Seepage low-vibration-frequency stress sensitivity testing device and using method

Abstract

The invention discloses a seepage low-vibration-frequency stress sensitivity testing device and a use method, and belongs to the field of unconventional natural gas exploitation, the seepage low-vibration-frequency stress sensitivity testing device comprises a gas supply system, a stress loading system, a low-vibration-frequency system and a data acquisition system, and the method comprises the steps of test piece placement, stress loading system starting, vacuum degassing, gas adsorption, vibration application and permeability measurement. A stress sensitivity test experiment is carried out on a test piece through the device platform and the method, the gas seepage condition of a low-frequency mechanical vibration coal body stress-seepage coupling field is analyzed through a system, the change rule of the coal body permeability influenced by low-frequency mechanical vibration is obtained, and the stress sensitivity rule is obtained according to related technical indexes and parameters. The influence of the low-frequency mechanical vibration effect and the gas seepage on outburst is discussed, so that outburst prevention measures are better implemented, and economic benefits are brought to mine safety production.

Description

Technical Field

[0001] The present invention relates to the technical field of unconventional natural gas exploitation, and in particular to a seepage low-frequency stress sensitivity testing device and a use method thereof. Background Art

[0002] With the depletion of shallow coal resources, the excavation depth increases, the ground stress increases, the gas content in the mine increases, and the original rock stress of the coal body changes during mechanical excavation, the gas adsorption equilibrium state of the coal body is broken, the internal pore fracture field changes, the gas shows the characteristics of excavation vibration seepage, the internal seepage volume of the coal body increases, and the gas is easy to accumulate inside the coal body, thereby increasing the danger of outburst during excavation. Due to the characteristics of low-permeability and tight reservoirs, such as tightness, low porosity and low permeability, low gas reservoir pressure coefficient, low closure amplitude, and low natural productivity, the research on reservoir stress sensitivity in low-permeability and tight reservoirs and reservoirs with microfractures has received more and more attention.

[0003] Therefore, through stress sensitivity test experiments, starting from the characteristics of coal reservoirs and combining the actual situation of coalbed methane development test areas, we carried out research on coal reservoir stress sensitivity, revealed the dynamic change law and influencing factors of coal reservoir permeability, obtained relevant technical indicators and research parameters, and scientifically summarized the laws and phenomena obtained, which has theoretical and practical significance for the rational and effective development of my country's coalbed methane resources.

[0004] At present, there are countless devices that only study the gas seepage conditions when the coal body is not affected by low-frequency mechanical vibration, but there are only a handful of devices that involve the changes in gas seepage caused by low-frequency mechanical vibration. In existing studies, the permeability under different effective stresses, that is, the reservoir stress sensitivity, is mainly determined by changing only the pore fluid pressure or only the confining pressure. However, when only the pore fluid pressure is changed to determine the reservoir stress sensitivity, the measured pore fluid pressure is not accurate and the zero drift is difficult to control, resulting in low accuracy of the determined reservoir stress sensitivity. When only the upper confining pressure is changed to determine the reservoir stress sensitivity, the effective stress actually measured does not objectively reflect the true effective stress, so the measured reservoir stress sensitivity is poorly consistent with the actual oil and gas reservoir, resulting in inaccurate experimental results, and there are also safety hazards such as poor stability and high danger. Summary of the invention

[0005] In order to solve the technical problems in the above-mentioned prior art that only changing a single experimental parameter in the stress sensitivity test experiment will lead to inaccurate experimental results and make the experiment have poor stability and high risk, the present invention provides a seepage low-frequency stress sensitivity test device and a use method.

[0006] In order to realize the above technical solution, the present invention provides a seepage low-frequency stress sensitivity test device, including a gas supply system, a stress loading system, a low-frequency system and a data acquisition system. It also includes a constant temperature system, which includes a heating pipe, a water inlet valve and a water outlet valve. The water inlet valve and the water outlet valve are connected to the heating pipe through a water pipe, and the heating pipe is connected to the transparent organic glass cylinder through a water pipe.

[0007] Furthermore, the gas supply system includes a vacuum pump, a pressure reducing valve, a first valve, a first pressure gauge, a gas cylinder, a gas supply pipe and a three-way valve. The pressure reducing valve is connected to the interface of the gas cylinder, the vacuum pump is connected to the degassing hole of the coal sample tank through a rubber gas pipe, and the vacuum pump, the coal sample tank and the gas cylinder are connected together through a three-way valve.

[0008] Furthermore, the stress loading system includes an external loading frame, a triaxial pressure chamber, an axial loading device and a confining pressure loading device; the axial loading device includes an axial pressure loading oil pump, a first pressure regulating valve, a second valve, a first hydraulic gauge, a displacement sensor, a hydraulic cylinder, and a pressure sensor. The first hydraulic gauge is connected to the axial pressure oil filling port of the coal sample tank through a pipeline; the displacement sensor is arranged on the crossbeam, the hydraulic cylinder is arranged below the lower pressure head, and the pressure sensor is connected to the low-frequency system via a data line; the triaxial pressure chamber is composed of a pressure chamber and a pressurizing system, and the pressure chamber is composed of an upper seat, a lower seat, a transparent plexiglass cylinder, and a coal sample tank. Exhaust holes are provided on the upper seat and the lower seat, and a sensor terminal is provided on the lower seat. The sensor terminal passes through the lower seat and is connected to the data acquisition system via a data line; the confining pressure loading device includes a confining pressure loading oil pump, a second pressure regulating valve, a third valve, and a second hydraulic gauge. The second hydraulic gauge is connected to the confining pressure oil filling port of the coal sample tank through a pipeline.

[0009] Furthermore, a movable piston divides the pressure chamber of the multiplier into two chambers.

[0010] Furthermore, the low-frequency system includes a vibration table, a specimen fixture and a mechanical decoupling device; the specimen fixture includes upper and lower clamping rings.

[0011] Furthermore, the hydraulic servo control system is arranged in the support base, and the hydraulic servo control system includes an axial pressure loading oil pump and a confining pressure loading oil pump. The axial pressure loading oil pump is connected to the oil inlet and oil outlet through a pipeline, and the confining pressure loading oil pump is connected to the oil inlet and outlet through a pipeline.

[0012] Furthermore, the data acquisition system includes a vibration force sensor, an air pressure sensor, data acquisition software, a data transmission wire, and a computer.

[0013] Furthermore, a method for using a seepage low-frequency stress sensitivity testing device comprises the steps of:

[0014] S1: Air tightness test of the experimental system: close the fourth valve, the first valve, and the fifth valve, connect the three-way valve to the gas supply system and the coal sample tank, and open the second valve and the third valve; then open the first valve, adjust the pressure reducing valve, fill the pipeline with nitrogen of a certain pressure, and then record the readings of the first air pressure gauge, the second air pressure gauge, the first hydraulic pressure gauge, and the second hydraulic pressure gauge; finally, close the first valve and leave it for 24 hours, then observe whether the readings of each gauge change. If the readings of the pressure gauges are consistent and do not drop, it indicates that the system is airtight. Otherwise, debug until the system is airtight.

[0015] S2: Place the test specimen: Place the prepared test specimen on the liftable axial pressure loading column, and manually switch on and off the axial pressure pump to continuously pressurize the coal sample to the stress loading system;

[0016] S3: Vacuum degassing: Set the loading confining pressure, close the first valve and the fifth valve, connect the three-way valve to the vacuum pump and the coal sample tank; open the second valve and the third valve, and apply a small axial pressure and confining pressure to the system; then open the vacuum pump and the fourth valve, and then turn on the vacuum pump to vacuum the entire experimental system until the vacuum degree does not change within 10 minutes after closing the fourth valve and the vacuum pump;

[0017] S4: Gas adsorption: Turn on the charge amplifier, data analyzer and the computer connected to the data analyzer to record the changes in the gas pressure in the coal sample tank during the test; after recording, open the gas cylinder and the pressure reducing valve, and wait for the inlet pressure to be equal to the outlet pressure;

[0018] S5: Apply vibration: Turn on the sweep signal generator and power amplifier to control the vibration table to send out an excitation signal. The vibration table generates corresponding horizontal or vertical axial vibrations. The vibrations are first transmitted to the mechanical decoupling device, and then the mechanical decoupling device transmits the motion to the specimen through the adapter and the fixture.

[0019] S6: Permeability measurement: open the first valve, wait for the coal sample gas permeability to stabilize, and then open the fifth valve at the same time to see the corresponding permeability data under the inlet pressure, axis, and confining pressure under external vibration on the data acquisition system;

[0020] S7: Obtain test results, and process the test results to obtain stress sensitivity data of the specimen.

[0021] Further, in step S7, the stress sensitivity data includes permeability calculation, effective stress calculation and permeability stress sensitivity coefficient calculation; wherein the permeability calculation formula is:

[0022]

[0023] The formula for calculating effective stress is:

[0024]

[0025] The calculation formula of permeability stress sensitivity coefficient is:

[0026]

[0027] In summary, the present invention has the following beneficial effects compared with the prior art:

[0028] On the basis of a conventional coal sample tank, the present invention applies horizontal or vertical axial vibration to the coal sample in the coal sample tank through a vibration table to realize the joint loading of triaxial pressure and dynamic disturbance force, can apply vibration dynamic disturbances of different frequencies in the conventional process of only measuring seepage and has the characteristics of automatic data collection, can more realistically simulate the vibration disturbance in the underground coal seam gas extraction process, under the joint action of these factors, the macro cracks and micro cracks of the coal body expand to form a crack network, increase the permeability of the coal seam, so as to more accurately analyze the evolution law of the permeability in the coal seam mining process, and then analyze the stress sensitivity law of the permeability, and then through computer analysis, can accurately measure the dynamic changes of the crack evolution; the frequency and amplitude of the vibration can be adjusted, and a changing vibration wave such as a sine wave can be selected to apply vibration force to the sample; the entire experimental process can accurately analyze the law of stress sensitivity when vibration and seepage exist at the same time, and many coal and gas outburst accidents are caused by vibration, so the present invention is of great significance for preventing mine gas disasters. The experimental device of the present invention can obtain the stress sensitivity law when simulating seepage and vibration at the same time, and can provide method support for stress sensitivity testing of unconventional natural reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0030] Figure 1 It is a schematic diagram of the overall structure of a seepage low-frequency stress sensitivity testing device;

[0031] Figure 2 It is a schematic diagram of the stress loading system, low vibration frequency system, and constant temperature system;

[0032] Figure 3 is a schematic diagram of a gas supply system;

[0033] Figure 4 Schematic diagram of the data acquisition system.

[0034] The above drawings include the following reference numerals:

[0035] 1. Gas supply system; 10. Gas cylinder; 11. Pressure reducing valve; 12. First valve; 13. First pressure gauge; 14. Three-way valve; 15. Vacuum pump; 16. Fourth valve; 2. Stress loading system; 20. External loading frame; 200. Upper crossbeam; 21. Three-axis pressure chamber; 2100. Upper seat; 2101. Lower seat; 2102. Transparent organic glass cylinder; 2103. Coal sample tank; 2104. Sensor connector; 2105. Confining pressure oil filling port; 221. First pressure regulating valve; 221a. Second pressure regulating valve; 222. Second valve; 222a. Third valve; 223. First hydraulic gauge; 223a. Second hydraulic gauge; 224. Displacement sensor; 2 25. Hydraulic cylinder; 2250. Oil inlet; 2251. Oil outlet; 2252. Oil inlet and outlet; 226. Pressure sensor; 227. Upper pressure head; 228. Lower pressure head; 229. Transmission column; 3. Low-frequency system; 30. Vibration table; 31. Test piece fixture; 32. Mechanical decoupling device; 4. Hydraulic servo control system; 40. Axial pressure loading oil pump; 41. Confining pressure loading oil pump; 5. Constant temperature system; 50. Drain valve; 51. Water inlet valve; 52. Heating pipe; 6. Data acquisition system; 65. Computer; 66. Power amplifier; 67. Signal generator; 65a. Second barometer; 65b. Fifth valve; 65c. Flow meter; 7. Support base; 8. Seepage pipe. DETAILED DESCRIPTION

[0036] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0037] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0038] See also Figures 1 to 3As shown, the present invention provides a seepage low-frequency stress sensitivity test device, which is the same as the prior art in that it includes: a gas supply system 1 for providing a gas source with controllable pressure, a stress loading system for providing controllable triaxial confining pressure, and a data acquisition system 6 for processing the signal data of the sensor in the coal sample tank 2103. Different from the prior art, the seepage low-frequency stress sensitivity test device applies horizontal or vertical axial vibration to the test piece on the basis of a conventional coal sample tank to achieve the joint loading of triaxial pressure and dynamic disturbance force, which can more realistically simulate the vibration disturbance suffered during the underground coal seam mining process, thereby more accurately analyzing the evolution law of permeability stress sensitivity.

[0039] In addition, the gas supply system 1 is composed of a vacuum pump 15, a pressure reducing valve 11, a first valve 12, a first barometer 13, a gas cylinder 10, a gas supply pipe and a three-way valve 14. The pressure reducing valve 11 is connected to the interface of the gas cylinder 10, and the pressure reducing valve 11 is connected to the air inlet of the coal sample tank 2103 by means of the gas supply pipe. The gas pressure in the coal sample tank 2103 is monitored by the first barometer 13. The vacuum pump 15 is connected to the degassing hole of the coal sample tank 2103 through a rubber gas pipe, and the other two ends of the three-way valve 14 are respectively connected to the vacuum device and the gas inlet of the coal sample tank 2103 through the gas supply pipe.

[0040] The stress loading system 2 includes an external loading frame 20, a three-axis pressure chamber 21, and an axial loading device. The three-axis pressure chamber 21 uses a high-pressure multiplier to control the loading (or displacement), and a movable piston divides the pressure chamber of the multiplier into two chambers. In this way, it can replace the four-column frame to support the large hydraulic cylinder 225, which also greatly increases the loading stiffness. The axial loading device includes an axial pressure loading oil pump 40, a first pressure regulating valve 221, a second valve 222, a first hydraulic gauge 223, a displacement sensor 224, a hydraulic cylinder 225, and a pressure sensor 226. The first hydraulic gauge 223 is connected to the axial pressure oil filling port of the coal sample tank 2103 through a pipeline. A displacement sensor 224 is installed on the upper crossbeam 200, and a hydraulic cylinder 225 is installed below the upper pressure head 227. The pressure sensor 226 is connected to the low-frequency system 3 via a data line. The triaxial pressure chamber 21 is composed of a pressure chamber and a pressurizing system. The pressure chamber is composed of an upper seat 2100, a lower seat 2101, a transparent organic glass cylinder 2102, and a coal sample tank 2103, which is used to place coal samples and keep the samples stable and dry during the experiment. The upper seat 2100 and the lower seat 2101 are provided with exhaust holes. The lower seat 2101 in the coal sample tank 2103 is provided with a sensor terminal, which passes through the lower seat 2101 and is connected to the data acquisition system 6 via a data line. The pressurizing system is used to apply axial pressure and confining pressure to the sample. The axial pressure is provided by the axial loading device, which can control the rate of axial strain. The confining pressure is provided by the confining pressure loading device, which includes a confining pressure loading oil pump 41, a second pressure regulating valve 221a, a third valve 222a, and a second hydraulic gauge 223a. The second hydraulic gauge 223a is connected to the confining pressure oil filling port of the coal sample tank 2103 through a pipeline.

[0041] The low-frequency system 3 includes a vibration table 30, a specimen fixture 31, and a mechanical decoupling device 32. The specimen fixture 31 includes upper and lower clamping rings for clamping and fixing the specimen. The bottom of the lower clamping ring has a bottom adapter block for fastening with the other end of the mechanical decoupling device 32 in the vertical direction. Both sides are connected to one end of the mechanical decoupling device 32 in the horizontal direction through a connecting device, and the other end of the mechanical decoupling device 32 in the horizontal direction is connected to the vibration table 30 surface.

[0042] The hydraulic servo control system 4 is arranged in the support base 7. The hydraulic servo control system 4 includes an axial pressure loading oil pump 40 and a confining pressure loading oil pump 41. The axial pressure loading oil pump 40 is connected to the oil inlet 2250, the oil outlet 2251 and the oil inlet and outlet 2252 through pipelines.

[0043] Constant temperature system 5 ensures that temperature changes during the test will not affect the test results, and keeps the temperature of the test environment stable through heating and cooling devices.

[0044] The data acquisition system 6 includes a vibration force sensor 61, an air pressure sensor 62, a charge amplifier 63, a data analyzer, and a computer 65. The vibration force sensor 61 and the air pressure sensor 62 both use piezoelectric sensors, which can accurately respond to the exciting force exerted on the coal sample tank 2103 and the changes in the air pressure in the coal sample tank 2103; the power amplifier 66 amplifies the sensor signal and transmits it to the data analyzer. The data analyzer converts the electrical signal into a digital signal and transmits it to the computer 65 via a cable, so that the data can be accurately analyzed.

[0045] To conduct the seepage low-frequency stress sensitivity test, the seepage low-frequency stress sensitivity test device can be tested by the following test method, which includes the following steps:

[0046] S1: Connect the experimental system and test the air tightness of the experimental system; specifically: close the fourth valve 16, the first valve 12, and the fifth valve 65b, and connect the three-way valve 14 to the gas supply system 1 and the coal sample tank 2103. Open the second valve 222 and the third valve 222a, and apply a smaller axial pressure and confining pressure to the experimental system to prevent air leakage caused by gaps in the machine during the inflation process. Then open the first valve 12, adjust the pressure reducing valve 11, fill the pipeline with nitrogen at a certain pressure, and record the readings of the first pressure gauge 13, the second pressure gauge 65a, the first hydraulic gauge 223, and the second hydraulic gauge 223a at this time. At the same time, close the first valve 12 and leave it for 24 hours to observe whether the readings of each gauge change. If the pressure gauge readings are consistent and do not drop, it indicates that the system is airtight. Otherwise, debug until the system is airtight.

[0047] Preparation before the experiment: Put the tested coal sample (specimen size: Φ50mm×100mm) into a drying oven for constant temperature drying to eliminate the influence of moisture on the experimental results. After taking out and cooling, measure and weigh the coal sample.

[0048] S2: Place the test specimen: There are two types of test specimens, one is the raw coal test specimen, and the other is the pressed test specimen. The prepared test specimen is placed on a liftable axial pressure loading column. The axial pressure pump is manually switched on and off to continuously pressurize the coal sample to the stress loading system 2;

[0049] S3: Vacuum degassing: After ensuring that the system is correctly connected and airtight, turn on the vacuum pump to perform vacuum degassing on the coal sample to eliminate the possible impact of the coal sample and other gases in the system on the experimental results. Specifically: load the confining pressure to the set value according to the experimental plan, close the first valve 12 and the fifth valve 65b, and connect the three-way valve 14 to the vacuum pump and the coal sample tank 2103. Open the second valve 222 and the third valve 222a to apply a smaller axial pressure and confining pressure to the system to prevent gaps and leaks during the vacuum process. Open the fourth valve 16 of the vacuum pump, turn on the vacuum pump 15, and vacuum the entire experimental system until the vacuum degree does not change within 10 minutes after closing the fourth valve 16 and the vacuum pump 15, and the vacuum step is completed.

[0050] S4: Gas adsorption: Turn on the computer 65, record the changes in gas pressure in the coal sample tank 2103 during the test, open the gas cylinder 10 and the pressure reducing valve 11, the gas enters the coal sample tank 2103 along the gas supply pipe, fill with nitrogen to a predetermined pressure, and keep the pressure stable, waiting for the inlet pressure to be equal to the outlet pressure.

[0051] S5: Apply vibration: Turn on the swept frequency signal generator 67 and the power amplifier 66. The swept frequency signal generator 67 provides a signal source. The power amplifier 66 amplifies the signal source and transmits it to the vibration table 30 to send an excitation signal. The vibration table 30 generates corresponding horizontal or vertical axial vibration. The vibration is first transmitted to the mechanical decoupling device 32. The mechanical decoupling device 32 then transmits the motion to the test piece through the adapter and the fixture.

[0052] S6: Permeability measurement: open the first valve 12, wait for the coal sample gas permeability to stabilize, and then open the fifth valve 65b to view the corresponding permeability data under the inlet pressure, axis, and confining pressure under external vibration on the data acquisition system 6.

[0053] S7: Experimental data processing: The permeability of the tectonic coal complex is calculated using the steady flow method based on Darcy's law. The formula is as follows:

[0054]

[0055] Where: K is the permeability of the specimen, mD; v is the gas seepage velocity, ml / s; L is the length of the specimen, cm; μ is the gas dynamic viscosity, Pa·s; P0 is the standard atmospheric pressure, MPa; A is the cross-sectional area of ​​the specimen, cm2; P1 and P2 are the inlet and outlet pressures, MPa, respectively.

[0056] Stress sensitivity is the change in permeability with effective stress. When a coal sample is deformed by external forces, the main object of action is the internal skeleton of the coal sample, that is, the effective stress on the coal sample is the difference between the external force on the coal sample and the gas pressure in the pores and cracks inside the coal sample. The effective stress during the experiment is generally expressed by the average effective stress. That is:

[0057]

[0058] In the formula, σ e is the average effective stress, MPa; σ a is the axial pressure, MPa; σ r is the confining pressure, MPa.

[0059] In the actual environment, the factors affecting coal seam permeability are very complex. Geological structure, stress state, coal seam burial depth, coal body structure, coal rock and coal quality characteristics, coal rank and natural cracks all affect coal seam permeability to varying degrees. It is difficult to describe the impression of each factor one by one. In order to characterize the sensitivity of specimen permeability to effective stress, the permeability stress sensitivity coefficient can be introduced, that is:

[0060]

[0061] In the formula, α e is the permeability pressure sensitivity coefficient, MPa -1 , K0 is the initial permeability of the tectonic coal complex, mD, ΔK is the change in permeability under effective stress, mD, Δσ e is the effective stress change, MPa.

[0062] In this implementation, the vibration frequency of the drill pipe is less than 10Hz, and the vibration frequency range of the whole device is 0 to 50Hz. The vibration frequency can be modified according to the market vibration frequency, which can fully simulate the influence of drilling vibrations of different frequencies on the coal body, and study the influence of vibration on the permeability of coalbed methane, and then derive the stress sensitivity law when vibration and seepage exist at the same time. This specification uses specific examples to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation of the present invention.

[0063] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0064] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. If not otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0065] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A seepage low-frequency stress sensitivity testing device, comprising a gas supply system (1), a stress loading system (2), a low-frequency system (3) and a data acquisition system (6), characterized in that: It also includes a constant temperature system (5), the constant temperature system (5) including a heating pipe (52), a water inlet valve (51) and a water outlet valve, the water inlet valve (51) and the water outlet valve are connected to the heating pipe (52) via a water pipe, and the heating pipe (52) is connected to the transparent organic glass cylinder (2102) via a water pipe.

2. The seepage low-frequency stress sensitivity testing device according to claim 1 is characterized in that: The gas supply system (1) comprises a vacuum pump (15), a pressure reducing valve (11), a first valve (12), a first barometer (13), a gas cylinder (10), a gas supply pipe and a three-way valve (14); the pressure reducing valve (11) is connected to the interface of the gas cylinder (10); the vacuum pump (15) is connected to the degassing hole of the coal sample tank (2103) through a rubber gas tube; the vacuum pump, the coal sample tank (2103) and the gas cylinder (10) are connected together through the three-way valve (14).

3. The seepage low-frequency stress sensitivity testing device according to claim 1, characterized in that: The stress loading system (2) comprises an external loading frame (20), a triaxial pressure chamber (21), an axial loading device and a confining pressure loading device; the axial loading device comprises an axial pressure loading oil pump (40), a first pressure regulating valve (221), a second valve (222), a first hydraulic gauge (223), a displacement sensor (224), a hydraulic cylinder (225), and a pressure sensor (226); the first hydraulic gauge (223) is connected to the axial pressure oil filling port of the coal sample tank (2103) through a pipeline; the displacement sensor (224) is arranged on the crossbeam, the hydraulic cylinder (225) is arranged below the lower pressure head (228), and the pressure sensor (226) is connected to the low-frequency vibration system (3) via a data line; the triaxial pressure chamber (21) comprises The invention relates to a pressure chamber and a pressurizing system, wherein the pressure chamber is composed of an upper seat (2100), a lower seat (2101), a transparent organic glass cylinder (2102), and a coal sample tank (2103); both the upper seat (2100) and the lower seat (2101) are provided with exhaust holes, and the lower seat (2101) is provided with a sensor terminal, and the sensor terminal passes through the lower seat (2101) and is connected to a data acquisition system (6) via a data line; the confining pressure loading device comprises a confining pressure loading oil pump (41), a second pressure regulating valve (221a), a third valve (222a), and a second hydraulic gauge (223a); the second hydraulic gauge (223a) is connected to a confining pressure oil filling port (2105) of the coal sample tank (2103) via a pipeline.

4. The seepage low-frequency stress sensitivity testing device according to claim 3 is characterized in that: A movable piston divides the multiplier's pressure chamber into two chambers.

5. The seepage low-frequency stress sensitivity testing device according to claim 1, characterized in that: The low-frequency system (3) comprises a vibration table (30), a specimen fixture (31) and a mechanical decoupling device (32); the specimen fixture (31) comprises upper and lower clamping rings.

6. The seepage low-frequency stress sensitivity testing device according to claim 1, characterized in that: The hydraulic servo control system (4) is arranged in the support base (7), and the hydraulic servo control system (4) comprises an axial pressure loading oil pump (40) and a confining pressure loading oil pump (41), the axial pressure loading oil pump (40) is connected to the oil inlet (2250) and the oil outlet (2251) through a pipeline, and the confining pressure loading oil pump (41) is connected to the oil inlet and outlet (2252) through a pipeline.

7. The seepage low frequency stress sensitivity testing device according to claim 1, characterized in that: The data acquisition system (6) comprises a vibration force sensor (61), an air pressure sensor (62), a charge amplifier (63), a data analyzer, and a computer (65).

8. A method for using a seepage low-frequency stress sensitivity testing device, comprising the seepage low-frequency stress sensitivity testing device according to any one of claims 1 to 7, characterized in that: Includes steps: S1: Air tightness test of the experimental system: close the fourth valve (16), the first valve (12), and the fifth valve (65b), connect the three-way valve (14) to the gas supply system (1) and the coal sample tank (2103), and open the second valve (222) and the third valve (222a); then open the first valve (12), adjust the pressure reducing valve (11), fill the pipeline with nitrogen of a certain pressure, and then record the readings of the first air pressure gauge (13), the second air pressure gauge (65a), the first hydraulic pressure gauge (223), and the second hydraulic pressure gauge (223a); finally, close the first valve (12) and leave it for 24 hours, then observe whether the readings of each gauge change. If the readings of the pressure gauges are consistent and do not drop, it indicates that the air tightness of the system is good. Otherwise, debug until the air tightness of the system is good. S2: Place the test specimen: Place the prepared test specimen on a liftable axial pressure loading column, and manually switch on and off the axial pressure pump to continuously pressurize the coal sample to the stress loading system (2); S3: Vacuum degassing: set the loading confining pressure, close the first valve (12) and the fifth valve (65b), connect the three-way valve (14) to the vacuum pump and the coal sample tank (2103); open the second valve (222) and the third valve (222a), and apply a small axial pressure and confining pressure to the system; then open the vacuum pump valve and the fourth valve (16), and then start the vacuum pump (15), and perform a vacuum pumping operation on the entire experimental system until the vacuum degree does not change within 10 minutes after the fourth valve (16) and the vacuum pump (15) are closed; S4: Gas adsorption: Turn on the charge amplifier (63), the data analyzer and the computer (65) connected to the data analyzer to record the change of gas pressure in the coal sample tank (2103) during the test; after the recording is completed, open the gas cylinder (10) and the pressure reducing valve (11), and wait for the air inlet pressure to be equal to the air outlet pressure; S5: Apply vibration: Turn on the sweep signal generator (67) and the power amplifier (66) to control the vibration table (30) to send out an excitation signal, and the vibration table (30) generates corresponding horizontal or vertical axial vibration, and the vibration is first transmitted to the mechanical decoupling device (32), and the mechanical decoupling device (32) then transmits the motion to the test piece through the adapter and the fixture; S6: Permeability measurement: open the first valve (12), wait for the coal sample gas permeability to stabilize, and then open the fifth valve (65b) to view the corresponding permeability data under the inlet pressure, axis, and confining pressure under external vibration on the data acquisition system (6); S7: Obtain test results, and process the test results to obtain stress sensitivity data of the specimen.

9. The method for using the seepage low-frequency stress sensitivity testing device according to claim 8, characterized in that: In step S7, the stress sensitivity data includes permeability calculation, effective stress calculation and permeability stress sensitivity coefficient calculation; wherein the permeability calculation formula is: The formula for calculating effective stress is: The calculation formula of permeability stress sensitivity coefficient is:

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