] Figure 2 This is a schematic diagram of the structure of the reaction unit provided in Embodiment 1 of the present invention.

[0108] Figure 3 This is a schematic diagram of the microfluidic chip provided in Embodiment 1 of the present invention.

[0109] The components are as follows: 1-Reaction unit; 11-Reaction vessel; 12-Microfluidic chip; 121-Inlet; 122-Outlet; 123-Main channel; 124-Branch capillary channel; 125-Dead end pore; 126-Natural core slice; 13-Pressure limiting structure; 2-Fluid transport and control unit; 21-Liquid storage device; 22-Constant flow pump; 23-Mass flow meter; 24-Back pressure valve; 25-Temperature control device; 3-Online detection and characterization unit; 4-Data acquisition and control unit. Detailed Implementation

[0110] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0111] Example 1 This embodiment provides a pressure-decoupled microfluidic device, such as... Figure 1 As shown, the pressure-decoupled microfluidic device includes a reaction unit 1, a fluid delivery and control unit 2, an online detection and characterization unit 3, and a data acquisition and control unit 4; the fluid delivery and control unit 2 and the online detection and characterization unit 3 are both connected to the reaction unit 1; the data acquisition and control unit 4 is connected to the reaction unit 1, the fluid delivery and control unit 2, and the online detection and characterization unit 3, respectively.

[0112] like Figure 2 As shown, the reaction unit 1 includes a reaction vessel 11, a microfluidic chip 12 disposed inside the reaction vessel 11, and a pressure limiting structure 13 disposed inside the microfluidic chip 12. The reaction vessel 11 has a slot structure inside. The microfluidic chip 12 is disposed within the slot structure. The pressure limiting structure 13 is disposed on the side of the microfluidic chip 12 near the slot. The pressure limiting structure 13 is a trapezoidal microchannel array. The trapezoidal microchannel array includes 10 parallel channels. The depth of each channel is 10 μm, the width near the slot structure is 10 μm, and the width away from the slot structure is 8 μm. The length of each channel is equal to the width of the microfluidic chip 12. The spacing between adjacent channels is 600 μm.

[0113] The microfluidic chip 12 is made of quartz glass, such as Figure 3 As shown, the microfluidic chip 12 includes an inlet 121 and an outlet 122; the interior of the microfluidic chip 12 has a biomimetic porous structure; the biomimetic porous structure includes a main channel 123, branch capillary channels 124 connected to the main channel 123, and a dead-end pore 125 disposed at one end of the main channel 123; and the dead-end pore 125 is close to the outlet 122 of the microfluidic chip 12; the interior of the microfluidic chip 12 also contains a natural rock core slice 126 with a length of 8 mm, a width of 8 mm, and a depth of 0.8 mm, wherein the main channel 123 has a width of 200 μm and a length of 15 mm; the branch capillary channel 124 has a width of 70 μm and a length of 6 mm; the dead-end pore 125 has a diameter of 80 μm; and the depths of the main channel 123, the branch capillary channel 124, and the dead-end pore 125 are all 100 μm.

[0114] On the outlet 122 side of the microfluidic chip 12, the reaction vessel 11 has a sapphire observation window; the fluid delivery and control unit 2 includes a liquid storage device 21, a constant flow pump 22, a mass flow meter 23, and a back pressure valve 24 connected in sequence to the outlet 122 of the microfluidic chip 12; the back pressure valve 24 is connected to the inlet 121 of the microfluidic chip 12; the fluid delivery and control unit 2 also includes a temperature control device 25 connected to the reaction vessel 11; the online detection and characterization unit 3 includes a high-speed camera and a confocal Raman spectrometer.

[0115] Example 2 This embodiment provides a pressure-decoupled microfluidic device, which includes a reaction unit, a fluid delivery and control unit, an online detection and characterization unit, and a data acquisition and control unit. The fluid delivery and control unit and the online detection and characterization unit are all connected to the reaction unit. The data acquisition and control unit is connected to the reaction unit, the fluid delivery and control unit, and the online detection and characterization unit, respectively.

[0116] The reaction unit includes a reaction vessel, a microfluidic chip disposed inside the reaction vessel, and a pressure limiting structure disposed inside the microfluidic chip. The reaction vessel has a slot structure inside. The microfluidic chip is disposed within the slot structure. The pressure limiting structure is disposed on the side of the microfluidic chip near the slot, and the pressure limiting structure is a trapezoidal microchannel array. The trapezoidal microchannel array includes four parallel channels. The depth of each channel is 15 μm, the width near the slot structure is 20 μm, and the width away from the slot structure is 16 μm. The length of each channel is equal to the width of the microfluidic chip. The spacing between adjacent channels is 1000 μm.

[0117] The microfluidic chip is made of quartz glass and includes an inlet and an outlet. The microfluidic chip has an internal biomimetic porous structure. This structure includes a main channel, branch capillary channels connected to the main channel, and dead-end pores at one end of the main channel. The dead-end pores are located near the outlet of the microfluidic chip. The microfluidic chip also contains a natural rock core slice with a length of 10 mm, a width of 5 mm, and a depth of 1 mm. The main channel has a width of 220 μm and a length of 20 mm; the branch capillary channels have a width of 100 μm and a length of 8 mm; the dead-end pores have a diameter of 100 μm; and the main channel, branch capillary channels, and dead-end pores all have a depth of 120 μm.

[0118] On the outlet side of the microfluidic chip, the reaction vessel has a sapphire observation window; the fluid delivery and control unit includes a liquid storage device, a constant flow pump, a mass flow meter, and a back pressure valve connected in sequence to the outlet of the microfluidic chip; the back pressure valve is connected to the inlet of the microfluidic chip; the fluid delivery and control unit also includes a temperature control device connected to the reaction vessel; the online detection and characterization unit includes an inverted microscope and a confocal Raman spectrometer.

[0119] Example 3 This embodiment provides a pressure-decoupled microfluidic device, which includes a reaction unit, a fluid delivery and control unit, an online detection and characterization unit, and a data acquisition and control unit. The fluid delivery and control unit and the online detection and characterization unit are all connected to the reaction unit. The data acquisition and control unit is connected to the reaction unit, the fluid delivery and control unit, and the online detection and characterization unit, respectively.

[0120] The reaction unit includes a reaction vessel, a microfluidic chip disposed inside the reaction vessel, and a pressure limiting structure disposed inside the microfluidic chip. The reaction vessel has a slot structure inside. The microfluidic chip is disposed within the slot structure. The pressure limiting structure is disposed on the side of the microfluidic chip near the slot, and the pressure limiting structure is a trapezoidal microchannel array. The trapezoidal microchannel array includes 20 parallel channels. The depth of each channel is 5 μm, the width near the slot structure is 8 μm, and the width away from the slot structure is 5 μm. The length of each channel is equal to the width of the microfluidic chip. The spacing between adjacent channels is 200 μm.

[0121] The microfluidic chip is made of quartz glass and includes an inlet and an outlet. The microfluidic chip has an internal biomimetic porous structure. This structure includes a main channel, branch capillary channels connected to the main channel, and dead-end pores at one end of the main channel. The dead-end pores are located near the outlet of the microfluidic chip. The microfluidic chip also contains a natural rock core slice with a length of 5 mm, a width of 10 mm, and a depth of 0.5 mm. The main channel has a width of 180 μm and a length of 10 mm; the branch capillary channels have a width of 50 μm and a length of 5 mm; the dead-end pores have a diameter of 50 μm; and the main channel, the branch capillary channels, and the dead-end pores all have a depth of 80 μm.

[0122] On the outlet side of the microfluidic chip, the reaction vessel has a sapphire observation window; the fluid delivery and control unit includes a liquid storage device, a constant flow pump, a mass flow meter, and a back pressure valve connected in sequence to the outlet of the microfluidic chip; the back pressure valve is connected to the inlet of the microfluidic chip; the fluid delivery and control unit also includes a temperature control device connected to the reaction vessel; the online detection and characterization unit includes an inverted microscope and a confocal Raman spectrometer.

[0123] Example 4 This embodiment provides a pressure-decoupled microfluidic device, which differs from Embodiment 1 only in that the pressure limiting structure is a porous spacer layer; the material of the porous spacer layer is alumina ceramic (grade N-99EP); and the pore size of the porous structure in the porous spacer layer is 0.5 μm and the porosity is 40%. All other aspects are the same as in Embodiment 1.

[0124] Example 5 This embodiment provides a pressure-decoupled microfluidic device. The only difference from Embodiment 1 is that, while keeping the angle between the waist and the bottom of the trapezoidal channel unchanged, the width of the channel near the slot structure in the microchannel array is adjusted from 10μm to 2μm. Otherwise, it is the same as Embodiment 1.

[0125] Example 6 This embodiment provides a pressure-decoupled microfluidic device. The only difference from Embodiment 1 is that, while keeping the angle between the waist and the bottom of the trapezoidal channel unchanged, the width of the channel near the slot structure in the microchannel array is adjusted from 10μm to 40μm. Otherwise, it is the same as Embodiment 1.

[0126] Example 7 This embodiment provides a pressure-decoupled microfluidic device, which differs from Embodiment 4 only in that the porosity of the porous structure in the porous spacer layer is adjusted from 40% to 20%, while the rest is the same as Embodiment 1.

[0127] Example 8 This embodiment provides a pressure-decoupled microfluidic device, which differs from Embodiment 4 only in that the porosity of the porous structure in the porous spacer layer is adjusted from 40% to 60%, while the rest is the same as Embodiment 1.

[0128] Comparative Example 1 This comparative example provides a microfluidic device, which differs from Example 1 only in that the reaction unit does not include a pressure limiting structure and the reaction unit also includes a confining pressure pump connected to the reaction vessel; otherwise, it is the same as Example 1.

[0129] Application Example 1 This application example provides a method for studying the secondary phase transition behavior of hydrates. This application example uses the pressure-decoupled microfluidic device provided in Example 1. The research method includes the following steps: (1) Establish background pressure: Start the constant flow pump and inject water into the microfluidic chip at a flow rate of 10 μL / min for 20 min until water flows out continuously from the outlet to expel the air in the microfluidic chip and pipeline. Then inject CH4 gas into the microfluidic chip to replace the water in the microfluidic chip and push the excess water out from the outlet. When only gas comes out of the outlet and no water comes out, close the outlet valve and use the pressure in the reactor to be 8 MPa and the temperature to be 3 °C for 24 h to synthesize hydrate. Reduce the pressure in the reactor so that the reactor applies a first pressure of 7.5 MPa to the outside of the microfluidic chip. (2) Displacement injection: Under the condition of maintaining the first pressure unchanged, water at a temperature of 3°C is injected into the interior of the microfluidic chip at a flow rate of 1 μL / min for 120 min to form a displacement pressure difference of 0.2 MPa. (3) Dynamic observation: The data acquisition and control unit is used to collect images and spectral data of hydrate phase transition in the microfluidic chip in real time; the images are recorded at 1 frame / s, the spectrum is collected once every 10s, and the hydrate decomposition rate and secondary nucleation frequency are obtained through the images and spectral data.

[0130] Application Example 2 This application example provides a method for studying the secondary phase transition behavior of hydrates. The only difference from application example 1 is that, except that this application example uses the pressure decoupling microfluidic device provided in example 2, and the temperature inside the reactor in step (1) is adjusted to 4°C, and the reactor applies a first pressure of 7.8 MPa to the outside of the microfluidic chip; step (2) is adjusted to: using the fluid delivery and control unit to inject a CO2 saturated aqueous solution at a temperature of 4°C into the inside of the microfluidic chip at a flow rate of 0.5 μL / min for 180 minutes to form a displacement pressure difference of 0.2 MPa; and step (3) is adjusted to: using the data acquisition and control unit to collect images, spectral data, first pressure and reaction temperature of the hydrate phase transition inside the microfluidic chip in real time to obtain a micro-macro cross-scale correlation model. All other steps are the same as application example 1.

[0131] Application Example 3 This application example provides a method for studying the secondary phase transition behavior of hydrates. The only difference from application example 1 is that, except that this application example uses the pressure-decoupled microfluidic device provided in example 3, and step (2) is adjusted to: under the condition of keeping the first pressure, reaction temperature and injection flow rate constant (2 μL / min), the concentration of the inhibitor methanol in the working fluid is changed in a gradient manner (3wt%, 5wt%, 7wt% and 10wt% in sequence), and each concentration is maintained for 40 min. Step (3) is adjusted to: using the data acquisition and control unit to collect the image and spectral data of the hydrate phase transition in the microfluidic chip in real time, so as to observe the concentration corresponding to the first complete suppression of the secondary nucleation phenomenon and obtain the critical inhibitor concentration. The rest are the same as application example 1.

[0132] This application example directly demonstrates that inhibitors can effectively block secondary nucleation pathways within micropores. The quantitative decomposition rate and critical inhibitor concentration data provided by the microfluidic device can be used to optimize the dosage of inhibitors in on-site mining, avoiding cost waste and environmental pollution caused by excessive use.

[0133] Application Example 4 This application example provides a method for studying the secondary phase transition behavior of hydrates. The only difference between this application example and application example 1 is that, except that this application example uses the pressure-decoupled microfluidic device provided in example 4, everything else is the same as application example 1.

[0134] Application Example 5 This application example provides a method for studying the secondary phase transition behavior of hydrates. The only difference between this application example and application example 1 is that, except that this application example uses the pressure-decoupled microfluidic device provided in example 5, everything else is the same as application example 1.

[0135] In this application example, the channel width in the microchannel array of the pressure-decoupled microfluidic device is too small (the channel width near the slot structure is 2 μm), resulting in a significant decrease in the gas permeation rate of the pressure-limiting structure. The pressure equilibrium time is extended from the normal value (about 5 minutes) to more than 30 minutes. During rapid injection or pressure regulation, a spike in instantaneous pressure difference occurs (measured at about 1.8 MPa), exceeding the safety threshold (<1 MPa). At the same time, the microchannel aspect ratio is large (5:1), making FIB etching difficult and reducing the yield of single-batch microfluidic chips from 90% to about 60%. In addition, the channel width is close to the characteristic size of tiny particles (1~5 μm) in the fluid, making it prone to clogging, and reducing the number of times the microfluidic chip can be reused from more than 20 times to less than 10 times. Therefore, the microchannel width of this invention should be no less than 5 μm to balance pressure-limiting performance, processing feasibility, and service life.

[0136] Application Example 6 This application example provides a method for studying the secondary phase transition behavior of hydrates. The only difference between this application example and application example 1 is that, except that this application example uses the pressure decoupling microfluidic device provided in example 6, everything else is the same as application example 1.

[0137] In this application example, the width of the channels in the microchannel array of the pressure-decoupled microfluidic device is too large (the width of the channel near the slot structure is 40 μm), causing the gas leakage rate of the pressure-limiting structure to exceed the normal value (approximately 10). -5 sccm) rose to 10 -2 The leakage was on the order of sccm, with the cumulative leakage exceeding 0.1% of the total gas volume inside the reactor during a 24-hour experimental period, and the background pressure P. bg The pressure continued to decrease (at a rate of approximately 0.02 MPa / h), accumulating a decrease of approximately 0.48 MPa over the 24-hour experimental period. This exceeded the allowable pressure fluctuation range, causing the hydrate synthesis conditions to deviate from the set values, and the fluctuation in kinetic parameter measurements increased from ±5% to ±20%. Simultaneously, the excessively wide channels reduced the non-channel contact area of ​​the microfluidic chip near the slot by approximately 30%, leading to a decrease in the main seal specific pressure and the appearance of a small macroscopic leak (approximately 10 MPa). -2 (on the order of sccm), disrupting the sealing balance of the pressure-limiting structure. Therefore, the microchannel width of this invention should not exceed 20μm to balance the comprehensive requirements of leakage rate control, sealing reliability, and pressure stability.

[0138] Application Example 7 This application example provides a method for studying the secondary phase transition behavior of hydrates. The only difference between this application example and application example 4 is that, except that this application example uses the pressure-decoupled microfluidic device provided in example 7, everything else is the same as application example 4.

[0139] In this application example, the porosity of the porous structure in the pressure-decoupling microfluidic device is too small (20%), causing the gas permeability of the porous spacer layer to drop to 10. -17 m 2 The pressure equilibration time inside and outside the microfluidic chip was extended from the normal value (2-5 minutes) to more than 20 minutes; the instantaneous pressure difference peak exceeded 1.5 MPa at the moment of background pressure dynamic adjustment or injection pump start-up, exceeding the safety threshold (<1 MPa), increasing the risk of microfluidic chip rupture; pressure fluctuations in the early stage of the experiment caused the fluctuation of kinetic parameter measurement to increase from ±5% to ±15%, reducing data reliability; in addition, porous materials with too low porosity have a high sintering temperature (about 1600℃) and a preparation cost of about 2-3 times that of normal materials, which is not conducive to mass application. Therefore, the porosity of the porous spacer layer of the present invention should not be less than 30% to balance pressure limiting response speed, safety and preparation economy.

[0140] Application Example 8 This application example provides a method for studying the secondary phase transition behavior of hydrates. The only difference between this application example and application example 4 is that, except that this application example uses the pressure-decoupled microfluidic device provided in example 8, everything else is the same as application example 4.

[0141] In this application example, the porosity of the porous structure in the pressure-decoupling microfluidic device's pressure-limiting structure is too high (60%), causing the compressive strength of the porous spacer layer to drop from 250 MPa to approximately 80 MPa. Under a high pressure of 15 MPa, compaction deformation and localized fragmentation occur, and the debris may clog the flow channels of the microfluidic chip; the leakage rate decreases from 10... -5 sccm increased to 10 -2 The leakage was on the order of sccm, with the cumulative leakage exceeding 0.1% of the total gas volume inside the reactor. The background pressure drop rate was approximately 0.02 MPa / h, exceeding the control precision (±0.01 MPa). Simultaneously, the equivalent thermal conductivity decreased from approximately 20 W / (m·K) to approximately 8 W / (m·K), resulting in a thermal response delay of approximately 5 minutes. The temperature difference between the microfluidic chip and the reactor was approximately 1.5°C, affecting the accuracy of in-situ observation data. Therefore, the porosity of the porous spacer layer in this invention should not exceed 50% to balance the comprehensive requirements of sealing performance, mechanical strength, thermal response speed, and safety.

[0142] Comparative Application Example 1 This application example provides a method for studying the secondary phase transition behavior of hydrates. The only difference between this application example and application example 1 is that, except that this application example uses the microfluidic device provided in comparative example 1, everything else is the same as application example 1.

[0143] In the microfluidic device used in this application example, the background pressure is coupled with the displacement pressure difference, making it impossible to achieve continuous micro-intrusion.

[0144] In summary, in this invention, the internal chamber of the reactor in the reaction unit is used to contain the pressure medium and form a first pressure field. The microfluidic chip is detachably disposed in the internal chamber of the reactor, and a second pressure field independent of the first pressure field is formed inside the microfluidic chip. The pressure limiting structure has flow limiting characteristics, which is used to dynamically limit the real-time pressure difference inside and outside the microfluidic chip within a preset safety threshold (less than 1 MPa). This enables independent control of the background pressure and the displacement pressure difference, breaking through the technical bottleneck that high pressure and high resolution cannot be achieved simultaneously. This allows the pressure-decoupled microfluidic device to quantitatively study the critical conditions of the secondary phase transition of hydrates.

[0145] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A pressure-decoupled microfluidic device, characterized in that, The pressure-decoupled microfluidic device includes a reaction unit, a fluid delivery and control unit, an online detection and characterization unit, and a data acquisition and control unit. The reaction unit includes a reaction vessel, a microfluidic chip disposed inside the reaction vessel, and a pressure limiting structure disposed inside the microfluidic chip; The fluid delivery and control unit is connected to the reaction unit; The online detection and characterization unit is connected to the reaction unit; The data acquisition and control unit is connected to the reaction unit, the fluid transport and control unit, and the online detection and characterization unit, respectively.

2. The pressure-decoupled microfluidic device according to claim 1, characterized in that, The reactor has an internal slot structure; Preferably, the microfluidic chip is disposed within the card slot structure; Preferably, the pressure limiting structure is disposed on the side of the microfluidic chip near the card slot.

3. The pressure-decoupled microfluidic device according to claim 2, characterized in that, The pressure limiting structure includes a microchannel array; Preferably, the microchannel array includes any one or a combination of at least two of the following: trapezoidal microchannel array, rectangular microchannel array, V-shaped microchannel array, or U-shaped microchannel array, with a trapezoidal microchannel array being the most preferred. Preferably, the microchannel array includes 4 to 20 channels; Preferably, the channels of the microchannel array are parallel to each other; Preferably, the width of the channels in the microchannel array is 5~20μm; Preferably, the depth of the channels in the microchannel array is 5~15μm; Preferably, the length of the channels in the microchannel array is comparable to the width of the microfluidic chip; Preferably, the spacing between adjacent channels in the microchannel array is 200~1000μm.

4. The pressure-decoupled microfluidic device according to claim 2, characterized in that, The pressure-limiting structure includes a porous spacer layer; Preferably, the material of the porous spacer layer includes any one or a combination of at least two of ceramics, sintered metals, or porous glass; Preferably, the pore size of the porous structure in the porous spacer layer is 0.1~1μm; Preferably, the porosity of the porous structure in the porous spacer layer is 30-50%.

5. The pressure-decoupled microfluidic device according to any one of claims 1-4, characterized in that, The microfluidic chip includes an inlet and an outlet; Preferably, the microfluidic chip has a biomimetic porous structure inside; Preferably, the biomimetic porous structure of the microfluidic chip includes a main channel, branch capillary channels connected to the main channel, and dead-end pores disposed at one end of the main channel. Preferably, the dead-end aperture is located near the outlet of the microfluidic chip; Preferably, the width of the main channel is 180~220μm; Preferably, the length of the main channel is 10~20mm; Preferably, the width of the branched capillary channel is 50~100μm; Preferably, the length of the branched capillary channel is 5-8 mm; Preferably, the diameter of the dead-end pore is 50~100μm; Preferably, the depths of the main channel, the branch capillary channel, and the dead-end pore are each independently 80~120μm.

6. The pressure-decoupled microfluidic device according to claim 5, characterized in that, On the outlet side of the microfluidic chip, the reaction vessel has an observation window; Preferably, the observation window is made of sapphire and / or quartz glass; Preferably, the material of the microfluidic chip includes any one or a combination of at least two of quartz glass, sapphire, stainless steel or ceramic; Preferably, the fluid delivery and control unit includes a liquid storage device, a constant flow pump, a mass flow meter, and a back pressure valve, which are sequentially connected to the outlet of the microfluidic chip; the back pressure valve is connected to the inlet of the microfluidic chip. Preferably, the fluid delivery and control unit further includes a temperature control device connected to the reactor; Preferably, the online detection and characterization unit includes an image detection device and a spectral detection device; Preferably, the image detection device includes any one or a combination of at least two of an inverted microscope, a high-speed camera, or a micro-CT imaging device; Preferably, the spectral detection device includes a confocal Raman spectrometer.

7. A method for studying the secondary phase transition behavior of hydrates, characterized in that, The research method described herein is performed using the pressure-decoupled microfluidic device as described in any one of claims 1-6.

8. The research method according to claim 7, characterized in that, The research method includes the following steps: (1) Establishing background pressure: Applying a first pressure to the outside of the microfluidic chip using a reaction vessel; (2) Displacement injection: Under the condition of maintaining the first pressure unchanged, working fluid is injected into the interior of the microfluidic chip using the fluid delivery and control unit to form a displacement pressure difference; (3) Dynamic observation: The data acquisition and control unit is used to acquire images and spectral data of the phase transition of hydrates in the microfluidic chip in real time; and the secondary phase transition behavior data of hydrates are obtained through the images and spectral data; The hydrate secondary phase transition behavior data includes any one or a combination of at least two of the following: hydrate decomposition rate, secondary nucleation frequency, decomposition front propagation speed, hydrate saturation evolution curve, or critical triggering conditions.

9. The research method according to claim 8, characterized in that, The first pressure is 0.1~15MPa; Preferably, the injection rate of the working fluid is 0.1~10 μL / min; Preferably, the injection time of the working fluid is ≥120 min; Preferably, the working fluid includes any one or a combination of at least two of the following: water, hot fluid, CO2 saturated aqueous solution, methanol solution, ethylene glycol solution, or tetrahydrofuran solution; Preferably, the temperature of the heat fluid is 30~100℃; Preferably, the hydrate includes CH4 hydrate and / or CO2 hydrate; Preferably, the displacement pressure difference is 0.1~1MPa.

10. The research method according to claim 8 or 9, characterized in that, The research method also includes using a data acquisition and control unit to collect the initial pressure and reaction temperature inside the reactor in real time; Preferably, the critical triggering condition includes any one of critical flow rate, critical supersaturation, or critical temperature gradient; Preferably, under the condition of keeping the first pressure and reaction temperature constant, the injection flow rate of the working fluid is changed in a gradient increasing manner, and the injection flow rate corresponding to the first observation of the secondary nucleation phenomenon in the dynamic observation step is the critical flow rate. Preferably, under the condition of keeping the first pressure and reaction temperature constant, the injection flow rate of the working fluid is changed in a gradient increasing manner, and the difference between the actual gas concentration and the equilibrium gas concentration when the secondary nucleation phenomenon is first observed in the dynamic observation step is the critical supersaturation. Preferably, under the condition of keeping the first pressure and the injection flow rate of the working fluid constant, the temperature difference between the inlet and outlet of the microfluidic chip is changed in a gradient increasing manner. When the secondary nucleation phenomenon is first observed in the dynamic observation step, the change in temperature difference per unit length of the microfluidic chip is calculated, which is the critical temperature gradient.

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