Visual determination system and method for moisture intrusion and microscopic damage of gas-containing coal

Abstract

The invention discloses a gas-containing coal moisture invasion and microscopic damage visual measurement system and method, and belongs to the technical field of gas-containing coal body tests. Comprising a visual triaxial coal sample holder, an environment control system, a fluid injection system, a desorption system and a coal sample microscopic damage evolution collaborative characterization unit, loading shaft confining pressure on the coal sample and then simulating a gas pressurization adsorption process on the coal sample; methane desorption is simulated through a desorption system, and the permeability of the coal sample is measured by adopting a transient method; coal matrix strain is analyzed by using a DIC technology, and micro-fracture evolution is monitored by using an acoustic emission technology; according to the invention, the response mechanism and the moisture penetration process of the coal seam after moisture intrusion in a real stratum environment can be truly simulated, and full-scale visual analysis from microscopic damage to macroscopic response is completed, so that theoretical support is better provided for a coal seam anti-reflection technology and gas outburst.

Description

Technical Field

[0001] This invention belongs to the field of gas-bearing coal testing technology, specifically a visualization measurement system and method for moisture intrusion and microscopic damage in gas-bearing coal. Background Technology

[0002] Coalbed methane (CBM), a multi-element gas mixture primarily composed of CH4, is an unconventional natural gas resource and a byproduct of coalification. Its efficient development is strategically significant for national energy security, mine safety, environmental pollution control, and economic benefits. However, the heterogeneity, low permeability, and low gas saturation of coal often affect CBM extraction efficiency. Hydraulic treatment, due to its high efficiency and cleanliness, has gradually become a major technical measure for improving CBM extraction and depressurization / permeability enhancement in coal seams. However, this method leaves a large amount of water in the coal seam, which significantly affects CBM desorption. On the one hand, water molecules promote methane desorption through displacement; on the other hand, under capillary forces, water is absorbed into pores and fractures, reducing coal seam permeability, blocking CBM migration channels, and creating a water-lock effect, severely impacting gas extraction efficiency. Therefore, revealing the influence and microscopic mechanism of water on methane desorption-permeability characteristics in coal samples under actual formation conditions is crucial for optimizing hydraulic treatment measures and extraction design.

[0003] Currently, the methods for injecting water into confined spaces containing gaseous coal are mainly divided into two categories: the saturated salt solution method (CN109540734A) and the injection method. The injection method can be implemented using high-pressure water pumps (CN116793920A), water-filling piston containers (CN110161083A), and water-storage glass bottles (CN 105910974 A). The saturated salt solution method is mainly suitable for pulverized coal, while the use of water-storage glass bottles requires customized coal samples, both of which have limitations and are not conducive to subsequent experimental research. Furthermore, after setting a fixed amount of water for the high-pressure water pump and water-filling piston container, it is difficult to observe the water adsorption of the coal sample in the sample container, leading to a deviation between the actual moisture content of the coal sample and the amount of water injected, affecting the accuracy of studies on the adsorption, desorption, and permeation characteristics of water on the coal sample's gas.

[0004] Furthermore, regarding moisture adsorption in gas-bearing coal, patent CN 116793920 A provides a method for measuring the decomposition and permeability characteristics of water in deep in-situ coal bodies. However, this equipment measures water decomposition and permeability characteristics separately, lacking integrated measurement conditions, which may affect the gas-water distribution during coal sample testing. Patent CN105910974 A provides an experimental method and apparatus for the isobaric permeation effect in gas-bearing coal bodies, but it does not consider the influence of axial pressure, and the permeation process is invisible. Therefore, the main problems currently are that the in-situ moisture permeation process in gas-bearing coal seams cannot be accurately measured and is invisible, and the microscopic mechanism of moisture's influence on the coal matrix is ​​still unclear.

[0005] Therefore, it is necessary to establish an integrated, visualized experimental device and method to simultaneously monitor the in-situ moisture intrusion and absorption process of gas-bearing coal and its dynamic damage to coal samples, and to analyze its methane desorption-permeation characteristics. Summary of the Invention

[0006] This invention overcomes the shortcomings of the prior art and proposes a visualization measurement system and method for moisture intrusion and microscopic damage in gas-bearing coal. It can study the water absorption characteristics and dynamic permeation process of gas-bearing coal samples, and solves the problems of the invisibility of the moisture intrusion process and the difficulty in characterizing dynamic water lock damage in traditional coalbed methane experiments.

[0007] This invention is achieved through the following technical solution:

[0008] A visualization system for measuring moisture intrusion and microscopic damage in gas-bearing coal includes a visualization triaxial coal sample holder, an environmental control system, a fluid injection system, a desorption system, and a coal sample microscopic damage evolution co-characterization unit. The environmental control system includes a temperature control unit and a triaxial pressurization unit. The visualization triaxial coal sample holder is housed within the temperature control unit, and the triaxial pressurization unit provides axial pressure and confining pressure to the coal sample within the holder. The fluid injection system includes a gas pressurization and adsorption unit and a quantitative water injection unit. The fluid injection system injects water into the coal sample within the visualization triaxial coal sample holder. The sample provides gas and water injection functions; the desorption system includes a displacement desorption unit and an atmospheric pressure desorption unit; the displacement desorption unit and the atmospheric pressure desorption unit are respectively connected to the coal sample in the visualization triaxial coal sample holder; the coal sample microscopic damage evolution collaborative characterization unit includes a DIC component and an acoustic emission component; the DIC component includes a dual-channel high-speed imaging system and an image processing workstation, used to capture the deformation observation area and seepage observation area on the coal sample surface; the acoustic emission component includes an acoustic emission probe and a signal amplifier, used to qualitatively analyze the evolution characteristics of microscopic cracks induced by moisture intrusion into the coal sample.

[0009] Furthermore, the aforementioned visual triaxial coal sample holder includes a transparent pressure-bearing cylinder and an upper end cap and a lower end cap respectively connected to the top and bottom of the transparent pressure-bearing cylinder; a high-transmittance FEP heat-shrinkable tube is coaxially built into the transparent pressure-bearing cylinder for wrapping the coal sample, and the two ends of the transparent pressure-bearing cylinder are respectively embedded in the sealing grooves of the upper end cap and the lower end cap; a confining pressure chamber is formed between the transparent pressure-bearing cylinder and the FEP heat-shrinkable tube, and the confining pressure chamber is used to store the pressurized confining pressure medium.

[0010] Furthermore, both the upper and lower end covers are equipped with axial pressure chambers, and a self-balancing piston is slidably connected inside the axial pressure chamber. The pressure head on the inner side of the self-balancing piston is in contact with the coal body; the bottom of the pressure head of the self-balancing piston is provided with a biomimetic fractal guide groove.

[0011] Furthermore, the biomimetic fractal guide channel is composed of radial channels radiating outward from the center and multiple concentric circular channels with equal spacing, and the channel depth changes in a gradient from the inside to the outside and from shallow to deep, forming a full-section fluid transport channel.

[0012] Furthermore, the constant temperature control unit is a constant temperature heating box; the constant temperature heating box has double-layer hollow optical observation windows with high light transmittance on both sides of the observation surface of the corresponding visualization triaxial coal sample holder, so as to ensure that the external industrial camera can clearly capture the surface image of the coal sample inside the box.

[0013] Furthermore, the triaxial pressurization unit includes a coaxial pressure loading controller, a coaxial pressure tracking pump, and a hydraulic station; the coaxial pressure loading controller is connected to the hydraulic station, the hydraulic station is connected to the coaxial pressure tracking pump, one coaxial pressure tracking pump is connected to the upper and lower coaxial pressure chambers respectively through pipelines, and the other coaxial pressure tracking pump is connected to the coaxial pressure chamber; the coaxial pressure loading controller controls the coaxial pressure tracking pump to make the coaxial pressure reach the set value.

[0014] Furthermore, the gas pressurization and adsorption unit includes a high-pressure methane cylinder, a booster pump, a buffer tank, an inlet metering container, and an outlet metering container; the high-pressure methane cylinder is connected to a first high-pressure shut-off valve and a second high-pressure shut-off valve via a three-way valve; the first high-pressure shut-off valve is connected to the booster pump; the booster pump is used to compress the gas and provide high-pressure gas to the buffer tank, and simultaneously the booster pump is connected to the second high-pressure shut-off valve and a first solenoid valve via a three-way valve; the first solenoid valve is sequentially connected to a first pressure sensor, a second solenoid valve, a fourth solenoid valve, a seventh solenoid valve, and a fifth solenoid valve. The pressure sensor, the visual triaxial coal sample holder, and the sixth pressure sensor are connected; the buffer tank is connected to the inlet metering container, which is connected to the fourth pressure sensor. The inlet metering container is connected to the biomimetic fractal guide groove at the bottom of the balance piston in the upper cover through a pipeline, and gas is injected into the coal sample through the gas inlet system; the outlet metering container is connected to the biomimetic fractal guide groove at the bottom of the balance piston in the lower cover through a pipeline. The pipelines at both ends of the outlet metering container are connected to the eighth and ninth solenoid valves, respectively, and the outlet metering container is connected to the sixth pressure sensor.

[0015] Furthermore, the displacement desorption unit includes a high-pressure back pressure valve, a gas-liquid separator, a beaker, an electronic balance, a seventh high-pressure shut-off valve, and a first desorber. The gas-liquid separator is connected to the inner surface of the bottom balance piston via the high-pressure back pressure valve. The bottom of the gas-liquid separator is connected to the beaker via a pipeline. The beaker is placed on the electronic balance. The top of the gas-liquid separator is connected to the first desorber via the high-pressure shut-off valve. The seventh high-pressure shut-off valve is located at the inlet of the first desorber. The high-pressure back pressure valve is used to maintain stable pressure inside the coal sample holder. The first desorber is used to determine the volume of methane displaced after a quantitative amount of water is injected into the coal body.

[0016] Furthermore, the self-balancing piston has a stepped hole inside, and the acoustic waveguide rod is placed at the lower end of the stepped hole, with its bottom end slightly convex and in hard contact with the coal sample; the acoustic emission probe is placed at the upper end of the stepped hole and is attached to the rear end of the acoustic waveguide rod through an acoustic coupling layer; the elastic constant force component is located above the acoustic emission probe, and a constant force is achieved by a helical spring, and is sealed and pressed by a threaded sealing cap at the top.

[0017] A method for visually measuring moisture intrusion and microscopic damage in gas-bearing coal, employing the aforementioned visualization measurement system, and comprising the following steps:

[0018] The first step is to test the airtightness of the entire system, and then to calibrate the free volume by placing the visual triaxial coal sample holder under a constant temperature condition.

[0019] The second step is to apply a certain axial pressure to the coal sample through the triaxial pressurization unit, and then turn on the gas pressurization adsorption unit to simulate the gas pressurization adsorption process of the coal sample.

[0020] The third step is to start the quantitative water injection unit to inject water into the coal sample in a quantitative manner, and simulate methane desorption through the displacement desorption unit, and collect methane gas to calculate the displacement desorption rate of water on the coal sample.

[0021] Step 4: After the displacement desorption is completed, the coal sample is desorbed at atmospheric pressure using an atmospheric pressure desorption unit;

[0022] Step 5: Immediately after desorption at atmospheric pressure, the permeability of the coal sample is determined using the transient method.

[0023] During the gas pressurization and adsorption process, quantitative water injection, and displacement desorption process described above, DIC technology was used to analyze the coal matrix strain, fluorescence tracing technology was used to extract the water seepage path, and acoustic emission technology was used to monitor the evolution of microcracks. The above three sets of data were collected simultaneously, and the full-field strain cloud map of the coal matrix from DIC, the fluid seepage route map from fluorescence tracing, and the location map of pore crack changes from acoustic emission were overlaid to achieve spatiotemporal coupled monitoring of the water injection seepage field, matrix deformation field, and pore crack evolution, thus completing the fluid-solid-loss coupled analysis of water intrusion on the coal body.

[0024] The beneficial effects of this invention compared to the prior art are as follows:

[0025] This invention can realistically simulate the response mechanism of coal seams after water intrusion in real-world geological environments, including gas displacement desorption, atmospheric pressure desorption, permeability, matrix deformation and pore fracture changes, as well as the water infiltration process. It achieves full-scale visualization analysis from microscopic damage to macroscopic response, thus providing better theoretical support for coal seam permeability enhancement technology and gas outburst prevention. Specifically:

[0026] 1. The visualization triaxial coal sample holder of the present invention uses a high-transmittance FEP heat shrink tubing to wrap the coal sample and a thick-walled transparent PC pressure-bearing cylinder to ensure internal visualization; and the visualization triaxial coal sample holder integrates adsorption-desorption-permeability measurement to ensure the accuracy of data in medium and low pressure formation simulation experiments and provides a reliable platform for clear observation of fluid migration.

[0027] 2. The synergistic use of a quantitative injector and a pressure-stabilized flow pump, along with the design of a biomimetic fractal flow-guiding structure on the end face, enables precise and uniform injection of trace amounts of moisture. Furthermore, a built-in suspended acoustic waveguide structure places the acoustic emission probe inside a self-balancing piston, achieving high-fidelity acquisition of acoustic emission signals. Simultaneously, the application of a dual-channel high-speed imaging system in DIC technology provides a technical foundation for analyzing the deformation and moisture seepage of coal samples. This provides a reliable experimental method for studying the water absorption characteristics and dynamic seepage process of gas-bearing coal samples.

[0028] 3. The simultaneous coupling of fluorescence tracing, DIC, and acoustic emission technologies enables dynamic, synchronous, and non-destructive detection of water seepage, coal matrix deformation, and microfracture damage evolution processes in real geological environments. Combined with displacement desorption, atmospheric pressure desorption, and permeability data, the dynamic response characteristics of gas-bearing coal samples after water intrusion are comprehensively characterized. Based on these data, the water displacement-dominant zone, transition zone, and water-locking effect-dominant zone are identified, providing precise theoretical support for the design of coal seam gas extraction engineering and hydraulic measures.

[0029] 4. This invention can simulate the formation process of liquid-gas and water-locking effects under real geological conditions and the seepage process of liquid media in coal bodies and the microscopic mechanism of their influence on coal matrix by changing experimental conditions such as gas medium, pressure, temperature, and liquid type, so as to accurately and realistically reflect the influence of external liquid intrusion on coal seams. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the device structure of the present invention;

[0031] Figure 2 This is a front view of a self-balancing piston.

[0032] Figure 3 Top view of a self-balancing piston;

[0033] Figure 4 This is a schematic diagram of data acquisition and intelligent control according to the present invention;

[0034] Figure 5 This is a flowchart of the testing method of the present invention. Detailed Implementation

[0035] To make the technical problems to be solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail with reference to the embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The technical solutions of this invention are described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection is not limited thereto.

[0036] Example 1

[0037] This invention proposes a visualization measurement system for moisture intrusion and microscopic damage in gas-bearing coal. (See [link to documentation]). Figures 1 to 4 The measurement system includes a visual triaxial coal sample holder as the core reactor, an environmental control system, a fluid injection system, a desorption system and other supporting systems connected to it, as well as a coal sample micro-damage evolution collaborative characterization unit and a data acquisition and intelligent control unit for monitoring.

[0038] I. Visualized Three-Axis Coal Sample Holder

[0039] The aforementioned visual triaxial coal sample holder includes a transparent pressure-bearing cylinder 20 and an upper end cap 16 and a lower end cap 26 respectively connected to the top and bottom of the transparent pressure-bearing cylinder 20; the transparent pressure-bearing cylinder 20 is made of thick-walled high-strength transparent PC material, with a pressure resistance of no more than 15 MPa, and is suitable for simulating medium and low pressure ground stress. The cylinder wall of the transparent pressure-bearing cylinder 20 has scale lines, which can clearly capture the changes in the moisture migration front and wetting area on the surface of the coal sample;

[0040] A transparent pressure-bearing cylinder 20 coaxially houses a high-transmittance FEP heat-shrink tubing 22 for wrapping the coal sample. This material has high light transmittance, high temperature resistance, and corrosion resistance, ensuring effective transmission of confining pressure while eliminating visual obstruction, clearly showing the seepage process of moisture under a gas atmosphere. To ensure the sealing of the FEP heat-shrink tubing 22, clamps are used at both ends to connect it to the upper end cap 16 and the lower end cap 26, and high-vacuum silicone grease is applied. A confining pressure chamber 21 is formed between the transparent pressure-bearing cylinder 20 and the FEP heat-shrink tubing 22. This confining pressure chamber 21 is used to store the pressurized confining pressure medium, which is selected from transparent materials. The liquid medium (such as deionized water, silicone oil, etc.) has a refractive index similar to that of PC material to minimize imaging distortion. The injection of the confining pressure medium is achieved through an L-shaped injection channel inside the lower end cover 26. One end of the L-shaped injection channel is connected to the connecting hole on the side of the lower end cover 26 and connected to the external shaft confining pressure tracking pump 35 to ensure the safety and sealing reliability of the device under high pressure. The other end of the L-shaped injection channel opens to the inner bottom surface of the lower end cover 26 and connects to the confining pressure chamber 21. During operation, water enters through the L-shaped injection channel and fills the entire annular confining pressure chamber 21, thereby achieving uniform application of confining pressure to the coal sample.

[0041] The two ends of the transparent pressure-bearing cylinder 20 are respectively embedded in the sealing grooves of the upper end cover 16 and the lower end cover 26, and high-strength O-rings are installed in the grooves. The upper end cover 16 and the lower end cover 26 are fastened together by tie rod bolts 15 distributed on the outer periphery of the cylinder. This connection structure allows the transparent pressure-bearing cylinder 20 to mainly bear the circumferential stress caused by the internal pressure during operation, while the axial separation force is borne by the external tie rod, thereby effectively avoiding the risk of brittle transparent materials breaking due to axial tension and ensuring the safety of the visualization experiment.

[0042] The upper end cover 16 and lower end cover 26 are made of alloy material. Each end cover 16 and 26 contains an axial pressure chamber 25. A self-balancing piston 24 is slidably connected within the axial pressure chamber 25. The pressure head on the inner side of the self-balancing piston 24 contacts the coal body. The bottom of the pressure head of the self-balancing piston 24 is provided with a biomimetic fractal guide groove 18. (See [reference]) Figure 2 and Figure 3The structure consists of radial grooves radiating outward from the center and multiple concentric circular grooves with equal spacing, and the groove depth changes in a gradient from the inside to the outside and from shallow to deep, forming a full-section fluid transport channel. This ensures that under axial load, water can quickly and evenly cover the entire seepage end face of the coal sample, eliminating the end face obstruction effect of traditional point source water injection.

[0043] The aforementioned visual triaxial coal sample holder is provided with eight connection holes 27. Three holes are arranged on the upper end cover 16 for connecting the axial pressure water inlet and water / gas inlet pipeline, respectively. Three holes are arranged on the bottom surface of the lower end cover 26 for connecting the axial pressure water inlet and water / gas outlet pipeline, respectively. Two holes are arranged on the side of the lower end cover 26 for confining pressure water inlet.

[0044] II. Environmental Control System

[0045] The environmental control system includes a constant temperature control unit and a triaxial pressurization unit. The constant temperature control unit is mainly a constant temperature heating chamber 38. A visual triaxial coal sample holder is installed inside the constant temperature heating chamber 38. The constant temperature heating chamber 38 has double-layered hollow optical observation windows with high light transmittance on both sides of the observation surface corresponding to the visual triaxial coal sample holder, ensuring that the external industrial camera 44 can clearly capture the surface image of the coal sample inside the chamber. The constant temperature heating chamber 38 provides a stable external temperature environment for the coal sample.

[0046] The triaxial pressurization unit includes a coaxial pressure loading controller 37, a coaxial pressure tracking pump 35, and a hydraulic station 36. The coaxial pressure loading controller 37 is connected to the hydraulic station 36, and the hydraulic station 36 is connected to the coaxial pressure tracking pump 35. One coaxial pressure tracking pump 35 is connected to the upper and lower coaxial pressure chambers 25 through pipelines, and the other coaxial pressure tracking pump 35 is connected to the coaxial pressure chamber 21. The coaxial pressure loading controller 37 controls the coaxial pressure tracking pump 35 to make the coaxial pressure reach the set value.

[0047] III. Fluid Injection System

[0048] The fluid injection system includes a gas pressurization and adsorption unit and a quantitative water injection unit.

[0049] The gas pressurization and adsorption unit includes a high-pressure methane cylinder 1, a booster pump 4, a buffer tank 6, an inlet metering container 9, and an outlet metering container 29. The high-pressure methane cylinder 1 is connected to a first high-pressure shut-off valve 301 and a second high-pressure shut-off valve 302 via a three-way valve. The first high-pressure shut-off valve 301 is connected to the booster pump 4. The booster pump 4 is used to compress gas, providing high-pressure gas to the buffer tank 6, and is also connected to the second high-pressure shut-off valve 302 and a first solenoid valve 501 via a three-way valve. The first solenoid valve 501 is connected in sequence to the first pressure sensor 701, the second solenoid valve 502, the fourth solenoid valve 504, the seventh solenoid valve 507, the fifth pressure sensor 705, the coal sample holder, and the sixth pressure sensor 706; the buffer tank 6 is connected to the air inlet metering container 9, which is connected to the fourth pressure sensor 704. The air inlet metering container 9 is connected to the biomimetic fractal guide groove 18 at the bottom of the balance piston 24 in the upper end cover 16 through a pipeline, and air is injected into the coal body through the air inlet system.

[0050] The gas outlet metering container 29 is connected to the biomimetic fractal guide groove 18 at the bottom of the balance piston 24 inside the lower end cover 26 via a pipeline. The eighth solenoid valve 508 and the ninth solenoid valve 509 are respectively connected to the pipelines at both ends of the gas outlet metering container 29. The gas outlet metering container 29 is also connected to the sixth pressure sensor 706.

[0051] The gas pressurized adsorption unit can be used to conduct gas pressurized adsorption tests on coal and also to determine permeability. The permeability determination unit uses the transient method.

[0052] The quantitative water injection unit includes a pressure-stabilizing horizontal flow pump 11 and a quantitative injector 12 connected together. A third high-pressure shut-off valve 303 is installed on the pipeline connecting the pressure-stabilizing horizontal flow pump 11 and the quantitative injector 12. The water outlet of the quantitative injector 12 is connected to the bottom of the upper balance piston 24 through a water inlet pipeline. The quantitative injector 12 contains a piston. The pressure-stabilizing horizontal flow pump 11 pushes the piston at a certain pressure to inject water into the coal sample to achieve quantitative water injection. A hydrophobic filter element is installed at the end of the water / gas inlet pipeline to prevent water from flowing back from the gas pipeline after entering.

[0053] The aforementioned multiple solenoid valves 5, buffer tanks 6, multiple pressure sensors 7, metering syringes 12, inlet metering containers 9, and outlet metering containers 29 are installed inside the constant temperature heating chamber 38.

[0054] IV. Desorption System

[0055] The desorption system includes a displacement desorption unit and an atmospheric pressure desorption unit. The displacement desorption unit includes a high-pressure back pressure valve 30, a gas-liquid separator 33, a beaker 31, an electronic balance 32, a seventh high-pressure shut-off valve 307, and a first desorber 34. The gas-liquid separator 33 is connected to the inner surface of the bottom balance piston 24 via the high-pressure back pressure valve 30. The bottom of the gas-liquid separator 33 is connected to the beaker 31 via a pipe. The beaker 31 is placed on the electronic balance 32. The top of the gas-liquid separator 33 is connected to the first desorber 34 via the high-pressure shut-off valve. The seventh high-pressure shut-off valve 307 is located at the inlet of the first desorber 34. The high-pressure back pressure valve 30 is used to maintain the coal sample clamping. The internal pressure is stable and is linked to the pressure sensor on the air inlet pipe via PLC control. When the pressure sensor value exceeds the set value, the high-pressure back pressure valve 30 opens. The air-water separator 33 has an air inlet on the right side, a water outlet on the lower left side, and is connected to the beaker 31. The air outlet on the upper left side is connected to the first desorption instrument 34. The beaker 31 is used to hold the water flowing out of the coal sample holder. The electronic balance 32 is placed below the beaker 31 to measure the mass of water in the beaker 31. The first desorption instrument 34 is used to measure the volume of methane replaced by a quantitative amount of water injected into the coal.

[0056] The atmospheric pressure desorption unit includes a second desorber 13, a seventh solenoid valve 507, and a fifth high-pressure shut-off valve 305; the coal sample holder is connected to the seventh solenoid valve 507, and is connected to the fifth high-pressure shut-off valve 305 and the second desorber 13 in sequence through a three-way valve; the second desorber 13 is used to determine the volume of methane during the atmospheric pressure desorption process.

[0057] V. Coal Sample Microscopic Damage Evolution Synergistic Characterization Unit

[0058] The coal sample microstructural damage evolution co-characterization unit includes fluorescence tracing, DIC (Dispersive Indication) technology, and acoustic emission technology. The fluorescence tracing uses pre-added sodium fluorescein tracer in the test water as the injection medium, combined with a specific wavelength laser light source to enhance the contrast of moisture in the coal matrix. The DIC technology includes a dual-channel high-speed imaging system and an image processing workstation. The dual-channel high-speed imaging system mounts an industrial camera 44 and an illumination source 45 externally to a three-axis visualization coal sample holder, arranged from multiple perspectives to capture the deformation observation area and seepage observation area of ​​the coal sample surface. The deformation observation area has pre-fabricated artificial speckle patterns, and speckle images are acquired using a white light source. The DIC algorithm is used to calculate the full-field strain data of the coal surface. The seepage observation area uses an excitation light source to acquire fluorescence images and extract the moisture migration front data. An affine transformation matrix for the deformation and seepage observation areas is established using a binocular vision calibration module to achieve pixel-level spatial registration of the two sets of image data. The acoustic emission technology includes an acoustic emission probe 46 and a signal amplifier 47. The acoustic emission probe 46 is placed inside a self-balancing piston 24 with a built-in suspended constant force contact structure. The self-balancing piston 24 has a stepped hole inside. The acoustic waveguide rod 48 is placed at the lower end of the stepped hole, with its bottom end slightly convex (0.5mm) and in hard contact with the coal sample. The acoustic emission probe 46 is placed at the upper end of the stepped hole and is attached to the rear end of the acoustic waveguide rod 48 through an acoustic coupling layer 49. The elastic constant force component 50 is located above the acoustic emission probe 46. It achieves constant force pushing through a customized helical spring and is sealed and tightened by a threaded sealing cap 51 at the top. The sensor connection line passes through the axial loading rod 52, which is connected to the threaded sealing cap 51 and built into the axial pressure chamber 25, and leads to the outside. This forms a built-in elastic waveguide monitoring path. By monitoring the ring count, accumulated energy, signal rise time / amplitude ratio, and average frequency parameters, the evolution characteristics of micro-cracks induced by moisture intrusion are qualitatively analyzed. The three modules are collected synchronously on a unified time axis. The full-field strain cloud map of the coal matrix, the fluid seepage route map of fluorescence tracer and the location map of acoustic emission pore fracture changes from DIC at the same time are superimposed to achieve spatiotemporal coupled monitoring of water injection seepage field, matrix deformation field and pore fracture evolution, and complete full-scale visualization desorption from micro-damage to macro-response.

[0059] VI. Data Acquisition and Intelligent Control Unit

[0060] The data acquisition and intelligent control unit consists of a PLC controller and a host computer 43 (IPC). The PLC controller collects and processes signals from each pressure sensor 7 and electronic balance 32 in real time, and controls the opening and closing of the corresponding solenoid valves 5 in conjunction with these signals. The high-pressure back pressure valve, the PLC controller, and the pressure sensor at the coal sample holder form a closed-loop feedback control circuit. The PLC controller dynamically adjusts the state of the high-pressure back pressure valve based on the real-time monitored internal pressure value to ensure that the pore pressure is maintained at the set value during the test. The host computer 43 establishes bidirectional communication with the PLC controller, enabling real-time visual monitoring and remote operation of the entire system's pipeline status and sensor values. On the other hand, it serves as a data aggregation center, centrally storing and associating DIC image data, acoustic emission data, and data collected by the PLC.

[0061] VII. Other Supporting Systems

[0062] The other supporting systems include: an airtightness testing and free volume calibration unit, and a vacuuming unit; the airtightness testing and free volume calibration unit includes a high-pressure helium cylinder 2, which is connected in parallel with a high-pressure methane cylinder 1. Helium is injected into the coal sample through the high-pressure helium cylinder 2 for airtightness testing and free volume calibration.

[0063] The vacuum pumping unit consists of a vacuum pump 10, which is connected to the air inlet pipe and is used to vacuum the system.

[0064] The high-pressure helium cylinder 2, the second high-pressure shut-off valve 302, the first solenoid valve 501, the buffer tank 6, the first pressure sensor 701, the second solenoid valve 502, the fourth solenoid valve 504, the seventh solenoid valve 507, the fifth pressure sensor 705, the coal sample holder, and the eighth solenoid valve 508 are connected in sequence. The second solenoid valve 502 is connected to the third solenoid valve 503, the fifth solenoid valve 505, and the fourth solenoid valve 504 via a four-way valve. The third solenoid valve 503 is used to control the venting of gas in the device. The fifth solenoid valve 505 is connected in sequence to the gas regulating valve 8, the inlet metering container 9, the fourth pressure sensor 704, the sixth solenoid valve 506, the seventh solenoid valve 507, and the coal sample holder. The buffer tank 6 is equipped with the first pressure sensor 701. The gas regulating valve 8 is equipped with the second pressure sensor 702 and the third pressure sensor 703 before and after it. The inlet metering container 9 is equipped with the fourth pressure sensor 704. The fifth pressure sensor 705 is used to measure the pressure of the coal sample holder and the connected pipeline.

[0065] The vacuum pump 10, the fourth high-pressure shut-off valve 304, the seventh solenoid valve 507, the coal sample holder, and the fifth pressure sensor 705 are connected in sequence; the fourth high-pressure shut-off valve 304 is connected to the sixth solenoid valve 506, the seventh solenoid valve 507 and the fourth solenoid valve 504 respectively through a four-way valve.

[0066] Example 2

[0067] This invention proposes a method for visually measuring moisture intrusion and microscopic damage in gas-bearing coal, employing the visual measurement system for moisture intrusion and microscopic damage in gas-bearing coal described in Example 1, and including the following steps:

[0068] Step 1: Airtightness Test: Close all valves in the device, open the high-pressure helium cylinder 2, the second pressure shut-off valve 302, and the first solenoid valve 501 at the inlet of the buffer tank 6 to fill the buffer tank 6 with helium to the predetermined pressure. Then close the second pressure shut-off valve 302 and the first solenoid valve 501, and open the second solenoid valve 502, the fourth solenoid valve 504, the fifth solenoid valve 505, the seventh solenoid valve 507, the eighth solenoid valve 508, and the gas regulating valve 8 to allow helium to fill the coal sample holder and related pipelines, and then close the valves. Maintain the system in a sealed state for 12 hours and monitor the values ​​of the corresponding pressure sensors. If the pressure reading fluctuation does not exceed the rated value, the device is considered to have good airtightness. After the test is completed, open the sixth solenoid valve 506 to discharge the helium in the device.

[0069] Step 2: Prepare and dry the coal column: Take a coal core from the coal reservoir to be evaluated, process it into a cylindrical sample with a diameter of 50 mm and a height of 100 mm, and place the prepared coal column in an environment of 80℃ for continuous drying for 12 h until the mass change does not exceed 0.1%, which is considered to have reached the dry state (moisture content of 0%). Weigh and record the weight of the dried coal column as M. Place the coal sample into a visual triaxial coal sample holder, set the axial pressure, and open the high-pressure methane cylinder 1. Use the permeability measurement method to determine the permeability of the dried coal sample, and record it as k1.

[0070] Step 3, Free Volume Calibration: Set the temperature of the constant temperature heating chamber 38 to keep the entire system in a constant temperature state until the temperature sensor 39 in the visual triaxial coal sample holder stabilizes at T; sequentially open the first solenoid valve 501, the second solenoid valve 502, the fourth solenoid valve 504, the sixth solenoid valve 506, the fifth high-pressure shut-off valve 305, and the vacuum pump 10 to evacuate the coal sample holder and related pipelines until the system vacuum drops below 10 Pa, and then close all valves. Given that the free volume between the first solenoid valve 501 and the second solenoid valve 502 at both ends of the buffer tank 6 is V1, open the high-pressure helium cylinder 2, the second high-pressure shut-off valve 302, and the first solenoid valve 501 at the inlet of the buffer tank 6 to fill the buffer tank 6 with helium. After the reading of the first pressure sensor 701 on the buffer tank 6 stabilizes, record its reading as P1, and then close the valve. Open the second solenoid valve 502 and the fourth solenoid valve 504, and after the reading of the first pressure sensor 701 stabilizes, record its reading as P2, and then close the valve. Open the seventh solenoid valve 507, and after the reading of the first pressure sensor 701 on the buffer tank 6 stabilizes, record its reading as P3. After the test is completed, open the sixth solenoid valve 506 and related valves to discharge the helium from the device. The free volume between the second solenoid valve 502 and the seventh solenoid valve 507 is V2, and the free volume between the seventh solenoid valve 507 and the eighth solenoid valve 508 and between the seventh solenoid valve 507 and the high-pressure back pressure valve 30 is V3, which can be calculated by equations (1) and (2) respectively:

[0071] (1);

[0072] (2);

[0073] In the formula: V2 is the free volume between the second solenoid valve 502 and the seventh solenoid valve 507, ml; V1 is the free volume between the first solenoid valve 501 and the second solenoid valve 502, ml; P1 is the reading of the first pressure sensor 701 when methane fills the V1 volume, MPa; P2 is the reading of the first pressure sensor 701 when methane fills the V2 volume, MPa; V3 is the free volume between the seventh solenoid valve 507 and the eighth solenoid valve 508 and the high-pressure back pressure valve 30, ml; P3 is the reading of the first pressure sensor 701 when methane fills the V3 volume, MPa; Z is the compressibility factor for different pressures; R is the molar gas constant, J / (mol·K).

[0074] Step 4, Gas Pressure Adsorption: Start vacuum pump 10, open relevant pipelines to evacuate the pipelines and coal sample holder. When the system vacuum level is below 10 Pa, close all valves. Then, open high-pressure methane cylinder 1 and the first high-pressure shut-off valve 301, start booster pump 4 and open the first solenoid valve 501 to fill the buffer tank 6 with methane gas. To ensure sufficient gas supply for subsequent adsorption processes, when the reading of the first pressure sensor 701 reaches 1.5 times the preset adsorption equilibrium pressure P4, sequentially close high-pressure methane cylinder 1, booster pump 4, and the first solenoid valve 501. Apply a certain axial confining pressure to the coal sample through axial confining pressure pump 35, hydraulic station 36, and axial confining pressure loading controller 37 to simulate medium and low pressure ground stress. Subsequently, the second solenoid valve 502 and the fourth solenoid valve 504 are opened to slowly fill the coal sample holder with methane gas from the buffer tank 6. The gas intake is precisely controlled by repeatedly adjusting the valve opening to maintain the adsorption equilibrium time for no less than 24 hours until the coal sample adsorption reaches equilibrium. The reading of the first pressure sensor 701 is recorded as P5. Based on the ideal state equation and the principle of mass conservation, the methane adsorption amount Q of the dry coal column is calculated according to equations (3), (4), and (5):

[0075] (3);

[0076] (4);

[0077] (5);

[0078] In the formula: v1 is the volume of methane gas introduced into the coal sample holder by the coal sample holder and pipeline (volume V1+V2), ml; P4 is the set coal sample adsorption gas pressure, MPa; P5 is the reading of the first pressure sensor 701 after adsorption equilibrium, MPa; Z is the compressibility factor; R is the molar gas constant, J / (mol·K); T is the temperature, K; v2 is the volume of methane gas introduced into the coal sample holder (volume V3), ml; M is the mass of the dry coal sample, g; Q is the amount of methane adsorbed by the coal body, ml / g.

[0079] Step 5, quantitative water injection and displacement desorption: Set the water injection volume, pre-inject the experimental water into the quantitative injector 12, start the pressure-stabilizing horizontal flow pump 11, set the water injection pressure and open the third high-pressure shut-off valve 303 to start injecting water into the coal sample; to achieve precise control of the water injection volume.

[0080] (1) Set the water injection volume to m1 and the volume to be... After water injection, observe the bottom for any residual moisture using a coal sample holder. If no residual moisture is observed, the actual moisture content of the coal sample is determined to be m1, and the moisture content of the coal sample is [missing information]. It can be calculated from equation (6):

[0081] (6);

[0082] In the formula: denoted as the moisture content of the coal sample (%), m1 as the moisture content of the coal sample (g), and M as the mass of the dried coal sample (g).

[0083] Due to the displacement of methane by moisture, the pressure inside the coal sample holder rises. At this point, the high-pressure back pressure valve 30 is activated to maintain the pressure inside the coal sample holder. The displaced methane gas is gradually discharged and collected by the first desorption unit 34. When the desorbed methane volume v3 reaches a stable value, the displacement desorption process is considered complete. The displacement desorption rate of moisture on the coal sample is... It can be calculated using equation (7):

[0084] (7);

[0085] In the formula: Moisture displacement and desorption rate of coal sample, %; v3 is the volume of methane displaced, ml; M is the mass of dry coal sample, g; Q is the amount of methane adsorbed by the coal body, ml / g.

[0086] (2) Set the water injection volume to m2 and the volume to be... Due to the displacement of methane by moisture, the pressure inside the coal sample holder gradually increases. Under the control of the PLC controller, the opening and closing of the high-pressure back pressure valve 30 is dynamically controlled in real time based on the value of the fifth pressure sensor 705, achieving precise and stable control of the coal sample holder pressure. Residual moisture and methane gas are efficiently separated by the gas-liquid separator 33 and discharged in batches. Finally, the moisture discharged from the coal sample holder accumulates in beaker 31, with a moisture mass of m³ and a volume of... The methane gas then enters the first desorber 34 for measurement. The displacement desorption process ends when the desorbed methane volume v4 tends to stabilize. The final moisture content of the coal sample is... The moisture content injected into the coal sample holder and the difference between the moisture content discharged after adsorption by the coal sample are obtained; the displacement desorption rate of moisture on the coal sample is... It can be calculated using equations (8) and (9):

[0087] (8);

[0088] In the formula: 1 represents the moisture content of the coal sample (%); m2 represents the mass of the injected coal sample with moisture (g); m3 represents the mass of the discharged coal sample with moisture (g); and M represents the mass of the dried coal sample (g).

[0089] (9);

[0090] In the formula: The displacement and desorption rate of moisture in the coal sample, %; v4 is the volume of methane displaced, ml. The volume of water discharged from the device is ml; M is the mass of the dried coal sample, g; Q is the amount of methane adsorbed by the coal, ml / g.

[0091] Step 6, Atmospheric Pressure Desorption: After displacement desorption is complete, close the valves and open the seventh solenoid valve 507 and the fifth high-pressure shut-off valve 305. At this time, the pressure of the coal sample holder returns to atmospheric pressure. When the volume of desorbed methane v5 remains constant, it indicates that the atmospheric pressure desorption process is complete. Atmospheric pressure desorption rate It can be calculated using equation (10):

[0092] (10);

[0093] In the formula: , where v5 is the methane desorption rate at atmospheric pressure (%), v5 is the volume of methane desorbed at atmospheric pressure (ml), M is the mass of the dry coal sample (g), and Q is the amount of methane adsorbed by the coal (ml / g).

[0094] Step 7, Permeability Measurement: After desorption at atmospheric pressure, the permeability of the coal sample is immediately measured using the transient method. Open the second solenoid valve 502, the fifth solenoid valve 505, the sixth solenoid valve 506, the seventh solenoid valve 507, and the eighth solenoid valve 508. Set the required pulse pressure through the gas regulating valve 8. The host computer 43 records the pressure changes of the inlet fixed value container 9 and the outlet fixed value container 29 over time. The permeability k2 of coal samples with different moisture contents can be calculated by formula (11):

[0095] (11);

[0096] In the formula: k2 is the permeability of the coal sample, m 2 ; Where is the fluid viscosity, Pa·s; Pa is the fluid compressibility coefficient. -1 L is the specimen length, in meters. and These represent the volumes of the upstream and downstream containers, respectively, in m. 3 ;e is Let t be the vertical axis and t be the slope of the horizontal axis. The measured pressure difference (Pa) between the inlet and outlet fluids in the setpoint container is given. This is the initial pulse pressure value, in Pa.

[0097] The rate of change of coal permeability It can be calculated using equation (12):

[0098] (12);

[0099] In the formula: k1 represents the rate of change in coal sample permeability, %; k2 represents the permeability of the water-bearing coal sample, m. 2k1 is the permeability of the dry coal sample, m 2 .

[0100] Step 8: Coordinated Characterization of In-situ Moisture Immersion in Gas-Bearing Coal and Microscopic Damage Evolution of Coal Samples: During the gas adsorption, quantitative water injection, and displacement desorption processes described above, DIC technology is used to analyze the coal matrix strain, fluorescence tracing technology is used to extract the moisture seepage path, and acoustic emission technology is used to monitor the evolution of microcracks. The above three sets of data are collected simultaneously, and the full-field strain cloud map of the coal matrix from DIC, the fluid seepage route map from fluorescence tracing, and the location map of pore crack changes from acoustic emission are overlaid to achieve spatiotemporal coupled monitoring of the water injection seepage field, matrix deformation field, and pore crack evolution, thus completing the fluid-solid-damage coupled analysis of moisture intrusion on the coal body.

[0101] Step 9: The testing process is now complete.

[0102] Before the experiment, ensure that the DIC and the acoustic emission acquisition system are strictly aligned on the time and space axes. Overlay the DIC’s full-field strain cloud map of the coal matrix, the fluid seepage route map of the fluorescence tracer, and the location map of the changes in the acoustic emission pore fractures to clarify the influence of moisture on the coal matrix under gas-containing conditions and quantitatively identify the matrix damage and fracture propagation mechanism induced by moisture intrusion.

[0103] The aforementioned device and method for visualizing moisture intrusion and microscopic damage in gas-bearing coal samples, based on measured displacement desorption, atmospheric pressure desorption, and permeability change data, identifies inflection points in the curves and determines the moisture content corresponding to the moisture displacement-dominant zone, transition zone, and water-locking effect-dominant zone. This provides a theoretical basis for subsequent engineering practice. Simultaneously, by combining the coal body moisture infiltration process, surface strain, and microscopic fracture characteristics, it qualitatively analyzes the moisture seepage field, matrix deformation, and microscopic fracture change characteristics of multiple corresponding sections, providing a comprehensive characterization of the moisture intrusion process in gas-bearing coal.

[0104] Example 3

[0105] This invention provides a method for determining the critical moisture content and analyzing the microscopic damage mechanism of gas-water replacement / water-locking effect in coal gas-containing environments, including the following steps:

[0106] 1. Preparation and drying of coal pillars: Coal cores from the coal reservoir to be evaluated are processed into cylindrical samples with a diameter of 50 mm and a height of 100 mm. The prepared coal pillars are placed in an environment of 80℃ and dried continuously for 12 hours until the mass change does not exceed the rated value, which is considered to have reached the dry state (moisture content of 0%).

[0107] 2. Experimental Preparation: Load the coal sample into the high-transmittance FEP heat shrink tubing 22, and use a hot air gun to tightly wrap the coal sample. Then, load it into the visual triaxial coal sample holder. During installation, ensure that the self-balancing piston 24 is in close contact with the end face of the coal sample. Adjust the elastic constant force component 50 so that the built-in acoustic waveguide rod 48 passes through the center of the piston and presses against the upper end face of the coal sample with constant pressure. Connect the acoustic emission probe 46.

[0108] 3. Stress Loading: Connect the pipeline, measure the airtightness of the equipment, and measure the free volume within the coal sample holder. Turn on the vacuum pump and evacuate the coal sample for at least 8 hours. Simultaneously, activate the coal sample microscopic damage evolution co-characterization unit to monitor the pore and fracture damage and deformation characteristics of the coal sample in real time through DIC and acoustic emission. Then, activate the axial confining pressure loading controller 37, set the axial confining pressure, simulate the stress environment of deep formations, and allow moisture to enter the confining pressure chamber through the L-shaped flow channel of the lower end cover 26 until the chamber is full.

[0109] 4. Gas Pressure Adsorption: The gas pressure adsorption unit is activated, and methane gas is introduced into the coal sample. The adsorption equilibrium pressure is set, and the coal sample reaches adsorption saturation when the reading of the fifth pressure sensor (705) remains constant. The amount of methane adsorbed by the coal sample is calculated using the formula. Then, using the atmospheric pressure desorption unit and permeability measurement unit, the ratio of methane adsorption to atmospheric pressure desorption, and permeability data of the dry coal sample are obtained. The gas pressure adsorption steps are then repeated for subsequent experiments.

[0110] 5. Quantitative Water Injection and Co-monitoring: Water containing sodium fluorescein tracer is prepared. Using a quantitative water injection unit, the single injection volume is set, and the pressure-stabilizing horizontal flow pump 11 is started. The water is uniformly injected through the biomimetic fractal guide channel 18. Through the transparent pressure-bearing cylinder 20, the green fluorescence front and the deformation evolution characteristics of the coal matrix are captured using DIC technology. Combined with acoustic emission results, the pore and fracture damage characteristics of the coal sample are analyzed.

[0111] 6. Integrated Desorption-Permeability Measurement: After moisture enters, gas and moisture compete for adsorption, increasing gas pressure. The high-pressure back pressure valve 30 is opened, and the volume of methane discharged due to moisture displacement is collected and measured, calculating the displacement desorption amount. Then, the fifth high-pressure shut-off valve 305 is opened for atmospheric pressure desorption, and the atmospheric pressure gas desorption amount of the coal sample is calculated. After desorption is complete, the permeability of the coal sample at the current moisture content is measured using the permeability characteristic measurement unit. Through multiple gradient water injection experiments and tests, the data is monitored and recorded by the host computer 43, and the relationship between moisture content and desorption and permeability characteristics is analyzed, including the relationship between moisture content and displacement desorption / atmospheric pressure desorption / total desorption / permeability. Relevant curves are statistically analyzed and plotted. Experimental data show that when the total desorption of the coal sample is consistent with that of the dry coal sample, the stage with a moisture content below this value is defined as the water replacement dominant zone; when the permeability of the coal sample changes gradually with the increase of moisture content, the stage with a moisture content above this value is defined as the water-locking effect dominant zone, and the stage with a moisture content between the above values ​​is defined as the transition zone.

[0112] 7. Coal Sample Microscopic Damage Measurement: Data and images from fluorescence, DIC, and acoustic emission are spatiotemporally aligned and synchronously coupled. Fluorescence images are transformed by matrix and projected onto the DIC strain contour map. The acoustic emission system records absolute time, while a high-speed camera records the time sequence of each frame. The zero points of the time axes of both systems are aligned by the rise of the trigger signal. The maximum principal strain field on the coal surface is calculated, rigid body displacement is eliminated, and the tensile strain concentration zone is extracted. The fluorescence images are binarized to extract the leading edge contour and saturation distribution of moisture migration. The location points of acoustic emission events are projected onto a two-dimensional plane. This clarifies the evolution process of moisture seepage, coal matrix deformation, and microcrack damage, as well as the mechanism of moisture adsorption, expansion, and cracking of the coal matrix, enabling dynamic, synchronous, and non-destructive detection of in-situ moisture intrusion in coal.

[0113] 8. Guiding Significance: Based on the above experimental results, it is recommended that when carrying out hydraulic permeability enhancement operations in this mining area, the water injection process parameters should be controlled to maintain the final residual moisture content of the coal seam within the moisture content limit corresponding to the water replacement dominant zone. This maximizes the utilization of water to replace adsorbed gas while avoiding channel blockage (water lock) caused by excessive water injection, thereby optimizing gas extraction efficiency. When injecting water to prevent gas outbursts, the minimum moisture content of the coal sample should be maintained outside the moisture content limit corresponding to the water lock effect dominant zone. At this point, the coal seam permeability decreases, water blocks the pores, resulting in the best outburst prevention effect.

[0114] Example 4

[0115] An analysis of the moisture absorption and micro-damage evolution mechanism in gas-bearing coal under dynamic load disturbance is provided, including the following steps:

[0116] 1. Preparation and drying of coal pillars: Coal cores from the coal reservoir to be evaluated are processed into cylindrical samples with a diameter of 50 mm and a height of 100 mm. The prepared coal pillars are placed in an environment of 80℃ and dried continuously for 12 hours until the mass change is less than the rated value, which is considered to be the state of drying.

[0117] 2. Experimental Preparation: Load the coal sample into a high-transmittance FEP heat shrink tubing 22, use a hot air gun to tightly wrap the coal sample, and then load it into a visual triaxial coal sample holder. Connect the relevant circuits of other units and check the airtightness of the equipment.

[0118] 3. Stress Loading. The coal sample microstructure damage evolution collaborative characterization unit is activated, and the pore and fracture damage and deformation characteristics of the coal sample are monitored in real time using DIC and acoustic emission. Then, the axial confining pressure loading controller 37 is activated, and the axial confining pressure is set to simulate the stress environment of deep formations.

[0119] 4. Gas pressurized adsorption. Turn on the gas pressurized adsorption unit and introduce methane gas into the coal sample. Set the adsorption equilibrium pressure, and when the reading of the fifth pressure sensor 705 remains unchanged, it indicates that the coal sample has reached adsorption saturation.

[0120] 5. Quantitative Water Injection and Co-monitoring: Water containing sodium fluorescein tracer is prepared. Using a quantitative water injection unit, the injection volume is set, and the pressure-stabilizing horizontal flow pump 11 is started to inject water evenly. The green fluorescent front is captured using DIC technology through the transparent pressure-bearing cylinder 20 to analyze the water transport process.

[0121] 6. Dynamic loading / unloading and multi-field data coupling analysis: The hydraulic station 36 is controlled by the axial pressure loading controller 37 to keep the confining pressure (axial pressure) constant and load / unload the axial pressure (confining pressure) at a certain rate. The water migration process in the coal body is observed. By using acoustic emission parameters such as ring count, cumulative energy, and signal rise time, as well as DIC cloud map, fluorescence saturation distribution map and DIC shear strain map, the data and images are coupled synchronously in time and space to analyze the evolution of pores and cracks and the deformation of coal matrix. This clarifies the changes in pores and cracks of the coal sample and the process of water infiltration and migration in these pores and cracks when the coal sample is subjected to stress disturbance.

[0122] Example 5

[0123] An evaluation of the mechanism by which an active agent solution affects the water-locking effect in gas-containing coal is provided, including the following steps:

[0124] 1. Experimental Preparation: Prepare a surfactant solution. Select two coal pillars, 50 mm in diameter and 100 mm in height, taken from the same coal seam with similar physical properties. Label them as Group A (pure water control) and Group B (pure water first, then surfactant solution). Wrap the selected coal samples with high-transmittance FEP heat shrink tubing 22 and place them in a visual triaxial coal sample holder.

[0125] 2. Axial pressure setting and gas saturation: Axial pressure simulates in-situ stress, and methane gas is introduced until adsorption equilibrium is reached. The initial permeability of the coal sample is measured using a triaxial pressurization and permeability measurement unit.

[0126] 3. Quantitative Water Injection: For coal sample A, quantitatively inject water with added sodium fluorescein. For coal sample B, first inject water with added sodium fluorescein, then add a surfactant solution. Simultaneously monitor the effect of the solution on the coal matrix using DIC and acoustic emission.

[0127] 4. Coal Sample Microscopic Damage Measurement: DIC technology is used to analyze the local expansion strain of coal samples; acoustic emission is used to monitor the pores and cracks and damage on the coal surface; at the same time, the full-field strain cloud map of the coal matrix from DIC, the fluid seepage path map from fluorescence tracer, and the location map of pore and crack changes from acoustic emission are overlaid to achieve spatiotemporal coupled analysis of water injection seepage field, matrix deformation field, and pore and crack evolution, and to complete the fluid-solid-damage coupled analysis of water intrusion on the coal body.

[0128] 5. Desorption and permeability characteristics determination: The amount of methane displaced during the liquid injection process was collected by the displacement desorption unit, followed by atmospheric pressure desorption and re-measurement of permeability. The data of group A and group B were compared to comprehensively evaluate the effect of the solution on the coal body from three aspects: pore fracture, gas desorption, and coal sample permeability.

[0129] 6. Engineering guidance and suggestions: Conduct experiments on solutions of different concentrations, types, and ratios in sequence. Based on the experimental results, select the solution most suitable for coalbed methane development.

[0130] To provide the public with a thorough understanding of the present invention, specific details have been described in detail in the above preferred embodiments. However, those skilled in the art can fully understand the invention even without these detailed descriptions. Several improvements and modifications can be made without departing from the principles of the invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A visualization system for measuring moisture intrusion and microscopic damage in gas-bearing coal, characterized in that, The system includes a visual triaxial coal sample holder, an environmental control system, a fluid injection system, a desorption system, and a coal sample microstructure damage evolution collaborative characterization unit. The environmental control system includes a temperature control unit and a triaxial pressurization unit. The visual triaxial coal sample holder is housed within the temperature control unit, and the triaxial pressurization unit provides axial pressure and confining pressure to the coal sample within the holder. The fluid injection system includes a gas pressurization and adsorption unit and a quantitative water injection unit, providing gas and water injection functions to the coal sample within the holder. The desorption system... The system includes a displacement desorption unit and an atmospheric pressure desorption unit; the displacement desorption unit and the atmospheric pressure desorption unit are respectively connected to the coal sample in the visualization triaxial coal sample holder; the coal sample micro-damage evolution collaborative characterization unit includes a DIC component and an acoustic emission component; the DIC component includes a dual-channel high-speed imaging system and an image processing workstation, used to capture the deformation observation area and seepage observation area on the surface of the coal sample; the acoustic emission component includes an acoustic emission probe (46) and a signal amplifier (47), which qualitatively analyzes the micro-crack evolution characteristics induced by moisture intrusion into the coal sample.

2. The visualization measurement system for moisture intrusion and microscopic damage in gas-bearing coal according to claim 1, characterized in that, The described visual triaxial coal sample holder includes a transparent pressure-bearing cylinder (20) and an upper end cap (16) and a lower end cap (26) respectively connected to the top and bottom of the transparent pressure-bearing cylinder (20); the transparent pressure-bearing cylinder (20) has a coaxially built-in high-transmittance FEP heat shrink tube (22) for wrapping the coal sample, and the two ends of the transparent pressure-bearing cylinder (20) are respectively embedded in the sealing grooves of the upper end cap (16) and the lower end cap (26); a confining pressure chamber (21) is formed between the transparent pressure-bearing cylinder (20) and the FEP heat shrink tube (22), and the confining pressure chamber (21) is used to store the pressurized confining pressure medium.

3. The visualization measurement system for moisture intrusion and microscopic damage in gas-bearing coal according to claim 2, characterized in that, Both the upper end cover (16) and the lower end cover (26) are provided with axial pressure chambers (25), and a self-balancing piston (24) is slidably connected in the axial pressure chamber (25). The pressure head on the inner side of the self-balancing piston (24) is in contact with the coal body; the bottom of the pressure head of the self-balancing piston (24) is provided with a biomimetic fractal guide groove (18).

4. The visualization measurement system for moisture intrusion and microscopic damage in gas-bearing coal according to claim 3, characterized in that, The biomimetic fractal guide channel (18) is composed of a radial channel radiating outward from the center and multiple concentric circular channels with equal spacing connected to each other. The depth of the channel changes in a gradient from the inside to the outside and from shallow to deep, forming a full-section fluid transport channel.

5. The visualization measurement system for moisture intrusion and microscopic damage in gas-bearing coal according to claim 1, characterized in that, The constant temperature control unit is a constant temperature heating box (38); the constant temperature heating box (38) has double-layer hollow optical observation windows with high light transmittance on both sides of the observation surface of the corresponding visualization triaxial coal sample holder, so as to ensure that the external industrial camera (44) can clearly capture the surface image of the coal sample inside the box.

6. The visualization measurement system for moisture intrusion and microscopic damage in gas-bearing coal according to claim 3, characterized in that, The triaxial pressurization unit includes a shaft confining pressure loading controller (37), a shaft confining pressure tracking pump (35), and a hydraulic station (36). The shaft confining pressure loading controller (37) is connected to the hydraulic station (36), and the hydraulic station (36) is connected to the shaft confining pressure tracking pump (35). One shaft confining pressure tracking pump (35) is connected to the upper and lower shaft pressure chambers (25) through pipelines, and the other shaft confining pressure tracking pump (35) is connected to the confining pressure chamber (21). The shaft confining pressure loading controller (37) controls the shaft confining pressure tracking pump (35) to make the shaft confining pressure reach the set value.

7. The visualization measurement system for moisture intrusion and microscopic damage in gas-bearing coal according to claim 4, characterized in that, The gas pressurization and adsorption unit includes a high-pressure methane cylinder (1), a booster pump (4), a buffer tank (6), an inlet metering container (9), and an outlet metering container (29). The high-pressure methane cylinder (1) is connected to a first high-pressure shut-off valve (301) and a second high-pressure shut-off valve (302) via a three-way valve. The first high-pressure shut-off valve (301) is connected to the booster pump (4). The booster pump (4) is used to compress gas and provide high-pressure gas to the buffer tank (6). At the same time, the booster pump (4) is connected to the second high-pressure shut-off valve (302) and the first solenoid valve (501) via a three-way valve. The first solenoid valve (501) is sequentially connected to a first pressure sensor (701), a second solenoid valve (502), a fourth solenoid valve (504), a seventh solenoid valve (507), and a fifth solenoid valve (508). Force sensor (705), visual triaxial coal sample holder and sixth pressure sensor (706) are connected; buffer tank (6) is connected to inlet metering container (9), inlet metering container (9) is connected to fourth pressure sensor (704), inlet metering container (9) is connected to the biomimetic fractal guide groove (18) at the bottom of balance piston (24) in upper end cover (16) through pipeline, and gas is injected into coal sample through inlet system; outlet metering container (29) is connected to the biomimetic fractal guide groove (18) at the bottom of balance piston (24) in lower end cover (26) through pipeline, outlet metering container (29) is connected to eighth solenoid valve (508) and ninth solenoid valve (509) respectively on pipelines at both ends, outlet metering container (29) is connected to sixth pressure sensor (706).

8. The visualization measurement system for moisture intrusion and microscopic damage in gas-bearing coal according to claim 3, characterized in that, The displacement desorption unit includes a high-pressure back pressure valve (30), a gas-liquid separator (33), a beaker (31), an electronic balance (32), a seventh high-pressure shut-off valve (307), and a first desorber (34). The gas-liquid separator (33) is connected to the inner surface of the bottom balance piston (24) through the high-pressure back pressure valve (30). The bottom of the gas-liquid separator (33) is connected to the beaker (31) through a pipeline. The beaker (31) is placed on the electronic balance (32). The top of the gas-liquid separator (33) is connected to the first desorber (34) through the high-pressure shut-off valve. The seventh high-pressure shut-off valve (307) is located at the inlet of the first desorber (34). The high-pressure back pressure valve (30) is used to maintain the pressure stability inside the coal sample holder. The first desorber (34) is used to determine the volume of methane displaced after a quantitative amount of water is injected into the coal body.

9. The visualization measurement system for moisture intrusion and microscopic damage in gas-bearing coal according to claim 3, characterized in that, The self-balancing piston (24) has a stepped hole inside. The acoustic waveguide rod (48) is placed at the lower end of the stepped hole, with its bottom end slightly convex and in hard contact with the coal sample. The acoustic emission probe (46) is placed at the upper end of the stepped hole and is attached to the rear end of the acoustic waveguide rod (48) through the acoustic coupling layer (49). The elastic constant force component (50) is located above the acoustic emission probe (46) and achieves constant force pushing through a helical spring. It is sealed and pressed by the threaded sealing cap (51) at the top.

10. A method for visually measuring moisture intrusion and microscopic damage in gas-bearing coal, characterized in that, The visualization measurement system according to any one of claims 1-9 is used, and includes the following steps: The first step is to test the airtightness of the entire system, and then to calibrate the free volume by placing the visual triaxial coal sample holder under a constant temperature condition. The second step is to apply a certain axial pressure to the coal sample through the triaxial pressurization unit, and then turn on the gas pressurization adsorption unit to simulate the gas pressurization adsorption process of the coal sample. The third step is to start the quantitative water injection unit to inject water into the coal sample in a quantitative manner, and simulate methane desorption through the displacement desorption unit, and collect methane gas to calculate the displacement desorption rate of water on the coal sample. Step 4: After the displacement desorption is completed, the coal sample is desorbed at atmospheric pressure using an atmospheric pressure desorption unit; Step 5: Immediately after desorption at atmospheric pressure, the permeability of the coal sample is determined using the transient method. During the gas pressurization and adsorption process, quantitative water injection, and displacement desorption process described above, DIC technology was used to analyze the coal matrix strain, fluorescence tracing technology was used to extract the water seepage path, and acoustic emission technology was used to monitor the evolution of microcracks. The above three sets of data were collected simultaneously, and the full-field strain cloud map of the coal matrix from DIC, the fluid seepage route map from fluorescence tracing, and the location map of pore crack changes from acoustic emission were overlaid to achieve spatiotemporal coupled monitoring of the water injection seepage field, matrix deformation field, and pore crack evolution, thus completing the fluid-solid-loss coupled analysis of water intrusion on the coal body.

Images