A microfluidic chip based on real core, visual experiment device and simulation experiment method

Abstract

This application belongs to the field of oil and gas reservoir engineering technology, and provides a microfluidic chip based on real rock cores, a visualization experimental device, and a simulation experimental method. The microfluidic chip provided in this application includes a rock substrate and microchannels formed on the surface of the rock substrate; the microchannels include several pore units and connecting microchannels connecting each pore unit; the depth of the pore unit is less than the depth of the connecting microchannels. The visualization experimental device provided in this application can continuously perform dynamic imaging recording of liquid phase saturation, heating and pressurization, mineral dissolution or corrosion reactions, CO2 displacement drying, and salt precipitation deposition within the same rock-based chip, to obtain process characteristics such as gas-liquid two-phase flow, water-rock reaction, residual liquid phase redistribution, drying front advancement, and salt crystallization deposition distribution.

Description

Technical Field

[0001] This application relates to the field of oil and gas reservoir engineering technology, specifically to a microfluidic chip based on real rock cores, a visualization experimental device, and a simulation experimental method. Background Technology

[0002] Carbon dioxide capture, utilization, and storage (CCUS) has become one of the important technological pathways for achieving low-carbon utilization and large-scale emission reduction of fossil energy. CCUS projects typically inject captured carbon dioxide into deep saline aquifers, depleted oil and gas reservoirs, and other geological bodies to achieve long-term storage or synergistically enhance oil and gas recovery. During this process, complex processes such as multiphase fluid migration, formation water concentration, mineral dissolution and precipitation, pore structure evolution, and changes in seepage capacity are commonly present within the reservoir. Especially in deep saline aquifers, high-salinity oil reservoirs, and depleted oil and gas reservoirs with well-developed high-salinity formation water, these processes can significantly impact the injection capacity and long-term operational stability of the near-wellbore zone.

[0003] During carbon dioxide injection, the injected gas promotes water migration and concentration in the residual brine within the pores. When the brine reaches supersaturation, dissolved salts precipitate out as crystals and deposit in pores, pore throats, microfractures, or dominant flow channels, resulting in reduced effective flow space, decreased porosity, and reduced permeability. Macroscopically, this manifests as increased injection pressure, decreased injection index, and reduced near-wellbore permeability. Simultaneously, carbon dioxide or acidic brine may react with real rock minerals through dissolution, corrosion, and secondary precipitation, further altering pore wall morphology, wettability, and local connectivity. Therefore, it is crucial to establish an experimental technique system capable of simultaneously reflecting real rock surface characteristics, multiphase flow, water-rock reactions, and salt precipitation processes to reveal the mechanism by which salt precipitation affects reservoir permeability.

[0004] To study pore-scale processes such as multiphase flow, salt precipitation, and water-rock reaction in reservoirs, existing techniques typically employ core displacement experiments, visual flat plate model experiments, and microfluidic chip experiments. Core displacement experiments can preserve the mineral composition, pore structure, and wettability characteristics of natural rocks relatively well; however, they often rely on indirect analysis based on pressure differences, permeability, or CT scan results before and after the experiment, making it difficult to continuously, in situ, and in real-time observe the dynamic processes of gas-liquid interface migration, brine concentration, salt crystal nucleation and growth, and pore throat blockage within the pores. While conventional glass, silicon-based, or polymer microfluidic chips offer excellent visualization advantages, their wall chemical properties, mineral composition, roughness, wettability, and reactivity differ significantly from those of real reservoir rocks, easily leading to inconsistencies between brine occurrence morphology, evaporation recharge pathways, and salt crystal deposition patterns and the actual reservoir. Summary of the Invention

[0005] In view of this, the technical problem to be solved by this application is to provide a microfluidic chip, a visualization experimental device and a simulation experimental method based on real rock cores. Based on real rock cores, it can realize an integrated experiment of liquid phase saturation, water-rock reaction, carbon dioxide displacement, residual brine drying, salt precipitation deposition and image quantitative evaluation under high temperature and high pressure conditions.

[0006] This application provides a microfluidic chip based on a real rock core, including a rock substrate and microchannels formed on the surface of the rock substrate; The microchannel comprises n repeating flow channel units, with adjacent repeating flow channel units connected. Each repeating flow channel unit includes a first rectangular microchannel, a second rectangular microchannel, a third rectangular microchannel, and a fourth rectangular microchannel. The length direction of the second rectangular microchannel is perpendicular to the length direction of the first rectangular microchannel, and the liquid inlet of the second rectangular microchannel is connected to the liquid outlet of the first rectangular microchannel. The length direction of the third rectangular microchannel is perpendicular to the length direction of the second rectangular microchannel, and the liquid inlet of the third rectangular microchannel is connected to the liquid outlet of the second rectangular microchannel. The length direction of the fourth rectangular microchannel is perpendicular to the length direction of the third rectangular microchannel, and the liquid inlet of the fourth rectangular microchannel is connected to the liquid outlet of the third rectangular microchannel. The repeating flow channel unit includes several pore units and connecting microchannels connecting each pore unit; The depth of the pore unit is less than the depth of the connecting microchannel.

[0007] In some specific implementations, the pore units are arranged in an array.

[0008] In some specific implementations, the pore units in adjacent rows are arranged in an alternating pattern.

[0009] In some specific implementations, the depth of the pore unit is 0; the maximum size of the pore unit in the direction parallel to the surface of the rock substrate is 100μm~500μm; The depth of the connecting microchannel is 20μm to 200μm; the width of the connecting microchannel in the direction parallel to the surface of the rock substrate is 100μm to 200μm.

[0010] In some specific implementations, the rock substrate is a sandstone substrate, a dolomite substrate, a marble substrate, or a limestone substrate; The thickness of the rock base is 1mm to 3mm.

[0011] In some specific implementations, it also includes a substrate supporting the rock substrate and / or a cover plate covering the surface of the rock substrate; And / or, it also includes a packaging structure for encapsulating the microfluidic chip.

[0012] This application also provides a visualization experimental device, including a cavity, a rock-based chip module, an imaging system, and a temperature and pressure control system; wherein, the rock-based chip module includes the microfluidic chip described in the above technical solution, and the rock-based chip module is disposed in the cavity; The imaging system is used for in-situ observation and image recording of the microfluidic chip; The temperature and pressure control system is used to control the temperature and pressure of the rock-based chip module.

[0013] In some specific implementations, the temperature and pressure control system includes a temperature control module and a pressure control module respectively connected to the cavity. The temperature control module is used to adjust the temperature of the cavity, and the pressure control module is used to adjust the pressure of the cavity.

[0014] In some specific implementations, the imaging system includes: A fluorescence microscope used to observe microfluidic chips; A fluorescent light source for illuminating the microfluidic chip; An image acquisition module for acquiring images or videos of the microfluidic chip; and an image storage module, wherein the image storage module is used to receive and store images or videos acquired by the image acquisition module.

[0015] In some specific implementations, an image processing module is also included, which is used to process the images or videos stored in the image storage module.

[0016] In some specific implementations, the image processing module includes: An image preprocessing module is used to preprocess the images stored in the image storage module; A gas phase region identification and processing module is used to receive a preprocessed image output by the image preprocessing module, identify the gas phase region of the preprocessed image and calculate the total number of pixels in the gas phase region, and calculate the gas phase saturation and estimate the evaporation-drying rate based on the total number of pixels in the gas phase region. A salt crystallization region identification and processing module is used to receive a preprocessed image output by the image preprocessing module, identify the salt crystallization region of the preprocessed image and calculate the total number of pixels in the salt crystallization region, and calculate the salt crystallization coverage and salt crystallization growth rate based on the total number of pixels in the salt crystallization region. A base map construction module is used to construct a salt crystallization layer, a matrix layer, and a base map enhancement layer based on the image stored in the image storage module, the gas phase region identified by the gas phase region identification and processing module, and the salt crystallization region identified by the salt crystallization region identification and processing module. The result output module is used to superimpose the salt crystallization layer, matrix layer and base map enhancement layer and output the result image.

[0017] This application also provides a simulation experimental method for gas-liquid-rock reaction and CO2 displacement drying salt precipitation deposition, which is carried out using the microfluidic chip or the visualization experimental device described in the above technical solution, and includes the following steps: Experimental fluid is injected into the microfluidic chip to saturate the microfluidic chip with liquid phase. The microfluidic chip is subjected to heating and pressurization treatment. After the temperature and pressure are stabilized, a reaction is carried out. The reaction is continuously monitored and images or videos of the microfluidic chip are collected during the reaction process. After the reaction is complete, the injection of the experimental fluid is stopped, and CO2 gas is injected into the microfluidic chip for displacement and drying. The displacement and drying are continuously monitored, and images or videos of the microfluidic chip are acquired during the displacement and drying process.

[0018] In some specific implementations, the experimental fluid comprises 10wt%~30wt% NaCl, 10wt%~30wt% acetic acid, 0.1wt%~1wt% rhodamine, and the balance being water; The termination pressure for the heating and pressurization process is 5MPa~10MPa, and the termination temperature is 50℃~80℃.

[0019] Compared with the prior art, this application has the following beneficial effects: (1) This application uses real core thin sections as the substrate of microfluidic chip. Compared with conventional microfluidic chip materials such as glass, silicon or polymer, it can more realistically preserve the mineral composition, surface functional groups, micro-roughness and wettability characteristics of the formation rocks, thereby reducing the systematic deviation caused by the difference between the surface chemical properties of conventional chip materials and natural rocks, and making the experimental results of gas-liquid two-phase flow, water-rock reaction and salt precipitation more closely resemble the real reservoir conditions.

[0020] (2) This application processes a geometrically regular “S”-shaped long pore medium structure on the surface of a real core thin section. Through the staggered arrangement of geometric square pore units and connecting microchannels, a regular and controllable pore-throat structure is formed. This not only preserves the characteristics of the real rock surface, but also facilitates the identification of the location and evolution characteristics of mineral dissolution, precipitation and salt precipitation under microscopic observation conditions.

[0021] (3) This application adopts a rock-based chip fabrication process with "etching-encapsulation" as the core. Through steps such as rock thin-film preparation, pattern etching, chip substrate pre-encapsulation, positioning assembly, fluid channel processing, degassing treatment, and overall potting, it can meet the experimental requirements for microstructure processing and visualization observation of rock substrates. Among them, heating or vacuum degassing treatment helps to remove residual air in the pores of rock thin films and reduce the risk of bubble generation in subsequent experiments; overall potting can form a package shell with sufficient mechanical strength and improve the stability of rock-based chip experiments.

[0022] (4) This application constructs a high-temperature and high-pressure in-situ visualization experimental platform with rock-based microfluidic chip as the core. The platform consists of rock-based chip module, imaging system and temperature and pressure control system. Furthermore, the use of fluorescence microscope and fluorescence light source can enhance the identification ability of multiphase boundary and solid phase deposition area. It can also be combined with fluorescent tracer to achieve clear distinction and quantitative analysis of gas phase, oil phase, salt water phase and reaction or deposition area.

[0023] (5) The chip fixture of this application adopts an active confining pressure loading scheme. By injecting confining pressure fluid as working medium into the outer periphery of the chip, and using the confining pressure system to actively adjust and track the confining pressure, the confining pressure changes synchronously with the internal pressure of the experiment, thereby providing more stable pressure bearing and sealing conditions for the rock-based microfluidic chip, and meeting the experimental requirements for long-term operation of the rock-based chip under high temperature and high pressure conditions.

[0024] (6) This application enables continuous imaging and recording of dynamic processes such as liquid phase saturation, temperature and pressure increase, mineral dissolution or corrosion reaction, CO2 displacement drying, and salt precipitation deposition within the same real core thin section microfluidic chip. Through this continuous experimental process, key process characteristics such as rock surface morphology, fluorescence signal distribution, pore changes, gas-liquid interface migration and reconstruction, residual liquid phase redistribution, drying front advancement, and the starting position, morphological evolution, and spatial distribution of salt precipitation deposition can be recorded in the same experimental system.

[0025] (7) The image processing module and image processing method proposed in this application can perform splicing, registration, exposure correction, color correction, noise reduction, sharpening and scale unification on the original image sequence obtained in the experiment, thereby improving the stability and comparability of image recognition; and through the construction of salt crystal layer, matrix layer and base map enhancement layer, the recognition and display of salt crystal region, matrix outline, channel boundary and salt crystal spatial distribution can be realized.

[0026] (8) This application can further transform real core microfluidic experimental images into quantitative results. By obtaining the total number of pixels in the gas phase region through image segmentation, the gas phase saturation can be calculated and the evaporation-drying rate can be estimated; by identifying the total number of pixels in the salt crystallization region, the salt crystallization coverage can be calculated and the salt crystallization growth rate can be obtained; at the same time, similar methods can also be used to obtain gas phase, water phase and oil phase regions, and combine the overall pore area to calculate gas, water and oil saturation, thereby providing visualized, repeatable and quantifiable data support for gas-liquid rock reaction, CO2 displacement drying and salt precipitation sedimentation evolution processes. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the microchannel structure; Figure 2 A schematic diagram illustrating the process of fabricating a microfluidic chip based on a real rock core for this application; Figure 3 This is a schematic diagram of the structure of the visualization experimental device provided in the embodiments of this application; Figure 4 A schematic diagram of the overall technical route for the simulation experiment provided in this application; Figure 5 Microscopic image of rock chip flow channel during CO2 displacement-drying stage (white represents salt crystallization); Figure 6 This is a bright-field micrograph of a localized area of ​​rock dissolution on a chip after the dissolution reaction has ended. Figure 7 This is a global observation diagram of the microfluidic chip after the dissolution reaction is completed (red indicates the dissolution area); Figure 8 This is a schematic diagram of the image processing flow of this application; Figure 9 A schematic diagram showing the change in salt crystallization coverage over time in different rock chips. Detailed Implementation

[0028] This application provides a microfluidic chip based on real rock cores, a visualization experimental device, and an experimental method. Those skilled in the art can refer to the content of this application and appropriately modify the process parameters to achieve the desired results. The methods and applications of this application have been described through preferred embodiments. Those skilled in the art can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this application to implement and apply the technology of this application.

[0029] In the processes of oil and gas development, carbon dioxide sequestration in deep saline water layers, and carbon dioxide displacement and sequestration in depleted oil and gas reservoirs, there are common engineering requirements such as high-salinity formation water concentration, salt crystallization, pore throat blockage, near-wellbore seepage capacity attenuation, and water-rock reaction coupling evolution. In view of the problems that existing core displacement experiments cannot achieve real-time in-situ observation at the pore scale, and that conventional glass or silicon-based microfluidic chips cannot accurately reflect the mineral composition, surface roughness, wettability, and reactivity of reservoir rocks, this application proposes an in-situ visualization experimental technology route with real core thin-film microfluidic chips as the core.

[0030] Based on this, this application provides a microfluidic chip based on a real rock core, including a rock substrate and microchannels formed on the surface of the rock substrate; The microchannel comprises n repeating flow channel units, with adjacent repeating flow channel units connected. Each repeating flow channel unit includes a first rectangular microchannel, a second rectangular microchannel, a third rectangular microchannel, and a fourth rectangular microchannel. The length direction of the second rectangular microchannel is perpendicular to the length direction of the first rectangular microchannel, and the liquid inlet of the second rectangular microchannel is connected to the liquid outlet of the first rectangular microchannel. The length direction of the third rectangular microchannel is perpendicular to the length direction of the second rectangular microchannel, and the liquid inlet of the third rectangular microchannel is connected to the liquid outlet of the second rectangular microchannel. The length direction of the fourth rectangular microchannel is perpendicular to the length direction of the third rectangular microchannel, and the liquid inlet of the fourth rectangular microchannel is connected to the liquid outlet of the third rectangular microchannel. The repeating flow channel unit includes several pore units and connecting microchannels connecting each pore unit; The depth of the pore unit is less than the depth of the connecting microchannel.

[0031] The microfluidic chip provided in this application includes a rock substrate. While preserving the rock's mineral composition and surface reaction characteristics, it enables visualized observation of gas-liquid two-phase distribution, gas-liquid interface migration, residual liquid phase redistribution, drying front advancement, and the initiation, growth, and deposition processes of salt crystallization. In some specific implementations, the rock substrate includes, but is not limited to, sandstone, dolomite, marble, or limestone substrates, which can be selected according to the specific research object. In some specific implementations, the rock substrate is a thin-section rock substrate; specifically, the thickness of the rock substrate is 1 mm to 3 mm, for example, 1 mm, 1.5 mm, or 2 mm.

[0032] In the microfluidic chip provided in this application, microchannels are formed on the surface of the rock substrate. The microchannels can contain experimental liquids and allow them to flow, so as to continuously carry out liquid phase saturation, mineral dissolution or corrosion reaction, CO2 displacement drying, salt precipitation deposition dynamic imaging recording, etc., thereby obtaining process characteristics such as gas-liquid two-phase flow, water-rock reaction, residual liquid phase redistribution, drying front advancement and salt crystal deposition distribution.

[0033] In some specific implementations, the microchannels are distributed non-linearly in a direction parallel to the surface of the rock substrate, for example, in an S-shape. See also Figure 1 , Figure 1 This is a schematic diagram of the microchannel structure, where 1 represents the microchannel, 2 represents the rock substrate, 11 represents the pore unit, and 12 represents the connecting microchannel. Specifically, the microchannels are distributed in a regular zigzag pattern in a direction parallel to the surface of the rock substrate. In some specific implementations, the microchannel 1 includes several repeating flow channel units C1, with adjacent repeating flow channel units connected together. Each repeating flow channel unit C1 includes a first rectangular microchannel C11, a second rectangular microchannel C12, a third rectangular microchannel C13, and a fourth rectangular microchannel C14. The length direction of the second rectangular microchannel C12 is perpendicular to the length direction of the first rectangular microchannel C11, and the liquid inlet of the second rectangular microchannel C12 is connected to the liquid outlet of the first rectangular microchannel C11. The length direction of the third rectangular microchannel C13 is perpendicular to the length direction of the second rectangular microchannel C12, and the liquid inlet of the third rectangular microchannel C13 is connected to the liquid outlet of the second rectangular microchannel C12. The length direction of the fourth rectangular microchannel C14 is perpendicular to the length direction of the third rectangular microchannel C13, and the liquid inlet of the fourth rectangular microchannel C14 is connected to the liquid outlet of the third rectangular microchannel C13. In some specific implementations, the first rectangular microchannel C11, the second rectangular microchannel C12, and the third rectangular microchannel C13 form an open box, that is, the length direction of the first rectangular microchannel C11 is parallel to the length direction of the third rectangular microchannel C13.

[0034] In some specific implementations, the repeating flow channel unit includes a plurality of pore units 11 and connecting microchannels 12 connecting each pore unit; the depth of the pore units is less than the depth of the connecting microchannels. In some specific implementations, the pore units 11 are arranged in an array. Specifically, the pore units 11 form multiple rows along a first direction and multiple columns along a second direction perpendicular to the first direction, with all pore units 11 arranged in a matrix row-column array. In some specific implementations, adjacent rows of pore units 11 are staggered. In some specific implementations, the gaps between each pore unit 11 form connecting microchannels 12, or the connecting microchannels 12 are formed in the gaps between each pore unit 11.

[0035] In some specific implementations, the depth of the pore unit 11 is 0, meaning the pore unit is unetched and its surface is coplanar with the original surface of the rock substrate. In some specific implementations, the maximum dimension of the pore unit 11 in the direction parallel to the surface of the rock substrate is 100μm~500μm, preferably 150μm~400μm, and more preferably 200μm~300μm. Those skilled in the art will understand that the depth of the pore unit 11 is its dimension in the direction perpendicular to the surface of the rock substrate; when the pore unit 11 has an irregular shape, this depth is taken as the average dimension of the pore unit 11 in the vertical direction. The maximum dimension of the pore unit 11 in the direction parallel to the surface of the rock substrate is defined as the straight-line distance between the two furthest points on the maximum cross-section of the pore unit 11 parallel to the surface of the rock substrate. For example, when the maximum cross-section of the pore unit 11 is circular, this maximum dimension corresponds to the diameter of the circle; when the maximum cross-section of the pore unit 11 is square or rectangular, this maximum dimension corresponds to the diagonal of the square or rectangle. In some specific implementations, the pore unit 11 is a cube, and its cross-section is square.

[0036] In some specific implementations, the depth of the connecting microchannel 12 is greater than the depth of the pore unit 11, facilitating observation of the effect of the experimental liquid on the rock substrate. In some specific implementations, the depth of the connecting microchannel 12 is 20 μm to 200 μm, preferably 30 μm to 150 μm, and more preferably 40 μm to 100 μm. In some specific implementations, the width of the connecting microchannel 12 in the direction parallel to the surface of the rock substrate is 100 μm to 200 μm, preferably 120 μm to 180 μm, and more preferably 140 μm to 160 μm. Those skilled in the art will understand that the depth of the connecting microchannel 12 is its dimension along the direction perpendicular to the surface of the rock substrate; when the connecting microchannel 12 has an irregular shape, this depth is taken as the average dimension of the connecting microchannel 12 along the vertical direction. The width of the connecting microchannel 12 in the direction parallel to the surface of the rock substrate is defined as the dimension perpendicular to the length direction of the connecting microchannel connecting two adjacent pore units. When the connecting microchannel 12 has an irregular shape, the width is taken as the average dimension of the connecting microchannel 12 in the vertical direction along its length.

[0037] In some specific implementations, the microchannel includes connecting microchannels 12 of different depths, such as connecting microchannels with depths of 50μm, 100μm, and 150μm, which can meet the processing requirements of different fluid channels and encapsulation structures, and also facilitate the observation of the different effects of experimental liquids on rock substrates at different depths.

[0038] In some specific implementations, the microchannel further includes a liquid inlet microchannel connected to the first repeating channel unit and a liquid outlet microchannel connected to the nth repeating channel unit. This application does not impose any particular limitation on the width of the liquid inlet microchannel and the liquid outlet microchannel in the direction parallel to the surface of the rock substrate, as long as it facilitates the inflow of experimental liquid into the repeating channel unit. In some specific implementations, the depth of the liquid inlet microchannel and the liquid outlet microchannel is greater than the depth of the connecting microchannels in the repeating channel unit, and can be independently 100μm~300μm, preferably 150μm~250μm.

[0039] In some specific implementations, the microchannel further includes a liquid inlet connected to the liquid inlet microchannel and a liquid outlet connected to the liquid outlet microchannel. This application does not impose any particular limitation on the width of the liquid inlet and liquid outlet in the direction parallel to the surface of the rock substrate, as long as it facilitates the inflow and outflow of the experimental liquid. In some specific implementations, the depth of the liquid inlet and liquid outlet is greater than the depth of the liquid inlet microchannel and liquid outlet microchannel, and can be independently 300 μm to 800 μm, preferably 400 μm to 600 μm.

[0040] The microchannel structure described above uses porous units as pores and connecting microchannels as pore throats to form a pore-throat structure. This allows the experimental model to more realistically reflect the surface, micro-roughness, pore wall reactivity, and fluid-rock interaction characteristics of rocks and minerals, thereby reducing the systematic bias caused by differences in conventional chip materials in the experimental results.

[0041] In some specific implementations, the total length of the microchannel is preferably 1cm to 10cm, more preferably 2cm to 8cm, and most preferably 3cm to 5cm.

[0042] In some specific implementations, the microfluidic chip further includes a substrate supporting the rock substrate. The substrate is laminated to the surface of the rock substrate on the side without microchannels, serving to support and protect the rock substrate. This application does not impose any special restrictions on the material of the substrate; it can be a potting compound. Using a potting compound as the substrate for the rock matrix can improve the strength and pressure resistance of the microfluidic chip and reduce its packaging difficulty.

[0043] In some specific implementations, the microfluidic chip further includes a cover plate covering the surface of the rock substrate. The cover plate covers the side of the rock substrate where the microchannels are located, and is used to seal the microchannels. This application does not impose any special limitations on the cover plate; it can be a transparent sealing film or a transparent cover plate, as long as it can seal the microchannels. Using a cover plate to initially seal the microfluidic chip can reduce the risk of bubble formation during subsequent experiments and is beneficial for imaging observation.

[0044] In some specific implementations, the microfluidic chip includes both a cover plate covering the surface of the rock substrate and a substrate supporting the rock substrate. The structure and materials are as described above and will not be repeated here.

[0045] In some specific implementations, the microfluidic chip further includes an encapsulation structure for encapsulating the microfluidic chip. This application does not impose any special limitations on the encapsulation structure; it can be an encapsulating adhesive that completely covers the microfluidic chip, or it can completely cover the microfluidic chip including the substrate, or it can completely cover the microfluidic chip including the substrate and a cover plate, or it can completely cover the microfluidic chip including the cover plate. Encapsulating the microfluidic chip to form an encapsulation structure can improve the mechanical strength of the microfluidic chip and solve the problems of brittleness and insufficient pressure resistance in real rock substrates, which easily lead to leakage, debonding, cracking, bubble residue, and observation instability in high-temperature, high-pressure carbon dioxide displacement and long-term salting-out experiments. In some specific implementations, the encapsulation structure is provided with an injection channel and an output channel. The injection channel is connected to the liquid inlet of the microfluidic channel for injecting experimental liquid into the microfluidic channel; the output channel is connected to the liquid outlet of the microfluidic channel for discharging experimental liquid from the microfluidic channel.

[0046] The microfluidic chip provided in this application uses rock as a substrate and sets microchannels on the surface of a real rock substrate. While preserving the characteristics of the real rock substrate, such as rock mineral composition and surface reaction characteristics, it forms a geometrically regular, well-defined microchannel flow structure that is easy to observe under microscopic conditions. This provides an experimental platform for subsequent gas-water displacement, water-rock reaction, drying salt precipitation deposition and their image quantitative analysis under high temperature and high pressure conditions. For example, it can be used to study the influence of potential water-rock reaction on the surface of real strata rock on the pore-scale gas-liquid two-phase flow behavior, or to identify the location and evolution characteristics of mineral dissolution, precipitation and salt precipitation deposition processes under microscopic observation conditions.

[0047] This application also provides a method for fabricating a microfluidic chip based on a real rock core, comprising the following steps: Microchannels are formed on the surface of a rock substrate. Each microchannel comprises n repeating channel units, with adjacent repeating channel units connected. Each repeating channel unit includes a first rectangular microchannel, a second rectangular microchannel, a third rectangular microchannel, and a fourth rectangular microchannel. The length direction of the second rectangular microchannel is perpendicular to the length direction of the first rectangular microchannel, and the liquid inlet of the second rectangular microchannel is connected to the liquid outlet of the first rectangular microchannel. The length direction of the third rectangular microchannel is perpendicular to the length direction of the second rectangular microchannel, and the liquid inlet of the third rectangular microchannel is connected to the liquid outlet of the second rectangular microchannel. The length direction of the fourth rectangular microchannel is perpendicular to the length direction of the third rectangular microchannel, and the liquid inlet of the fourth rectangular microchannel is connected to the liquid outlet of the third rectangular microchannel. The repeating flow channel unit includes a plurality of pore units and connecting microchannels connecting each pore unit, wherein the depth of the pore unit is less than the depth of the connecting microchannel.

[0048] This application describes the fabrication of microfluidic chips using rock as a substrate. There are no particular limitations on the rock substrate, but it is preferably prepared using the following method: first, the original rock core is cut and sampled, then successively ground and polished to obtain a rock substrate with a smooth surface and low roughness. There are no particular limitations on the parameters for the cutting, sampling, grinding, and polishing processes; parameters commonly used by those skilled in the art are acceptable.

[0049] After obtaining the rock substrate, the rock substrate is etched according to a predetermined microchannel pattern to form microchannels on its surface. In this application, the microchannels are as described above, and will not be repeated here. This application preferably employs laser etching to form microchannels on the surface of a rock substrate. In some specific implementations, the laser etching wavelength is 400nm~600nm, for example 515nm; the pulse width is 200fs~400fs, for example 300fs; the repetition frequency is 50kHz~150kHz, for example 100kHz; a 20x objective lens is used, with a focused spot diameter of 10μm~15μm, for example approximately 12μm; the single pulse energy is 0.5μJ~0.7μJ, for example 0.65μJ; the scanning speed is 50mm / s~150mm / s, for example 100mm / s; the fill line spacing is 1μm~5μm, for example 4μm; the number of scans is 1~10, for example 5; the focal point is located on the rock core surface, and the scanning directions of adjacent scan layers are set to 0° and 90° respectively. After forming the microchannels, this application preferably pre-packages the microfluidic chip to form a substrate supporting the rock substrate. In some specific implementations, the pre-packaging includes the following steps: After pre-curing the potting compound to a semi-gel state, the microfluidic chip prepared above is added, and the mixture is pressed, cured, and injection and output channels are formed to form a pre-encapsulated microfluidic chip.

[0050] This application first pre-cures the potting compound in a mold to achieve a semi-gel state. This application does not impose any particular limitation on the potting compound; it can be a two-component potting compound, such as EpoxiCure2 cold-mount epoxy resin produced by Buehler, Inc., which includes an EpoxiCure 2 Resin component and an EpoxiCure 2 Hardener component. In some specific implementations, the pre-curing temperature is room temperature, preferably 10℃~40℃, more preferably 15℃~30℃, and most preferably 20℃~25℃. Those skilled in the art will understand that a semi-gel state refers to an intermediate phase between a liquid sol and a rigid solid gel. This system forms a continuous three-dimensional elastic network framework, with the network gaps encapsulating the free liquid phase; it possesses self-supporting molding capabilities, does not flow freely, and can undergo slight plastic deformation and micro-flow under external pressure and microchannel constraint.

[0051] After obtaining the semi-gel potting compound, the microfluidic chip prepared above is placed in the semi-gel potting compound for pressing and initial curing, so that the potting compound encapsulates the rock substrate to form a pre-encapsulated microfluidic chip. This application does not impose any special limitations on the pressing process; it is sufficient to ensure that the surface of the resulting microfluidic chip is initially flat. In some specific implementations, the pressing process further includes flattening and positioning calibration of the potting compound surface to achieve precise alignment and adhesion with the surface of the rock thin section. In some specific implementations, the flattening process can be sanding, which makes the surface of the resulting microfluidic chip flat, which is beneficial for uniform incident light and improves the microscopic imaging effect. This application does not impose any special limitations on the positioning calibration process; it is sufficient to achieve positioning and facilitate subsequent drilling.

[0052] After pressing and molding, the obtained microfluidic chip is cured to form a pre-encapsulated structure. In some specific implementations, the curing temperature is room temperature, preferably 10℃~40℃, more preferably 15℃~30℃, and most preferably 20℃~25℃. Those skilled in the art will understand that the pre-curing and curing parameters, including temperature and time, are related to the potting compound used. Those skilled in the art can adjust the curing parameters according to the specific requirements of the potting compound. The above curing temperatures are merely examples and are not specifically limited in this application. After curing, injection channels and output channels are formed on the surface of the pre-encapsulated structure, and the injection channels are connected to the liquid inlet of the microfluidic channel, and the output channels are connected to the liquid outlet of the microfluidic channel. This application preferably uses an etching method to form the injection channels and output channels. This application does not have specific limitations on the etching parameters; parameters commonly used by those skilled in the art are acceptable. After etching to form the injection channels and output channels, holes are drilled at the liquid inlet of the injection channels and the liquid outlet of the output channels to form liquid inlets and outlets.

[0053] After forming the injection and output channels, the microfluidic chip, including the microchannels and the surfaces where no microchannels are formed, is preferably cleaned to remove dust and residual adhesive. After removing dust and residual adhesive, residual air in the microfluidic chip is preferably discharged to reduce the risk of bubble formation during subsequent experiments. Specifically, this application uses heating or vacuum degassing to discharge residual air from the pores of the rock substrate. This application does not have specific limitations on the specific parameters of the heating or vacuum degassing, as long as it can discharge air from the pores of the rock substrate.

[0054] In some specific implementations, after forming the microchannels or pre-encapsulation, a cover sheet is placed on the surface of the rock substrate to form a preliminary seal. In some specific implementations, the cover sheet is a transparent sealing film or a transparent cover sheet. This application does not have any particular restrictions on the method of covering the cover sheet; it is preferred to apply it as a mat to form a preliminary seal.

[0055] After the initial sealing is completed, the process preferably further includes encapsulating the microfluidic chip to form an encapsulation structure for the microfluidic chip, specifically including the following steps: The pre-cured or initially sealed microfluidic chip is encapsulated using potting compound.

[0056] Specifically, this application places the pre-cured or pre-encapsulated microfluidic chip in a mold, adds encapsulating adhesive to cover and pot the surface and periphery of the microfluidic chip, and after curing, forms an encapsulation structure with sufficient mechanical strength.

[0057] See Figure 2 , Figure 2The schematic diagram of the process for preparing the microfluidic chip based on real rock cores for this application includes the following steps: S1. Cut the original rock core to obtain rock thin sections; S2. Grind and polish the rough rock slices to obtain smooth rock slices with a flat surface and low roughness. S3. Using a smooth rock slice as a substrate, the rock substrate is etched according to a predetermined microchannel pattern to form microchannels on its surface. S4. Pour potting compound into a shallow mold for pre-curing. When the potting compound reaches a semi-gel state, place the microfluidic chip obtained in step S3 into the semi-gel potting compound and press it into shape using a press. At the same time, perform flattening and positioning calibration on the semi-gel surface to achieve precise alignment and adhesion with the surface of the rock sheet. S5. Completely solidify the pre-packaged structure obtained in step S4, remove the mold, perform secondary etching of the injection channel and output channel on the chip, and perform inlet and outlet hole drilling. S6. Clean the chip obtained in step S5 to remove dust and residual adhesive from the surface and pores; then remove the residual air in the pores of the rock sheet by heating or vacuum degassing to reduce the risk of bubble formation in subsequent experiments; finally, cover the chip surface with a transparent sealing film or transparent cover to complete the initial sealing. S7. Place the chip model obtained in step S6 into a deep mold, add potting compound, and completely cover and pot the upper surface and periphery of the chip model. After complete curing, remove the mold to obtain a microfluidic chip based on a real rock core.

[0058] This application also provides a visualization experimental device, including a cavity, a rock-based chip module, an imaging system, and a temperature and pressure control system; wherein, the rock-based chip module includes the microfluidic chip described in the above technical solution, and the rock-based chip module is disposed in the cavity; The imaging system is used for in-situ observation and image recording of the microfluidic chip; The temperature and pressure control system is used to control the temperature and pressure of the rock-based chip module.

[0059] See Figure 3 , Figure 3This is a schematic diagram of the structure of the visualization experimental device provided in the embodiments of this application, wherein 31 is a cavity, 311 is a medium inlet, 312 is an experimental fluid supply device, 313 is a first gas supply device, 314 is a gas inlet, 315 is a second gas supply device, and 316 is a confining pressure fluid medium inlet; 32 is a temperature control module, 321 is a temperature measuring device, 322 is a heating jacket, and 323 is a heating box; 33 is a pressure control module, and 331 is a confining pressure fluid medium supply unit; 34 is a fluorescence microscope, 35 is an image acquisition module, and 36 is an image storage module.

[0060] The visualization experimental device provided in this application includes a cavity 31, inside which the rock-based chip module (not shown in the figure) is fixed. The cavity 31 is provided with a medium inlet 311, which communicates with the microchannel inlet of the microfluidic chip in the rock-based chip module, for inputting experimental fluids or media such as CO2, allowing the experimental fluids or CO2 to enter the microchannels of the rock-based chip. The medium inlet 311 is connected to an experimental fluid supply device 312 for providing experimental fluids and a first gas supply device 313 for providing CO2. The cavity 31 is provided with a gas inlet 314, which communicates with the microchannel outlet of the microfluidic chip in the rock-based chip module, for injecting CO2 into the cavity 31 from the microchannel outlet end of the microfluidic chip to maintain a corresponding pressure boundary. The gas inlet 314 is connected to a second gas supply device 315.

[0061] The visualization experimental device provided in this application includes a rock-based chip module, which includes the microfluidic chip described in the above technical solution, enabling experimental fluids to undergo gas-liquid two-phase flow, water-rock reaction, and drying salt precipitation deposition processes in the pore-throat structure on the surface of rock thin sheets.

[0062] The visualization experimental device provided in this application includes a temperature and pressure control system, which includes a temperature control module 32 and a pressure control module 33 respectively connected to the cavity. The temperature control module 32 is used to adjust the temperature of the cavity, and the pressure control module 33 is used to adjust the pressure of the cavity.

[0063] In some specific implementations, the temperature control module 32 includes a temperature measuring device 321 disposed inside the cavity 31 for measuring the temperature inside the cavity 31. The temperature control module 32 includes a heating jacket 322 disposed outside the cavity 31 and a heating chamber 323 for heating the heating jacket 322.

[0064] In some specific implementations, the pressure control module 33 includes a confining pressure fluid medium supply unit 331 for the confining pressure fluid medium. The confining pressure fluid medium supply unit 331 is connected to the confining pressure fluid medium inlet 316 located on the cavity 31, inputting the confining pressure fluid medium into the cavity 31. By actively adjusting and tracking the confining pressure, the confining pressure changes synchronously with the internal experimental pressure, providing stable pressure-bearing and sealing conditions for the microfluidic chip and meeting the long-term operational requirements of the rock-based chip module under high temperature and high pressure conditions. In some specific implementations, the confining pressure fluid medium is fresh water. This application, through a chip fixture and an active confining pressure loading structure, enables the confining pressure to be adjusted and tracked with the internal experimental pressure, providing more stable pressure-bearing and sealing conditions for the microfluidic chip. This solves the problem of insufficient sealing and pressure-bearing stability of real core thin-film chips under high temperature and high pressure conditions, meeting the long-term operational requirements of carbon dioxide displacement, gas-brine reaction, and drying salting-out experiments under high temperature and high pressure conditions.

[0065] During the experiment, the experimental liquid and the first gas can enter the microchannel inlet of the microfluidic chip in the rock-based chip through corresponding intermediate containers and injection units, respectively. The second gas maintains the corresponding pressure boundary from the other end of the microfluidic chip (i.e., the microchannel outlet end). Simultaneously, the confining pressure fluid supply unit 331 provides confining pressure fluid to the outer periphery of the rock-based chip module to achieve pressure sealing in conjunction with the internal pressure changes of the microfluidic chip. With the above structure, the experimental device can perform in-situ visualization observation of gas-brine displacement, water-rock reaction, drying process, and salt precipitation deposition process in a real core thin-section microfluidic chip under high temperature and high pressure conditions.

[0066] The visualization experimental apparatus provided in this application includes an imaging system for in-situ observation and image recording of the microfluidic chip. In some specific implementations, the imaging system includes: 34. Fluorescence microscope for observing microfluidic chips; A fluorescent light source for illuminating the microfluidic chip; Image acquisition module 35 for acquiring images or videos of the microfluidic chip; and image storage module 36, which is used to receive and store images or videos acquired by the image acquisition module.

[0067] The imaging system includes a fluorescence microscope 34 positioned above the rock-based chip module and a fluorescence light source (not shown in the figure) for illuminating the microfluidic chip. The fluorescence microscope 34 and the fluorescence light source can combine with a fluorescent tracer to more clearly distinguish the gas phase, oil phase, brine phase, and reaction or deposition areas, and provide an image basis for subsequent quantitative analysis.

[0068] The imaging system includes an image acquisition module 35, such as a camera, for acquiring images or videos of the microfluidic chip. The image acquisition module 35 is positioned directly above the microfluidic chip and can acquire images or videos of the microfluidic chip in situ.

[0069] The imaging system includes an image storage module 36, which receives and stores images or videos acquired by the image acquisition module. In some specific implementations, the imaging system can continuously or at fixed time intervals acquire images or videos during the experiment to record rock surface morphology, fluorescence signal distribution, pore changes, gas-liquid interface migration, residual liquid phase redistribution, drying front advancement, and the morphological evolution and spatial distribution of salting-out deposits.

[0070] Furthermore, the imaging system also includes an image processing module, which processes the images or videos stored in the image storage module. Specifically, the imaging system processes the raw image sequences acquired during the aforementioned microfluidic chip experiments and identifies and quantitatively analyzes the gas-liquid two-phase distribution, gas phase intrusion interface migration, gas-connection evolution, salt crystal morphology characteristics, and spatial distribution of salt crystals during the evaporation and drying stage. When conducting salt precipitation deposition experiments under multiphase flow conditions, continuous visual observation of the complete evaporation and drying process is required. The key focus during the experiment is acquiring images of the gas-liquid two-phase distribution during the evaporation and drying stage to characterize the gas phase intrusion interface migration and gas-connection evolution process; simultaneously, the morphological characteristics and spatial distribution of salt crystals during the salt precipitation stage are recorded to depict the starting position, expansion path, and coverage area of ​​salt crystals.

[0071] In some specific implementations, the image processing module includes: An image preprocessing module is used to preprocess the images stored in the image storage module; A gas phase region identification and processing module is used to receive a preprocessed image output by the image preprocessing module, identify the gas phase region of the preprocessed image and calculate the total number of pixels in the gas phase region, and calculate the gas phase saturation and estimate the evaporation-drying rate based on the total number of pixels in the gas phase region. A salt crystallization region identification and processing module is used to receive a preprocessed image output by the image preprocessing module, identify the salt crystallization region of the preprocessed image and calculate the total number of pixels in the salt crystallization region, and calculate the salt crystallization coverage and salt crystallization growth rate based on the total number of pixels in the salt crystallization region. A base map construction module is used to construct a salt crystallization layer, a matrix layer, and a base map enhancement layer based on the image stored in the image storage module, the gas phase region identified by the gas phase region identification and processing module, and the salt crystallization region identified by the salt crystallization region identification and processing module. The result output module is used to superimpose the salt crystallization layer, matrix layer and base map enhancement layer and output the result image.

[0072] The image processing module includes an image preprocessing module, which preprocesses the images stored in the image storage module. In some specific implementations, the image preprocessing module can perform stitching, registration, exposure correction, color correction, noise reduction, sharpening, and scale unification on the original image sequence stored in the image storage module, ensuring that images from different time frames maintain consistency in spatial location, brightness, color, and scale, thereby ensuring the stability and comparability of subsequent target recognition. Preprocessing the original image sequence guarantees the reliability of subsequent quantitative results.

[0073] The image processing module includes a gas phase region identification and processing module. This module receives the preprocessed image output by the image preprocessing module, identifies the gas phase regions of the preprocessed image, calculates the total number of pixels in the gas phase regions, and calculates gas phase saturation and estimates the evaporation-drying rate based on the total number of pixels in the gas phase regions. In some specific implementations, after receiving the preprocessed image output by the image preprocessing module, the gas phase region identification and processing module identifies the gas-liquid two-phase distribution image within it, performs image segmentation on the gas-liquid two-phase distribution image to obtain the total number of pixels in the gas phase regions, calculates the gas phase saturation based on the total number of pixels in the gas phase regions, and further estimates the evaporation-drying rate. The gas phase region identification and processing module can characterize the dynamic changes in gas phase intrusion, gas-liquid connection, and the drying process during the evaporation-drying stage. In some specific implementations, the gas phase saturation is calculated using the following method: using grayscale recognition, the original image is converted into a grayscale image, the grayscale threshold range where the gas phase is located is identified, and the gas phase proportion is calculated; this gas phase proportion is equivalent to the gas phase saturation. In some specific implementations, the evaporation-drying rate is estimated as follows: using grayscale recognition, the original image is converted into a grayscale image, the grayscale threshold range of the liquid phase is identified, and the proportion of the liquid phase is calculated. This proportion of the liquid phase is equivalent to the liquid phase saturation. The rate at which the liquid phase saturation decreases over time is the evaporation rate, and the rate at which the solid salt phase increases is the drying rate.

[0074] The image processing module includes a salt crystallization region identification and processing module. This module receives a preprocessed image output by the image preprocessing module, identifies the salt crystallization regions in the preprocessed image, calculates the total number of pixels in the salt crystallization regions, and calculates the salt crystallization coverage and growth rate based on the total number of pixels. In some specific implementations, the salt crystallization region identification and processing module receives the preprocessed image output by the image preprocessing module, identifies the salt precipitation stage image and the salt crystallization regions within it, obtains the total number of pixels in the salt crystallization regions, calculates the salt crystallization coverage based on the total number of pixels, and further obtains the salt crystallization growth rate. The salt crystallization region identification and processing module can characterize the starting position, expansion path, coverage area, and growth process of salt crystals over time. In some specific implementations, the salt crystallization coverage is calculated as follows: using grayscale recognition, the original image is converted into a grayscale image, and the proportion of salt crystals within the grayscale threshold range where the salt crystals are located is calculated; this proportion is equivalent to the salt crystallization coverage. In some specific implementations, the salt crystal growth rate is the rate at which the salt crystal coverage increases over time.

[0075] The image processing module includes a basemap construction module, which is used to construct a salt crystal layer, a matrix layer, and a basemap enhancement layer based on the image stored in the image storage module, the gas phase region identified by the gas phase region identification and processing module, and the salt crystal region identified by the salt crystal region identification and processing module. The basemap construction module can construct the salt crystal layer, matrix layer, and basemap enhancement layer respectively to obtain salt crystal distribution results that can be used for quantitative analysis and visualization.

[0076] In some specific implementations, the construction of the salt crystallization layer includes the following steps: Select several representative regions as training sets in the "Trainable Weka Segmentation" module of ImageJ, and label "salt crystallization regions" and "non-salt regions" respectively. The non-salt regions include liquid phase, gas phase and matrix boundaries; then select features such as texture, edge, and brightness, train a classifier, perform batch prediction on the entire sequence image, and output a binary mask of salt crystallization for subsequent coverage calculation and distribution analysis.

[0077] In some specific implementations, the construction of the matrix layer includes the following steps: using the salt-free moment image as a reference, extracting the matrix contour and channel boundaries to form a fixed matrix base map or matrix mask. The matrix map is used to define the effective area of ​​the pores, avoiding the miscounting of areas outside the channels in the statistical range, and improving the structural recognizability of the final overlay image.

[0078] In some specific implementations, the construction of the base image enhancement layer includes the following steps: converting the original image stored in the image storage module into a grayscale image, and appropriately reducing the exposure or adjusting the color level to make the background darker; enhancing the contrast between the salt crystals and the background to highlight the salt crystal boundaries and details, making it easier to display and verify the segmentation effect.

[0079] The image processing module includes a result output module, which is used to overlay the salt crystallization layer, matrix layer, and basemap enhancement layer and output a result image. In some specific implementations, the result output module overlays the salt crystallization layer, matrix layer, and basemap enhancement layer to generate a result image that can intuitively distinguish the spatial distribution of salt crystals. The final overlay image can be used for the identification and comparison of the salt crystallization initiation position, expansion path, and aggregation area, and it is also easy to correlate with the pixel statistical results of different time frames, thereby supporting the quantitative analysis of salt crystallization coverage and salt crystallization growth rate.

[0080] In some specific implementations, the image processing module further includes a multiphase region saturation calculation module. This module is used to acquire gas, water, and oil phase regions, and, in conjunction with pore area, calculate the gas, water, and oil saturation, converting the multiphase distribution results in the experimental image into quantitatively comparable saturation data. In some specific implementations, the gas, water, and oil saturation are obtained using a threshold segmentation method, which will not be elaborated further in this application.

[0081] Those skilled in the art will understand that in this application, gas phase saturation, liquid phase saturation, salt crystallization coverage, gas content, water content, and oil content saturation can all be obtained by converting the original image into a grayscale image, identifying the corresponding grayscale threshold, and calculating the corresponding proportion, thereby obtaining each parameter, and then calculating the corresponding rate through the proportion at different times.

[0082] The image processing module provided in this application can convert continuously acquired image sequences from real core microfluidic experiments into quantitative results such as gas phase saturation, evaporation-drying rate, salt crystallization coverage, salt crystallization growth rate, and gas, water, and oil saturation. At the same time, it can generate a visual overlay map of the spatial distribution of salt crystals, providing a data foundation for analyzing the gas-liquid two-phase transport, residual liquid drying, and salt precipitation deposition evolution processes.

[0083] This application addresses the problem of insufficient stability in the quantitative processing of salt precipitation deposition images by stitching, registering, exposure correction, color correction, noise reduction, sharpening, and scale unification of experimental image sequences, and further identifies gas phase regions, salt crystallization regions, rock matrix regions, and reaction deposition regions. It also calculates indicators such as gas phase saturation, evaporation-drying rate, salt crystallization coverage, and salt crystallization growth rate. This improves the quantification and reproducibility of real core microfluidic salt precipitation experimental results.

[0084] This application also provides a simulation experimental method for gas-liquid-rock reaction and CO2 displacement drying salt precipitation deposition, which is carried out using the microfluidic chip or visualization experimental device described above, and includes the following steps: Experimental fluid is injected into the microfluidic chip to saturate the microfluidic chip with liquid phase. The microfluidic chip is subjected to heating and pressurization treatment. After the temperature and pressure stabilize, a reaction is carried out. The reaction is continuously monitored, and images or videos of the microfluidic chip are acquired during the reaction process. Based on the images or videos of the microfluidic chip during the reaction process, features for characterizing the corrosion process are obtained. After the reaction is complete, the injection of the experimental fluid is stopped, and CO2 gas is injected into the microfluidic chip for displacement and drying. The displacement and drying are continuously monitored, and images or videos of the microfluidic chip are acquired during the displacement and drying process. Based on the images or videos of the microfluidic chip during the displacement and drying process, the characteristics of gas-liquid interface migration and reconstruction, residual liquid phase redistribution, drying front advancement, and the starting position, morphological evolution, and spatial distribution of salt precipitation deposition are obtained.

[0085] This application employs the microfluidic chip or visualization experimental device described above to study the influence of potential water-rock reactions on the surface of real strata rocks on the behavior of gas-liquid two-phase flow at the pore scale, and to identify the location and evolution characteristics of mineral dissolution, precipitation, and salt precipitation processes under microscopic observation conditions. Specifically, it can continuously perform dynamic imaging recordings of liquid phase saturation, heating and pressurization, mineral dissolution or corrosion reactions, CO2 displacement drying, and salt precipitation deposition within the same rock-based chip to obtain process characteristics such as gas-liquid two-phase flow, water-rock reaction, residual liquid phase redistribution, drying front advancement, and salt crystallization deposition distribution.

[0086] This application first injects an experimental fluid into the microfluidic chip to saturate it in the liquid phase. In some specific implementations, the experimental fluid is a salt solution, preferably comprising 10wt%~30wt% NaCl, 10wt%~30wt% acetic acid, 0.1wt%~1wt% rhodamine, and the balance being water; more preferably, it comprises 20wt% NaCl, 20wt% acetic acid, 0.5wt% rhodamine, and the balance being water. During injection, the experimental fluid fills the microchannel region of the microfluidic chip, and injection is stopped when liquid phase saturation is achieved. In some specific implementations, the microchannel region of the microfluidic chip is observed under an imaging system, and the liquid phase saturation step ends when the microchannel region is substantially filled with liquid. Because acetic acid reacts with rock minerals and produces gas, complete saturation cannot be achieved in the low-pressure saturation stage.

[0087] After the microfluidic chip reaches liquid phase saturation, it is subjected to heating and pressurization. Once the temperature and pressure stabilize, a reaction is initiated. The reaction is continuously monitored, and images or videos of the microfluidic chip are acquired during the reaction process. Characteristics for characterizing the corrosion process are obtained from these images or videos. After the microfluidic chip reaches liquid phase saturation, the temperature and pressure are increased while maintaining the experimental fluid at a static or low injection rate. Specifically, the inlet and outlet ends of the microchannel of the microfluidic chip are pressurized, with a termination pressure of 5 MPa to 10 MPa, preferably 6 MPa to 7 MPa, and a pressurization rate of 0.1 MPa / 10 min to 1 MPa / 10 min, preferably 0.5 MPa / 10 min. Simultaneously with the pressurization, the temperature is increased, with a termination temperature of 50℃ to 80℃, preferably 60℃ to 70℃, and temperature fluctuations within ±2℃.

[0088] After the temperature and pressure stabilize, the rock substrate can react with the experimental fluid in its microchannels, and the minerals in the rock substrate are dissolved or corroded by the acidic experimental fluid. In some specific implementations, the reaction is carried out at the aforementioned temperature and pressure for 3-4 hours, preferably 4 hours. During the reaction, the reaction is continuously monitored, and images or videos of the microfluidic chip are acquired. Features characterizing the corrosion process are obtained from these images or videos. In some specific implementations, images or videos are acquired at fixed time intervals, preferably 5-15 minutes, preferably 10 minutes. The images or videos of the microfluidic chip during this stage can be used to characterize the corrosion process, including rock surface morphology, fluorescence signal distribution, and pore changes.

[0089] After obtaining the characteristics of the corrosion process (i.e., after the reaction is complete), if necessary, the injection of the experimental fluid is stopped, and CO2 gas is injected into the microfluidic chip for displacement and drying. The displacement and drying are continuously monitored, and images or videos of the microfluidic chip are acquired during the displacement and drying process. Based on the images or videos of the microfluidic chip during the displacement and drying process, the characteristics of gas-liquid interface migration and reconstruction, residual liquid phase redistribution, drying front advancement, and the starting position, morphological evolution, and spatial distribution of salt precipitation deposition are obtained. Specifically, the experimental fluid at both ends of the microchannel inlet and outlet of the microfluidic chip is switched to a CO2 medium consistent with the experimental pressure to achieve a stable pressure supply. CO2 medium is injected from the microchannel inlet of the microfluidic chip, and the injection rate is preferably 0.1 mL / min to 0.5 mL / min, preferably 0.25 mL / min. The outlet end of the microchannel maintains a constant pressure boundary condition. During the CO2 displacement and drying process, images are preferably acquired at fixed time intervals; preferably, the fixed time interval is every 5 min to 15 min, more preferably every 10 min. This stage focuses on recording key process characteristics such as gas-liquid interface migration and reconstruction, residual liquid phase redistribution, drying front advancement, and the starting location, morphological evolution, and spatial distribution of salt precipitation deposition.

[0090] After obtaining images of rock surface morphology, fluorescence signal distribution and pore changes, gas-liquid interface migration and reconstruction, residual liquid phase redistribution, drying front advancement, and the starting position, morphological evolution and spatial distribution of salt precipitation deposition, this application preferably uses the image processing system described above to process the images, identify and quantitatively analyze the gas-liquid two-phase distribution, gas phase intrusion interface migration, gas-liquid communication evolution, salt crystallization morphology characteristics and salt crystallization spatial distribution during the evaporation and drying stage, and realize an integrated experiment of liquid phase saturation, water-rock reaction, carbon dioxide displacement, residual brine drying, salt precipitation deposition and image quantitative evaluation under high temperature and high pressure conditions.

[0091] This application establishes a dynamic imaging system for water-rock reaction processes, residual liquid phase distribution changes, and salt precipitation deposition by sequentially conducting liquid phase saturation, temperature and pressure increases, mineral dissolution or corrosion reactions, carbon dioxide displacement drying, and salt precipitation deposition within the same rock-based microfluidic chip. This solves the problem of continuously characterizing the co-evolution of water-rock reactions and salt precipitation deposition in the same experimental system. It provides a visualized, repeatable, and quantifiable experimental system and method for studying the mechanisms of brine concentration, salt crystal deposition, pore throat blockage, water-rock reactions, and near-wellbore seepage capacity attenuation during carbon dioxide injection in high-salinity formations.

[0092] See Figure 4 , Figure 4This application provides a schematic diagram of the overall technical route for the simulation experiment. First, a microfluidic chip based on a real core thin section is prepared. Then, it is integrated with a temperature and pressure control system and an imaging system to prepare an in-situ visualization platform based on the core thin section. Next, using this visualization platform as an experimental device, experiments are conducted to test the mineral dissolution behavior and differences under acidic conditions and to test salt precipitation-crystallization under different mineral matrix conditions. Finally, the obtained images are processed by an image processing system, thereby enabling in-situ visualization observation of the gas-water displacement, water-rock reaction, drying process, and salt precipitation deposition process in the microfluidic chip of the real core thin section under high temperature and high pressure conditions. The gas-liquid two-phase distribution, gas phase intrusion interface migration, gas-liquid interconnection evolution during the evaporation and drying stage, as well as the salt crystallization morphology and spatial distribution during the salt precipitation stage are identified and quantitatively analyzed.

[0093] The following embodiments further illustrate the microfluidic chip, visualization experimental device, and experimental method based on real rock cores provided in this application.

[0094] Examples 1-4

[0095] Using sandstone, dolomite, marble, and limestone as the rock base respectively, according to Figure 2 The process shown is used to construct a microfluidic chip: S1. The original rock core was cut and sampled to obtain a rock thin section with a thickness of 1.5 mm; S2. Grind and polish the rough rock slices to obtain smooth rock slices with a flat surface and low roughness. S3. Using a smooth rock slice as a base, according to Figure 1 The microchannel pattern shown is laser-etched onto the rock substrate to form microchannels on its surface. The parameters of the laser etching are as follows: wavelength 515nm, pulse width approximately 300fs, repetition frequency 100kHz, 20x objective lens, focused spot diameter approximately 12μm, single pulse energy 0.65μJ, scanning speed 100mm / s, fill line spacing 4μm, 5 scans, focal point located on the core surface, and scanning directions of adjacent scanning layers set to 0° and 90° respectively. The microchannel comprises n repeating channel units C1, with adjacent repeating channel units connected. Each repeating channel unit C1 includes a first rectangular microchannel C11, a second rectangular microchannel C12, a third rectangular microchannel C13, and a fourth rectangular microchannel C14. The length direction of the second rectangular microchannel C12 is perpendicular to the length direction of the first rectangular microchannel C11, and the liquid inlet of the second rectangular microchannel C12 is connected to the liquid outlet of the first rectangular microchannel C11. The length direction of the third rectangular microchannel C13 is perpendicular to the length direction of the second rectangular microchannel C12, and the liquid inlet of the third rectangular microchannel C13 is connected to the liquid outlet of the second rectangular microchannel C12. The length direction of the fourth rectangular microchannel C14 is perpendicular to the length direction of the third rectangular microchannel C13, and the liquid inlet of the fourth rectangular microchannel C14 is connected to the liquid outlet of the third rectangular microchannel C13. The surface structure of the repeating flow channel unit includes cubic pore units 11 arranged in a matrix array and connecting microchannels 12 connecting each pore unit. The cubic pore units 11 in adjacent rows are staggered. The depth of each cubic pore unit 11 is 0 μm and the side length of its cross-section is 200 μm. The depth of the connecting microchannel 12 is 100 μm and the width is 150 μm (this width is the distance between the adjacent side lengths of two adjacent cubic pore units in the same column). The total length of the connecting microchannel is 3.8 cm. The microchannel further includes a liquid inlet 13, a liquid inlet channel 14 connected to the liquid inlet, an outlet of the liquid inlet channel 14 connected to the liquid inlet of the first repeating channel unit, a liquid outlet channel 15 connected to the liquid outlet of the nth repeating channel unit, and a liquid outlet 16 connected to the liquid outlet of the liquid outlet channel 15. The depth of the liquid inlet 13 and the liquid outlet 16 is 500 μm, and the depth of the liquid inlet channel 14 and the liquid outlet channel 15 is 150 μm. S4. Using the EpoxiCure 2 epoxy embedding system manufactured by Buehler, USA, including EpoxiCure 2 Resin and EpoxiCure 2 Hardener components, measure out the EpoxiCure 2 Resin and EpoxiCure 2 Hardener components respectively according to a volume ratio of 4:1 and add them to a clean, dry shallow mold. Use a glass rod or stirring rod to slowly stir in the same direction to ensure that the resin and hardener components are fully mixed. During the stirring process, avoid rapid stirring and repeated lifting of the stirring rod as much as possible to reduce the entry of air into the mixture. Continue stirring until the mixture has a uniform color, transparency, and flowability, and there are no obvious streaks, flocculent matter, or unmixed areas. The uniformly mixed epoxy resin mixture is placed in a vacuum degassing device for degassing treatment. When the number of bubbles on the surface of the mixture is significantly reduced and no new bubbles are continuously generated, the pressure is slowly restored to normal and room temperature curing is carried out at 20~25℃. During the curing period, the ambient temperature is kept relatively stable and dust, moisture and other impurities are prevented from entering the uncured epoxy resin. After curing for 2 hours, the epoxy resin enters a semi-solid state. The microfluidic chip obtained in step S3 is placed in the mixture, and a heavy object is placed on the shallow mold to press it into shape. At the same time, the semi-gel surface is flattened and positioned and calibrated to achieve precise alignment and adhesion with the surface of the microfluidic chip. S5. The pre-encapsulated structure obtained in step S4 is cured at 20~25℃ for about 4 hours to allow the resin to reach a preliminary curing state that can maintain the encapsulation shape and fix the chip. The mold is removed, and the chip is subjected to secondary etching of the injection channel and the output channel, and inlet and outlet holes are drilled. S6. Clean the chip obtained in step S5 to remove dust and residual adhesive from the surface and pores; then remove the residual air in the pores of the rock sheet by heating or vacuum degassing to reduce the risk of bubble formation in subsequent experiments; finally, cover the chip surface with a transparent sealing film or transparent cover to complete the initial sealing. S7. Place the chip model obtained in step S6 into a deep mold, add potting compound, and completely cover and pot the upper surface and periphery of the chip model. After complete curing, remove the mold to obtain a microfluidic chip based on a real rock core.

[0096] The real core thin-section microfluidic chip prepared in this embodiment can form a regular and controllable pore-throat flow structure on a real rock substrate, and meet the experimental requirements for microstructure processing and visualization observation of the rock substrate. The chip can be used as an experimental carrier for subsequent gas-water displacement, water-rock reaction, CO2 displacement drying and in-situ observation of salt precipitation deposition.

[0097] Example 5

[0098] The microfluidic chips constructed using Examples 1-4 are as follows: Figure 3 The visualization experimental setup shown includes: The rock-based chip module, on which the microfluidic chip is installed, provides an experimental platform for gas-brine displacement, water-rock reaction, and dry salt precipitation deposition processes. The cavity 31 contains the aforementioned rock chip module. The cavity 31 is provided with a medium inlet 311, which is connected to the microchannel inlet of the microfluidic chip in the rock-based chip module. This inlet is used to input experimental fluids or media such as CO2, allowing the experimental fluids or CO2 to enter the microchannels of the rock-based chip. The medium inlet 311 is connected to an experimental fluid supply device 312 for providing experimental fluids and a first gas supply device 313 for providing CO2. The cavity 31 is also provided with a gas inlet 314, which is connected to the microchannel outlet of the microfluidic chip in the rock-based chip module. This gas inlet 314 is used to introduce CO2 into the cavity 31 from the microchannel outlet of the microfluidic chip to maintain a corresponding pressure boundary. The gas inlet 314 is connected to a second gas supply device 315.

[0099] The visualization experimental device includes a temperature and pressure control system for providing set temperature, pressure, and stable pressure-bearing and sealing conditions for rock-based chip experiments. The temperature and pressure control system includes a temperature control module 32 and a pressure control module 33, both connected to the cavity. The temperature control module 32 includes a temperature measuring device 321 located inside the cavity 31 for measuring the internal temperature. The temperature control module 32 also includes a heating jacket 322 located outside the cavity 31 and a heating chamber 323 for heating the heating jacket 322. The pressure control module 33 includes a confining pressure fluid supply unit 331 for inputting a confining pressure fluid medium. The confining pressure fluid supply unit 331 is connected to a confining pressure fluid inlet 316 located on the cavity 31, inputting the confining pressure fluid medium into the cavity 31. By actively adjusting and tracking the confining pressure, the confining pressure changes synchronously with the internal experimental pressure, providing stable pressure-bearing and sealing conditions for the microfluidic chip and meeting the long-term operational requirements of the rock-based chip module under high temperature and high pressure conditions.

[0100] The visualization experimental setup includes an imaging system for in-situ observation of the multiphase fluid distribution, reaction region, and solid-phase deposition region within the chip. This imaging system uses a fluorescence microscope and fluorescence light source instead of the stereo microscope and cold light source used in the silicon-based chip visualization platform, enhancing the ability to identify multiphase boundaries and solid-phase deposition regions. The imaging system includes a fluorescence microscope 34 for observing the microfluidic chip, a fluorescence light source for illuminating the microfluidic chip, an image acquisition module 35 (specifically a CCD camera) for acquiring images or videos of the microfluidic chip, and an image storage module 36 for receiving and storing the images or videos acquired by the image acquisition module. During the experiment, the imaging system can be combined with a fluorescent tracer to achieve clear differentiation and quantitative analysis of the gas phase, oil phase, brine phase, and reaction or deposition regions.

[0101] The visualization experimental device provided in this application addresses the visualization experimental needs of solid-phase coupled gas-brine displacement and drying salt precipitation deposition. It improves and expands upon the silicon-based chip visualization experimental platform, constructing a rock-based chip visualization experimental platform with a rock-based microfluidic chip as its core. During the experiment, experimental fluids can enter the microchannels of the rock-based chip, and CO2 can be switched into the chip microchannels in subsequent stages to carry out gas-phase displacement and drying processes. The confining pressure system provides confining pressure fluid to the outer periphery of the chip to maintain stable pressure and sealing in response to changes in the internal pressure of the chip.

[0102] Through the above-mentioned device structure, this application can perform in-situ visual observation of gas-water displacement, water-rock reaction, drying process and salt precipitation deposition process in microfluidic chips of real core thin sections under high temperature and high pressure conditions, and provide an experimental platform for subsequent continuous experimental procedures and quantitative image analysis.

[0103] Example 6

[0104] The visualization experimental device constructed in Example 5 was used to conduct simulation experiments of gas-liquid-rock reaction and CO2 displacement drying salt precipitation deposition using microfluidic chips prepared in Examples 1-4, respectively. The specific steps included: (1) Chip saturated liquid phase An experimental liquid, comprising 20 wt% NaCl, 20 wt% acetic acid, 0.5 wt% rhodamine, and the remainder water, was injected into the microfluidic chip. The microchannel region of the microfluidic chip was observed under a fluorescence microscope. The liquid-phase saturation step was completed when the microchannel region was approximately filled with the experimental liquid. Because acetic acid reacts with minerals to produce gas, complete saturation cannot be achieved in the low-pressure saturation stage.

[0105] (2) Heating and pressurization and system stability.

[0106] While keeping the experimental liquid still or injecting at a low speed, the pressure at both ends of the microfluidic chip (i.e., the inlet and outlet of the microchannel) is gradually increased to the target pressure of 6 MPa, with the pressure increase step controlled at 0.5 MPa. At the same time, the constant temperature chamber is turned on to raise the system temperature to the set temperature of 60°C, and closed-loop control is performed using the readings of the built-in temperature sensor to keep the temperature fluctuation within ±2°C. After the temperature and pressure stabilize, the reaction and imaging stages begin.

[0107] (3) Mineral dissolution or corrosion stage and dynamic imaging recording. Under constant temperature and pressure conditions, the experimental liquid was kept in full contact with the rock surface for 4 hours to simulate the mineral dissolution process under acidic conditions. The fluorescence microscopy system was started to continuously monitor the reaction process and images or videos were acquired at 10-minute intervals. During this stage, key features characterizing the corrosion process, such as rock surface morphology, fluorescence signal distribution, and pore changes, were recorded.

[0108] (4) CO2 displacement-drying stage and dynamic imaging recording.

[0109] The experimental fluid at both ends of the microfluidic chip was switched to CO2 at the same experimental pressure to achieve a stable pressure supply. CO2 was injected into the chip at a constant flow rate of 0.25 mL / min from the microchannel inlet, while constant pressure boundary conditions were maintained at the other end. Images were acquired at 10-minute intervals during the experiment. This stage focused on recording key process characteristics such as gas-liquid interface migration and reconstruction, residual liquid phase redistribution, drying front advancement, and the initiation location, morphological evolution, and spatial distribution of salt precipitation deposition.

[0110] The method provided in this application can sequentially complete liquid phase saturation, heating and pressurization, mineral dissolution or corrosion reaction, CO2 displacement drying and salt precipitation deposition dynamic imaging within the same real core thin section microfluidic chip, providing raw image data for subsequent salt crystallization region identification, salt crystallization coverage calculation, salt crystallization growth rate analysis, and gas phase saturation and evaporation-drying rate calculation.

[0111] See Figure 5 , Figure 6 and Figure 7 , Figure 5 Microscopic image of rock chip flow channel during CO2 displacement-drying stage (white area represents salt crystallization). Figure 6 This is a bright-field micrograph of a localized area of ​​dissolution on a rock chip after the dissolution reaction has ended. Figure 7 The images show the global observation of the microfluidic chip after the dissolution reaction (red indicates the dissolution area). In the images, (a) shows sandstone, (b) shows dolomite, (c) shows marble, and (d) shows limestone.

[0112] Depend on Figure 5 , Figure 6 and Figure 7 It can be known that: Four hours after acid corrosion, the flow channel structures of different rocks underwent differentiated evolution: Sandstone, due to its relatively loose grain structure and strong pore connectivity, was more prone to acid infiltration and local scouring along the channels, thus showing more obvious intrusion traces and surface structural loosening. Marble and limestone also underwent acid intrusion and dissolution, but their morphological response was more prominent, with pits and eroded patches appearing on the surface. Local dissolution was distributed in a dotted or patchy manner, indicating that the acid dissolved on its surface and formed pore expansion and surface coarsening, but the overall geometric contour remained relatively intact.

[0113] like Figure 7 As shown, during the CO2 displacement-drying stage, different lithologies exhibited significant differences under the coupled effects of acid etching weakening and CO2 erosion. This indicates that the airflow scouring during the drying stage is not a simple dehydration process, but rather a secondary modification of the loosened structure after acidification. Among the four different rock types, dolomite showed the most significant channel changes, with the largest overall area of ​​change exhibiting certain spatial patterns: on the one hand, the closer to the central region of the main flow line, the more concentrated the change area; on the other hand, the closer to the CO2 injection end, the larger the area of ​​change. This phenomenon suggests that during the CO2 drying injection process, the loose mineral particles formed after acid action are more easily detached and migrated under the shearing and scouring effects of airflow, exhibiting enhanced characteristics near the inlet and main flow line. The sandstone sample also showed relatively concentrated change areas in the early section, but almost no significant changes in the middle and later sections, indicating that its channel changes were more controlled by cementation loosening and airflow scouring, rather than acid etching dissolution. The marble channel changes showed a similar trend to the sandstone, but the change areas in the middle and later sections were relatively more numerous, indicating a stronger degree of structural reconstruction during the airflow injection stage. The limestone samples did not show obvious signs of strong local erosion, but variations were observed throughout the entire sample, indicating that the channel changes were more likely caused by surface dissolution and pore expansion due to acid etching, while the contribution of airflow scouring to further reconstruction was relatively limited. Furthermore, the channel regions before and after the experiment can be compared, and the changes can be used to characterize the combined effects of channel boundary migration, pore expansion, and particle exfoliation and transport.

[0114] like Figure 6As shown, bright-field micrographs of the rock chips after the experiment further revealed different local morphological characteristics after acid reaction and CO2 drying. Specifically, the original square porous media geometry of some rock chips was significantly weakened, with the overall morphology becoming more rounded and blunt, surface roughness significantly increased, and local boundary irregularities markedly enhanced. Increased roughness increases microscale irregularities and retention sites, providing more potential nucleation sites for local brine enrichment and salt crystallization. The changes in marble and limestone were mainly concentrated on surface dissolution caused by the acid dissolution reaction of carbonate minerals. Both showed varying degrees of pore, pit, and microcrack development, indicating that acid preferentially penetrated and spread along local weak surfaces or primary pores, leading to surface roughening and pore structure remodeling.

[0115] Therefore, the microfluidic chip based on real core thin sections provided in this application can be used to characterize the differences in mineral dissolution of different lithologies under acidic environments, the changes in channel boundaries during the CO2 drying stage, and the evolution of pore structure under the coupled effects of acid erosion weakening and airflow erosion. Overall, marble and limestone tend to exhibit acid-dissolution-dominated pore or micro-fracture corrosion, dolomite shows more prominent boundary reconstruction after acid erosion weakening followed by further airflow erosion, while sandstone exhibits selective cement removal and grain detachment characteristics.

[0116] Example 7

[0117] During the image acquisition process in Example 6, the original images may exhibit problems such as uneven brightness or color, insufficient contrast, and low clarity due to the susceptibility of CCD camera recording to interference from microcurrents, changes in microscope magnification, uneven illumination, and focus drift. To ensure the reliability of subsequent quantitative results, this example provides an image processing module, including: The image preprocessing module is used to preprocess the images stored in the image storage module, including stitching, registration, exposure correction, color correction, noise reduction, sharpening, and scale unification of the original image sequence, so that the images of different time frames are consistent in spatial position, brightness, color and scale, thereby ensuring the stability and comparability of subsequent target recognition.

[0118] A gas phase region identification and processing module is used to receive the preprocessed image output by the image preprocessing module, identify the gas-liquid two-phase distribution image therein, perform image segmentation on the gas-liquid two-phase distribution image to obtain the total number of pixels in the gas phase region, and calculate the gas phase saturation based on the total number of pixels in the gas phase region to further estimate the evaporation-drying rate. The gas phase saturation is calculated using the following method: using grayscale recognition, the original image is converted into a grayscale image, and the proportion of the gas phase is calculated based on the grayscale threshold range where the gas phase is located; this proportion is equivalent to the gas phase saturation. The evaporation-drying rate is estimated using the following method: using grayscale recognition, the original image is converted into a grayscale image, and the proportion of the liquid phase is calculated based on the grayscale threshold range where the liquid phase is located; this proportion is equivalent to the liquid phase saturation. The rate of decrease of the liquid phase saturation over time is the evaporation rate, and the rate of increase of the solid salt phase is the drying rate. A salt crystallization region identification and processing module is used to receive a preprocessed image output by the image preprocessing module, identify the salt precipitation stage image and the salt crystallization region of the salt precipitation stage image, obtain the total number of pixels in the salt crystallization region, calculate the salt crystallization coverage based on the total number of pixels in the salt crystallization region, and further obtain the salt crystallization growth rate. The salt crystallization coverage is calculated using the following method: using grayscale recognition, the original image is converted into a grayscale image, and the proportion of salt crystallization is calculated within the grayscale threshold range where the salt crystals are located; this proportion is equivalent to the salt crystallization coverage. The salt crystallization growth rate is the rate at which the salt crystallization coverage increases over time. The base map construction module is used to construct a salt crystal layer, a matrix layer, and a base map enhancement layer based on the images stored in the image storage module, the gas phase regions identified by the gas phase region recognition and processing module, and the salt crystal regions identified by the salt crystal region recognition and processing module. Specifically, the construction of the salt crystal layer includes the following steps: selecting several representative regions as a training set in the "Trainable Weka Segmentation" module of ImageJ, and labeling them as "salt crystal regions" and "non-salt regions," where the non-salt regions include liquid phase, gas phase, and matrix boundaries; then selecting features such as texture, edge, and brightness, training a classifier, and performing batch prediction on the entire sequence of images to output a binary mask of salt crystals for subsequent coverage calculation and distribution analysis. The construction of the matrix layer includes the following steps: using the salt-free moment image as a reference, extracting the matrix contour and channel boundaries to form a fixed matrix base map or matrix mask. The matrix map is used to define the effective area of ​​pores, avoid miscounting areas outside the channels in the statistical range, and improve the structural recognition of the final overlay image. The construction of the base image enhancement layer includes the following steps: converting the original image stored in the image storage module into a grayscale image, and appropriately reducing the exposure or adjusting the color level to make the background darker, thereby enhancing the contrast between the salt crystals and the background, highlighting the salt crystal boundaries and details, and facilitating the display and verification of the segmentation effect; The results output module overlays the salt crystallization layer, matrix layer, and base map enhancement layer to generate a result map that visually distinguishes the spatial distribution of salt crystals. The final overlay map can be used for identifying and comparing the starting position, expansion path, and aggregation areas of salt crystals, and also facilitates correlation with pixel statistics from different time frames, thereby supporting quantitative analysis of salt crystallization coverage and growth rate. Similar image recognition methods can also be used to acquire gas, water, and oil phase regions, and calculate gas, water, and oil saturation based on the overall pore area.

[0119] See Figure 8 , Figure 8 The diagram below illustrates the image processing flow of this application. First, the image stored in the image storage module is preprocessed. Then, a salt crystal layer, a matrix layer, and a base image enhancement layer are constructed based on the identified gas phase region and salt crystal region. Finally, the salt crystal layer, matrix layer, and base image enhancement layer are superimposed.

[0120] Using the aforementioned image processing module, images from different times after switching to CO2 in Example 6 were processed, and their salt crystallization coverage was calculated. The results are shown below. Figure 9 , Figure 9 Schematic diagram showing the change in salt crystallization coverage over time in different rock chips. Figure 9As shown, the salt crystallization coverage in different rock chips exhibits significant differences over time. Based on the experimental phenomena, it can be seen that the growth curve of salt crystallization coverage in dolomite and sandstone is significantly higher and faster than that in marble and limestone. In contrast, marble and limestone enter a state of limited liquid supply earlier in the middle and late stages. The subsequent insufficient supply causes the coverage growth to slow down earlier and enter a plateau, resulting in a relatively low final coverage level.

[0121] The aforementioned differences are related to the brine adsorption, retention, and infiltration replenishment capabilities of the rock chips. During the drying injection process of dolomite and sandstone, in addition to the evaporation of free brine in the main channel, a certain proportion of brine can be retained in the gaps and micropores between rock particles. As the brine in the main channel gradually decreases, this adsorbed brine can continuously infiltrate into the channel under capillary action and replenish the evaporation interface, thereby prolonging the subsequent dehydration process and manifesting as more pronounced residual water content in the middle and later stages and a longer evaporation duration. This brine infiltration replenishment mechanism results in a more significant increase in salt crystallization coverage in dolomite and sandstone, with the plateau value of salt crystallization coverage in dolomite being 8.2% higher than that in sandstone.

[0122] Furthermore, differences in rock surface roughness also affect the formation and accumulation of salt crystals. Dolomite exhibits significantly increased surface roughness under the combined effects of acid corrosion and gas erosion, resulting in more microscopic irregularities and retention sites. This makes it easier for salt water films to remain on the surface and form localized enrichments, while also providing more sites for crystal attachment and growth, thus forming denser salt crystal grains and a higher coverage. Similar enhanced roughness and retention effects are observed in sandstone samples; however, because the overall acid and erosion levels of sandstone are weaker than those of dolomite, its salt crystal coverage plateau is lower.

[0123] The above experimental results show that the image processing module and method provided in this application can convert the continuous image sequence in the real core microfluidic salt precipitation experiment into quantitative results such as salt crystal distribution map, gas phase saturation, evaporation-drying rate, salt crystal coverage, salt crystal growth rate and multiphase saturation, and can be used to compare the differences in salt precipitation deposition process in different rock chips.

[0124] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

Claims

1. A simulation experimental method for gas-liquid-rock reaction and CO2 displacement drying salt precipitation deposition, characterized in that, The process employs a microfluidic chip based on a real rock core, the microfluidic chip comprising a rock substrate and microchannels formed on the surface of the rock substrate; The microchannel comprises n repeating flow channel units, with adjacent repeating flow channel units connected. Each repeating flow channel unit includes a first rectangular microchannel, a second rectangular microchannel, a third rectangular microchannel, and a fourth rectangular microchannel. The length direction of the second rectangular microchannel is perpendicular to the length direction of the first rectangular microchannel, and the liquid inlet of the second rectangular microchannel is connected to the liquid outlet of the first rectangular microchannel. The length direction of the third rectangular microchannel is perpendicular to the length direction of the second rectangular microchannel, and the liquid inlet of the third rectangular microchannel is connected to the liquid outlet of the second rectangular microchannel. The length direction of the fourth rectangular microchannel is perpendicular to the length direction of the third rectangular microchannel, and the liquid inlet of the fourth rectangular microchannel is connected to the liquid outlet of the third rectangular microchannel. The repeating flow channel unit includes several pore units and connecting microchannels connecting each pore unit; The depth of the pore unit is less than the depth of the connecting microchannel; The microfluidic chip also includes a transparent cover plate covering the surface of the rock substrate; The simulation experiment method includes the following steps: Experimental fluid is injected into the microfluidic chip to saturate the microfluidic chip with liquid phase. The microfluidic chip is subjected to heating and pressurization treatment. After the temperature and pressure are stabilized, a reaction is carried out. The reaction is continuously monitored and images or videos of the microfluidic chip are collected during the reaction process. After the reaction is complete, the injection of the experimental fluid is stopped, and CO2 gas is injected into the microfluidic chip for displacement and drying. The displacement and drying are continuously monitored, and images or videos of the microfluidic chip are acquired during the displacement and drying process.

2. The simulation experiment method according to claim 1, characterized in that, In the microfluidic chip, the pore units are arranged in an array.

3. The simulation experiment method according to claim 2, characterized in that, In the microfluidic chip, adjacent rows of pore units are arranged alternately.

4. The simulation experiment method according to any one of claims 1 to 3, characterized in that, In the microfluidic chip, the depth of the pore unit is 0; the maximum size of the pore unit in the direction parallel to the surface of the rock substrate is 100μm~500μm; The depth of the connecting microchannel is 20μm to 200μm; the width of the connecting microchannel in the direction parallel to the surface of the rock substrate is 100μm to 200μm.

5. The simulation experiment method according to claim 1, characterized in that, In the microfluidic chip, the rock substrate is a sandstone substrate, a dolomite substrate, a marble substrate, or a limestone substrate; The thickness of the rock base is 1mm to 3mm.

6. The simulation experiment method according to claim 1, characterized in that, The microfluidic chip also includes a substrate that supports the rock substrate; And / or, it also includes a packaging structure for encapsulating the microfluidic chip.

7. The simulation experiment method according to claim 1, characterized in that, The experimental fluid consisted of 10wt%~30wt% NaCl, 10wt%~30wt% acetic acid, 0.1wt%~1wt% rhodamine, and the balance being water. The termination pressure for the heating and pressurization process is 5MPa~10MPa, and the termination temperature is 50℃~80℃.

8. A simulation experimental method for gas-liquid-rock reaction and CO2 displacement drying salt precipitation deposition, characterized in that, The experiment was conducted using a visualization experimental device, which includes a cavity, a rock-based chip module, an imaging system, and a temperature and pressure control system. The rock-based chip module includes a microfluidic chip based on a real rock core, and the rock-based chip module is disposed within the cavity. The microfluidic chip includes a rock substrate and microchannels formed on the surface of the rock substrate. The microchannel comprises n repeating flow channel units, with adjacent repeating flow channel units connected. Each repeating flow channel unit includes a first rectangular microchannel, a second rectangular microchannel, a third rectangular microchannel, and a fourth rectangular microchannel. The length direction of the second rectangular microchannel is perpendicular to the length direction of the first rectangular microchannel, and the liquid inlet of the second rectangular microchannel is connected to the liquid outlet of the first rectangular microchannel. The length direction of the third rectangular microchannel is perpendicular to the length direction of the second rectangular microchannel, and the liquid inlet of the third rectangular microchannel is connected to the liquid outlet of the second rectangular microchannel. The length direction of the fourth rectangular microchannel is perpendicular to the length direction of the third rectangular microchannel, and the liquid inlet of the fourth rectangular microchannel is connected to the liquid outlet of the third rectangular microchannel. The repeating flow channel unit includes several pore units and connecting microchannels connecting each pore unit; The depth of the pore unit is less than the depth of the connecting microchannel; The microfluidic chip also includes a transparent cover plate covering the surface of the rock substrate; The imaging system is used for in-situ observation and image recording of the microfluidic chip; The temperature and pressure control system is used to control the temperature and pressure of the rock-based chip module; The simulation experiment method includes the following steps: Experimental fluid is injected into the microfluidic chip to saturate the microfluidic chip with liquid phase. The microfluidic chip is subjected to heating and pressurization treatment. After the temperature and pressure are stabilized, a reaction is carried out. The reaction is continuously monitored and images or videos of the microfluidic chip are collected during the reaction process. After the reaction is complete, the injection of the experimental fluid is stopped, and CO2 gas is injected into the microfluidic chip for displacement and drying. The displacement and drying are continuously monitored, and images or videos of the microfluidic chip are acquired during the displacement and drying process.

9. The simulation experiment method according to claim 8, characterized in that, In the visualization experimental device, the temperature and pressure control system includes a temperature control module and a pressure control module that are respectively connected to the cavity. The temperature control module is used to adjust the temperature of the cavity, and the pressure control module is used to adjust the pressure of the cavity.

10. The simulation experiment method according to claim 9, characterized in that, In the visualization experimental device, the imaging system includes: A fluorescence microscope used to observe microfluidic chips; A fluorescent light source for illuminating the microfluidic chip; An image acquisition module for acquiring images or videos of the microfluidic chip; and an image storage module, wherein the image storage module is used to receive and store images or videos acquired by the image acquisition module.

11. The simulation experiment method according to claim 10, characterized in that, The visualization experimental device also includes an image processing module, which is used to process the images or videos stored in the image storage module.

12. The simulation experiment method according to claim 11, characterized in that, The image processing module includes: An image preprocessing module is used to preprocess the images stored in the image storage module; A gas phase region identification and processing module is used to receive a preprocessed image output by the image preprocessing module, identify the gas phase region of the preprocessed image and calculate the total number of pixels in the gas phase region, and calculate the gas phase saturation and evaporation-drying rate based on the total number of pixels in the gas phase region. A salt crystallization region identification and processing module is used to receive a preprocessed image output by the image preprocessing module, identify the salt crystallization region of the preprocessed image and calculate the total number of pixels in the salt crystallization region, and calculate the salt crystallization coverage and salt crystallization growth rate based on the total number of pixels in the salt crystallization region. A base map construction module is used to construct a salt crystallization layer, a matrix layer, and a base map enhancement layer based on the image stored in the image storage module, the gas phase region identified by the gas phase region identification and processing module, and the salt crystallization region identified by the salt crystallization region identification and processing module. The result output module is used to superimpose the salt crystallization layer, matrix layer and base map enhancement layer and output the result image.

13. The simulation experiment method according to claim 12, characterized in that, The experimental fluid consisted of 10wt%~30wt% NaCl, 10wt%~30wt% acetic acid, 0.1wt%~1wt% rhodamine, and the balance being water. The termination pressure for the heating and pressurization process is 5MPa~10MPa, and the termination temperature is 50℃~80℃.

Images