A shale gas reservoir methane multistage pulse combustion fracturing device and a fracturing method thereof

Abstract

The present application provides a kind of shale gas reservoir methane multistage pulse combustion fracturing device and its fracturing method, first set vertical shaft and horizontal branch well, then install sealing wall and combustion fracturing device in horizontal branch well, make horizontal branch well form closed area;When carrying out combustion fracturing, first inject oxygen and combustion gas into combustion fracturing device, detect gas concentration in real time by detection device, stop gas injection when reaching explosion limit value, control ignition head ignition, make explosion occur in combustion fracturing device, detonation shock wave produced by gas explosion makes combustion fracturing device increase, impact on shale reservoir, at the same time, the surrounding shale is impacted and fractured again through the hole on combustion fracturing device, repeated combustion fracturing makes the horizontal branch well surrounding form longitudinal and transverse intersecting fracture network;Meanwhile, explosion fracturing device can also support fracture network to maintain connectivity for a long time, ensure shale gas extraction.Belongs to the field of shale gas exploitation.

Description

Technical Field

[0001] This invention relates to a multi-stage pulse combustion and fracturing device and method for methane in shale gas reservoirs, which is suitable for efficient extraction of low-permeability shale gas reservoirs and belongs to the field of shale gas extraction. Background Technology

[0002] With the gradual maturation of shale gas extraction technology, the proportion of shale gas production in total natural gas production has been steadily increasing, significantly altering the global energy structure. Shale gas reservoirs generally exhibit low porosity and low permeability, making shale gas development extremely difficult. Commercial exploitation necessitates the adoption of enhancement measures. Currently, the commonly used enhancement measure is hydraulic fracturing, but this method suffers from several problems: firstly, fracturing fluid is prone to contamination and flowback is difficult; secondly, it requires substantial water resources, making implementation challenging in water-scarce regions; and thirdly, the fracture network is often monotonous and prone to water-locking effects on the reservoir. Therefore, there is an urgent need to develop a novel enhanced extraction method for shale gas wells to improve shale gas extraction efficiency. Summary of the Invention

[0003] This invention provides a multi-stage pulse combustion and detonation fracturing device and method for shale gas reservoirs containing methane. It does not require large amounts of water and fracturing fluid and can construct a three-dimensional fracture network around multi-branch horizontal wells, providing a solution to the problems of increasing shale gas production, reducing development costs, and mitigating severe environmental pollution.

[0004] To achieve the above objectives, a multi-stage pulse combustion and detonation fracturing method for methane in shale gas reservoirs is proposed. The specific steps of this method are as follows:

[0005] A. After selecting a good sweet spot for shale gas, drill a vertical shaft from the surface to the shale reservoir to be exploited, and run cementing casing into the shaft to complete the shaft;

[0006] B. Operate the directional drilling rig to drill a horizontal branch well connected to the vertical shaft at the planned shale reservoir. A cementing screen is installed in the horizontal branch well, and the lower end of the cementing casing is connected to the end of the cementing screen. The cementing screen has screen holes that are compatible with the combustion and fracturing device. A sealing wall is constructed at the connection between the cementing casing and the cementing screen to seal and separate the horizontal branch well from the vertical shaft, so that the horizontal branch well is isolated from the outside gas.

[0007] C. A combustion-induced fracturing device is installed inside the cementing screen corresponding to the screen hole. The device contains a gas concentration monitor and an ignition head. Oxygen and methane inlet pipes pass through the device. The portions of the oxygen and methane inlet pipes inside the device are equipped with oxygen and methane valves, respectively. The other end of the methane inlet pipe extends out of the vertical shaft and splits into two pipelines, connecting to the extraction device on the surface and the outlet of the No. 1 gas booster pump, respectively. The inlet of the No. 1 gas booster pump is connected to… The methane storage chamber is connected, and a methane storage chamber valve is installed at the connection point. The oxygen inlet pipe is connected to the outlet of the No. 2 gas booster pump, and the inlet of the No. 2 gas booster pump is connected to the oxygen storage chamber, and an oxygen storage chamber valve is installed at the connection point. The gas concentration monitor and ignition head are both fixed inside the combustion and explosion fracturing device. The oxygen pipe valve, methane pipe valve, methane storage chamber valve, oxygen storage chamber valve, gas concentration monitor, and ignition head are all connected to the ground control center through communication lines to complete the assembly of the combustion and explosion fracturing system.

[0008] D. Open the valves of the methane storage chamber and the oxygen storage chamber, and start the No. 1 and No. 2 gas booster pumps to continuously supply methane and oxygen through the oxygen inlet pipe, the methane inlet pipe, the oxygen pipe valve, and the methane pipe valve into the combustion-explosion fracturing device. At this time, the control center collects the gas concentration in the combustion-explosion fracturing device in real time through the gas concentration monitor. When the collected real-time gas concentration reaches the explosion limit value, stop the No. 1 and No. 2 gas booster pumps and close the oxygen pipe valve and the methane pipe valve. The control center controls the ignition head to ignite, thereby causing the mixed gas in the combustion-explosion fracturing device to explode, generating a detonation shock wave. This causes the four movable fracturing heads of the combustion-explosion fracturing device to extend and press into the shale reservoir. At the same time, the detonation shock wave impacts the shale reservoir through the energy-concentrating holes on the combustion-explosion fracturing device. Meanwhile, the inner walls of the four movable fracturing heads of the combustion-explosion fracturing device are equipped with anti-retraction serrations to prevent the movable fracturing heads from retracting due to ground stress.

[0009] E. Repeat step D to ensure that all four movable fracturing heads of each combustion-induced fracturing device are pressed into the shale reservoir, and the detonation shock wave repeatedly impacts the shale reservoir to form a fracture network. After completion, close the oxygen pipe valve, methane storage chamber valve, and oxygen storage chamber valve, open the methane pipe valve, and activate the extraction device to extract shale gas from the shale reservoir through the methane inlet pipe.

[0010] F. Repeat steps A to E to extract shale gas from the remaining shale reservoirs that need to be exploited.

[0011] In step C), a combustion fracturing device is installed at the position corresponding to the screen hole inside the cementing screen pipe by a fixing rope. Each combustion fracturing device is fixed by multiple fixing ropes. One end of the fixing rope is fixed to the rope fixing connection point distributed on the inner wall of the cementing screen pipe, and the other end is fixed to the combustion fracturing device so that the combustion fracturing device is held in the set position inside the cementing screen pipe.

[0012] This invention also provides a multi-stage pulse combustion-explosion fracturing device for methane in shale gas reservoirs, comprising a vertical shaft drilled from the surface into a shale reservoir, a horizontal branch well drilled at the lower end of the vertical shaft along the shale reservoir, a cementing casing and a cementing screen pipe respectively installed in the vertical shaft and the horizontal branch well, with their ends fixedly connected, a combustion-explosion fracturing device fixedly distributed along the length of the middle of the cementing screen pipe, a gas concentration monitor and an ignition head installed in the combustion-explosion fracturing device, movable fracturing heads distributed circumferentially along the cementing screen pipe on the combustion-explosion fracturing device, the movable fracturing heads and the combustion-explosion fracturing device being detachably connected, screen pipe holes corresponding to the positions of the movable fracturing heads being opened on the cementing screen pipe for the movable fracturing heads to pass through, and cylindrical structures coaxial with the corresponding screen pipe holes on the combustion-explosion fracturing device corresponding to the positions of the movable fracturing heads, the inner end of the movable fracturing head being slidably disposed on the cylindrical structure along the axial direction of the cylindrical structure. Inside, the outer end of the movable fracturing head is cone-shaped, and energy-concentrating holes are distributed on the outer end of the movable fracturing head to facilitate its insertion into the shale reservoir. Both the oxygen and methane inlet pipes extend into the combustion-explosion fracturing device, and oxygen and methane inlet pipes are respectively equipped with oxygen and methane valves. The other end of the methane inlet pipe extends out of the vertical shaft and splits into two pipelines, which are respectively connected to the extraction device on the surface and the outlet of the No. 1 gas booster pump. The inlet of the No. 1 gas booster pump is connected to the methane storage chamber, and a methane storage chamber valve is installed at the connection. The oxygen inlet pipe is connected to the outlet of the No. 2 gas booster pump, and the inlet of the No. 2 gas booster pump is connected to the oxygen storage chamber, and an oxygen storage chamber valve is installed at the connection. The oxygen valve, methane valve, methane storage chamber valve, oxygen storage chamber valve, gas concentration monitor, and ignition head are all connected to the ground control center via communication lines.

[0013] In the aforementioned shale gas reservoir methane multi-stage pulse combustion and explosion fracturing device, the combustion and explosion fracturing device has a cross-shaped structure, and the four cross ends of the combustion and explosion fracturing device are four movable fracturing heads and the matching cylindrical structure.

[0014] In the aforementioned shale gas reservoir methane multi-stage pulse combustion and fracturing device, anti-retraction serrations are distributed on the inner wall of the cylindrical structure.

[0015] Compared with existing technologies, this invention utilizes gas delivery facilities to supply combustible gas to a combustion-explosion fracturing device. An ignition head then detonates the gas, generating a detonation shock wave that forces the fracturing device into the shale reservoir. Furthermore, the fracturing device has pores, allowing the detonation shock wave to further pressurize the shale reservoir and create artificial fractures. This method is safer and more environmentally friendly, and is particularly suitable for the extraction of low-permeability shale gas reservoirs. This invention also has the following advantages:

[0016] (1) The combustion-explosion fracturing device can penetrate deep into the shale reservoir, with a larger fracturing range, and the combustion-explosion fracturing device can support the shale reservoir to prevent the fracture network from reclosing under the action of geostress.

[0017] (2) The explosion is completed in the combustion-detonation fracturing device, which generates more concentrated kinetic energy and higher fracturing efficiency.

[0018] (3) The part of the combustion and fracturing device that is pressed into the shale reservoir has holes. After multiple explosions, crisscrossing artificial fractures can be formed, which improves the permeability of shale gas.

[0019] (4) A sealing wall at the connection between the casing and the screen pipe separates the horizontal branch well from the vertical well. After fracturing is completed, the downhole pressure is higher than before fracturing, which is beneficial for shale gas extraction from the normal pressure shale reservoir.

[0020] (5) After fracturing is completed, if necessary, the methane pipe valve can be closed and CO2 can be injected into the well using the oxygen pipe to drive shale gas. At the same time, if the shale reservoir meets the requirements of the carbon dioxide capture layer, the gas transmission device of this invention can be used to inject CO2 into the reservoir. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall layout of the present invention;

[0022] Figure 2 This is a cross-sectional view of the combustion-explosion fracturing device along the xz axis;

[0023] Figure 3 This is a cross-sectional view of the combustion-explosion fracturing device along the yz axis;

[0024] Figure 4 This is a cross-sectional view of the movable fracturing head of the combustion-explosion fracturing device along the xy axis.

[0025] Figure 5 It is a movable fracturing head of a combustion-explosion fracturing device. Figure 4 Tangent screenshot

[0026] In the diagram: 1. Overlying strata, 2. Shale reservoir, 3. Shale, 4. Cementing casing, 5. Horizontal branch well, 6. Cementing screen, 6-1. Screen hole, 6-2. Fixing rope, 7. Sealing wall, 8. Explosion-induced fracturing device, 8-1. Gas concentration monitor, 8-2. Ignition head, 8-3. Oxygen pipe valve, 8-4. Methane pipe valve, 8-5. Movable fracturing head, 8-6. Focusing hole, 8-7. Protection 8-8 Movable fracture head baffle, 9. Oxygen inlet pipe, 10. Methane inlet pipe, 11. Extraction device, 12. Gas booster pump No. 1, 13. Methane storage chamber, 13-1. Methane storage chamber valve, 14. Gas booster pump No. 2, 15. Oxygen storage chamber, 15-1. Oxygen storage chamber valve, 16. Communication line, 17. Control center, 18. Fracture network, 19. Deep rock strata. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0028] Example

[0029] Reference Figures 1 to 3This embodiment improves the multi-stage pulse combustion and fracturing device for methane in shale gas reservoirs. The improved device includes a vertical shaft 3 drilled from the surface into the shale reservoir 2. A horizontal branch well 5 is drilled along the lower end of the vertical shaft 3 within the shale reservoir 2. A cementing casing 4 and a cementing screen 6 are respectively installed in the vertical shaft 3 and the horizontal branch well 5, with their ends fixedly connected. A combustion and fracturing device 8 is fixedly distributed along the length of the cementing screen 6. The combustion and fracturing device 8 also includes a gas concentration monitor 8-1 and an ignition head 8-2. Movable fracturing heads 8-5 are distributed circumferentially along the cementing screen 6 on the explosive fracturing device 8. The movable fracturing heads 8-5 and the explosive fracturing device 8 are separable. Screen holes 6-1 are provided on the cementing screen 6 at positions corresponding to the movable fracturing heads 8-5, allowing the movable fracturing heads 8-5 to pass through. The explosive fracturing device 8 at positions corresponding to the movable fracturing heads 8-5 are all coaxial cylindrical structures with the corresponding screen holes 6-1. The inner end of the movable fracturing head 8-5 is slidably disposed within the cylindrical structure along its axial direction. -5 has a pointed cone-shaped outer end, and the movable fracturing head 8-5 has energy-concentrating holes 8-6 distributed on its outer end to facilitate injection into the shale reservoir 2. Both the oxygen inlet pipe 9 and the methane inlet pipe 10 extend into the combustion-explosion fracturing device 8, and oxygen valves 8-3 and methane valves 8-4 are respectively installed on the oxygen inlet pipe 9 and methane inlet pipe 10 within the combustion-explosion fracturing device 8. The other end of the methane inlet pipe 10 extends out of the vertical shaft 3 and splits into two pipelines, which are respectively connected to the outlets of the extraction device 11 and the No. 1 gas booster pump 12 on the surface. The inlet of the pressure pump 12 is connected to the methane storage chamber 13, and a methane storage chamber valve 13-1 is installed at the connection. The oxygen inlet pipe 9 is connected to the outlet of the second gas booster pump 14. The inlet of the second gas booster pump 14 is connected to the oxygen storage chamber 15, and an oxygen storage chamber valve 15-1 is installed at the connection. The oxygen pipe valve 8-3, the methane pipe valve 8-4, the methane storage chamber valve 13-1, the oxygen storage chamber valve 15-1, the gas concentration monitor 8-1, and the ignition head 8-2 are all connected to the ground control center 17 via the communication line 16.

[0030] The combustion-explosion fracturing device 8 has a cross-shaped structure. The four cross ends of the combustion-explosion fracturing device 8 are four movable fracturing heads 8-5 and the matching cylindrical structure. Anti-retraction serrations 8-7 are distributed on the inner wall of the cylindrical structure.

[0031] The specific steps of the method for multi-stage pulse combustion-induced fracturing of methane in shale gas reservoirs using the above-mentioned device are as follows:

[0032] A. After selecting a good sweet spot for shale gas, drill a vertical shaft 3 from the surface to the planned shale reservoir 2, and run cementing casing 4 into the vertical shaft to complete the vertical shaft;

[0033] B. The directional drilling rig drills a horizontal branch well 5 connected to the vertical well 3 at the planned shale reservoir 2. A cementing screen 6 is installed in the horizontal branch well 5, and the lower end of the cementing casing 4 is connected to the end of the cementing screen 6. The cementing screen 6 has a screen hole 6-1 that matches the combustion and fracturing device 8. A sealing wall 7 is constructed at the connection between the cementing casing 4 and the cementing screen 6 to seal and separate the horizontal branch well 5 from the vertical well 3, so that the horizontal branch well 5 is isolated from the outside gas.

[0034] C. A combustion-induced fracturing device 8 is installed inside the cementing screen 6 at the position corresponding to the screen hole 6-1. The combustion-induced fracturing device 8 is equipped with a gas concentration monitor 8-1 and an ignition head 8-2. An oxygen inlet pipe 9 and a methane inlet pipe 10 pass through the combustion-induced fracturing device 8. The portions of the oxygen inlet pipe 9 and the methane inlet pipe 10 inside the combustion-induced fracturing device 8 are respectively equipped with an oxygen pipe valve 8-3 and a methane pipe valve 8-4. The other end of the methane inlet pipe 10 extends out of the vertical shaft 3 and splits into two pipelines, which are respectively connected to the outlet of the extraction device 11 on the surface and the outlet of the No. 1 gas booster pump 12. The inlet of the No. 1 gas booster pump 12 is connected to the methane storage chamber 13. The connection is provided with a methane storage chamber valve 13-1, and the oxygen inlet pipe 9 is connected to the outlet of the second gas booster pump 14. The inlet of the second gas booster pump 14 is connected to the oxygen storage chamber 15, and the connection is provided with an oxygen storage chamber valve 15-1. The gas concentration monitor 8-1 and the ignition head 8-2 are both fixed inside the combustion and explosion fracturing device 8. The oxygen pipe valve 8-3, the methane pipe valve 8-4, the methane storage chamber valve 13-1, the oxygen storage chamber valve 15-1, the gas concentration monitor 8-1, and the ignition head 8-2 are all connected to the ground control center 17 through the communication line 16 to complete the assembly of the combustion and explosion fracturing system.

[0035] A combustion fracturing device 8 is installed inside the cementing screen pipe 6 at the position corresponding to the screen pipe hole 6-1 by a fixing rope 6-2. Each combustion fracturing device 8 is fixed by multiple fixing ropes 6-2. One end of the fixing rope 6-2 is fixed to the rope fixing connection point distributed on the inner wall of the cementing screen pipe 6, and the other end is fixed to the combustion fracturing device 8 so that the combustion fracturing device 8 is held in a set position inside the cementing screen pipe 6.

[0036] D. Open the methane storage chamber valve 13-1 and the oxygen storage chamber valve 15-1, and start the No. 1 gas booster pump 12 and the No. 2 gas booster pump 14 to continuously supply methane and oxygen through the oxygen inlet pipe 9, the methane inlet pipe 10, the oxygen pipe valve 8-3, and the methane pipe valve 8-4 into the combustion and detonation device 8. At this time, the control center 17 collects the gas concentration in the combustion and detonation device 8 in real time through the gas concentration monitor 8-1. When the collected real-time gas concentration reaches the explosion limit value, stop the No. 1 gas booster pump 12 and the No. 2 gas booster pump 14, and close the valve. The oxygen pipe valve 8-3 and the methane pipe valve 8-4 are closed; the control center 17 controls the ignition head 8-2 to ignite, thereby causing the mixed gas in the combustion-explosion fracturing device 8 to explode, generating a detonation shock wave, which causes the four movable fracturing heads 8-5 of the combustion-explosion fracturing device 8 to extend and press into the shale reservoir. At the same time, the detonation shock wave impacts the shale reservoir 2 through the energy-concentrating hole 8-6 on the combustion-explosion fracturing device 8. Meanwhile, the inner walls of the four movable fracturing heads 8-5 of the combustion-explosion fracturing device 8 are equipped with anti-retraction serrations 8-7 to prevent the movable fracturing heads 8-5 from retracting due to ground stress.

[0037] E. Repeat step D to force all four movable fracturing heads 8-5 of each combustion-induced fracturing device 8 into the shale reservoir 2, and repeatedly impact the shale reservoir 2 with the detonation shock wave to form a fracture network 18. After completion, close the oxygen pipeline valve 8-3, the methane storage chamber valve 13-1, and the oxygen storage chamber valve 15-1, open the methane pipeline valve 8-4 and start the extraction device 11 to extract shale gas from the shale reservoir 2 through the methane inlet pipe 10.

[0038] F. Repeat steps A to E to extract shale gas from the remaining shale reservoirs that need to be exploited.

[0039] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for fracturing shale gas reservoirs using multi-stage pulse combustion of methane, characterized in that, The specific steps of this method are as follows: A. After selecting a sweet spot for shale gas, drill a vertical shaft (3) from the surface to the shale reservoir (2) to be exploited, and run cemented casing (4) into the vertical shaft to complete the vertical shaft; B. Operate the directional drilling rig to drill a horizontal branch well (5) connected to the vertical shaft (3) at the planned shale reservoir (2). A cementing screen (6) is installed in the horizontal branch well (5), and the lower end of the cementing casing (4) is connected to the end of the cementing screen (6). A screen hole (6-1) matching the combustion and fracturing device (8) is opened on the cementing screen (6). A sealing wall (7) is constructed at the connection between the cementing casing (4) and the cementing screen (6) to seal and separate the horizontal branch well (5) from the vertical shaft (3), so that the horizontal branch well (5) is isolated from the outside gas. C. A combustion-induced fracturing device (8) is installed inside the cementing screen (6) at the position corresponding to the screen hole (6-1). The combustion-induced fracturing device (8) is equipped with a gas concentration monitor (8-1) and an ignition head (8-2). An oxygen inlet pipe (9) and a methane inlet pipe (10) pass through the combustion-induced fracturing device (8). The oxygen inlet pipe (9) and the methane inlet pipe (10) inside the combustion-induced fracturing device (8) are respectively equipped with an oxygen pipe valve (8-3) and a methane pipe valve (8-4). The other part of the methane inlet pipe (10) The end extends out of the vertical shaft (3) and splits into two pipelines, which are respectively connected to the extraction device (11) on the ground and the outlet of the No. 1 gas booster pump (12). The inlet of the No. 1 gas booster pump (12) is connected to the methane storage chamber (13) and a methane storage chamber valve (13-1) is installed at the connection. The oxygen inlet pipe (9) is connected to the outlet of the No. 2 gas booster pump (14). The inlet of the No. 2 gas booster pump (14) is connected to the oxygen storage chamber (15) and an oxygen storage chamber valve (15-1) is installed at the connection. The gas concentration monitor (8-1) and ignition head (8-2) are both fixed inside the combustion-explosion fracturing device (8). The oxygen pipe valve (8-3), methane pipe valve (8-4), methane storage chamber valve (13-1), oxygen storage chamber valve (15-1), gas concentration monitor (8-1), and ignition head (8-2) are all connected to the ground control center (17) via communication line (16) to complete the assembly of the combustion-explosion fracturing system. Movable components are distributed along the circumference of the cementing screen (6) on the combustion-explosion fracturing device (8). The movable fracturing head (8-5) and the combustion and explosion fracturing device (8) are detachable. The positions of the movable fracturing head (8-5) on the combustion and explosion fracturing device (8) are all cylindrical structures coaxial with the corresponding screen holes (6-1). The inner end of the movable fracturing head (8-5) is slidably disposed in the cylindrical structure along the axial direction of the cylindrical structure. The outer end of the movable fracturing head (8-5) is conical, and energy-concentrating holes (8-6) are distributed on the outer end of the movable fracturing head (8-5). D. Open the methane storage chamber valve (13-1) and the oxygen storage chamber valve (15-1), and start the No. 1 gas booster pump (12) and the No. 2 gas booster pump (14) to continuously introduce methane and oxygen into the combustion and detonation device (8) through the oxygen inlet pipe (9), the methane inlet pipe (10), the oxygen pipe valve (8-3), and the methane pipe valve (8-4). At this time, the control center (17) collects the gas concentration in the combustion and detonation device (8) in real time through the gas concentration monitor (8-1). When the collected real-time gas concentration reaches the explosion limit value, stop the No. 1 gas booster pump (12) and the No. 2 gas booster pump (14), and close the valve. Close the oxygen pipe valve (8-3) and methane pipe valve (8-4); the control center (17) controls the ignition head (8-2) to ignite, thereby causing the mixed gas in the combustion-explosion fracturing device (8) to explode, generating a detonation shock wave, causing the four movable fracturing heads (8-5) of the combustion-explosion fracturing device (8) to extend and press into the shale reservoir. At the same time, the detonation shock wave impacts the shale reservoir (2) through the energy-concentrating hole (8-6) on the combustion-explosion fracturing device (8). Meanwhile, the inner walls of the four movable fracturing heads (8-5) of the combustion-explosion fracturing device (8) are provided with anti-retraction serrations (8-7) to prevent the movable fracturing heads (8-5) from retracting due to ground stress. E. Repeat step D to press all four movable fracturing heads (8-5) of each combustion-induced fracturing device (8) into the shale reservoir (2), and the detonation shock wave repeatedly impacts the shale reservoir (2) to form a fracture network (18). After completion, close the oxygen pipe valve (8-3), methane storage chamber valve (13-1), and oxygen storage chamber valve (15-1), open the methane pipe valve (8-4), and start the extraction device (11) to extract shale gas from the shale reservoir (2) through the methane inlet pipe (10). F. Repeat steps A to E to extract shale gas from the remaining shale reservoirs that need to be exploited.

2. The method according to claim 1, characterized in that: In step C), a combustion fracturing device (8) is installed in the cementing screen (6) at the position corresponding to the screen hole (6-1) by a fixing rope (6-2). Each combustion fracturing device (8) is fixed by multiple fixing ropes (6-2). One end of the fixing rope (6-2) is fixed to the rope fixing connection point distributed on the inner wall of the cementing screen (6), and the other end is fixed to the combustion fracturing device (8) so that the combustion fracturing device (8) is held in the set position inside the cementing screen (6).

3. A shale gas reservoir methane multi-stage pulse combustion and fracturing device for use in the method of claim 1 or 2, characterized in that: The system includes a vertical shaft (3) drilled from the ground into the shale reservoir (2). A horizontal branch well (5) is drilled at the lower end of the vertical shaft (3) along the shale reservoir (2). Cementing casing (4) and cementing screen (6) are respectively installed in the vertical shaft (3) and the horizontal branch well (5). The ends of the cementing casing (4) and the cementing screen (6) are fixedly connected. A combustion-induced fracturing device (8) is fixedly distributed along the length direction in the middle of the cementing screen (6). A gas concentration monitor (8-1) and an ignition head (8-2) are also installed in the combustion-induced fracturing device (8). Movable components are distributed along the circumference of the cementing screen (6) on the combustion-induced fracturing device (8). The fracturing head (8-5) and the movable fracturing head (8) are detachably connected. The cementing screen (6) has screen holes (6-1) at positions corresponding to the movable fracturing head (8-5) for the movable fracturing head (8-5) to pass through. The fracturing device (8) has a cylindrical structure coaxial with the corresponding screen hole (6-1) at positions corresponding to the movable fracturing head (8-5). The inner end of the movable fracturing head (8-5) is slidably disposed within the cylindrical structure along its axial direction. The outer end of the movable fracturing head (8-5) is a pointed cone shape. Energy-concentrating holes (8-6) are distributed on the outer end of 8-5 to facilitate injection into the shale reservoir (2). The oxygen inlet pipe (9) and the methane inlet pipe (10) both extend into the combustion-explosion fracturing device (8). The oxygen inlet pipe (9) and the methane inlet pipe (10) in the combustion-explosion fracturing device (8) are respectively equipped with oxygen pipe valves (8-3) and methane pipe valves (8-4). The other end of the methane inlet pipe (10) extends out of the vertical shaft (3) and splits into two pipelines, which are respectively connected to the outlet of the extraction device (11) on the ground and the outlet of the No. 1 gas booster pump (12). The inlet of the No. 1 gas booster pump (12) is connected to the outlet of the extraction device (11) on the ground and the outlet of the No. 1 gas booster pump (12). The methane storage chamber (13) is connected and a methane storage chamber valve (13-1) is installed at the connection. The oxygen inlet pipe (9) is connected to the outlet of the No. 2 gas booster pump (14). The inlet of the No. 2 gas booster pump (14) is connected to the oxygen storage chamber (15) and an oxygen storage chamber valve (15-1) is installed at the connection. The oxygen pipe valve (8-3), methane pipe valve (8-4), methane storage chamber valve (13-1), oxygen storage chamber valve (15-1), gas concentration monitor (8-1), and ignition head (8-2) are all connected to the ground control center (17) via a communication line (16).

4. The shale gas reservoir methane multi-stage pulse combustion and fracturing device according to claim 3, characterized in that: The combustion-explosion fracturing device (8) has a cross-shaped structure. The four cross ends of the combustion-explosion fracturing device (8) are four movable fracturing heads (8-5) and the matching cylindrical structure.

5. The shale gas reservoir methane multi-stage pulse combustion and fracturing device according to claim 3, characterized in that: The inner wall of the cylindrical structure is provided with four sets of anti-retraction serrations (8-7). The end of the cylindrical structure without anti-retraction serrations (8-7) is provided with a movable rupture head baffle (8-8). When the movable rupture head (8-5) increases to its maximum size under the influence of the detonation shock wave, the movable rupture head baffle (8-8) will limit the movable rupture head (8-5) from continuing to increase outward.

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