A method of workover of low pressure gas wells

Abstract

This invention provides a low-pressure gas well workover method, specifically including: S1 determining the workover location of the low-pressure gas well; S2 sequentially connecting a drive tool, a setting tool, and a through-tubing expansion bridge plug via coiled tubing, and driving them into the well starting with the through-tubing expansion bridge plug until it reaches below the determined workover location; S3 setting the through-tubing expansion bridge plug and removing all equipment except the through-tubing expansion bridge plug from the well; S4 injecting workover fluid at the workover location above the through-tubing expansion bridge plug to perform the workover operation; S5 after the workover operation is completed, using a gas lift tool to perform a gas lift and fluid removal operation at the workover location; S6 after completing the gas lift and fluid removal, unsealing the through-tubing expansion bridge plug and setting it, thus completing the workover. This invention overcomes the problem of severe formation contamination caused by existing low-pressure gas well workover methods, performing workover operations on low-pressure gas wells in a low-damage manner. By reducing the amount of workover fluid injected into the well, the contamination of the formation by the injected fluid is reduced, thereby shortening the workover cycle and saving operating costs.

Description

Technical Field

[0001] This invention relates to the field of low-pressure gas well workover technology, and more specifically, to a low-pressure gas well workover method. Background Technology

[0002] As gas field development deepens, some older wells are being exploited at low pressure, producing sand and water that buries the formation and cannot be cleaned up in time, leading to reduced or even halted gas well production. Currently, well workover operations in the absence of external energy replenishment from the formation face two main technological challenges: First, the well-killing technology for low-pressure gas wells. For wellbore safety during operations, well control requires injecting workover fluid into the well, resulting in significant fluid leakage into the formation and severe contamination. Over time, this contamination worsens, prolonging the post-operation drainage cycle, increasing costs, and making post-operation recovery difficult and sometimes impossible. Second, the fluid drainage process for low-pressure gas wells. As fluid accumulates at the bottom of the well, production drops rapidly, making normal production impossible. To drain the fluid and improve reservoir development, intermittent production or conventional downhole operations are typically required to restore normal production.

[0003] Given the technological challenges of working out low-pressure gas wells with moving tubing, it is necessary to explore new workout methods that can protect the reservoir from contamination and achieve good production recovery. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem of serious formation contamination caused by existing low-pressure gas well workover methods, and to provide a low-pressure gas well workover method that performs workover operations in a low-damage manner. By reducing the amount of workover fluid injected into the well, the contamination of the formation by the injected fluid is reduced, thereby shortening the workover cycle and saving operating costs.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] A method for working over a low-pressure gas well includes the following steps:

[0007] S1: Determine the location for well repair of low-pressure gas wells;

[0008] S2: The insertion tool, setting tool and tubing expansion bridge plug are connected in sequence through coiled tubing. The tubing expansion bridge plug is lowered into the well until it reaches below the determined workover position.

[0009] S3: Seal the tubing expansion bridge plug and remove all equipment except the tubing expansion bridge plug from the well;

[0010] S4: Inject workover fluid at the workover position above the tubing expansion bridge plug to perform workover operations;

[0011] S5: After the well workover operation is completed, use an air lift tool to perform air lift drainage of the workover site;

[0012] S6: After completing the gas lift and fluid discharge, unseal the tubing expansion bridge plug to complete the well workover.

[0013] It should be noted that this invention achieves targeted isolation and blockage by inserting an expansion plug through the tubing between the wellbore and the reservoir in a low-pressure gas well. This separates the workover location from the reservoir, allowing conventional workover operations such as wellbore fluid injection and tubing string tripping to be performed in the workover area. After the workover is completed, gas lift is used to drain the workover fluid, thus protecting the reservoir from contact with the workover fluid and preventing it from entering and contaminating the reservoir. Finally, the isolation of the expansion plug through the tubing is removed, and production can be resumed. This invention provides good reservoir protection, effectively ensures well control safety, and has the advantage of zero pollution during production resumption.

[0014] Furthermore, step S2 specifically includes the following steps:

[0015] S21: Before entering the well, check and test the pulling strength and duct diameter of the coiled tubing.

[0016] S22: Before entering the well, the appearance and integrity of the tubing expansion bridge plug were checked;

[0017] S23: Connect the upper delivery tool, the setting tool, and the through-tubing expansion bridge plug sequentially to the lower end of the coiled tubing. Lower the through-tubing expansion bridge plug first into the low-pressure gas well until the through-tubing expansion bridge plug reaches below the desired workover location, thus completing the lowering process.

[0018] It should be noted that the pull-up strength test performed on the coiled tubing is to ensure that the coiled tubing can safely and effectively complete the lowering and retrieval of various tools. The pull-up strength test is conducted by connecting a pull-up test disc to the coiled tubing, with the disc and tubing connected via a connector. The pull-up test disc is subjected to pull-ups of varying strengths to complete the test. The coiled tubing bore diameter working condition test involves a ball-passing test inside the coiled tubing to ensure smooth inner diameter flow. For example, the inner diameter of a 1.5-inch coiled tubing is 30.74 mm, and the maximum outer diameter of the test ball should not exceed 30 mm. This confirms that the coiled tubing bore diameter meets the operational requirements.

[0019] It should also be noted that the feeding tool is existing technology and is used in conjunction with the oil pipe expansion bridge plug and the setting tool. The feeding tool generally includes structures such as an injection valve, a double-disc pressure reserve valve, a hydraulic release connector and a dual-drive circulation connector. The hydraulic release connector is connected to the oil pipe expansion bridge plug and can be disconnected from the oil pipe expansion bridge plug after a certain hydraulic pressure is reached.

[0020] Furthermore, step S3 specifically includes the following steps:

[0021] S31: Pressurize the coiled tubing to expand the expansion bridge plug.

[0022] S32: Pressurize until the inserted tool disengages from the expansion bridge plug of the oil pipe, completing the expansion seat of the expansion bridge plug of the oil pipe;

[0023] S33: After the setting is completed, a sealing test is performed on the expansion bridge plug through the tubing and the space above it in the wellbore to confirm that the setting of the expansion bridge plug through the tubing is qualified;

[0024] S34: Remove the feed tool, setting tool, and coiled tubing, excluding the tubing expansion bridge plug.

[0025] Furthermore, the pressurizing medium in step S31 is nitrogen.

[0026] Furthermore, the pressurization method in step S31 is to apply pressure to the continuous tubing in equal stages, and after each pressurization, maintain the pressure for 10 minutes to allow the rubber of the tubing expansion bridge plug to fully expand, and repeat the operation.

[0027] It should be noted that during the setting process, the success of the setting can be determined by observing the changes in the pulling strength and the pressure. After the step pressurization of the tubing expansion plug is completed, the tubing string is slowly pulled up. If there is an over-pulling indicator of the pulling strength, it means that the setting is successful, indicating that the tubing expansion plug has been successfully installed in the wellbore of the low-pressure gas well. At this time, continue to pressurize to disengage the delivery tool from the tubing expansion plug (called release). When the delivery tool is released, there will be a significant drop in hydraulic pressure.

[0028] Furthermore, the specific steps of step S5 are as follows:

[0029] S51: Connect the gas lift tool through coiled tubing and run it into the well until the gas lift tool reaches the upper end of the over-tubing expansion bridge plug;

[0030] S52: Gas is injected into the coiled tubing and transported to the top of the tubing expansion bridge plug through the gas lift tool. The workover fluid is gradually pushed out from the annulus between the coiled tubing and the well wall and discharged toward the annulus wellhead until all the workover fluid is discharged.

[0031] S53: Remove the sequentially connected coiled tubing and air lift tool.

[0032] Furthermore, the gas in step S52 is nitrogen.

[0033] It should be noted that the gas lift tool is existing technology and generally includes a motor head assembly and a nozzle connected in sequence. The motor head assembly is connected to the coiled tubing via a coiled tubing connector. Nitrogen gas is used to displace the workover fluid in the wellbore. After all the workover fluid in the wellbore has been gas-lifted out, the coiled tubing and the gas lift tool are retrieved. During the gas lift fluid removal process, it is necessary to closely monitor the return parameters, such as nitrogen gas records: nitrogen injection volume, cumulative nitrogen injection volume, and surface gas injection pressure; coiled tubing records: gas lift depth, surface suspended weight test data, wellhead pressure, annular pressure, etc.; and accurately measure the returned fluid volume, and increase sampling frequency as needed.

[0034] As a preferred option, the specific steps for unsealing the expansion bridge plug seat in step S6 are as follows: a retrieval tool is lowered into the continuous tubing, the rubber expansion of the expansion bridge plug in the tubing is released by the retrieval tool, and the expansion bridge plug in the tubing is retrieved by the retrieval tool.

[0035] Furthermore, the unsealing and salvage tools include a hydraulically releasable and retractable salvage cylinder. The method to release the rubber expansion is to press down the hydraulically releasable and retractable salvage cylinder to open the balance valve of the expansion bridge plug of the oil pipe to balance the upper and lower pressures of the expansion bridge plug of the oil pipe. The hydraulically releasable and retractable salvage cylinder is slowly lifted up to allow the rubber to naturally depressurize and retract, thus completing the unsealing.

[0036] It should be noted that, under normal circumstances, the unsealing and retrieval tools typically include, in sequence, a motor head assembly, a mechanical stabilizer, a universal joint, and a JDC hydraulic releasable retrieval cylinder. The motor head assembly is connected to the continuous tubing via a continuous tubing connector. Before unsealing, a release function test of the retrieval cylinder is conducted on the ground, and the required displacement and pressure for activation are recorded. When unsealing the tool string, the JDC hydraulic releasable retrieval cylinder reaches approximately 10 meters above the bridge plug. The pulling force of the continuous tubing during lifting and lowering is tested and recorded. The tool string is slowly lowered. Once the retrieval cylinder covers the bridge plug's head, the upper balance valve of the bridge plug is opened by pressing down, and the pressure above and below the bridge plug is balanced over a certain period. After pressure balance, the unsealed bridge plug is slowly lifted, and the rubber is allowed to fully retract over a certain period while closely observing changes in suspended weight. Once unsealing is confirmed to be successful, the unsealing and retrieval tools can be used to remove the expanded bridge plug along with the tubing.

[0037] As another preferred option, the specific steps for unsealing the through-tubing expansion bridge plug in step S6 are as follows: a piercing sub is inserted through the coiled tubing, the rubber expansion of the through-tubing expansion bridge plug is released by the piercing sub, and the through-tubing expansion bridge plug is pushed to the bottom of the well by the piercing sub, thus completing the unsealing and restoring the production channel; the piercing sub includes a CT shock device and a piercing sub, and the rubber expansion is released by piercing the rubber of the through-tubing expansion bridge plug by piercing the piercing sub, causing the rubber to passively depressurize and retract, thus completing the unsealing.

[0038] It should be noted that the use of the piercing sub tool is a backup unsealing method when the expansion bridge plug in the tubing cannot be unsealed normally. The piercing sub tool generally includes a motor head assembly, a CT shock device, and a piercing sub connected in sequence. The motor head assembly is connected to the coiled tubing through a coiled tubing connector. The piercing sub tool is lowered to the setting position of the expansion bridge plug in the tubing, and a pressure of 3-5T is applied to pierce the rubber of the bridge plug, causing the rubber to passively depressurize and retract, thus completing the unsealing. The bridge plug is then pushed down by the piercing sub tool and falls to the bottom of the well. At this point, the production channel in the wellbore of the low-pressure gas well has been restored, and the retrieval of the expansion bridge plug in the tubing can be disregarded.

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] This invention achieves targeted isolation and blockage by inserting an expansion bridge plug through the tubing between the wellbore and the reservoir in a low-pressure gas well. This separates the workover site from the reservoir, allowing conventional workover operations such as wellbore fluid injection and tubing string tripping to be performed in the workover area. After the workover is completed, gas lift is used to remove the workover fluid, thus protecting the reservoir from contact with the workover fluid and preventing contamination. Finally, the expansion bridge plug through the tubing is retrieved, and production can be resumed. This invention provides excellent reservoir protection, effectively ensures well control safety, and has the advantage of zero pollution during production resumption. Attached Figure Description

[0041] Figure 1 This is a flowchart illustrating the overall steps of the present invention;

[0042] Figure 2 This is a flowchart of step 2 in the present invention;

[0043] Figure 3 This is a flowchart of step 3 in the present invention;

[0044] Figure 4 This is a flowchart of step 5 in the present invention. Detailed Implementation

[0045] The present invention will be further described below with reference to specific embodiments. The accompanying drawings are for illustrative purposes only, representing schematic diagrams rather than actual physical objects, and should not be construed as limiting the scope of this patent. To better illustrate the embodiments of the present invention, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0046] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present patent. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0047] Example 1

[0048] like Figure 1 As shown, a low-pressure gas well workover method specifically includes the following steps:

[0049] S1: Determine the location for well repair of low-pressure gas wells;

[0050] S2: The insertion tool, setting tool and tubing expansion bridge plug are connected in sequence through coiled tubing. The tubing expansion bridge plug is lowered into the well until it reaches below the determined workover position.

[0051] S3: Seal the tubing expansion bridge plug and remove all equipment except the tubing expansion bridge plug from the well;

[0052] S4: Inject workover fluid at the workover position above the tubing expansion bridge plug to perform workover operations;

[0053] S5: After the well workover operation is completed, use an air lift tool to perform air lift drainage of the workover site;

[0054] S6: After completing the gas lift and fluid discharge, unseal the expansion bridge plug seat in the tubing to complete the well workover.

[0055] It should be noted that targeted isolation and blockage are achieved by inserting an expansion plug through the tubing between the low-pressure gas well and the reservoir, separating the workover location from the reservoir. Conventional workover operations such as wellbore fluid injection and tubing string tripping are then performed in the workover area. After the workover is completed, gas lift is used to drain the workover fluid. This protects the reservoir from contact with the workover fluid, preventing it from entering the reservoir and causing contamination. Finally, the isolation of the expansion plug through the tubing is removed, and production can be resumed. This embodiment demonstrates good reservoir protection, effectively ensures well control safety, and has the advantage of zero pollution during production resumption.

[0056] Example 2

[0057] like Figure 1 As shown, a low-pressure gas well workover method specifically includes the following steps:

[0058] S1: Determine the location for well repair of low-pressure gas wells;

[0059] S2: The insertion tool, setting tool and tubing expansion bridge plug are connected in sequence through coiled tubing. The tubing expansion bridge plug is lowered into the well until it reaches below the determined workover position.

[0060] S3: Seal the tubing expansion bridge plug and remove all equipment except the tubing expansion bridge plug from the well;

[0061] S4: Inject workover fluid at the workover position above the tubing expansion bridge plug to perform workover operations;

[0062] S5: After the well workover operation is completed, use an air lift tool to perform air lift drainage of the workover site;

[0063] S6: After completing the gas lift and fluid discharge, unseal the expansion bridge plug seat in the tubing to complete the well workover.

[0064] It should be noted that targeted isolation and blockage are achieved by inserting an expansion plug through the tubing between the low-pressure gas well and the reservoir, separating the workover location from the reservoir. Conventional workover operations such as wellbore fluid injection and tubing string tripping are then performed in the workover area. After the workover is completed, gas lift is used to drain the workover fluid. This protects the reservoir from contact with the workover fluid, preventing it from entering the reservoir and causing contamination. Finally, the isolation of the expansion plug through the tubing is removed, and production can be resumed. This embodiment demonstrates good reservoir protection, effectively ensures well control safety, and has the advantage of zero pollution during production resumption.

[0065] like Figure 2 As shown, step S2 in this embodiment specifically includes the following steps:

[0066] S21: Before entering the well, check and test the pulling strength and duct diameter of the coiled tubing.

[0067] S22: Before entering the well, the appearance and integrity of the tubing expansion bridge plug were checked;

[0068] S23: Connect the upper setting tool, the delivery tool, and the through-tubing expansion bridge plug sequentially to the lower end of the coiled tubing. Lower the through-tubing expansion bridge plug first into the low-pressure gas well until the through-tubing expansion bridge plug reaches below the desired well workover location to complete the lowering process.

[0069] It should be noted that the purpose of connecting the coiled tubing for pull strength testing is to ensure that the coiled tubing can safely and effectively complete the lowering and retrieval of various tools in the future. In this embodiment, the pull strength test is performed by connecting a pull test plate to the coiled tubing. The pull test plate and the coiled tubing are connected by a coiled tubing connector. The pull test plate is pulled at different strengths to complete the test.

[0070] In this embodiment, the coiled tubing diameter operation condition test is performed by passing a ball through the coiled tubing to ensure smooth inner diameter. In this embodiment, a 1.5-inch coiled tubing with an inner diameter of 30.74 mm is used. Therefore, the maximum outer diameter of the test ball does not exceed 30 mm. The check confirms that the coiled tubing diameter meets the operation requirements.

[0071] It should also be noted that the setting tool in this embodiment is a tool that is matched with the oil pipe expansion bridge plug. Different oil pipe expansion bridge plugs require different setting tools. In this embodiment, the oil pipe expansion bridge plug is a TTI bridge plug, and the setting tool is a matching TTI setting tool.

[0072] The insertion tool in this embodiment is existing technology and is used in conjunction with the TTI through-pipe expansion bridge plug and the seat sealing tool. The TTI insertion tool includes structures such as an injection valve, a double-disc pressure reserve valve, a hydraulic release connector, and a dual-drive circulation connector. The hydraulic release connector is connected to the through-pipe expansion bridge plug and can be disconnected from the through-pipe expansion bridge plug after reaching a certain hydraulic pressure.

[0073] like Figure 3 As shown, in this embodiment, step S3 specifically includes the following steps:

[0074] S31: Pressurize nitrogen into the coiled tubing by applying pressure in stages, maintaining the pressure for 10 minutes after each pressurization to allow the rubber of the expansion bridge plug in the tubing to fully expand, and repeat the process.

[0075] S32: Pressurize until the inserted tool disengages from the expansion bridge plug of the oil pipe, completing the expansion seat of the expansion bridge plug of the oil pipe;

[0076] S33: After the setting is completed, a sealing test is performed on the expansion bridge plug through the tubing and the space above it in the wellbore to confirm that the setting of the expansion bridge plug through the tubing is qualified;

[0077] S34: Remove the feed tool, setting tool, and coiled tubing, excluding the tubing expansion bridge plug.

[0078] It should be noted that during the setting process, the success of the setting can be determined by observing the changes in the pulling strength and the pressure. After the step pressurization of the tubing expansion plug is completed, the tubing string is slowly pulled up. If there is an over-pulling indicator of the pulling strength, it means that the setting is successful, indicating that the tubing expansion plug has been successfully installed in the wellbore of the low-pressure gas well. At this time, continue to pressurize to disengage the delivery tool from the tubing expansion plug (called release). When the delivery tool is released, there will be a significant drop in hydraulic pressure.

[0079] like Figure 4 As shown, in this embodiment, the specific operation steps of step S5 are as follows:

[0080] S51: Connect the gas lift tool through coiled tubing and run it into the well until the gas lift tool reaches the upper end of the over-tubing expansion bridge plug;

[0081] S52: Nitrogen is injected into the coiled tubing and the gas is transported to the top of the tubing expansion bridge plug through the gas lift tool. The workover fluid is gradually pushed out from the annulus between the coiled tubing and the well wall and discharged toward the annulus wellhead until all the workover fluid is discharged.

[0082] S53: Remove the sequentially connected coiled tubing and air lift tool.

[0083] It should be noted that the air lift tool is existing technology, and generally includes a motor head assembly and a nozzle connected in sequence. The motor head assembly is connected to the coiled tubing through a coiled tubing connector. Nitrogen gas is used to displace the workover fluid in the wellbore. After all the workover fluid in the wellbore is airlifted out, the coiled tubing and the air lift tool are pulled out.

[0084] During the gas lift fluid discharge process, it is necessary to closely monitor the return parameters, such as nitrogen records: nitrogen injection volume, cumulative nitrogen injection volume, and surface gas injection pressure; coiled tubing records: gas lift depth, surface suspended weight test data, wellhead pressure, annular pressure, etc.; as well as accurately measuring the returned fluid volume and, as appropriate, increasing the frequency of sampling.

[0085] In this embodiment, the specific steps for unsealing the expansion bridge plug seat in step S6 are as follows: a retrieval tool is lowered into the continuous tubing, the rubber expansion of the expansion bridge plug in the oil pipe is released by the retrieval tool, and the expansion bridge plug in the oil pipe is retrieved by the retrieval tool.

[0086] In this embodiment, the unsealing and retrieval tool includes a motor head assembly, a mechanical stabilizer, a universal joint, and a JDC hydraulic releasable retrieval cylinder connected in sequence. The motor head assembly is connected to a continuous oil pipe via a continuous oil pipe connector. Before lowering, a release function test of the retrieval cylinder is conducted on the ground, and the required displacement and pressure for activation are recorded. The method to release the rubber expansion is to press down the hydraulic releasable retrieval cylinder to open the balance valve of the expansion bridge plug in the oil pipe, balancing the upper and lower pressures of the expansion bridge plug. The hydraulic releasable retrieval cylinder is then slowly lifted to allow the rubber to naturally depressurize and retract, completing the unsealing process.

[0087] Under normal circumstances, when the unsealing and retrieval tools are lowered, the JDC hydraulic releasable recovery retrieval cylinder reaches approximately 10m above the bridge plug during the unsealing process. The pulling force of the continuous tubing during lifting and lowering is tested and recorded. The tool string is slowly lowered, and once the retrieval cylinder covers the bridge plug's head, the upper balance valve of the bridge plug is opened by pressing down. A certain amount of time is allowed to balance the pressure above and below the bridge plug. After pressure balance, the unsealed bridge plug is slowly lifted, and a certain amount of time is allowed for the rubber to fully retract while closely observing changes in suspended weight. Once the unsealing is confirmed to be successful, the unsealing and retrieval tools can be used to remove the expanded bridge plug along with the tubing.

[0088] Example 3

[0089] This embodiment is similar to Embodiment 2, except that:

[0090] In this embodiment, the specific steps for unsealing the expansion bridge plug seat in step S6 are as follows: A piercing sub is lowered into the coiled tubing. The piercing sub generally includes a motor head assembly, a CT shock absorber, and a piercing sub connected in sequence. The motor head assembly is connected to the coiled tubing via a coiled tubing connector. The expansion of the rubber is released by piercing the rubber of the expansion bridge plug through the piercing sub, causing the rubber to passively depressurize and retract. The expansion bridge plug is then pushed into the bottom of the well using the piercing sub, thus completing the unsealing and restoring the production channel.

[0091] This embodiment describes the use of a piercing sub tool as a backup unsealing method when the expansion bridge plug in the tubing cannot be unsealed normally. The piercing sub tool is lowered to the setting position of the expansion bridge plug in the tubing, and a pressure of 3-5T is applied to pierce the rubber of the bridge plug, causing the rubber to passively depressurize and retract, thus completing the unsealing. The bridge plug is then pushed down by the piercing sub tool until it falls to the bottom of the well. At this point, the production channel in the wellbore of the low-pressure gas well has been restored, and the retrieval of the expansion bridge plug in the tubing is not required.

[0092] The other structures and principles of this embodiment are the same as those of Embodiment 2.

[0093] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for working over a low-pressure gas well, characterized in that, Specifically, the steps include the following: S1: Determine the location for well repair of low-pressure gas wells; S2: The insertion tool, setting tool and tubing expansion bridge plug are connected in sequence through coiled tubing. The tubing expansion bridge plug is lowered into the well until it reaches below the determined workover position. S3: Seal the tubing expansion bridge plug and remove all equipment except the tubing expansion bridge plug from the well; S4: Inject workover fluid at the workover position above the tubing expansion bridge plug to perform workover operations; S5: After the well workover operation is completed, use an air lift tool to perform air lift drainage of the fluid at the workover location; S6: After completing the gas lift and fluid discharge, unseal the tubing expansion bridge plug seat to complete the well workover; Step S2 specifically includes the following steps: S21: Before entering the well, check and test the pulling strength and duct diameter of the coiled tubing. S22: Before entering the well, the appearance and integrity of the tubing expansion bridge plug were checked; S23: Connect the upper delivery tool, the setting tool, and the through-tubing expansion bridge plug sequentially to the lower end of the coiled tubing. Lower the through-tubing expansion bridge plug into the low-pressure gas well, starting with the through-tubing expansion bridge plug, until the through-tubing expansion bridge plug reaches below the location to be repaired, thus completing the lowering process. Step S3 specifically includes the following steps: S31: Pressurize the coiled tubing to expand the expansion bridge plug. S32: Pressurize until the inserted tool disengages from the expansion bridge plug of the oil pipe, completing the expansion seat of the expansion bridge plug of the oil pipe; S33: After completing the setting, check the sealing performance of the expansion bridge plug in the oil pipe; S34: Remove the feed tool, setting tool, and coiled tubing, excluding the tubing expansion bridge plug; The specific steps of step S5 are as follows: S51: Connect the gas lift tool through coiled tubing and run it into the well until the gas lift tool reaches the upper end of the over-tubing expansion bridge plug; S52: Gas is injected into the coiled tubing and transported to the top of the tubing expansion bridge plug through the gas lift tool. The workover fluid is gradually pushed out from the annulus between the coiled tubing and the well wall and discharged toward the annulus wellhead until all the workover fluid is discharged. S53: Remove the sequentially connected coiled tubing and air lift tool.

2. A method of workover of a low pressure gas well according to claim 1, characterized in that, The pressurization medium in step S31 is nitrogen.

3. A method of workover of a low pressure gas well according to claim 2, characterized in that, The pressurization method in step S31 is to apply pressure to the continuous tubing in equal stages, and after each pressurization, maintain the pressure for 10 minutes to allow the rubber of the tubing expansion bridge plug to fully expand, and repeat the operation.

4. A method of workover of low pressure gas wells according to claim 1, characterized in that, The gas used in step S52 is nitrogen.

5. A method of workover of low pressure gas wells according to claim 1, characterized in that, The specific steps for unsealing the expansion bridge plug seat in step S6 are as follows: a retrieval tool is lowered into the continuous tubing, the rubber expansion of the expansion bridge plug in the tubing is released by the retrieval tool, and the expansion bridge plug in the tubing is retrieved by the retrieval tool.

6. A low-pressure gas well workover method according to claim 5, characterized in that, The unsealing and salvage tool includes a hydraulically releasable and retractable salvage cylinder. The method to release the rubber expansion is to press down the hydraulically releasable and retractable salvage cylinder to open the balance valve of the expansion bridge plug of the oil pipe to balance the upper and lower pressures of the expansion bridge plug of the oil pipe, and then slowly lift the hydraulically releasable and retract the rubber naturally to complete the unsealing.

7. A method for working over a low-pressure gas well according to claim 1, characterized in that, The specific steps for unsealing the through-tubing expansion bridge plug in step S6 are as follows: a piercing sub is inserted through the coiled tubing, the rubber expansion of the through-tubing expansion bridge plug is released by the piercing sub, and the through-tubing expansion bridge plug is pushed to the bottom of the well by the piercing sub, thus completing the unsealing and restoring the production channel; the piercing sub includes a CT shock device and a piercing sub, and the rubber expansion is released by piercing the rubber of the through-tubing expansion bridge plug by the piercing sub, causing the rubber to passively depressurize and retract, thus completing the unsealing.

Images