A convenient device for detecting the gas tightness of salt cavern hydrogen storage facilities to measure the depth of the gas-liquid interface.

Abstract

This invention relates to a device and method for conveniently detecting the gas-liquid interface depth in a salt cavern hydrogen storage facility. The salt cavern hydrogen storage facility includes a cavity and a wellbore connecting to the top of the cavity. The device includes a production casing, a test tube, a gas supply device, a gas transmission pipeline, and a gas-liquid interface measuring device. The production casing is fixed to the wellbore wall. The test tube extends into the production casing, with a gap between its lower end and the bottom of the cavity, forming an annulus between the test tube and the production casing. The gas supply device is connected to the annulus for injecting gas into it. The gas transmission pipeline connects the test tube and the annulus after some brine has been discharged from the test tube by injecting gas into the annulus, ensuring that the gas-liquid interface depth in the test tube and the annulus remains consistent. The gas-liquid interface measuring device extends into the test tube for detecting the gas-liquid interface depth within the test tube. This invention connects the annulus and the test tube via the gas transmission pipeline, thereby enabling convenient, direct, continuous, and real-time measurement of the gas-liquid interface depth in the test tube.

Description

Technical Field

[0001] This invention relates to the field of salt cavern gas storage construction, and specifically to a device and method for detecting the gas tightness of salt cavern hydrogen storage facilities that facilitates the detection of the gas-liquid interface depth. Background Technology

[0002] Salt cavern underground gas storage facilities are artificial caverns formed by water dissolution within thick underground salt layers for storing gases. Currently, my country has several salt cavern natural gas storage facilities and salt cavern compressed air energy storage power plants. The gas tightness of a salt cavern gas storage facility directly affects its storage capacity and operational safety. Testing should be conducted during the construction phase of the salt cavern to ensure its long-term safe operation.

[0003] The overall sealing performance of a salt cavern gas storage system mainly consists of wellbore sealing and cavity sealing. Currently, there are two main methods used internationally for testing the gas tightness of salt cavern gas storage systems: one is the gas tightness testing method recommended by API, and the other is the gas tightness testing method recommended by Geostock. The method used domestically is an evolution of these two methods: after running a test string into the wellbore, gas is injected into the annulus between the casing and the test string. A gas-liquid interface measuring device is placed in the test string filled with brine to test the change in the gas-liquid interface depth over 24 hours. The sealing performance of the wellbore and cavity is evaluated based on the change in the gas-liquid interface depth combined with the change in pressure on the wellhead pressure gauge.

[0004] There are generally two methods for measuring the gas-liquid interface depth. One method involves directly placing the gas-liquid interface measurement device into a test string filled with brine, measuring the gas-liquid interface depth in the annulus through the string. In China, gamma-ray detectors are commonly used as the gas-liquid interface measurement device. By emitting neutrons, the gamma-ray detector measures the gamma rays emitted by the neutrons, obtaining a gamma logging curve, thus determining the gas-liquid interface depth. This method generates nuclear radiation pollution during the measurement process, and is complex, costly, and most importantly, cannot provide continuous measurements. The other method involves fixing the gas-liquid interface measurement device to the outer wall of the test string, then lowering the test string into the production casing to directly measure the gas-liquid interface depth in the annulus. This method typically uses fiber optic or sonar probes fixed to the outer wall of the test string. Although continuous measurements are possible, the technology is more complex, and recovery is difficult. Furthermore, the inventors of this application considered using a steel wire rope to lower optical fiber or sonar into the annulus for measurement. However, considering the small size of the annulus at the wellhead, it was impossible to insert the optical fiber or sonar through the steel wire rope. The optical fiber or sonar would need to be lowered into the production casing first, and then the test tube lowered. After testing, the test tube would also need to be removed before the optical fiber or sonar probe could be retrieved. This cumbersome operation is less efficient than fixing the test tube to the outer wall for measurement. This eliminates concerns about damage to the optical fiber or sonar probe during lowering and the impact of instability on the results. Additionally, when testing directly fixed to the outer wall of the test tube, the annulus valve can be closed, whereas if a steel wire rope is used, a blowout preventer must be installed during testing. Considering these issues, the method of lowering the optical fiber or sonar into the annulus using a steel wire rope was not adopted. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of related technologies and provide a convenient gas-liquid interface depth detection device for salt cavern hydrogen storage. It connects the annulus and the test tube through a gas pipeline, thereby conveniently, directly, continuously and in real time measuring the gas-liquid interface depth in the test tube. It is simple to operate, provides a lot of detection data and has high detection efficiency.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is: a gas-tightness detection device for a salt cavern hydrogen storage tank that facilitates the detection of the gas-liquid interface depth. The salt cavern hydrogen storage tank includes a cavity and a wellbore communicating with the top of the cavity, comprising:

[0007] Production casing, fixed to the well wall of the wellbore;

[0008] The test tube extends into the production sleeve, with a distance between its lower end and the bottom of the cavity, forming an annular space between the test tube and the production sleeve;

[0009] A gas supply device, connected to the annulus, is used to inject gas into the annulus;

[0010] A gas pipeline is used to connect the test tube and the annulus after some brine is discharged from the test tube by injecting gas into the annulus, so that the gas-liquid interface depth in the test tube and the annulus is kept consistent.

[0011] A gas-liquid interface measuring device extends into the test tube to detect the depth of the gas-liquid interface within the test tube.

[0012] Furthermore, the gas-liquid interface measuring device is a distributed optical fiber or sonar.

[0013] Furthermore, the sleeve shoe of the production sleeve is located on top of the cavity.

[0014] Furthermore, the wellhead portion of the test tube has an openable and closable test tube opening, and the wellhead portion of the annulus is configured with an openable and closable independent first annulus opening and a second annulus opening; wherein,

[0015] The test tube opening is used to discharge brine in the open state or to connect with the first annular opening in the open state through the gas pipeline. The second annular opening is used to inject gas into the gas supply device in the open state.

[0016] Furthermore, to facilitate the control of the opening and closing of each opening, the test tube opening is equipped with a test tube valve, the annular first opening is equipped with an annular first valve, and the annular second opening is equipped with an annular second valve.

[0017] Furthermore, to facilitate the measurement of the flow rate of the discharged brine and the gas pressure at the wellhead, the test tube opening is equipped with a test tube flow meter and a test tube pressure gauge, and both the first annular opening and the second annular opening are equipped with an annular pressure gauge.

[0018] This invention also provides a convenient method for detecting the gas tightness of a salt cavern hydrogen storage tank by measuring the depth of the gas-liquid interface. The method includes:

[0019] S1. Lower the test tube to the bottom of the cavity through the production sleeve. After connecting the oil injector and the wire rope to the gas-liquid interface measuring equipment, lower it into the test tube.

[0020] S2. Connect the gas supply equipment to the annulus and inject gas into the annulus;

[0021] S3. After a certain volume of brine is discharged from the test tube, the annulus is connected to the test tube through the gas pipeline so that the gas-liquid interface depth of the test tube and the annulus is consistent. When the gas pressure at the casing shoe of the production casing reaches a certain value, the gas injection is stopped.

[0022] S4. Measure the gas-liquid interface depth in the test tube using the gas-liquid interface measuring device, and simultaneously record the pressure at the annulus wellhead and the test tube wellhead. Evaluate the gas tightness of the wellbore and cavity by measuring the changes in gas-liquid interface depth and wellhead pressure.

[0023] Furthermore, to prevent the end of the test tube from being blocked by insoluble substances such as soil and gravel, the distance between the lower end of the test tube and the bottom of the cavity is 2-5m.

[0024] Furthermore, after connecting the annulus to the test tube via a gas pipeline, the gas-liquid interface depths of the test tube and the annulus are consistent and located below the casing shoe of the production casing.

[0025] Furthermore, in step S3, the volume of the discharged brine is the sum of the volumes of the annulus above the top of the cavity and the test tube.

[0026] Furthermore, in steps S2 and S3, the gas supply equipment supplies nitrogen. If the wellbore and cavity gas tightness test using injected nitrogen as the test medium is qualified, the method also includes:

[0027] S5, nitrogen gas is discharged and hydrogen gas is injected. When the gas pressure at the casing shoe of the production casing reaches a certain value, hydrogen gas injection is stopped, and the gas-liquid interface depth and pressure data are recorded to evaluate the gas tightness of the wellbore and cavity.

[0028] By adopting the above technical solution, this invention utilizes a gas pipeline to connect the annulus and the test tube, ensuring that the gas-liquid interface depths of the annulus and the test tube are consistent. The gas-liquid interface depth is measured using a gas-liquid interface measuring device. By measuring the pressure in the annulus and the test tube, the gas tightness of the salt cavern hydrogen storage wellbore and cavity is evaluated based on the changes in gas-liquid interface depth and the gas leakage rate. This invention can conveniently, directly, and continuously measure the gas-liquid interface depth in the test tube, shorten the recording time interval during testing, increase the amount of detection data, and thus more accurately determine the gas tightness performance of the salt cavern hydrogen storage wellbore and cavity. Attached Figure Description

[0029] Figure 1 A schematic diagram of the structure of the salt cavern hydrogen storage gas tightness detection device for convenient detection of gas-liquid interface depth according to the present invention.

[0030] In the diagram, 1. Cavity; 2. Production casing; 3. Test tube; 4. Annulus; 5. Gas pipeline; 6. Brine; 7. Gas-liquid interface measuring device; 8. Casing shoe; 9. Gas supply equipment; 10. Test tube valve; 11. Annulus first valve; 12. Annulus second valve; 13. Test tube flow meter; 14. Test tube pressure gauge; 15. Annulus pressure gauge; 16. Wire rope; 17. Oil injector. Detailed Implementation

[0031] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0032] In one embodiment, such as Figure 1 As shown, a device for detecting the gas tightness of a salt cavern hydrogen storage tank, which facilitates the detection of the gas-liquid interface depth, is disclosed. The salt cavern hydrogen storage tank includes a cavity 1 and a wellbore communicating with the top of the cavity 1.

[0033] Production casing 2 is fixed to the well wall of the wellbore;

[0034] Test tube 3 extends into production sleeve 2, with a distance between its lower end and the bottom of cavity 1, forming an annular space 4 between test tube 3 and production sleeve 2;

[0035] Gas supply device 9 is connected to annulus 4 and is used to inject gas into annulus 4;

[0036] Gas pipeline 5 is used to connect test tube 3 and annulus 4 after some brine 6 is discharged from test tube 3 by injecting gas into annulus 4 so that the gas-liquid interface depth in test tube 3 and annulus 4 is kept consistent.

[0037] The gas-liquid interface measuring device 7 extends into the test tube 3 to detect the depth of the gas-liquid interface within the test tube 3.

[0038] The gas supply equipment 9 is either a nitrogen or hydrogen vehicle. The gas-liquid interface measuring device 7 is raised or lowered via a steel wire rope 16 at the wellhead. The test tube 3 is secured at the wellhead using a four-way connector.

[0039] Specifically, in this embodiment, the annulus 4 and the test tube 3 are connected by a gas pipeline 5, so that the gas-liquid interface depths of the annulus and the test tube are consistent. The gas-liquid interface depth is measured by a gas-liquid interface measuring device 7. By measuring the pressure in the annulus 4 and the test tube 3, the gas tightness of the salt cavern hydrogen storage wellbore and cavity is evaluated based on the change in gas-liquid interface depth and the gas leakage rate. This embodiment can conveniently, directly and continuously measure the gas-liquid interface depth in the test tube 3, shorten the time interval for recording during testing, increase the amount of detection data, and more accurately determine the gas tightness performance of the salt cavern hydrogen storage wellbore and cavity 1.

[0040] In one embodiment, such as Figure 1 As shown, the gas-liquid interface measuring device 7 is a distributed optical fiber or sonar.

[0041] It is important to note that distributed optical fibers work by detecting changes in their own thermal field distribution to determine changes in interface depth. If the fiber is positioned too high, it may not be able to contact the liquid, thus failing to detect changes in the gas-liquid interface depth. To be on the safe side, when the gas-liquid interface measuring device 7 is a distributed optical fiber, the fiber must be inserted below the top of the cavity 1 to ensure it is below the gas-liquid interface. Sonar works by calculating distance based on the time between receiving and emitting sound waves to determine changes in gas-liquid interface depth. Since the probe is located below the device, it can only emit sound waves downwards. Therefore, when the gas-liquid interface measuring device 7 is a sonar, it must be positioned above the gas-liquid interface.

[0042] In one embodiment, such as Figure 1 As shown, the casing shoe 8 for producing casing 2 is located above the top of the cavity 1. The portion between the casing shoe 8 and the top of the cavity 1 forms the well neck section.

[0043] In one embodiment, such as Figure 1 As shown, the wellhead portion of test tube 3 has an openable and closable test tube opening, and the wellhead portion of annulus 4 is equipped with an openable and closable independent annulus first opening and annulus second opening; wherein,

[0044] The test tube opening is used to discharge brine 6 in the open state or to connect with the first opening of the annulus in the open state through the gas pipeline 5. The second opening of the annulus is used to inject gas into the gas supply device 9 in the open state.

[0045] like Figure 1 As shown, in order to facilitate the control of the opening and closing of each opening, the test tube opening is equipped with a test tube valve 10, the annular first opening is equipped with an annular first valve 11, and the annular second opening is equipped with an annular second valve 12.

[0046] During testing, the first annular valve 11 is closed, and the second annular valve 12 and test tube valve 10 are opened. Gas supply equipment 9 injects gas into the annulus 4 through the second annular opening, while brine 6 is discharged from the test tube opening. The gas-liquid interface depth in the annulus 4 gradually decreases. After a certain volume of brine 6 is discharged, the test tube valve 10 is closed, and the test tube opening and the first annular opening are connected by the gas pipeline 5. Then, the test tube valve 10 and the first annular valve 11 are opened again, connecting the annulus 4 to the test tube 3. Gas continues to be injected into the annulus 4 through the second annular opening. The gas-liquid interface depth in the test tube 3 gradually decreases, while the gas-liquid interface depth in the annulus 4 gradually increases until it reaches a certain depth at the top of the cavity 1. When the pressure at the wellhead of the annulus 4 reaches a certain value, the second annular valve 12 is closed, and gas injection stops. Then, the gas-liquid interface depth is measured using the gas-liquid interface measurement device 7, and the pressure at the wellhead of the annulus 4 and test tube 3 is tested. The gas pressure in the annulus 4, the gas pressure in the test tube 3, and the gas-liquid interface depth in the test tube 3 are recorded at regular intervals. This is continuously monitored for 24 hours. The gas leakage rate can be calculated by analyzing the changes in the gas-liquid interface depth and the pressure changes at the wellhead pressure gauge. The gas tightness of the wellbore and cavity is evaluated based on the gas leakage rate and the changes in the gas-liquid interface depth. Existing technology uses neutron-gamma logging to measure the gas-liquid interface depth. Due to the complexity of the construction, it requires raising or lowering the gamma ray detector, thus requiring measurements of the gas-liquid interface depth every hour. In this embodiment, however, the gas-liquid interface depth in the test tube 3 can be continuously measured using fiber optics or sonar based on the pressure balance principle. This method is simple to operate, provides more data, and has high detection efficiency.

[0047] In one embodiment, such as Figure 1 As shown, to facilitate the measurement of the discharged brine 6 and the gas pressure, a test tube flow meter 13 and a test tube pressure gauge 14 are installed at the test tube opening, and an annular pressure gauge 15 is installed at both the first and second annular openings. The flow meter 13 is used to record the discharged brine 6, the test tube pressure gauge 14 is used to detect the gas pressure at the wellhead of test tube 3, and the annular pressure gauge 15 is used to measure the gas pressure at the wellhead of annular 4.

[0048] In one embodiment, a method for detecting the gas tightness of a salt cavern hydrogen storage tank, which facilitates the detection of the gas-liquid interface depth, includes:

[0049] S1. Lower the test tube 3 to the bottom of the cavity 1 through the production sleeve 2. After the gas-liquid interface measuring device 7 is connected to the oil injector 17 and the wire rope 16, it is lowered into the test tube 3.

[0050] S2. Connect the gas supply device 9 to the annulus 4 and inject gas into the annulus 4;

[0051] S3. After a certain volume of brine 6 is discharged from the test tube 3, the annulus 4 is connected to the test tube 3 through the gas pipeline 5 so that the gas-liquid interface depth of the test tube 3 and the annulus 4 is consistent. When the gas pressure at the sleeve shoe 8 of the production sleeve 2 reaches a certain value, the gas injection is stopped.

[0052] It should be noted that the volume of discharged brine 6 is the sum of the volumes of the annulus 4 above the top of cavity 1 and the test tube 3. The set volume v of discharged brine 6 is the volume of brine 6 in the annulus 4 above the top of cavity 1 and the test tube 3 when the salt cavern and cavity 1 are full of brine, calculated as follows:

[0053]

[0054] Where v is the volume of brine 6 to be discharged, l is the top depth of cavity 1, d1 is the inner diameter of production sleeve 2, d2 is the outer diameter of test tube 3, and d3 is the inner diameter of test tube 3.

[0055] S4. Measure the gas-liquid interface depth inside the test tube 3 using the gas-liquid interface measuring device 7, and simultaneously record the pressure at the wellhead of the annulus 4 and the wellhead of the test tube 3. Evaluate the gas tightness of the wellbore and cavity 1 by measuring the changes in gas-liquid interface depth and wellhead pressure.

[0056] It should be noted that in steps S2 and S3, the gas supply device 9 supplies nitrogen, but it can also supply hydrogen.

[0057] In one embodiment, in steps S2 and S3, the gas supply device 9 supplies nitrogen gas, that is, nitrogen gas is used as the test medium first.

[0058] If the gas tightness of the wellbore and cavity 1 tested with nitrogen as the test medium fails, the gas tightness test ends and there is no need to conduct a gas tightness test with hydrogen, which has a smaller molecular structure. If the gas tightness of the wellbore and cavity 1 tested with nitrogen as the test medium passes, the next step is to test the gas tightness of the wellbore and cavity using hydrogen, which has a smaller molecular structure, as the test medium.

[0059] The standards for evaluating the airtightness of salt cavern wellbores and cavities are as follows:

[0060] Standard A: The gas leakage rate gradually decreases over time and eventually reaches a stable level;

[0061] Standard B: The change in the depth of the gas-liquid interface during the test period is less than 1.0 m.

[0062] If the test results meet both Standard A and Standard B, the airtightness of the salt cavern wellbore and cavity 1 is deemed qualified; if the test results do not meet Standard A, the airtightness of the salt cavern wellbore and cavity 1 is deemed unqualified; if the test results meet Standard A but not Standard B, the changes in gas-liquid interface depth and pressure within 24 hours can be recorded again to test the airtightness.

[0063] Assuming the wellbore and cavity airtightness test using nitrogen as the test medium is satisfactory, the test method also includes:

[0064] S5, remove the gas pipeline 5, purge the nitrogen from the test pipe 3 and annulus 4, and after no more nitrogen is purged, reconnect the test pipe 3 and annulus 4 through the gas pipeline 5. Inject hydrogen into annulus 4 through the gas supply device 9. When the gas pressure at the casing shoe 8 of the production casing 2 reaches a certain value, stop injecting hydrogen and continue to record the gas-liquid interface depth and pressure gauge data to evaluate the gas tightness of the wellbore and cavity.

[0065] It is important to note that the wellbore and cavity gas-tightness test for nitrogen-based media must pass the gas-tightness test before the test for hydrogen-based media can proceed. If the gas-tightness test for hydrogen-based media fails, the salt cavern can be used to store natural gas or compressed air; if the gas-tightness test for hydrogen-based media passes, the salt cavern can be used to store hydrogen.

[0066] In one embodiment, the distance between the lower end of the test tube 3 and the bottom of the cavity 1 is 2-5m. This prevents the end of the test tube 3 from being blocked by insoluble substances such as soil and gravel.

[0067] In one embodiment, after the annulus 4 is connected to the test tube 3 via the gas pipeline 5, the gas-liquid interface depths of the test tube 3 and the annulus 4 are the same and located below the sleeve shoe 8 of the production sleeve 2.

[0068] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A device for conveniently detecting the gas-liquid interface depth in a salt cavern hydrogen storage facility, the salt cavern hydrogen storage facility comprising a cavity (1) and a wellbore communicating with the top of the cavity (1), characterized in that, include: Production casing (2) is fixed to the well wall of the wellbore; The test tube (3) extends into the production sleeve (2), with a distance between its lower end and the bottom of the cavity (1), and an annular space (4) is formed between the test tube (3) and the production sleeve (2). Gas supply equipment (9) is connected to the annulus (4) and is used to inject gas into the annulus (4); A gas pipeline (5) is used to connect the test tube (3) and the annulus (4) after some brine (6) is discharged from the test tube (3) by injecting gas into the annulus (4) so ​​that the gas-liquid interface depth in the test tube (3) and the annulus (4) remains consistent. A gas-liquid interface measuring device (7) extends into the test tube (3) to detect the gas-liquid interface depth inside the test tube (3); The wellhead portion of the test tube (3) has an openable and closable test tube opening, and the wellhead portion of the annulus (4) is equipped with an openable and closable first annulus opening and a second annulus opening that are independent of each other; wherein, The test tube opening is used to discharge brine (6) in the open state or to connect with the first annular opening in the open state through the gas pipeline (5). The second annular opening is used to inject gas into the gas supply device (9) in the open state.

2. The salt cavern hydrogen storage gas tightness detection device for convenient detection of gas-liquid interface depth according to claim 1, characterized in that, The gas-liquid interface measuring device (7) is a distributed optical fiber or sonar.

3. The salt cavern hydrogen storage gas tightness detection device for convenient detection of gas-liquid interface depth according to claim 1, characterized in that, The sleeve shoe (8) of the production sleeve (2) is located on top of the cavity (1).

4. The device for detecting the gas tightness of a salt cavern hydrogen storage tank that facilitates the detection of the gas-liquid interface depth according to claim 1, characterized in that, The test tube opening is equipped with a test tube valve (10), the annular first opening is equipped with an annular first valve (11), and the annular second opening is equipped with an annular second valve (12).

5. The salt cavern hydrogen storage gas tightness detection device for convenient detection of gas-liquid interface depth according to claim 1, characterized in that, The test tube opening is equipped with a test tube flow meter (13) and a test tube pressure gauge (14), and the annular first opening and the annular second opening are both equipped with an annular pressure gauge (15).

6. A convenient method for detecting the gas tightness of a salt cavern hydrogen storage tank based on the convenient gas-liquid interface depth detection device according to any one of claims 1-5, characterized in that, The methods include: S1. Lower the test tube (3) to the bottom of the cavity (1) through the production sleeve (2). After connecting the oil injector (17) and the wire rope (16) to the gas-liquid interface measuring device (7), lower it into the test tube (3). S2. Connect the gas supply device (9) to the annulus (4) and inject gas into the annulus (4); S3. After a certain volume of brine (6) is discharged from the test tube (3), the annulus (4) is connected to the test tube (3) through the gas pipeline (5) so that the gas-liquid interface depth of the test tube (3) and the annulus (4) is consistent. When the gas pressure at the sleeve shoe (8) of the production sleeve (2) reaches a certain value, the gas injection is stopped. S4. Measure the gas-liquid interface depth in the test tube (3) using the gas-liquid interface measuring device (7), and record the pressure at the wellhead of the annulus (4) and the wellhead of the test tube (3). Evaluate the gas tightness of the wellbore and cavity (1) by measuring the changes in gas-liquid interface depth and wellhead pressure.

7. The method for detecting the gas tightness of a salt cavern hydrogen storage tank by conveniently detecting the depth of the gas-liquid interface as described in claim 6, characterized in that, The distance between the lower end of the test tube (3) and the bottom of the cavity (1) is 2-5m.

8. The method for detecting the gas tightness of a salt cavern hydrogen storage tank by conveniently detecting the depth of the gas-liquid interface as described in claim 6, characterized in that, After the annulus (4) and the test tube (3) are connected by the gas pipeline (5), the gas-liquid interface depths of the test tube (3) and the annulus (4) are consistent and located below the sleeve shoe (8) of the production sleeve (2).

9. The method for detecting the gas tightness of a salt cavern hydrogen storage tank by conveniently detecting the depth of the gas-liquid interface as described in claim 6, characterized in that, In steps S2 and S3, the gas supply equipment (9) supplies nitrogen. If the wellbore and cavity 1 gas sealing is qualified when nitrogen is injected as the test medium, the method further includes: S5, nitrogen gas is discharged and hydrogen gas is injected. When the gas pressure at the casing shoe (8) of the production casing (2) reaches a certain value, hydrogen gas injection is stopped, and the gas-liquid interface depth and pressure data are recorded to evaluate the gas tightness of the wellbore and cavity (1).

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