Hydraulic composite axial shock absorber for well

Abstract

The utility model relates to a hydraulic composite axial shock absorber for a well, which is used for reducing vibration and pressurizing in underground operation and comprises an outer cylinder, the upper end of the outer cylinder is fixedly connected with an upper joint, and the lower end of the outer cylinder is internally and fixedly connected with a limiting base plate; an inner cylinder fixedly connected with the upper connector is installed in the outer cylinder, a first through hole, a second through hole and a third through hole which are communicated with one another are sequentially formed in the inner cylinder from top to bottom, and a spring damper is arranged between the first through hole and the second through hole. A pressure cylinder and a buffering cushion block are sequentially arranged between the limiting cushion plate and the inner barrel from top to bottom, a first piston and a second piston are sequentially arranged in the pressure cylinder from top to bottom, and a plurality of vibration reduction rods are arranged on the side, facing the buffering cushion block, of the second piston. The damping device is simple in structure and reliable in operation, the synergistic effect of multi-section pressure is achieved through circulation of drilling fluid, effective damping can be achieved in underground operation, the required pressurizing effect can be provided, and an efficient and reliable damping device is provided for underground industrial application.

Description

Technical Field

[0001] The utility model relates to a vibration damper for a well, in particular to a hydraulic composite axial vibration damper for a well, belonging to the technical field of drilling equipment. Background Art

[0002] During geothermal exploration and drilling, the vibration problem of the device is mainly caused by the vibration between the drill collar and the formation during the drilling process. Due to the influence of the power of the drilling operation and the characteristics of the formation, traditional drilling operations are facing increasingly severe challenges. In drilling operations, when the drilling parameters are improper, the drill bit is unevenly worn, or encounters hard rock formations, fault zones, or rock interfaces of different hardness, the drill tool may produce sudden torque changes and shocks when passing through these formations, causing vibrations. These vibrations are one of the main causes of problems such as drill pipe wear, drill bit damage, and wellbore instability, which not only reduces drilling efficiency, but also increases operational risks and costs. Therefore, it is of great theoretical significance and practical value to develop a new type of hydraulic composite axial shock absorber that can effectively reduce vibration and shock and improve the stability and safety of drilling operations.

[0003] At present, some vibration reduction devices and methods have been proposed to solve the problems of vibration and impact, such as spring shock absorbers, hydraulic shock absorbers, etc. However, these traditional vibration reduction devices often fail to achieve the desired effect under complex geological conditions. Existing downhole shock absorbers usually use simple mechanical damping or a single hydraulic damping mechanism. These devices are less efficient in dealing with high-frequency and large-amplitude vibrations. Especially in deep well drilling, the complexity of the formation and the high-speed operation of the drilling equipment require the shock absorber to have a higher response speed and adjustment ability. In addition, most of the existing downhole shock absorbers lack an effective pressure regulation mechanism. Under different drilling conditions, the same shock absorber often fails to adapt to the changing working conditions, affecting drilling efficiency and safety.

[0004] Therefore, there is an urgent need to propose a hydraulic composite axial vibration damper for wells with simple structure, convenient operation and significant vibration reduction effect to meet the needs of drilling operations under different conditions. Utility Model Content

[0005] The utility model is mainly aimed at the above-mentioned problems existing in the prior art, and provides a hydraulic composite axial vibration damper for wells. The hydraulic composite axial vibration damper for wells has good vibration damping ability and good sealing, can adapt to harsh underground environments, and has a pressurization function at the same time.

[0006] The purpose of this utility model is mainly achieved through the following solutions:

[0007] A hydraulic composite axial vibration damper for wells comprises an outer cylinder, wherein an upper joint is fixedly connected to the upper end of the outer cylinder, and a limiting pad is fixedly connected to the lower end of the outer cylinder; an inner cylinder fixedly connected to the upper joint is installed in the outer cylinder, and a first through hole, a second through hole and a third through hole are sequentially provided in the inner cylinder from top to bottom, which are interconnected, and a spring damper is provided between the first through hole and the second through hole; a boosting cylinder and a buffer pad are sequentially provided between the limiting pad and the inner cylinder from top to bottom, and a first piston and a second piston are sequentially provided in the boosting cylinder from top to bottom, and a plurality of vibration damping rods are provided on the side of the second piston facing the buffer pad.

[0008] Preferably, the outer wall of the lower end of the upper joint is provided with a first external thread, the inner wall of the upper end of the outer tube is provided with a first internal thread, the upper joint and the outer tube are connected via the first external thread and the first internal thread, the inner wall of the lower end of the upper joint is provided with a second internal thread, the outer wall of the upper end of the inner tube is provided with a second external thread, and the upper joint and the inner tube are connected via the second internal thread and the second external thread.

[0009] Preferably, at least one group of the first through hole, the second through hole and the third through hole is provided, and the diameter of the second through hole is larger than the diameter of the first through hole, and the diameter of the first through hole is larger than the diameter of the third through hole.

[0010] Preferably, the spring damper comprises a telescopic spring and a damping block, the lower end of the telescopic spring is fixedly connected to the lower part of the second through hole, the upper end of the telescopic spring is fixedly connected to the damping block, and the damping block is slidably connected to the first through hole, and the damping block is penetrated by a fourth through hole for circulation of drilling fluid.

[0011] Preferably, an inner joint is installed at the connection between the inner tube and the boost cylinder, the outer wall of the inner joint is provided with a plurality of first limit grooves along a uniform circumference of its axis, the inner wall of the inner joint is provided with a plurality of third limit blocks along a uniform circumference of its axis, the outer wall of the inner tube is provided with a plurality of second limit grooves along a uniform circumference of its axis, the inner wall of the outer tube is provided with a plurality of second limit blocks corresponding to the second limit grooves and a first limit block corresponding to the first limit grooves along a uniform circumference of its axis, and the upper end outer wall of the boost cylinder is provided with a plurality of third limit grooves corresponding to the third limit blocks along a uniform circumference of its axis.

[0012] Preferably, the boost cylinder is provided with a first sliding chamber, a second sliding chamber and a third sliding chamber in sequence from top to bottom, and the diameters of the first sliding chamber and the third sliding chamber are both larger than the diameter of the second sliding chamber.

[0013] Preferably, the upper outer wall and the lower outer wall of the first piston are respectively provided with a first sliding block and a second sliding block, the first sliding block is slidably connected to the first sliding cavity, and the second sliding block is slidably connected to the second sliding cavity, the upper outer wall and the lower outer wall of the second piston are respectively provided with a third sliding block and a fourth sliding block, the third sliding block is slidably connected to the second sliding cavity, and the fourth sliding block is slidably connected to the third sliding cavity, and a fifth through hole is provided in the middle of the first piston, and at least one sixth through hole is penetrated from top to bottom of the part of the third sliding block protruding from the second piston body, and a plurality of seventh through holes are uniformly circumferentially provided on the lower outer wall of the booster cylinder along its axis.

[0014] Preferably, the inner wall of the lower end of the outer cylinder is provided with a plurality of limiting bosses evenly circumferentially along its axis, and the limiting pad is fixedly connected to the limiting bosses.

[0015] Preferably, the lower end of the buffer block is in a truncated cone structure, and the diameter of the lower end is smaller than the diameter of the upper end.

[0016] Preferably, an eighth through hole is provided in the middle of the limiting pad, the buffer pad block is inserted into the eighth through hole from top to bottom, and the diameter of the eighth through hole is larger than the diameter of the lower end of the buffer pad block and smaller than the diameter of the upper end of the buffer pad block, and a plurality of ninth through holes for drilling fluid to pass through are provided at the edge of the limiting pad in a uniform circle along its axis.

[0017] Therefore, compared with the prior art, the utility model has the following advantages:

[0018] (1) The utility model ensures that the drilling fluid can flow continuously by arranging the first through hole, the second through hole and the third through hole inside the inner tube, which not only reduces the liquid resistance, but also maintains the stability of the pressure and flow rate, further enhancing the pressurization effect;

[0019] (2) The utility model adopts a spring damping and multi-stage piston design, which can not only absorb and reduce the vibration generated during the drilling process, but also increase the pressure through changes in liquid pressure. This combined effect makes the vibration reduction effect more significant, while ensuring the drilling efficiency and the service life of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of the utility model;

[0021] Figure 2 It is a cross-sectional view of the utility model;

[0022] Figure 3 It is an exploded schematic diagram of the utility model;

[0023] Figure 4 It is a schematic diagram of the connection between the inner tube, the booster cylinder and the inner joint in the utility model;

[0024] Figure 5 It is a structural schematic diagram of the spring damper in the utility model;

[0025] Figure 6 It is a structural schematic diagram of the second piston in the utility model;

[0026] Figure 7 It is a schematic diagram of the connection between the limit pad and the outer cylinder in the utility model.

[0027] Illustration: 1-outer cylinder, 2-upper joint, 3-limiting pad, 4-inner cylinder, 5-first through hole, 6-second through hole, 7-third through hole, 8-boosting cylinder, 9-buffer pad, 10-first piston, 11-second piston, 12-damping rod, 13-telescopic spring, 14-damping block, 15-fourth through hole, 16-inner joint, 17-first limiting groove, 18-third limiting block, 19-second limiting groove, 20-second limiting block, 21-first limiting block, 22-third limiting groove, 23-first sliding chamber, 24-second sliding chamber, 25-third sliding chamber, 26-first sliding block, 27-second sliding block, 28-third sliding block, 29-fourth sliding block, 30-fifth through hole, 31-sixth through hole, 32-seventh through hole, 33-limiting boss, 34-eighth through hole, 35-ninth through hole. DETAILED DESCRIPTION

[0028] The technical solution of the utility model is further described in detail below through specific embodiments and in combination with the accompanying drawings. It should be understood that the implementation of the utility model is not limited to the following embodiments, and any form of modification and / or change made to the utility model will fall within the protection scope of the utility model.

[0029] In the present invention, unless otherwise specified, all parts and percentages are weight units, and the equipment and raw materials used can be purchased from the market or are commonly used in the field. The methods in the following embodiments, unless otherwise specified, are conventional methods in the field. The components or equipment in the following embodiments, unless otherwise specified, are universal standard parts or components known to those skilled in the art, and their structures and principles are known to those skilled in the art through technical manuals or conventional experimental methods.

[0030] Embodiment 1:

[0031] like Figure 1 , 2As shown in Figure 3, the utility model provides a technical solution, a hydraulic composite axial vibration damper for wells, comprising an outer cylinder 1 which is hollow inside and opened at both ends, the interior of the outer cylinder 1 is a drilling fluid channel, the upper end of the outer cylinder 1 is fixedly connected to an upper joint 2, and the lower end of the outer cylinder 1 is fixedly connected to a limiting pad 3; an inner cylinder 4 fixedly connected to the upper joint 2 is installed in the outer cylinder 1, and a first through hole 5, a second through hole 6 and a third through hole 7 which are interconnected are arranged in sequence from top to bottom in the inner cylinder 4, and a spring damper is arranged between the first through hole 5 and the second through hole 6, and the drilling fluid is damped by the spring damper in the drilling fluid channel, and the flow rate is slowed down; between the limiting pad 3 and the inner cylinder 4 A booster cylinder 8 and a buffer block 9 are provided from top to bottom, a first piston 10 and a second piston 11 are provided in the booster cylinder 8 from top to bottom, and a plurality of damping rods 12 are provided on the side of the second piston 11 facing the buffer block 9, a plug-in groove is provided on the lower end face of the second piston 11, and the upper end of the damping rod 12 is fixedly inserted in the plug-in groove, and the buffer block 9 will contact with the measuring device below, and the measuring device is fixedly connected to the lower end of the outer tube 1, and the measuring device includes a downhole measuring short circuit, and the push of the drilling fluid and the piston makes the damping rod 12 abut against the upper surface of the buffer block 9 to resist the axial vibration force extending from the measuring device below and the drill bit, so as to achieve the effect of boosting and damping.

[0032] Embodiment 2:

[0033] like Figure 1 , 2 As shown in Figure 3, the utility model provides another technical solution, a hydraulic composite axial vibration damper for wells, which is different from Example 1 in that the lower end outer wall of the upper joint 2 is provided with a first external thread, the upper end inner wall of the outer tube 1 is provided with a first internal thread, the upper joint 2 and the outer tube 1 are threadedly connected by the first external thread and the first internal thread to form an integral structure, the lower end inner wall of the upper joint 2 is provided with a second internal thread, the upper end outer wall of the inner tube 4 is provided with a second external thread, the upper joint 2 and the inner tube 4 are threadedly connected by the second internal thread and the second external thread to achieve fixed installation of the inner tube 4 and ensure stable circulation of the drilling fluid.

[0034] Embodiment 3:

[0035] like Figure 2 , 5 As shown, the utility model provides another technical solution, a hydraulic composite axial vibration damper for wells, which is different from Example 1 in that the first through hole 5, the second through hole 6 and the third through hole 7 are provided with at least one group, and in this embodiment, the first through hole 5, the second through hole 6 and the third through hole 7 are provided with two groups, and the diameter of the second through hole 6 is greater than the diameter of the first through hole 5, and the diameter of the first through hole 5 is greater than the diameter of the third through hole 7.

[0036] Specifically, the spring damper is composed of a telescopic spring 13 and a vibration-damping block 14. The lower end of the telescopic spring 13 is fixedly connected to the lower part of the second through hole 6, the upper end of the telescopic spring 13 is fixedly connected to the vibration-damping block 14, and the vibration-damping block 14 is slidably connected to the first through hole 5. The vibration-damping block 14 is penetrated by a fourth through hole 15 for the circulation of drilling fluid. In this embodiment, each vibration-damping block 14 is provided with two fourth through holes 15; the telescopic spring 13 is made of stainless steel material, and the vibration-damping block 14 is made of rubber material, which is used to achieve a damping effect on the flow of drilling fluid, thereby reducing impact.

[0037] The drilling fluid enters the inner tube 4 from the drilling fluid channel, flows through the first through hole 5, the second through hole 6 and the third through hole 7 with smaller inner diameters in turn, and finally flows into the larger channel in the booster cylinder 8 after the flow rate is slowed down by the spring damper; the setting of the first through hole 5, the second through hole 6 and the third through hole 7 effectively avoids excessive liquid pressure and ensures stable operation of the system.

[0038] Embodiment 4:

[0039] like Figure 2 , 3 As shown in Figure 4, the utility model provides another technical solution, a hydraulic composite axial shock absorber for wells, which is different from the embodiment 1 in that an inner joint 16 is installed at the connection between the inner cylinder 4 and the booster cylinder 8, and the outer wall of the inner joint 16 is provided with a plurality of first limiting grooves 17 along the uniform circumference of its axis, and the inner wall of the inner joint 16 is provided with a plurality of third limiting blocks 18 along the uniform circumference of its axis, and the outer wall of the inner cylinder 4 is provided with a plurality of second limiting grooves 19 along the uniform circumference of its axis, and the inner wall of the outer cylinder 1 is provided with a plurality of second limiting blocks 20 corresponding to the second limiting grooves 19 and corresponding to the first limiting grooves along the uniform circumference of its axis. The first limit block 21 corresponds to the groove 17, and the upper outer wall of the booster cylinder 8 is evenly circumferentially provided with multiple third limit grooves 22 corresponding to the third limit block 18 along its axis. In this embodiment, the first limit groove 17, the first limit block 21, the second limit groove 19, the second limit block 20, the third limit groove 22 and the third limit block 18 are evenly provided with four groups along their axes. On the one hand, it can realize the accurate positioning and installation between the inner cylinder 4, the booster cylinder 8 and the outer cylinder 1, and on the other hand, it can avoid the shaking or rotation of the inner cylinder 4 and the booster cylinder 8 during use, and has good stability and sealing.

[0040] Embodiment 5:

[0041] like Figure 2 , 3 As shown, the utility model provides another technical solution, a hydraulic composite axial shock absorber for wells, which is different from Example 1 in that a first sliding chamber 23, a second sliding chamber 24 and a third sliding chamber 25 are sequentially connected inside the booster cylinder 8 from top to bottom, and the diameters of the first sliding chamber 23 and the third sliding chamber 25 are both larger than the diameter of the second sliding chamber 24.

[0042] Specifically, the upper outer wall and the lower outer wall of the first piston 10 are respectively integrally provided with a first sliding block 26 and a second sliding block 27, the first sliding block 26 is slidably connected in the first sliding cavity 23, and the second sliding block 27 is slidably connected in the second sliding cavity 24, the upper outer wall and the lower outer wall of the second piston 11 are respectively integrally provided with a third sliding block 28 and a fourth sliding block 29, the third sliding block 28 is slidably connected in the second sliding cavity 24, and the fourth sliding block 29 is slidably connected in the third sliding cavity 25, and there is a gap between the fourth sliding block 29 and the third sliding cavity 25 for the drilling fluid to pass through, and a fifth through hole 30 is provided in the middle of the first piston 10, as shown in FIG. Figure 6 As shown, the part of the third sliding block 28 protruding from the main body of the second piston 11 is penetrated by at least one sixth through hole 31 from top to bottom, and two sixth through holes 31 are provided in this embodiment. The outer wall of the lower end of the boosting cylinder 8 is evenly circumferentially provided with multiple seventh through holes 32 along its axis, and four seventh through holes 32 are provided in this embodiment.

[0043] Specifically, the drilling fluid pushes the first piston 10 to move, and part of the drilling fluid flows into the second sliding chamber 24 through the fifth through hole 30; the drilling fluid and the first piston 10 push the second piston 11 and the damping rod 12, and the vibration and impact are reduced by the movement and adjustment of the damping rod 12; the first piston 10 and the second piston 11 are both made of aluminum alloy material, and the first piston 10 has a stroke in the booster cylinder 8. By using the hydraulic principle, the pressure generated by the drilling fluid pushes the first piston 10, and together with the first piston 10, pushes the second piston 11 in the booster cylinder 8, generating a third section of high pressure to push the damping rod 12, and finally resisting the buffer pad 9, thereby achieving a vibration reduction and pressurization effect, thereby improving the stability and safety of the operation.

[0044] Embodiment 6:

[0045] like Figure 2 , 7 As shown, the utility model provides another technical solution, a hydraulic composite axial shock absorber for wells, which is different from Example 1 in that the inner wall of the lower end of the outer cylinder 1 is provided with four limiting bosses 33 evenly circumferentially along its axis, and the limiting pad 3 is fixedly connected to the limiting boss 33 by bolts.

[0046] Specifically, the lower end of the buffer block 9 is in a truncated cone structure, and the diameter of the lower end is smaller than the diameter of the upper end.

[0047] Specifically, an eighth through hole 34 is provided in the middle of the limiting pad 3, and the buffer pad block 9 is inserted into the eighth through hole 34 from top to bottom. The diameter of the eighth through hole 34 is larger than the diameter of the lower end of the buffer pad block 9 and smaller than the diameter of the upper end of the buffer pad block 9. A plurality of ninth through holes 35 for drilling fluid to pass through are uniformly provided at the edge of the limiting pad 3 along its axis. In this embodiment, the buffer pad block 9 is made of rubber material.

[0048] The utility model provides a hydraulic composite axial vibration damper for wells. By arranging a first through hole, a second through hole and a third through hole inside an inner cylinder, the drilling fluid can be ensured to flow continuously, which not only reduces the liquid resistance, but also maintains the stability of pressure and flow rate, and further enhances the pressurization effect. The design of spring damping and multi-stage piston can not only absorb and reduce the vibration generated during the drilling process, but also increase the pressure through the change of liquid pressure. This composite effect makes the vibration reduction effect more significant, while ensuring the drilling efficiency and the service life of the equipment, and can adapt to drilling operation environments with different specifications and requirements.

[0049] It should be understood that this embodiment is only used to illustrate the present invention and is not used to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A hydraulic composite axial vibration damper for wells, characterized in that: The invention comprises an outer cylinder (1), the upper end of the outer cylinder (1) is fixedly connected to an upper joint (2), and the lower end of the outer cylinder (1) is fixedly connected to a limiting pad (3); an inner cylinder (4) fixedly connected to the upper joint (2) is installed in the outer cylinder (1), a first through hole (5), a second through hole (6) and a third through hole (7) which are interconnected are arranged in sequence from top to bottom in the inner cylinder (4), and a spring damper is arranged between the first through hole (5) and the second through hole (6); a booster cylinder (8) and a buffer pad (9) are arranged in sequence from top to bottom between the limiting pad (3) and the inner cylinder (4), a first piston (10) and a second piston (11) are arranged in sequence from top to bottom in the booster cylinder (8), and a plurality of damping rods (12) are arranged on the side of the second piston (11) facing the buffer pad (9).

2. A hydraulic composite axial vibration damper for wells according to claim 1, characterized in that: The lower end outer wall of the upper joint (2) is provided with a first external thread, the upper end inner wall of the outer tube (1) is provided with a first internal thread, the upper joint (2) and the outer tube (1) are connected via the first external thread and the first internal thread, the lower end inner wall of the upper joint (2) is provided with a second internal thread, the upper end outer wall of the inner tube (4) is provided with a second external thread, and the upper joint (2) and the inner tube (4) are connected via the second internal thread and the second external thread.

3. A hydraulic composite axial vibration damper for wells according to claim 1, characterized in that: At least one group of the first through hole (5), the second through hole (6) and the third through hole (7) is provided, and the diameter of the second through hole (6) is greater than the diameter of the first through hole (5), and the diameter of the first through hole (5) is greater than the diameter of the third through hole (7).

4. A hydraulic composite axial vibration damper for wells according to claim 3, characterized in that: The spring damper comprises a telescopic spring (13) and a vibration-damping block (14); the lower end of the telescopic spring (13) is fixedly connected to the lower part of the second through hole (6); the upper end of the telescopic spring (13) is fixedly connected to the vibration-damping block (14); the vibration-damping block (14) is slidably connected to the inside of the first through hole (5); and a fourth through hole (15) is penetrated through the vibration-damping block (14) for the circulation of drilling fluid.

5. The hydraulic composite axial vibration damper for wells according to claim 1, characterized in that: An inner joint (16) is installed at the connection between the inner cylinder (4) and the boost cylinder (8); the outer wall of the inner joint (16) is provided with a plurality of first limiting grooves (17) along a uniform circumference of its axis; the inner wall of the inner joint (16) is provided with a plurality of third limiting blocks (18) along a uniform circumference of its axis; the outer wall of the inner cylinder (4) is provided with a plurality of second limiting grooves (19) along a uniform circumference of its axis; the inner wall of the outer cylinder (1) is provided with a plurality of second limiting blocks (20) corresponding to the second limiting grooves (19) and a first limiting block (21) corresponding to the first limiting grooves (17) along a uniform circumference of its axis; and the upper outer wall of the boost cylinder (8) is provided with a plurality of third limiting grooves (22) corresponding to the third limiting blocks (18) along a uniform circumference of its axis.

6. The hydraulic composite axial vibration damper for wells according to claim 1, characterized in that: The booster cylinder (8) is provided with a first sliding chamber (23), a second sliding chamber (24) and a third sliding chamber (25) which are connected in sequence from top to bottom, and the diameters of the first sliding chamber (23) and the third sliding chamber (25) are both larger than the diameter of the second sliding chamber (24).

7. A hydraulic composite axial vibration damper for wells according to claim 6, characterized in that: A first sliding block (26) and a second sliding block (27) are respectively provided on the upper outer wall and the lower outer wall of the first piston (10), the first sliding block (26) being slidably connected to the first sliding chamber (23), and the second sliding block (27) being slidably connected to the second sliding chamber (24); a third sliding block (28) and a fourth sliding block (29) are respectively provided on the upper outer wall and the lower outer wall of the second piston (11), the third sliding block (28) being slidably connected to the second sliding chamber (24), and the fourth sliding block (29) being slidably connected to the third sliding chamber (25); a fifth through hole (30) is provided in the middle of the first piston (10), and at least one sixth through hole (31) is provided through the part of the third sliding block (28) protruding from the body of the second piston (11) from top to bottom; and a plurality of seventh through holes (32) are uniformly provided on the lower outer wall of the booster cylinder (8) along the axis thereof.

8. The hydraulic composite axial vibration damper for wells according to claim 1, characterized in that: The inner wall of the lower end of the outer cylinder (1) is provided with a plurality of limiting bosses (33) evenly spaced along the circumference of its axis, and the limiting pad (3) is fixedly connected to the limiting bosses (33).

9. A hydraulic composite axial vibration damper for wells according to claim 8, characterized in that: The lower end of the buffer pad (9) is in a truncated cone-shaped structure, and the diameter of the lower end is smaller than the diameter of the upper end.

10. A hydraulic composite axial vibration damper for wells according to claim 9, characterized in that: An eighth through hole (34) is provided in the middle of the limiting pad (3), the buffer pad (9) is inserted into the eighth through hole (34) from top to bottom, and the diameter of the eighth through hole (34) is larger than the diameter of the lower end of the buffer pad (9) and smaller than the diameter of the upper end of the buffer pad (9), and a plurality of ninth through holes (35) for drilling fluid to pass through are uniformly provided at the edge of the limiting pad (3) along the circumference of its axis.

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