A microfluidic chip for filling seabed sediments, a preparation method thereof and application thereof

Abstract

The application provides a microfluidic chip for filling seabed sediments, a preparation method and application thereof. The microfluidic chip comprises a transparent cover plate layer and a substrate layer which are arranged in close contact. A main flow channel cavity, an injection channel and an outflow channel are arranged on one side of the substrate layer close to the transparent cover plate layer. The main flow channel cavity is filled with seabed sediment particles to form a porous medium area. An inflow port and an outflow port are arranged on the transparent cover plate layer. The inflow port is connected to the injection channel, and the outflow port is connected to the outflow channel. The application can simulate the pore structure characteristics of real seabed sediments, realize the visualization of hydrate phase transformation, solid particle and multiphase fluid migration process in sediments, break through the limitation of artificial pore micro-observation, and has important significance for analyzing phase transformation and multiphase seepage problems in the process of hydrate exploitation.

Description

Technical Field

[0001] This invention belongs to the field of microfluidics technology, and particularly relates to a microfluidic chip for filling seabed sediments, its preparation method and application. Background Technology

[0002] Microfluidics, due to its advantages of miniaturization, visualization, and precise fluid manipulation, has been widely applied in the study of multiphase flow in porous media. In the field of hydrates, domestic and foreign scholars have used microfluidic chips to simulate the pores of sedimentary layers and observe the formation, decomposition, and gas-water two-phase flow behavior of hydrates. For example, by etching glass or PDMS (polydimethylsiloxane) chips, researchers have constructed regularly arranged micropillar arrays or random network channels, revealing to some extent the influence of hydrate occurrence morphology on permeability at the pore throat scale. However, these chips share a common limitation: their porous media structure is an artificially designed "idealized" model, far removed from the physicochemical properties of real seabed sediment particles. Seepage sand is one of the main obstacles restricting the long-term stable production of hydrates. The essence of seepage sand is the shedding and migration of fine particles in the sediment skeleton under the drag force and decomposition impact of fluids, which may block sand-control media or enter the wellbore. Existing microfluidic research mostly focuses on the phase change of hydrates themselves, rarely involving sediment particles as mobile media participating in the flow process. In addition, for sediments with high mud content, fine particles can easily clog the injection and outlet channels, and conventional microfluidic chips lack targeted seepage and sand control designs.

[0003] Recently, a few studies have begun to explore "filled" microfluidic chips, which involve directly filling the chip cavity with real rock fragments or artificial sand particles. While this method is closer to the natural state, it faces the following three technical challenges: First, the filled particles are prone to displacement under fluid erosion, disrupting the stability of the pore structure; second, it is difficult to quantitatively characterize and repeatedly control the pore characteristics of the filling layer; and third, sealing the chip under high pressure is difficult, making it impossible to simulate the low-temperature, high-pressure environment in which hydrates are stably present.

[0004] Therefore, there is a need to provide a microfluidic platform that can accommodate real sediments, has good pressure resistance and sealing properties, and provides visualization capabilities. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a microfluidic chip for filling seabed sediments, its preparation method, and its application. It can flexibly adjust the combination of seabed sediment particles with different sizes, shapes, and mineral compositions according to experimental needs to construct a porous media region with real heterogeneous characteristics, which can simulate the pore structure of in-situ sediments and realize the visualization of multiphase flow.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a microfluidic chip, the microfluidic chip comprising a transparent cover layer and a substrate layer bonded together; the substrate layer having a main channel cavity, an injection channel and an outflow channel formed on the side near the transparent cover layer, the injection channel and the outflow channel being disposed opposite to each other on both sides of the main channel cavity and respectively communicating with the main channel cavity, the main channel cavity being filled with seabed sediment particles to form a porous medium region; the transparent cover layer having an inflow port and an outflow port, the inflow port being connected to the injection channel and the outflow port being connected to the outflow channel.

[0007] In this invention, the cavity of the main channel is filled with real seabed sediment particles as a porous medium. The size, shape and combination of seabed sediments can be flexibly adjusted according to experimental needs to construct a porous medium region with real heterogeneous characteristics. This helps to establish a physical model corresponding to real reservoir parameters and provides an experimental means that is closer to in-situ conditions for studying phase transformation, particle migration and sand control mechanisms in the hydrate mining process. It is expected to break through the bottleneck of existing microscopic simulation technology.

[0008] As a preferred embodiment of the present invention, the seabed sediment particles include any one or a combination of at least two of clay, muddy sediments, silty sediments, quartz sand, or glass microspheres.

[0009] As a preferred embodiment of the present invention, the shape of the seabed sediment particles includes any one or a combination of at least two of the following: spherical, cylindrical, regular polygonal, ellipsoidal, or irregular polygonal.

[0010] This invention allows for flexible configuration of particle combinations with different particle sizes, shapes, and mineral components according to experimental requirements, thereby constructing porous media regions with true heterogeneous characteristics.

[0011] As a preferred embodiment of the present invention, two filter grooves are provided on both sides of the main channel cavity, and the filter grooves are at least partially located in the inner cavity of the main channel cavity; the main channel cavity is connected to the injection channel and the outflow channel through the two filter grooves respectively, and the filter grooves are filled with filter material.

[0012] As a preferred embodiment of the present invention, the filter material includes sand-proof filter stone.

[0013] The pore size of the sand-proof filter stone is 0.1~50.0μm.

[0014] This invention employs a sand-proof design to prevent fine particles from clogging fluid ports or damaging downstream equipment.

[0015] As a preferred embodiment of the present invention, both the injection channel and the outflow channel are L-shaped structures, each independently including a connected transverse flow channel and a longitudinal flow channel. The transverse flow channel is connected to the main flow channel cavity, and the longitudinal flow channel is connected to the inflow port or the outflow port.

[0016] The L-shaped channel design of this invention helps to reduce the direct impact of fluid on the filter material and extend its service life.

[0017] As a preferred embodiment of the present invention, the transparent cover layer is detachably connected to the substrate layer.

[0018] In one embodiment of the present invention, the transparent cover layer is bonded to the substrate layer.

[0019] This invention has good pressure resistance and sealing performance, ensuring that the chip does not leak in a simulated high-pressure underwater environment.

[0020] In one embodiment of the present invention, a plurality of first positioning holes and a plurality of second positioning holes are respectively provided on the transparent cover layer and the substrate layer. The first positioning holes and the second positioning holes correspond one-to-one and are detachably connected by fasteners.

[0021] This invention utilizes fasteners to connect and lock the transparent cover layer and the substrate layer, achieving alignment and positioning, which helps improve chip sealing and overall structural strength.

[0022] In a second aspect, the present invention provides a method for fabricating the microfluidic chip described in the first aspect, the method comprising: S1: Etching is performed on the substrate surface to form the main channel cavity, injection channel and outflow channel; S2: Preset the porosity, pore size distribution, grain size distribution and permeability conditions of the required seabed sediments; S3: Provide the seabed sediment particles to be filled, and measure their particle morphology, particle size distribution, density and specific surface area. Based on the preset conditions in step S2, determine the filling form and combination of the seabed sediment particles, and fill them into the main channel cavity to form a porous media area. S4: Cover the substrate with a transparent cover layer so that the inflow port is connected to the injection channel and the outflow port is connected to the outflow channel to obtain a microfluidic chip.

[0023] As a preferred embodiment of the present invention, the preparation method further includes: etching two filter grooves at the junction of the main channel cavity and the injection channel, and at the junction of the main channel cavity and the outflow channel, respectively, and filling the filter grooves with sand-proof filter stones.

[0024] As one embodiment of the present invention, the preparation method further includes: using fasteners to connect the transparent cover layer and the substrate layer, so that the transparent cover layer and the substrate layer are bonded and sealed with adhesive.

[0025] Thirdly, the present invention provides an application of the microfluidic chip described in the first aspect, wherein the microfluidic chip is applied to microscopic experiments of multiphase flow in porous media.

[0026] This invention has a wide range of applications and is suitable for microscopic experiments on multiphase flow in porous media of various fluids, especially for microscopic experiments and phase change-seepage experiments on natural gas hydrates.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Realistic simulation: This invention is the first to directly fill real seabed sediment particle samples into a microfluidic chip, preserving their original particle morphology, particle size distribution and mineral composition, breaking through the limitations of idealization of artificial porous media. (2) Flexible and adjustable heterogeneity: The present invention can freely combine different shapes, types and quantities of seabed sediment particles as needed to construct a porous medium region with specified heterogeneous characteristics, and can quantitatively characterize its pore properties; (3) Visualization: A transparent high-pressure resistant cover plate is used to ensure that the chip does not leak under simulated high pressure environment (≥10MPa) on the seabed, while allowing high-resolution microscopic observation of hydrate phase transformation and particle transport process; (4) Wide applicability: The chip of the present invention is not only applicable to the research on natural gas hydrate extraction, but can also be extended to microscopic experimental fields involving porous media and multiphase flow, such as groundwater remediation, CO2 geological storage, and oil and gas reservoir development. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of a microfluidic chip provided in an embodiment of the present invention.

[0029] Figure 2 This is a top view of the microfluidic chip provided in an embodiment of the present invention.

[0030] Among them, 011-inflow port; 012-outflow port; 01-longitudinal flow channel; 02-transverse flow channel; 03-sand filter stone; 04-seabed sediment; 05-positioning bolt; 051-first positioning hole; 052-second positioning hole; 06-transparent cover plate layer; 07-substrate layer; 08-main flow channel cavity. Detailed Implementation

[0031] It should be understood that in the description of this invention, the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0032] It should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "set," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0033] In this invention, "a combination of at least two" refers to a quantity greater than or equal to 2, unless otherwise specified. For example, "any one or a combination of at least two" means that any one of the listed items can be selected, or a combination of at least two of the listed items formed in a manner that does not conflict and enables the implementation of this invention. In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" cover any one of two or more related listed items, as well as any and all combinations of the related listed items. The arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items.

[0034] In this invention, technical features or solutions described using open-ended terms such as "comprising" or "including" do not exclude additional non-conflicting elements beyond those listed unless otherwise specified. They are considered to disclose both closed-ended features or solutions consisting solely of the listed elements and open-ended features or solutions that may include additional non-conflicting elements beyond the listed elements. The term "embodiment" in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment can be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. Those skilled in the art can explicitly and implicitly understand that the embodiments described in this invention can be combined with other embodiments that do not conflict with existing ones.

[0035] In this invention, the order in which the steps are written in the methods described in each embodiment does not imply a strict execution order. The actual execution order of each step should be determined based on its function and possible internal logic. Unless otherwise specified, all steps of this invention can be executed in the order they are written, or in any order without technical conflict. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) executed sequentially, or it may include steps (b) and (a) executed sequentially. If the method also includes step (c), then step (c) can be added to the method in any order without conflict, including but not limited to the execution order of steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), etc.

[0036] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0037] Natural gas hydrates (commonly known as "combustible ice") are a highly promising clean energy source with abundant resources. However, hydrate reservoirs are mostly weakly cemented, high-muddy-content silty sediments, facing a series of engineering challenges during extraction, including low gas production efficiency, severe sand production, and poor reservoir stability. The root cause of these problems lies in the fact that hydrate decomposition and fluid migration occur within the complex pore network of natural sediments, and their microscopic mechanisms remain unclear. Therefore, developing an experimental platform capable of realistically reproducing the pore structure of seabed sediment particles and enabling in-situ observation has become crucial for advancing hydrate extraction technology. Real sediment particles have complex shapes, wide size distributions, and diverse mineral compositions (including clay minerals and organic matter), and possess natural pore connectivity and heterogeneity. Idealized artificial pores cannot simulate clay expansion, fine particle transport and blockage, and the dynamic feedback of changes in the internal stress field of sediments on the pore structure, often resulting in deviations from actual extraction responses.

[0038] To address this, the present invention provides a microfluidic chip for filling seabed sediments, comprising a transparent cover layer and a substrate layer bonded together; the substrate layer has a main channel cavity, an injection channel, and an outflow channel on the side near the transparent cover layer, the injection channel and the outflow channel are disposed opposite to each other on both sides of the main channel cavity and are respectively connected to the main channel cavity, the main channel cavity is filled with seabed sediment particles to form a porous medium region; the transparent cover layer has an inflow port and an outflow port, the inflow port is connected to the injection channel, and the outflow port is connected to the outflow channel, which can accommodate real sediments and has good pressure resistance, sealing and visualization capabilities.

[0039] The present invention will now be described in further detail. However, the examples described below 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.

[0040] The transparent cover layer described in this invention is a high-pressure resistant cover layer, designed to withstand significant external pressure and prevent the microfluidic chip's main channel cavity from cracking or being damaged under high pressure, allowing for real-time visual monitoring of the microfluidic chip's internal state. Specifically, the transparent cover layer is made of materials including, but not limited to, borosilicate glass, fused silica glass, high borosilicate glass, or soda-lime glass, possessing good light transmittance, pressure resistance (withstanding pressure ≥15MPa), and chemical stability.

[0041] The inlet port on the transparent cover plate is connected to the injection channel of the substrate layer, used for flow control during microfluidic experiments and to maintain internal pressure of the chip by injecting fluid. The outlet port is connected to the outlet channel of the substrate layer, used to control the discharge rate or flow rate of fluid flowing out of the chip, and to guide and collect the fluid. The fluid can be water, solution, gas, or oil; those skilled in the art can select different fluids according to actual experimental needs. Specifically, the inlet and outlet ports are connected to a high-pressure advection pump and a back pressure valve, etc., to regulate the inflow and outflow fluid flow rates.

[0042] Furthermore, the inlet and outlet ports are circular threaded holes for easy installation and sealing. This invention uses CNC machining or laser etching to form two circular threaded holes at both ends of the transparent cover layer, serving as the inlet and outlet ports. The diameter of the inlet port matches the size of the injection channel, and the diameter of the outlet port matches the size of the outlet channel.

[0043] The transparent cover layer described in this invention is detachably connected to the substrate layer, which facilitates assembly and disassembly.

[0044] In some embodiments, a number of first positioning holes and a number of second positioning holes are respectively formed on the transparent cover plate layer and the substrate layer. The first positioning holes and the second positioning holes correspond to each other one by one and are connected by fasteners. The number of the first positioning holes and the second positioning holes can be 4, 6, 8, 10, 12, etc., but is not limited to the listed values. The first positioning holes and the second positioning holes can be circumferentially formed at the edges of the transparent cover plate layer or the substrate layer, facilitating alignment and positioning of each layer. The fasteners can use positioning bolts to connect and fix the transparent cover plate layer and the substrate layer.

[0045] Furthermore, the transparent cover plate layer is adhesively connected to the substrate layer to ensure high-pressure tightness, ensuring that there is no leakage of the chip under the simulated undersea high-pressure environment (≥10 MPa), and at the same time allowing high-resolution microscopic observation of the phase transformation of hydrates and the process of particle migration. The high-strength glue includes, but is not limited to, epoxy resin high-strength glue, ultraviolet curing glue, thermal curing glue, or nano glue, etc.

[0046] The present invention uses high-strength glue to bond the transparent cover plate layer and the substrate layer, and then cures under pressure. In order to ensure complete sealing, a sealing check is carried out after curing the glue under pressure. Exemplarily, the ways of sealing check include: injecting nitrogen between the transparent cover plate layer and the substrate layer, maintaining pressure for a period of time, and if there is no pressure drop, it indicates that the seal is qualified, otherwise, the seal is poor.

[0047] The material of the substrate layer in the present invention includes, but is not limited to, borosilicate glass, fused silica glass, high borosilicate glass, or soda-lime glass, etc. The present invention uses wet etching or plasma etching to form a main flow channel cavity, an injection channel, and an outflow channel on the substrate layer.

[0048] The main flow channel cavity in the present invention is located in the middle of the substrate layer, which provides a space for hydrate phase change reaction and multiphase fluid migration for microfluidic experiments, and is the core part for realizing precise control, reaction, and monitoring of microfluids. The present invention does not specifically limit the size of the main flow channel cavity, and those skilled in the art can adjust the specification size of the main flow channel cavity according to actual experimental needs.

[0049] The undersea sediment filled into the main flow channel cavity in the present invention can freely combine different shapes, types, and quantities of particles as needed to construct a porous medium region with specified heterogeneous characteristics, and can quantitatively characterize its pore characteristics.

[0050] In some embodiments, the particle type of the seabed sediment includes any one or a combination of at least two of clay, muddy sediments, silty sediments, quartz sand, or glass microspheres. Depending on the actual experimental requirements, the present invention may select a single type of seabed sediment or a combination of different types of seabed sediments. Typical but non-limiting combinations include: combinations of clay, muddy sediments, and silty sediments; combinations of silty sediments, quartz sand, and glass microspheres; combinations of clay, muddy sediments, and quartz sand; combinations of muddy sediments, silty sediments, and quartz sand; combinations of muddy sediments and silty sediments; combinations of clay, quartz sand, and glass microspheres; combinations of muddy sediments, silty sediments, and glass microspheres, etc., but are not limited to the above examples.

[0051] The shape of the seabed sediment particles described in this invention includes any one or a combination of at least two of the following: spherical, cylindrical, regular polygonal, ellipsoidal, or irregular polygonal. Polygons include, but are not limited to, square, rectangular, pentagonal, hexagonal, octagonal, and decagonal. Seabed sediment particles of the same type can have multiple different shapes. Depending on the actual experimental requirements, this invention can select a single shape of seabed sediment or a combination of multiple different shapes. Typical but non-limiting combinations include: combinations of spherical, cylindrical, and square particles; combinations of spherical, cylindrical, and ellipsoidal particles; combinations of cylindrical, spherical, square, and irregular quadrilateral particles; combinations of square, spherical, or irregular pentagonal particles, etc., but are not limited to the above examples.

[0052] Furthermore, this invention mixes particles of different types and shapes in a certain proportion to form a porous media zone with a specific heterogeneous distribution within the main channel cavity. Typical but not limiting combinations include: combinations of spherical clay, cylindrical argillaceous sediments, and square silty sediments; combinations of spherical quartz sand, cylindrical silty sediments, and ellipsoidal spherical clay; combinations of cylindrical silty sediments, spherical glass microspheres, square argillaceous sediments, and irregular quadrilateral clay; combinations of square argillaceous sediments, spherical quartz sand, or irregular pentagonal clay; and combinations of cylindrical quartz sand, spherical glass microspheres, and square clay, etc. After filling, this invention measures the porosity of the sediments and combines this with image analysis or Raman scanning to establish a physical model corresponding to the actual reservoir parameters based on the particle location, porosity, pore size distribution, particle size distribution, and permeability of the seafloor sediments within the porous media zone.

[0053] In this invention, two filter grooves are also provided on both sides of the main channel cavity. The filter grooves are at least partially located within the main channel cavity, and the main channel cavity is connected to the injection channel and the outflow channel respectively through the two filter grooves. This invention can employ wet etching or plasma etching to form the filter grooves at the connection between the main channel cavity and the injection channel or outflow channel. This invention does not specifically limit the size of the filter grooves; those skilled in the art can design the specifications and dimensions of the filter grooves according to actual experimental needs.

[0054] The filter tank is filled with filter material to filter and remove any impurities or solid particles that may appear, preventing fine particles from flowing into the injection or outflow channels. After filling the filter tank, the filter material is fixed using high-temperature sintering or medical-grade adhesive to ensure a good seal between the material and the inner wall of the filter tank. When fluid flows from the inlet, it sequentially passes through the injection channel and the filter tank on one side, then enters the main channel cavity filled with seabed sediment, interacting with the porous media area. Upon outflow, it is filtered by the filter material on the other side, ensuring that fine particles do not clog the outflow channel or downstream equipment as the fluid is discharged.

[0055] In some embodiments, the filter tank is filled with sand-proof filter stones to filter and remove impurities, particulate matter, or solid particles that may appear in the microfluidic chip, preventing smaller particles or sand from clogging the flow channels, thereby ensuring that the fluid flows unimpeded inside the chip and avoiding interference with experimental results.

[0056] The sand-control filter stone can be made of sintered metal balls, porous ceramics, or polymer filter media. Its pore size is selected according to the particle size of the finest particles in the seabed sediment being filled. Its average pore size is usually 0.1μm to 50.0μm, for example, it can be 0.1μm, 0.5μm, 1μm, 2μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, or 50μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0057] Furthermore, the present invention can use a combination of sand-control filter stones of different particle sizes to fill the filter tank according to different fluid properties. For example, the sand-control filter stones in the filter tank are distributed in segments, and the particle size of the sand-control filter stones increases or decreases along the fluid flow direction. For instance, the sand-control filter stones filling the filter tank are divided into four filtration zones, sequentially designated as the first filtration zone, the second filtration zone, the third filtration zone, and the fourth filtration zone along the fluid flow direction. The particle size distribution of the sand control filter stone in each filtration zone can be adopted in the following ways: (1) The average pore size of the sand control filter stone in the first filtration zone is 50 μm, the average pore size of the sand control filter stone in the second filtration zone is 35 μm, the average pore size of the sand control filter stone in the third filtration zone is 20 μm, and the average pore size of the sand control filter stone in the fourth filtration zone is 5 μm; (2) The average pore size of the sand control filter stone in the first filtration zone is 1 μm, the average particle size of the sand control filter stone in the second filtration zone is 5 μm, the average pore size of the sand control filter stone in the third filtration zone is 10 μm, and the average pore size of the sand control filter stone in the fourth filtration zone is 25 μm.

[0058] In this invention, the injection channel and the outflow channel are located at opposite ends of the main channel cavity, so that the fluid enters the main channel cavity from the inflow port through the injection channel and one side filter tank, then flows out through the outflow channel, passes through the other side filter tank, and is discharged from the outflow port.

[0059] In some embodiments, both the injection channel and the outflow channel are L-shaped, each independently including a connected transverse flow channel and a longitudinal flow channel. The transverse flow channel connects to the main flow channel cavity, and the longitudinal flow channel connects to the inflow port or the outflow port. The L-shaped channel design helps to mitigate the direct impact of fluid on the filter material, extending its sand-proof life. This invention does not specifically limit the dimensions of the injection channel and the outflow channel; those skilled in the art can adjust the dimensions according to actual experimental needs.

[0060] This invention features filter grooves at both the inlet and outlet ends of the main channel cavity, combined with an L-shaped channel design, which significantly reduces the risk of fine particles clogging the injection and outflow channels, achieving sand prevention and anti-clogging, and is suitable for long-term experiments with high-mud sediments.

[0061] In another specific embodiment, the present invention provides a method for fabricating a microfluidic chip according to a specific embodiment, the method comprising: S1: Etching is performed on the substrate surface to form the main channel cavity, injection channel and outflow channel; S2: Preset the porosity, pore size distribution, grain size distribution and permeability conditions of the required seabed sediments; S3: Provide the seabed sediment particles to be filled, and measure their particle morphology, particle size distribution, density and specific surface area. Based on the preset conditions in step S2, determine the filling form and combination of the seabed sediment particles, and fill them into the main channel cavity to form a porous media area. S4: Cover the substrate with a transparent cover layer so that the inflow port is connected to the injection channel and the outflow port is connected to the outflow channel to obtain a microfluidic chip.

[0062] This invention uses wet etching or plasma etching to form main channel cavities, injection channels and outflow channels on the substrate.

[0063] This invention allows for the free selection of the type and shape of seafloor sediment particles according to experimental requirements. The particle types include any one or a combination of at least two of clay, muddy sediments, silty sediments, quartz sand, or glass microspheres. Particle shapes include any one or a combination of at least two of spherical, cylindrical, regular polygonal, ellipsoidal, or irregular polygonal shapes. In step S3, by mixing seafloor sediment particles of different types and shapes in a certain proportion, a porous medium region with a specific heterogeneous distribution can be formed within the main channel cavity. After filling, by measuring the porosity of the sediment and combining it with image analysis or Raman scanning, characteristic parameters such as particle location, porosity, pore size distribution, particle size distribution, and permeability of the region are determined, thereby establishing a physical model corresponding to the actual reservoir parameters.

[0064] In the process of filling seabed sediments, the present invention controls the filling density by vibration or compaction, thereby satisfying the porosity and particle distribution characteristics.

[0065] In some embodiments, a first filter groove is formed at the connection between the main channel cavity and the injection channel by an etching process, and a second filter groove is formed at the connection between the main channel cavity and the outflow channel. Filter materials are then filled into both the first and second filter grooves. The filter materials include sand-controlling filter stones, which can be made of sintered metal spheres, porous ceramics, or polymer filter media. The pore size is selected based on the particle size of the finest particles in the filling sediment, with an average particle size typically ranging from 0.1 μm to 50.0 μm.

[0066] In some embodiments, the assembly of the transparent cover layer and the substrate layer includes: drilling holes in both the transparent cover layer and the substrate layer to form multiple first positioning holes or second positioning holes distributed circumferentially along their respective edges, with the positions of the first positioning holes and second positioning holes corresponding one-to-one; after the transparent cover layer is placed on the substrate layer, positioning pins are used for alignment and positioning; and high-strength adhesive is applied to the surfaces of the transparent cover layer and the substrate layer that are close to each other, followed by pressure fixing to achieve adhesive sealing. The drilling process can be performed using CNC machining or laser etching.

[0067] It should be noted that the CNC machining, laser etching, wet etching, plasma etching, pressure curing, high-temperature sintering, and adhesive fixing involved in this invention are all common processes in the field, and this invention does not specifically limit their operation steps.

[0068] In addition, after assembly, the present invention performs an overall pressure resistance test on the microfluidic chip to ensure that there is no leakage or rupture under simulated high-pressure underwater environment, and verifies the fluid sealing performance inside the chip.

[0069] In another specific embodiment, the present invention provides an application of the microfluidic chip described in a specific embodiment, wherein the microfluidic chip is applied to microscopic experiments of multiphase flow in porous media.

[0070] It should be noted that the microscopic experiment of multiphase flow in porous media refers to the physical experiment of directly observing and measuring the flow process of two or more immiscible fluids (such as oil-water, gas-water) inside a porous medium at the pore scale, such as microscopic experiments of multiphase flow in porous media such as hydrates, water remediation, CO2, methane, and oil and gas.

[0071] For example, the present invention provides a test experiment on the phase change and seepage process of hydrate formation, specifically including: The microfluidic chip was placed in a cryogenic chamber, and deionized water was injected through the inlet port to saturate the pores of the seabed sediment in the main channel cavity. Then, methane gas was injected through the inlet port to gradually increase the internal pressure of the chip to the first pressure, maintain the pressure and cool down to the required temperature for a period of time. During this period, the hydrate phase transition process in the pores of the seabed sediment in the main channel cavity was observed in real time using a high-resolution microscope. Maintaining a constant temperature, the outlet pressure is controlled through the outflow port, gradually reducing the internal pressure of the chip from the first pressure to the second pressure, which is lower than the equilibrium pressure of the methane hydrate phase. During this process, the gas and water production rates are recorded in real time, and the multiphase permeation behavior at the pore scale is captured using a microscopic imaging system.

[0072] Example This embodiment provides a microfluidic chip, such as Figure 1 and Figure 2 As shown, it includes a transparent cover layer 06 and a substrate layer 07 that are bonded together; The transparent cover layer 06 is made of borosilicate glass, and its edge has six first positioning holes 051 distributed circumferentially. Inflow ports 011 and outflow ports 012 are provided on both sides of the end face of the transparent cover layer 06. Both inflow ports 011 and 012 are circular threaded holes with a specification of 1 / 4-28 UNF. High-pressure connecting bolts are installed on inflow ports 011 and 012 to connect to polyetheretherketone (PEEK) pipelines, and they are also connected to back pressure valves. A main channel cavity 08, an injection channel, and an outflow channel are formed in the middle of the side of the substrate layer 07 near the transparent cover layer 06. The injection channel and the outflow channel are connected to the two ends of the main channel cavity 08, respectively. The main channel cavity 08 is rectangular, with a length of 50 mm, a width of 10 mm, and a depth of 2 mm. Both the injection channel and the outflow channel have an "L"-shaped structure, each independently including a connected transverse flow channel 02 and a longitudinal flow channel 01. A filter groove is formed at the connection between the transverse flow channel 02 of the injection channel and the main channel cavity 08, with part of the filter groove located inside the main channel cavity 08, while the longitudinal flow channel 01 is connected to the inflow port 011. A filter groove is formed at the connection between the transverse flow channel 02 of the outflow channel and the main channel cavity 08, with part of the filter groove located inside the main channel cavity 08, while the longitudinal flow channel 01 is connected to the outflow port 012. The filter groove is rectangular, with a length of 5 mm, a width of 5 mm, and a depth of 2 mm. The main channel cavity 08 is filled with seafloor sediment particles 04 from the Shenhu area of ​​the South China Sea, forming a porous media zone. The seafloor sediment particles 04 include clay, muddy sediments, and silty sediments, with particle shapes including spherical, square, elliptical, and cylindrical, and a filling density of 2.65 g / cm³. 3 Its specific surface area is 12.5 m². 2 / g, porosity is 42%. The filter tank is filled with sintered stainless steel ball sand-proof filter stone 03, with an average pore size of 30μm; The edge of the substrate layer 07 has six second positioning holes 052 distributed circumferentially, which correspond one-to-one with the first positioning holes 051 of the transparent cover layer 06. The first positioning holes 051 and the second positioning holes 052 are connected by stainless steel positioning bolts 05. The transparent cover layer 06 and the substrate layer 07 are also bonded together by epoxy resin high-strength adhesive.

[0073] Preparation Example This preparation example is used to prepare the microfluidic chip provided in the embodiment, and specifically includes the following steps: Processing the transparent cover plate layer 06: Using CNC machining technology, two circular threaded holes are machined at both ends of the transparent cover plate layer 06 to facilitate connection with the high-pressure horizontal flow pump and back pressure valve. At the same time, six first positioning holes 051 are machined on the edge of the transparent cover plate layer 06 so that the hole diameter is clearance-fitted with the positioning bolt 05. Fabricating substrate layer 07: Wet etching is used to etch the main channel cavity 08 into substrate layer 07; L-shaped channels are etched at both ends of the main channel cavity 08 to serve as injection channels and outflow channels; then two filter trenches are etched at the connection between the L-shaped channels at both ends and the main channel cavity 08; at the same time, six second positioning holes 052 are processed on the edge of substrate layer 07 to correspond one-to-one with the first positioning holes 051 of transparent cover layer 06; Install the sand-proof filter stone 03: Embed the two sintered stainless steel ball sand-proof filter stones 03 into the two filter tanks respectively, and fix them with medical-grade glue to ensure that the sand-proof filter stone 03 is well sealed to the tank wall; Selecting seabed sediment 04: Pre-determine the required porosity, pore size distribution, particle size distribution, and permeability conditions for seabed sediment 04. Based on these conditions, determine the filling form and combination of the seabed sediment 04 particles. Collect seabed sediment 04 samples from the Shenhu area of ​​the South China Sea. After freeze-drying and sieving, remove coarse particles larger than 500 μm. Use a scanning electron microscope to measure particle morphology, a laser particle size analyzer to detect particle size distribution D50≈45 μm, and measure density. Use the BET method (Brunauer-Emmett-Teller, specific surface area method) to measure specific surface area. Then, use a micro-syringe to fill the main channel cavity 08 layer by layer with seabed sediment 04. After each layer, gently tap the chip to compact the particles until the cavity is full, making the surface of the seabed sediment 04 flush with the upper edge of the main channel cavity 08. Assembly and Sealing: Remove residual deposit particles from the main channel cavity 08, align and lock the transparent cover layer 06 and the substrate layer 07 using six stainless steel positioning bolts 05, apply high-strength epoxy resin adhesive to the contact surfaces of the two, and apply pressure to cure, so that the transparent cover layer 06 and the substrate layer 07 are bonded together; after curing, check the sealing performance by injecting nitrogen to 10MPa and holding the pressure for 30 minutes without pressure drop, indicating that the sealing is qualified. Subsequently, perform an overall pressure resistance test on the microfluidic chip to ensure that there is no leakage or rupture under the simulated high pressure environment of the seabed, and verify the fluid sealing performance inside the chip; Installation interface: Install high-pressure connecting bolts on the inflow port 011 and outflow port 012 of the transparent cover layer 06 respectively to connect the polyether ether ketone pipeline.

[0074] Application examples This application example uses the microfluidic chip provided in the embodiment to conduct microscopic experiments on hydrate phase transformation and multiphase flow, specifically including the following steps: Hydrate phase transition process: The chip was placed in a cryogenic chamber at 4°C, and deionized water was injected through the injection port at a rate of 0.1 mL / min to saturate the pores of the seabed sediment 04. Then, methane gas was injected and pressurized to 10 MPa at a rate of 0.5 MPa / min. This pressure was maintained and the temperature was lowered to 2°C for 12 hours. The hydrate phase transition process in the pores of the seabed sediment 04 in the main channel cavity 08 was observed in real time using a high-resolution microscope. Observations show that hydrates first nucleate at the gas-water interface, growing in a flocculent or fibrous manner, gradually enveloping the surface of sediment particles, and eventually filling part of the pore throats. This process clearly demonstrates the phase transition from free water / free gas to the hydrate solid phase.

[0075] Decomposition and percolation observation: Maintain a constant temperature of 2℃, control the outlet pressure through the back pressure valve at the outlet port 012, and gradually reduce the pressure inside the chip from 10MPa to 3MPa, which is lower than the equilibrium pressure of methane hydrate phase. During this process, the gas and water production rates are recorded in real time, and the multiphase percolation behavior at the pore scale is captured using a microscopic imaging system.

[0076] Observations show that in the initial stage of depressurization, hydrate decomposition produces microbubbles and liquid water, forming a complex seepage network of gas and water phases in the pores. A small amount of fine particles aggregated upstream of the sand control filter 03, but the filter effectively prevented particles from entering the outlet channel. In the middle stage of depressurization, the hydrate decomposition front advanced from both ends of the main channel cavity 08 towards the center. Significant phase interface movement was observed at the decomposition front, with bubbles merging, migrating, and preferentially seeping along the large pore channels. In the later stage of depressurization, the seabed sediment particles 04 remained in situ without significant scouring or migration, while the residual hydrates gradually decomposed, and the gas-water two-phase seepage tended to stabilize. The entire experiment lasted 8 hours, with a cumulative gas production of 12.6 mL (standard conditions) and a water production of 5.8 mL. The outlet pipe was clear with no solid discharge. The above experiment fully reproduced the coupled seepage process of hydrate decomposition phase change and multiphase fluid in the pores of real sediments.

[0077] This invention overcomes the technical shortcomings of existing microfluidic chips, such as the inability to fill real seabed sediment O4 particles, lack of sand-proof design, and insufficient high-pressure sealing. It can not only simulate the pore structure of in-situ sediments and has sand-proof and high-pressure sealing capabilities, but also realize the visualization of multiphase flow, providing a reliable experimental platform for microscopic research on natural gas hydrate mining.

[0078] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A microfluidic chip filled with seabed sediment, characterized in that, The microfluidic chip includes a transparent cover layer and a substrate layer that are bonded together. The substrate layer has a main channel cavity, an injection channel and an outflow channel on the side near the transparent cover layer. The injection channel and the outflow channel are arranged opposite to each other on both sides of the main channel cavity and are respectively connected to the main channel cavity. The main channel cavity is filled with seabed sediment particles to form a porous medium region. The transparent cover layer has an inflow port and an outflow port. The inflow port is connected to the injection channel, and the outflow port is connected to the outflow channel.

2. The microfluidic chip according to claim 1, characterized in that, The seabed sediment particles include any one or a combination of at least two of the following: clay, muddy sediments, silty sediments, quartz sand, or glass microspheres.

3. The microfluidic chip according to claim 1 or 2, characterized in that, The shape of the seabed sediment particles includes any one or a combination of at least two of the following: spherical, cylindrical, regular polygonal, ellipsoidal, or irregular polygonal.

4. The microfluidic chip according to any one of claims 1-3, characterized in that, Two filter slots are also provided on both sides of the main channel cavity, and the filter slots are at least partially located in the inner cavity of the main channel cavity. The main channel cavity is connected to the injection channel and the outflow channel through the two filter slots, respectively. The filter tank is filled with filter material.

5. The microfluidic chip according to claim 4, characterized in that, The filter material includes sand-proof filter stones; The pore size of the sand-proof filter stone is 0.1μm~50.0μm.

6. The microfluidic chip according to any one of claims 1-5, characterized in that, Both the injection channel and the outflow channel have an "L" shaped structure, and each independently includes a connected transverse flow channel and a longitudinal flow channel. The transverse flow channel is connected to the main flow channel cavity, and the longitudinal flow channel is connected to the inflow port or the outflow port.

7. The microfluidic chip according to any one of claims 1-6, characterized in that, The transparent cover layer is detachably connected to the substrate layer; And / or, the transparent cover layer is bonded to the substrate layer; And / or, the transparent cover layer and the substrate layer are respectively provided with a plurality of first positioning holes and a plurality of second positioning holes, the first positioning holes and the second positioning holes are in one-to-one correspondence and are connected by fasteners.

8. A method for preparing a microfluidic chip filled with seabed sediment as described in any one of claims 1-7, characterized in that, The preparation method includes: S1: Etching is performed on the substrate surface to form the main channel cavity, injection channel and outflow channel; S2: Preset the porosity, pore size distribution, grain size distribution and permeability conditions of the required seabed sediments; S3: Provide the seabed sediment particles to be filled, and measure their particle morphology, particle size distribution, density and specific surface area. Based on the preset conditions in step S2, determine the filling form and combination of the seabed sediment particles, and fill them into the main channel cavity to form a porous media area. S4: Cover the substrate with a transparent cover layer so that the inflow port is connected to the injection channel and the outflow port is connected to the outflow channel to obtain a microfluidic chip.

9. The preparation method according to claim 8, characterized in that, The preparation method further includes: etching two filter grooves at the junction of the main channel cavity and the injection channel, and at the junction of the main channel cavity and the outflow channel, and filling the filter grooves with sand-proof filter stones. And / or, fasteners are used to connect the transparent cover layer and the substrate layer, so that the transparent cover layer and the substrate layer are bonded and sealed.

10. An application of the microfluidic chip according to any one of claims 1-7, characterized in that, The microfluidic chip is used for microscopic experiments on multiphase flow in porous media.

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