A natural gas hydrate freezing sampling device and method

Abstract

The present invention provides a natural gas hydrate freezing sampling device, which is arranged in a drill pipe with a drill bit connected to the bottom, comprising an inner pipe, wherein a cold source chamber upper connector, a cold source chamber lower connector and a sealing plate are sequentially arranged in sequence from top to bottom in the inner pipe, a cold source storage chamber is formed between the cold source chamber upper connector and the cold source chamber lower connector, a freezing chamber is arranged between the cold source chamber lower connector and the sealing plate, and a freezing pressure holding chamber is formed between the sealing plate and the retaining spring seat; a core tube is coaxially arranged in the freezing chamber, and further comprises a valve stem arranged parallel to the axis of the inner pipe, a first through hole is provided on the cold source chamber lower connector, a second through hole is provided on the sealing plate, the valve stem is slidably penetrated through the cold source chamber upper connector, the first through hole and the second through hole, and a first piston and a second piston are spaced apart on the valve stem and respectively engaged with the first through hole and the second through hole; the present invention solves the problem that current freezing coring mostly only freezes the side wall of the core tube while the lower end of the core tube is not frozen, resulting in poor freezing effect and pressure holding effect.

Description

Technical Field

[0001] The present invention relates to the technical field of freezing sampling, and in particular to a natural gas hydrate freezing sampling device and method. Background Art

[0002] Natural gas hydrates are solid, crystalline substances composed of natural gas and water molecules. They are primarily combustible, containing methane. Their high energy density, wide distribution, and vast reserves make them an important alternative to conventional energy sources. Furthermore, combustion of natural gas hydrates does not produce pollutants, effectively protecting the environment. Therefore, the large-scale development of natural gas hydrate resources can help transform energy consumption.

[0003] Natural gas hydrates are primarily found in seafloor sediments at the ocean margins and in permafrost on land. Drilling sampling is the most direct method for identifying natural gas hydrates and is essential for validating the findings of other survey methods. By obtaining cores, we can visually observe and understand the rock types, structure, and tectonic characteristics of the Earth's crust, as well as detect its oil, gas, and water content, without disrupting the formation. Laboratory testing and analysis provide a clear understanding of the distribution, stability, and various physical properties of natural gas hydrates, providing a basis for formulating appropriate development plans and production enhancement measures.

[0004] Because natural gas hydrates can only exist stably under certain temperatures and pressures, thermal insulation and pressure maintenance are required during coring. Currently, there are two main methods for maintaining accurate sampling: thermal insulation and pressure maintenance sampling, and bottom-hole freeze sampling. Thermal insulation and pressure maintenance sampling primarily utilizes ball valves and flap valves to maintain pressure within the core barrel, along with passive insulation using insulation materials. However, due to its complex mechanical structure, lack of guaranteed sealing, and high heat conduction during drilling, this method results in a high coring failure rate. Bottom-hole freeze sampling utilizes cryogenic temperatures to inhibit the decomposition of natural gas hydrates. After drilling is complete, a cooling catalyst is injected into the freezing chamber via a cold source control device. When the cold source contacts the catalyst, it absorbs a significant amount of heat, lowering the core barrel's temperature to a low temperature range. This prevents the decomposition of natural gas hydrates during extraction. This method offers a high coring success rate and ensures that the material remains unchanged. However, current freeze coring methods typically freeze only the core barrel's sidewalls, leaving the lower end unfrozen. This results in poor freezing and pressure maintenance, leading to inaccurate subsequent testing results. Summary of the Invention

[0005] The purpose of the present invention is to provide a natural gas hydrate freezing sampling device and method, which solves the problems that current freezing coring mostly only freezes the side wall of the core tube, while the lower end of the core tube is not frozen, resulting in poor freezing effect and pressure maintenance effect, leading to inaccurate subsequent detection results.

[0006] The embodiments of the present invention are achieved through the following technical solutions: a natural gas hydrate freezing sampling device is arranged in a drill pipe with a drill bit connected to the bottom, comprising an inner tube, a retaining spring seat is provided at the lower end of the inner tube, an upper cold source chamber connector, a lower cold source chamber connector and a sealing plate are sequentially arranged in the inner tube from top to bottom, a cold source storage chamber is formed between the upper cold source chamber connector and the lower cold source chamber connector, a freezing chamber is provided between the lower cold source chamber connector and the sealing plate, and a freezing pressure holding chamber is formed between the sealing plate and the retaining spring seat;

[0007] A core tube is coaxially arranged in the freezing chamber, the lower end of the core tube passes through the sealing plate and is slidably connected to a clamping spring, and the clamping spring seat is sleeved on the clamping spring and slidably abuts against the clamping spring;

[0008] It also includes a valve stem arranged parallel to the axis of the inner tube, a first through hole is provided on the lower handle of the cold source chamber, a second through hole is provided on the sealing plate, the valve stem is slidably passed through the upper handle of the cold source chamber, the first through hole and the second through hole, a first piston and a second piston are arranged on the valve stem at intervals, the first piston is engaged with the first through hole, and the second piston is engaged with the second through hole.

[0009] Furthermore, the valve stem is a metal tube, a guide hole communicating with an inner cavity of the valve stem is provided on the valve stem, a plug is provided at the lower end of the inner cavity of the valve stem, and the guide hole is located in the cold source storage chamber.

[0010] Furthermore, a limit block is provided on the upper end of the valve stem, and a return spring is sleeved on the valve stem. The upper and lower ends of the return spring are respectively in contact with the limit block and the upper handle of the cold source chamber.

[0011] Furthermore, a hinge seat is provided on the top of the upper handle of the cold source chamber, a hitting plate is hinged on the hinge seat, and the limit block is located on the rotation path of the hitting plate;

[0012] The beating plate is further provided with a magnet block, and the top of the upper handle of the cold source chamber is further provided with an electromagnet, which is located on the rotation path of the magnet block.

[0013] Furthermore, the electromagnet is located between the hinge seat and the valve stem, and the electromagnet and the magnet block attract each other;

[0014] It also includes a limit spring, which is arranged on the side of the hinge seat away from the magnet block, and the two ends of the limit spring are respectively connected to the hitting plate and the cold source chamber.

[0015] Furthermore, the electromagnet is located on a side of the hinge seat away from the valve stem, and the electromagnet and the magnet block repel each other.

[0016] Furthermore, an axial flow tube is coaxially arranged on the upper end of the inner tube, a partition is sealed on the lower end of the axial flow tube, and a plurality of branch channels are circumferentially arranged on the axial flow tube, and the plurality of branch channels are connected to the inner cavity of the axial flow tube;

[0017] A generator is provided in the inner cavity of the inner tube, a rotating shaft is provided on the partition, the upper end of the rotating shaft extends to the inner cavity of the axial flow tube and is coaxially sleeved with a turbine, and the lower end of the rotating shaft is transmission-connected to the input end of the generator; the generator is electrically connected to the electromagnet.

[0018] Furthermore, a first channel is provided between the cold source storage chamber and the outer wall of the inner tube, and a first one-way pressure relief valve is provided on the first channel. The first one-way pressure relief valve is used for one-way flow from the cold source storage chamber to the outside of the inner tube;

[0019] A second channel is provided between the freezing chamber and the outer wall of the inner tube. A second one-way pressure relief valve is provided on the second channel. The second one-way pressure relief valve is used for one-way flow from the freezing chamber to the outside of the inner tube.

[0020] Furthermore, a third channel is radially provided on the upper edge of the lower connecting piece of the cold source chamber, an overflow hole is provided on the top of the core tube, the overflow hole is connected to the third channel, a third one-way pressure relief valve is provided on the third channel, and the third one-way pressure relief valve is used for one-way flow from the inside of the core tube to the outside of the inner tube.

[0021] Furthermore, a natural gas hydrate freezing sampling method using a natural gas hydrate freezing sampling device is provided, characterized in that it comprises the following steps:

[0022] S1. Select a target sampling area and lower the drill pipe;

[0023] S2. Injecting a cold source into the cold source storage chamber on the surface, placing a cooling catalyst into the freezing chamber, and then lowering the inner tube into the drill pipe using a salvage device. After reaching the bottom of the hole, retrieving the salvage device and continuing drilling and sampling;

[0024] S3. After the sampling is completed, the drilling fluid circulation is stopped, and the inner tube is lifted up by a fishing device for a certain distance, so that the core sample is separated and moved upward by the cooperation between the retaining spring and the retaining spring seat;

[0025] S4. Increase the supply of drilling fluid. The drilling fluid drives the turbine to rotate, which in turn drives the generator to rotate at a high speed. The generator generates current to drive the electromagnet to rotate the striking plate, which drives the valve stem to move downward, so that the first piston and the second piston are simultaneously separated from the first through hole and the second through hole. The cold source first enters the freezing chamber and then enters the freezing pressure holding chamber, thereby freezing the core sample.

[0026] S5. After freezing for 10-20 minutes, remove the inner tube and store the core sample in a liquid nitrogen storage tube or a high-pressure container.

[0027] The technical solutions of the embodiments of the present invention have at least the following advantages and beneficial effects:

[0028] 1. When the core tube sampling is completed, the valve stem is driven to move downward, thereby driving the first piston and the second piston to move downward to open the first through hole and the second through hole. At this time, the cold source storage chamber, the freezing chamber and the freezing pressure holding chamber are all connected. The cold source in the cold source storage chamber first enters the freezing chamber and then enters the freezing pressure holding chamber. The cold source and the cooling catalyst are mixed in the freezing chamber to cool and freeze the core tube, and then enter the freezing pressure holding chamber, forming an ice-sealing effect at the sample where the retaining spring is broken, and then forming a layer of ice at the contact point between the end of the core tube and the core, so that the core is in a sealed environment, thereby achieving the effect of pressure maintenance, improving the success rate of freezing sampling and maximally maintaining the original state of the sample, which helps to improve the accuracy of subsequent test results.

[0029] 2. The valve stem is a metal tube. A guide hole connected to its inner cavity is provided on the valve stem. A plug is provided at the lower end of the inner cavity of the valve stem to prevent the cold source from flowing out from the lower end. The guide hole is located in the cold source storage chamber. During specific implementation, the liquid cold source in the cold source storage chamber enters the metal tube through the guide hole. The metal tube is made of metal with high thermal conductivity, and thus it is easy to conduct heat, which can pre-cool the cooling catalyst in the freezing chamber to prevent the freezing room temperature from being too high during drilling, causing the hydrate in the core tube to decompose, resulting in subsequent sampling failure. Furthermore, multiple groups of metal tubes can be provided to improve the pre-cooling effect of the cooling catalyst in the freezing chamber.

[0030] 3. When the drill bit is drilling downward and sampling, the drilling fluid is pumped normally. At this time, the drilling fluid is insufficient to drive the turbine or drives it at a low speed. The turbine drives the rotor of the generator through the rotating shaft. The rotor rotates inside the stator. The current generated by the electromagnet is insufficient to generate a magnetic force that is insufficient to overcome the elastic force of the return spring and the limit spring. In other words, the magnetic force generated by the electromagnet is insufficient to drive the valve stem downward through the plate. When the valve stem needs to be driven downward, high-pressure drilling fluid can be pumped to drive the turbine to rotate at a high speed. The current generated by the generator then increases to generate sufficient magnetic force. After overcoming the elastic force of the return spring and the limit spring, the plate continues to rotate, and finally the valve stem is driven downward, making the freezing operation simple and convenient.

[0031] 4. When it is expected that all the cold sources enter the freezing chamber and the freezing pressure holding chamber for freezing, you can choose to stop pumping the drilling fluid, which will help to freeze the lower end of the core barrel, thereby achieving better freezing and pressure holding effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 A schematic diagram of the internal structure of a natural gas hydrate freezing sampling device provided by the present invention;

[0034] Figure 2 for Figure 1 A magnified schematic diagram of the structure at A in the middle;

[0035] Figure 3 for Figure 1 A magnified schematic diagram of the structure at B in the middle;

[0036] Icons: 1. Drill bit, 2. Drill pipe, 3. Inner pipe, 31. Upper handle of cold source chamber, 32. Lower handle of cold source chamber, 321. First through hole, 322. Third channel, 323. Third one-way pressure relief valve, 33. Closing plate, 331. Second through hole, 34. Cold source storage chamber, 341. First channel, 342. First one-way pressure relief valve, 35. Freezer chamber, 351. Second channel, 352. Second one-way pressure relief valve, 36. Freezer chamber Pressure chamber, 4, core tube, 41, retaining ring, 42, retaining ring seat, 43, overflow hole, 5, valve stem, 51, first piston, 52, second piston, 53, guide hole, 54, plug, 55, limit block, 56, return spring, 6, hinge seat, 61, hitting plate, 62, magnet block, 63, limit spring, 7, electromagnet, 71, rotating shaft, 72, turbine, 73, generator, 8, axial flow tube, 81, partition, 82, diversion channel. DETAILED DESCRIPTION

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0038] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0039] Reference Figures 1 to 3 As shown, this embodiment provides a natural gas hydrate freezing sampling device, which is arranged in a drill pipe 2 with a drill bit 1 connected to the bottom, including an inner tube 3, a rope corer is arranged above the inner tube 3, a spring seat 42 is arranged at the lower end of the inner tube 3, and a cold source chamber upper hand 31, a cold source chamber lower hand 32 and a sealing plate 33 are arranged in sequence from top to bottom in the inner tube 3, a cold source storage chamber 34 is formed between the cold source chamber upper hand 31 and the cold source chamber lower hand 32, a freezing chamber 35 is provided between the cold source chamber lower hand 32 and the sealing plate 33, and a freezing pressure holding chamber 36 is formed between the sealing plate 33 and the spring seat 42.

[0040] More specifically, the cold source in the cold source storage chamber 34 is liquid carbon dioxide, and the cooling catalyst in the freezing chamber 35 is alcohol. The mixture of liquid carbon dioxide and alcohol helps them to vaporize and absorb heat, thereby having a better freezing effect; or alcohol is stored in the cold source storage chamber 34, and dry ice is stored in the freezing chamber 35; or liquid nitrogen is stored in the cold source storage chamber 34, and alcohol is stored in the freezing chamber 35. The combination of liquid nitrogen and alcohol can also achieve better cooling; dry ice can also be placed in the freezing chamber 35, and liquid nitrogen can be injected into the cold source storage chamber 34. The combination of the two also has a better refrigeration effect.

[0041] like Figure 1 As shown, a core tube 4 is coaxially arranged in the freezing chamber 35. The lower end of the core tube 4 passes through the sealing plate 33 and is slidably connected to a retaining spring 41. The retaining spring seat 42 is sleeved on the retaining spring 41 and slidably abuts against the retaining spring 41. The core tube 4 is mainly used to store core samples. When the core tube 4 is filled with the mixture sample, the core tube 4 is frozen by injecting a cold source into the freezing chamber 35, thereby keeping the core sample in a solid state, which is helpful for subsequent sample detection.

[0042] More specifically, it also includes a valve stem 5 arranged parallel to the axis of the inner tube 3, a first through hole 321 is provided on the lower handle 32 of the cold source chamber, and a second through hole 331 coaxial with the first through hole 321 is provided on the sealing plate 33. The valve stem 5 is slidably passed through the upper handle 31 of the cold source chamber, the first through hole 321 and the second through hole 331, and a first piston 51 and a second piston 52 are arranged at intervals on the valve stem 5. The first piston 51 is engaged with the first through hole 321, and the second piston 52 is engaged with the second through hole 331.

[0043] When implementing it specifically, Figure 1As shown, when the sampling of the core tube 4 is completed, the valve stem 5 is driven to move downward, thereby driving the first piston 51 and the second piston 52 to move downward to open the first through hole 321 and the second through hole 331. At this time, the cold source storage chamber 34, the freezing chamber 35 and the freezing pressure holding chamber 36 are all connected, and the cold source in the cold source storage chamber 34 first enters the freezing chamber 35 and then enters the freezing pressure holding chamber 36. The cold source and the cooling catalyst are mixed in the freezing chamber 35 to cool and freeze the core tube 4, and then enter the freezing pressure holding chamber 36, forming an ice-sealing effect at the sample where the retaining spring 41 is broken, and then forming a layer of ice at the place where the end of the core tube 4 contacts the core, so that the core is in a sealed environment, thereby achieving the effect of pressure maintenance, improving the success rate of freezing sampling and maximally keeping the sample in its original state, which helps to improve the accuracy of subsequent test results.

[0044] More specifically, Figure 1-3 As shown, the valve stem 5 is a metal tube, and a guide hole 53 connected to its inner cavity is provided on the valve stem 5. A plug 54 is provided at the lower end of the inner cavity of the valve stem 5. The plug 54 is used to prevent the cold source from flowing out from the lower end. The guide hole 53 is located in the cold source storage chamber 34. During implementation, the liquid cold source in the cold source storage chamber 34 enters the metal tube through the guide hole 53. The metal tube is made of metal with high thermal conductivity, and thus it is easy to conduct heat, which can cool down and pre-cool the cooling catalyst in the freezing chamber 35 to prevent the temperature of the freezing chamber 35 from being too high during drilling, causing the hydrate in the core tube 4 to decompose, resulting in subsequent sampling failure. Furthermore, multiple groups of metal tubes can be provided to improve the pre-cooling effect of the cooling catalyst in the freezing chamber 35.

[0045] like Figure 1 As shown, a limit block 55 is provided at the upper end of the valve stem 5, and the limit block 55 blocks the upper end of the inner cavity of the valve stem 5. A return spring 56 is sleeved on the valve stem 5, and the upper and lower ends of the return spring 56 are respectively in contact with the limit block 55 and the upper handle 31 of the cold source chamber, and then the valve stem 5 is driven to move upward by the return spring 56, so that the first piston 51 and the second piston 52 respectively block the first through hole 321 and the second through hole 331, preventing the cold source from entering the freezing chamber 35 and the freezing pressure holding chamber 36 too early, and at the same time ensuring that the cooling catalyst does not enter the freezing pressure holding chamber 36 too early.

[0046] A hinge seat 6 is provided at the top of the cold source chamber upper handle 31, to which a plate 61 is hingedly connected, and a limit block 55 is located in the rotation path of the plate 61. A magnet block 62 is also provided on the plate 61, and an electromagnet 7 is also provided at the top of the cold source chamber upper handle 31, and the electromagnet 7 is located in the rotation path of the magnet block 62. The electromagnet 7 generates magnetism to drive the magnet block 62, which in turn drives the plate 61 to rotate. When the plate 61 rotates, it acts on the limit block 55, which in turn drives the valve stem 5 to move downward, allowing the cold source to enter the freezing chamber 35 and the freezing pressure holding chamber 36, and perform the freezing operation.

[0047] As one example, Figure 1-3 As shown, the electromagnet 7 is located between the hinge seat 6 and the valve stem 5, and the electromagnet 7 and the magnet block 62 attract each other. It also includes a limit spring 63, which is set on the side of the hinge seat 6 away from the magnet block 62. The two ends of the limit spring 63 are respectively connected to the hitting plate 61 and the upper handle 31 of the cold source chamber, which is used to limit the hitting plate 61 and prevent the magnet block 62 from being too far away from the electromagnet 7. However, the limit spring 63 can also be omitted if the hitting plate 61 does not deviate. Then, the electromagnet 7 attracts the magnet block 62, which in turn drives the hitting plate 61 to press the valve stem 5 downward.

[0048] As another embodiment, the electromagnet 7 is located on the side of the hinge 6 away from the valve stem 5, and the electromagnet 7 and the magnet block 62 repel each other. Then, the electromagnet 7 generates magnetism and the magnet block 62 repel each other, so as to drive the striking plate 61 to press the valve stem 5 downward.

[0049] More specifically, Figure 1 and 2 As shown, an axial flow tube 8 is coaxially disposed between the upper end of the inner tube 3 and the rope corer. A partition 81 is sealed at the lower end of the axial flow tube 8. A plurality of branch channels 82 are circumferentially disposed on the axial flow tube 8. The branch channels 82 are in communication with the inner cavity of the axial flow tube 8. Drilling fluid flows through the inner cavity of the axial flow tube 8. After passing through the turbine 72, the drilling fluid flows from the branch channels 82 to between the inner tube 3 and the drill pipe 2.

[0050] A generator 73 is provided in the inner cavity of the inner tube 3, and a rotating shaft 71 is provided on the partition 81. The upper end of the rotating shaft 71 extends to the inner cavity of the axial flow tube 8 and is coaxially sleeved with a turbine 72. The lower end of the rotating shaft 71 is transmission-connected to the input end of the generator 73; the generator 73 is electrically connected to the electromagnet 7.

[0051] In specific implementation, when the drill bit 1 is drilling downward and sampling, the drilling fluid is pumped normally. At this time, the drilling fluid is insufficient to drive the turbine 72 or drives it at a low speed. The turbine 72 drives the rotor of the generator to rotate through the rotating shaft 71. The rotor rotates inside the stator. The magnetic force generated by the current generated by the electromagnet 7 is insufficient to overcome the elastic force of the return spring 56 and the limit spring 63, that is, the magnetic force generated by the electromagnet 7 is insufficient to drive the valve stem 5 to move downward through the striking plate 61. When it is necessary to drive the valve stem 5 downward, high-pressure drilling fluid can be pumped to drive the turbine 72 to rotate at a high speed. Then, the current generated by the generator 73 increases to generate sufficient magnetic force, which overcomes the elastic force of the return spring 56 and the limit spring 63 and continues to drive the striking plate 61 to rotate, ultimately driving the valve stem 5 downward.

[0052] The relationship between current, coil turns, and magnetic field strength can be expressed by the formula H = N * I / Le, where H is the magnetic field strength (A / m); N is the number of turns in the excitation coil; I is the measured excitation current (A); and Le is the effective magnetic path length of the test sample (m). Therefore, for a given number of coil turns N and effective magnetic path length Le, the greater the current I, the greater the magnetic field strength H. Therefore, we increase the drilling fluid pump rate until the current supplied by turbine 72-driven generator 73 reaches a certain value. This increases the magnetic field strength of electromagnet 7 to a level sufficient to attract the magnet, thereby driving plate 61 downward and simultaneously driving valve stem 5 downward.

[0053] like Figure 1 and 2 As shown, a first channel 341 is provided between the cold source storage chamber 34 and the outer wall of the inner tube 3, and a first one-way pressure relief valve 342 is provided on the first channel 341. The first one-way pressure relief valve 342 is used for one-way flow from the cold source storage chamber 34 to the outside of the inner tube 3; in specific implementation, a cold source is stored in the cold source storage chamber 34. If the pressure in the cold source storage chamber 34 increases during filling or subsequent vaporization of the cold source, the pressure can be relieved through the first one-way pressure relief valve 342.

[0054] like Figure 1 As shown, a second passage 351 is provided between the freezing chamber 35 and the outer wall of the inner tube 3. A second one-way pressure relief valve 352 is provided on the second passage 351. The second one-way pressure relief valve 352 ensures one-way flow of air from the freezing chamber 35 to the outside of the inner tube 3. Similarly, after the cold source enters the freezing chamber 35, if the pressure in the freezing chamber 35 increases, the pressure can be relieved through the second one-way pressure relief valve 352.

[0055] like Figure 1 and 3 As shown, a third channel 322 is radially provided on the lower handle 32 of the cold source chamber, an overflow hole 43 is provided on the top of the core tube 4, the overflow hole 43 is connected to the third channel 322, and a third one-way pressure relief valve 323 is provided on the third channel 322. The third one-way pressure relief valve 323 is used for one-way flow from the inside of the core tube 4 to the outside of the inner tube 3; therefore, when the core sample enters the core tube 4, the air or liquid inside the core tube 4 can be discharged through the third one-way pressure relief valve 323.

[0056] More specifically, the inner walls of the cold source storage chamber 34, the freezing chamber 35 and the freezing pressure holding chamber 36 are paved with thermal insulation materials, usually materials with relatively low thermal conductivity such as rock wool boards, glass wool boards, polyurethane foam boards, etc., to ensure that the heat generated during the drilling process will hardly be conducted in and to ensure that the "coldness" of the cold source during the freezing process will not be wasted.

[0057] At the same time, multiple sealing rings are provided between the valve stem 5 and the upper handle 31 of the cold source chamber to maintain the pressure of the cold source storage chamber 34 under the premise of ensuring the normal sliding of the valve stem 5. Similarly, when the first piston 51 and the second piston 52 cooperate with the first through hole 321 and the second through hole 331 respectively, they also have a pressure maintaining effect.

[0058] A natural gas hydrate freezing sampling method, using a natural gas hydrate freezing sampling device, comprises the following steps:

[0059] S1. Select the target sampling area, set up the drilling platform, and lower the drill pipe 2 and its assembly, that is, drill down to the target depth;

[0060] S2. Inject a cold source into the cold source storage chamber 34 on the ground surface, place a cooling catalyst into the freezing chamber 35, and then use a salvage device to lower the inner tube 3 into the drill pipe 2 as a whole. After reaching the bottom of the hole, continue drilling and sampling;

[0061] S3. After sampling is complete, stop the drilling fluid circulation and use the overshot tool to lift the inner tube 3 a certain distance. The core sample is then separated and moved upwards via the retaining spring 41 and retaining spring seat 42. The upward movement of the inner tube 3 does not need to be too great. As the inner tube 3 moves upwards, the retaining spring 41, due to its own gravity and the positional constraints of the retaining spring seat 42, will engage the core through friction. The retaining spring seat 42, resting on the step inside the drill bit 1, drives the retaining spring 41 further, breaking the core and ensuring core recovery. After the core is broken, the lifting of the inner tube 3 assembly can be stopped.

[0062] S4. The drilling fluid supply is then increased. The drilling fluid drives the turbine 72 to rotate, which in turn drives the generator 73 to rotate at high speed, generating current to drive the electromagnet 7 to drive the plate 61 to rotate, thereby driving the valve stem 5 to move downward, so that the first piston 51 and the second piston 52 are separated from the first through hole 321 and the second through hole 331 at the same time. The cold source first enters the freezing chamber 35 and then enters the freezing pressure holding chamber 36 to achieve pressure-maintained freezing of the core sample. When it is expected that all the cold source enters the freezing chamber 35 and the freezing pressure holding chamber 36 for freezing, the drilling fluid pumping can be stopped, which helps to freeze the lower end of the core barrel.

[0063] S5. After freezing for 10-20 minutes, remove the inner tube 3 and store the core sample in a liquid nitrogen storage tube or a high-pressure container.

[0064] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A natural gas hydrate freezing sampling device, arranged in a drill pipe (2) with a drill bit (1) connected to the bottom, characterized in that: The invention comprises an inner tube (3), a retaining spring seat (42) is provided at the lower end of the inner tube (3), an upper cold source chamber handpiece (31), a lower cold source chamber handpiece (32) and a sealing plate (33) are sequentially arranged in the inner tube (3) from top to bottom, a cold source storage chamber (34) is formed between the upper cold source chamber handpiece (31) and the lower cold source chamber handpiece (32), a freezing chamber (35) is provided between the lower cold source chamber handpiece (32) and the sealing plate (33), and a freezing pressure holding chamber (36) is formed between the sealing plate (33) and the retaining spring seat (42); A core tube (4) is coaxially arranged in the freezing chamber (35); the lower end of the core tube (4) passes through the sealing plate (33) and is slidably connected to a retaining spring (41); the retaining spring seat (42) is sleeved on the retaining spring (41) and slidably abuts against the retaining spring (41); It also includes a valve stem (5) arranged parallel to the axis of the inner tube (3), a first through hole (321) is provided on the lower handle (32) of the cold source chamber, and a second through hole (331) is provided on the sealing plate (33), the valve stem (5) is slidably inserted into the upper handle (31) of the cold source chamber, the first through hole (321) and the second through hole (331), and a first piston (51) and a second piston (52) are arranged at intervals on the valve stem (5), the first piston (51) is engaged with the first through hole (321), and the second piston (52) is engaged with the second through hole (331); The valve stem (5) is a metal tube. A guide hole (53) communicating with the inner cavity of the valve stem (5) is provided on the valve stem (5). A sealing plug (54) is provided at the lower end of the inner cavity of the valve stem (5). The guide hole (53) is located in the cold source storage chamber (34). A limit block (55) is provided at the upper end of the valve stem (5), and a return spring (56) is sleeved on the valve stem (5), and the upper and lower ends of the return spring (56) are respectively in contact with the limit block (55) and the upper handle (31) of the cold source chamber; A hinge seat (6) is provided on the top of the cold source chamber upper handle (31), a beating plate (61) is hingedly connected to the hinge seat (6), and the limit block (55) is located on the rotation path of the beating plate (61); A magnet block (62) is also provided on the beating plate (61), and an electromagnet (7) is also provided on the top of the cold source chamber upper handle (31), and the electromagnet (7) is located on the rotation path of the magnet block (62).

2. A natural gas hydrate freezing sampling device according to claim 1, characterized in that: The electromagnet (7) is located between the hinge seat (6) and the valve stem (5), and the electromagnet (7) and the magnet block (62) attract each other; It also includes a limit spring (63), which is arranged on the side of the hinge seat (6) away from the magnet block (62), and the two ends of the limit spring (63) are respectively connected to the hitting plate (61) and the upper handle (31) of the cold source chamber.

3. A natural gas hydrate freezing sampling device according to claim 1, characterized in that: The electromagnet (7) is located on a side of the hinge seat (6) away from the valve stem (5), and the electromagnet (7) and the magnet block (62) repel each other.

4. A natural gas hydrate freezing sampling device according to claim 2 or 3, characterized in that: An axial flow tube (8) is coaxially arranged at the upper end of the inner tube (3), a partition (81) is sealed at the lower end of the axial flow tube (8), and a plurality of branch flow channels (82) are circumferentially arranged on the axial flow tube (8), and the plurality of branch flow channels (82) are in communication with the inner cavity of the axial flow tube (8); A generator (73) is provided in the inner cavity of the inner tube (3), a rotating shaft (71) is provided on the partition (81), the upper end of the rotating shaft (71) extends into the inner cavity of the axial flow tube (8) and is coaxially sleeved with a turbine (72), and the lower end of the rotating shaft (71) is transmission-connected to the input end of the generator (73); the generator (73) is electrically connected to the electromagnet (7).

5. The natural gas hydrate freezing sampling device according to claim 4, characterized in that: A first channel (341) is provided between the cold source storage chamber (34) and the outer wall of the inner tube (3), and a first one-way pressure relief valve (342) is provided on the first channel (341). The first one-way pressure relief valve (342) is used for one-way flow from the inside of the cold source storage chamber (34) to the outside of the inner tube (3); A second channel (351) is provided between the freezing chamber (35) and the outer wall of the inner tube (3). A second one-way pressure relief valve (352) is provided on the second channel (351). The second one-way pressure relief valve (352) is used for one-way flow from the inside of the freezing chamber (35) to the outside of the inner tube (3).

6. A natural gas hydrate freezing sampling device according to claim 5, characterized in that: A third channel (322) is radially provided on the lower connector (32) of the cold source chamber, an overflow hole (43) is provided on the top of the core tube (4), the overflow hole (43) is communicated with the third channel (322), a third one-way pressure relief valve (323) is provided on the third channel (322), and the third one-way pressure relief valve (323) is used for one-way flow from the inside of the core tube (4) to the outside of the inner tube (3).

7. A method for freezing and sampling natural gas hydrates, using the natural gas hydrate freezing and sampling device according to claim 6, characterized in that: The following steps are involved: S1, selecting a target sampling area and lowering the drill pipe (2); S2, injecting a cold source into the cold source storage chamber (34) on the surface, placing a cooling catalyst into the freezing chamber (35), and then using a salvage device to lower the inner tube (3) into the drill pipe (2). After reaching the bottom of the hole, the salvage device is retrieved and drilling and sampling are continued; S3. After the sampling is completed, the drilling fluid circulation is stopped, and the inner tube (3) is lifted up by a salvage device for a certain distance, and then the core sample is separated and moved upward by the cooperation of the retaining spring (41) and the retaining spring seat (42); S4. Increase the supply of drilling fluid. The drilling fluid drives the turbine (72) to rotate and then drives the generator (73) to rotate at a high speed. The generator (73) generates current to enable the electromagnet (7) to drive the hitting plate (61) to rotate. The hitting plate (61) drives the valve stem (5) to move downward, so that the first piston (51) and the second piston (52) are separated from the first through hole (321) and the second through hole (331) at the same time. The cold source first enters the freezing chamber (35) and then enters the freezing pressure holding chamber (36), thereby achieving freezing of the core sample. S5. After freezing for 10-20 minutes, remove the inner tube (3) and store the core sample in a liquid nitrogen storage tube or a high-pressure container.

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