A cavitation oscillation stimulation tool and method for natural gas hydrates

Abstract

The present invention discloses a cavitation oscillation stimulation tool and method for natural gas hydrates, which includes an upper joint, a flow-disturbing fixed disk, an oscillating flow-disturbing movable disk, a Venturi tube, a swirl cavitation chamber, and a cavitation nozzle. A plurality of flow-disturbing holes are distributed on the disk surfaces of the flow-disturbing fixed disk and the oscillating flow-disturbing movable disk; the upper joint, the Venturi tube, and the swirl cavitation chamber are connected in sequence. A cavitation nozzle is provided at the injection hole on the cavity wall of the swirl cavitation chamber. The flow-disturbing fixed disk and the oscillating flow-disturbing movable disk are placed closely at the connection between the upper joint and the Venturi tube. The stimulation method in the present invention utilizes the stimulation tool of the present invention to generate a large number of microbubbles through cavitation. Under the action of hydraulic transmission, the microbubbles enter the natural gas hydrate reservoir and explode and collapse, destroying the lattice structure of the natural gas hydrates, promoting the decomposition of the natural gas hydrates, greatly improving the exploitation efficiency of the natural gas hydrate reservoir, thereby maintaining the integrity and continuity of the fluid migration channels in the reservoir and achieving the purpose of increasing production.

Description

Technical Field

[0001] The present invention relates to the technical field of natural gas hydrate exploitation, and particularly to a cavitation oscillation stimulation tool and method for natural gas hydrates. Background Art

[0002] Natural Gas Hydrate, commonly known as "flammable ice", is an ice-like, non-stoichiometric cage-shaped crystalline compound composed of water molecules and gas molecules (mainly methane) under high pressure and low temperature conditions. As an unconventional natural gas, natural gas hydrates are widely distributed in marine, lake, and permafrost sediments with a water depth exceeding 300 meters, and the resource volume is extremely rich. The total carbon content of global natural gas hydrates is twice that of existing fossil fuels (oil, natural gas, coal), and it is recognized as the most potential new type of efficient, clean alternative energy in the future and is a strategic breakthrough point for the global energy revolution.

[0003] Its exploitation principles include methods such as pressure reduction decomposition method, heating method, chemical agent injection method, carbon dioxide replacement method, and solid direct excavation method. Analyzing from the practice of multiple global natural gas hydrate trial productions, the pressure reduction decomposition method is currently the lowest-cost exploitation method. The pressure reduction decomposition method is based on the phase equilibrium diagram of natural gas hydrates, that is, reducing the reservoir pressure of natural gas hydrates below the equilibrium pressure, causing the natural gas hydrates to undergo a phase change and decompose into gaseous methane and liquid water.

[0004] However, pressure reduction decomposition requires a good seepage channel in the reservoir to conduct the pressure drop in the wellbore to the deep reservoir. The initial permeability of the reservoir containing hydrates ranges from 0.01 to dozens of millidarcies. During the exploitation of natural gas hydrates, the solid natural gas hydrates in the pores decompose into liquid water and gaseous methane and seep into the wellbore, the effective stress in the pores increases, the sediment structure becomes dense, the porosity decreases, and the permeability of the sediment layer containing natural gas hydrates decreases. In addition, the water generated by the decomposition of hydrates will change the salinity of the formation water in the sediment pores, which may cause the swelling of expansive clay minerals, resulting in pore blockage and a decrease in the permeability of the sediment. Moreover, since the decomposition of natural gas hydrates is an endothermic process, a large amount of decomposition heat will also cause the temperature of the surrounding reservoir to decrease, which in turn reduces the decomposition rate of natural gas hydrates. At the same time, it may trigger the formation of secondary hydrates, blocking the fluid migration channel and reducing permeability. The formation heat conduction process is relatively slow and cannot provide sufficient heat supplement for the hydrate reservoir in time, making it impossible to effectively relieve the blockage of the seepage channel.

[0005] Therefore, artificially increasing and maintaining the integrity of seepage channels by transforming the reservoir is the key to increasing the gas production of natural gas hydrates. Patent CN103498648A discloses a natural gas hydrate extraction method that combines pressure reduction and hydraulic fracturing technology. By means of hydraulic fracturing, the permeability of the reservoir is improved, and the fluid flow channels and pressure reduction gas extraction are smooth. Patent CN111287708A discloses a reservoir transformation device and method for improving the recovery rate of hydrate deposits. By creating cracks, the permeability is increased and the starting migration channels are increased. Patent CN103206199A discloses a thermal fluid fracturing device and method for extracting natural gas hydrates. By injecting thermal fluid into the reservoir, thermal excitation and pressure reduction are combined to give full play to the advantages of both, thereby improving the extraction efficiency of hydrate deposits.

[0006] Since natural gas hydrate reservoirs are mainly weakly consolidated sediments that have not yet been diagenesized and have poor mechanical strength, hydraulic fracturing cannot effectively control the development direction of cracks. In addition, unlike conventional oil and gas, natural gas molecules and water molecules are interconnected by van der Waals forces to form solid crystals. Natural gas hydrates participate in the construction of hydrate reservoirs in the form of solid lattices, and the content of adsorbed gas and free gas in the pores is relatively small. If the temperature and pressure environment of the reservoir does not change, even if the reservoir is completely broken up by hydraulic fracturing, the gas stored in the hydrate ore body in the form of a lattice cannot be fully released. Therefore, how to effectively destroy the structure of the hydrate lattice is one of the key factors in transforming the hydrate reservoir. Summary of the Invention

[0007] The purpose of the present invention is to provide a natural gas hydrate cavitation oscillation stimulation tool to solve one or more technical problems existing in the prior art and at least provide a beneficial option or create conditions.

[0008] The present invention also aims to provide a method for increasing the production of natural gas hydrates by using a natural gas hydrate cavitation oscillation stimulation tool.

[0009] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0010] A natural gas hydrate cavitation oscillation production enhancement tool comprises an upper joint, a flow disturbance fixed plate, an oscillating flow disturbance plate, a venturi tube, a swirl cavitation chamber and a cavitation nozzle, wherein the flow disturbance fixed plate and the oscillating flow disturbance plate are both provided with a plurality of flow disturbance holes; the upper joint is connected to one end of the venturi tube, the other end of the venturi tube is connected to the swirl cavitation chamber, the cavity wall of the swirl cavitation chamber is provided with an injection hole, the injection hole is provided with the cavitation nozzle, and the flow disturbance fixed plate and the oscillating flow disturbance plate are placed on the connection between the upper joint and the venturi tube.

[0011] Furthermore, a plurality of diversion grooves are distributed on the inner wall surface of the Venturi tube; the diversion grooves are in a spiral structure.

[0012] Furthermore, the upper joint is rotationally and sealingly connected to the Venturi tube through a rotary seal.

[0013] Furthermore, the rotary seal includes a rotary seal cylinder, a support ring, a disc spring, a wear-resistant ring, a ball bearing and a sealing ring. One end of the upper joint extends into one end of the rotary seal cylinder and is fixedly connected to the tubular joint of the flow-disturbing fixed plate. The sealing ring is arranged between the inner wall of the rotary seal cylinder and the outer wall of the tubular joint of the flow-disturbing fixed plate. The ball bearing is arranged between the inner wall of the rotary seal cylinder and the outer wall of the upper joint. The support ring, the disc spring and the wear-resistant ring are sleeved on the upper joint. The wear-resistant ring presses against the end face of the ball bearing. The support ring presses against the step surface on the inner surface of the rotary seal cylinder. Both ends of the disc spring press against between the support ring and the wear-resistant ring. The other end of the rotary seal cylinder is threadedly connected to the end of the Venturi tube. The oscillating flow-disturbing disc is fixed in the Venturi tube and can rotate relative to the flow-disturbing fixed plate but cannot rotate relative to the Venturi tube.

[0014] Furthermore, a wear-resistant sleeve is arranged between the inner wall of the rotary seal cylinder and the outer wall of the upper joint.

[0015] Furthermore, an annular groove is arranged on the outer wall surface of the upper joint. A plurality of threaded through holes corresponding to the annular groove are distributed along the circumferential direction on the barrel wall of the rotary seal cylinder. Steel balls, sealant plugs and plugs are arranged in the threaded through holes. The plug is threadedly connected to the threaded through hole and presses against the sealant plug. The sealant plug presses the steel balls into the annular groove. Annular seal grooves are arranged on both sides of the threaded through holes on the inner barrel wall of the rotary seal cylinder. Lip seals are arranged in the annular seal grooves.

[0016] Furthermore, there are 3 injection holes, and the 3 injection holes are evenly distributed along the circumferential direction of the swirl cavitation chamber.

[0017] Furthermore, the cavitation nozzle includes a tubular body, a liquid booster sleeve and a liquid diffuser sleeve. A liquid cavitation chamber is arranged in the middle of the tubular body. An annular flow-disturbing boss is arranged on the inner wall of the liquid cavitation chamber. The annular flow-disturbing boss is close to the water inlet end of the liquid cavitation chamber. The liquid booster sleeve is inserted into the water inlet end of the tubular body and is threadedly connected to the tubular body. The liquid diffuser sleeve is inserted into the water outlet end of the tubular body and is threadedly connected to the tubular body.

[0018] Furthermore, the upper joint is connected to one end of a steel pipe. The other end of the steel pipe extends upward out of the natural gas hydrate reservoir and is connected to a water source. A water pump is connected in series on the steel pipe.

[0019] A method for increasing production of natural gas hydrate by using a cavitation oscillation production-increasing tool for natural gas hydrate, comprising the following steps:

[0020] Step S1: Create a natural gas hydrate well in the natural gas hydrate mining area;

[0021] Step S2: Connect the upper joint of the cavitation oscillation production-increasing tool for natural gas hydrate by using a steel pipe, lower the cavitation oscillation production-increasing tool for natural gas hydrate into the natural gas hydrate reservoir section in the natural gas hydrate well, and seal the natural gas hydrate well by using the sealing device at the wellhead;

[0022] Step S3: Pump liquid from the ground by using a water pump, transport it through the steel pipe to the cavitation oscillation production-increasing tool for natural gas hydrate. A large number of microbubbles are generated after cavitation in the cavitation oscillation production-increasing tool for natural gas hydrate, are ejected through the cavitation nozzle and squeezed into the natural gas hydrate reservoir. The microbubbles in the natural gas hydrate reservoir collapse and burst, and the generated microjets and microshock waves act on the natural gas hydrate lattice to break the van der Waals force connection bond between natural gas molecules and water molecules, destroy the natural gas hydrate lattice structure, and promote the decomposition of natural gas hydrate.

[0023] The beneficial effects of the present invention are as follows: In the production-increasing method of the present invention, the production-increasing tool of the present invention is used to create a large number of microbubbles through cavitation. Under the action of hydraulic transmission, the microbubbles enter the natural gas hydrate reservoir. The microbubbles explode and collapse near the hydrate lattice. The shock waves or high-speed microjets generated by the explosion and collapse of the microbubbles are used to break the van der Waals force connection bond between natural gas molecules and water molecules, destroy the natural gas hydrate lattice structure, and promote the decomposition of natural gas hydrate, greatly improving the production efficiency of the natural gas hydrate reservoir; As the natural gas hydrate continuously decomposes, the gas concentration in the pores increases and the fluid pressure in the pores rises. According to the gas diffusion mechanism, the produced natural gas will inevitably migrate towards the wellbore direction, thereby maintaining the integrity and continuity of the fluid migration channel in the reservoir. Description of the Drawings

[0024] The present invention is further described with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation to the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the following drawings without creative efforts:

[0025] Figure 1 is a schematic internal structure diagram of the cavitation oscillation production-increasing tool for natural gas hydrate of the present invention;

[0026] Figure 2 is Figure 1 an enlarged view of the A position shown in;

[0027] Figure 3 is Figure 1An enlarged view of part B shown;

[0028] Figure 4 is Figure 1 A perspective view of the Venturi tube shown;

[0029] Figure 5 is Figure 1 A schematic diagram of the internal structure of the cavitation nozzle shown;

[0030] Figure 6 is Figure 1 A schematic diagram of the end face structure of the oscillating turbulent flow disk shown;

[0031] Figure 7 A diagram showing the working state of the present invention.

[0032] In the figure: 1 - upper joint; 2 - turbulent flow fixed disk; 3 - oscillating turbulent flow disk; 4 - Venturi tube; 5 - swirling cavitation chamber; 6 - cavitation nozzle; 7 - turbulent flow holes; 8 - injection holes; 9 - rotating seal; 10 - rotating seal cylinder; 11 - support ring; 12 - disc spring; 13 - wear-resistant ring; 14 - ball bearing; 15 - sealing ring; 16 - tubular joint; 17 - stepped surface; 18 - wear-resistant sleeve; 19 - annular groove; 20 - threaded through hole; 21 - steel ball; 22 - sealing rubber plug; 23 - plug; 24 - annular sealing groove; 25 - lip seal; 26 - diversion groove; 27 - tubular body; 28 - liquid booster sleeve; 29 - liquid diffusion sleeve; 30 - liquid cavitation chamber; 31 - annular turbulent flow boss; 32 - natural gas hydrate cavitation oscillation stimulation tool; 33 - steel pipe; 34 - water pump; 35 - natural gas hydrate well; 36 - natural gas hydrate reservoir section; 37 - sealing device. Detailed implementation manners

[0033] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, without conflict, the embodiments of the present application and the features in the embodiments may be combined with each other.

[0034] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper surface", "lower surface", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "forward rotation", "reverse rotation", "axial direction", "radial direction", "circumferential direction", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0035] AsFigure 1 , 6 As shown, a cavitation oscillation stimulation tool for natural gas hydrates includes an upper joint 1, a flow disturbance fixed disk 2, an oscillating flow disturbance moving disk 3, a Venturi tube 4, a swirl cavitation chamber 5, and a cavitation nozzle 6. A plurality of flow disturbance holes 7 are distributed on the disk surfaces of the flow disturbance fixed disk 2 and the oscillating flow disturbance moving disk 3. One end of the upper joint 1 is connected to one end of the Venturi tube 4, and the other end of the Venturi tube 4 communicates with the swirl cavitation chamber 5. Injection holes 8 are provided on the chamber wall of the swirl cavitation chamber 5, and the cavitation nozzle 6 is provided at the injection holes 8. The flow disturbance fixed disk 2 and the oscillating flow disturbance moving disk 3 are placed against the connection part of the upper joint 1 and the Venturi tube 4.

[0036] The upper joint 1 is rotationally and sealingly connected to the Venturi tube 4 through a rotary seal 9.

[0037] As Figure 2 shown, the rotary seal 9 includes a rotary seal cylinder 10, a support ring 11, a disc spring 12, a wear-resistant ring 13, a ball bearing 14, and a sealing ring 15. One end of the upper joint 1 extends into one end of the rotary seal cylinder 10 and is fixedly connected to the tubular joint 16 of the flow disturbance fixed disk 2. The sealing ring 15 is arranged between the inner wall of the rotary seal cylinder 10 and the outer wall of the tubular joint 16 of the flow disturbance fixed disk 2. The ball bearing 14 is arranged between the inner wall of the rotary seal cylinder 10 and the outer wall of the upper joint 1. The support ring 11, the disc spring 12, and the wear-resistant ring 13 are sleeved on the upper joint 1. The wear-resistant ring 13 presses against the end face of the ball bearing 14, the support ring 11 presses against the step surface 17 on the inner surface of the rotary seal cylinder 10, and both ends of the disc spring 12 press against between the support ring 11 and the wear-resistant ring 13. The other end of the rotary seal cylinder 10 is threadedly connected to the end of the Venturi tube 4. The oscillating flow disturbance moving disk 3 is fixed in the Venturi tube 4 and can rotate relative to the flow disturbance fixed disk 2 but not relative to the Venturi tube 4. A wear-resistant sleeve 18 is arranged between the inner wall of the rotary seal cylinder 10 and the outer wall of the upper joint 1.

[0038] As Figure 3 shown, an annular groove 19 is provided on the outer wall surface of the upper joint 1. A plurality of threaded through holes 20 corresponding to the annular groove 19 are distributed along the circumferential direction on the barrel wall of the rotary seal cylinder 10. Steel balls 21, sealing rubber plugs 22, and plugs 23 are arranged in the threaded through holes 20. The plug 23 is threadedly connected to the threaded through hole 20 and presses against the sealing rubber plug 22, and the sealing rubber plug 22 presses the steel balls 21 into the annular groove 19. Annular sealing grooves 24 are provided on both sides of the threaded through holes 20 on the inner barrel wall of the rotary seal cylinder 10, and lip seals 25 are arranged in the annular sealing grooves 24.

[0039] As Figure 4As shown, multiple flow guiding grooves 26 are distributed on the inner wall surface of the Venturi tube 4; the flow guiding grooves 26 are of a spiral structure. There are 3 injection holes 8, and the 3 injection holes 8 are evenly distributed along the circumferential direction of the swirling cavitation chamber 5.

[0040] As Figure 5 shown, the cavitation nozzle 6 includes a tubular body 27, a liquid booster sleeve 28 and a liquid diffusion sleeve 29. A liquid cavitation chamber 30 is provided in the middle of the tubular body 27. An annular flow disturbing boss 31 is provided on the inner wall of the liquid cavitation chamber 30. The annular flow disturbing boss 31 is close to the water inlet end of the liquid cavitation chamber 30. The liquid booster sleeve 28 is inserted into the water inlet end of the tubular body 27 and is threadedly connected to the tubular body 27. The liquid diffusion sleeve 29 is inserted into the water outlet end of the tubular body 27 and is threadedly connected to the tubular body 27.

[0041] As Figure 7 shown, the upper joint 1 of the natural gas hydrate cavitation oscillation stimulation tool 32 is connected to one end of the steel pipe 33. The other end of the steel pipe 33 extends upward to the ground outside the natural gas hydrate reservoir and is connected to a water source. A water pump 34 is connected in series on the steel pipe 33.

[0042] A method for stimulating natural gas hydrate production by using a natural gas hydrate cavitation oscillation stimulation tool includes the following steps:

[0043] Step S1: Create a natural gas hydrate well 35 in the natural gas hydrate mining area;

[0044] Step S2: Connect the upper joint of the natural gas hydrate cavitation oscillation stimulation tool 32 by using the steel pipe 33, lower the natural gas hydrate cavitation oscillation stimulation tool 32 into the natural gas hydrate reservoir section 36 in the natural gas hydrate well 35, and seal the natural gas hydrate well 35 by using the sealing device 37 at the wellhead;

[0045] Step S3: Pump liquid from the ground by using the water pump 34, transport it through the steel pipe to the natural gas hydrate cavitation oscillation stimulation tool. A large number of microbubbles are generated after the liquid is cavitated in the natural gas hydrate cavitation oscillation stimulation tool, are ejected through the cavitation nozzle and squeezed into the natural gas hydrate reservoir. The microbubbles in the natural gas hydrate reservoir collapse and break, and the generated microjets and microshock waves act on the natural gas hydrate lattice to break the van der Waals force connection bond between natural gas molecules and water molecules and destroy the natural gas hydrate lattice structure, so as to promote the decomposition of natural gas hydrate.

[0046] Working principle: During operation, after the steel pipeline is connected to the upper joint of the natural gas hydrate cavitation oscillation stimulation tool 32, the upper joint is fixed, and the rotating seal cylinder 10, the oscillation disturbing flow disk 3, and the Venturi tube 4 are fixed together and can rotate relative to the upper joint 1 and the disturbing flow fixed disk 2 simultaneously. In the present invention, by pumping liquid, after the liquid flows through the disturbing flow fixed disk 2 and the oscillation disturbing flow disk 3, it then flows into the Venturi tube 4 and the swirl cavitation chamber 5 where the liquid is cavitated, and finally sprays out from the cavitation nozzle 6, generating a large number of cavitation bubbles. Through the action of hydraulics, the cavitation bubbles are transported to the deep reservoir. By using the micro shock waves and micro jets generated by the explosion and collapse of the cavitation bubbles, the lattice of natural gas hydrates is destroyed, promoting the decomposition of natural gas hydrates and achieving the effect of cavitation oscillation stimulation.

[0047] In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A cavitation oscillation stimulation tool for natural gas hydrate, characterized in that: It includes an upper joint, a spoiler fixed disk, an oscillating spoiler moving disk, a Venturi tube, a swirling cavitation chamber and a cavitation nozzle. A plurality of spoiler holes are distributed on the disk surfaces of the spoiler fixed disk and the oscillating spoiler moving disk; one end of the upper joint is connected to one end of the Venturi tube, the other end of the Venturi tube communicates with the swirling cavitation chamber, injection holes are provided on the chamber wall of the swirling cavitation chamber, and the cavitation nozzle is provided at the injection holes. The spoiler fixed disk and the oscillating spoiler moving disk are placed against the connection part of the upper joint and the Venturi tube. The oscillating spoiler moving disk is fixed in the Venturi tube and can rotate relative to the spoiler fixed disk but not relative to the Venturi tube; a plurality of flow guiding grooves are distributed on the inner wall surface of the Venturi tube; the flow guiding grooves adopt a spiral structure; the upper joint is rotationally and sealingly connected to the Venturi tube through a rotary seal; the cavitation nozzle includes a tubular body, a liquid booster sleeve and a liquid diffusion sleeve. A liquid cavitation chamber is provided in the middle of the tubular body. An annular spoiler boss is provided on the inner wall of the liquid cavitation chamber. The annular spoiler boss is close to the water inlet end of the liquid cavitation chamber. The liquid booster sleeve is inserted into the water inlet end of the tubular body and is threadedly connected to the tubular body. The liquid diffusion sleeve is inserted into the water outlet end of the tubular body and is threadedly connected to the tubular body.

2. The cavitation oscillation stimulation tool for natural gas hydrate according to claim 1, characterized in that: The rotary seal includes a rotary seal cylinder, a support ring, a disc spring, a wear-resistant ring, a ball bearing and a sealing ring. One end of the upper joint extends into one end of the rotary seal cylinder and is fixedly connected to the tubular joint of the spoiler fixed disk. The sealing ring is provided between the inner wall of the rotary seal cylinder and the outer wall of the tubular joint of the spoiler fixed disk. The ball bearing is provided between the inner wall of the rotary seal cylinder and the outer wall of the upper joint. The support ring, the disc spring and the wear-resistant ring are sleeved on the upper joint. The wear-resistant ring presses against the end face of the ball bearing. The support ring presses against the step surface on the inner surface of the rotary seal cylinder. Two ends of the disc spring press against between the support ring and the wear-resistant ring. The other end of the rotary seal cylinder is threadedly connected to the end of the Venturi tube.

3. The cavitation oscillation stimulation tool for natural gas hydrate according to claim 2, wherein: A wear-resistant sleeve is provided between the inner wall of the rotary seal cylinder and the outer wall of the upper joint.

4. The gas hydrate cavitation oscillation stimulation tool according to claim 3, wherein: An annular groove is provided on the outer wall surface of the upper joint. A plurality of threaded through holes corresponding to the annular groove are distributed along the circumferential direction on the barrel wall of the rotary seal cylinder. Steel balls, sealant plugs and plugs are provided in the threaded through holes. The plug is threadedly connected to the threaded through hole and presses against the sealant plug. The sealant plug presses the steel balls into the annular groove; annular seal grooves are provided on the inner barrel wall of the rotary seal cylinder and on both sides of the threaded through holes. Lip seals are provided in the annular seal grooves.

5. The gas hydrate cavitation oscillation stimulation tool according to claim 4, wherein: There are 3 injection holes, and the 3 injection holes are evenly distributed along the circumferential direction of the swirling cavitation chamber.

6. The gas hydrate cavitation oscillation stimulation tool according to claim 5, characterized in that: The upper joint is connected to one end of a steel pipe. The other end of the steel pipe extends upward out of the natural gas hydrate reservoir and is connected to a water source. A water pump is connected in series on the steel pipe.

7. A stimulation method for exploiting natural gas hydrates by using the natural gas hydrate cavitation oscillation stimulation tool according to claim 6, comprising the following steps: Step S1, creating a natural gas hydrate well in the natural gas hydrate mining area; Step S2: Connect the upper joint of the natural gas hydrate cavitation oscillation stimulation tool using a steel pipe, lower the natural gas hydrate cavitation oscillation stimulation tool to the natural gas hydrate reservoir section in the natural gas hydrate well, and seal the natural gas hydrate well using the sealing device at the wellhead. Step S3: Pump liquid from the ground using a water pump, transport it through the steel pipe to the natural gas hydrate cavitation oscillation stimulation tool. A large number of micro-bubbles are generated after cavitation occurs inside the natural gas hydrate cavitation oscillation stimulation tool, and are ejected through the cavitation nozzle and squeezed into the natural gas hydrate reservoir. Inside the natural gas hydrate reservoir, the micro-bubbles collapse and break, and the generated micro-jet and micro-shock wave act on the natural gas hydrate lattice to break the van der Waals force connection bond between natural gas molecules and water molecules, destroy the natural gas hydrate lattice structure, and promote the decomposition of natural gas hydrate.

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