A cementing anti-backoff device and anti-backoff method

Abstract

The application discloses a cementing anti-reversing device and an anti-reversing method, relates to the technical field of downhole tools for cementing in oil and gas fields, and aims to solve the problem of cement slurry backflow caused by the failure of the anti-reversing device under high-pressure reverse impact. The device comprises a shell body, a pressure-encountering seat and a pressure-encountering head. The pressure-encountering seat is fixed in the shell body and is provided with a channel and a first locking member; the pressure-encountering head is arranged in the shell body and is provided with a circulating hole communicating with a central through hole and a second locking member matched with the first locking member, and a guide matching structure is arranged between the pressure-encountering head and the shell body. When the pressure-encountering head is pushed to move downward, the guide matching structure generates circumferential rotation, the circulating hole is blocked by the pressure-encountering seat, and the second locking member is rotated into the first locking member to form mechanical locking. The application realizes anti-retraction self-locking by using a rigid structure, and improves the cementing quality and safety.

Description

Technical Field

[0001] This invention belongs to the technical field of cementing downhole tools in oil and gas fields, specifically relating to a cementing anti-backflow device and method. Background Technology

[0002] In oil and gas well cementing operations, during the setting phase after cementing, it is crucial to ensure the cement slurry stably settles and solidifies within the annulus. However, after cementing is completed and the pump pressure is removed, the annular pressure at the bottom of the well often exceeds the pressure inside the casing, easily inducing cement slurry backflow into the casing. This backflow not only forms a hard cement plug at the bottom of the casing that is difficult to drill out, making subsequent plugging difficult, but more seriously, it directly causes the annular cement surface to fall back, resulting in sealing quality defects in the lower critical well sections, severely impacting subsequent reservoir stimulation and oil and gas production. Therefore, configuring a highly reliable anti-backflow device in the casing string is a core technical means to ensure cementing quality and avoid engineering accidents.

[0003] Currently, Chinese patent application CN105257243A discloses a shut-in sleeve device for cementing pressure testing. This device uses a valve sleeve within the casing, and a self-locking ring and a backlash groove are installed on the upper part of the shut-in sleeve and valve sleeve. After pressure testing, the shut-in sleeve moves downwards, and the self-locking ring expands and engages in the backlash groove, thus restricting the retraction of the shut-in sleeve and achieving channel closure and anti-backflow prevention. However, this prior art still has significant drawbacks in practical applications. Its locking function highly depends on the elastic deformation of the self-locking ring. After cementing pressure testing closes the bottom hole channel, if pressure fluctuations or high-pressure reverse impacts occur downhole, the self-locking ring, subjected to long-term high-pressure pushing, is prone to plastic expansion or deformation, causing it to slip out of the backlash groove. Once the self-locking ring fails, the shut-in sleeve loses its restraint and is pushed back to its original position by the upward push of the high-pressure fluid inside the casing, causing the previously covered circulation hole to reopen, and cement slurry to instantly flow back into the casing, completely destroying the anti-backflow function. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies that rely on elastic self-locking rings for locking and are susceptible to impact failure, leading to backflow prevention failure, and to provide a cementing backflow prevention device and method.

[0005] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution: According to a first aspect of the present invention, a cementing anti-reverse device is provided, comprising: Outer shell; The pressure seat is fixed inside the outer casing and has a channel for fluid to pass through and a first locking element; The pressure head is disposed inside the housing body and above the pressure seat. It has a central through hole for fluid to pass through and a circulation hole communicating with the central through hole. The pressure head is also provided with a second locking member suitable for cooperating with the first locking member. A guide engagement structure is provided between the pressure head and the housing body, so that the pressure head has a degree of freedom of movement to move downward and rotate circumferentially. In the initial state, the pressing head is fixed relative to the outer shell body, the circulation hole is connected to the channel, and the first locking member and the second locking member are staggered in the circumferential direction; In the locked state, the pressing head is pushed downward and rotates circumferentially by the guide and mating structure, causing the circulation hole to be blocked and closed by the pressing seat. At the same time, the second locking member is screwed into the first locking member to form a mechanical lock.

[0006] In one possible implementation of the first aspect, the pressing head is a hollow sleeve structure composed of a first large-diameter section and a first small-diameter section coaxially connected; The impact seat is composed of a second large diameter section and a second small diameter section coaxially connected; The guiding and mating structure includes a guide member disposed on the outer peripheral wall of the first large-diameter section, and a guide groove formed on the inner wall of the outer shell body and mating with the guide member. The guide groove includes a longitudinal guide section extending axially, a transverse guide section extending circumferentially, and an obtuse-angle transition section connecting the longitudinal guide section and the transverse guide section. The circulation hole and the second locking member are both located on the outer peripheral wall of the first small diameter section; the channel and the first locking member are both located on the second large diameter section; In the locked state, the first small diameter segment is sleeved outside the second small diameter segment, and the circulation hole moves to the outer peripheral wall of the second small diameter segment and is completely blocked by the second small diameter segment.

[0007] In one possible implementation of the first aspect, an installation groove is provided on the outer peripheral wall of the first large-diameter section, and the guide is a guide ball that is embedded in the installation groove and partially protrudes from the outer peripheral wall of the first large-diameter section.

[0008] In one possible implementation of the first aspect, an annular groove is provided on the upper end face of the second large diameter segment, the channel is located at the bottom of the annular groove and extends through the second large diameter segment, and the first locking member is located in the annular groove.

[0009] In one possible implementation of the first aspect, a raised limiting step is provided in the lower part of the inner wall of the outer shell body; In the locked state, the lower end face of the first large-diameter section is attached to the limiting step, thereby limiting the axial position of the pressing head downward.

[0010] In one possible implementation of the first aspect, a second sealing ring receiving groove is provided on the inner wall of the first small diameter segment near the lower end, and a third sealing ring receiving groove is provided on the outer peripheral wall of the second small diameter segment near the upper end; a sealing ring is provided in the second sealing ring receiving groove and the third sealing ring receiving groove respectively; In the locked state, the inner wall of the first small diameter segment and the outer peripheral wall of the second small diameter segment form a radial seal through the sealing ring.

[0011] In one possible implementation of the first aspect, a first sealing ring receiving groove is provided on the outer peripheral wall of the first large-diameter section, a sealing ring is provided in the first sealing ring receiving groove, and the sealing ring in the first sealing ring receiving groove forms a sealing fit with the inner wall of the outer shell body.

[0012] In one possible implementation of the first aspect, the number of guide grooves is multiple and they are evenly distributed along the circumference of the outer shell body; the turning angle of the guide groove transitioning from the longitudinal guide section to the transverse guide section is 95° to 105°. The first locking element is a hook-shaped locking block with a bayonet, and there are multiple of them. The cross-section is shaped like the number 7, and they are evenly distributed along the circumference of the pressing seat. The second locking element is a locking protrusion, the number of which corresponds one-to-one with the number of the hook-shaped locking blocks, and they are evenly distributed along the circumference of the pressing head.

[0013] In one possible implementation of the first aspect, the outer shell body is provided with a plurality of outer shell pin holes evenly distributed in the circumferential direction near the upper end, and the outer peripheral wall of the pressing head is provided with pressing head pin holes corresponding to the outer shell pin holes. In the initial state, the pressing head is fixed inside the housing body by passing through the housing pin hole and inserting into the pressing head pin hole via a shear pin.

[0014] According to a second aspect of the present invention, a cementing anti-backflow method is provided, using the aforementioned cementing anti-backflow device, the method comprising: Under the action of thrust, the impact head is released from its relatively fixed state and moves downward along the axial direction; The guiding and engaging structure forces the impact head to rotate circumferentially while it continues to descend. As the pressing head rotates, the second locking member rotates synchronously and slides into the first locking member to form a mechanical lock; in this state, the circulation hole on the pressing head is blocked and closed by the pressing seat, the circulation hole is disconnected from the channel, and the fluid channel is cut off.

[0015] Compared with the prior art, the present invention has at least the following beneficial effects: Existing shut-in sliding sleeve devices rely heavily on the elastic deformation of the self-locking ring. After cementing and pump pressure is removed, if the device encounters a reverse impact from the bottom of the well due to high pressure, the elastic self-locking ring is prone to plastic expansion deformation and slips out of the anti-reverse groove. This causes the shut-in sliding sleeve to be pressed back to its original position, the circulation hole to be reopened, and consequently, the anti-backflow function is completely lost and cement slurry backflow occurs. The cementing anti-backflow device provided by this invention provides a guiding fit structure between the pressure head and the outer shell body, which allows the pressure head to rotate circumferentially when it is pushed downward by the guiding fit structure. Based on this composite motion trajectory, the second locking member on the pressure head can slide into the first locking member fixed on the pressure seat at the lower end of the inner cavity under the guidance of the circumferential rotation, so that the circulation hole is completely blocked and closed by the pressure seat and forms a rigid mechanical lock. When high-pressure reverse fluid thrust is generated at the bottom of the well, this reverse thrust is directly converted into rigid physical bearing between the first and second locking elements. If the pressure head is to retract upwards, it must follow the guide structure to complete the reverse rotation. Without the application of a specific external rotational torque, the pressure head cannot generate spontaneous reverse rotation. This eliminates the hidden danger of locking failure due to pressure fluctuations or reverse pushing from a physical and mechanical structure perspective, ensuring reliable cut-off of the casing channel, ensuring the stability of the annular cement surface and preventing it from falling back, effectively preventing backflow of cement slurry, improving the sealing quality of key well sections, and making the entire cementing project reliable and safe. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings used in the description of the specific embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the cementing anti-backflow device provided in the embodiment of the present invention in its initial state before impact, wherein (a) is a partial sectional view and (b) is a three-dimensional view of the impact head and impact seat in action; Figure 2 This is a schematic diagram of the state of the cementing anti-backflow device provided in the embodiment of the present invention during the impact pressure process, wherein (a) is a partial cross-sectional view and (b) is a three-dimensional view of the impact pressure head and the impact pressure seat in action; Figure 3This is a schematic diagram of the locking state of the cementing anti-backflow device provided in the embodiment of the present invention after the impact pressure is completed, wherein (a) is a partial cross-sectional view and (b) is a three-dimensional view of the impact pressure head and the impact pressure seat in cooperation; Figure 4 A longitudinal half-sectional view of the cementing anti-backflow device provided in an embodiment of the present invention before impact (showing the cementing plug). Figure 5 A longitudinal half-sectional view of the cementing anti-backflow device provided in this embodiment of the invention after the impact pressure is completed (showing the cementing plug). Figure 6 A longitudinal half-sectional view of the outer casing of the cementing anti-reverse device provided in an embodiment of the present invention; Figure 7 This is a schematic diagram of the impact head of the cementing anti-backflow device provided in an embodiment of the present invention, wherein (a) is a longitudinal half-sectional view and (b) is a three-dimensional view; Figure 8 The diagram shows the structure of the impact seat of the cementing anti-backflow device provided in the embodiment of the present invention, wherein (a) is a longitudinal half-sectional view and (b) is a three-dimensional view.

[0018] In the diagram: 1. Cementing plug; 10. Outer shell body; 11. Guide groove; 12. Outer shell pin hole; 13. Limiting step; 20. Press head; 20a. First large diameter section; 20b. First small diameter section; 21. Shear pin; 22. Mounting groove; 23. Circulation hole; 24. Second locking element; 25. Press head pin hole; 26. First sealing ring receiving groove; 27. Second sealing ring receiving groove; 30. Press seat; 30a. Second large diameter section; 30b. Second small diameter section; 31. First locking element; 32. Channel; 33. Third sealing ring receiving groove. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 See Figures 1 to 3 This embodiment provides a cementing anti-backflow device, including a housing body 10, a pressure seat 30, and a pressure head 20.

[0021] A guide engagement structure is provided between the pressing head 20 and the outer shell body 10, so that the pressing head 20 has the freedom of movement to move downward and rotate in the circumferential direction.

[0022] The inner wall of the outer casing 10 is provided with a guide groove 11, which includes a longitudinal guide section extending along the axial direction, a transverse guide section extending along the circumferential direction, and an obtuse angle transition section connecting the longitudinal guide section and the transverse guide section.

[0023] The pressure seat 30 is fixedly connected to the lower end of the inner cavity of the outer shell body 10. The pressure seat 30 is provided with a channel 32 for fluid to pass through and a plurality of first locking members 31 arranged in the circumferential direction. The first locking members 31 have bayonets.

[0024] The pressing head 20 is disposed in the inner cavity of the outer shell body 10 and is sealed to fit the inner cavity, and is located above the pressing seat 30. The pressing head 20 has a central through hole for fluid to pass through, and the outer peripheral wall of the pressing head 20 has a circulation hole 23 that connects to the central through hole; the outer peripheral wall of the pressing head 20 is provided with a guide member that forms a guiding fit with the guide groove 11, and a second locking member 24 suitable for cooperating with the first locking member 31.

[0025] The guiding and mating structure is formed by the above-mentioned guide component and guide groove 11 mating together.

[0026] When in the initial state before impact, the impact head 20 is fixed at a high position inside relative to the outer shell body 10, the circulation hole 23 is connected to the channel 32, and the second locking member 24 and the first locking member 31 are staggered in the circumferential direction. Each second locking member 24 is located in the gap between two adjacent first locking members 31 and does not interfere with each other.

[0027] When in the locked state after the impact is completed, the guide is located in the transverse guide section of the guide groove 11, the circulation hole 23 is blocked and closed by the outer peripheral wall of the impact seat 30, and the second locking member 24 is screwed into the bayonet of the first locking member 31 to form a rigid mechanical lock.

[0028] Specifically, during the cementing and displacement operation, the device remains in its initial state. Fluid flows into the channel 32 of the impact seat 30 through the central through hole and circulation hole 23 of the impact head 20, forming a complete fluid circulation path to meet the flow requirements of normal cementing operations. When the displacement operation is nearing completion and the impact operation is initiated, the cementing plug 1 descends along the inner cavity of the casing and impacts the upper end face of the impact head 20. When the force reaches the unlocking threshold of the fixed structure of the impact head 20, the impact head 20 releases its relative fixed state with the outer shell 10 and moves axially downward under the thrust of the cementing plug 1. During the downward movement, the guide moves along the longitudinal guide section of the guide groove 11. During this stage, the impact head 20 only generates axial displacement and does not rotate circumferentially. The second locking member 24 and the first locking member 31 always maintain a circumferentially misaligned avoidance state. When the guide member descends to the obtuse-angle transition section of the guide groove 11, it is forced by the groove trajectory to enter the transverse guide section from the longitudinal guide section, causing the impact head 20 to deflect circumferentially while continuing to descend. As the impact head 20 rotates circumferentially, the second locking member 24 at its bottom rotates synchronously and eventually screws into the bayonet corresponding to the first locking member 31, completing the rigid mechanical locking. At this time, the circulation hole 23 descends with the impact head 20 to the outer peripheral wall of the impact seat 30 and is completely blocked, the fluid circulation passage is completely cut off, and the anti-backflow function is realized.

[0029] Optionally, the outer shell body 10 has an overall cylindrical structure, with connecting threads for coaxial connection of the sleeve at its upper and lower ends; the pressing seat 30 is fixedly connected to the lower end of the inner cavity of the outer shell body 10 by threads.

[0030] Preferably, the turning angle of the guide groove 11 transitioning from the longitudinal guide section to the transverse guide section is 95° to 105°. When this turning angle is in the range of 95° to 105°, it can ensure that the guide member's trajectory is smooth when transitioning from the longitudinal guide section to the transverse guide section, avoid stress concentration and movement stagnation caused by right-angle turns, reduce the downward movement resistance of the pressing head 20, and ensure that the locking action is completed smoothly; at the same time, it can enable the transverse guide section of the guide groove 11 to form a sufficient circumferential deflection stroke, ensure that the second locking member 24 has a sufficient insertion depth, and if the pressing head 20 wants to retract upward, it must simultaneously overcome axial resistance and complete a reverse circumferential rotation. Within this angle range, the circumferential component of the force generated when the reverse pushing force acts on the locking contact surface is insufficient to overcome the static friction of the contact surface, and the pressing head 20 cannot spontaneously generate reverse rotation, thus strengthening the self-locking reliability from a mechanical perspective; if the angle is too small and close to a right angle, jamming is likely to occur at the transition point and the impact load is large; if the angle is too large, the second locking member 24 will not be able to be inserted deeply enough, the circumferential limiting ability will decrease, and it will be easily disengaged by impact.

[0031] In this embodiment, the guide groove 11 with an obtuse-angle transition section cooperates with the guide component to transform the axial downward movement of the impact head 20 into a composite movement of axial movement and circumferential rotation. This, in turn, drives the second locking component 24 to rotate and engage with the first locking component 31, forming a purely rigid mechanical locking structure. The locking function is achieved without relying on the deformation of elastic elements throughout the process. When a reverse impact force is generated downhole, pushing the impact head 20 upward, the force acts directly on the rigid contact surface between the second locking component 24 and the first locking component 31. The greater the reverse pressure, the tighter the fit between the two, and the locking force is self-reinforcing. This avoids the potential risk of loss of anti-backflow function due to plastic deformation failure of elastic elements, thus improving the operational reliability of the cementing anti-backflow structure.

[0032] Example 2 like Figure 7 , Figure 8 As shown, the pressing head 20 is a hollow sleeve structure composed of a first large-diameter section 20a and a first small-diameter section 20b coaxially connected. The overall shape is a stepped shaft with a through central hole inside. The pressing seat 30 is composed of a second large-diameter section 30a and a second small-diameter section 30b coaxially connected, with the lower end of the second small-diameter section 30b connected to the upper end face of the second large-diameter section 30a.

[0033] The guide is located on the outer peripheral wall of the first large diameter section 20a. The circulation hole 23 and the second locking member 24 are both located on the outer peripheral wall of the first small diameter section 20b near the bottom, and the second locking member 24 is evenly distributed along the circumferential direction of the first small diameter section 20b. The channel 32 and the first locking member 31 are both located on the second large diameter section 30a.

[0034] The inner diameter of the first minor diameter section 20b is larger than the outer diameter of the second minor diameter section 30b, forming an active gap between them, which provides clearance for the downward movement and rotation of the impact head 20.

[0035] In the locked state, the first minor diameter section 20b is fitted outside the second minor diameter section 30b, and the circulation hole 23 moves to the outer peripheral wall of the second minor diameter section 30b and is completely blocked by the second minor diameter section 30b.

[0036] In detail, in the initial state, the first large-diameter section 20a of the impact head 20 is positioned high within the inner cavity of the outer shell 10, and the first small-diameter section 20b is suspended above the impact seat 30. The stepped structures of the two are nested together while maintaining a gap for movement. The circulation hole 23 is connected to the channel 32 on the second large-diameter section 30a, allowing fluid to flow into the channel 32 through the circulation hole 23, keeping the passage unobstructed. After the impact is triggered, the first large-diameter section 20a drives the first small-diameter section 20b to move axially downwards synchronously. The guide member moves along the longitudinal guide section of the guide groove 11, following the movement of the outer wall of the first large-diameter section 20a. When it reaches the obtuse angle transition section, the first large-diameter section 20a drives the entire impact head 20 to rotate circumferentially. The second locking member 24 at the bottom of the first small-diameter section 20b rotates circumferentially synchronously and finally screws into the bayonet of the first locking member 31 on the second large-diameter section 30a. At this time, the first small diameter section 20b is completely fitted outside the second small diameter section 30b. The circulation hole 23 moves down with the first small diameter section 20b to the outer wall area of ​​the second small diameter section 30b, and is completely blocked by the solid side wall of the second small diameter section 30b, thus closing the passage.

[0037] This embodiment employs a stepped shaft structure to divide the functional areas of the pressing head 20 and the pressing seat 30, allowing the guiding engagement, fluid circulation, and locking engagement to be achieved independently on different diameter sections. Each functional area operates without interference, resulting in higher positioning accuracy. Simultaneously, the outer peripheral wall of the second smaller diameter section 30b serves as a shielding structure, enabling the closure of the circulation hole 23 simultaneously with the downward locking of the pressing head 20, ensuring timely closure of the channel.

[0038] Example 3 A mounting groove 22 is formed on the outer peripheral wall of the first large diameter section 20a. The guide component is a guide ball that is embedded in the mounting groove 22 and partially protrudes from the outer peripheral wall of the first large diameter section 20a. The mounting groove 22 is a spherical groove adapted to the shape of the guide ball. The depth of the groove is less than the diameter of the guide ball. After the guide ball is embedded in the mounting groove 22, it can roll freely in the groove and will not fall out of the groove. Part of its spherical surface protrudes from the outer peripheral wall of the first large diameter section 20a, forming a rolling contact fit with the bottom of the guide groove 11. The number and position of the guide balls correspond one-to-one with the number and position of the guide grooves 11 on the inner wall of the outer shell body 10, and the two form a rolling guide fit.

[0039] Specifically, during the downward movement of the pressing head 20, the guide balls rotate freely within the mounting groove 22, rolling forward along the bottom of the longitudinal guide section of the guide groove 11, transforming the surface contact friction of traditional sliding guides into point contact rolling friction. When the ball reaches the obtuse-angle transition section of the guide groove 11, it rolls smoothly along the transition section into the transverse guide section without overcoming significant sliding resistance. Throughout the entire movement, the balls remain in contact with the bottom of the groove, smoothly driving the pressing head 20 to complete the combined action of axial movement and circumferential rotation, avoiding jamming or jerking.

[0040] Alternatively, the guide can be replaced with a guide slider or guide pin fixed to the outer wall of the pressing head 20, which can also achieve a limiting fit with the guide groove 11.

[0041] In this embodiment, a guide ball is used as a guide mating component, which converts the sliding friction between the guide and the guide groove 11 into rolling friction. This significantly reduces the frictional resistance during the downward movement of the pressing head 20, making the axial movement and circumferential rotation of the pressing head 20 smoother and avoiding the problem of jamming or incomplete locking action due to excessive frictional resistance, thus improving the overall reliability of the mechanism.

[0042] Example 4 An annular groove is formed on the upper end face of the second large diameter section 30a. A channel 32 is located at the bottom of the annular groove and extends through the second large diameter section 30a. The first locking member 31 is located in the annular groove. For example, the channel 32 is a fan-shaped hole evenly distributed circumferentially, extending through the upper and lower end faces of the second large diameter section 30a; the first locking member 31 is evenly arranged along the circumferential direction of the inner wall of the annular groove. The annular groove creates a receiving cavity inside the upper end face of the second large diameter section 30a of the pressing seat 30.

[0043] When the pressing head 20 moves downward and rotates circumferentially, the bottom of the first small diameter section 20b and the second locking member 24 enter the receiving space of the annular groove. The radial dimension of the annular groove is larger than the outer diameter of the first small diameter section 20b, providing sufficient clearance for the circumferential rotation of the second locking member 24, effectively preventing interference between the lower part of the first small diameter section 20b of the pressing head 20 and the second large diameter section 30a of the pressing seat 30 when rotating and locking.

[0044] Optionally, the upper end face of the second large diameter section 30a can also be set as a flat end face, and the channel 32 and the first locking member 31 are directly set on the flat end face, both of which can realize the corresponding fluid flow and locking functions.

[0045] Example 5 like Figure 6 As shown, a raised limiting step 13 is provided in the lower part of the inner wall of the outer shell body 10. In the locked state, the lower end face of the first large diameter section 20a is attached to the limiting step 13, which limits the axial position of the pressing head 20 downward.

[0046] In the initial state, the bottom surface of the first large-diameter section 20a maintains an axial distance from the upper surface of the limiting step 13, which corresponds to the effective downward stroke of the impact head 20. After the impact is triggered, the impact head 20 moves downward axially. When the guide moves to the end of the transverse guide section of the guide groove 11, the lower surface of the first large-diameter section 20a is exactly in complete contact with the upper surface of the limiting step 13, and the impact head 20 stops moving downward axially. At this time, the second locking member 24 is exactly fully engaged in the slot of the first locking member 31, reaching the preset locking position. When the impact head 20 is subjected to a downward impact load, the limiting step 13 directly bears the axial load, preventing the second locking member 24 from bearing excessive vertical pressure.

[0047] In this embodiment, by setting a limiting step 13 to rigidly limit the downward stroke of the pressing head 20, the axial stop position of the pressing head 20 can be precisely controlled, ensuring that the second locking member 24 can be accurately engaged in the slot of the first locking member 31, thereby improving the accuracy of the locking fit.

[0048] Example 6 A second sealing ring receiving groove 27 is formed on the inner wall of the first minor diameter section 20b near its lower end, and a third sealing ring receiving groove 33 is formed on the outer peripheral wall of the second minor diameter section 30b near its upper end; sealing rings are respectively provided in the second sealing ring receiving groove 27 and the third sealing ring receiving groove 33. In the locked state, the inner wall of the first minor diameter section 20b and the outer peripheral wall of the second minor diameter section 30b form a radial seal through the sealing rings.

[0049] In the initial state, the first minor diameter section 20b and the second minor diameter section 30b partially overlap axially. When the pressing head 20 descends and locks in place, the sealing rings in the second sealing ring receiving groove 27 on the inner wall of the first minor diameter section 20b and the third sealing ring receiving groove 33 on the outer wall of the second minor diameter section 30b form a continuous radial sealing ring between the mating surfaces of the first minor diameter section 20b and the second minor diameter section 30b, blocking the path of fluid leakage upward through the gap between the two.

[0050] In this embodiment, a sealing ring structure is provided on the mating surface of the pressing head 20 and the pressing seat 30, forming a reliable radial seal in the locked state, which can effectively prevent fluid from leaking through the mating gap between the two, and further enhance the sealing effect after the channel is closed.

[0051] Example 7 A first sealing ring receiving groove 26 is provided on the outer peripheral wall of the first large diameter section 20a. A sealing ring is provided in the first sealing ring receiving groove 26, and the sealing ring in the first sealing ring receiving groove 26 forms a sealing fit with the inner wall of the outer shell body 10.

[0052] Throughout the downward movement and rotation of the pressure head 20, the sealing ring on the outer wall of the first large-diameter section 20a remains in close contact with the inner wall of the outer casing 10, blocking the upward flow of fluid through the gap between the outer wall of the pressure head 20 and the inner wall of the outer casing 10. Once locked, this external seal, together with the internal radial seal between the first small-diameter section 20b and the second small-diameter section 30b, forms two sealing barriers inside the device, ensuring good anti-backflow performance under high pressure differential conditions.

[0053] Example 8 like Figure 4 As shown, the outer casing 10 has a plurality of casing pin holes 12 evenly spaced around the same height near the upper end, and the outer peripheral wall of the pressing head 20 has pressing head pin holes 25 corresponding to the casing pin holes 12. In the initial state, the pressing head 20 is fixed inside the outer casing 10 by passing through the casing pin holes 12 and inserting the shear pins 21 into the pressing head pin holes 25 through the shear pins 21.

[0054] During normal cementing operations, the shear pin 21 securely locks the impact head 20 at a high position inside the outer casing 10, bearing the scouring and pressure fluctuations of the fluid inside the pipe and maintaining the stability and unobstructed flow path. When the impact operation is initiated and the cementing plug 1 impacts the impact head 20, the axial thrust acting on the impact head 20 continuously increases as the pump pressure rises. When the thrust reaches the preset shearing value of the shear pin 21, the shear pin 21 is sheared, the impact head 20 is released from axial constraint, and then begins to move downward under the thrust of the cementing plug 1, triggering subsequent locking actions.

[0055] In this embodiment, a shear pin 21 is used to reliably fix the initial position of the pressure head 20, which can keep the position of the pressure head 20 stable during normal injection and replacement operations, ensuring continuous unobstructed fluid passage. When the pressure reaches the preset shearing value of the shear pin 21, the pin automatically shears off and triggers subsequent locking actions. The triggering timing is controllable and can be matched with the cementing operation process.

[0056] Example 9 The number of guide grooves 11 is multiple, and they are evenly distributed along the circumference of the outer shell body 10, preferably three.

[0057] The first locking element 31 is a hook-shaped locking block with a bayonet. There are multiple of them, and their cross-section is in the shape of a number 7. They are evenly distributed along the circumference of the pressing seat 30.

[0058] The second locking element 24 is a locking protrusion, the number of which corresponds one-to-one with the number of hook-shaped locking blocks, preferably 4 in each case, and evenly distributed along the circumference of the corresponding component.

[0059] During the downward movement and rotation of the pressing head 20, multiple sets of guide components move synchronously along the corresponding circumferentially distributed guide grooves 11, ensuring uniform circumferential force on the pressing head 20 and preventing jamming caused by unilateral load. After locking, multiple 7-shaped hook-shaped locking blocks engage with the corresponding locking protrusions at multiple points, allowing the reverse thrust to be evenly distributed across each locking contact surface, preventing structural damage due to overload at a single point. The 7-shaped hook-shaped locking blocks form an inward-facing bayonet structure, providing axial and radial dual restraint on the locking protrusions and enhancing the locking stability.

[0060] Example 10 This embodiment provides a cementing anti-backflow method, using the cementing anti-backflow device as described in any one of embodiments 1 to 9, combined with... Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 As shown, the method includes: Under the action of thrust, the impact head 20 is released from its relatively fixed state and moves downward along the axis; by means of the guide fit structure, the impact head 20 is forced to rotate circumferentially while continuing to move downward; as the impact head 20 rotates, the second locking member 24 rotates synchronously and slides into the first locking member 31 to form a mechanical lock; in this state, the circulation hole 23 on the impact head 20 is blocked and closed by the impact seat 30, the circulation hole 23 is disconnected from the channel 32, and the fluid channel is cut off.

[0061] The above methods will be explained in detail below with reference to specific work procedures.

[0062] S1. Initial State Preparation The cementing anti-backflow device is connected to the casing string via the connecting threads at the upper and lower ends of the outer casing 10, and is lowered into the well to a preset position along with the casing string. During the cementing operation, the device maintains its initial state: the pressure head 20 is fixed at a high position inside the outer casing 10 by shear pins 21, the second locking member 24 and the first locking member 31 are staggered in the circumferential direction, and the circulation hole 23 is interconnected with the channel 32 on the pressure seat 30, forming a complete fluid circulation path. Cement slurry and other fluids can flow downwards through the central through hole of the pressure head 20, the circulation hole 23, and the channel 32, meeting the flow requirements of normal cementing and replacement.

[0063] S2, Impact Trigger and Axial Downward Movement When the injection and replacement operation is completed and the impact operation is initiated, the cement plug 1 is inserted and pumped downwards. The cement plug 1 falls along the inner cavity of the casing to the upper end face of the impact head 20 and impacts it. As the pump pressure continues to increase, the axial thrust acting on the impact head 20 continuously increases. When the thrust reaches the preset shearing value of the shear pin 21, the shear pin 21 is sheared, and the impact head 20 is released from its relative fixed state with the outer casing 10. Under the continuous thrust of the cement plug 1, the impact head 20 moves downwards along the axial direction of the outer casing 10, and the guide balls on its outer wall roll downwards along the longitudinal guide section of the guide groove 11. During this stage, the impact head 20 only produces axial displacement and does not rotate circumferentially. The second locking member 24 and the first locking member 31 always maintain a circumferentially misaligned avoidance state and do not interfere with each other.

[0064] S3, Circumferential Rotation and Rigid Locking When the guide ball descends to the obtuse-angle transition section of the guide groove 11, constrained by the groove's trajectory, the guide ball rolls along the smooth extension trajectory through the obtuse-angle transition section into the transverse guide section, forcing the pressing head 20 to rotate circumferentially while continuing to descend. As the pressing head 20 deflects circumferentially, the second locking member 24 on its bottom first small diameter section 20b rotates synchronously, gradually approaching the latching position of the first locking member 31. When the lower end face of the first large diameter section 20a of the pressing head 20 contacts the limiting step 13 of the outer shell body 10, the pressing head 20 stops axially descending. At this time, the guide ball reaches the end of the transverse guide section of the guide groove 11, and the second locking member 24 slides completely into the latching position of the corresponding first locking member 31, forming a rigid mechanical lock.

[0065] Upon completion of the locking process, the circulation hole 23 on the pressure head 20 descends with the first small diameter section 20b to the outer wall of the second small diameter section 30b of the pressure seat 30, where it is completely blocked by the side wall of the second small diameter section 30b. The circulation hole 23 is then disconnected from the channel 32, and the fluid circulation path is completely cut off. Simultaneously, the sealing rings of the inner wall of the first small diameter section 20b and the outer wall of the second small diameter section 30b form a radial seal, which, together with the seal between the outer wall of the first large diameter section 20a and the inner wall of the outer casing 10, forms a complete seal.

[0066] S4. Preventing Backflow During the Condensation Stage During the cement slurry setting stage, when the annular pressure at the bottom of the well is higher than the internal pressure of the casing, generating an upward reverse impact force, the reverse pressure acts directly on the lower end face of the impact head 20, pushing the impact head 20 to tend to retract upward. At this time, the second locking member 24 is rigidly blocked by the latch of the first locking member 31.

[0067] Because the guide groove 11 adopts an obtuse angle transition section design, for the pressure head 20 to retract upwards, it must simultaneously complete two actions: axial upward movement and reverse circumferential rotation. However, under the high-pressure reverse pushing action, the contact surface between the second locking member 24 and the first locking member 31 generates a large static friction force. Since there is no additional rotational torque in the downhole environment to drive the pressure head 20 to rotate in the reverse direction, the pressure head 20 cannot physically rotate in the reverse direction and therefore cannot retract upwards from the locked state. The greater the reverse pressure, the greater the positive pressure and static friction force on each contact surface, resulting in a more secure lock and forming a self-reinforcing self-locking effect. This can stably maintain the channel closed state for a long time, preventing cement slurry from flowing back into the casing.

[0068] In the description of this invention, it should be understood that the terms "upper", "lower", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this 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, they should not be construed as limitations on this invention.

[0069] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0070] In this invention, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0071] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0072] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0073] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit them. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the scope of the technology disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention.

Claims

1. A cementing anti-reverse device, characterized in that, include: Outer shell (10); The impact seat (30) is fixed inside the outer shell body (10) and has a channel (32) for fluid to pass through and a first locking member (31). The pressure head (20) is disposed inside the outer shell body (10) and above the pressure seat (30), and has a central through hole for fluid to pass through and a circulation hole (23) communicating with the central through hole. The pressure head (20) is also provided with a second locking member (24) suitable for cooperating with the first locking member (31). A guide fit structure is provided between the pressure head (20) and the outer shell body (10), so that the pressure head (20) has the freedom of movement to move downward and rotate circumferentially. In the initial state, the pressing head (20) is fixed relative to the outer shell body (10), the circulation hole (23) is connected to the channel (32), and the first locking member (31) and the second locking member (24) are staggered in the circumferential direction; In the locked state, the pressing head (20) is pushed downward and rotates circumferentially by the guide and mating structure, causing the circulation hole (23) to be blocked and closed by the pressing seat (30), while the second locking member (24) is screwed into the first locking member (31) to form a mechanical lock.

2. The cementing anti-reverse flow device according to claim 1, characterized in that, The impact head (20) is a hollow sleeve structure composed of a first large diameter section (20a) and a first small diameter section (20b) connected coaxially; The impact seat (30) is composed of a second large diameter section (30a) and a second small diameter section (30b) connected coaxially; The guiding and mating structure includes a guide member disposed on the outer peripheral wall of the first large diameter section (20a), and a guide groove (11) formed on the inner wall of the outer shell body (10) and mating with the guide member. The guide groove (11) includes a longitudinal guide section extending along the axial direction, a transverse guide section extending along the circumferential direction, and an obtuse angle transition section connecting the longitudinal guide section and the transverse guide section. The circulation hole (23) and the second locking member (24) are both located on the outer peripheral wall of the first small diameter section (20b); the channel (32) and the first locking member (31) are both located on the second large diameter section (30a); In the locked state, the first small diameter segment (20b) is sleeved outside the second small diameter segment (30b), and the circulation hole (23) moves to the outer peripheral wall of the second small diameter segment (30b) and is completely blocked by the second small diameter segment (30b).

3. The cementing anti-reverse flow device according to claim 2, characterized in that, An installation groove (22) is provided on the outer peripheral wall of the first large diameter section (20a), and the guide is a guide ball that is embedded in the installation groove (22) and partially protrudes from the outer peripheral wall of the first large diameter section (20a).

4. The cementing anti-reverse flow device according to claim 2, characterized in that, The upper end face of the second large diameter section (30a) is provided with an annular groove, the channel (32) is provided at the bottom of the annular groove and passes through the second large diameter section (30a), and the first locking member (31) is located in the annular groove.

5. The cementing anti-reverse flow device according to claim 2, characterized in that, The lower part of the inner wall of the outer shell body (10) is provided with a protruding limiting step (13). In the locked state, the lower end face of the first large diameter section (20a) is attached to the limiting step (13) to limit the axial position of the pressing head (20) downward.

6. The cementing anti-reverse flow device according to claim 2, characterized in that, A second sealing ring receiving groove (27) is provided on the inner wall of the first small diameter section (20b) near the lower end, and a third sealing ring receiving groove (33) is provided on the outer peripheral wall of the second small diameter section (30b) near the upper end; sealing rings are respectively provided in the second sealing ring receiving groove (27) and the third sealing ring receiving groove (33); In the locked state, the inner wall of the first small diameter section (20b) and the outer peripheral wall of the second small diameter section (30b) form a radial seal through the sealing ring.

7. The cementing anti-reverse device according to claim 6, characterized in that, A first sealing ring receiving groove (26) is provided on the outer peripheral wall of the first large diameter section (20a). A sealing ring is provided in the first sealing ring receiving groove (26), and the sealing ring in the first sealing ring receiving groove (26) forms a sealing fit with the inner wall of the outer shell body (10).

8. The cementing anti-reverse flow device according to claim 2, characterized in that, The number of guide grooves (11) is multiple and they are evenly distributed along the circumference of the outer shell body (10); the turning angle of the guide grooves (11) from the longitudinal guide section to the transverse guide section is 95° to 105°. The first locking member (31) is a hook-shaped locking block with a bayonet, and there are multiple of them. The cross-section is shaped like the number 7 and they are evenly distributed along the circumference of the pressing seat (30). The second locking member (24) is a locking protrusion, the number of which corresponds one-to-one with the number of the hook-shaped locking blocks, and is evenly distributed along the circumferential direction of the pressing head (20).

9. The cementing anti-reverse flow device according to claim 1, characterized in that, The outer shell body (10) has a plurality of outer shell pin holes (12) evenly opened in the circumferential direction near the upper end, and the outer peripheral wall of the pressing head (20) has a pressing head pin hole (25) corresponding to the outer shell pin holes (12). In the initial state, the pressing head (20) passes through the outer shell pin hole (12) and is inserted into the pressing head pin hole (25) via the shear pin (21), and is fixed inside the outer shell body (10).

10. A cementing anti-backflow method, characterized in that, Using the cementing anti-backflow device as described in any one of claims 1 to 9, the method comprises: Under the action of thrust, the impact head (20) is released from its relatively fixed state and moves downward along the axial direction; The guiding and fitting structure forces the impact head (20) to rotate circumferentially while it continues to move downwards; As the pressing head (20) rotates, the second locking member (24) rotates synchronously and slides into the first locking member (31) to form a mechanical lock; in this state, the circulation hole (23) on the pressing head (20) is blocked and closed by the pressing seat (30), the circulation hole (23) is disconnected from the channel (32), and the fluid channel is cut off.

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