Method for testing the airtightness of the salt cavity below the top of the cannula shoe

Abstract

This invention discloses a method for detecting the gas tightness of salt caverns where the casing shoe is located below the top of the cavity. The method includes the following steps: Step A, performing sonar measurements on the salt cavern; Step B, lowering the gas tightness testing string and equipment; Step C, injecting saturated brine for pre-pressurization; Step D, injecting gas to the top of the cavity; Step E, injecting saturated brine to pressurize to the test pressure; Step F, performing gas tightness testing on the wellbore and cavity. The gas tightness of the production casing and the cement sheath at the top of the cavity is determined by monitoring the change trend of the gas leakage rate in the annulus over time and the change value of the gas-liquid interface depth. Compared with existing technologies, this method uses less gas and has a wider range of applicable conditions for detecting the gas tightness of the wellbore and cavity. This invention is simple, easy to implement, and low in cost, and is of great significance for detecting the gas tightness of wellbore and cavity in salt caverns where the casing shoe is located below the top of the cavity, and for converting these areas into salt cavern storage facilities.

Description

Technical Field

[0001] This invention relates to the field of salt cavern gas storage construction engineering, and specifically to a method for detecting the gas tightness of salt caverns when the casing shoe is located below the top of the cavity. Background Technology

[0002] The construction of salt cavern gas storage facilities is divided into two types: newly built caverns and utilization of existing caverns. Newly built caverns refer to drilling a well to the underground rock salt layer according to the standards of salt cavern gas storage facilities. The injected clean water is then used to intentionally dissolve the underground rock salt to gradually form underground space. The shape and structural parameters of the salt caverns constructed in this way are controllable, and the sealing performance is good, but the construction period is relatively long, generally requiring four to five years. Existing caverns refer to underground caverns formed by dissolving the rock salt layer for the purpose of brine extraction and salt production. my country has numerous brine extraction and salt production enterprises, and years of brine extraction have created a large number of existing caverns underground. If these are utilized and converted into salt cavern gas storage facilities, they can store more strategic energy resources.

[0003] Before converting a salt cavity into a salt cavern gas storage facility, a gas tightness test is required. Due to the simple mining method of the old cavity, the lack of specific control over cavity expansion, and the rapid upward dissolution rate of rock salt, the cavity top is higher than the production casing shoe. Influenced by the production casing clamping and cementing, precise cutting of the production casing is difficult, resulting in a certain distance between the production casing shoe and the cementing sheath at the cavity top where gas leakage may occur. Conventional gas tightness testing methods control the gas-liquid interface at a position 5-10m below the production casing shoe. If this conventional method is used to test the gas tightness of a salt cavity where the casing shoe is located below the cavity top and at a significant distance, a large amount of gas needs to be injected when the cavity top is relatively flat. Furthermore, during the creation of a new cavity through water-soluble brine extraction, the cavity shape is controlled, and the production casing is periodically cut to encourage upward expansion of the salt cavern. However, sometimes construction problems during the cutting of the production casing lead to incomplete cutting, resulting in the production casing shoe being located below the cavity top.

[0004] In summary, the existing technology has the following problems: For the salt cavity where the production sleeve shoe is located below the top of the cavity, if the conventional gas tightness testing method, which controls the gas-liquid interface depth to 5-10m below the production sleeve shoe, is used, a large amount of test gas needs to be injected, resulting in excessive testing costs and high construction difficulty. Furthermore, during depressurization after testing, the large amount of pressurized gas remaining above the sleeve shoe is difficult to expel, posing a significant safety hazard. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a method for detecting the gas tightness of the salt cavern when the sleeve shoe is located below the top of the cavity, so as to solve the problem that the existing method for detecting the gas tightness of the salt cavern when the sleeve shoe is located below the top of the cavity requires a large amount of test gas and is too costly.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is: a method for detecting the airtightness of a salt cavern located below the top of a sleeve shoe, comprising the following steps:

[0007] Step A, Sonar Measurement: Insert a sonar probe into the production casing to perform sonar measurements on the cavity and determine the cavity's morphological parameters;

[0008] Step B, Equipment insertion: Insert the test tube into the production sleeve, and insert the gas-liquid interface measuring device into the test tube;

[0009] Step C, Pre-pressurization: Saturated brine is injected into the annulus between the production casing and the test tube. When the wellhead liquid pressure of the test tube reaches the wellhead liquid pre-pressurization pressure, the injection of saturated brine is stopped, and the water tightness of the salt cavern cavity is tested.

[0010] Step D, Inject gas to the top of the cavity: Inject gas into the annulus between the production sleeve and the test tube. Stop injecting gas after the gas-liquid interface depth reaches the production sleeve shoe. Check the gas sealing of the test tube. If it passes the test, continue injecting gas so that the gas escapes from the production sleeve shoe. Stop injecting gas when the gas at the top of the cavity reaches the preset gas volume.

[0011] Step E, Inject saturated brine to pressurize to the test pressure: Inject saturated brine into the test tube. When the wellhead annular gas pressure reaches the wellhead annular test pressure value, stop injecting saturated brine.

[0012] Step F: Perform wellbore and cavity air tightness testing: Conduct temperature compensation monitoring for no less than 8 hours, and after passing the test, conduct wellbore and cavity air tightness monitoring for no less than 24 hours. Record the test pipe wellhead liquid pressure, wellhead annular gas pressure, and annular air-liquid interface depth at certain time intervals, calculate the gas leakage rate, obtain the curves of gas leakage rate and annular air-liquid interface depth changing over time, and evaluate the air tightness of the wellbore and cavity.

[0013] Furthermore, in the salt cavern well structure, a production casing is fixed to the inner wall of the surface casing, and the position of the production casing shoe at the bottom of the production casing is lower than the position of the top of the salt cavern cavity.

[0014] Furthermore, in step B, the bottom end of the test tube is sealed with a plug, and several small holes are made on the tube wall near the bottom opening.

[0015] Furthermore, in step C, the wellhead fluid pressure is increased to the wellhead fluid pre-pressurization pressure by means of staged pressurization, and the pressurization rate is not greater than 1.5 MPa / h;

[0016] Furthermore, in step C, after stopping the injection of saturated brine, it is necessary to monitor the changes in the wellhead fluid pressure and the wellhead annulus fluid pressure, and to test the water tightness of the salt cavern cavity under the current pre-pressurization pressure. The monitoring frequency should be greater than once / min, and the continuous monitoring time should be no less than 4 hours. If the water tightness test of the salt cavern cavity fails, the wellhead fluid pre-pressurization pressure should be reduced, and the pre-pressurization operation should be repeated for another test.

[0017] Furthermore, in step D, the gas tightness of the test tube is determined by observing the changes in the pressure gauge reading at the wellhead and whether there is gas at the wellhead. If the gas tightness test fails, the test tube should be replaced, and step D should be repeated.

[0018] Furthermore, in step F, during wellbore and cavity gas tightness monitoring, there are two gas-liquid interfaces: one in the annulus between the production casing and the test pipe, and one below the cementing sheath at the top of the cavity. The gas-liquid interface in the annulus is located no lower than the production casing shoe; the gas-liquid interface below the cementing sheath at the top of the cavity is located between the top of the cavity and the production casing shoe.

[0019] Furthermore, in step F, the evaluation criteria for the gas tightness of the wellbore and cavity are:

[0020] Scenario A: The gas leakage rate gradually decreases over time and approaches 0;

[0021] Scenario B: The change in gas-liquid interface depth is within the set range during the gas tightness monitoring period;

[0022] If the monitoring results meet both conditions A and B, the wellbore and cavity are deemed to be in good condition; if the monitoring results do not meet condition A, the wellbore and cavity are deemed to be in bad condition; if the monitoring results meet condition A but not condition B, a certain amount of gas is injected into the cement sheath at the top of the cavity by injecting gas / brine, and step F is repeated until a judgment result is obtained.

[0023] Furthermore, the standard for testing the water tightness of salt cavern cavities is:

[0024] During continuous monitoring, if the pressure drop of the test tube wellhead liquid pressure and the wellhead annulus liquid pressure is less than 0.01 MPa and the pressure drop gradually decreases over time and approaches 0, it indicates that the salt cavern has good water sealing performance under the current wellhead pre-rise pressure.

[0025] Furthermore, the standard for testing the gas tightness of the test tube is as follows:

[0026] After gas injection, observe the change in the pressure gauge reading at the wellhead of the test tube. If the pressure rises rapidly, it indicates that the test tube is not properly sealed.

[0027] If the pressure gauge reading at the wellhead of the test tube changes normally after gas injection, then after stopping gas injection when the gas-liquid interface depth reaches the production casing shoe, slowly open the gate valve at the wellhead of the test tube and observe whether gas is discharged. If no gas is discharged, it indicates that the test tube is well sealed; if gas is discharged, it indicates that the test tube is not well sealed.

[0028] By adopting the above technical solution, this invention utilizes a test tube and gas-liquid interface measurement equipment to detect the sealing performance of the wellbore and cavity. First, brine is injected into the salt cavity and wellbore to test the water tightness of the salt cavity. Then, gas is injected to test the gas tightness of the test tube. Finally, gas is injected again until the cement sheath at the top of the cavity comes into contact with gas at a certain pressure. The changes in the gas-liquid interface depth and gas leakage rate over time reflect the changes in the gas-liquid interface depth and gas leakage at the cement sheath at the top of the cavity, thereby determining the gas tightness of the wellbore and cavity. Compared with existing technologies, this method can meet the requirements for testing the gas tightness performance of the salt cavity and wellbore below the top of the casing shoe. It reduces the amount of injected gas while ensuring effective gas tightness testing. Therefore, using this invention to test the sealing performance of the gas storage wellbore and cavity requires less injected gas, effectively reducing the cost of compressed gas, accurately determining the gas tightness performance of the salt cavity below the top of the casing shoe, and shortening the testing time while improving testing efficiency.

[0029] In this invention, "cavity" refers to the salt-dissolving cavity formed after the rock salt layer is water-dissolved and mined, and is used interchangeably with "salt cavity" and "salt cave". Attached Figure Description

[0030] Figure 1 This is a schematic diagram of sonar measurement of the cavity according to the present invention;

[0031] Figure 2 This is a schematic diagram of the pre-pressurization process of injecting saturated brine into the annulus according to the present invention.

[0032] Figure 3 This is a schematic diagram of the state of the test tube air tightness test according to the present invention;

[0033] Figure 4 This is a schematic diagram illustrating the state of continued gas injection after the test tube gas sealing performance of the present invention has passed the test.

[0034] Figure 5 This is a schematic diagram of the wellbore and cavity airtightness monitoring status according to the present invention;

[0035] Explanation of icon numbers:

[0036] 1. Wellhead annular gate valve one; 2. Wellhead annular gas flow meter; 3. Wellhead annular pressure gauge; 4. Steel wire rope; 5. Test tube wellhead pressure gauge; 6. Test tube wellhead liquid flow meter; 7. Test tube wellhead gate valve; 8. Wellhead annular liquid flow meter; 9. Wellhead annular gate valve two; 10. Four-way device; 11. Cementing cement; 12. Guide tube; 13. Surface casing; 14. Production casing; 15. Sonar probe; 16. Test tube; 17. Gas-liquid interface measuring equipment; 18. Cementing sheath at the top of the cavity; 19. Gas at the top of the cavity; 20. Production casing shoe; 21. Brine inside the cavity; 22. Cavity; 23. Gas supply equipment; 24. Liquid supply equipment. Detailed Implementation

[0037] 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.

[0038] The method for detecting salt cavern gas tightness when the casing shoe is located below the top of the wellbore is based on the wellbore structure, such as... Figure 2 As shown, the well structure includes a production casing 14 and a test tube 16. The upper part of the production casing 14 is fixed to the inner wall of the surface casing 13 of the wellbore by cementing 11, and the lower part is fixed to the surrounding rock by cementing 11. The surface casing 13 is fixed to the inner wall of the guide tube 12 by cementing 11. The production casing shoe 20 at the bottom of the production casing 14 extends into the cavity 22 of the salt cavern and is located below the top of the cavity 22. The test tube 16 is lowered into the production casing 14 and fixed to the wellhead by a four-way device 10. An annulus is formed between the test tube 16 and the production casing 14. The four-way device 10 is equipped with a wellhead annulus gate valve 1 and a wellhead annulus gate valve 9. A wellhead annulus gas flow meter 2 and a wellhead annulus pressure gauge 3 are installed on the side of the wellhead annulus inlet gate valve 1; a wellhead annulus liquid flow meter 8 is installed on the side of the wellhead annulus gate valve 9. The wellhead of test tube 16 is equipped with a test tube wellhead pressure gauge 5, a test tube wellhead liquid flow meter 6, and a test tube inlet gate valve 7.

[0039] The method for detecting the airtightness of brine wells in this invention includes the following steps:

[0040] Step A: Perform sonar measurements on the salt cavity: such as Figure 1 As shown, the sonar probe 15 is lowered to the bottom of the cavity 22 through the production casing 14. By lifting and measuring at the same time, the shape and parameters of multiple planes of the cavity 22 are obtained, thereby determining the shape and structural parameters of the cavity 22, such as the depth data of the production casing shoe 20 and the cement sheath 18 at the top of the cavity, which is convenient for controlling the subsequent gas-liquid interface depth, the test tube 16 and the lowering depth of the gas-liquid interface measuring equipment 17.

[0041] Step B, lower the airtightness testing string and equipment: such as Figure 2As shown, a test tube 16 is lowered into the production casing 14 to the middle of the cavity 22. A four-way connector 10 is installed at the wellhead to fix the test tube 16 to the wellhead. A gas-liquid interface measuring device 17 is lowered into the test tube 16, and the gas-liquid interface measuring device 17 is raised or lowered via a wire rope 4 at the wellhead. The bottom of the test tube 16 is sealed with a plug to prevent the device from falling into the cavity 22 during operation. At the same time, several small holes are opened on the tube wall near the bottom opening to allow brine to flow in and out.

[0042] Step C, inject saturated brine for pre-pressurization: (e.g.) Figure 2 As shown, confirm that the wellhead annular gate valve 29 is open, and the wellhead annular gate valve 1 and the test pipe wellhead gate valve 7 are closed. Connect the fluid supply equipment 24, and start injecting saturated brine into the annulus between the production casing 14 and the test pipe 16 through the wellhead annular gate valve 29. Control the wellhead liquid pressure change to not exceed 1.5 MPa / h. When the pressure gauge 5 at the test pipe wellhead rises to a certain pressure, stop injecting saturated brine, close the wellhead annular gate valve 29, and monitor the pressure gauges 5 at the test pipe wellhead and 3 at the wellhead annulus. For at least 4 hours of continuous monitoring, if the pressure drop of the wellhead liquid pressure and the wellhead annulus liquid pressure in test tube 16 is less than 0.01 MPa and the pressure drop gradually decreases over time and approaches 0, it indicates that the water seal of the salt cavern is intact under the current wellhead liquid pre-pressurization pressure, and the next step can be carried out; if the water seal of the salt cavern cavity 22 fails the test under the wellhead liquid pre-pressurization pressure, the wellhead liquid pre-pressurization pressure is reduced, and the pre-pressurization operation is repeated for another test.

[0043] Step D, Injecting Gas to the Top of the Chamber: After the salt cavern water sealing test is passed, open the wellhead annulus gate valve 1, confirm that the test pipe wellhead gate valve 7 and the wellhead annulus gate valve 9 are closed, connect the gas supply equipment 23, and inject gas into the annulus between the production casing 14 and the test pipe 16 through the wellhead annulus gate valve 1, so that the gas-liquid interface reaches the production casing shoe 20. Record the temperature of the injected gas during the injection process, and observe the change in the pressure gauge 5 at the wellhead of the test pipe and the depth of the gas-liquid interface. Stop the gas injection when the gas-liquid interface depth reaches the production casing 20, and close the wellhead annulus gate valve 1. At this time, the annulus above the production casing shoe 20 is filled with gas at a certain pressure, and the gas is in contact with the inner wall of the production casing and the outer wall of the test pipe. If the value of the pressure gauge 5 at the wellhead of the test pipe rises rapidly after gas injection, it indicates that the test pipe seal is not good. If the pressure gauge 5 at the wellhead of the test tube changes normally after gas injection, then after stopping gas injection when the gas-liquid interface depth reaches the production casing shoe 20, slowly open the gate valve 7 at the wellhead of the test tube and observe whether gas is discharged. If no gas is discharged, it indicates that the test tube 16 is well sealed; if gas is discharged, it indicates that the test tube 16 is not well sealed.

[0044] Then, open the wellhead annulus gate valve 1 and continue injecting gas, allowing the gas to escape from the production casing shoe 20, move to the top of the cavity, replace the original brine at the top of the cavity, and contact the cement sheath 18 at the top of the cavity. Figure 4 As shown, the cavity 22 containing the casing shoe 20 and above contains a cavity top gas 19. The volume of the injected gas is controlled by the wellhead annular gas flow meter 2, so that the cavity top gas 19 is not less than a certain amount.

[0045] Step E, Inject saturated brine to pressurize to the test pressure: Close wellhead annular gate valve 1 and wellhead annular gate valve 2, open test pipe wellhead valve 7, connect the liquid supply device 24, and inject saturated brine into test pipe 16. Observe the wellhead annular pressure gauge 3 until the pressure gauge reading reaches the wellhead annular test pressure value. Simultaneously observe the annular air-liquid interface depth, test pipe wellhead liquid pressure, and injected saturated brine volume. Determine when to stop injecting saturated brine based on these three values. Ensure that the test pipe wellhead liquid pressure does not exceed the test pipe wellhead test pressure, and that the annular gas-liquid interface is above the production casing shoe 20. After stopping the injection of saturated brine, close test pipe gate valve 7, measure the annular air-liquid interface depth at this time, and then begin 8 hours of temperature compensation monitoring.

[0046] Step F: Conduct wellbore and cavity airtightness monitoring: If, during the 8-hour temperature compensation monitoring process, the wellhead liquid pressure, wellhead annular gas pressure, and annular gas-liquid interface depth do not change significantly, proceed to 24-hour monitoring. Figure 5 As shown. If gas leakage occurs at the cement sheath 18 at the top of the cavity, the gas 19 at the top of the cavity will continuously decrease, the gas-liquid interface depth in the annulus will decrease accordingly, and the values ​​of the test tube wellhead pressure gauge 5 and the wellhead annulus pressure gauge 3 will also decrease. Record the annulus air-liquid interface depth, the values ​​of the test tube wellhead pressure gauge 5 and the wellhead annulus pressure gauge 3 at the beginning of the monitoring, as well as the monitoring start time. Then, record the annulus air-liquid interface depth, the wellhead liquid pressure of the test tube 16, and the wellhead annulus gas pressure every hour, with equal test intervals, for 24 consecutive hours. Calculate the volume of leaked compressed gas based on the change in the annulus air-liquid interface depth per unit time and the cross-sectional area at the gas-liquid interface depth. Combined with the pressure and temperature at the cement sheath 18 at the top of the cavity, calculate the volume of leaked gas under standard conditions. Finally, obtain the gas leakage rate and its trend over time, and then evaluate the gas tightness of the wellbore or cavity 22 according to the judgment criteria.

[0047] The criteria for judging the airtightness of the wellbore and cavity 22 are as follows:

[0048] If the detection results can satisfy both Condition A and Condition B at the same time, the gas tightness of the wellbore and the cavity 22 is determined to be qualified; if the detection result does not satisfy Condition A, the gas tightness of the wellbore and the cavity 22 is determined to be unqualified; if the detection result satisfies Condition A but does not satisfy Condition B, whether the gas tightness of the wellbore and the cavity 22 is qualified can be further determined by extending the test duration; wherein,

[0049] Condition A: the change trend of gas leakage rate over time gradually decreases and approaches 0;

[0050] Condition B: the depth change of the gas-liquid interface within the gas tightness monitoring period is within the set range;

[0051] Inspired by the above preferred embodiments of the present invention, relevant staff can make various changes and modifications without departing from the technical idea of the present invention through the above description. The technical scope of the present invention is not limited to the content in the description, and must be determined according to the scope of the claims.

Claims

1. A method for detecting the airtightness of a salt cavity below the top of a sleeve shoe, characterized in that... Includes the following steps: Step A, sonar measurement: Insert a sonar probe (15) into the production sleeve (14) to perform sonar measurement on the cavity (22) and determine the morphological parameters of the cavity (22); Step B, Equipment insertion: Insert test tube (16) into the production sleeve (14), and insert gas-liquid interface measuring device (17) into the test tube (16). Step C, pre-pressurization: Saturated brine is injected into the annulus between the production casing (14) and the test tube (16). When the wellhead liquid pressure of the test tube (16) reaches the wellhead liquid pre-pressurization pressure, the injection of saturated brine is stopped, and the water tightness of the salt cavern cavity (22) is tested. Step D, Inject gas to the top of the cavity (22): Inject gas into the annulus between the production sleeve (14) and the test tube (16). Stop injecting gas after the gas-liquid interface depth reaches the production sleeve shoe (20). Check the gas tightness of the test tube (16). If it is qualified, continue to inject gas so that the gas escapes from the production sleeve shoe (20). Stop injecting gas after the top gas (19) of the cavity (22) reaches the preset gas volume. Step E, Inject saturated brine to pressurize to the test pressure: Inject saturated brine into the test tube (16), and stop injecting saturated brine when the wellhead annular gas pressure reaches the wellhead annular test pressure value; Step F, conduct gas tightness test of wellbore and cavity (22): conduct temperature compensation monitoring for no less than 8 hours, and after passing the test, conduct gas tightness monitoring of wellbore and cavity (22) for no less than 24 hours. Record the wellhead liquid pressure, wellhead annular gas pressure and annular air-liquid interface depth at certain time intervals, calculate the gas leakage rate, obtain the curves of gas leakage rate and annular air-liquid interface depth changing with time, and evaluate the gas tightness of wellbore and cavity (22).

2. The method for detecting the airtightness of the salt cavity below the top of the cavity in the sleeve shoe according to claim 1, characterized in that, In the salt cavern well structure, the inner wall of the surface casing (13) is fixed with a production casing (14), and the position of the production casing shoe (20) at the bottom of the production casing (14) is lower than the position of the top of the salt cavern.

3. The method for detecting the airtightness of the salt cavity below the top of the cavity in the sleeve shoe according to claim 1, characterized in that, In step B, the bottom end of the test tube (16) is sealed with a plug, and several small holes are made on the tube wall near the bottom opening.

4. The method for detecting the airtightness of the salt cavity below the top of the cavity in the sleeve shoe according to claim 1, characterized in that, In step C, the wellhead fluid pressure is increased to the wellhead fluid pre-pressurization pressure by means of staged pressurization, and the pressurization rate is not greater than 1.5 MPa / h.

5. The method for detecting the airtightness of the salt cavity below the top of the cavity in the sleeve shoe according to claim 1, characterized in that, In step C, after stopping the injection of saturated brine, monitor the changes in the wellhead liquid pressure and wellhead annulus liquid pressure of the test tube (16), and test the water tightness of the salt cavern cavity (22) under the current pre-pressurization pressure. The monitoring frequency is greater than 1 time / min, and the continuous monitoring time is not less than 4 hours. If the water tightness test of the salt cavern cavity (22) fails, reduce the wellhead liquid pre-pressurization pressure and repeat the pre-pressurization operation to test again.

6. The method for detecting the airtightness of the salt cavity below the top of the cavity in the sleeve shoe according to claim 1, characterized in that, In step D, the gas tightness of the test tube (16) is judged by observing the change in the pressure gauge (5) at the wellhead of the test tube and whether there is gas at the wellhead of the test tube (16). If the gas tightness test of the test tube (16) fails, the test tube (16) is replaced and the operation of step D is repeated.

7. The method for detecting the airtightness of the salt cavity below the top of the cavity in the sleeve shoe according to claim 1, characterized in that, In step F, during the gas tightness monitoring of the wellbore and cavity (22), there is a gas-liquid interface in the annulus between the production casing (14) and the test pipe (16) and below the cementing sheath (18) at the top of the cavity. The gas-liquid interface in the annulus is not lower than the production casing shoe (20); the gas-liquid interface below the cementing sheath (18) at the top of the cavity is located between the top of the cavity and the production casing shoe (20).

8. The method for detecting the airtightness of the salt cavity below the top of the cavity in the sleeve shoe according to claim 1, characterized in that, In step F, the evaluation criteria for the gas tightness of the wellbore and cavity (22) are: Scenario A: The gas leakage rate gradually decreases over time and approaches 0; Scenario B: The change in gas-liquid interface depth is within the set range during the gas tightness monitoring period; If the monitoring results meet both conditions A and B, the wellbore and cavity are deemed to be in good condition; if the monitoring results do not meet condition A, the wellbore and cavity are deemed to be in bad condition; if the monitoring results meet condition A but not condition B, a certain amount of gas is introduced into contact with the cement sheath (18) at the top of the cavity by injecting gas or brine, and step F is repeated until the judgment result is obtained.

9. The method for detecting the airtightness of the salt cavity below the top of the cavity in the sleeve shoe according to claim 5, characterized in that, The standard for testing the water tightness of salt caverns is: During continuous monitoring, if the pressure drop of the wellhead liquid pressure and the wellhead annulus liquid pressure in the test tube (16) is less than 0.01 MPa and the pressure drop gradually decreases over time and approaches 0, it indicates that the water seal of the salt cavern is intact under the current wellhead pre-rise pressure.

10. The method for detecting the airtightness of the salt cavity below the top of the cavity in the sleeve shoe according to claim 6, characterized in that, The standard for testing the airtightness of test tube (16) is as follows: After gas injection, observe the change in the wellhead pressure value of the test tube (16). If the pressure rise rate exceeds the preset rate, it indicates that the test tube (16) is not properly sealed. If the pressure value at the wellhead of the test tube (16) changes normally after gas injection, then when the gas-liquid interface depth reaches the production casing shoe (20) and gas injection is stopped, slowly open the gate valve (7) at the wellhead of the test tube and observe whether gas is discharged. If no gas is discharged, it indicates that the test tube (16) is well sealed. If gas is discharged, it indicates that the test tube (16) is not well sealed.

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