Ultrasonic excitation and acid fracturing integrated permeability enhancement coal seam enhanced extraction system and method

Abstract

The invention discloses an ultrasonic excitation and acid fracturing integrated permeability enhancement coal seam enhanced extraction system, comprising an ultrasonic excitation and acid fracturing integrated drilling and delivery device, an ultrasonic control box, and a mixing liquid box. The invention also discloses an ultrasonic excitation and acid fracturing integrated permeability enhancement coal seam enhanced extraction method, comprising the following steps: step S1, collecting samples in the coal seam; step S2, constructing four extraction boreholes with different distances to the coal seam; step S3, performing gas concentration detection on the extraction boreholes; step S4, starting an ultrasonic transducer, starting a fracturing pump for fracturing; starting the ultrasonic transducer again; step S5, closing the fracturing pump after repeating step S4 five times, and then starting the ultrasonic transducer; step S6, performing gas concentration detection on all extraction boreholes. The invention has the advantages of mutual coupling of ultrasonic excitation and acid fracturing, improving coal body pore structure, increasing pore and fracture connectivity, promoting gas desorption, and improving coal seam gas extraction efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of permeability enhancement coal seam extraction, and in particular relates to a permeability enhancement coal seam enhanced extraction system and method integrating ultrasonic excitation and acid fracturing. Background Art

[0002] The depth of coal mining in my country is extending at a rate of 10 to 25 meters per year, and the coal seams are showing increasingly obvious characteristics of high ground stress, strong gas adsorption and low permeability. On the other hand, my country's coal seams are affected by geological structure and geological metamorphism. Some coal bodies are soft, and the pores and cracks are often filled with some minerals, which hinder the diffusion and seepage of gas, resulting in low permeability of coal seams.

[0003] At present, hydraulic fracturing technology has been promoted and applied in coal seams. However, due to the continuous extension of coal mining depth in my country, the maximum horizontal principal stress effect is more obvious, resulting in the fact that most of the cracks generated by hydraulic fracturing extend parallel to the maximum horizontal principal stress, and it is impossible to ensure that the pressure is evenly unloaded inside the coal body, forming more blank zones. The increase in mining depth will cause the cracks generated by fracturing to close faster, and the expected extraction effect cannot be achieved. Due to the lack of full life cycle assessment of the scope of applicability and environmental effects of gas fracturing, and the limitations of the immature supporting technology during the fracturing process, gas fracturing coal seam technology is still in the experimental research stage. Although ultrasonic excitation has been used to improve the original pore fracture structure of coal seams to a certain extent, it is difficult to solve the problem of pore fractures in coal seams being filled with minerals, which easily leads to low gas extraction efficiency. Summary of the invention

[0004] The present invention aims to provide a system and method for enhancing the permeability of coal seams by integrating ultrasonic excitation and acid fracturing. The ultrasonic excitation and acid fracturing are integrated to complement each other's advantages, thereby improving the gas extraction efficiency and solving the problem that the current pores and cracks are filled with some minerals, which hinders the diffusion and seepage of gas, resulting in low permeability of coal seams and low gas extraction efficiency.

[0005] To this end, the technical solution adopted by the present invention is: an ultrasonic excitation and acid fracturing integrated permeability enhancement coal seam enhanced extraction system, including an ultrasonic excitation and acid fracturing integrated drilling and delivery device located in the extraction borehole and an ultrasonic control box and a mixing liquid box located outside the extraction borehole. The liquid inlet end of the ultrasonic excitation and acid fracturing integrated drilling and delivery device is connected to the mixing liquid box through a fracturing pump. The ultrasonic excitation and acid fracturing integrated drilling and delivery device includes a liquid inlet push rod, an ultrasonic transducer, a fracturing chamber, a conical drill bit and a plurality of mirror-symmetrically located on the left and right sides of the fracturing chamber. The openable and closable tool assembly includes a storage groove, a storage tank arranged next to the storage groove, and a The cam is provided with a toothed rack which is movable up and down on the valve core, a tool gear which is fixed at the lower left corner of the storage groove, and a tool which is fixed on the rotating shaft of the tool gear. The tool gear is meshed with the vertically movable rack of the valve core. The side of the tool away from the rotating shaft of the tool gear adopts an arc-shaped blade. The back of the tool which is recovered into the storage groove is matched with the notch of the storage groove. A reset spring connected to the blade of the tool is arranged in the center of the horizontal surface on the inner side of the storage groove. When the fracturing chamber reaches the set pressure, the vertically movable rack of the valve core moves upward, and the tool gear rotates clockwise, thereby driving the tool to open. When the fracturing chamber does not reach the set pressure, the tool is retracted into the storage groove under the pulling force of the reset spring.

[0006] As a preferred embodiment of the above scheme, six openable and closable tool assemblies are used, and the number and position of the openable and closable tool assemblies can be selected according to the coal quality solidity coefficient or the size of the directional anti-permeability area. It can be flexibly selected and adapted to various coal seam environments, with a wide range of applications.

[0007] Further preferably, the liquid inlet push rod is equipped with a high-pressure corrosion-resistant hose introduced into the fracturing chamber, the liquid inlet of the liquid inlet push rod, the fracturing pump and the mixing tank are connected by a high-pressure corrosion-resistant hose, and a regulating valve is installed between the fracturing pump and the mixing tank to facilitate the transportation of the fracturing fluid and the connection is reasonable. The ultrasonic control box is connected to the ultrasonic transducer by a cable, and the connection is reasonable.

[0008] The present invention also provides a method for enhanced extraction of coal seams by integrating ultrasonic excitation and acid fracturing, comprising the following steps:

[0009] Step S1, collecting samples from the coal seam, transporting them back to the laboratory for gas desorption tests under ultrasonic waves of different frequencies, determining the optimal frequency f1, and then performing industrial analysis, elemental analysis and mineral content analysis on the collected samples, and obtaining the optimal acid fracturing fluid ratio through theoretical analysis and experimental research;

[0010] Step S2, constructing four extraction boreholes at different distances into the coal seam, selecting one of the extraction boreholes to install any one of the above-mentioned ultrasonic excitation and acid fracturing integrated permeability enhancement coal seam enhanced extraction systems, and installing extraction screens in the remaining extraction boreholes, and connecting them to the negative pressure branch with a hose;

[0011] Step S3, performing gas concentration detection on the extraction borehole equipped with the extraction screen;

[0012] Step S4, start the ultrasonic control box to adjust the ultrasonic frequency of the ultrasonic transducer to f1, start it for 20 minutes to 30 minutes and then turn it off, then start the fracturing pump to inject the fracturing fluid in the mixing tank into the extraction borehole for fracturing; when the fracturing fluid pressure in the extraction borehole is close to the maximum horizontal stress, start the ultrasonic control box again to adjust the ultrasonic frequency of the ultrasonic transducer to f1, start it for 20 minutes to 30 minutes and then turn it off again;

[0013] Step S5, after repeating step S4 five times, turn off the fracturing pump, then start the ultrasonic control box to adjust the ultrasonic frequency of the ultrasonic transducer to f1, and turn it off after starting for 20 minutes to 30 minutes;

[0014] Step S6: After the ultrasonic excitation and acid fracturing integrated permeability enhancement coal seam enhanced extraction system is extracted, the extraction boreholes there are connected to the negative pressure branch with a hose, and the gas concentration of all the extraction boreholes is tested.

[0015] As a preferred embodiment of the above scheme, in step S1, the theoretical analysis and experimental research process for obtaining the optimal acid fracturing fluid ratio is to first test the original permeability of the sample as a reference, then select the acid according to the type of minerals in the coal body, and then determine the mass fraction of the required acid according to the mineral content in the test results and the chemical reaction ratio of the minerals. Finally, based on the mineral content in the coal seam and the relative proportion of the mineral components, and taking into account the actual pre-pumping and permeability enhancement time of the coal seam, design a coal powder dissolution test and a permeability test, so as to obtain the optimal ratio of acid fracturing fluid, and the design steps are reasonable.

[0016] It is further preferred that capsules are used to seal the extraction borehole openings on which the extraction screen is installed, so as to effectively avoid gas overflow during gas extraction, reduce safety hazards, and ensure the accuracy of gas concentration detection data.

[0017] Further preferably, the method further includes step S7, replacing clean water in the mixing tank, starting the fracturing pump, and cleaning the pump body and the ultrasonic excitation and acid fracturing integrated permeability enhancement coal seam enhanced extraction system to effectively prevent the acid remaining inside the fracturing equipment from corroding the equipment and ensure the service life of the equipment.

[0018] It is further preferred that in step S2, the second extraction borehole from left to right is used to install an ultrasonic excitation and acid fracturing integrated permeability enhancement system for coal seams, and the first, third and fourth extraction boreholes are 10m, 20m and 40m away from the second extraction borehole, respectively, so as to perform concentration detection on coal seam gas at three distances around the ultrasonic excitation and acid fracturing integrated permeability enhancement system for coal seams, thereby understanding the gas radiation distance affected by ultrasonic excitation and acid fracturing, and the design is reasonable.

[0019] It is further preferred that in step S4, when the coal quality solidity coefficient is less than 1.5, only two openable and closable tool assemblies are retained for operation; when directional anti-permeability is performed on a set area, the openable and closable tool assembly close to the area is retained for operation, and the design is reasonable.

[0020] Beneficial effects of the present invention:

[0021] (1) Compared with the existing pores and cracks filled with some minerals, which hinder the diffusion and seepage of gas, this scheme adopts a combination of ultrasonic excitation and acid fracturing. Ultrasonic excitation disturbs the original stress field by generating mechanical vibration. Under the action of vibration, the pore pressure and structure of the coal body are constantly changing, and micro-cracks are generated inside the coal body, which accelerates the desorption of coal seam gas and forms a large amount of free gas. However, the inner surface and cracks of the coal seam contain a large amount of minerals, which will seriously affect the flow of gas. Therefore, acid fracturing is used to continuously dissolve the minerals inside the pores and cracks to dredge the gas. Flow channels increase the permeability of coal seams. The original cracks under acid fracturing are connected with the cracks generated by ultrasonic excitation, further forming a complex seepage network channel, and a large amount of free gas generated by ultrasonic excitation flows into the extraction borehole through the fracture network. The mutual coupling of ultrasonic excitation and acid fracturing greatly improves the pore structure of the coal body, increases the connectivity of pores and fractures, promotes gas desorption, avoids the influence of principal stress effect, and produces a complex fracture network. The permeability of coal seams is effectively improved, and the efficiency of coal seam gas extraction is improved. The design idea is novel and the conception is ingenious.

[0022] (2) Construct four extraction boreholes at different distances from the coal seam to measure the influence of gas concentration in the extraction boreholes at different distances. Before and after the ultrasonic excitation and acid fracturing coupling effect is performed on the selected extraction borehole, the gas concentration in other extraction boreholes is detected to fully understand the radiation distance of the permeability-enhanced coal seam. After repeating step S4 five times, the fracturing pump is turned off, and then the ultrasonic control box is started to adjust the ultrasonic transducer for separate excitation, so that the acid fracturing fluid can further fully react with the minerals, improve the permeability of the coal seam, and ensure the permeability-enhancing effect of the coal seam. When the fracturing fluid pressure in the extraction borehole approaches the maximum horizontal stress, the ultrasonic control box is started again. Because exceeding the maximum horizontal stress will easily generate tensile cracks, and tensile cracks are easy to close. Therefore, fracturing close to the maximum horizontal stress can allow secondary cracks and primary cracks to fully communicate with each other, resulting in shear or difficult-to-close cracks.

[0023] (3) An integrated ultrasonic excitation and acid fracturing permeability enhancement system for coal seam enhanced extraction is used to realize the combination of ultrasonic excitation and acid fracturing. When the fracturing chamber reaches the set pressure, the vertical movable rack of the valve core moves upward, and the tool gear rotates clockwise, thereby driving the tool to open. When the fracturing chamber does not reach the set pressure, the tool is stored in the storage groove under the pullback force of the reset spring. When the set pressure is not reached, the downward movement force of the vertical movable rack of the valve core is less than the pullback force of the reset spring. The design is reasonable and the structure is interlocking. The side of the tool away from the rotating axis of the tool gear adopts an arc-shaped blade to ensure safe use. After opening, the blade cuts the coal seam on the inner wall of the extraction borehole, thereby further increasing the fracture surface and ensuring that the free gas will eventually flow into the extraction borehole through the fracture network. The back of the tool fits with the notch of the storage groove to reduce the overflow of the fracturing fluid. The flat and long shape of the tool is easy to hold pressure and not easy to block. The design is reasonable.

[0024] (4) The ultrasonic control box is used to control the ultrasonic frequency of the ultrasonic transducer and provide ultrasonic excitation. The mixing box is used to inject acidic fracturing fluid into the extraction borehole to dissolve the minerals inside the hole and fissure. The liquid push rod is used to ensure that the fracturing cavity can penetrate deep into the extraction borehole. The conical drill bit is used to break large coal slag fragments during installation and drilling. The design structure is reasonable and the practical value is high.

[0025] In summary, the present invention has the advantages of mutual coupling of ultrasonic excitation and acid fracturing, improving coal body pore structure, increasing pore and fracture connectivity, promoting gas desorption, improving coal seam gas extraction efficiency, and having an interlocking structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the installation and use of the present invention.

[0027] Figure 2 This is a schematic diagram of the structure of an integrated drilling and delivery device for acid fracturing.

[0028] Figure 3 It is a schematic diagram of the structure of the openable and closable tool assembly. DETAILED DESCRIPTION

[0029] The present invention will be further described below by way of embodiments and in conjunction with the accompanying drawings:

[0030] Combination Figure 1 — Figure 3 As shown, an ultrasonic excitation and acid fracturing integrated permeability enhancement coal seam enhanced extraction system is composed of an ultrasonic excitation and acid fracturing integrated drilling and delivery device a located in the extraction borehole 2 and an ultrasonic control box 6 and a mixing liquid box 8 located outside the extraction borehole 2.

[0031] The liquid inlet end of the ultrasonic excitation and acid fracturing integrated drilling and delivery device a is connected to the mixing box 8 through the fracturing pump 7.

[0032] The ultrasonic excitation and acid fracturing integrated drilling and delivery device a is composed of a liquid inlet push rod a5, an ultrasonic transducer a1, a fracturing chamber a2, a conical drill bit a4 and a plurality of openable and closable tool assemblies a3 which are arranged in sequence from left to right and are mirror-symmetrically located on the left and right sides of the fracturing chamber a2.

[0033] The liquid inlet push rod a5 is internally provided with a high-pressure corrosion-resistant hose 9 which is introduced into the fracturing chamber a2.

[0034] The liquid inlet of the liquid inlet push rod a5, the fracturing pump 7 and the liquid mixing box 8 are all connected by a high-pressure corrosion-resistant hose 9.

[0035] A regulating valve 4 is installed between the fracturing pump 7 and the mixing tank 8 .

[0036] The ultrasonic control box 6 is connected to the ultrasonic transducer a1 through a cable.

[0037] The openable and closable tool assembly a3 consists of a storage groove a31, a valve core vertical movable rack a32 arranged beside the storage groove a31 and movable up and down, a tool gear a33 fixed at the lower left corner of the storage groove a31, and a tool a34 fixed on the rotating shaft of the tool gear a33.

[0038] The tool gear a33 is meshed with the valve core vertical movable rack a32.

[0039] The side of the tool a34 away from the rotation axis of the tool gear a33 adopts an arc-shaped blade, and the back of the tool a34 collected in the receiving groove a31 fits with the notch of the receiving groove a31.

[0040] A return spring a35 connected to the blade of the tool a34 is provided in the center of the inner horizontal surface of the storage groove a31.

[0041] When the fracturing chamber a2 reaches the set pressure, the vertical movable rack a32 of the valve core moves upward, and the tool gear a33 rotates clockwise, thereby driving the tool a34 to open.

[0042] When the fracturing chamber a2 does not reach the set pressure, the tool a34 is retracted into the receiving groove a31 under the pulling force of the return spring a35.

[0043] It is preferred that six openable and closable tool assemblies a3 are used, and the number and position of the openable and closable tool assemblies a3 can be selected according to the coal quality solidity coefficient or the size of the directional anti-permeability area.

[0044] A conical drill bit a4 is installed at the right end of the fracturing chamber a2.

[0045] A method for enhancing the permeability of coal seams by integrating ultrasonic excitation and acid fracturing, the specific implementation steps are as follows:

[0046] Step S1, collect samples from the coal seam 1, transport them back to the laboratory for gas desorption tests under ultrasonic waves of different frequencies, determine the optimal frequency f1, and then perform industrial analysis, elemental analysis and mineral content analysis on the collected samples, and obtain the optimal acid fracturing fluid ratio through theoretical analysis and experimental research.

[0047] In step S1, the theoretical analysis and experimental research process for obtaining the optimal acid fracturing fluid ratio is to first test the original permeability of the sample as a reference, then select the acid according to the type of minerals in the coal body, and then determine the mass fraction of the required acid according to the mineral content in the test results and the chemical reaction ratio of the minerals. Finally, based on the mineral content in the coal seam and the relative content of the mineral components, and taking into account the actual pre-pumping and permeability enhancement time of the coal seam, design the coal powder dissolution test and the permeability test, so as to obtain the optimal ratio of acid fracturing fluid.

[0048] Step S2, constructing four extraction boreholes 2 at different distances to the coal seam 1, selecting one of the extraction boreholes 2 to install any of the above-mentioned ultrasonic excitation and acid fracturing integrated permeability enhancement coal seam enhanced extraction systems, the ultrasonic transducer a1 is connected to the ultrasonic control box 6 located outside the extraction borehole 2 through a cable, the fracturing chamber a2 is connected to the mixing box 8 located outside the extraction borehole 2 through a fracturing pump 7, and the remaining extraction boreholes 2 are installed with extraction screens 3, and are connected to the negative pressure branch 11 with a hose 10;

[0049] In step S2, the second extraction borehole 2 from left to right is installed with an ultrasonic excitation and acid fracturing integrated permeability enhancement coal seam extraction system, and the first, third and fourth extraction boreholes 2 are 10m, 20m and 40m away from the second extraction borehole 2 respectively.

[0050] Step S3, performing gas concentration detection on the extraction borehole 2 installed with the extraction screen 3;

[0051] Step S4, start the ultrasonic control box 6 to adjust the ultrasonic frequency of the ultrasonic transducer a1 to f1, start it for 20min to 30min and then turn it off, then start the fracturing pump 7 to inject the fracturing fluid in the mixing tank 8 into the extraction borehole 2 for fracturing; when the fracturing fluid pressure in the extraction borehole 2 is close to the maximum horizontal stress, start the ultrasonic control box 6 again to adjust the ultrasonic frequency of the ultrasonic transducer a1 to f1, start it for 20min to 30min and then turn it off again;

[0052] In step S4, when the coal quality solidity coefficient is less than 1.5, only two openable and closable tool assemblies a3 are retained to work; when directional anti-reflection is performed on a specific area, the openable and closable tool assembly a3 close to the area is retained to work.

[0053] Step S5, after repeating step S4 five times, turn off the fracturing pump 7, then start the ultrasonic control box 6 to adjust the ultrasonic frequency of the ultrasonic transducer a1 to f1, and turn it off after 20 minutes to 30 minutes;

[0054] Step S6, after the ultrasonic excitation and acid fracturing integrated permeability enhancement coal seam enhanced extraction system is extracted, the extraction borehole 2 at the location is connected to the negative pressure branch 11 with a hose 10, and the gas concentration of all the extraction boreholes 2 is tested.

[0055] The capsule 5 is used to seal the opening of the extraction borehole 2 installed with the extraction screen tube 3.

[0056] Step S7, replace the mixed liquid box 8 with clean water, start the fracturing pump 7, and then clean the pump body and the ultrasonic excitation and acid fracturing integrated permeability enhancement coal seam enhanced extraction system.

Claims

1. An ultrasonic excitation and acid fracturing integrated permeability enhancement coal seam enhanced extraction system, characterized by: The invention comprises an ultrasonic excitation and acid fracturing integrated drilling and delivery device (a) located in a drainage borehole (2) and an ultrasonic control box (6) and a liquid mixing box (8) located outside the drainage borehole (2). The liquid inlet end of the ultrasonic excitation and acid fracturing integrated drilling and delivery device (a) is connected to the liquid mixing box (8) via a fracturing pump (7). The ultrasonic excitation and acid fracturing integrated drilling and delivery device (a) comprises a liquid inlet push rod (a5), an ultrasonic transducer (a1), a fracturing chamber (a2), a conical drill bit (a4), and a plurality of openable and closable tool assemblies (a3) ​​arranged in sequence from left to right and located on the left and right sides of the fracturing chamber (a2) in a mirror-symmetrical manner. The openable and closable tool assembly (a3) ​​comprises a receiving groove (a31), a valve core vertically movable rack (a32) arranged on the side of the receiving groove (a31) and movable up and down, and a tool gear (a33) fixed at the lower left corner of the receiving groove (a31). ) and a cutter (a34) fixed on the rotating shaft of the cutter gear (a33), the cutter gear (a33) meshes with the vertical movable rack (a32) of the valve core, the side of the cutter (a34) away from the rotating shaft of the cutter gear (a33) adopts an arc-shaped blade, the back of the cutter (a34) collected in the receiving groove (a31) fits with the notch of the receiving groove (a31), and a return spring (a35) connected to the blade of the cutter (a34) is provided in the center of the horizontal surface inside the receiving groove (a31); when the fracturing chamber (a2) reaches the set pressure, the vertical movable rack (a32) of the valve core moves upward, and the cutter gear (a33) rotates clockwise, thereby driving the cutter (a34) to open; when the fracturing chamber (a2) does not reach the set pressure, the cutter (a34) is retracted into the receiving groove (a31) under the pulling force of the return spring (a35).

2. The ultrasonic excitation and acid fracturing integrated permeability enhancement coal seam enhanced extraction system according to claim 1, characterized in that: The number of the openable and closable tool assemblies (a3) ​​is six, and the number and position of the openable and closable tool assemblies (a3) ​​can be selected according to the coal quality solidity coefficient or the size of the directional permeability enhancement area.

3. The ultrasonic excitation and acid fracturing integrated permeability enhancement coal seam enhanced extraction system according to claim 1, characterized in that: The liquid inlet push rod (a5) is internally provided with a high-pressure corrosion-resistant rubber hose (9) for introducing into the fracturing chamber (a2); the liquid inlet of the liquid inlet push rod (a5), the fracturing pump (7), and the liquid mixing box (8) are all connected via the high-pressure corrosion-resistant rubber hose (9); a regulating valve (4) is installed between the fracturing pump (7) and the liquid mixing box (8); and the ultrasonic control box (6) is connected to the ultrasonic transducer (a1) via a cable.

4. A method for enhanced extraction of coal seams by integrating ultrasonic excitation and acid fracturing, characterized in that: The following steps are involved: Step S1: Collect samples from the coal seam (1) and transport them back to the laboratory for gas desorption tests under ultrasonic waves of different frequencies to determine the optimal frequency. f 1. Then conduct industrial analysis, element analysis and mineral content analysis on the collected samples, and obtain the optimal acid fracturing fluid ratio through theoretical analysis and experimental research; Step S2, constructing four extraction boreholes (2) at different distances from the coal seam (1), selecting one of the extraction boreholes (2) to install an ultrasonic excitation and acid fracturing integrated permeability enhancement coal seam extraction system as described in any one of claims 1 to 3, and installing extraction screens (3) in the remaining extraction boreholes (2), and connecting them to the negative pressure branch (11) with a hose (10); Step S3, performing gas concentration detection on the extraction borehole (2) equipped with the extraction screen tube (3); Step S4, start the ultrasonic control box (6) to adjust the ultrasonic frequency of the ultrasonic transducer (a1) to f 1. After starting for 20 to 30 minutes, shut down, and then start the fracturing pump (7) to inject the fracturing fluid in the mixing tank (8) into the extraction borehole (2) for fracturing; when the fracturing fluid pressure in the extraction borehole (2) approaches the maximum horizontal stress, start the ultrasonic control box (6) again to adjust the ultrasonic frequency of the ultrasonic transducer (a1) to f 1. Turn it off again after 20 to 30 minutes of starting; Step S5, after repeating step S4 five times, turn off the fracturing pump (7), then start the ultrasonic control box (6) to adjust the ultrasonic frequency of the ultrasonic transducer (a1) to f 1. Turn off after 20 to 30 minutes of startup; Step S6: After the ultrasonic excitation and acid fracturing integrated permeability enhancement coal seam enhanced extraction system is extracted, the extraction borehole (2) at the location is connected to the negative pressure branch (11) using a hose (10), and gas concentration detection is performed on all the extraction boreholes (2).

5. The method for enhanced coal seam extraction by integrating ultrasonic excitation and acid fracturing according to claim 4, characterized in that: In step S1, the theoretical analysis and experimental research process for obtaining the optimal acid fracturing fluid ratio is to first test the original permeability of the sample as a reference, then select the acid according to the type of minerals in the coal body, and then determine the mass fraction of the required acid according to the mineral content in the test results and the chemical reaction ratio of the minerals. Finally, based on the mineral content in the coal seam and the relative content of the mineral components, and taking into account the actual pre-pumping and permeability enhancement time of the coal seam, design a coal powder dissolution test and a permeability test, so as to obtain the optimal ratio of acid fracturing fluid.

6. The method for enhanced coal seam extraction by integrating ultrasonic excitation and acid fracturing according to claim 4, characterized in that: The opening of the extraction borehole (2) on which the extraction screen tube (3) is installed is sealed using a capsule (5).

7. The method for enhanced coal seam extraction by integrating ultrasonic excitation and acid fracturing according to claim 4, characterized in that: The method further comprises step S7, replacing clean water in the mixing liquid box (8), starting the fracturing pump (7), and then cleaning the pump body and the ultrasonic excitation and acid fracturing integrated permeability-enhancing coal seam enhanced extraction system.

8. The method for enhanced coal seam extraction by integrating ultrasonic excitation and acid fracturing according to claim 4, characterized in that: In step S2, the second extraction borehole (2) from left to right is used to install an ultrasonic excitation and acid fracturing integrated permeability enhancement coal seam extraction system, and the first, third and fourth extraction boreholes (2) are 10m, 20m and 40m away from the second extraction borehole (2), respectively.

9. The method for enhanced coal seam extraction by integrating ultrasonic excitation and acid fracturing according to claim 4, characterized in that: In the step S4, when the coal quality solidity coefficient is less than 1.5, only two openable and closable tool assemblies (a3) ​​are retained to work; when directional anti-reflection is performed on a specific area, the openable and closable tool assembly (a3) ​​close to the area is retained to work.

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