An acid-base solution impact fracturing coal body gas extraction device and method

Abstract

The application discloses an acid-alkali solution impact fracturing coal body gas extraction device and method, acid liquid containing fissure support balls is first injected into a permeability hole to perform pulsating fracturing, the acid liquid can corrode and dissolve the coal body and has an impact effect during fracturing, the fissure is cracked along the coal body weak surface, and the fissure support balls enter the fissure to support the fissure after the fissure is generated, and the acid liquid is discharged; then, alkali liquid is injected into the borehole, part of the alkali liquid is neutralized with the residual acid liquid, the remaining alkali liquid further impacts and corrodes and dissolves minerals in the coal body, and the alkali liquid makes the micropores of the fissure support balls unobstructed, and then the alkali liquid enters the fissure support balls through the micropores and has an exothermic reaction with calcium oxide, the temperature in the fissure continuously rises, the impact and corrosion and dissolution of the alkali liquid are further improved, the effect of fracturing the coal body is improved, the coal body permeability pressure relief is fully realized, the fissure network closure is delayed, the permeability effect is effectively improved, and the gas extraction efficiency is ensured.

Description

Technical Field

[0001] This invention relates to an enhanced gas extraction device and method, specifically an enhanced gas extraction device and method for coal seams fractured by acid and alkali solution impact. Background Technology

[0002] my country's coal mines have complex geological conditions, with high-gas coal seams accounting for 50% to 70%, and high-gas, low-permeability coal seams making up about 70% of the high-gas coal seams. Furthermore, the high-gas, low-permeability coal seams in my country are characterized by microporosity, low permeability, and high adsorption. This geological condition often leads to large-scale gas outbursts during mining, especially with the increasing efficiency and depth of coal production, resulting in larger gas outbursts and a more serious threat of gas explosions and outbursts. Pre-drainage of gas from undepressurized coal seams in poorly permeable mines is often ineffective; therefore, improving coal permeability to enhance gas drainage is crucial. Hydraulic fracturing technology, as a hydraulic permeability enhancement measure, has been widely used in coal mines; however, existing hydraulic fracturing technologies suffer from unstable effects, insufficient depressurization, and the tendency for fractures to close automatically under ground stress, severely impacting the effectiveness of hydraulic fracturing. Therefore, it is urgent to improve the permeability enhancement effect of hydraulic fracturing to strengthen gas drainage. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides an acid-base solution-induced fracturing coal seam enhanced gas extraction device and method. Through the combined action of acid, alkali and fracture support balls, the coal seam is sufficiently permeable and depressurized, and the closure of the fracture network is delayed, effectively improving the permeability and ensuring gas extraction efficiency.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is: an acid and alkali solution impact-induced fracture coal body enhanced gas extraction device, comprising a fracture support ball container, a pulse pump, a storage tank, an acid tank, an alkali tank, a first water pump and a second water pump;

[0005] The outlet of the fissure-supported spherical container is connected to one port of the second tee connector via a third pipe. The other two ports of the second tee connector are connected to one end of the fourth pipe and one end of the second pipe, respectively. The other end of the fourth pipe is connected to the outlet of the pulse pump. The other end of the second pipe is connected to one port of the first tee connector. The other two ports of the first tee connector are connected to one end of the first pipe and one end of the twelfth pipe, respectively. The other end of the twelfth pipe is connected to the inlet of the second water pump. The outlet of the second water pump is connected to one port of the third tee connector via an eleventh pipe. The other two ports of the third tee connector are connected to the first inlet of the acid tank and the first inlet of the alkali tank via the ninth pipe and the tenth pipe, respectively.

[0006] The storage tank is equipped with an inlet, an outlet, an acid reflux port, and an alkali reflux port. The inlet of the pulse pump is connected to the outlet of the storage tank through a fifth pipeline. The inlet of the storage tank is connected to the outlet of the first water pump. The first inlet of the first water pump is connected to the outlet of the acid tank through an eighth pipeline. The second inlet of the first water pump is connected to the outlet of the alkali tank through a seventh pipeline. The acid reflux port of the storage tank is connected to the second inlet of the acid tank through an acid discharge pipe. The alkali reflux port of the storage tank is connected to the second inlet of the alkali tank through an alkali discharge pipe.

[0007] Initially, the fracture support ball container contains multiple fracture support balls, the acid tank contains acid, the alkali tank contains alkali, and the storage tank is empty.

[0008] Furthermore, the fracture support sphere has an internal spherical hollow structure, and multiple micropores are formed on its outer shell. These micropores are radially and uniformly distributed around the center of the sphere, and each micropore is sealed with an acid-resistant but not alkali-resistant material. The spherical hollow structure is filled with calcium oxide powder. This structure not only supports the generated fractures to prevent them from automatically closing under ground stress, but also provides heat energy for subsequent alkaline solution injection, further improving the fracturing effect of the alkaline solution.

[0009] Furthermore, the diameter of the spherical hollow structure is 2 / 3 to 4 / 5 of the diameter of the fissure support sphere, the pore size of each micropore is 1 mm to 2 mm, the number of micropores on the outer shell of the fissure support sphere is 6 to 9 per square centimeter, and the volume of calcium oxide is 2 / 3 to 3 / 4 of the volume of the spherical hollow structure.

[0010] Furthermore, a pressure gauge is installed on the first pipeline, and a check valve is installed on the sixth pipeline. The pressure gauge is used to monitor the pressure inside the permeability enhancement orifice, and the check valve ensures that the acid or alkali solution can only flow in one direction when the first pump injects acid or alkali solution into the storage tank, preventing backflow of acid or alkali solution when injection stops.

[0011] Furthermore, the first pipeline is equipped with a first control valve, the third pipeline with a second control valve, the fifth pipeline with a third control valve, the alkali discharge pipe with a fourth control valve, the seventh pipeline with a fifth control valve, the eighth pipeline with a sixth control valve, the ninth pipeline with a seventh control valve, the tenth pipeline with an eighth control valve, the eleventh pipeline with a ninth control valve, the twelfth pipeline with a tenth control valve, and the acid discharge pipe with an eleventh control valve. These control valves are configured to allow for the corresponding function to be achieved by opening each valve under different circumstances.

[0012] Furthermore, all components are coated with an acid- and alkali-resistant coating at the points where they come into contact with acid or alkali solutions during use. This design extends the service life of each component and reduces the frequency of maintenance.

[0013] The working method of the above-mentioned acid-base solution impact-induced fracturing coal seam enhanced gas extraction device includes the following specific steps:

[0014] A. Construct permeability enhancement holes according to the coal seam permeability enhancement design, and use high-pressure capsules for sealing to ensure that the borehole can withstand 40-50MPa water pressure after sealing. The inner surface of the capsule is coated with an acid and alkali corrosion resistant coating, and one end of the sealing tube is passed through the high-pressure capsule and extended into the permeability enhancement hole.

[0015] B. Assemble the acid and alkali solution impact-induced fracturing coal body enhanced gas extraction device, and connect the other end of its first pipeline to the end of the sealing pipe outside the permeability enhancement hole, and initially all control valves are in the closed state.

[0016] C. When co-injecting acid and fracture support balls, first open the sixth control valve and start the first pump. The first pump injects acid from the acid tank into the storage tank through the eighth and sixth pipelines. After a period of time, close the sixth control valve and stop the first pump. Then, open the third and first control valves and start the pulse pump. The pulse pump pulsates acid from the storage tank through the second, first, and sealing pipes into the permeability enhancement hole. Control the pulsation pressure at 35–40 MPa and the pulsation frequency at [missing value]. 200-250Hz; Simultaneously open the second control valve, and the fracture support ball is discharged from the fracture support ball container into the second pipeline, and enters the permeability enhancement hole with the pulsating acid; Continuously observe the pressure gauge reading. When the pressure gauge shows a sudden drop in the acid pressure in the permeability enhancement hole, it indicates that under the corrosive dissolution and impact of the pulsating acid, the fracture opens along the weak surface of the coal body. Then, the acid and fracture support ball will enter the fracture. At this time, the fracture support ball fills and supports the fracture to prevent the fracture from closing automatically under the action of ground stress.

[0017] D. Close the third control valve and the first control valve and stop the pulse pump. Let it stand for 18-24 hours. The acid in the permeability enhancement pore will continue to dissolve and erode the cement, minerals and blockages in the coal body, and further improve the permeability of the coal body.

[0018] E. Open the tenth, ninth, and seventh control valves and start the second water pump. The acid in the permeation hole is drawn out by the suction of the second water pump and injected into the acid tank after passing through the first, twelfth, eleventh, and ninth pipelines. After all the acid has been extracted, close the tenth, ninth, and seventh control valves and stop the second water pump. Then open the eleventh control valve to return the remaining acid in the storage tank to the acid tank through the acid discharge pipe, completing the acid recovery work. Then close the eleventh control valve.

[0019] F. Open the fifth control valve and start the first water pump. The first water pump injects the alkali solution in the alkali tank into the storage tank through the seventh and sixth pipelines. After a period of time, close the fifth control valve and stop the first water pump. Then, open the third and first control valves and start the pulse pump. The pulse pump pulsates the alkali solution from the storage tank through the second pipeline, the first pipeline, and the sealing pipe into the anti-permeability hole. Part of the alkali solution entering the anti-permeability hole reacts and neutralizes with the residual acid solution in the anti-permeability hole. Control the pulsation pressure at 20-25 MPa and the pulsation frequency at 100-150 Hz. The pulsating alkali solution acts as a corrosive, dissolving, and impact agent. The process involves pulsating the already formed fracture network for 5–10 hours to further expand and develop the fracture network. After this time, the third and first control valves are closed, and the pulsating pump is stopped. The mixture is then left to stand for 12–18 hours. The alkaline solution further dissolves the minerals in the coal body. Simultaneously, because the micropore sealing material of the fracture support ball is acid-resistant but not alkali-resistant, the alkaline solution corrodes and dissolves the sealing material, making the micropores of the fracture support ball unobstructed. The alkaline solution then enters the fracture support ball through each micropore and reacts exothermically with calcium oxide, causing the temperature inside the fracture to rise continuously. This further enhances the synergistic effect of the alkaline solution's impact and corrosion-dissolution on the fractured coal body.

[0020] G. Open the tenth, ninth, and eighth control valves and start the second water pump. The acid solution in the permeation hole is drawn out from the permeation hole by the suction of the second water pump, and then injected into the alkali tank after passing through the first, twelfth, eleventh, and tenth pipelines. After all the alkali solution has been extracted, close the tenth, ninth, and eighth control valves and stop the second water pump. Then open the fourth control valve to return the remaining alkali solution in the storage tank to the alkali tank through the alkali discharge pipe, completing the alkali recovery work, and then close the fourth control valve.

[0021] H. Disconnect the first pipeline from the sealing pipe and connect the sealing pipe to the underground gas extraction network to begin gas extraction. During continuous extraction, stop extraction when the extracted gas concentration is below 30%, and repeat steps B to G before extracting gas again. Repeat this cycle until the gas content of the coal body meets the requirements for safe mining.

[0022] Furthermore, the pH value of the acid solution is 2.5 to 4.5, and the pH value of the alkaline solution is 11 to 12.

[0023] Compared with existing technologies, this invention injects acid containing fracture support balls into the enhanced permeability borehole for pulsating fracturing. During fracturing, the acid corrodes, dissolves, and impacts the coal body, while the fracture support balls, due to inertia, impact the coal body. The two work together to cause fractures to open along the weak surfaces of the coal body. After the fractures are formed, the fracture support balls enter the fractures to support them and delay their closure. At the same time, the acid entering the fractures dissolves and corrodes cementitious materials, minerals in the pores and fractures, and blockages in the coal body, further improving the permeability of the coal body. After completion, the borehole pressure is slowly reduced and the acid is slowly discharged for reuse. Next, alkaline solution is injected into the borehole. Part of the alkaline solution neutralizes the remaining acid, increasing the temperature within the permeability-enhancing hole and facilitating subsequent permeability enhancement. The remaining alkaline solution further impacts and corrodes, dissolving minerals within the coal seam. Since the micropore sealing material of the fracture support ball is acid-resistant but not alkali-resistant, the alkaline solution corrodes and dissolves this material, opening the micropores of the fracture support ball. The alkaline solution then enters the fracture support ball through these micropores, reacting exothermically with calcium oxide. This continuously increases the temperature within the fracture, further enhancing the synergistic effect of the alkaline solution's impact and corrosion on the fractured coal seam, and accelerating gas desorption. Due to the presence of micropores in the fracture support ball, even if the fracture partially closes during subsequent extraction, multiple micropores ensure unobstructed gas flow channels. Therefore, through the synergistic effects of the fracture support ball and acid, as well as the synergistic effects of the fracture support ball and alkaline solution, the combined effect of acid, alkaline solution, and fracture support ball is achieved. This ensures sufficient permeability enhancement and pressure relief of the coal seam, delays fracture network closure, effectively improves permeability, and guarantees gas extraction efficiency. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the layout of the device of the present invention;

[0025] Figure 2 This is a schematic diagram showing the distribution of the crack support spheres after they enter the crack in this invention;

[0026] Figure 3 This is a schematic diagram of the structure of the fissure-supported sphere in this invention.

[0027] In the diagram: 1. Weak surface of coal seam; 2. Coal seam; 3. Permeability enhancement hole; 4. Sealing section; 5. Sealing pipe; 6. First pipeline; 7. Pressure gauge; 8. First tee joint; 9. First control valve; 10. Second pipeline; 11. Second tee joint; 12. Second control valve; 13. Third pipeline; 14. Fracture-supported spherical container; 15. Fourth pipeline; 16. Pulsating pump; 17. Fifth pipeline; 18. Third control valve; 19. Storage tank; 20. Fourth control valve; 21. Alkali discharge pipe; 22. Sixth pipeline; 23. Check valve; 24. First water pump; 25. 5. Control valve; 26. Seventh pipeline; 27. Alkali tank; 28. Sixth control valve; 29. ​​Eighth pipeline; 30. Acid tank; 31. Seventh control valve; 32. Ninth pipeline; 33. Tenth pipeline; 34. Eighth control valve; 35. Third tee joint; 36. Ninth control valve; 37. Eleventh pipeline; 38. Second water pump; 39. Twelfth pipeline; 40. Tenth control valve; 41. Acid discharge pipe; 42. Eleventh control valve; 43. Crack; 44. Crack support ball; 44-1. Micropore; 44-2. Outer shell; 44-3. Calcium oxide powder. Detailed Implementation

[0028] The present invention will be further described below.

[0029] like Figure 1 As shown, an enhanced gas extraction device for coal seam fractured by acid and alkali solution impact includes a fracture support ball container 14, a pulse pump 16, a storage tank 19, an acid tank 30, an alkali tank 27, a first water pump 24, and a second water pump 38.

[0030] The outlet of the fissure support ball container 14 is connected to one port of the second tee connector 11 via the third pipe 13. The other two ports of the second tee connector 11 are connected to one end of the fourth pipe 15 and one end of the second pipe 10, respectively. The other end of the fourth pipe 15 is connected to the outlet of the pulse pump 16. The other end of the second pipe 10 is connected to one port of the first tee connector 8. The other two ports of the first tee connector 8 are connected to one end of the first pipe 6 and one end of the twelfth pipe 39, respectively. The other end of the twelfth pipe 39 is connected to the inlet of the second water pump 38. The outlet of the second water pump 38 is connected to one port of the third tee connector 35 via the eleventh pipe 37. The other two ports of the third tee connector 35 are connected to the first inlet of the acid tank 30 and the first inlet of the alkali tank 27 via the ninth pipe 32 and the tenth pipe 33, respectively.

[0031] The storage tank 19 is provided with an inlet, an outlet, an acid reflux port, and an alkali reflux port. The inlet of the pulse pump 16 is connected to the outlet of the storage tank 19 through the fifth pipeline 17. The inlet of the storage tank 19 is connected to the outlet of the first water pump 24. The first inlet of the first water pump 24 is connected to the outlet of the acid tank 30 through the eighth pipeline 29. The second inlet of the first water pump 24 is connected to the outlet of the alkali tank 27 through the seventh pipeline 26. The acid reflux port of the storage tank 19 is connected to the second inlet of the acid tank 30 through the acid discharge pipe 41. The alkali reflux port of the storage tank 19 is connected to the second inlet of the alkali tank 27 through the alkali discharge pipe 21. A pressure gauge 7 is installed on the first pipeline 6, and a check valve 23 is installed on the sixth pipeline 22. Pressure gauge 7 is set to monitor the pressure in the permeability enhancement hole 3. Check valve 23 is set to allow only unidirectional flow when the first water pump 24 injects acid or alkali into the storage tank 19, preventing backflow of acid or alkali when injection stops.

[0032] Initially, the fracture support sphere container 14 contains multiple fracture support spheres 44, the acid tank 30 contains acid, the alkali tank 27 contains alkali, and the storage tank 19 is empty; Figure 3 As shown, the fracture support ball 44 has a spherical hollow structure inside. Multiple micropores 44-1 are formed on the outer shell 44-2 of the fracture support ball 44. These micropores 44-1 are radially and uniformly distributed around the center of the fracture support ball. The outer shell 44-2 is made of plastic. Each micropore 44-1 is sealed with an acid-resistant but not alkali-resistant material (water glass acid-resistant cement is used in this embodiment) to withstand a liquid pressure of 45-50 MPa. When the micropores 44-1 are sealed (i.e., before the sealing material is corroded and dissolved by the alkali solution), the overall density of the fracture support ball 44 is 0.95-1.05 times the density of water. This ensures that the fracture support ball 44 remains inside the acid solution as it flows with the acid, preventing interference with transportation due to excessively high or low density. The spherical hollow structure contains calcium oxide powder 44-3. This structure not only supports the generated cracks to prevent them from closing automatically under ground stress, but also provides heat energy for subsequent alkali injection, further improving the crack-inducing effect of the alkali solution. The diameter of the spherical hollow structure is 2 / 3 to 4 / 5 of the diameter of the crack support sphere, and the diameter of each micropore 44-1 is 1mm to 2mm. The number of micropores 44-1 on the outer shell 44-2 of the crack support sphere is 6 to 9 per square centimeter, and the volume of the calcium oxide powder 44-3 is 2 / 3 to 3 / 4 of the volume of the spherical hollow structure.

[0033] The first control valve 9 is installed on the first pipeline 6, the second control valve 12 is installed on the third pipeline 13, the third control valve 18 is installed on the fifth pipeline 17, the fourth control valve 20 is installed on the alkali discharge pipeline 21, the fifth control valve 25 is installed on the seventh pipeline 26, the sixth control valve 28 is installed on the eighth pipeline 29, the seventh control valve 31 is installed on the ninth pipeline 32, the eighth control valve 34 is installed on the tenth pipeline 33, the ninth control valve 36 is installed on the eleventh pipeline 37, the tenth control valve 40 is installed on the twelfth pipeline 39, and the eleventh control valve 42 is installed on the acid discharge pipeline 41. The various control valves are configured to allow for the corresponding function to be achieved by opening each valve under different circumstances.

[0034] As an improvement of the present invention, all parts of the components that come into contact with acid or alkali solutions during use are coated with an acid and alkali corrosion resistant coating. This design can extend the service life of each component and reduce the frequency of maintenance.

[0035] The working method of the above-mentioned acid-base solution impact-induced fracturing coal seam enhanced gas extraction device includes the following specific steps:

[0036] A. Construct permeability enhancement hole 3 according to the coal seam permeability enhancement design, and use a high-pressure capsule for sealing to ensure that the hole can withstand 40-50MPa water pressure after drilling and sealing. The inner surface of the capsule is coated with an acid and alkali corrosion resistant coating, and one end of the sealing tube 5 is passed through the high-pressure capsule and inserted into the permeability enhancement hole 3.

[0037] B. Assemble the acid and alkali solution impact-induced cracking coal body enhanced gas extraction device, and connect the other end of its first pipeline 6 to the end of the sealing pipe 5 outside the permeability enhancement hole 3, and initially all control valves are in the closed state.

[0038] C. When co-injecting acid and fracture support ball 44, first open the sixth control valve 28 and start the first water pump 24. The first water pump 24 injects the acid in the acid tank 30 into the storage tank 19 through the eighth pipeline 29 and the sixth pipeline 22. The pH value of the acid is 2.5 to 4.5. After a period of time, close the sixth control valve 28 and stop the first water pump 24. Then open the third control valve 18 and the first control valve 9 and start the pulse pump 16. The pulse pump 16 pumps the acid from the storage tank 19 through the second pipeline 10, the first pipeline 6, and the sealing... The acid solution pulsates into the permeability enhancement hole 3 via the pore tube 5, with the pulsating pressure controlled at 35–40 MPa and the pulsating frequency at 200–250 Hz. Simultaneously, the second control valve 12 is opened, and the fracture support ball 44 is discharged from the fracture support ball container 14 into the second pipeline 10, and then enters the permeability enhancement hole 3 along with the pulsating acid solution. The reading of pressure gauge 7 is continuously observed. When the acid pressure in the permeability enhancement hole 3 suddenly drops as shown by pressure gauge 7, it indicates that under the corrosive dissolution and impact of the pulsating acid solution, fracture 43 has cracked along the weak surface 1 of the coal body. Consequently, the acid solution and the fracture support ball 44 will enter the fracture 43. Figure 2As shown, at this time, the fracture support ball 44 fills and supports the generated fracture 43 to prevent the fracture 43 from closing automatically under the action of ground stress.

[0039] D. Close the third control valve 18 and the first control valve 9 and stop the pulse pump 16. Let it stand for 18 to 24 hours. The acid in the permeability enhancement hole 3 will continue to dissolve and erode the cement in the coal body 2, the minerals in the fissure 43 and the blockages, further improving the permeability of the coal body 2.

[0040] E. Open the tenth control valve 40, the ninth control valve 36, and the seventh control valve 31, and start the second water pump 38. The acid in the permeability hole 3 is drawn out from the permeability hole 3 by the suction of the second water pump 38, and then injected into the acid tank 30 after passing through the first pipeline 6, the twelfth pipeline 39, the eleventh pipeline 37, and the ninth pipeline 32. After all the acid has been extracted, close the tenth control valve 40, the ninth control valve 36, and the seventh control valve 31, and stop the second water pump 38. Then open the eleventh control valve 42 to return the remaining acid in the storage tank 19 to the acid tank 30 through the acid discharge pipe 41, completing the acid recovery work, and then close the eleventh control valve 42.

[0041] F. Open the fifth control valve 25 and start the first water pump 24. The first water pump 24 injects the alkali solution in the alkali tank 27 into the storage tank 19 through the seventh pipe 26 and the sixth pipe 22. The pH value of the alkali solution is 11-12. After a period of time, close the fifth control valve 25 and stop the first water pump 24. Then open the third control valve 18 and the first control valve 9 and start the pulse pump 16. The pulse pump 16 pulsates the alkali solution from the storage tank 19 through the second pipe 10, the first pipe 6, and the sealing pipe 5 into the permeability enhancement hole 3. Part of the alkali solution entering the permeability enhancement hole 3 reacts and neutralizes with the residual acid solution in the permeability enhancement hole 3. The pulsation pressure is controlled at 20-25 MPa and the pulsation frequency is 100-150 Hz. Under the corrosive dissolution and impact of the pulsating alkaline solution, the existing fracture network is further expanded and developed, with a pulsation time of 5-10 hours. After the time is reached, the third control valve 18 and the first control valve 9 are closed and the pulsating pump 16 is stopped. Then, the mixture is left to stand for 12-18 hours. The alkaline solution further dissolves the minerals in the coal body. At the same time, since the micropore sealing material of the fracture support ball 44 is acid-resistant but not alkali-resistant, the alkaline solution corrodes and dissolves the sealing material, making the micropores 44-1 of the fracture support ball 44 unobstructed. Then, the alkaline solution enters the fracture support ball 44 through each micropore 44-1 and reacts with calcium oxide in an exothermic reaction. The temperature in the fracture 43 continues to rise, further enhancing the synergistic effect of the alkaline solution's impact and corrosive dissolution on the fractured coal body.

[0042] G. Open the tenth control valve 40, the ninth control valve 36, and the eighth control valve 34, and start the second water pump 38. The acid solution in the permeability hole 3 is drawn out from the permeability hole 3 by the suction of the second water pump 38, and then flows through the first pipeline 6, the twelfth pipeline 39, the eleventh pipeline 37, and the tenth pipeline 33 before being injected into the alkali tank 27. After all the alkali solution has been extracted, close the tenth control valve 40, the ninth control valve 36, and the eighth control valve 34, and stop the second water pump 38. Then open the fourth control valve 20 to return the remaining alkali solution in the storage tank 19 to the alkali tank 27 through the alkali discharge pipe 21, completing the alkali recovery work, and then close the fourth control valve 20.

[0043] H. Disconnect the first pipeline 6 from the sealing pipe 5, and connect the sealing pipe 5 to the underground gas extraction network to start gas extraction. During continuous extraction, stop extraction when the extracted gas concentration is below 30%, and repeat steps B to G before extracting gas again. Repeat this cycle until the gas content of coal body 2 meets the requirements for safe mining.

[0044] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A gas extraction device for enhanced coal seam fracturing induced by acid and alkali solution, characterized in that, It includes a fracture-supported ball container, a pulse pump, a storage tank, an acid tank, an alkali tank, a first water pump, and a second water pump; The outlet of the fissure-supported spherical container is connected to one port of the second tee connector via a third pipe. The other two ports of the second tee connector are connected to one end of the fourth pipe and one end of the second pipe, respectively. The other end of the fourth pipe is connected to the outlet of the pulse pump. The other end of the second pipe is connected to one port of the first tee connector. The other two ports of the first tee connector are connected to one end of the first pipe and one end of the twelfth pipe, respectively. The other end of the twelfth pipe is connected to the inlet of the second water pump. The outlet of the second water pump is connected to one port of the third tee connector via an eleventh pipe. The other two ports of the third tee connector are connected to the first inlet of the acid tank and the first inlet of the alkali tank via the ninth pipe and the tenth pipe, respectively. The storage tank is equipped with an inlet, an outlet, an acid reflux port, and an alkali reflux port. The inlet of the pulse pump is connected to the outlet of the storage tank through a fifth pipeline. The inlet of the storage tank is connected to the outlet of the first water pump. The first inlet of the first water pump is connected to the outlet of the acid tank through an eighth pipeline. The second inlet of the first water pump is connected to the outlet of the alkali tank through a seventh pipeline. The acid reflux port of the storage tank is connected to the second inlet of the acid tank through an acid discharge pipe. The alkali reflux port of the storage tank is connected to the second inlet of the alkali tank through an alkali discharge pipe. Initially, the fracture support sphere container contains multiple fracture support spheres, the acid tank contains acid, the alkali tank contains alkali, and the storage tank is empty. The fracture support sphere has a hollow spherical structure inside, and multiple micropores are opened on the outer shell of the fracture support sphere. The multiple micropores are evenly distributed radially around the center of the fracture support sphere. Each micropore is sealed with an acid-resistant but not alkali-resistant material, and the hollow spherical structure is filled with calcium oxide powder.

2. The acid-base solution impact-induced fracturing coal seam enhanced gas extraction device according to claim 1, characterized in that, The diameter of the spherical hollow structure is 2 / 3 to 4 / 5 of the diameter of the fissure support sphere, the diameter of each micropore is 1 mm to 2 mm, the number of micropores on the outer shell of the fissure support sphere is 6 to 9 per square centimeter, and the volume of calcium oxide is 2 / 3 to 3 / 4 of the volume of the spherical hollow structure.

3. The acid-base solution impact-induced fracturing coal seam enhanced gas extraction device according to claim 1, characterized in that, A pressure gauge is installed on the first pipeline, and a check valve is installed on the sixth pipeline.

4. The acid-base solution impact-induced fracturing coal seam enhanced gas extraction device according to claim 1, characterized in that, The first pipeline is equipped with a first control valve, the third pipeline is equipped with a second control valve, the fifth pipeline is equipped with a third control valve, the alkali discharge pipe is equipped with a fourth control valve, the seventh pipeline is equipped with a fifth control valve, the eighth pipeline is equipped with a sixth control valve, the ninth pipeline is equipped with a seventh control valve, the tenth pipeline is equipped with an eighth control valve, the eleventh pipeline is equipped with a ninth control valve, the twelfth pipeline is equipped with a tenth control valve, and the acid discharge pipe is equipped with an eleventh control valve.

5. The acid-base solution impact-induced fracturing coal seam enhanced gas extraction device according to claim 1, characterized in that, All components are coated with an acid and alkali corrosion resistant coating at the locations where they come into contact with acid or alkali solutions during use.

6. A method for operating the acid-base solution impact-induced fracturing coal seam enhanced gas extraction device according to any one of claims 1 to 5, characterized in that, The specific steps are as follows: A. Construct permeability enhancement holes according to the coal seam permeability enhancement design, and use high-pressure capsules for sealing to ensure that the borehole can withstand 40-50MPa water pressure after sealing. The inner surface of the capsule is coated with an acid and alkali corrosion resistant coating, and one end of the sealing tube is passed through the high-pressure capsule and extended into the permeability enhancement hole. B. Assemble the acid and alkali solution impact-induced fracturing coal body enhanced gas extraction device, and connect the other end of its first pipeline to the end of the sealing pipe outside the permeability enhancement hole, and initially all control valves are in the closed state. C. When co-injecting acid and fracture support balls, first open the sixth control valve and start the first pump. The first pump injects acid from the acid tank into the storage tank through the eighth and sixth pipelines. After a period of time, close the sixth control valve and stop the first pump. Then, open the third and first control valves and start the pulse pump. The pulse pump pulsates acid from the storage tank through the second, first, and sealing pipes into the permeability enhancement hole. Control the pulsation pressure at 35–40 MPa and the pulsation frequency at [missing value]. 200-250Hz; Simultaneously open the second control valve, and the fracture support ball is discharged from the fracture support ball container into the second pipeline, and enters the permeability enhancement hole with the pulsating acid; Continuously observe the pressure gauge reading. When the pressure gauge shows a sudden drop in the acid pressure in the permeability enhancement hole, it indicates that under the corrosive dissolution and impact of the pulsating acid, the fracture opens along the weak surface of the coal body. Then, the acid and fracture support ball will enter the fracture. At this time, the fracture support ball fills and supports the fracture to prevent the fracture from closing automatically under the action of ground stress. D. Close the third control valve and the first control valve and stop the pulse pump. Let it stand for 18-24 hours. The acid in the permeability enhancement pore will continue to dissolve and erode the cement, minerals and blockages in the coal body, and further improve the permeability of the coal body. E. Open the tenth, ninth, and seventh control valves and start the second water pump. The acid in the permeation hole is drawn out by the suction of the second water pump and injected into the acid tank after passing through the first, twelfth, eleventh, and ninth pipelines. After all the acid has been extracted, close the tenth, ninth, and seventh control valves and stop the second water pump. Then open the eleventh control valve to return the remaining acid in the storage tank to the acid tank through the acid discharge pipe, completing the acid recovery work. Then close the eleventh control valve. F. Open the fifth control valve and start the first water pump. The first water pump injects the alkali solution in the alkali tank into the storage tank through the seventh and sixth pipelines. After a period of time, close the fifth control valve and stop the first water pump. Then, open the third and first control valves and start the pulse pump. The pulse pump pulsates the alkali solution from the storage tank through the second pipeline, the first pipeline, and the sealing pipe into the anti-permeability hole. Part of the alkali solution entering the anti-permeability hole reacts and neutralizes with the residual acid solution in the anti-permeability hole. Control the pulsation pressure at 20-25 MPa and the pulsation frequency at 100-150 Hz. The pulsating alkali solution acts as a corrosive, dissolving, and impact agent. The process involves pulsating the already formed fracture network for 5–10 hours to further expand and develop the fracture network. After this time, the third and first control valves are closed, and the pulsating pump is stopped. The mixture is then left to stand for 12–18 hours. The alkaline solution further dissolves the minerals in the coal body. Simultaneously, because the micropore sealing material of the fracture support ball is acid-resistant but not alkali-resistant, the alkaline solution corrodes and dissolves the sealing material, making the micropores of the fracture support ball unobstructed. The alkaline solution then enters the fracture support ball through each micropore and reacts exothermically with calcium oxide, causing the temperature inside the fracture to rise continuously. This further enhances the synergistic effect of the alkaline solution's impact and corrosion-dissolution on the fractured coal body. G. Open the tenth, ninth, and eighth control valves and start the second water pump. The alkaline solution in the permeation hole is drawn out from the permeation hole by the suction of the second water pump, and then injected into the alkaline solution tank after passing through the first, twelfth, eleventh, and tenth pipelines. After all the alkaline solution has been extracted, close the tenth, ninth, and eighth control valves and stop the second water pump. Then open the fourth control valve to return the remaining alkaline solution in the storage tank to the alkaline solution tank through the alkali discharge pipe, completing the alkaline solution recovery work, and then close the fourth control valve. H. Disconnect the first pipeline from the sealing pipe and connect the sealing pipe to the underground gas extraction network to begin gas extraction. During continuous extraction, stop extraction when the extracted gas concentration is below 30%, and repeat steps B to G before extracting gas again. Repeat this cycle until the gas content of the coal body meets the requirements for safe mining.

7. The working method of the acid-base solution impact-induced fracturing coal seam enhanced gas extraction device according to claim 6, characterized in that, The pH value of the acid solution is 2.5 to 4.5, and the pH value of the alkaline solution is 11 to 12.

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