A gas seepage law testing system and method based on a microfluidic coal body model

Abstract

This invention discloses a gas seepage law testing system and method based on a microfluidic coal body model, relating to the field of microfluidic coal body models under stress and gas seepage laws. The system includes: a coal column, a microfluidic chip, and a chip clamping device, with the microfluidic chip horizontally placed in the chip clamping device. One end of the chip clamping device is connected to a gas-driven pipeline; the other end is connected to a liquid-driven pipeline. A light source is located at the bottom of the chip clamping device, and a microscope and a high-speed camera are located at the top of the chip clamping device for real-time observation and recording of the internal displacement of the microfluidic chip, and the recorded results are transmitted to an image acquisition unit for analysis. This invention, through a dual-chip model system combined with adjustable confining pressure loading and independently switchable gas-liquid two-phase displacement function, achieves full-process visual observation and quantitative analysis of coal body pore fracture deformation, gas seepage dynamics, and chemical dissolution processes under simulated stress conditions.

Description

Technical Field

[0001] This invention relates to the field of microfluidic coal body models under stress and gas seepage laws, specifically to a gas seepage law testing system and method based on microfluidic coal body models. Background Technology

[0002] Coal, as a complex porous medium, has an internal pore and fracture structure that forms the main channels for the storage and migration of gases such as methane (primarily composed of gas), as well as liquids such as fracturing fluid and groundwater. Under mining-induced stress or changes in geostress, the pore and fracture structure of coal undergoes dynamic evolution, significantly affecting its permeability. Therefore, a thorough understanding of the evolution mechanism of coal pore and fracture structure under stress and its impact on gas seepage behavior is of significant theoretical and practical value for engineering practices such as achieving efficient coalbed methane production, precise prevention and control of coal mine gas outbursts, and safety assessment of CO2 geological storage.

[0003] Currently, research on coal seepage characteristics mainly relies on macroscopic core displacement experiments and numerical simulation methods. While core displacement experiments can obtain macroscopic parameters such as overall permeability, they are limited by observation methods and cannot capture in real time and intuitively the microscopic seepage mechanisms such as gas flow paths, throat opening and closing states, local blockage / clearing processes, and gas-solid-liquid multiphase interactions at the pore scale. Numerical simulation methods, on the other hand, are highly dependent on the accuracy of pore structure models. Due to the strong heterogeneity, anisotropy, and significant stress sensitivity of coal, constructing a digital model that can truly reflect its microstructural characteristics and mechanical response still faces considerable challenges, and the reliability of simulation results urgently needs to be supported and verified by high-precision experimental data.

[0004] No effective solutions have yet been proposed to address the problems in the relevant technologies. Summary of the Invention

[0005] To address the problems in related technologies, this invention proposes a gas seepage law testing system and method based on a microfluidic coal body model, in order to overcome the aforementioned technical problems existing in the existing related technologies.

[0006] Therefore, the specific technical solution adopted by the present invention is as follows:

[0007] According to one aspect of the present invention, a gas seepage law testing system based on a microfluidic coal body model is provided. The system includes: a coal column, a microfluidic chip and a chip clamping device, wherein the microfluidic chip is horizontally placed in the chip clamping device.

[0008] One end of the chip clamping device is connected to the gas drive pipeline, and gas is injected into the chip from the gas cylinder at the inlet of the gas drive pipeline. The gas injection rate is changed by the gas flow controller. A gas flow meter is connected to the outlet of the gas drive pipeline. A shut-off valve assembly is installed on the gas drive pipeline and is connected to the confining pressure pump.

[0009] The other end of the chip clamping device is connected to the liquid drive pipeline, and the inlet of the liquid drive pipeline is injected by the injection pump to inject the displacement liquid in the storage tank into the microfluidic chip. The outlet of the liquid drive pipeline is connected to an electronic balance to record and collect the displaced liquid.

[0010] A light source is installed at the bottom of the chip clamping device, and a microscope and a high-speed camera are installed at the top of the chip clamping device to observe and record the displacement inside the microfluidic chip in real time, and transmit the recording results to the image acquisition unit for analysis.

[0011] Furthermore, the microfluidic chip includes a polydimethylsiloxane chip and a real coal sample chip;

[0012] The coal pillar is sliced, and the sliced ​​results are CT scanned to obtain three-dimensional pore structure data. The three-dimensional pore structure data is reconstructed in polydimethylsiloxane material to obtain polydimethylsiloxane chip.

[0013] The slices were polished and then encapsulated in polydimethylsiloxane material to obtain a real coal sample chip.

[0014] Furthermore, both the polydimethylsiloxane chip and the real coal sample chip have cracks of a predetermined width etched in their middle sections.

[0015] Furthermore, the shut-off valve assembly includes a first shut-off valve, a second shut-off valve, a third shut-off valve, a fourth shut-off valve, a fifth shut-off valve, a sixth shut-off valve, a seventh shut-off valve, and an eighth shut-off valve disposed on the pneumatic pipeline;

[0016] The first shut-off valve is located on one side of the gas flow controller, the second shut-off valve is located on one side of the chip clamping device, the third shut-off valve is located on the other side of the chip clamping device, the fourth shut-off valve is located on one side of the electronic balance, the fifth shut-off valve is located in the middle of the injection pump and the storage tank, the sixth shut-off valve is located on one side of the storage tank and is connected to the first and second shut-off valves, the seventh shut-off valve is located in the middle of the light source and the confining pressure pump, and the eighth shut-off valve is located on one side of the gas flow meter and is connected to the third and fourth shut-off valves.

[0017] Furthermore, the gas drive pipeline and the liquid drive pipeline are connected in parallel in the chip clamping device, and the gas drive pipeline and the liquid drive pipeline are independent of each other.

[0018] According to another aspect of the present invention, a method for testing the gas seepage law based on a microfluidic coal body model is also provided, the method comprising:

[0019] S1. After the prepared microfluidic chip is placed horizontally inside the chip clamping device, the gas-liquid two-phase injection unit is started. The gas-liquid two-phase injection unit includes a gas-driven module and a liquid-driven module.

[0020] S2. During the operation of the gas-liquid two-phase injection unit, the pressure sensor built into the chip clamping device monitors and records the confining pressure data acting on the microfluidic chip under simulated stress conditions in real time, and simultaneously starts the image acquisition unit to capture and record the deformation process of the microfluidic chip's internal pore fracture structure under pressure and the internal displacement fluid flow process. Based on the recorded results, the permeability of the coal body under different stress conditions is calculated.

[0021] S3. The confining pressure data is fused with the permeability under the corresponding stress conditions. Based on the fusion results, the relationship between pressure and permeability of the coal body under stress is established to analyze the evolution law of coal body deformation and permeability.

[0022] Furthermore, the gas-driven module is used to analyze the seepage law of gas in coal under stress conditions, while the liquid-driven module is used to analyze the flow and dissolution effect of the displacing fluid in coal.

[0023] Furthermore, the operation of the air-driven module includes:

[0024] After placing the microfluidic chip horizontally inside the chip clamping device, close the fifth, sixth, and fourth shut-off valves related to the liquid drive pipeline, and turn on the light source and the seventh shut-off valve. Apply a preset confining pressure to the inside of the chip clamping device through the confining pressure pump, and monitor and record the confining pressure data acting on the microfluidic chip under simulated stress conditions in real time.

[0025] After the confining pressure stabilizes, the first shut-off valve, the second shut-off valve, the third shut-off valve and the eighth shut-off valve are opened in sequence to connect the gas drive pipeline and open the gas cylinder. The gas injection rate is adjusted by the gas flow controller.

[0026] During the gas injection process, the deformation process of the microfluidic chip's internal pore crack structure under pressure is captured and recorded using a microscope and a high-speed camera to obtain image data;

[0027] The image data is transmitted to the image acquisition unit, and the permeability change of the microfluidic chip under different stress conditions is calculated by comparing the gas flow data recorded by the gas flow meter before and after gas displacement.

[0028] Furthermore, the operation of the liquid drive module includes:

[0029] After the microfluidic chip is placed horizontally inside the chip clamping device, the first and eighth shut-off valves related to the air drive pipeline are closed, and the light source and the seventh shut-off valve are turned on. A preset confining pressure is applied to the inside of the chip clamping device through the confining pressure pump, and the confining pressure data acting on the microfluidic chip under simulated stress conditions is monitored and recorded in real time.

[0030] After the confining pressure stabilizes, the fifth, sixth, second, third and fourth shut-off valves are opened in sequence to connect the liquid drive pipeline and the injection pump is started to inject the displacement fluid stored in the tank into the microfluidic chip at a constant flow rate.

[0031] During the injection of the displacement fluid, the flow path and corresponding dynamic changes of the displacement fluid in the microfluidic chip are captured and recorded using a microscope and a high-speed camera to obtain image data.

[0032] Image data is transmitted to the image acquisition unit, and the displacing fluid flowing out of the microfluidic chip outlet is collected and weighed using an electronic balance. By comparing the displacing fluid flow rate data before and after displacing, the permeability change of the microfluidic chip under different stress conditions is calculated.

[0033] Furthermore, the operation of the liquid drive module also includes:

[0034] During the operation of the liquid-driven module, if a real coal sample chip is used for testing, a chemically active displacement fluid is injected into the real coal sample chip. The dissolution effect of the displacement fluid on the surface of the pores and cracks inside the real coal sample chip, as well as the evolution of the pore and crack structure and the formation of new fluid channels caused by the dissolution effect are observed in real time using a microscope and a high-speed camera.

[0035] The beneficial effects of this invention are as follows:

[0036] This invention integrates a dual-chip model system of real coal samples and three-dimensional reconstructed polydimethylsiloxane, combined with precisely controllable confining pressure loading and independently switchable gas-liquid two-phase displacement function. Under simulated stress conditions, it realizes full-process visualization observation and quantitative analysis of coal pore fracture deformation, gas seepage dynamics, and chemical dissolution processes. It effectively solves the technical problems of insufficient realism and limited functionality of traditional experimental methods, and has the advantages of realistic simulation conditions, comprehensive data acquisition, and intuitive mechanism revelation. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of a gas seepage law testing system based on a microfluidic coal body model according to an embodiment of the present invention;

[0039] Figure 2 This is a flowchart of a gas seepage law testing method based on a microfluidic coal body model according to an embodiment of the present invention.

[0040] In the picture:

[0041] 1. Coal pillar; 2. Microfluidic chip; 2-1. Polydimethylsiloxane chip; 2-2. Real coal sample chip; 3. Chip clamping device; 4. Gas cylinder; 5. Gas flow controller; 6. Microscope; 7. High-speed camera; 8. Electronic balance; 9. Injection pump; 10. Storage tank; 11. Light source; 12. Gas flow meter; 13. Confining pressure pump; 14. Image acquisition unit; 15. Shut-off valve assembly; 15-1. First shut-off valve; 15-2. Second shut-off valve; 15-3. Third shut-off valve; 15-4. Fourth shut-off valve; 15-5. Fifth shut-off valve; 15-6. Sixth shut-off valve; 15-7. Seventh shut-off valve; 15-8. Eighth shut-off valve. Detailed Implementation

[0042] To further illustrate the various embodiments, the present invention provides accompanying drawings, which are part of the disclosure of the present invention. These drawings are mainly used to illustrate the embodiments and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these drawings, those skilled in the art should be able to understand other possible implementation methods and the advantages of the present invention.

[0043] According to an embodiment of the present invention, a gas seepage law testing system and method based on a microfluidic coal body model is provided.

[0044] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments, such as... Figure 1As shown, according to an embodiment of the present invention, a gas seepage law testing system based on a microfluidic coal body model includes: a coal column 1, a microfluidic chip 2, and a chip clamping device 3, wherein the microfluidic chip 2 is horizontally placed in the chip clamping device 3; one end of the chip clamping device 3 is connected to a gas-driven pipeline, and gas is injected into the chip from a gas cylinder 4 at the inlet of the gas-driven pipeline, and the gas injection rate is changed by a gas flow controller 5; a gas flow meter 12 is connected to the outlet of the gas-driven pipeline, and a shut-off valve assembly 15 is provided on the gas-driven pipeline. 15 is connected to the confining pressure pump 13; the other end of the chip clamping device 3 is connected to the liquid drive pipeline, and the inlet of the liquid drive pipeline is injected by the injection pump 9 into the microfluidic chip 2 from the storage tank 10. The outlet of the liquid drive pipeline is connected to an electronic balance 8 for recording and collecting the displaced liquid; a light source 11 is provided at the bottom of the chip clamping device 3, and a microscope 6 and a high-speed camera 7 are provided at the top of the chip clamping device 3 for real-time observation and recording of the internal displacement of the microfluidic chip 2, and the recording results are transmitted to the image acquisition unit 14 for analysis.

[0045] It should be noted that gas cylinder 4 serves as the gas source, and its outlet is connected in sequence to gas flow controller 5 and first shut-off valve 15-1; the gas drive pipeline is connected to the fluid inlet of chip clamping device 3; the pipeline leading out from the fluid outlet of chip clamping device 3 is connected in sequence to third shut-off valve 15-3, gas flow meter 12 and eighth shut-off valve 15-8, and finally to the gas outlet.

[0046] The storage tank 10 is used to store the displacement fluid and is connected to the injection pump 9 through a pipeline. The outlet of the injection pump 9 is connected in sequence to the fifth shut-off valve 15-5, the storage tank 10 and the sixth shut-off valve 15-6, and then flows into the inlet of the chip clamping device 3. The outlet pipeline is connected to the fourth shut-off valve 15-4 after the third shut-off valve 15-3. An electronic balance 8 is placed at the rear end of the valve to collect and measure the outflowing liquid.

[0047] The light source 11 is placed below the chip clamping device 3 to provide transmitted illumination; the observation system consisting of the microscope 6 and the high-speed camera 7 is located directly above the clamping device to capture the dynamic process inside the chip; the signal output terminal of the high-speed camera 7 is connected to the image acquisition unit 14 to transmit the image data to the computer for processing, storage and analysis.

[0048] In this optional embodiment, the microfluidic chip 2 includes a polydimethylsiloxane chip 2-1 and a real coal sample chip 2-2; the coal column 1 is sliced, and the sliced ​​results are CT scanned to obtain three-dimensional pore structure data, and the three-dimensional pore structure data is reconstructed in polydimethylsiloxane material to obtain polydimethylsiloxane chip 2-1; the sliced ​​results are polished, and the polished slices are encapsulated in polydimethylsiloxane material to obtain real coal sample chip 2-2.

[0049] It should be further explained that the polydimethylsiloxane chip 2-1 and the real coal sample chip 2-2 are horizontally installed in the internal cavity of the chip clamping device 3; the chip clamping device 3 itself is provided with a confining pressure interface, which is connected to the confining pressure pump 13 through a pipeline. The pipeline is provided with a seventh shut-off valve 15-7, which is used to control the application and removal of confining pressure; the pipeline is provided with a second shut-off valve 15-2 and a third shut-off valve 15-3, which are used to switch the displacement mode, specifically to switch between the gas drive module and the liquid drive module.

[0050] In this optional embodiment, both the polydimethylsiloxane chip 2-1 and the real coal sample chip 2-2 have cracks of a preset width etched in their middle portions.

[0051] It should be further explained that a real coal sample slice was cut from coal column 1, and the three-dimensional pore structure data inside the coal slice was obtained using high-precision CT scanning technology. The obtained structural data was used for three-dimensional modeling and digital reconstruction, and the reconstructed pore network model was imported into the microfluidic chip 2 design. Using PDMS (polydimethylsiloxane), a polymer material with good deformation ability and optical transparency, a PDMS chip 2-1 embedded with the real coal pore structure was fabricated using soft photolithography. The cut coal slice was then polished to obtain the real coal sample chip 2-2. Both types of chips have a size of 10. The microfluidic chip 2 is 10 mm thick and 500 μm thick. To facilitate fluid flow, a 300 μm gap is etched between the polydimethylsiloxane chip 2-1 and the real coal sample chip 2-2. During testing, the polydimethylsiloxane chip 2-1 or the real coal sample model 2-2 is placed horizontally in the chip clamping device 3. A certain confining pressure can be applied inside the device, as follows: a controllable confining pressure is applied to the microfluidic chip 2 carried by the pressure application component inside the device; a pressure sensor integrated in the chip clamping device 3 detects the pressure data of the confining pressure in real time and transmits the detected pressure data to the computer. The computer receives and processes the pressure data for subsequent analysis and monitoring. A seventh shut-off valve 15-7 is connected to the pipeline.

[0052] In this optional embodiment, the shut-off valve assembly 15 includes a first shut-off valve 15-1, a second shut-off valve 15-2, a third shut-off valve 15-3, a fourth shut-off valve 15-4, a fifth shut-off valve 15-5, a sixth shut-off valve 15-6, a seventh shut-off valve 15-7, and an eighth shut-off valve 15-8 disposed on the gas drive pipeline; the first shut-off valve 15-1 is located on one side of the gas flow controller 5, the second shut-off valve 15-2 is located on one side of the chip clamping device 3, and the third shut-off valve 15-3 is located on the other side of the chip clamping device 3. The fourth shut-off valve 15-4 is located on one side of the electronic balance 8. The fifth shut-off valve 15-5 is located in the middle between the injection pump 9 and the storage tank 10. The sixth shut-off valve 15-6 is located on one side of the storage tank 10 and is connected to the first shut-off valve 15-1 and the second shut-off valve 15-2. The seventh shut-off valve 15-7 is located in the middle between the light source 11 and the confining pressure pump 13. The eighth shut-off valve 15-8 is located on one side of the gas flow meter 12 and is connected to the third shut-off valve 15-3 and the fourth shut-off valve 15-4.

[0053] In this optional embodiment, the gas drive pipeline and the liquid drive pipeline are arranged in parallel in the chip clamping device 3, and the gas drive pipeline and the liquid drive pipeline are independent of each other.

[0054] like Figure 2 As shown, according to another embodiment of the present invention, a method for testing the gas seepage law based on a microfluidic coal body model is also provided, the method comprising:

[0055] S1. After the prepared microfluidic chip 2 is placed horizontally inside the chip clamping device 3, the gas-liquid two-phase injection unit is started. The gas-liquid two-phase injection unit includes a gas-driven module and a liquid-driven module.

[0056] S2. During the operation of the gas-liquid two-phase injection unit, the pressure sensor built into the chip clamping device 3 monitors and records the confining pressure data acting on the microfluidic chip 2 under simulated stress conditions in real time, and simultaneously starts the image acquisition unit 14 to capture and record the deformation process of the internal pore fracture structure of the microfluidic chip 2 under pressure and the internal displacement fluid flow process. Based on the recording results, the permeability of the coal body under different stress conditions is calculated.

[0057] S3. The confining pressure data is fused with the permeability under the corresponding stress conditions. Based on the fusion results, the relationship between pressure and permeability of the coal body under stress is established to analyze the evolution law of coal body deformation and permeability.

[0058] In this optional embodiment, the gas-driven module is used to analyze the seepage law of gas in the coal body under stress conditions, and the liquid-driven module is used to analyze the flow and dissolution effect of the displacement fluid in the coal body.

[0059] It should be added that a gas seepage law testing system based on a microfluidic coal body model can realize two displacement modes: gas-driven module and liquid-driven module.

[0060] In this optional embodiment, the operation of the air-driven module includes:

[0061] After placing the microfluidic chip 2 horizontally inside the chip clamping device 3, close the fifth shut-off valve 15-5, the sixth shut-off valve 15-6, and the fourth shut-off valve 15-4 related to the liquid drive pipeline, and turn on the light source 11 and the seventh shut-off valve 15-7. Apply a preset confining pressure to the inside of the chip clamping device 3 through the confining pressure pump 13, and monitor and record the confining pressure data acting on the microfluidic chip 2 under simulated stress conditions in real time. After the confining pressure stabilizes, open the first shut-off valve 15-1, the second shut-off valve 15-2, the third shut-off valve 15-3, and the eighth shut-off valve 15-8 in sequence to connect the gas drive pipeline, and turn on the gas cylinder 4. Adjust the gas injection rate through the gas flow controller 5. During the gas injection process, capture and record the deformation process of the internal pore crack structure of the microfluidic chip 2 under pressure through the microscope 6 and the high-speed camera 7 to obtain image data. Transmit the image data to the image acquisition unit 14, and calculate the permeability change of the microfluidic chip 2 under different stress conditions by comparing the gas flow data recorded by the gas flow meter 12 before and after gas displacement.

[0062] In this optional embodiment, the operation of the liquid drive module includes:

[0063] After placing the microfluidic chip 2 horizontally inside the chip clamping device 3, close the first shut-off valve 15-1 and the eighth shut-off valve 15-8 related to the gas drive pipeline, and turn on the light source 11 and the seventh shut-off valve 15-7. Apply a preset confining pressure to the inside of the chip clamping device 3 through the confining pressure pump 13, and monitor and record the confining pressure data acting on the microfluidic chip 2 under simulated stress conditions in real time. After the confining pressure stabilizes, open the fifth shut-off valve 15-5, the sixth shut-off valve 15-6, the second shut-off valve 15-2, the third shut-off valve 15-3, and the fourth shut-off valve 15-4 in sequence to connect the circuit. The liquid-driven pipeline is activated, and the injection pump 9 is started to inject the displacing fluid stored in the storage tank 10 into the microfluidic chip 2 at a constant flow rate. During the injection of the displacing fluid, the flow path and corresponding dynamic changes of the displacing fluid in the microfluidic chip 2 are captured and recorded by the microscope 6 and the high-speed camera 7 to obtain image data. The image data is transmitted to the image acquisition unit 14, and the displacing fluid flowing out of the outlet of the microfluidic chip 2 is collected and weighed by the electronic balance 8. The flow rate data of the displacing fluid before and after the displacing is compared, and the permeability change of the microfluidic chip 2 under different stress conditions is calculated.

[0064] In this optional embodiment, the operation of the liquid drive module further includes:

[0065] During the operation of the liquid-driven module, if a real coal sample chip 2-2 is used for testing, a chemically active displacement fluid is injected into the real coal sample chip 2-2. The dissolution effect of the displacement fluid on the surface of the pores and fissures inside the real coal sample chip 2-2, as well as the evolution of the pore and fissure structure and the formation of new fluid channels caused by the dissolution effect, are observed in real time using a microscope 6 and a high-speed camera 7.

[0066] It should be further noted that a method for testing gas seepage patterns based on a microfluidic coal body model specifically includes:

[0067] Step 1: Cut coal pillar 1 into 10mm pieces. 10mm A 500μm real coal sample slice was used. Based on this slice, a microfluidic chip was prepared in two ways: First, the coal sample slice was CT scanned to obtain precise three-dimensional pore structure data, and this structure was reconstructed in a deformable and transparent material made of PDMS (polydimethylsiloxane) to obtain a polydimethylsiloxane chip 2-1; Second, the cut coal sample slice was directly polished to obtain a real coal sample chip 2-2. An artificial crack with a width of 300μm was etched in the middle of both chips. During testing, the prepared polydimethylsiloxane chip 2-1 or real coal sample chip 2-2 was placed horizontally in the cavity of the chip clamping device 3.

[0068] Step 2: The gas-driven module (pneumatic mode) is used to study the gas seepage law in coal under stress conditions; specifically as follows: the microfluidic chip 2 is placed horizontally inside the chip clamping device 3, and the fifth shut-off valve 15-5, the sixth shut-off valve 15-6, and the fourth shut-off valve 15-4 related to the liquid drive pipeline are closed; the light source 11 is turned on to provide backlight, and the seventh shut-off valve 15-7 is opened. A preset confining pressure is applied to the inside of the chip clamping device 3 through the confining pressure pump 13 to simulate the geostress environment; after the confining pressure stabilizes, the first shut-off valve 15-1 and the second shut-off valve 15-4 are opened sequentially. -2. The third shut-off valve 15-3 and the eighth shut-off valve 15-8 are connected to the gas drive pipeline; the gas cylinder 4 is opened, and the gas injection rate is precisely controlled and adjusted by the gas flow controller 5; during this process, the microscope 6 and the high-speed camera 7 perform real-time dynamic observation and recording of the deformation of the pore structure inside the chip, the opening and closing of the throat, and the gas transport process. The image data is finally transmitted to the image acquisition unit 14 for processing and analysis; at the same time, by comparing the gas flow data recorded by the gas flow meter 12 before and after displacement, the permeability change of the chip model under different stress conditions can be calculated.

[0069] Step 3: The liquid-driven module (liquid-driven mode) is used to study the flow and dissolution effect of fluids in coal. Specifically, the microfluidic chip 2 is placed horizontally inside the chip clamping device 3, and the first shut-off valve 15-1 and the eighth shut-off valve 15-8 related to the gas-driven pipeline are closed. Similarly, the light source 11 and the seventh shut-off valve 15-7 are turned on first, and a predetermined confining pressure is applied through the confining pressure pump 13. After the confining pressure stabilizes, the fifth shut-off valve 15-5, the sixth shut-off valve 15-6, the second shut-off valve 15-2, the third shut-off valve 15-3, and the fourth shut-off valve 15-4 are opened sequentially to connect the liquid-driven pipeline. The injection pump 9 is started to... The displacing fluid stored in the storage tank 10 is injected into the chip at a constant flow rate; the microscope 6 and the high-speed camera 7 will capture and record the dominant flow path of the fluid in the chip and its dynamic changes in real time, and the image data will be transmitted to the image acquisition unit 14; the liquid flowing out of the chip outlet is collected and weighed by the electronic balance 8 for subsequent analysis; when using a real coal sample chip 2-2 in the liquid-driven mode, a chemically active displacing fluid is injected into it, and the dissolution effect of the liquid on the surface of the coal pores and fractures, as well as the resulting changes in pore structure and the formation of new dominant fluid channels can be directly observed by the microscope 6 and the high-speed camera 7.

[0070] Step 4: Establish the stress-porosity relationship to achieve a quantitative study of the relationship between coal deformation and permeability changes under stress conditions. The effective stress is calculated using the stress applied by the confining pressure pump 13.

[0071] ;

[0072] In the formula, Indicates effective stress; Indicates the total stress; This represents the Biot coefficient, which characterizes the interaction between solid particles and the framework. This represents pore pressure.

[0073] Step 5: Analyze the changes in porosity inside the chip under stress using image acquisition unit 14, and couple stress and porosity to obtain the stress-porosity relationship:

[0074] ;

[0075] In the formula, This represents the porosity under the current effective stress. Indicates effective stress Initial porosity; Indicates the pore compressibility coefficient; This represents the effective stress under the initial state.

[0076] Step 6: Couple porosity and permeability to obtain the porosity-permeability relationship:

[0077] ;

[0078] In the formula, Indicates the current penetration rate; Indicates the initial penetration rate; This represents the porosity under the current effective stress. Indicates effective stress Initial porosity; Indicates the degree of tortuosity; Indicates the initial tortuosity; Represents specific surface area; This represents the initial specific surface area.

[0079] Step 7: Couple the formulas in the stress-porosity relationship with the porosity-permeability relationship to obtain the stress-porosity-permeability relationship:

[0080] ;

[0081] In the formula, Indicates the current penetration rate; Indicates the initial penetration rate; Indicates the pore compressibility coefficient; Indicates the total stress; Represents the Biot coefficient; Indicates pore pressure; This represents the effective stress in the initial state; Indicates effective stress Initial porosity; This represents the porosity under the current effective stress. Indicates the degree of tortuosity; Indicates the initial tortuosity; Represents specific surface area; This represents the initial specific surface area.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A gas seepage law testing system based on a microfluidic coal body model, characterized in that, The system includes: a coal pillar (1), a microfluidic chip (2) and a chip clamping device (3), wherein the microfluidic chip (2) is placed horizontally in the chip clamping device (3); One end of the chip clamping device (3) is connected to the gas drive pipeline, and gas is injected into the chip from the gas cylinder (4) at the inlet of the gas drive pipeline. The gas injection rate is changed by the gas flow controller (5). A gas flow meter (12) is connected to the outlet of the gas drive pipeline. A shut-off valve assembly (15) is provided on the gas drive pipeline. The shut-off valve assembly (15) is connected to the confining pressure pump (13). The other end of the chip clamping device (3) is connected to the liquid drive pipeline, and the inlet of the liquid drive pipeline is injected by the injection pump (9) into the microfluidic chip (2) from the storage tank (10). The outlet of the liquid drive pipeline is connected to an electronic balance (8) for recording and collecting the displaced liquid. The bottom of the chip clamping device (3) is provided with a light source (11), and the top of the chip clamping device (3) is provided with a microscope (6) and a high-speed camera (7) for real-time observation and recording of the displacement inside the microfluidic chip (2), and transmitting the recording results to the image acquisition unit (14) for analysis. The shut-off valve assembly (15) includes a first shut-off valve (15-1), a second shut-off valve (15-2), a third shut-off valve (15-3), a fourth shut-off valve (15-4), a fifth shut-off valve (15-5), a sixth shut-off valve (15-6), a seventh shut-off valve (15-7), and an eighth shut-off valve (15-8) disposed on the gas drive pipeline; the first shut-off valve (15-1) is located on one side of the gas flow controller (5), the second shut-off valve (15-2) is located on one side of the chip clamping device (3), the third shut-off valve (15-3) is located on the other side of the chip clamping device (3), and the fourth shut-off valve (15-4) is located on the other side of the gas drive pipeline. On one side of the electronic balance (8), the fifth shut-off valve (15-5) is located in the middle of the injection pump (9) and the storage tank (10), the sixth shut-off valve (15-6) is located on one side of the storage tank (10), and the sixth shut-off valve (15-6) is connected to the first shut-off valve (15-1) and the second shut-off valve (15-2), the seventh shut-off valve (15-7) is located in the middle of the light source (11) and the confining pressure pump (13), the eighth shut-off valve (15-8) is located on one side of the gas flow meter (12), and the eighth shut-off valve (15-8) is connected to the third shut-off valve (15-3) and the fourth shut-off valve (15-4).

2. The gas seepage law testing system based on a microfluidic coal body model according to claim 1, characterized in that, The microfluidic chip (2) includes a polydimethylsiloxane chip (2-1) and a real coal sample chip (2-2). The coal pillar (1) is sliced, and the sliced ​​results are CT scanned to obtain three-dimensional pore structure data. The three-dimensional pore structure data is reconstructed in polydimethylsiloxane material to obtain polydimethylsiloxane chip (2-1). The slices were polished and then encapsulated in polydimethylsiloxane material to obtain a real coal sample chip (2-2).

3. The gas seepage law testing system based on a microfluidic coal body model according to claim 2, characterized in that, Both the polydimethylsiloxane chip (2-1) and the real coal sample chip (2-2) have cracks of a preset width etched in their middle portions.

4. The gas seepage law testing system based on a microfluidic coal body model according to claim 1, characterized in that, The gas drive pipeline and the liquid drive pipeline are connected in parallel in the chip clamping device (3), and the gas drive pipeline and the liquid drive pipeline are independent of each other.

5. A method for testing the gas seepage law based on a microfluidic coal body model, using the gas seepage law testing system based on a microfluidic coal body model as described in any one of claims 1-4, characterized in that, The method includes: S1. After placing the prepared microfluidic chip (2) horizontally inside the chip clamping device (3), start the gas-liquid two-phase injection unit, which includes a gas-driven module and a liquid-driven module. S2. During the operation of the gas-liquid two-phase injection unit, the pressure sensor built into the chip clamping device (3) is used to monitor and record the confining pressure data of the microfluidic chip (2) under simulated stress conditions in real time, and the image acquisition unit (14) is started simultaneously to capture and record the deformation process of the microfluidic chip (2) internal pore fracture structure under pressure and the internal displacement fluid flow process. Based on the recording results, the permeability of the coal body under different stress conditions is calculated. S3. The confining pressure data is fused with the permeability under the corresponding stress conditions. Based on the fusion results, the relationship between pressure and permeability of the coal body under stress is established to analyze the evolution law of coal body deformation and permeability.

6. The method for testing gas seepage law based on a microfluidic coal body model according to claim 5, characterized in that, The gas-driven module is used to analyze the seepage law of gas in coal under stress conditions, and the liquid-driven module is used to analyze the flow and dissolution effect of the displacement fluid in coal.

7. The method for testing the gas seepage law based on a microfluidic coal body model according to claim 6, characterized in that, The operation of the air-driven module includes: After placing the microfluidic chip (2) horizontally inside the chip clamping device (3), close the fifth shut-off valve (15-5), the sixth shut-off valve (15-6) and the fourth shut-off valve (15-4) related to the liquid drive pipeline, and turn on the light source (11) and the seventh shut-off valve (15-7). Apply a preset confining pressure to the inside of the chip clamping device (3) through the confining pressure pump (13), and monitor and record the confining pressure data of the microfluidic chip (2) under simulated stress conditions in real time. After the confining pressure stabilizes, the first shut-off valve (15-1), the second shut-off valve (15-2), the third shut-off valve (15-3) and the eighth shut-off valve (15-8) are opened in sequence to connect the gas drive pipeline and the gas cylinder (4) is opened. The gas injection rate is adjusted by the gas flow controller (5). During the gas injection process, the deformation process of the microfluidic chip (2) internal hole crack structure under pressure is captured and recorded by a microscope (6) and a high-speed camera (7) to obtain image data; The image data is transmitted to the image acquisition unit (14), and the permeability change of the microfluidic chip (2) under different stress conditions is calculated by comparing the gas flow data recorded by the gas flow meter (12) before and after gas displacement.

8. The method for testing the gas seepage law based on a microfluidic coal body model according to claim 7, characterized in that, The operation of the liquid drive module includes: After placing the microfluidic chip (2) horizontally inside the chip clamping device (3), close the first shut-off valve (15-1) and the eighth shut-off valve (15-8) related to the gas drive pipeline, and turn on the light source (11) and the seventh shut-off valve (15-7). Apply a preset confining pressure to the inside of the chip clamping device (3) through the confining pressure pump (13), and monitor and record the confining pressure data acting on the microfluidic chip (2) under simulated stress conditions in real time. After the confining pressure stabilizes, the fifth shut-off valve (15-5), the sixth shut-off valve (15-6), the second shut-off valve (15-2), the third shut-off valve (15-3), and the fourth shut-off valve (15-4) are opened in sequence to connect the liquid drive pipeline and start the injection pump (9) to inject the displacement fluid stored in the storage tank (10) into the microfluidic chip (2) at a constant flow rate. During the displacing fluid injection process, the flow path and corresponding dynamic changes of the displacing fluid in the microfluidic chip (2) are captured and recorded by a microscope (6) and a high-speed camera (7) to obtain image data; The image data is transmitted to the image acquisition unit (14), and the displacement liquid flowing out of the microfluidic chip (2) is collected and weighed by the electronic balance (8). The displacement liquid flow data before and after displacement are compared, and the permeability change of the microfluidic chip (2) under different stress conditions is calculated.

9. The method for testing the gas seepage law based on a microfluidic coal body model according to claim 8, characterized in that, The operation of the liquid drive module also includes: During the operation of the liquid-driven module, if a real coal sample chip (2-2) is used for testing, a chemically active displacement liquid is injected into the real coal sample chip (2-2), and the dissolution effect of the displacement liquid on the surface of the pores and fissures of the real coal sample chip (2-2) and the evolution of the pore and fissure structure and the formation of new fluid channels caused by the dissolution effect are observed in real time by a microscope (6) and a high-speed camera (7).

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