A bailing arrangement employing a combination piston

Abstract

The application discloses a combined piston for a bailing row and belongs to the technical field of natural gas production tools. In order to solve the problem that the bailing row cannot guarantee the passability, the sealing property and the pressure safety at the same time during the bailing row production, the combined piston for the bailing row comprises at least one expansion piston (1), at least one pad type piston (2) and a pad type guide piston (3), universal joint ball heads are arranged at the upper ends of the expansion piston (1), the pad type piston (2) and the pad type guide piston (3), universal joint ball seats are arranged at the lower ends of the expansion piston (1) and the pad type piston (2), the universal joint ball heads are connected with the universal joint ball seats, and the pad type guide piston (3) is located at the lower end of the combined piston for the bailing row. The combined piston for the bailing row has the advantages of simple structure and low cost and can be widely applied to the bailing type row liquid production gas technology.

Description

Technical Field

[0001] This invention relates to the field of natural gas extraction tools, specifically a lifting and retrieval system using a combined piston. Background Technology

[0002] Retrieval-type drainage gas production technology falls under the category of wireline operations for natural gas wells, but it differs significantly from conventional wireline operations: the wire diameter is larger, the outer diameter of the downhole tool string is larger, and the downhole tool string needs to have good passageability, sealing, and long service life. Currently, most gas wells requiring retrieval-type drainage technology are old wells, with tubing that has been in service downhole for 5 years or even more than 10 years. Due to scaling, wax deposition, and corrosion, the inner surface of the tubing is very rough, severely affecting the passageability and sealing of the tool string. Ensuring that the tool string can pass smoothly through such tubing and reliably seal is a difficult problem to solve. Furthermore, during operations, the gas well may be suddenly activated, and the oil pressure and casing pressure may increase suddenly, potentially causing the tool string to be rapidly lifted by the gas, leading to turbulence of the wireline inside the tubing and triggering complex downhole accidents.

[0003] Currently available technical solutions address the problem of difficult downhole tool insertion and poor maneuverability caused by tubing scaling during retrieval operations. These typically employ mechanical drilling and milling or chemical descaling, which are costly. For complex downhole accidents caused by pressure surges, existing solutions address this through wellhead pressure control: on one hand, by relieving pressure at the wellhead through valve stem rotation to prevent blowouts; on the other hand, by improving the blowout preventer's (BOP) sealing performance through adding gaskets, modifying the BOP device, and reducing the BOP sealing pressure, thus enhancing the safety of the wellhead equipment for retrieval operations. However, these solutions are complex to implement. Currently, no existing system provides a technical solution that simultaneously guarantees maneuverability, sealing, and pressure safety, presenting certain limitations. Summary of the Invention

[0004] To address the challenge of simultaneously ensuring passability, sealing, and pressure safety during the retrieval and drainage process, this invention provides a combined piston for the retrieval and drainage system. This combined piston comprises an expansion piston, a pad-type piston, and a pad-type guide piston, connected by a universal joint quick-connect coupling, allowing for arbitrary combinations as needed. When passing through the inner wall of the tubing, the spring rebound force and the elasticity of the open thin-walled tube ensure good passability and sealing of the tool string. When the gas reservoir is activated and pressure surges, the piston's mobility and the established pressure relief channel quickly balance the pressure, preventing the piston from being rapidly pushed upwards and causing accidents. Furthermore, the combined piston structure of this retrieval and drainage system is simple and low-cost, making it widely applicable to retrieval-type fluid drainage and gas production processes.

[0005] The technical solution adopted by this invention to solve its technical problem is:

[0006] A lifting column employs a combined piston, comprising at least one expansion piston, at least one pad-type piston, and one pad-type guide piston. The upper ends of the expansion piston, the pad-type piston, and the pad-type guide piston are all provided with universal joint ball heads, and the lower ends of the expansion piston and the pad-type piston are all provided with universal joint ball seats. The universal joint ball heads are connected to the universal joint ball seats, and the pad-type guide piston is located at the lower end of the combined piston in the lifting column.

[0007] The beneficial effects of this invention are:

[0008] 1. The pistons of each part are connected by universal joint quick couplings, which can be combined in any way and are flexible in use.

[0009] 2. It achieves good passability and sealing performance of the downhole tool string. During use, it can ensure that the tool string can pass smoothly up and down the tubing, and ensure sufficient sealing to avoid serious leakage of the fluid column when ascending. Under abnormal high pressure, it can quickly balance the pressure of the tool string or lock the tool string at a certain position in the tubing to prevent the wire from being disturbed by rapid ascent, thereby improving operation efficiency and safety.

[0010] 3. It has a simple structure, low cost, and flexible application, and can be widely used in the retrieval-type liquid drainage gas extraction process. Attached Figure Description

[0011] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0012] Figure 1 This is a schematic diagram of the combined piston used in the lifting and retrieval system described in this invention.

[0013] Figure 2 This is a schematic diagram of an expansion piston.

[0014] Figure 3 This is a schematic diagram of the first upper connector.

[0015] Figure 4 This is a schematic diagram of a pad-type piston.

[0016] Figure 5 This is a schematic diagram of the second upper connector.

[0017] Figure 6 This is a schematic diagram of a pad-type guide piston.

[0018] Figure 7 This is a schematic diagram of the third upper connector.

[0019] The annotations in the attached figures are explained as follows:

[0020] 1. Expansion piston; 2. Pad-type piston; 3. Pad-type guide piston;

[0021] 11. First upper connector; 12. Central tube; 13. Expansion cylinder; 14. Sealing ball; 15. Transition sub; 16. First lower connector; 17. Annular cavity; 18. Connecting sub; 19. Annular space;

[0022] 111. The first ball head section; 112. The first small diameter section; 113. The first large diameter section; 114. External through hole;

[0023] 121. Internal through hole;

[0024] 21. Second upper connector; 22. First mandrel nut; 23. First retaining ring; 24. First pad; 25. First elastic component; 26. First mandrel tube; 27. First mandrel ball seat; 28. First lower ball seat; 29. ​​Second lower connector;

[0025] 211. The second ball head section; 212. The second upper medium diameter section; 213. The second large diameter section; 214. The second lower medium diameter section; 215. The second small diameter section;

[0026] 2141. Second groove;

[0027] 31. Third upper connector; 32. Second mandrel nut; 33. Second retaining ring; 34. Second pad; 35. Second elastic component; 36. Second mandrel tube; 37. Second mandrel ball seat; 38. Second lower ball seat; 39. Third lower connector;

[0028] 311. Third ball head segment; 312. Third upper middle diameter segment; 313. Third large diameter segment; 314. Third lower middle diameter segment; 315. Third small diameter segment;

[0029] 3141. The third groove. Detailed Implementation

[0030] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0031] A lifting retrieval bar employs a combined piston system, comprising at least one expansion piston 1, at least one pad-type piston 2, and one pad-type guide piston 3. The upper ends of the expansion piston 1, the pad-type piston 2, and the pad-type guide piston 3 are all provided with universal joint ball heads, and the lower ends of the expansion piston 1 and the pad-type piston 2 are all provided with universal joint ball seats. Any one of the universal joint ball heads can be matched and connected to any one of the universal joint ball seats. The pad-type guide piston 3 is located at the lower end of the combined piston system in the lifting retrieval bar. Figure 1 As shown.

[0032] In the combined piston system used in the retrieval column, the number and position of expansion pistons 1 can be arbitrarily selected as needed, as can the number and position of pad pistons 2. There is only one pad guide piston 3, located at the bottom of the combined piston system. The universal joint ball seat of one expansion piston 1 can be matched and connected to the universal joint ball head of another expansion piston 1, a pad piston 2, or a pad guide piston 3. Similarly, the universal joint ball seat of one pad piston 2 can be matched and connected to the universal joint ball head of one expansion piston 1, another pad piston 2, or a pad guide piston 3. For example, the combined piston system used in the retrieval column includes expansion pistons 1, pad pistons 2, and pad guide pistons 3 connected sequentially from top to bottom.

[0033] In this embodiment, the expansion piston 1 includes a first upper connector 11, a central tube 12, a conversion short section 15, and a first lower connector 16 connected sequentially from top to bottom. An expansion cylinder 13 is sleeved on the central tube 12, forming an annular cavity 17 between the expansion cylinder 13 and the central tube 12. The lower end of the expansion cylinder 13 is sealed and fixedly connected to the conversion short section 15 via a connecting short section 18. The lower end of the expansion cylinder 13 is threadedly connected to the connecting short section 18. A sealing ball 14 is provided inside the central tube 12, and the sealing ball 14 can be seated and sealed with the conversion short section 15. Figure 2 As shown.

[0034] In this embodiment, the first upper connector 11 includes a first ball joint section 111, a first small diameter section 112, and a first large diameter section 113 arranged sequentially from top to bottom. The universal joint ball joint at the upper end of the expansion piston 1 is the first ball joint section 111. The upper end of the central tube 12 is fitted inside the first large diameter section 113. The central tube 12 is threadedly connected to the first large diameter section 113. The side wall of the central tube 12 is provided with multiple internal through holes 121. The lower end of the central tube 12 is fixedly connected to the conversion short section 15 through a connecting short section 18. The conversion short section 15 has a cylindrical structure. The two ends of the connecting short section 18 are threadedly connected to the central tube 12 and the conversion short section 15, respectively. The universal joint ball seat at the lower end of the expansion piston 1 is located at the lower part of the first lower connector 16. The upper end of the first lower connector 16 is threadedly connected to the lower end of the conversion short section 15. The interior of the universal joint ball seat at the lower end of the expansion piston 1 is connected to the interior of the conversion short section 15. Figure 2 and Figure 3 As shown.

[0035] The side wall of the universal joint ball seat is provided with a T-shaped notch, and the universal joint ball head can enter the interior of the universal joint ball seat from the upper part of the T-shaped notch. The lower end of the universal joint ball seat is provided with an inner convex ring. The inner diameter of the inner convex ring is smaller than the outer diameter of the universal joint ball head. The universal joint ball head and the inner convex ring prevent the universal joint ball head from detaching from the universal joint ball seat.

[0036] In this embodiment, an annular space 19 is formed between the first large-diameter section 113 and the central tube 12. The annular space 19 is connected to the annular cavity 17. An external through hole 114 is provided on the side wall of the first large-diameter section 113. The upper end of the expansion cylinder 13 is threadedly connected to the lower end of the first large-diameter section 113. The lower end of the expansion cylinder 13 is threadedly connected to the upper end of the conversion short section 15. The expansion cylinder 13 is made of 65 metal. The expansion cylinder 13 can expand radially after being subjected to internal pressure.

[0037] The expansion cylinder 13 comprises a straight cylindrical section and a conical cylindrical section connected sequentially between its upper and lower ends. The outer diameter of the lower end of the conical cylindrical section is smaller than that of its upper end. High-pressure fluid outside the expansion piston 1 can pass sequentially through the outer through-hole 114 and the annular space 19 before entering the annular cavity 17, causing the straight cylindrical section and the conical cylindrical section to expand. The outer diameter of the straight cylindrical section can increase by 4mm-8mm. The material of the expansion cylinder 13 (such as 65Mn steel) is a metal with good elasticity. The specific dimensions and material of the expansion cylinder 13 can be obtained through a limited number of experiments.

[0038] In this embodiment, the pad-type piston 2 includes a second upper connector 21 and a second lower connector 29 connected vertically. A first mandrel tube 26 is sleeved on the second upper connector 21. From top to bottom, a first mandrel nut 22, an upper first retaining ring 23, a first pad assembly, a lower first retaining ring 23, and a first mandrel ball seat 27 are sequentially sleeved on the first mandrel tube 26. The first pad assembly includes multiple strip-shaped first pads 24, which extend axially along the second upper connector 21. A first elastic member 25 is provided between the first pads 24 and the first mandrel tube 26. The first pads 24 can move along the diameter of the second upper connector 21, and the first elastic member 25 can move the first pads 24 away from the first mandrel tube 26. Figure 4 As shown.

[0039] In this embodiment, the second upper connector 21 includes, from top to bottom, a second ball joint section 211, a second upper intermediate diameter section 212, a second large diameter section 213, a second lower intermediate diameter section 214, and a second small diameter section 215. The universal joint ball joint at the upper end of the second pad-type piston 2 is the second ball joint section 211. The first mandrel tube 26 is sleeved outside the second lower intermediate diameter section 214. The second small diameter section 215 is threadedly connected to the second lower connector 29. The universal joint ball seat at the lower end of the pad-type piston 2 is located at the lower part of the second lower connector 29. An axial groove is provided on the inner surface of the lower end of the first mandrel ball seat 27. A first lower ball seat 28 is provided between the first mandrel ball seat 27 and the second lower connector 29. The first mandrel ball seat 27 can abut against the first lower ball seat 28. The first lower ball seat 28 is sleeved outside the second small diameter section 215. The first lower ball seat 28 is threadedly connected to the second small diameter section 215. Figure 4 and Figure 5 As shown.

[0040] In this embodiment, the outer surface of the second lower middle diameter section 214 is provided with a plurality of second grooves 2141. The second grooves 2141 extend axially along the second upper connector 21, and the plurality of second grooves 2141 are arranged circumferentially at intervals along the second upper connector 21. The upper part of the first mandrel nut 22 and the upper part of the first mandrel ball seat 27 are connected through the second grooves 2141. The first mandrel nut 22 is threadedly connected to the first mandrel tube 26, and the first mandrel nut 22 fixes the upper first retaining ring 23 to the first mandrel tube 26. In addition, the upper end of the first pad 24 is located between the upper first retaining ring 23 and the first spindle tube 26. The first spindle ball seat 27 is threadedly connected to the first spindle tube 26, and the first spindle ball seat 27 fixes the lower first retaining ring 23 to the outside of the first spindle tube 26. The lower end of the first pad 24 is located between the lower first retaining ring 23 and the first spindle tube 26. The upper and lower first retaining rings 23 can prevent the first pad 24 from disengaging from the pad-type piston 2. The material of the first pad 24 is metal. Two first elastic components 25 are provided between the first pad 24 and the first spindle tube 26. The first elastic components 25 are springs, and the two ends of the springs are connected to the first pad 24 and the first spindle tube 26 respectively.

[0041] In this embodiment, the pad-type guide piston 3 includes a third upper connector 31 and a third lower connector 39 connected vertically. A second mandrel tube 36 is sleeved on the third upper connector 31. From top to bottom, a second mandrel nut 32, an upper second retaining ring 33, a second pad assembly, a lower second retaining ring 33, and a second mandrel ball seat 37 are sequentially sleeved on the second mandrel tube 36. The second pad assembly includes multiple strip-shaped second pads 34, which extend axially along the third upper connector 31. A second elastic member 35 is provided between the second pads 34 and the second mandrel tube 36. The second pads 34 can move along the diameter of the third upper connector 31, and the second elastic member 35 can move the second pads 34 away from the second mandrel tube 36. Figure 6 As shown.

[0042] In this embodiment, the third upper connector 31 includes a third ball joint section 311, a third upper intermediate diameter section 312, a third large diameter section 313, a third lower intermediate diameter section 314, and a third small diameter section 315 arranged sequentially from top to bottom. The universal joint ball joint at the upper end of the pad-type guide piston 3 is the third ball joint section 311. The second mandrel tube 36 is sleeved outside the third lower intermediate diameter section 314. The third small diameter section 315 is threadedly connected to the third lower connector 39. The lower end of the third lower connector 39 has a tapered structure with the top facing downwards. The inner surface of the lower end of the second mandrel ball seat 37 is provided with an axial groove. A second lower ball seat 38 is provided between the second mandrel ball seat 37 and the third lower connector 39. The second mandrel ball seat 37 can abut against the second lower ball seat 38. The second lower ball seat 38 is sleeved outside the third small diameter section 315. The second lower ball seat 38 is threadedly connected to the second small diameter section 315. Figure 6 and Figure 7 As shown.

[0043] In this embodiment, the outer surface of the third lower diameter section 314 is provided with a plurality of third grooves 3141. The third grooves 3141 extend axially along the third upper connector 31, and the plurality of third grooves 3141 are arranged circumferentially at intervals along the third upper connector 31. The upper part of the second mandrel nut 32 and the upper part of the second mandrel ball seat 37 are connected through the third grooves 3141. The second mandrel nut 32 is threadedly connected to the second mandrel tube 36, and the second mandrel nut 32 fixes the upper second retaining ring 33 to the outside of the second mandrel tube 36. The upper end of the second pad 34 is located between the upper second retaining ring 33 and the second spindle tube 36. The second spindle ball seat 37 is threadedly connected to the second spindle tube 36, and the second spindle ball seat 37 fixes the lower second retaining ring 33 to the outside of the second spindle tube 36. The lower end of the second pad 34 is located between the lower second retaining ring 33 and the second spindle tube 36. The upper and lower second retaining rings 33 can prevent the second pad 34 from disengaging from the pad-type guide piston 3. The material of the second pad 34 is metal. Two second elastic components 35 are provided between the second pad 34 and the second spindle tube 36. The second elastic components 35 are springs, and the two ends of the springs are connected to the second pad 34 and the second spindle tube 36 respectively.

[0044] The assembly relationship in the expansion piston 1 is as follows: the lower part of the conversion short section 15 is connected to the first lower connector 16, the upper part of the connecting short section is connected to the central tube 12 and the expansion cylinder 13, and after the sealing ball 14 is inserted into the central tube 12, the first upper connector 11 is connected to the top of the central tube 12. The expansion piston 1, the pad-type piston 2, and the pad-type guide piston 3 all contain no rubber parts; all parts are metal, exhibiting high temperature resistance, good wear resistance, and long service life.

[0045] The assembly relationship in the pad-type piston 2 is as follows: the first mandrel nut 22, the first retaining ring 23, the first pad 24, the first elastic component 25, the first mandrel tube 26, and the first mandrel ball seat 27 form the first movable piston. The first elastic component 25 is installed on the outside of the first mandrel tube 26, and the first pad 24 presses on the first elastic component 25. The first retaining ring 23 and the first mandrel nut 22 are installed sequentially on the upper part of the first mandrel tube 26, and the first retaining ring 23 and the first mandrel ball seat 27 are installed sequentially on the lower part of the first mandrel tube 26. After the first movable piston is installed on the second upper connector 21, the first lower ball seat 28 and the second lower connector 29 are connected sequentially on the lower part of the second upper connector 21. The assembly relationship of the pad-type guide piston 3 is basically the same as that of the pad-type piston 2. Correspondingly, the pad-type guide piston 3 contains a second movable piston.

[0046] The following describes the working process of the lifting rack using a combined piston, which includes an expansion piston 1, a pad-type piston 2, and a pad-type guide piston connected sequentially from top to bottom.

[0047] During the downward movement of the lifting and retrieval pump using a combined piston, there is no liquid column above the expansion piston 1, and the expansion cylinder 13 is in its natural state. There is a gap of 2mm-5mm between the expansion cylinder 13 and the inner wall of the oil pipe. The first pad 24 in the pad-type piston 2 and the second pad 34 in the pad-type guide piston 3 are only in contact with the inner wall of the oil pipe under the force of the spring (first elastic component 25 and second elastic component 35). The elastic coefficient of the spring is 3-5, and the friction is small. The lifting and retrieval pump using a combined piston has low downward resistance and good passability.

[0048] The lifting manifold employs a combined piston system. During its upward movement, a liquid column rises above the expansion piston 1, allowing the viscous liquid to enter the expansion cylinder 13, causing it to expand radially. The expansion cylinder 13 then contacts the inner wall of the oil pipe. The first pad 24 in the pad-type piston 2 and the second pad 34 in the pad-type guide piston 3, under the combined action of spring force and liquid column pressure, maintain contact with the inner wall of the oil pipe, ensuring a tight seal. The expansion cylinder 13 of the expansion piston 1 is an open, thin-walled structure with elasticity and an outer diameter variation range of 4mm-8mm. The first pad 24 of the pad-type piston 2 and the second pad 34 of the pad-type guide piston 3 each have 3-4 segments, each supported by 2 springs, with an outer diameter variation range of 5mm-10mm. Specifically, the outer diameter variation range at the first pad 24 and the second pad 34 is 5mm-10mm.

[0049] When the gas reservoir is activated and the pressure suddenly increases, the sealing ball 14 in the expansion piston 1 is lifted, and the upper and lower pressure relief channels of the expansion piston 1 are opened. That is, the lower part and the upper part of the expansion piston 1 are connected through the interior of the expansion piston 1. The first movable piston of the pad-type piston 2 and the second movable piston of the pad-type guide piston 3 will automatically move upward. The upper and lower pressure relief channels of the first movable piston and the second movable piston are opened, and the upper and lower pressures of the pad-type piston 2 and the pad-type guide piston 3 are relieved, thus preventing the combined piston of the lifting column from being quickly pushed up and causing an accident.

[0050] For ease of understanding and description, this invention uses absolute positional relationships for description. Unless otherwise specified, the directional term "above" indicates... Figure 1 The direction above, the directional word "down" indicates Figure 1 The direction is below the center. This invention is described from the perspective of a reader or user, but the above directional terms should not be understood or interpreted as limiting the scope of protection of this invention.

[0051] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, substitutions of equivalent components, or equivalent changes and modifications made within the scope of protection of this patent, should still fall within the scope of this patent. Furthermore, the technical features, technical solutions, and embodiments of the present invention can be freely combined and used.

Claims

1. A lifting retrieval device employing a combined piston, characterized in that, The lifting rack uses a combination piston, including at least one expansion piston (1), at least one pad piston (2), and one pad guide piston (3). The upper ends of the expansion piston (1), the pad piston (2), and the pad guide piston (3) are all provided with universal joint ball heads, and the lower ends of the expansion piston (1) and the pad piston (2) are all provided with universal joint ball seats. The universal joint ball heads are connected to the universal joint ball seats, and the pad guide piston (3) is located at the lower end of the combination piston in the lifting rack. The expansion piston (1) includes a first upper connector (11), a central tube (12), a conversion short section (15), and a first lower connector (16) connected sequentially from top to bottom. An expansion cylinder (13) is provided on the outer sleeve of the central tube (12). An annular cavity (17) is formed between the expansion cylinder (13) and the central tube (12). The lower end of the expansion cylinder (13) is sealed and fixedly connected to the conversion short section (15) through a connecting short section (18). A sealing ball (14) is provided inside the central tube (12). The sealing ball (14) can be seated and sealed with the conversion short section (15). An annular space (19) is formed between the first large diameter section (113) and the central tube (12). The annular space (19) is connected to the annular cavity (17). An external through hole (114) is provided on the side wall of the first large diameter section (113). The upper end of the expansion cylinder (13) is threaded to the lower end of the first large diameter section (113). The lower end of the expansion cylinder (13) is threaded to the upper end of the conversion short section (15). The expansion cylinder (13) is made of metal. The expansion cylinder (13) can expand radially after being subjected to internal pressure. The pad-type piston (2) includes a second upper connector (21) and a second lower connector (29) connected vertically. The second upper connector (21) is fitted with a first mandrel tube (26). The first mandrel tube (26) is fitted with a first mandrel nut (22), an upper first retaining ring (23), a first pad assembly, a lower first retaining ring (23) and a first mandrel ball seat (27) from top to bottom. The first pad assembly includes a plurality of strip-shaped first pads (24). The first pads (24) extend axially along the second upper connector (21). A first elastic member (25) is provided between the first pads (24) and the first mandrel tube (26). The first pads (24) can move along the diameter direction of the second upper connector (21). The outer surface of the second lower middle diameter section (214) is provided with a plurality of second grooves (2141). The second grooves (2141) extend axially along the second upper connector (21), and the plurality of second grooves (2141) are arranged circumferentially at intervals along the second upper connector (21). The upper part of the first mandrel nut (22) and the upper part of the first mandrel ball seat (27) are connected through the second grooves (2141). The first mandrel nut (22) is threadedly connected to the first mandrel tube (26). The first mandrel nut (22) fixes the upper first retaining ring (23) to the outside of the first mandrel tube (26). The first pad The upper end of the block (24) is located between the upper first retaining ring (23) and the first spindle tube (26). The first spindle ball seat (27) is threadedly connected to the first spindle tube (26). The first spindle ball seat (27) fixes the lower first retaining ring (23) to the outside of the first spindle tube (26). The lower end of the first pad (24) is located between the lower first retaining ring (23) and the first spindle tube (26). The upper first retaining ring (23) and the lower first retaining ring (23) can prevent the first pad (24) from disengaging from the pad-type piston (2). The material of the first pad (24) is metal.

2. The lifting retrieval device according to claim 1 employs a combined piston, characterized in that, The first upper connector (11) includes a first ball head section (111), a first small diameter section (112), and a first large diameter section (113) arranged sequentially from top to bottom. The universal joint ball head at the upper end of the expansion piston (1) is the first ball head section (111). The upper end of the central tube (12) is fitted inside the first large diameter section (113). The central tube (12) is threadedly connected to the first large diameter section (113). The side wall of the central tube (12) is provided with multiple internal through holes (121). The lower end of the central tube (12) is fixedly connected to the conversion short section (15) through the connecting short section (18). The conversion short section (15) is a cylindrical structure. The universal joint ball seat at the lower end of the expansion piston (1) is located at the lower part of the first lower connector (16). The upper end of the first lower connector (16) is threadedly connected to the lower end of the conversion short section (15). The interior of the universal joint ball seat at the lower end of the expansion piston (1) is connected to the interior of the conversion short section (15).

3. The lifting rack according to claim 1 employs a combined piston, characterized in that, The second upper connector (21) includes, from top to bottom, a second ball joint section (211), a second upper intermediate diameter section (212), a second large diameter section (213), a second lower intermediate diameter section (214), and a second small diameter section (215). The universal joint ball head at the upper end of the second pad-type piston (2) is the second ball joint section (211). The first mandrel tube (26) is sleeved outside the second lower intermediate diameter section (214). The second small diameter section (215) is connected to the second lower connector. (29) Threaded connection, the universal joint ball seat at the lower end of the pad-type piston (2) is located at the lower part of the second lower joint (29), and a first lower ball seat (28) is provided between the first spindle ball seat (27) and the second lower joint (29). The first spindle ball seat (27) can abut against the first lower ball seat (28). The first lower ball seat (28) is sleeved outside the second small diameter section (215). The first lower ball seat (28) is threadedly connected to the second small diameter section (215).

4. The lifting rack according to claim 1 employs a combined piston, characterized in that, The pad-type guide piston (3) includes a third upper connector (31) and a third lower connector (39) connected vertically. The third upper connector (31) is fitted with a second mandrel tube (36). The second mandrel tube (36) is fitted with a second mandrel nut (32), an upper second retaining ring (33), a second pad assembly, a lower second retaining ring (33), and a second mandrel ball seat (37) from top to bottom. The second pad assembly includes a plurality of strip-shaped second pads (34). The second pads (34) extend axially along the third upper connector (31). A second elastic member (35) is provided between the second pads (34) and the second mandrel tube (36). The second pads (34) can move along the diameter direction of the third upper connector (31).

5. The lifting rack according to claim 4 employs a combined piston, characterized in that, The third upper connector (31) includes a third ball head section (311), a third upper middle diameter section (312), a third large diameter section (313), a third lower middle diameter section (314), and a third small diameter section (315) arranged sequentially from top to bottom. The universal joint ball head at the upper end of the pad-type guide piston (3) is the third ball head section (311). The second spindle tube (36) is sleeved outside the third lower middle diameter section (314). The third small diameter section (315) is threadedly connected to the third lower connector (39). The lower end of the third lower connector (39) is a tapered structure with the top facing down. A second lower ball seat (38) is provided between the second spindle ball seat (37) and the third lower connector (39). The second spindle ball seat (37) can abut against the second lower ball seat (38). The second lower ball seat (38) is sleeved outside the third small diameter section (315). The second lower ball seat (38) is threadedly connected to the second small diameter section (215).

6. The lifting rack according to claim 4 employs a combined piston, characterized in that, The outer surface of the third lower middle diameter section (314) is provided with multiple third grooves (3141). The third grooves (3141) extend axially along the third upper connector (31), and the multiple third grooves (3141) are arranged circumferentially at intervals along the third upper connector (31). The upper part of the second mandrel nut (32) and the upper part of the second mandrel ball seat (37) are connected through the third grooves (3141). The second mandrel nut (32) is threadedly connected to the second mandrel tube (36). The second mandrel nut (32) fixes the upper second retaining ring (33) to the outside of the second mandrel tube (36). The second pad block The upper end of (34) is located between the upper second retaining ring (33) and the second mandrel tube (36). The second mandrel ball seat (37) is threadedly connected to the second mandrel tube (36). The second mandrel ball seat (37) fixes the lower second retaining ring (33) to the outside of the second mandrel tube (36). The lower end of the second pad (34) is located between the lower second retaining ring (33) and the second mandrel tube (36). The upper second retaining ring (33) and the lower second retaining ring (33) can prevent the second pad (34) from disengaging from the pad-type guide piston (3). The material of the second pad (34) is metal.

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