Nanofluid-power ultrasonic synergistic anti-reflection system and method for soft outburst coal seam gas control

Abstract

The invention discloses a nanofluid-power ultrasonic synergistic anti-reflection system and method for soft outburst coal seam gas control, belongs to the technical field of coal seam gas control, and aims to solve the problems that a discharge hole of an injection system is easy to block, the diffusion range is limited and the injection process is unstable. According to the technical scheme, the system integrates an anti-blocking injection pipe and a 18kW high-power underground ultrasonic transducer. According to the method, an acidic SiO nanofluid with the pH value of 3 and the concentration of 2.0% is adopted, and 25.0-82.5 kHz broadband ultrasonic segmented excitation is matched. And the cross-scale pores of the coal body are accurately regulated and controlled by utilizing the coupling effect of fluid acidification moistening and ultrasonic cavitation / mechanical vibration. Tests show that the coal body contact angle is reduced to 25.2 degrees, the macropore volume is maximally increased by 828.73%, and the gas diffusion coefficient is increased by about 24%; the engineering application shows that the gas extraction concentration is increased by 58.35%-119.90%, and the flow rate is increased by 29.37%-136.72%.

Description

Technical Field

[0001] This invention relates to the field of coalbed methane control technology, and in particular to a nanofluid-power ultrasound synergistic permeability enhancement system and method for controlling methane in soft, outburst-prone coalbeds. Background Technology

[0002] Soft coal seams have a loose coal body structure and uneven distribution of pores and fractures. Coal seam water injection is a common gas control method. By injecting high-pressure water, the original gas system of the coal body is disrupted, promoting the desorption and discharge of gas, thereby reducing the gas content and the risk of outburst. However, there are areas for improvement in the existing injection system. When the injection tube is inserted into the coal seam borehole, some of the holes are easily blocked by coal fragments, which prevents the fluid from being transported normally. This makes it difficult to carry out water injection operations in some areas, and the fluid can only penetrate through the surrounding area. Moreover, the diffusion range after spraying is small, which makes it difficult to fully cover the coal seam fracture penetration area, resulting in low penetration efficiency. In recent years, nanofluids have been gradually applied to coalbed methane control due to their good permeability. Therefore, it is necessary to develop a nanofluid power-ultrasound synergistic permeability enhancement system that can solve the above problems, so as to improve the efficiency of coalbed methane control in soft and outburst-prone coalbeds. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of existing technologies, such as easy clogging of perforations and limited diffusion range of nanofluids, and to propose a nanofluid-power ultrasound synergistic permeability enhancement system and method for the treatment of gas in soft and protruding coal seams.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A nanofluid-power ultrasound synergistic permeability enhancement system for the control of gas in soft and outburst-protruding coal seams includes an injection tube with multiple sets of holes arranged along its length on its outer wall. Each set of holes consists of multiple holes arranged in a ring at equal intervals. The inner wall has a movable groove, and the holes are connected to the movable groove. Multiple protective rings are located inside the injection tube and each is matched with multiple sets of drainage holes. Adjacent protective rings are fixedly connected to a connecting frame I. The spiral blade is located inside the injection tube, with multiple protective rings surrounding it; A metal tip is attached to one end of the syringe. When installing the injection tube, a protective ring is used to seal the drainage holes to prevent coal fragments from entering the injection tube.

[0005] In one possible design, a threaded ring I is fixed at one end of the metal head, and a threaded section is opened at one end of the inner wall of the injection tube, with the threaded ring I screwed into the threaded section. A connecting ring is fixed to the end of the injection tube away from the metal head. A threaded ring II is fixed to the side wall of the connecting ring, and the threaded ring II is screwed to the threaded section of another injection tube.

[0006] In one possible design, a fixing seat is fixedly connected to the side of the injection tube near the metal head, and the surface of the fixing seat has multiple connecting holes. Both ends of the spiral blade are fixedly connected to connecting rods. One end of the connecting rod is rotatably connected to the fixed base, and the other end of the connecting rod is rotatably connected to the mounting bracket fixed inside the injection tube near the connecting ring. The side of the mounting bracket facing the connecting ring is inclined.

[0007] In one possible design, a shielding ring is fixed to the sidewall of the protective ring near the metal head, and a compression spring is sleeved on the outer wall of the shielding ring, with one end of the compression spring fixed to the protective ring. The inner wall of the movable groove is provided with an annular slot, one end of the shielding ring is inserted into the annular slot, and the other end of the compression spring is fixedly connected to the inner wall of the movable groove.

[0008] One possible design also includes a frustum-shaped impact seat; The inner wall of the injection tube is fixed to the limiting seat, and the frustum-shaped impact seat is located on the side of the limiting seat away from the connecting ring and is sleeved on the outer wall of the connecting rod. The limiting seat is sleeved on the conical surface of the frustum-shaped impact seat. The outer wall of the frustum-shaped impact seat is provided with an integrated impact ring, and the impact ring is fixedly connected to the adjacent protective ring by a connecting frame II.

[0009] In one possible design, the limiting seat has a frustum-shaped groove on the side facing the connecting ring, which is used to guide the flow of nanofluid.

[0010] One possible design also includes a water injection pump; The injection tube has a connecting ring at one end connected to a connecting pipe, which is connected to a water pump and is equipped with a pressure valve.

[0011] One possible design also includes a nanofluid storage tank; The water injection pump is connected to the nanofluid storage tank and is used to extract the nanofluid from the nanofluid storage tank.

[0012] One possible design also includes a moisture content meter, a gas concentration meter, and a directional drilling rig; The directional drilling rig is used for drilling holes in the coal seam, and the moisture content detector and gas concentration detector are used to monitor coal seam parameters.

[0013] A gas control method based on a dual-number system includes the following steps: S1. Preparation of acidic nanofluid: White spherical hydrophilic SiO2 nanoparticles with a particle size of 20 nm and a purity >99.9% were selected. Deionized water with a conductivity <0.1 μS / cm was used as the base liquid to prepare a SiO2 nanofluid solution with a mass fraction of 2.0%. Then, 0.1 mol / L glacial acetic acid solution was added to adjust the pH value of the nanofluid to 3, forming an acidic SiO2 nanofluid wetting solution. After stirring and mixing, the solution was placed in an ultrasonic vibration device with an ultrasonic power of 200 W and a time of 20 min until there were no white lumpy insoluble substances and the nanoparticles were uniformly distributed in the base liquid. S2. Use a directional drilling rig to complete the drilling of the coal seam. After connecting the injection pipe to the water injection pump, insert it into the hole. At this time, the protective ring will seal the drainage hole. S3. Drive the water injection pump to draw acidic SiO2 nanofluid (mass concentration 2.0%, pH=3) from the nanofluid storage tank and deliver it to the injection tube. The nanofluid impacts the frustum-shaped impact seat and impact ring, causing the protective ring to move and open the discharge hole. At the same time, it impacts the rotating spiral blade, causing the nanofluid to diffuse and inject into the coal seam in a fan shape. Simultaneously, the ultrasonic generator is activated to perform a coordinated anti-reflection operation, as follows: By powering the transducer, mechanical waves of axial-radial composite vibration are generated using the inverse piezoelectric effect. A multi-frequency synergistic strategy is employed, with the frequency setting range from 25.0 kHz to 82.5 kHz. Specifically, the cavitation effect of 25.0 kHz low-frequency ultrasound is used to enhance the development of macropores larger than 10 μm and seepage pores, while the mechanical vibration effect of 82.5 kHz high-frequency ultrasound is used to promote the connectivity between micropores and mesopores. High-power segmented operation: Set the maximum power of the ultrasonic generator to 18kW, and apply segmented ultrasonic excitation to the coal seam, with each segment lasting 120 minutes; After being injected into the coal seam, the acidic fluid undergoes a physicochemical reaction with the coal body. By utilizing the expansion effect of hydrogen ions on pores and the surface tension reduction properties of nanoparticles, the gas desorption capacity increases by more than 4.5378 mL / g compared to conventional water injection. Finally, by utilizing the "mechanical vibration-cavitation-heat" coupling effect of the ultrasonic field and the synergistic effect of the chemical modification of the acidic nanofluid, efficient displacement of coal seam gas is achieved.

[0014] To achieve effective transmission and excitation of ultrasonic waves downhole, this system also includes an ultrasonic excitation subsystem, which consists of the following core components: High-power ultrasonic generator: with a maximum output power of 18kW, used to drive the transducer.

[0015] Downhole ultrasonic transducer: It adopts a piezoelectric structure and is integrated into the injection tube. It can convert electrical signals into mechanical waves of axial-radial composite vibration, forming a physical excitation field that radiates outward in the radial direction.

[0016] Power supply and delivery system: including an explosion-proof transformer. Ensures stable power supply and precise delivery of the transducer to deep coal seams even in a water-filled environment.

[0017] In this application, the preparation method of the nanofluid is as follows: white spherical hydrophilic SiO2 nanoparticles with a particle size of 20 nm and a purity greater than 99.9% are selected, and deionized water with an electrical conductivity of less than 0.1 μs / cm is used as the base liquid. After stirring and mixing the two, the mixed solution is added to an ultrasonic vibration device, the ultrasonic power is set to 200 W, and the ultrasonic time is 20 min, so that the nanoparticles are evenly distributed in the base liquid. The process is completed when there are no white blocky insoluble substances in the solution. After coal seam exploration is completed and boreholes are drilled using a directional drilling rig, one end of the injection tube is connected to the connecting pipe of the water injection pump and then inserted into the borehole. A pressure valve is installed on the connecting pipe. During the installation of the injection tube, the drainage hole is sealed by a protective ring to prevent coal fragments from entering the injection tube. When the injection tube is inserted into the fractured permeable zone of the coal seam, the water injection pump is driven to extract nanofluid from the nanofluid storage tank and deliver it to the inside of the injection tube. When the nanofluid enters the injection tube, it impacts the end of the frustum-shaped impact seat, causing it to move axially along the injection tube, and simultaneously through connecting frame II and connecting frame I... Multiple protective rings move synchronously, causing them to move out of the range of the discharge holes, thus opening them. The impact rings on the outer wall of the frustum-shaped impact seat will be impacted simultaneously, thereby increasing the impact force on the frustum-shaped impact seat, enabling it to overcome the force of the compression spring and ensuring that the injection tube remains in a continuously open state. Subsequently, the nanofluid will impact the spiral blades, causing them to rotate continuously, thus allowing the nanofluid to be transported in a rotating manner. When it is transported to the range of the discharge holes, it will be ejected. Due to the influence of the spiral blades, the nanofluid injected into the coal seam will diffuse in a fan shape, thereby increasing the diffusion area in this region and improving the permeability.

[0018] In this invention, the method includes the steps of preparing acidic nanofluid, drilling and inserting pipes with a directional drilling rig, and injecting the nanofluid. The nanofluid used is an acidic SiO2 nanofluid with a mass concentration of 2.0% and a pH of 3. Through the synergistic effect of acidic environment corrosion dissolving coal minerals and nanoparticles, the number of oxygen-containing functional groups in the coal body is increased, significantly reducing the coal contact angle and converting closed pores into open pores. Its main application is in the control of gas in soft, outburst-prone coal seams, significantly improving the permeability efficiency of the nanofluid and the reliability of gas control.

[0019] In this invention, the nanofluid-power ultrasound synergistic permeability enhancement system for controlling gas in soft, outburst-prone coal seams employs an acidic SiO2 nanofluid with a mass concentration of 2.0% and a pH of 3, delivered via a rotating spiral plate, and has the following significant beneficial effects: 1. Utilizing the synergistic effect of ultrasonic cavitation in liquid media and the chemical dissolution of acidic fluids, precise cross-scale porosity control is achieved. Experimental data shows that under 25.0kHz low-frequency ultrasonic excitation, the impact generated by the cavitation effect increases the maximum mercury ingress into the coal body by 73.47%-210.30%, and significantly improves the pore volume of macropores larger than 10μm (increasing by 192.73%-828.73%), effectively constructing gas seepage channels. Simultaneously, under 82.5kHz high-frequency ultrasonic excitation, the high-frequency fatigue effect of mechanical vibration increases the gas diffusion coefficient of the coal body by 13.01%-23.97%, significantly reducing the adsorption capacity of micropores for gas and promoting the conversion of adsorbed gas to free gas.

[0020] 2. Through segmented excitation (120 min / segment) with a high-power ultrasonic field (18 kW), the effective drainage radius can reach 14 m. Engineering tests show that after treatment by this system, the gas drainage concentration is increased by 58.35%-119.90% compared to the original concentration, and the gas drainage flow rate is increased by 29.37%-136.72%, with no significant attenuation within 60 days after the excitation ends, achieving long-term and efficient control of gas in soft, outburst-prone coal seams.

[0021] 3. Ultimate wettability enhancement: Acidic SiO2 nanofluid can significantly improve the wettability of coal, reducing the contact angle of coal from 99.7° in raw coal to 25.2°, a reduction of 74.5°, and the contact angle enhancement rate reaches 74.72%. This transforms the coal from hydrophobic to strongly hydrophilic, greatly enhancing the self-absorption and penetration ability of the fluid in soft coal seams.

[0022] 4. Enhanced Gas Desorption: Through the synergistic effect of the acidic environment and nanofluids, the total area of ​​absorption peaks of hydrophilic oxygen-containing functional groups such as COC and C=O in coal increases by 368.19%, enhancing the competitive adsorption advantage of water molecules. Experimental data show that this system can increase the gas desorption rate from 6.9607 mL / g with water injection to 13.2794 mL / g, significantly increasing the initial gas desorption rate and achieving a total desorption rate of 74.837%, thereby greatly improving gas extraction efficiency.

[0023] 5. Pore expansion and permeability enhancement mechanism: The acidic environment (pH=3) can effectively dissolve some minerals in coal, expand the pores and fractures of the coal body, promote the transformation of closed pores into open pores, reduce the resistance to gas flow, and, together with the fan-shaped diffusion of the spiral blades, achieve the dual treatment effect of physical impact and chemical permeability enhancement. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of the injection tube proposed in this invention; Figure 2 This is a schematic diagram of the exploded structure of the injection tube proposed in this invention; Figure 3This is a schematic cross-sectional view of the injection tube proposed in this invention; Figure 4 For the present invention Figure 3 Enlarged view of the structure of section A; Figure 5 For the present invention Figure 3 Enlarged view of the structure of section B; Figure 6 This is a schematic diagram of the assembly structure of the injection tube proposed in this invention; Figure 7 This is a schematic diagram of the assembly structure of the injection tube and the water pump proposed in this invention; Figure 8 This is a schematic diagram of the steps of the nanofluid-power ultrasound synergistic permeation enhancement system for gas control in soft, outburst-prone coal seams proposed in this invention. Figure 9 This is a schematic diagram of the steps involved in preparing the nanofluid proposed in this invention.

[0025] In the diagram: 1. Injection tube; 2. Drain hole; 3. Protective ring; 4. Connecting ring; 5. Metal head; 6. Threaded ring I; 7. Shielding ring; 8. Compression spring; 9. Connecting frame I; 10. Connecting rod; 11. Spiral blade; 12. Connecting frame II; 13. Frustum-shaped impact seat; 14. Fixed seat; 15. Annular slot; 16. Movable groove; 17. Limiting seat; 18. Frustum-shaped groove; 19. Impact ring; 20. Mounting frame; 21. Threaded section; 22. Threaded ring II; 23. Connecting hole; 24. Connecting pipe; 25. Pressure valve; 26. Water injection pump; 27. Nanofluid storage tank; 28. Directional drilling rig; 29. ​​Moisture content analyzer; 30. Gas concentration analyzer. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0027] In one embodiment: a coal seam water injection system, used to prevent coal fragments from entering the injection pipe during insertion and causing blockage, includes: an injection pipe 1, a protective ring 3, a spiral blade 11, a metal head 5, a frustum-shaped impact seat 13, a water injection pump 26, a nanofluid storage tank 27, a moisture content detector 29, and a gas concentration detector 30, etc.

[0028] refer to Figure 1-2The outer wall of the injection tube 1 has multiple sets of holes 2 arranged along its length. Each set of holes 2 has multiple holes arranged in a ring at equal intervals to ensure that the nanofluid can be ejected from different directions. The inner wall of the injection tube 1 has a movable groove 16, and the holes 2 are connected to the movable groove 16 to provide space for the movement of the protective rings 3. Multiple protective rings 3 are located inside the injection tube 1 and are respectively matched with multiple sets of holes 2. Adjacent protective rings 3 are connected by a fixed connecting frame I9 to achieve synchronous movement. The spiral plate 11 is located inside the injection tube 1, and multiple protective rings 3 are sleeved on the periphery of the spiral plate 11. When the nanofluid impacts the spiral plate 11, it can drive it to rotate, so that the nanofluid can be rotated and transported.

[0029] A metal head 5 is installed at one end of an injection tube 1. A threaded ring I6 is provided at one end of the metal head 5. A threaded section 21 is provided at one end of the inner wall of the injection tube 1. The threaded ring I6 and the threaded section 21 cooperate to realize the detachable connection between the metal head 5 and the injection tube 1.

[0030] refer to Figure 3-5 A fixing seat 14 is fixedly installed inside the injection tube 1 on the side near the metal head 5. A connecting rod 10 is fixedly installed at both ends of the spiral blade 11. The end of one of the connecting rods 10 is rotatably set with the fixing seat 14. A mounting bracket 20 is fixedly installed inside the injection tube 1 on the side near the connecting ring 4. The end of the other connecting rod 10 is rotatably set with the mounting bracket 20 to ensure that the spiral blade 11 rotates. The side of the mounting bracket 20 facing the connecting ring 4 is set as an inclined surface, which can guide the nanofluid to flow smoothly to the spiral blade 11.

[0031] A shielding ring 7 is fixedly installed on the side wall of the protective ring 3 near the metal head 5. A compression spring 8 is sleeved on the outer wall of the shielding ring 7. One end of the compression spring 8 is fixedly installed with the protective ring 3. An annular slot 15 is opened on the inner side wall of the movable groove 16. One end of the shielding ring 7 is inserted into the interior of the annular slot 15, and the other end of the compression spring 8 is fixedly installed with the inner side wall of the movable groove 16. When the injection tube 1 is not injected with nanofluid, the compression spring 8 is in its natural state, and the protective ring 3 closes the discharge hole 2 to prevent coal fragments from entering the interior of the injection tube 1.

[0032] The frustum-shaped impact seat 13 is located inside the injection tube 1. A limiting seat 17 is fixedly installed on the inner wall of the injection tube 1. The frustum-shaped impact seat 13 is located on the side of the limiting seat 17 away from the connecting ring 4, and the frustum-shaped impact seat 13 is sleeved on the outer wall of the connecting rod 10. The limiting seat 17 is sleeved on the conical surface of the frustum-shaped impact seat 13. A frustum-shaped groove 18 is opened on the side of the limiting seat 17 facing the connecting ring 4 to guide the flow of nanofluid. An integral impact ring is provided on the outer wall of the frustum-shaped impact seat 13. A connecting frame II 12 is fixedly installed between the impact ring and the adjacent protective ring 3. When the nanofluid impacts the frustum-shaped impact seat 13 and the impact ring, the protective ring 3 can be moved through the connecting frame II 12.

[0033] Water injection pump 26 is connected to one end of injection tube 1 via connecting pipe 24. A pressure valve 25 is installed on connecting pipe 24. Water injection pump 26 is connected to nanofluid storage tank 27. Nanofluid storage tank 27 is used to store prepared nanofluid. Moisture content detector 29 and gas concentration detector 30 are used to monitor the moisture content and gas concentration of coal seam in real time, providing data support for gas control.

[0034] This embodiment also provides a gas control method based on the above system, the specific steps of which are as follows: First, the nanofluid was prepared by selecting white spherical hydrophilic SiO2 nanoparticles with a particle size of 20 nm and a purity greater than 99.9%, and using deionized water with an electrical conductivity of less than 0.1 μs / cm as the base liquid. After stirring and mixing the two, the mixed solution was added to an ultrasonic vibration device, and the ultrasonic power was set to 200 W and the ultrasonic time was 20 min, so that the nanoparticles were evenly distributed in the base liquid. The preparation of the nanofluid was completed when there were no white lumpy insoluble substances in the solution. After the coal seam exploration is completed and the directional drilling rig 28 is used to complete the drilling, one end of the injection tube 1 is connected to the connecting pipe 24 of the water injection pump 26, and then it is placed into the hole. When the injection tube 1 is installed, due to the action of the compression spring 8, the protective ring 3 closes the discharge hole 2 to prevent coal fragments from entering the injection tube 1. When the injection tube 1 is placed into the coal seam fracture permeability zone, the water injection pump 26 is driven to extract the nanofluid inside the nanofluid storage tank 27 and transport it to the inside of the injection tube 1. When the nanofluid enters the injection tube 1, it impacts the end of the frustum-shaped impact seat 13 and the impact ring, causing the frustum-shaped impact seat 13 to move axially along the injection tube 1. Simultaneously, the connecting frame II 12 and connecting frame I 9 drive multiple protective rings 3 to move synchronously, causing the protective rings 3 to move out of the range of the outlet hole 2, thereby opening the outlet hole 2. The impact ring is used to increase the impact force on the frustum-shaped impact seat 13, ensuring that the injection tube 1 is in a continuously open state. Afterward, the nanofluid impacts the spiral blade 11, causing the spiral blade 11 to rotate continuously, so that the nanofluid is rotated and transported during transportation. When it is transported to the range of the outlet hole 2, it is ejected. Due to the influence of the spiral blade 11, the nanofluid injected into the coal seam diffuses in a fan shape, increasing the diffusion area in this region and improving the permeation efficiency.

[0035] To achieve effective transmission and excitation of ultrasonic waves downhole, this system also includes an ultrasonic excitation subsystem, which consists of the following core components: High-power ultrasonic generator: with a maximum output power of 18kW, used to drive the transducer.

[0036] Downhole ultrasonic transducer: It adopts a piezoelectric structure and is integrated into the injection tube 1. It can convert electrical signals into mechanical waves of axial-radial composite vibration, forming a physical excitation field that radiates outward in the radial direction.

[0037] Power supply and delivery system: including an explosion-proof transformer. Ensures stable power supply and precise delivery of the transducer to deep coal seams even in a water-filled environment.

[0038] This application can be used in the field of coalbed methane control, or in other fields applicable to this application.

[0039] In another embodiment: Reference Figure 2-3 A nanofluid-power ultrasound synergistic permeability enhancement system for the treatment of gas in soft and protruding coal seams is applied to the field of coal seam gas treatment. The structure of this embodiment is basically the same as that of the previous embodiment, except that: a connecting ring 4 is fixedly provided at the end of the injection tube 1 away from the metal head 5, and a threaded ring II 22 is fixedly provided on the side wall of the connecting ring 4. The threaded ring II 22 cooperates with the threaded section 21 inside another injection tube 1. refer to Figure 6-7 When it is necessary to extend the length of the injection tube 1, the metal head 5 on the top of one of the injection tubes 1 can be removed, and the two injection tubes 1 can be connected and assembled by the threaded ring II 22 engaging with the threaded section 21 of the other injection tube 1.

[0040] The surface of the fixing base 14 has multiple connecting holes 23 for the flow of nanofluids during the assembly of multiple injection tubes 1.

[0041] However, as is well known to those skilled in the art, the working principles and wiring methods of water injection pumps, directional drilling rigs and testing instruments are all conventional methods or common knowledge, and will not be elaborated here. Those skilled in the art can make any selections according to their needs or convenience.

[0042] The accompanying drawings in this application are for illustrative purposes only. The dimensions and shapes of the components shown are not actual limitations but are merely schematic representations. In actual implementation, the components can be reasonably configured and adjusted according to specific needs and actual conditions.

[0043] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A nanofluid-power ultrasound synergistic permeability enhancement system for gas control in soft, outburst-prone coal seams, characterized in that, include: The injection tube (1) has multiple sets of holes (2) arranged along its length on its outer wall. Each set of holes (2) consists of multiple holes arranged in a ring at equal intervals. The inner wall has a movable groove (16) that connects the holes (2) to the movable groove (16). Multiple protective rings (3) are located inside the injection tube (1) and are respectively matched with multiple sets of drainage holes (2). Adjacent protective rings (3) are fixedly connected to the connecting frame I (9). The spiral blade (11) is located inside the injection tube (1), and multiple protective rings (3) are fitted around it; A metal head (5) is attached to one end of the injection tube (1); When installing the injection tube (1), the protective ring (3) closes the drain hole (2) to prevent coal fragments from entering the injection tube (1).

2. The nanofluid-power ultrasonic synergistic permeability enhancement system for gas control in soft, outburst-prone coal seams according to claim 1, characterized in that, One end of the metal head (5) is fixed with a threaded ring I (6), and one end of the inner wall of the injection tube (1) is provided with a threaded section (21). The threaded ring I (6) is screwed to the threaded section (21). The end of the injection tube (1) away from the metal head (5) is fixed to a connecting ring (4). A threaded ring II (22) is fixed on the side wall of the connecting ring (4). The threaded ring II (22) is screwed to the threaded section (21) of another injection tube (1).

3. The nanofluid-power ultrasonic synergistic permeability enhancement system for gas control in soft, outburst-prone coal seams according to claim 2, characterized in that, The injection tube (1) is fixed to a fixing seat (14) on the side near the metal head (5), and the surface of the fixing seat (14) is provided with multiple connecting holes (23). Both ends of the spiral blade (11) are fixedly connected to connecting rods (10). The end of one connecting rod (10) is rotatably connected to the fixed seat (14), and the end of the other connecting rod (10) is rotatably connected to the mounting bracket (20) fixed inside the injection tube (1) near the connecting ring (4). The side of the mounting bracket (20) facing the connecting ring (4) is an inclined surface.

4. The nanofluid-power ultrasonic synergistic permeability enhancement system for gas control in soft, outburst-prone coal seams according to claim 3, characterized in that, A shielding ring (7) is fixedly connected to the side wall of the protective ring (3) near the metal head (5). A compression spring (8) is sleeved on the outer wall of the shielding ring (7). One end of the compression spring (8) is fixedly connected to the protective ring (3). The inner wall of the movable groove (16) is provided with an annular slot (15), one end of the shielding ring (7) is inserted into the annular slot (15), and the other end of the compression spring (8) is fixedly connected to the inner wall of the movable groove (16).

5. The nanofluid-power ultrasonic synergistic permeability enhancement system for gas control in soft, outburst-prone coal seams according to claim 4, characterized in that, It also includes a frustum-shaped impact seat (13); The inner wall of the injection tube (1) is fixed to the limiting seat (17), the frustum-shaped impact seat (13) is located on the side of the limiting seat (17) away from the connecting ring (4) and is sleeved on the outer wall of the connecting rod (10), and the limiting seat (17) is sleeved on the conical surface of the frustum-shaped impact seat (13). The outer wall of the frustum-shaped impact seat (13) is provided with an integral impact ring (19), and the impact ring (19) is fixedly connected to the adjacent protective ring (3) by a connecting frame II (12).

6. The nanofluid-power ultrasonic synergistic permeability enhancement system for gas control in soft, outburst-prone coal seams according to claim 5, characterized in that, The limiting seat (17) has a frustum-shaped groove (18) on the side facing the connecting ring (4), which is used to guide the flow of nanofluid.

7. The nanofluid-power ultrasonic synergistic permeability enhancement system for gas control in soft, outburst-prone coal seams according to claim 6, characterized in that, It also includes a water injection pump (26); The injection tube (1) has a connecting ring (4) at one end connected to a connecting tube (24), which is connected to a water pump (26). A pressure valve (25) is installed on the connecting tube (24).

8. The nanofluid-power ultrasonic synergistic permeability enhancement system for gas control in soft, outburst-prone coal seams according to claim 7, characterized in that, It also includes nanofluid storage tanks (27); The water pump (26) is connected to the nanofluid storage tank (27), and the water pump (26) is used to extract the nanofluid in the nanofluid storage tank (27).

9. The nanofluid-power ultrasonic synergistic permeability enhancement system for gas control in soft, outburst-prone coal seams according to claim 8, characterized in that, It also includes a moisture content meter (29), a gas concentration meter (30), and a directional drilling rig (28). The directional drilling rig (28) is used for drilling holes in the coal seam, and the moisture content detector (29) and gas concentration detector (30) are used to monitor coal seam parameters.

10. A gas control method based on the nanofluid-power ultrasonic synergistic permeability enhancement system for soft, outburst-prone coal seams according to any one of claims 1 to 9, characterized in that, Includes the following steps: S1. Preparation of acidic nanofluid: White spherical hydrophilic SiO2 nanoparticles with a particle size of 20 nm and a purity >99.9% were selected. Deionized water with a conductivity <0.1 μS / cm was used as the base liquid to prepare a SiO2 nanofluid solution with a mass fraction of 2.0%. Then, 0.1 mol / L glacial acetic acid solution was added to adjust the pH value of the nanofluid to 3, forming an acidic SiO2 nanofluid wetting solution. After stirring and mixing, the solution was placed in an ultrasonic vibration device with an ultrasonic power of 200 W and a time of 20 min until there were no white lumpy insoluble substances and the nanoparticles were uniformly distributed in the base liquid. S2. Use a directional drilling rig (28) to complete the drilling of the coal seam, integrate a high-power ultrasonic transducer into the injection tube (1), and connect it to the downhole ultrasonic generator through an explosion-proof transformer. After connecting the injection tube (1) to the connecting pipe (24) of the water injection pump (26), place it into the hole. At this time, the protective ring (3) closes the drainage hole (2). S3. Drive the water injection pump (26) to draw the nanofluid in the nanofluid storage tank (27) and deliver it to the injection tube (1). The nanofluid impacts the frustum-shaped impact seat (13) and impact ring (19), causing the protective ring (3) to move and open the outlet hole (2). At the same time, the impact spiral blade (11) rotates, so that the nanofluid diffuses into the coal seam in a fan shape. Simultaneously, the ultrasonic generator is activated to perform a coordinated anti-reflection operation, as follows: By powering the transducer, mechanical waves of axial-radial composite vibration are generated using the inverse piezoelectric effect. A multi-frequency synergistic strategy is employed, with the frequency setting range from 25.0 kHz to 82.5 kHz. Specifically, the cavitation effect of 25.0 kHz low-frequency ultrasound is used to enhance the development of macropores larger than 10 μm and seepage pores, while the mechanical vibration effect of 82.5 kHz high-frequency ultrasound is used to promote the connectivity between micropores and mesopores. High-power segmented operation: Set the maximum power of the ultrasonic generator to 18kW, and apply segmented ultrasonic excitation to the coal seam, with each segment lasting 120 minutes; After being injected into the coal seam, the acidic fluid undergoes a physicochemical reaction with the coal body. By utilizing the expansion effect of hydrogen ions on pores and the surface tension reduction properties of nanoparticles, the gas desorption capacity increases by more than 4.5378 mL / g compared to conventional water injection. Finally, by utilizing the "mechanical vibration-cavitation-heat" coupling effect of the ultrasonic field and the synergistic effect of the chemical modification of the acidic nanofluid, efficient displacement of coal seam gas is achieved.

Images