Injection device and method for marine CO2 hydrate sealing and storage method

Abstract

The invention provides an injection device and method for marine CO2 hydrate sealing and storage. The injection device comprises an injection well; the injection well comprises an injection platform arranged above the sea level and an injection pipeline arranged below the sea level; the injection pipeline comprises a surface sleeve and a CO2 injection pipe arranged in the surface sleeve in a sleeving manner; a perforation layer section is arranged at the bottom end of the CO2 injection pipe; in the downward direction from the sea level, the injection device comprises a carbon dioxide detection device arranged in seawater and a perforation layer section arranged below the bottom boundary of a CO2 hydrate stable region. The CO2 hydrate sealing method is high in sealing efficiency, good in thermodynamic stability and huge in sealing potential, well drilling and operation cost can be effectively reduced, and economic benefits are increased; and the carbon dioxide detection device can change the injection rate of CO2 according to the formation pressure, safety accidents such as CO2 leakage are rapidly monitored, and safe and efficient storage of CO2 is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of CO2 storage, and in particular relates to an injection device and method for offshore CO2 hydrate storage. Background Art

[0002] Since the 1990s, carbon dioxide emissions have increased year by year. If carbon dioxide emissions are not strictly controlled, it will have serious consequences for my country's and even the world's economy, environment and public health. In order to reduce carbon dioxide emissions, carbon capture and storage (CCUS) technology must be implemented, so CCUS technology has become a necessary way to save energy and reduce emissions. This technology is being applied in various ways around the world and has achieved significant reductions in carbon dioxide emissions. The storage process of CCUS technology involves a variety of storage technologies, among which marine storage has become a research hotspot in recent years due to its many advantages.

[0003] However, current research mainly focuses on storing carbon dioxide gas in traditional saline aquifers. For example, CN 104909366A discloses a method for storing carbon dioxide in a submarine saline aquifer using hydrate closure. The method injects carbon dioxide into the submarine saline aquifer through an injection device. The injected carbon dioxide moves to the upper layer of the saline aquifer under the action of buoyancy, and forms a carbon dioxide accumulation zone under the sealing effect of the cap layer. A small portion of the carbon dioxide escapes into the marine sedimentary layer through geological cracks in the cap layer, and combines with water in the sedimentary layer under the action of formation pressure and temperature to form carbon dioxide hydrates. A hydrate layer is formed in the sedimentary layer to prevent further escape of carbon dioxide, and a very small portion of the carbon dioxide leaked into the deep sea water is dissolved to achieve complete sealing.

[0004] However, the application of marine CCUS technology has always faced the challenges of high energy consumption and high costs. Traditional marine CCUS projects require the use of offshore drilling platforms to drill wells thousands of meters deep to store CO2 in deep depleted oil and gas reservoirs or saline aquifers. This traditional carbon storage method ignores the fact that CO2 can be stored in shallow formations in the form of hydrates. Hydrate carbon storage technology is a new type of seabed storage technology. This technology injects carbon dioxide into the seabed formation and uses hydrate formation to stably store carbon dioxide in the seabed formation. Compared with other carbon dioxide storage technologies, the use of hydrates to store carbon dioxide has many characteristics such as high gas storage density, mild storage conditions, simple storage methods, and long-term stable storage.

[0005] CN 117418898A discloses a method for enhanced hydrate method carbon dioxide storage, which comprises: injecting liquid CO2 into the stable zone or sedimentary layer of deep-sea CO2 hydrate and injecting tryptophan solution at the same time. The method mainly emphasizes the main role of chemical reagents in the formation of CO2 hydrate.

[0006] In summary, it is necessary to provide a storage method that can store carbon dioxide in shallow seabed areas and reduce the cost of offshore CO2 storage. Summary of the invention

[0007] The purpose of the present invention is to provide an injection device and method for offshore CO2 hydrate storage. The CO2 hydrate storage method provided by the present invention has high storage efficiency, good thermodynamic stability, and huge storage potential, and can effectively reduce drilling and operation costs and increase economic benefits.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides an injection device for offshore CO2 hydrate storage, the injection device comprising an injection well;

[0010] The injection well includes an injection platform arranged above the sea level, and an injection pipeline arranged below the sea level;

[0011] The injection pipeline includes a surface casing and a CO2 injection pipe sleeved inside the surface casing; a perforation layer section is arranged at the bottom end of the CO2 injection pipe;

[0012] From the sea level downward direction, the injection device includes a carbon dioxide detection device arranged in the seawater, and a perforation layer section arranged below the bottom boundary of the CO2 hydrate stability domain.

[0013] In the present invention, the injection platform and the injection pipeline are provided to realize the storage of CO2 in the form of liquid CO2 hydrate, thereby greatly increasing the storage capacity and storage efficiency;

[0014] In addition, the carbon dioxide detection device can change the injection rate of CO2 according to the formation pressure, quickly monitor safety accidents such as CO2 leakage, and realize safe and efficient storage of CO2;

[0015] Furthermore, the injection device for offshore CO2 hydrate storage provided by the present invention has a simple structure and can store carbon dioxide in shallow seabed areas, which is beneficial to reducing the cost of offshore CO2 storage.

[0016] As a preferred technical solution of the present invention, according to the CO2 gas transportation direction, the injection platform includes a storage and transportation pipeline, a gas compression device and a wellhead blowout preventer connected in sequence.

[0017] As a preferred technical solution of the present invention, the length of the perforation layer section is 10 to 200 m, for example, it can be 10 m, 50 m, 100 m, 120 m, 140 m, 160 m, 180 m or 200 m, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] Preferably, the perforation aperture of the perforation layer section ranges from 10 to 20 mm, for example, 10 mm, 12 mm, 14 mm, 16 mm, 18 mm or 20 mm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0019] Preferably, a CO2 injection control device is provided at the top of the perforated layer section, and the CO2 injection control device is used to control the injection temperature, pressure and rate of CO2.

[0020] Preferably, a reservoir in-situ monitoring device is provided between the CO2 injection control device and the perforation layer section.

[0021] In the present invention, the reservoir in-situ monitoring device is used to monitor the temperature, pressure and carbon dioxide concentration of the reservoir.

[0022] As a preferred technical solution of the present invention, the carbon dioxide detection device includes a first carbon dioxide detection device and a second carbon dioxide detection device.

[0023] Preferably, the carbon dioxide detection device is used for detecting leakage of CO2 on the seabed;

[0024] Preferably, the first carbon dioxide detection device is arranged on the side wall of the surface casing;

[0025] Preferably, the distance between the setting position of the second carbon dioxide detection device and the surface casing is 180 to 220 m, for example, it can be 180 m, 190 m, 200 m, 210 m or 220 m, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] It is worth noting that the purpose of arranging two carbon dioxide detection devices in the injection device of the present invention is to monitor the carbon dioxide concentration around the well and 200 meters away from the injection well respectively, so as to further accurately determine the leakage standard of carbon dioxide.

[0027] In a second aspect, the present invention provides a method for offshore CO2 hydrate storage, which is carried out using the injection device provided in the first aspect.

[0028] As a preferred technical solution of the present invention, the method comprises the following steps:

[0029] (1) Calculate the depth of the bottom boundary of the CO2 hydrate stability zone based on formation parameters, and inject liquid CO2 below the bottom boundary of the CO2 hydrate stability zone;

[0030] (2) setting the injection device provided in the first aspect according to the depth of the bottom boundary of the CO2 hydrate stability zone obtained in step (1);

[0031] (3) Liquid CO2 is repeatedly injected into the bottom of the injection well through an injection platform, and then cementing operations are performed to achieve the storage of CO2.

[0032] In the present invention, the carbon dioxide storage method using the injection device provided in the first aspect can achieve rapid storage by the CO2 hydrate method, which is specifically manifested as follows: liquid CO2 is injected into the target layer. At this time, the density of liquid CO2 is less than that of water, and it continuously floats up into the stable domain of CO2 hydrate. The generated high-saturation CO2 hydrate forms an impermeable cap layer and blocks the further floating of CO2. Subsequently, the injected CO2 mainly diffuses laterally in the liquid phase, thereby achieving the seabed storage of CO2; at the same time, the carbon dioxide detection device can monitor multiple seabed parameters (temperature, pressure, CO2 hydrate saturation, gaseous / liquid carbon dioxide concentration) in real time. When the seabed parameters are abnormal, measures such as well closure are taken in time to achieve safe storage of CO2;

[0033] Furthermore, in the process of injecting liquid CO2 above the bottom boundary of the CO2 hydrate stability domain in step (1), CO2 and water will automatically generate CO2 hydrates when they meet in the high-pressure and low-temperature seabed environment. CO2 is mainly present in the pores in the form of CO2 hydrates. Below the bottom boundary of the CO2 hydrate stability domain, CO2 hydrates cannot be generated. CO2 is mainly present in the pores in liquid form, thereby further realizing the storage of CO2.

[0034] As a preferred technical solution of the present invention, the perforation layer section in the injection device is arranged at a depth of 0 to 100 m below the bottom boundary of the CO2 hydrate stability zone, for example, it can be 10 m, 20 m, 30 m, 40 m, 50 m, 60 m, 70 m, 80 m, 90 m or 100 m, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] As a preferred technical solution of the present invention, the repeated injection of liquid CO2 in step (3) includes: (a) when the bottom boundary pressure of the CO2 hydrate stability domain is ≥5MPa, the injection of liquid CO2 is stopped, and the injection of liquid CO2 is repeated when the pressure is lower than 5MPa; or (b) when the second carbon dioxide detection device detects leakage of seabed CO2, the injection of liquid CO2 is stopped, and the injection of liquid CO2 is repeated when the second carbon dioxide detection device no longer detects CO2.

[0036] As a preferred technical solution of the present invention, the end point of the repeated injection of liquid CO2 in step (3) includes: when the first carbon dioxide detection device detects leakage of CO2 on the seabed.

[0037] As a preferred technical solution of the present invention, the injection rate of liquid CO2 in step (3) is 0-1000m 3 / d, and not 0, for example, it can be 10m 3 / d, 100m 3 / d, 200m 3 / d, 400m 3 / d, 600m 3 / d, 800m 3 / d or 1000m 3 / d, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0038] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) The injection device provided by the present invention can simultaneously store CO2 in the form of liquid and CO2 hydrate, greatly increasing the storage capacity and storage efficiency;

[0041] (2) The carbon dioxide detection device in the injection device for offshore CO2 hydrate storage provided by the present invention can change the CO2 injection rate according to the formation pressure, quickly monitor safety accidents such as CO2 leakage, and realize safe and efficient storage of CO2;

[0042] (3) The injection device for offshore CO2 hydrate storage provided by the present invention has a simple structure and is easy to install, which is conducive to industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A schematic diagram of the structure of the injection device for offshore CO2 hydrate storage provided by the present invention;

[0044] Figure 2 A diagram showing the relationship between formation temperature, formation pressure and depth provided in Example 1 of the present invention;

[0045] Figure 3 The phase equilibrium curve of carbon dioxide hydrate provided in Example 1 of the present invention;

[0046] Figure 4 This is a relationship diagram between phase equilibrium pressure and bottom layer pressure at different depths provided in Example 1 of the present invention.

[0047] Among them, 1 is the injection platform, 2 is the wellhead blowout preventer, 3 is the gas compression device, 4 is the storage and transportation pipeline, 5 is seawater, 6 is the bottom boundary of the CO2 hydrate stability zone, 7 is the surface casing, 8 is the CO2 injection pipe, 9 is the reservoir in-situ monitoring device, 10 is the CO2 injection control device, 11 is the perforation layer, 12 is the second carbon dioxide detection device, and 13 is the first carbon dioxide detection device. DETAILED DESCRIPTION

[0048] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0049] In a specific embodiment, the present invention provides an injection device for offshore CO2 hydrate storage, such as Figure 1 As shown, the injection device includes the injection well including an injection platform 1 arranged above the sea level, and an injection pipeline arranged below the sea level;

[0050] The injection pipeline includes a surface casing 7 and a CO2 injection pipe 8 sleeved inside the surface casing; a perforation layer section 11 is provided at the bottom end of the CO2 injection pipe 8;

[0051] From the sea level downward, the injection device includes a carbon dioxide detection device arranged in the seawater 5, and a perforation layer section 11 arranged below the bottom boundary 6 of the CO2 hydrate stability domain.

[0052] According to the CO2 gas delivery direction, the injection platform includes a storage and transportation pipeline 4, a gas compression device 3 and a wellhead blowout preventer 2 connected in sequence;

[0053] The length of the perforation section 11 is 10 to 200 m; the perforation aperture of the perforation section 11 is in the range of 10 to 20 mm; a CO2 injection control device is provided at the top of the perforation section 11, and the CO2 injection control device 10 is used to control the injection temperature, pressure and rate of CO2; a reservoir in-situ monitoring device 9 is provided between the CO2 injection control device 10 and the perforation section 11;

[0054] The carbon dioxide detection device includes a first carbon dioxide detection device 13 and a second carbon dioxide detection device 12; the carbon dioxide detection device is used to detect the leakage of CO2 on the seabed; the first carbon dioxide detection device 13 is arranged on the side wall of the surface casing 7; the second carbon dioxide detection device 12 is arranged at a distance of 180 to 220 m from the surface casing 7.

[0055] In another specific embodiment, the present invention provides an offshore CO2 hydrate storage method using the above-mentioned injection device, the method comprising the following steps:

[0056] (1) Calculate the depth of the bottom boundary of the CO2 hydrate stability zone based on formation parameters, and inject liquid CO2 below the bottom boundary of the CO2 hydrate stability zone;

[0057] (2) setting the injection device according to the depth of the bottom boundary of the CO2 hydrate stability zone obtained in step (1);

[0058] The perforation layer section in the injection device is set at a depth of 0 to 100 m below the bottom boundary of the CO2 hydrate stability zone;

[0059] (3) repeatedly injecting liquid CO2 into the bottom of the injection well through the injection platform, and then performing cementing operations to achieve the storage of CO2;

[0060] Wherein, the repeated injection of liquid CO2 includes: (a) when the bottom pressure of the CO2 hydrate stability domain is ≥5MPa, the injection of liquid CO2 is stopped, and the injection of liquid CO2 is repeated when the pressure is lower than 5MPa; or (b) when the second carbon dioxide detection device detects the leakage of seabed CO2, the injection of liquid CO2 is stopped, and the injection of liquid CO2 is repeated when the second carbon dioxide detection device detects no CO2;

[0061] The end point of the repeated injection of liquid CO2 includes: when the first carbon dioxide detection device detects leakage of CO2 on the seabed.

[0062] Example 1

[0063] This embodiment provides an injection device for offshore CO2 hydrate storage, such as Figure 1 As shown, the injection device includes the injection well including an injection platform 1 arranged above the sea level, and an injection pipeline arranged below the sea level;

[0064] The injection pipeline includes a surface casing 7 and a CO2 injection pipe 8 sleeved inside the surface casing; a perforation layer section 11 is provided at the bottom end of the CO2 injection pipe 8;

[0065] From the sea level downward, the injection device includes a carbon dioxide detection device arranged in the seawater 5, and a perforation layer section 11 arranged below the bottom boundary 6 of the CO2 hydrate stability domain.

[0066] According to the CO2 gas delivery direction, the injection platform includes a storage and transportation pipeline 4, a gas compression device 3 and a wellhead blowout preventer 2 connected in sequence;

[0067] The length of the perforated layer section 11 is 100m; the perforation aperture of the perforated layer section 11 ranges from 10 to 20mm; a CO2 injection control device is provided at the top of the perforated layer section 11, and the CO2 injection control device 10 is used to control the injection temperature, pressure and rate of CO2; a reservoir in-situ monitoring device 9 is provided between the CO2 injection control device 10 and the perforated layer section 11;

[0068] The carbon dioxide detection device includes a first carbon dioxide detection device 13 and a second carbon dioxide detection device 12; the carbon dioxide detection device is used to detect the leakage of CO2 on the seabed; the first carbon dioxide detection device 13 is arranged on the side wall of the surface casing 7; the second carbon dioxide detection device 12 is arranged at a distance of 200m from the surface casing 7.

[0069] Example 2

[0070] This embodiment provides an injection device for offshore CO2 hydrate storage, and the injection device is different from that of embodiment 1 only in that:

[0071] In this embodiment, the distance between the installation position of the second carbon dioxide detection device 12 and the surface casing 7 is adjusted to 150m.

[0072] Example 3

[0073] This embodiment provides an injection device for offshore CO2 hydrate storage, and the injection device is different from that of embodiment 1 only in that:

[0074] In this embodiment, the distance between the installation position of the second carbon dioxide detection device 12 and the surface casing 7 is adjusted to 250m.

[0075] Comparative Example 1

[0076] This comparative example provides an injection device for offshore CO2 hydrate storage, and the injection device is different from Example 1 only in that:

[0077] In this comparative example, the carbon dioxide detection device disposed in the seawater is omitted.

[0078] Application Example 1

[0079] This application example provides a CO2 hydrate storage method using the injection device for offshore CO2 hydrate storage provided in Example 1, the method comprising the following steps:

[0080] (1) Calculate the depth of the bottom boundary of the CO2 hydrate stability zone based on formation parameters, and inject liquid CO2 below the bottom boundary of the CO2 hydrate stability zone;

[0081] The calculation process of the depth of the bottom boundary of the CO2 hydrate stability domain is as follows:

[0082] (a) The temperature and pressure of the seabed and the temperature gradient of the CO2 hydrate stability zone are detected by a detection device to obtain a relationship diagram between the formation temperature and formation pressure and depth of the CO2 hydrate stability zone (e.g. Figure 2 shown);

[0083] (b) According to Figure 3 The temperature-pressure phase equilibrium curve of the CO2 hydrate stability domain shown in the figure obtains the phase equilibrium temperature and phase equilibrium pressure;

[0084] (c) Combining the formation temperature and formation pressure obtained in step (a) and the phase equilibrium pressure obtained in step (b), the following is obtained: Figure 4 The relationship diagram between phase equilibrium pressure and bottom pressure at different depths is shown. According to the diagram, the bottom boundary depth of the CO2 hydrate stability domain (i.e., the intersection of the two curves) is obtained;

[0085] (2) setting the injection device according to the depth of the bottom boundary of the CO2 hydrate stability zone obtained in step (1);

[0086] The perforation layer section in the injection device is set at a depth of 50m below the bottom boundary of the CO2 hydrate stability zone;

[0087] (3) repeatedly injecting liquid CO2 into the bottom of the injection well through the injection platform, and then performing cementing operations to achieve the storage of CO2;

[0088] Wherein, the repeated injection of liquid CO2 includes: (a) when the bottom pressure of the CO2 hydrate stability domain is ≥5MPa, the injection of liquid CO2 is stopped, and the injection of liquid CO2 is repeated when the pressure is lower than 5MPa; or (b) when the second carbon dioxide detection device detects the leakage of seabed CO2, the injection of liquid CO2 is stopped, and the injection of liquid CO2 is repeated when the second carbon dioxide detection device detects no CO2;

[0089] The end point of the repeated injection of liquid CO2 includes: when the first carbon dioxide detection device detects leakage of CO2 on the seabed.

[0090] Application Example 2

[0091] This application example provides a CO2 hydrate storage method using the injection device for offshore CO2 hydrate storage provided in Example 2, and the method is the same as that in Application Example 1.

[0092] Compared with Application Example 1, the distance between the second carbon dioxide detection device 12 in the injection device used in this application example and the surface casing 7 is relatively small, which will lead to a decrease in the storage amount of carbon dioxide.

[0093] Application Example 3

[0094] This application example provides a CO2 hydrate storage method using the injection device for offshore CO2 hydrate storage provided in Example 3, and the method is the same as that in Application Example 1.

[0095] Compared with Application Example 1, the distance between the second carbon dioxide detection device 12 in the injection device used in this application example and the surface casing 7 is too large, which will result in failure to effectively monitor whether the injected carbon dioxide is leaking.

[0096] Comparative application example 1

[0097] This comparative application example provides a CO2 hydrate storage method using the injection device for offshore CO2 hydrate storage provided in Comparative Example 1, and the method is the same as that in Application Example 1.

[0098] Compared with Application Example 1, the injection device used in this comparative application example omits the carbon dioxide detection device set in the seawater, which will cause the injection device to be unable to effectively monitor the concentration of carbon dioxide on the seabed, and thus unable to know whether the carbon dioxide has leaked. Therefore, it is impossible to accurately determine the delivery end point of carbon dioxide, which may cause a reduction in the carbon dioxide storage capacity or damage to the marine system.

[0099] In summary, the CO2 hydrate storage method provided by the present invention has high storage efficiency, good thermodynamic stability, and huge storage potential, which can effectively reduce drilling and operating costs and increase economic benefits; and the carbon dioxide detection device can change the CO2 injection rate according to the formation pressure, quickly monitor CO2 leakage and other safety accidents, and realize safe and efficient storage of CO2.

[0100] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. An injection device for offshore CO2 hydrate storage, characterized in that: The injection device includes an injection well; The injection well includes an injection platform disposed above the sea level, and an injection pipeline disposed below the sea level; The injection pipeline includes a surface casing and a CO2 injection pipe sleeved inside the surface casing; a perforation layer section is arranged at the bottom end of the CO2 injection pipe; From the sea level downward direction, the injection device includes a carbon dioxide detection device arranged in the seawater, and a perforation layer section arranged below the bottom boundary of the CO2 hydrate stability domain.

2. The injection device according to claim 1, characterized in that According to the CO2 gas delivery direction, the injection platform includes a storage and transportation pipeline, a gas compression device and a wellhead blowout preventer connected in sequence.

3. The injection device according to claim 1, characterized in that The length of the perforated layer section is 10 to 200 m; Preferably, the perforation aperture of the perforation layer section ranges from 10 to 20 mm; Preferably, a CO2 injection control device is provided at the top of the perforated layer section, and the CO2 injection control device is used to control the injection temperature, pressure and rate of CO2; Preferably, a reservoir in-situ monitoring device is provided between the CO2 injection control device and the perforation layer section.

4. The injection device according to any one of claims 1 to 3, characterized in that: The carbon dioxide detection device comprises a first carbon dioxide detection device and a second carbon dioxide detection device; Preferably, the carbon dioxide detection device is used for detecting leakage of CO2 on the seabed; Preferably, the first carbon dioxide detection device is arranged on the side wall of the surface casing; Preferably, the second carbon dioxide detection device is located at a distance of 180 to 220 m from the surface casing.

5. A method for storing CO2 hydrates at sea, characterized in that: The method is carried out using the injection device described in any one of claims 1 to 4.

6. The method for offshore CO2 hydrate storage according to claim 5, characterized in that: The method comprises the following steps: (1) Calculate the depth of the bottom boundary of the CO2 hydrate stability zone based on formation parameters, and inject liquid CO2 below the bottom boundary of the CO2 hydrate stability zone; (2) setting the injection device according to any one of claims 1 to 4 according to the depth of the bottom boundary of the CO2 hydrate stability zone obtained in step (1); (3) Liquid CO2 is repeatedly injected into the bottom of the injection well through an injection platform, and then cementing operations are performed to achieve the storage of CO2.

7. The method for offshore CO2 hydrate storage according to claim 6, characterized in that: The perforation layer section in the injection device is arranged at a depth of 0 to 100 m below the bottom boundary of the CO2 hydrate stability zone.

8. The method for offshore CO2 hydrate storage according to claim 6 or 7, characterized in that: The repeated injection of liquid CO2 in step (3) includes: (a) when the bottom boundary pressure of the CO2 hydrate stability domain is ≥5MPa, stopping the injection of liquid CO2, and repeating the injection of liquid CO2 when the pressure is lower than 5MPa; or (b) when the second carbon dioxide detection device detects leakage of CO2 on the seabed, stopping the injection of liquid CO2, and repeating the injection of liquid CO2 when the second carbon dioxide detection device no longer detects CO2.

9. The method for storing CO2 hydrate at sea according to any one of claims 6 to 8, characterized in that: The end point of the repeated injection of liquid CO2 in step (3) includes: when the first carbon dioxide detection device detects leakage of CO2 on the seabed.

10. The method for storing CO2 hydrate at sea according to any one of claims 6 to 9, characterized in that: The injection rate of liquid CO2 in step (3) is 0-1000m 3 / d.

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