Wellhead device suitable for air salt cavern gas storage and method for protecting casing pipe of air salt cavern gas storage

Abstract

The invention relates to the technical field of compressed air energy storage and underground gas storage, in particular to a wellhead device suitable for an air salt cavern gas storage and a method for protecting a casing pipe of the air salt cavern gas storage. The problems that the inner wall of a sleeve is prone to corrosion, and the safety and the service life of a gas storage are affected are solved. Comprising a main channel, a first valve, a gas storage device, a first branch, a second branch, a second valve and a third valve, the first valve is arranged on the main channel, and the first branch and the second branch are communicated with pipe sections on the two sides of the main channel and the gas storage device respectively. At the end of the energy storage process, the ground energy storage and release system fills air into the air storage device; and after the energy release process is finished, air in the air storage device is injected into the sleeve of the salt cavern air storage through the second branch, so that an air isolation section is formed in the sleeve, and the rising high-humidity and high-salt air in the salt cavern is isolated from being in direct contact with the inner wall of the sleeve. The corrosion risk of the sleeve can be reduced, the hidden danger of air leakage is reduced, and the service life of the air salt cavern gas storage is prolonged.

Description

Technical Field

[0001] This invention relates to the fields of compressed air energy storage and underground gas storage technology, specifically to a wellhead device suitable for air salt cavern gas storage and a method for protecting the casing of air salt cavern gas storage. Background Technology

[0002] Advanced compressed air energy storage systems offer advantages such as large storage capacity, high efficiency, long lifespan, flexible dispatch, low pollution, and low water consumption, making them promising for large-scale energy storage applications. Currently, underground salt caverns are commonly used as storage spaces in compressed air energy storage systems. Salt rock possesses characteristics such as low permeability, good creep performance, and strong self-healing ability, thus salt cavern gas storage facilities offer high sealing and safety, making them suitable as underground storage sites for high-pressure air.

[0003] However, during the operation of air-salt cavern gas storage facilities, the well casing is subjected to a high-pressure, high-humidity, and high-salt environment for extended periods. Especially during injection, production, and shutdown transitions, the air conditions inside the well constantly change. The high-humidity, high-salt gases within the salt cavern easily come into direct contact with the inner wall of the casing, causing chemical corrosion. With increasing operating time, casing corrosion can lead to a decline in wellbore sealing performance and even trigger gas leakage risks, thereby affecting the safety, reliability, and service life of the gas storage facility.

[0004] In existing technologies, long-term protection measures for air-salt cavern gas storage casings in high-humidity and high-salt environments remain relatively limited. There is a lack of a wellhead device and control method that is simple in structure, easy to control, and can effectively reduce the risk of casing inner wall corrosion during energy storage and release operations. Therefore, it is necessary to provide a wellhead device suitable for air-salt cavern gas storage. By setting up a gas storage device and corresponding valve control structure, air can be supplied to the casing during specific operating phases to reduce the direct impact of high-humidity and high-salt gases on the casing inner wall and extend the service life of the gas storage facility. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, namely the issue that the casing of an air-salt cavern gas storage facility is subjected to a high-pressure, high-humidity, and high-salt environment for extended periods during energy storage and release operations, which can lead to internal wall corrosion and affect the safety and service life of the gas storage facility, this invention provides a wellhead device suitable for air-salt cavern gas storage facilities and a method for protecting the casing of air-salt cavern gas storage facilities.

[0006] In a first aspect, the present invention provides a wellhead device suitable for air-salt cavern gas storage, comprising a main channel, a first valve, a gas storage device, a first branch, a second branch, a second valve, and a third valve;

[0007] One end of the main channel is used to connect to the ground energy storage and release system, and the other end is used to connect to the wellhead of the salt cavern gas storage facility. The first valve is installed on the main channel and divides the main channel into a first pipe section located between the first valve and the ground energy storage and release system and a second pipe section located between the first valve and the wellhead body; The first branch connects the first pipe section to the gas storage device, and the second valve is located on the first branch. The second branch connects the second pipe section to the gas storage device, and the third valve is located on the second branch; The gas storage device is used to store air from the ground-based energy storage and release system at the end of the energy storage process, and to inject air into the casing of the salt cavern gas storage tank after the energy release process is completed.

[0008] Furthermore, the gas storage device is a high-pressure gas cylinder group.

[0009] Furthermore, the wellhead body includes a wellhead cross-junction and a casing head, and the main channel is connected to the wellhead cross-junction.

[0010] Furthermore, a first gate valve and a second gate valve are sequentially installed between the wellhead four-way valve and the casing head.

[0011] Furthermore, one end of the first gate valve is connected to the wellhead four-way valve, and the other end is connected to the second gate valve; one end of the second gate valve is connected to the first gate valve, and the other end is connected to the casing head.

[0012] In a second aspect, the present invention provides a method for protecting the casing of an air-salt cavern gas storage tank using the wellhead device described in the first aspect, comprising: At the beginning of the energy storage process, the second and third valves are closed and the first valve is opened to allow the ground-based energy storage and release system to inject air into the salt cavern gas storage tank. At the end of the energy storage process, the second valve is opened and the first valve is closed, allowing the ground-based energy storage and release system to fill the gas storage device with air. At the end of the energy storage process, close the first and second valves; During the energy release process, the second and third valves are closed, and the first valve is opened, allowing the salt cavern gas storage to output air to the ground-based energy storage and release system. After the energy release process is completed, the first and second valves are closed, and the third valve is opened to allow air from the gas storage device to be injected into the casing of the salt cavern gas storage tank.

[0013] Furthermore, after the energy release process is completed, the air in the gas storage device is injected into the casing using the pressure difference between the gas storage device and the salt cavern gas storage tank.

[0014] Furthermore, when the gas storage device and the salt cavern gas storage tank reach pressure balance, the third valve is closed.

[0015] Furthermore, the gas storage capacity of the gas storage device is configured such that when air is injected into the casing via the third valve after the energy release process is completed, an air isolation section from the wellhead to a predetermined depth is formed inside the casing.

[0016] Furthermore, the air isolation section is used to isolate the high-humidity, high-salt air rising from the salt cavern from direct contact with the inner wall of the casing during the shutdown phase after the energy release process.

[0017] The beneficial effects of this invention are: This invention, by installing a gas storage device outside the main wellhead channel and utilizing branch lines and valve switching structures connecting both sides of the main channel, enables the gas storage device to both receive air from the surface energy storage and release system at the end of the energy storage process and replenish air into the casing of the salt cavern gas storage tank after the energy release process. Compared to protection methods that rely on the natural evolution of the gas environment inside the casing or solely on the corrosion resistance of the material itself, this invention actively introduces air into the casing through the wellhead device, thus regulating the gas environment inside the casing. Therefore, it is an active protection scheme, rather than a passive one.

[0018] After the energy release process is completed, the present invention injects air from the gas storage device into the casing, which can form an air isolation section within the casing during the shutdown phase. This air isolation section can isolate the high-humidity, high-salt air rising from the salt cavern from direct contact with the inner wall of the casing within the range from the wellhead to a predetermined depth, thereby helping to mitigate the adverse effects of the corrosive environment on the inner wall of the casing and reducing the risk of casing corrosion.

[0019] In this invention, the air used in the gas storage device originates from the air supplied by the ground-based energy storage and release system at the end of the energy storage process. The air replenishment process is scheduled to occur after the energy release process is completed, and the overall control timing is coordinated with the energy storage and release operation process of the air-salt cavern gas storage facility. This scheme does not change the basic energy storage and release principle of the gas storage facility, but adds gas storage and air replenishment links to the existing operation process. Therefore, it has good process adaptability and is easy to implement control in conjunction with the operation phase of the gas storage facility.

[0020] This invention utilizes the coordination of a first valve, a second valve, and a third valve to achieve switching control of gas flow between the surface energy storage and release system, the gas storage device, and the salt cavern gas storage tank. Specifically, air can be introduced into the gas storage device at the end of the energy storage process, and air from the gas storage device can be introduced into the casing after the energy release process. The gas path is clearly defined, and the functional division is clear, facilitating the control of the wellhead equipment according to different operating conditions.

[0021] In the replenishment stage after the energy release process, this invention utilizes the pressure difference between the gas storage device and the salt cavern gas storage tank to inject air, and ends the replenishment process after pressure equilibrium is reached. This method uses the system's own pressure conditions to complete air delivery, making the replenishment process more direct and facilitating timely adjustment of the environment inside the casing after energy release.

[0022] Furthermore, this invention allows for the setting of the gas storage volume in the gas storage device to ensure that the air injected into the casing reaches a predetermined depth range, thereby forming an air isolation section of appropriate length according to the wellbore structure and operational requirements. Thus, this invention enables the design of the gas replenishment range in conjunction with casing protection requirements, improving the targeted nature of the wellhead device in casing environment adjustment.

[0023] In summary, by storing air at the end of the energy storage process and actively replenishing air into the casing after the energy release process, this invention can form a gaseous region inside the casing to isolate high-humidity and high-salt rising air, thereby providing active protection for the inner wall of the casing and helping to reduce the corrosion risk and operational hazards of the gas storage wellbore. Attached Figure Description

[0024] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the structure of a wellhead device suitable for an air-salt cavern gas storage facility according to the present invention. Detailed Implementation

[0025] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0026] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0027] See Figure 1 The first embodiment of the present invention proposes a wellhead device suitable for air salt cavern gas storage, including a main channel 1, a first valve 2, a gas storage device 3, a first branch 4, a second branch 5, a second valve 6, and a third valve 7; One end of the main channel 1 is used to connect to the ground energy storage and release system 8, and the other end is used to connect to the wellhead body of the salt cavern gas storage facility. The first valve 2 is disposed on the main channel 1 and divides the main channel 1 into a first pipe section 11 located between the first valve 2 and the ground energy storage and release system 8 and a second pipe section 12 located between the first valve 2 and the wellhead body; The first branch 4 connects the first pipe section 11 to the gas storage device 3, and the second valve 6 is installed on the first branch 4; The second branch 5 connects the second pipe section 12 to the gas storage device 3, and the third valve 7 is installed on the second branch 5; The gas storage device 3 is used to store air from the ground-based energy storage and release system 8 at the end of the energy storage process, and to inject air into the casing of the salt cavern gas storage tank after the energy release process is completed.

[0028] In this embodiment, the main channel 1 constitutes the main gas transmission path between the surface energy storage and release system 8 and the wellhead of the salt cavern gas storage tank. One end of the main channel is connected to the compressor, heat exchange equipment, manifold, or other surface energy storage and release equipment in the compressed air energy storage system, and the other end is connected to the wellhead body to inject compressed air into the salt cavern during the energy storage stage and return the high-pressure air in the salt cavern to the surface energy release system during the energy release stage. A first valve 2 is arranged on the main channel 1 to control the opening or closing of the main channel 1 and structurally divides the main channel 1 into a first pipe section 11 near the surface energy storage and release system 8 and a second pipe section 12 near the wellhead body. A first branch 4 is led out from the first pipe section 11 and connected to the gas storage device 3. A second valve 6 is arranged on the first branch 4 to control the gas charging process of the surface energy storage and release system 8 to the gas storage device 3. The second branch line 5 leads out from the second pipe section 12 and connects to the gas storage device 3. The third valve 7 is installed on the second branch line 5 to control the gas release process of the gas storage device 3 to the wellhead and casing side. Through the above structure, the gas storage device 3 can store a portion of fresh air from the surface energy storage and release system 8 at the end of the energy storage process, and inject the stored air into the casing through the second branch line 5 after the energy release process is completed. The fresh air here is relative to the high-humidity, high-salt air that may rise back at the end of the salt cavern energy release. It comes from the compressed air of the surface energy storage and release system 8, has a high degree of cleanliness, and has not been in long-term contact with the high-humidity, high-salt environment inside the salt cavern.

[0029] With this structure, the wellhead device can not only perform the conventional gas injection and production functions of the gas storage tank, but also actively reserve a portion of air for casing environment regulation during the energy storage and release operation cycle, ensuring favorable gas conditions inside the casing during shutdown. This invention does not passively rely on the casing material itself to withstand corrosion after a corrosive environment forms; instead, it actively establishes a gas supply channel and gas storage unit during the operation cycle through the coordination of wellhead pipelines, branches, and valves, thereby creating conditions for subsequent air replenishment into the casing, exhibiting the characteristics of active protection.

[0030] In a preferred embodiment, the gas storage device 3 is a high-pressure gas storage cylinder group.

[0031] In this embodiment, the gas storage device 3 preferably employs a high-pressure gas cylinder group. The high-pressure gas cylinder group can be composed of one or more pressure-resistant containers connected in parallel or series, and is connected to the first branch 4 and the second branch 5 via a manifold. Its material, pressure rating, volume, and arrangement can be selected based on the working pressure of the air-salt cavern gas storage tank, the casing volume, the expected depth of the air isolation section, and the amount of gas that can be provided at the end of the energy storage process. The high-pressure gas cylinder group can be arranged at a suitable location on the well site surface and installed using fixed supports, a foundation platform, and necessary safety accessories.

[0032] To adapt to the high-pressure operating environment of the air-salt cavern gas storage facility, the high-pressure gas cylinder group should be a pressure vessel capable of withstanding repeated filling and discharging cycles over a long period. It can be equipped with pressure gauges, safety valves, temperature monitoring elements, or other conventional auxiliary devices to monitor its operating status. During the final stage of energy storage and release, when the ground-based energy storage and release system 8 is filled with gas, the high-pressure gas cylinder group can store air with a certain pressure and cleanliness. After energy release, the stored air can be released into the casing using the pressure difference between the system and the salt cavern gas storage facility. The advantages of using high-pressure gas cylinder groups are that the technology is mature, the pressure-bearing capacity is strong, and the gas storage capacity can be adjusted by the number of cylinders and the volume of each cylinder. It can better adapt to the dual operating conditions of gas storage at the end of energy storage and gas replenishment at the end of energy release, and facilitates maintenance, replacement, and capacity matching on the ground.

[0033] In a preferred embodiment, the wellhead body includes a wellhead cross-junction 9 and a casing head 10, and the main channel 1 is connected to the wellhead cross-junction 9.

[0034] In this embodiment, the wellhead body adopts a wellhead pressure-bearing structure commonly found in air-salt cavern gas storage facilities, including at least a wellhead four-way connector 9 and a casing head 10. The main channel 1 is connected to the wellhead four-way connector 9, allowing air in the main channel to enter the wellhead body and further into the downhole casing and salt cavern gas storage space. The wellhead four-way connector 9, as a fluid conduit at the wellhead, enables communication between the main channel and the downhole wellbore, and provides interfaces for other monitoring, testing, or auxiliary pipelines.

[0035] The casing head 10 is used to support the casing inside the well and form a corresponding wellhead sealing structure, so as to maintain a reliable connection between the casing and the wellhead equipment. When the surface energy storage and release system 8 is in energy storage mode, compressed air enters the casing through the main channel 1 and the wellhead four-way 9 and is injected into the salt cavern; When the surface energy storage and release system 8 is in energy release mode, the high-pressure air in the salt cavern returns to the wellhead four-way connector 9 via the casing, and is then transported to the surface energy release equipment via the main channel 1. Simultaneously, when the gas storage device 3 injects air into the casing via the second branch 5 after energy release, this air also enters the casing through the second pipe section 12 and the wellhead four-way connector 9. The wellhead body is constructed using the wellhead four-way connector 9 and the casing head 10, allowing the device to be compatible with the existing wellhead structure of the salt cavern gas storage facility, facilitating the coupling of conventional gas transmission and active gas replenishment functions in the wellhead area. This invention utilizes the existing pressure-bearing and connectivity functions of the wellhead body to complete its implementation, resulting in a relatively centralized engineering layout that facilitates installation, control, and maintenance.

[0036] In a preferred embodiment, a first gate valve 13 and a second gate valve 14 are sequentially arranged between the wellhead four-way valve 9 and the casing head 10.

[0037] In this embodiment, a first gate valve 13 and a second gate valve 14 are sequentially arranged between the wellhead four-way 9 and the casing head 10 to form a graded isolation and control structure inside the wellhead body. The first gate valve 13 and the second gate valve 14 can be gate valves suitable for high-pressure air conditions, and their nominal pressure, diameter, and sealing form are matched with the design parameters of the wellhead body and the main channel 1. The arrangement of the first gate valve 13 and the second gate valve 14 creates two-stage cutoff positions between the wellhead four-way 9 and the casing head 10. When wellhead maintenance, pressure isolation, state switching, or safety handling is required, the wellhead fluid passage can be isolated or restored by opening or closing the corresponding gate valves. In the operation of this invention, the first gate valve 13 and the second gate valve 14 are usually kept in an open state that matches the operating state of the main channel to ensure that the energy storage gas injection, energy release gas output, and gas replenishment processes after energy release can proceed smoothly. When maintenance of the wellhead four-way, casing head, or related connecting components is required, the two-stage gate valves can be used to isolate different parts of the wellhead. The advantages of setting up a two-stage gate valve are: it can improve the operational safety and maintenance convenience of the wellhead body, and provide more reliable wellhead boundary conditions for the implementation of the casing gas supply function.

[0038] More specifically, one end of the first gate valve 13 is connected to the wellhead four-way 9 and the other end is connected to the second gate valve 14, and one end of the second gate valve 14 is connected to the first gate valve 13 and the other end is connected to the casing head 10.

[0039] In this embodiment, the first gate valve 13 is located near the wellhead four-way 9, and the second gate valve 14 is located near the casing head 10. These two valves are connected in series between the wellhead four-way 9 and the casing head 10. Through this connection, the gas in the main channel 1, as well as the gas introduced into the second pipe section 12 via the second branch 5, must pass through the wellhead four-way 9, the first gate valve 13, and the second gate valve 14 before entering the casing head 10 and the casing space below it. This series arrangement facilitates the formation of a clear top-to-bottom wellhead structure hierarchy and also helps to implement step-by-step isolation of the fluid passage between the wellhead four-way and the casing head. During actual installation, the first gate valve 13 and the second gate valve 14 can be connected to adjacent components via flanges, threads, or welded transition joints, and seals suitable for high-pressure air conditions are used to ensure the sealing of the connection points. The effect of this connection method is that the main wellhead structure is more clearly defined, the gas flow path is clear, and it provides stable and reliable channel conditions for the main channel gas delivery and make-up air to enter the casing in this invention.

[0040] A second embodiment of the present invention discloses a method for protecting the casing of an air-salt cavern gas storage tank using a wellhead device, comprising: At the beginning of the energy storage process, the second valve 6 and the third valve 7 are closed, and the first valve 2 is opened, so that the ground energy storage and release system 8 injects air into the salt cavern gas storage tank. At the end of the energy storage process, the second valve 6 is opened and the first valve 2 is closed, so that the ground energy storage and release system 8 can fill the gas storage device 3 with air. At the end of the energy storage process, the first valve 2 and the second valve 6 are closed; during the energy release process, the second valve 6 and the third valve 7 are closed, and the first valve 2 is opened, so that the salt cavern gas storage tank outputs air to the ground energy storage and release system 8. After the energy release process is completed, the first valve 2 and the second valve 6 are closed, and the third valve 7 is opened to allow the air in the gas storage device 3 to be injected into the casing of the salt cavern gas storage tank.

[0041] In this embodiment, the method fully corresponds to the wellhead control logic within one energy storage-release operation cycle of an air-salt cavern gas storage facility. At the beginning of the energy storage process, the second valve 6 and the third valve 7 are closed, while the first valve 2 is open. At this time, the main channel 1 is open, while the first branch 4 and the second branch 5 are closed. Compressed air output from the surface energy storage and release system 8 directly enters the casing and is injected into the salt cavern via the first pipe section 11, the first valve 2, the second pipe section 12, and the wellhead body, achieving conventional energy storage injection. As the energy storage process nears its end, to ensure that air can be replenished into the casing after the subsequent energy release, the second valve 6 is opened and the first valve 2 is closed at the end of the energy storage process. This prevents air from the surface energy storage and release system 8 from entering the salt cavern, instead allowing it to enter the gas storage device 3 via the first pipe section 11 and the first branch 4. During this stage, the third valve 7 remains closed to prevent air in the gas storage device 3 from prematurely leaking into the wellhead side via the second branch 5. In this embodiment, the end of the energy storage process refers to the point where the gas storage pressure in the salt cavern reaches the design value.

[0042] At the end of energy storage, the first valve 2 and the second valve 6 are closed, cutting off both the main channel and the first branch. The high-pressure air injected at the end of the energy storage phase is retained in the gas storage device 3. After entering the energy release process, the second valve 6 and the third valve 7 are closed again, and the first valve 2 is opened, allowing the high-pressure air in the salt cavern gas storage to flow through the wellhead body, the second pipe section 12, the first valve 2, and the first pipe section 11 to the surface energy storage and release system 8, and then enter the expansion energy release system to generate electricity.

[0043] At this time, the air output from the salt cavern typically exhibits high pressure, high humidity, and high salinity, which is a significant reason why the casing inner wall is susceptible to adverse environmental influences during long-term operation. After the energy release process is completed, the first valve 2 and the second valve 6 are closed, and the third valve 7 is opened, allowing the pre-stored air in the gas storage device 3 to enter the second pipe section 12 via the second branch 5, and then be injected into the casing through the wellhead body to regulate the gas environment inside the casing. By arranging the gas replenishment action after the energy release process, conditions for isolating and replacing any residual or rising high-humidity, high-salt air inside the casing can be established at the point when the salt cavern stops outputting air to the surface. This invention embeds the gas storage and replenishment actions into the normal operating rhythm of energy storage and release, without altering the basic working principle of the compressed air energy storage system, thereby proactively establishing a casing protection mechanism at the wellhead side and reducing corrosion problems caused by the casing being exposed to a high-pressure, high-humidity, and high-salt environment for a long time.

[0044] In a preferred embodiment, after the energy release process is completed, the air in the gas storage device 3 is injected into the casing using the pressure difference between the gas storage device 3 and the salt cavern gas storage tank.

[0045] In this embodiment, after the energy release is completed, the air pressure stored in the gas storage device 3 is usually higher than the pressure at the corresponding location on the casing and salt cavern wellhead. Therefore, when the third valve 7 is opened, the air in the gas storage device 3 can spontaneously enter the second pipe section 12 and be injected into the casing via the second branch 5, relying on the pressure difference formed between itself and the salt cavern gas storage tank, without the need for additional dedicated pressurization equipment. To ensure the stable operation of the differential pressure injection process, factors such as the charging pressure at the end of the energy storage stage, the volume of the gas storage device, the salt cavern pressure at the end of the energy release, and the gas column distribution in the wellbore can be comprehensively considered during the design and operation, so that the gas replenishment process after the energy release can meet the expected injection depth and injection volume requirements. During the differential pressure injection process, the air will form a corresponding gas column distribution in the wellbore after entering the casing.

[0046] Because relatively clean and unsaturated air is injected, it forms an isolating gas zone in the upper part of the casing relative to the rising saturated humid air within the cavity, thereby inhibiting the inner surface of the casing from being further affected by the high humidity and high salinity environment. Using differential pressure for injection reduces the need for additional power equipment, simplifies the control process, and makes the gas replenishment operation easier to coordinate with existing wellhead operating conditions. Its advantages include a more direct gas replenishment process and lower implementation costs and system complexity.

[0047] In a preferred embodiment, when the gas storage device 3 and the salt cavern gas storage tank reach pressure balance, the third valve 7 is closed.

[0048] In this embodiment, the timing of closing the third valve 7 can be determined by monitoring the pressure between the gas storage device 3 and the wellhead body or casing side. When the pressure between the gas storage device 3 and the salt cavern gas reservoir reaches equilibrium, it indicates that the air injection process driven by pressure difference has been basically completed. At this time, the third valve 7 is closed to terminate the continued gas release from the gas storage device 3 into the casing. Pressure equilibrium can be determined by comparing pressure sensor and pressure gauge readings, or by comprehensively judging the pressure change pattern based on a predetermined operating time. After closing the third valve 7, the passage between the gas storage device 3 and the wellhead side is cut off, and the injected air isolation section is retained in the casing until the start of the next operating cycle. This invention can avoid maintaining the connection between the gas storage device and the wellhead side after the pressure difference disappears, reducing unnecessary gas backflow, pressure fluctuations, or control uncertainties, making the gas replenishment process have clear start and end conditions, and also helping to maintain the stability of the gas area already formed in the casing.

[0049] In a preferred embodiment, the gas storage capacity of the gas storage device 3 is configured such that when air is injected into the casing via the third valve 7 after the energy release process is completed, an air isolation section from the wellhead to a predetermined depth is formed inside the casing.

[0050] In this embodiment, the gas storage volume of the gas storage device 3 is not arbitrarily set, but is determined in combination with the casing geometry, well depth, predetermined protection zone depth, wellbore pressure at the end of energy release, and the temperature and pressure parameters of the injected air. The so-called air isolation zone from the wellhead to the predetermined depth refers to a gas region formed from top to bottom within the casing after replenishment following energy release, primarily consisting of injected air. The lower boundary of this region corresponds to the predetermined depth. This predetermined depth can be selected based on the casing corrosion-sensitive section, wellbore temperature and pressure distribution, the range of influence of rising gas, and engineering protection requirements. A typical depth is the overall length of the casing. To form this air isolation zone, the amount of air to be injected into the casing after energy release can be calculated in advance based on the casing inner diameter, wellbore volume corresponding to the target depth, gas state equation, and actual operating pressure and temperature conditions. Based on this, the total gas storage volume and filling pressure of the high-pressure gas cylinder group are determined. If the wellbore is deep and the depth range requiring protection is large, the capacity of the gas storage device 3 can be appropriately increased. If only the area near the wellhead or the upper casing needs protection, the capacity can be reduced accordingly. The technical disclosure document indicates that the volume of the high-pressure gas storage cylinder group is related to the casing depth and the salt cavern injection and production patterns; this embodiment achieves this through parameter matching. The gas replenishment volume of this invention is targeted, enabling the formed air isolation section to cover the actual casing area requiring protection, thus improving the effectiveness of casing environment regulation.

[0051] More specifically, the design volume of the gas storage tank is calculated as follows:

[0052] Where V is the design volume of the gas storage tank, D is the size of the casing, and L is the total length of the casing. The initial density of the storage tank, Density after the storage tank and casing are filled with gas.

[0053] The air isolation section is used to isolate the high-humidity, high-salt air rising from the salt cavern from direct contact with the inner wall of the casing during the shutdown phase after the energy release process.

[0054] In the engineering and environmental fields, salt spray concentrations exceeding 3 mg / m³ are particularly problematic. 3 This is considered a high-humidity, high-salt environment, posing a corrosive risk, with typical coastal levels reaching 60 mg / m³. 3 above.

[0055] In this embodiment, after the energy release process, the original air in the salt cavern may cause the gas returning to the casing to exhibit high humidity and high salinity characteristics due to temperature, humidity, and salinity carrying capacity. If this type of gas continues to be in contact with the inner wall of the casing, it will exacerbate the chemical corrosion of the inner surface of the casing. By injecting air from the gas storage device 3 into the casing after the energy release, an air isolation section can be formed in the upper part of the casing during the shutdown phase, so that the returning high humidity and high salinity air is no longer in direct contact with the inner wall of the casing. The technical disclosure states that the air injected into the casing is clean air, which is unsaturated air, and its density is lower than that of the saturated humid air in the cavity. Therefore, this high-pressure air can suppress the effects of the high humidity and high salinity environment on the inner surface of the casing. In combination with the structure and operation mode of the present invention, this suppression effect is not formed by natural environmental changes after shutdown, but is achieved by pre-storing gas in the final stage of energy storage and actively replenishing gas after the energy release. Once the air isolation section is formed, a more favorable gas environment can be maintained in the upper part of the casing before the next energy storage cycle begins, thereby reducing the risk of casing corrosion and minimizing the potential for gas leakage caused by casing corrosion. This invention can provide active protection for the casing during the shutdown phase between energy storage and release cycles, helping to delay casing degradation and improve the long-term safety and stability of air-salt cavern gas storage facilities.

[0056] In practical applications, air-salt cavern gas storage wellbores operate under high pressure for extended periods, and the gas conditions within the casing are affected by humidity, salinity, and rising gas within the salt cavern, easily creating a corrosive environment unfavorable for long-term casing service. This embodiment, by installing a gas storage device and coordinating with a wellhead-side gas path switching structure, regulates the gas environment within the casing during the energy storage and release cycle, creating an air isolation section extending downwards from the wellhead during shutdown. This air isolation section reduces direct contact between the high-humidity, high-salt air rising from the salt cavern and the inner wall of the casing within a certain depth range, thereby reducing the corrosive environment affecting the inner surface of the casing. Compared to methods that rely solely on the corrosion resistance of the casing material or the natural changes in gas state after shutdown, this embodiment proactively implements casing protection in conjunction with the gas storage's operating rhythm, without altering the original basic energy storage and release processes of the air-salt cavern gas storage. It is easy to configure and apply based on existing wellhead systems, helping to reduce casing corrosion risks and improve the safety and stability of gas storage operation.

[0057] The terms “first”, “second”, etc., are used to distinguish similar objects, not to describe or indicate a specific order or sequence.

[0058] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus / device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent in such process, method, article, or apparatus / device.

[0059] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A wellhead device suitable for air-salt cavern gas storage, characterized in that, It includes the main channel (1), the first valve (2), the gas storage device (3), the first branch (4), the second branch (5), the second valve (6), and the third valve (7); One end of the main channel (1) is used to connect to the ground energy storage and release system (8), and the other end is used to connect to the wellhead of the salt cavern gas storage tank. The first valve (2) is installed on the main channel (1) and divides the main channel (1) into a first pipe section (11) located between the first valve (2) and the ground energy storage and release system (8) and a second pipe section (12) located between the first valve (2) and the wellhead body. The first branch (4) connects the first pipe section (11) and the gas storage device (3), and the second valve (6) is installed on the first branch (4); The second branch (5) connects the second pipe section (12) to the gas storage device (3), and the third valve (7) is installed on the second branch (5); The gas storage device (3) is used to store air from the ground energy storage and release system (8) at the end of the energy storage process and to inject air into the casing of the salt cavern gas storage after the energy release process is completed.

2. The wellhead device according to claim 1, characterized in that, The gas storage device (3) is a high-pressure gas storage cylinder group.

3. The wellhead device according to claim 1, characterized in that, The wellhead body includes a wellhead cross-connector (9) and a casing head (10), and the main channel (1) is connected to the wellhead cross-connector (9).

4. The wellhead device according to claim 3, characterized in that, A first gate valve (13) and a second gate valve (14) are sequentially installed between the wellhead four-way valve (9) and the casing head (10).

5. The wellhead device according to claim 4, characterized in that, One end of the first gate valve (13) is connected to the wellhead four-way (9), and the other end is connected to the second gate valve (14). One end of the second gate valve (14) is connected to the first gate valve (13), and the other end is connected to the casing head (10).

6. A method for protecting the casing of an air-salt cavern gas storage tank using the wellhead device according to any one of claims 1-5, characterized in that, include: At the beginning of the energy storage process, the second valve (6) and the third valve (7) are closed, and the first valve (2) is opened, so that the ground energy storage and release system (8) injects air into the salt cavern gas storage tank; At the end of the energy storage process, the second valve (6) is opened and the first valve (2) is closed, so that the ground energy storage and release system (8) fills the gas storage device (3) with air; At the end of the energy storage process, close the first valve (2) and the second valve (6); During the energy release process, the second valve (6) and the third valve (7) are closed, and the first valve (2) is opened, so that the salt cavern gas storage tank outputs air to the ground energy storage and release system (8); After the energy release process is completed, the first valve (2) and the second valve (6) are closed, and the third valve (7) is opened to allow the air in the gas storage device (3) to be injected into the casing of the salt cavern gas storage tank.

7. The method according to claim 6, characterized in that, After the energy release process is completed, the air in the gas storage device (3) is injected into the casing using the pressure difference between the gas storage device (3) and the salt cavern gas storage tank.

8. The method according to claim 7, characterized in that, When the gas storage device (3) and the salt cavern gas storage tank reach pressure balance, the third valve (7) is closed.

9. The method according to claim 6, characterized in that, The gas storage capacity of the gas storage device (3) is set such that when air is injected into the casing through the third valve (7) after the energy release process is completed, an air isolation section from the wellhead to a predetermined depth is formed in the casing.

10. The method according to claim 9, characterized in that, The air isolation section is used to isolate the high-humidity, high-salt air rising from the salt cavern from direct contact with the inner wall of the casing during the shutdown phase after the energy release process.

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