A device and method for multi-stage water-sealed loose blasting and cracking of long boreholes on the ground

Abstract

The present invention discloses a ground long borehole multi-stage water-sealed loosening blasting and fracturing method, belonging to the field of ground long borehole deep hole blasting. The method comprises setting an L-shaped long borehole in a coal seam, water-sealing the borehole, injecting a reducing agent and an oxidizing agent into the borehole, and igniting and detonating the gas. The long borehole is used to continuously increase the pressure of the oxidizing agent and the reducing agent in the borehole, thereby achieving multi-stage blasting in the long borehole, forming a larger pressure relief range, causing damage and developing cracks in the coal body through the explosive impact, and continuously extending the cracks through multiple blasting, thereby providing a seepage channel for gas stored in the coal body, increasing the permeability of the coal body, and facilitating gas extraction. At the same time, a water-sealed section is constructed in the turning section of the long borehole. During the explosion process, the impact effect of the blasting on the coal body is increased, and due to the energy absorption effect of the water-sealed section, the damage to the wellbore casing caused by the blasting is reduced, thereby keeping the wellbore intact, being more conducive to subsequent extraction, and significantly enhancing the beneficial effects of loosening blasting.

Description

Technical Field

[0001] The present invention belongs to the field of ground long borehole deep hole blasting, and in particular relates to a ground long borehole multi-stage water seal loosening blasting and fracturing device and method. Background Art

[0002] The traditional method of using long ground drilling holes to loosen coal seams by blasting has problems such as difficulty in loading and delivering explosives and poor controllability due to the long distance. In addition, the loosening and pressure relief blasting of long ground drilling holes and deep holes is a single-stage blasting method, and the explosives used are generally solid explosives. After one loading and explosion, it is impossible to carry out two or more consecutive blasts in the same hole; the explosion shock wave has a certain destructive effect on the wellbore. These problems have hindered the application of loosening blasting in long ground drilling holes.

[0003] The existing technology also uses explosive gas as explosive material to overcome the problem of difficult charging, but it is necessary to install detonators or chain detonators at multiple locations in the borehole to blast the coal seam in the borehole area. At the same time, since the detonator can only be used once, only one blast can be carried out in one area, and the blasting effect is limited. Summary of the Invention

[0004] In response to the above-mentioned technical deficiencies, the present invention provides a ground long borehole multi-stage water-seal loosening blasting fracturing device and method, which is applied to coal mine pressure relief and permeability enhancement, and can achieve multi-stage blasting. Cracks are formed inside the coal body through explosion, making the cracks in the coal body around the borehole more abundant and extending farther, overcoming the problem of poor effect of one blasting, thereby providing a channel for the gas stored in the coal body, increasing the permeability of the coal body, and facilitating gas extraction. This method solves the problem of ground long borehole loosening blasting and significantly improves the blasting pressure relief and permeability enhancement effect.

[0005] To solve the above-mentioned technical problems, the present invention provides a ground long borehole multi-stage water-seal loosening blasting and fracturing device, comprising an L-shaped long borehole constructed from a rock stratum to a coal seam, the L-shaped long borehole comprising a vertical section penetrating the rock stratum to near the coal seam floor, an arc-shaped transition inclined turning section with an arc angle of less than 90° in the coal seam, and a horizontal section drilled toward the coal seam roof, the horizontal section drilling distance being no less than 50m and covering as much of the coal seam as possible, and a water-sealed section for accumulating water formed in the inclined turning section and part of the horizontal section by coordinating the angles of the inclined turning section and the horizontal section; the water-sealed section is used to absorb the explosion shock wave transmitted from the front during the explosion process, thereby reducing damage to the wellbore of the vertical section of the L-shaped long borehole;

[0006] An ignition and extraction pipeline system is provided in the L-shaped long borehole, and the ignition and extraction pipeline system includes a fire pipe provided in the L-shaped long borehole to the bottom of the hole, and an extraction casing with an end located at the water sealing section of the inclined turning section. The end of the extraction casing is provided with a screen pipe, and the tail end is connected to a mixing pipe and an oil pump arranged on the surface; the fire pipe includes two air pipes and cables for conveying an oxidant and a reducing agent respectively, and an ignition head is connected to the end of the fire pipe. A mixing chamber is provided in the ignition head for mixing the oxidant and the reducing agent, and a temperature controller is provided at the mixing chamber for connecting to the ends of the two air pipes and mixing the oxidant and the reducing agent. The probe and the ignition needle, the other end of the cable is connected to the igniter set on the surface, and the ignition needle is controlled by the igniter to realize remote ignition; the outside of the fire tube is wrapped with a thermal insulation sleeve; a combustion gas source and an extraction pump are arranged at the mouth of the L-shaped long borehole on the surface, wherein the combustion gas source includes two gas cylinders for filling oxidant and reducing agent respectively, and the outlet of each gas cylinder is connected to the tail end of an air pipe through a backfire preventer, wherein the air pipe connected to the oxidant is provided with a first valve, a flow meter, a quick connector and a second valve in sequence; the gas cylinder connected to the reducing agent is provided with a valve and a flow meter in sequence.

[0007] Furthermore, the combustion gas source and the extraction pump are connected to the two gas pipes through a tee that can be switched by a switch; or the interfaces of the combustion gas source and the extraction pump are both provided with quick-disconnect and quick-install structures, which facilitate quick-disconnect and quick-installation with the two gas pipes to achieve switching.

[0008] A fracturing method for a multi-stage water-seal loosening blasting fracturing device for a long ground borehole, comprising the following steps:

[0009] S1. Open the vertical section of an L-shaped long borehole from the ground to enter the coal seam floor, then construct an inclined turning section to achieve the turning, and then gradually drill close to the roof to form a horizontal section with an inclined upward structure, and set a sealing section in the vertical section; perform ground ignition test and air tightness test on the fire pipe to ensure that it can be ignited smoothly and there is no gas leakage in the pipeline, then send the fire pipe into the L-shaped long borehole until the end is close to the bottom of the horizontal section, and then install the extraction casing in the vertical section, install the screen pipe at the front end of the extraction casing, and place the extraction casing at the lowest point of the inclined turning section of the borehole. At this time, if there is no water accumulation in the L-shaped long borehole, or the water sealing section formed by the accumulated water in the L-shaped long borehole is smaller than the diameter of the L-shaped long borehole, water is injected into the L-shaped long borehole until the water level depth is higher than the diameter of the L-shaped long borehole to form a water sealing section. After the setting is completed, the parts of the extraction casing and the fire pipe in the rock formation are sealed to form a sealing section; the upper end of the extraction casing is connected to the pumping unit and the mixing pipe to prepare for drainage after loosening blasting;

[0010] S2. Close the valves on the two gas cylinders and fill the two gas cylinders with oxidant and reducing agent respectively according to the complete combustion ratio. After filling, test the air tightness of the system; if qualified, open all valves on the pipelines of the two gas cylinders and the valve on the mixing pipe at the same time, and inject oxidant and reducing agent into the L-shaped long drilled hole through the fire pipe to the set pressure (preferably 0.1MPa, and each subsequent blast increases by 0.5MPa on the basis of the previous one), and then close all valves on the pipelines of the two gas cylinders and the mixing pipe;

[0011] S3. Start the igniter to ignite and blast the oxidant and reducing agent injected into the L-shaped long borehole. Simultaneously, use the temperature probe data to determine whether the ignition is successful. Maintain ignition until successful blasting to increase the permeability of the coal seam. After blasting, blast the section from the bottom of the hole to the water seal. During the blasting process, the water seal effectively absorbs the blasting energy, thereby protecting the blasting effect of the coal body in front and effectively protecting the vertical section of the wellbore from the impact of the explosion.

[0012] S4. After the blast is successful, disconnect the quick connector, remove the previously connected gas cylinder, and replace it with an extraction pump to extract the gas generated after the explosion in the coal seam in the horizontal section of the L-shaped long borehole. At this time, the water sealing effect of the water sealing section reduces the gas in the vertical section and the inclined turning section from being extracted. The post-explosion mixed gas in front of the horizontal borehole can be extracted promptly and effectively until the gas concentration in the extracted gas reaches more than 60%. Then, extraction is stopped, completing one blast.

[0013] S5, repeating steps S2 to S4, performing multiple blasting operations until the blasting peak in the coal seam reaches the compressive strength of the roof and floor;

[0014] S6. After the blasting is completed, close the valves on the two gas pipes, open the valve on the mixing pipe, and start the pumping unit to drain the coalbed methane.

[0015] Furthermore, the water sealing section effectively seals along the horizontal section of the L-shaped long borehole, with a water depth exceeding the hole diameter and a length exceeding 2 meters.

[0016] Furthermore, in addition to ignition through the ignition needle, the igniter also continuously monitors and displays the temperature in the borehole through the temperature probe.

[0017] Furthermore, when the gas concentration inside the L-shaped long borehole exceeds 50%, only oxidant can be injected, and blasting can be performed by utilizing the reaction between gas and oxidant.

[0018] Furthermore, in step S2, after two blastings, in order to improve the blasting pressure effect, before injecting the oxidant and the reducing agent, the valve on the mixing pipe is closed to seal the wellhead, and the pressure injected into the L-shaped long borehole is increased, so that there is more oxidant-reducer mixture and higher pressure in the L-shaped long borehole, thereby increasing the blasting pressure and improving the blasting effect.

[0019] The beneficial effects of the present invention are as follows: This method, applied to coal mine pressure relief and permeability enhancement, can achieve multi-stage blasting within the same long borehole on the ground until a predetermined pressure relief state is reached. Therefore, the pressure relief effect is more reliable than traditional loosening blasting, and the effective pressure relief range is larger. This method uses gas as the explosive material, overcoming the difficulty of delivering solid explosives through long boreholes. It can also utilize gas released from the coal seam to participate in the blasting, reducing the consumption of reducing agents. This method uses water for sealing, and the explosion shock wave is transmitted from the gas to the water, absorbing some of the energy. The water then transmits it to the gas before finally impacting the wellbore, weakening the energy and protecting the wellbore. In the coal seam, the shock wave directly impacts the coal body, reducing damage to the wellbore without reducing damage to the coal body, thus facilitating subsequent coalbed methane (gas) extraction. The explosion creates cracks within the coal body, providing pathways for gas stored within the coal body, increasing the coal body's permeability and facilitating gas extraction. This invention eliminates the risk of duds and presents no hidden dangers on site. The internal oxidant and reducing agent are easily diluted with air to a concentration below the lower flammable limit and promptly pumped out. The entire solution requires no human intervention underground; all operations and implementation can be completed remotely from the surface. This solution is safe, reliable, and highly automated, offering broad practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 A schematic diagram illustrating the connection of various devices in the ground long-hole multi-stage water-seal loosening blasting fracturing method provided by an embodiment of the present invention;

[0022] Figure 2 This is a schematic diagram of the internal structure of an ignition head provided in an embodiment of the present invention.

[0023] Description of reference numerals:

[0024] 1. Gas cylinder; 2. Backfire arrester; 4. Valve; 5. Flow meter; 3. Gas pipe; 6. Quick connector; 7. Ignitor; 8. Cable; 9. Mixing tube; 10. Pumping unit; 11. Extraction pump; 12. Sealing section; 13. Extraction casing; 14. Fire tube; 15. Ignition head; 15-1. Temperature probe; 15-2. Ignition needle; 15-3. Mixing chamber; 16. Insulating casing; 17. L-shaped long borehole; 18. Water sealing section; 19. Screen; 20. Rock stratum; 21. Coal seam. DETAILED DESCRIPTION

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention:

[0026] like Figure 1 As shown, a ground long borehole multi-stage water-sealed loosening blasting and fracturing device of the present invention includes an L-shaped long borehole 17 constructed from a rock stratum 20 toward a coal seam 21. The L-shaped long borehole 17 includes a vertical section that passes through the rock stratum 20 and reaches near the bottom plate of the coal seam 21, an inclined turning section that forms a bend greater than 270 degrees in the coal seam 21, and a horizontal section that is drilled toward the top plate of the coal seam 21. The horizontal section is drilled for a distance of not less than 50 meters and covers as much of the coal seam 21 as possible. By coordinating the angles of the inclined turning section and the horizontal section, a water-sealed section 18 for accumulating water is formed in the inclined turning section and part of the horizontal section. The water-sealed section 18 absorbs the explosion shock wave transmitted from the front during the explosion process, thereby reducing damage to the vertical section of the wellbore of the L-shaped long borehole 17.

[0027] An ignition and extraction pipeline system is provided in the L-shaped long borehole 17. The ignition and extraction pipeline system includes a fire pipe 14 provided in the L-shaped long borehole 17 to the bottom of the hole, and an extraction casing 13 whose end is located at the water sealing section 18 of the inclined turning section. The end of the extraction casing 13 is provided with a screen pipe 19 and the tail is connected to a mixing pipe 9 and an oil pumping unit 10 arranged on the surface; the fire pipe 14 includes two gas pipes 3 and a cable 8 for conveying an oxidant and a reducing agent respectively. The end of the fire pipe 14 is connected to an ignition head 15. Figure 2As shown, the ignition head 15 is provided with a mixing chamber 15-3 connected to the ends of the two gas pipes 3 and mixing the oxidant and the reducing agent. The mixing chamber 15-3 is also provided with a temperature probe 15-1 and an ignition needle 15-2 connected to the cable 8. The other end of the cable 8 is connected to the igniter 7 arranged on the surface. The ignition needle 15-2 is controlled by the igniter 7 to realize remote ignition. The combustion temperature is detected by the temperature probe 15-1 and monitored by the igniter 7; the outside of the fire tube 14 is wrapped with an insulating sleeve 16; a combustion gas source and an extraction pump 11 are arranged at the borehole mouth of the L-shaped long borehole 17 on the surface, wherein the combustion gas source includes two gas cylinders 1 for filling the oxidant and the reducing agent respectively, and the outlet of each gas cylinder 1 is connected to the tail end of a gas pipe 3 through a backfire preventer 2, wherein the gas pipe 3 connected to the oxidant is provided with a first valve 4, a flow meter 5, a quick connector 6 and a second valve in sequence; the gas cylinder 1 connected to the reducing agent is provided with a valve and a flow meter 5 in sequence.

[0028] The combustion gas source and the extraction pump 11 are connected to the two gas pipes 3 through a three-way switch; or the interfaces of the combustion gas source and the extraction pump 11 are provided with a quick-disconnect and quick-install structure, which is convenient for quick-disconnect and quick-installation with the two gas pipes 3 to achieve switching.

[0029] A method for fracturing a multi-stage water-seal loosening blasting fracturing device for a long ground borehole, comprising the following steps:

[0030] S1. Open the vertical section of an L-shaped long borehole 17 from the ground to enter the bottom plate of the coal seam 21, then construct an inclined turning section to achieve the turning, and then gradually drill close to the top plate to form a horizontal section with an inclined upward structure, and set a sealing section 12 in the vertical section; perform a ground ignition test and an airtightness test on the fire tube 14 to ensure that it can be ignited smoothly and there is no gas leakage in the pipeline, then send the fire tube 14 into the inside of the L-shaped long borehole 17 until the end is close to the bottom of the horizontal section, and then install the extraction casing 13 in the vertical section, install the screen 19 at the front end of the extraction casing 13, and put the extraction casing 13 at the lowest point of the vertical section of the borehole. At this time, if the L-shaped long borehole 17 If there is no water accumulation, or the water sealing section 18 formed by the accumulated water in the L-shaped long borehole 17 is smaller than the diameter of the L-shaped long borehole 17, water is injected into the L-shaped long borehole 17 until the water level is higher than the diameter of the L-shaped long borehole 17 to form a water sealing section 18. After the setting is completed, the parts of the extraction casing 13 and the fire pipe 14 in the rock formation 20 are sealed to form a sealing section 12; the upper end of the extraction casing 13 is connected to the pumping unit 10 and the mixing pipe 9 to prepare for drainage after loosening blasting; the water sealing section 18 is effectively sealed along the horizontal section of the L-shaped long borehole 17, the water depth is higher than the hole diameter, and the length exceeds 2 meters.

[0031] S2. Close the valves on the two gas cylinders 1, and fill the two gas cylinders 1 with oxidant and reducing agent respectively according to the complete combustion ratio. After filling, test the air tightness of the system; after passing the test, open all valves on the pipelines of the two gas cylinders 1, and at the same time open the valve on the mixing tube 9, and inject oxidant and reducing agent into the L-shaped long borehole 17 through the fire tube 14 to the set pressure. Preferably, the pressure is 0.1MPa, and each subsequent blasting increases 0.5MPa on the basis of the previous one, and then close all valves on the pipelines of the two gas cylinders 1 and on the mixing tube 9; after performing two blasts, in order to improve the blasting pressure effect, before injecting the oxidant and reducing agent, close the valve on the mixing tube 9 to seal the wellhead, increase the pressure injected into the L-shaped long borehole 17, so that there is more oxidant-reducing agent mixture and higher pressure in the L-shaped long borehole 17, thereby increasing the blasting pressure and improving the blasting effect.

[0032] S3. Start the igniter 7 to ignite and blast the oxidant and reducing agent injected into the L-shaped long borehole 17. At the same time, use the data from the temperature probe 15-1 to determine whether the ignition of the igniter 7 is successful. Maintain the ignition until the blasting to increase the permeability of the coal seam. Due to the energy absorption effect of the water seal 18, the blasting effect of the coal body in the front is not affected, effectively protecting the vertical section of the wellbore from the impact of the explosion.

[0033] S4. After the blasting is successful, disconnect the quick connector 6, remove the previously connected gas cylinder 1, and replace it with the extraction pump 11 to extract the gas generated after the explosion in the horizontal section of the L-shaped long borehole 17 in the coal seam 21. At this time, the water sealing effect of the water sealing section 18 reduces the gas in the vertical section and the inclined turning section from being extracted, and can effectively and timely extract the post-explosion mixed gas in front of the horizontal borehole until the gas concentration in the extracted gas reaches more than 60%. Then, the extraction is stopped, and one blasting is completed;

[0034] S5, repeating steps S2 to S4, performing multiple blasting operations until the blasting peak in the coal seam 21 reaches the compressive strength of the roof and floor;

[0035] S6. After the blasting is completed, the valves on the two gas pipes 3 are closed, the valve on the mixing pipe 9 is opened, and the pumping unit 10 is started to drain the coalbed methane.

[0036] 6. The method for loosening and fracturing a long ground borehole with multi-stage water seal by blasting according to claim 3 is characterized in that when the gas concentration inside the L-shaped long borehole 17 exceeds 50%, only oxidant can be injected, and blasting is performed by utilizing the reaction between the gas and the oxidant.

[0037] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A multi-stage water seal loosening blasting and fracturing device for long ground boreholes, characterized by: The invention comprises an L-shaped long borehole (17) constructed in a rock layer (20) toward a coal seam (21), wherein the L-shaped long borehole (17) comprises a vertical section passing through the rock layer (20) until it reaches a bottom plate of the coal seam (21), an arc-shaped transition inclined turning section with an arc angle of less than 90 degrees formed in the coal seam (21), and a horizontal section drilled toward the top plate of the coal seam (21), wherein the drilling distance of the horizontal section is not less than 50 meters and the coal seam (21) is covered as much as possible, and a water sealing section (18) for accumulating water is formed in the inclined turning section and part of the horizontal section by coordinating the angles of the inclined turning section and the horizontal section; and the water sealing section (18) is used to absorb the explosion shock wave transmitted from the front during the explosion process, thereby reducing damage to the vertical section of the wellbore of the L-shaped long borehole (17); An ignition and extraction pipeline system is provided in an L-shaped long borehole (17), the ignition and extraction pipeline system comprising a fire pipe (14) provided in the L-shaped long borehole (17) up to the bottom of the hole, and an extraction casing (13) whose end is located at a water sealing section (18) of an inclined turning section, a screen pipe (19) provided at the end of the extraction casing (13), and a mixing pipe (9) and an oil pump (10) arranged on the surface connected to the tail end; the fire pipe (14) comprises two gas pipes (3) for conveying an oxidant and a reducing agent respectively, and a cable (8), an ignition head (15) is connected to the end of the fire pipe (14), a mixing chamber (15-3) is provided in the ignition head (15) for mixing the oxidant and the reducing agent, and a temperature controller (15-3) is provided at the mixing chamber (15-3) connected to the cable (8). The invention relates to a method for producing a flame retardant gas by using a flame retardant gas probe (15-1) and an ignition needle (15-2). The other end of the cable (8) is connected to an igniter (7) arranged on the ground surface, and the ignition needle (15-2) is controlled by the igniter (7) to realize remote ignition. The outer side of the fire tube (14) is wrapped with a heat-insulating sleeve (16). A combustion gas source and an extraction pump (11) are arranged at the borehole mouth of the L-shaped long borehole (17) on the ground surface, wherein the combustion gas source includes two gas cylinders (1) for filling an oxidant and a reducing agent respectively. The outlet of each gas cylinder (1) is connected to the tail end of a gas pipe (3) through a backfire preventer (2). The gas pipe (3) connected to the oxidant is provided with a first valve (4), a flow meter (5), a quick connector (6) and a second valve in sequence; the gas cylinder (1) connected to the reducing agent is provided with a valve and a flow meter (5) in sequence.

2. The multi-stage water seal loosening blasting and fracturing device for long ground boreholes according to claim 1, characterized in that: The combustion gas source and the extraction pump (11) are connected to the two gas pipes (3) through a three-way switch; or the interfaces of the combustion gas source and the extraction pump (11) are both provided with a quick-disconnect and quick-install structure, which facilitates quick-disconnect and quick-installation with the two gas pipes (3) to achieve switching.

3. A fracturing method using the ground long-hole multi-stage water-seal loosening blasting fracturing device according to claim 1, characterized in that Here are the steps: S1. Open the vertical section of the L-shaped long borehole (17) from the ground to enter the bottom plate of the coal seam (21), then construct the inclined turning section to achieve the turning, gradually drill close to the top plate to form a horizontal section with an inclined upward structure, and set a sealing section (12) in the vertical section; perform a ground ignition test and an airtightness test on the fire pipe (14) to ensure that it can be ignited smoothly and there is no air leakage in the pipeline, then send the fire pipe (14) into the inside of the L-shaped long borehole (17) until the end is close to the bottom of the horizontal section, and then install the extraction casing (13) in the vertical section, install the screen pipe (19) at the front end of the extraction casing (13), and put the extraction casing (13) into the borehole. At the lowest point of the inclined turning section, if there is no water accumulation in the L-shaped long borehole (17), or the water sealing section (18) formed by the accumulated water in the L-shaped long borehole (17) is smaller than the diameter of the L-shaped long borehole (17), water is injected into the L-shaped long borehole (17) until the water level is higher than the diameter of the L-shaped long borehole (17) to form the water sealing section (18). After the setting is completed, the parts of the extraction casing (13) and the fire pipe (14) in the rock formation (20) are sealed to form a sealing section (12); the upper end of the extraction casing (13) is connected to the pumping unit (10) and the mixing pipe (9) to prepare for drainage after loosening blasting; S2. Close the valves on the two gas cylinders (1), and fill the two gas cylinders (1) with oxidant and reducing agent according to the complete combustion ratio. After filling, test the air tightness of the system. After passing the test, open all valves on the pipelines of the two gas cylinders (1), and at the same time open the valve on the mixing pipe (9), and inject oxidant and reducing agent into the L-shaped long drilled hole (17) through the fire pipe (14) to the set pressure, and then close all valves on the pipelines of the two gas cylinders (1) and on the mixing pipe (9); S3, start the igniter (7) to ignite and blast the oxidant and reducing agent injected into the L-shaped long borehole (17), and at the same time use the data of the temperature probe (15-1) to judge whether the igniter (7) is successful, and maintain the ignition until the blasting is successful to increase the permeability of the coal seam. After the blasting, blast the area from the bottom of the hole to the water sealing section (18). During the blasting process, the water sealing section (18) effectively absorbs the blasting energy, thereby protecting the blasting effect of the coal body in front from being affected, and effectively protecting the vertical section of the wellbore from the impact of the explosion; S4. After the blasting is successful, the quick connector (6) is disconnected and the previously connected gas cylinder (1) is removed and replaced with an extraction pump (11). The gas generated after the explosion of the horizontal section of the L-shaped long borehole (17) in the coal seam (21) is extracted. At this time, the water sealing effect of the water sealing section (18) reduces the gas in the vertical section and the inclined turning section from being extracted. The mixed gas after the explosion in front of the horizontal borehole can be extracted in a timely and effective manner until the gas concentration in the extracted gas reaches more than 60%. The extraction is stopped and one blasting is completed. S5, repeating steps S2 to S4, performing multiple blasting until the blasting peak in the coal seam (21) reaches the compressive strength of the top and bottom plates; S6. After the blasting is completed, the valves on the two gas pipes (3) are closed, the valve on the mixing pipe (9) is opened, and the pumping unit (10) is started to drain the coalbed methane.

4. The fracturing method according to claim 3, wherein: The water sealing section (18) effectively seals along the horizontal section of the L-shaped long borehole (17), with a water depth exceeding the hole diameter and a length exceeding 2 meters.

5. The fracturing method according to claim 3, wherein: In addition to ignition via the ignition needle (15-2), the igniter (7) also continuously monitors and displays the temperature in the borehole via the temperature probe (15-1).

6. The fracturing method according to claim 3, wherein: When the gas concentration inside the L-shaped long borehole (17) exceeds 50%, only oxidant can be injected to perform blasting by utilizing the reaction between the gas and the oxidant.

7. The fracturing method according to claim 3, wherein: In step S2, after the second blasting, in order to improve the blasting pressure effect, before injecting the oxidant and the reducing agent, the valve on the mixing pipe (9) is closed to seal the wellhead, thereby increasing the pressure injected into the L-shaped long borehole (17), so that there is more oxidant-reducing agent mixture and higher pressure in the L-shaped long borehole (17), thereby increasing the blasting pressure and improving the blasting effect.

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