A device for automatically temporarily closing the casing and changing the wellhead.

Abstract

This invention relates to the field of downhole tools for oil and gas field development, and particularly to a device for automatically temporarily closing casing and changing wellheads, aiming to shorten the time and reduce the cost of wellhead replacement. The invention includes a release connector and a self-sealing plug. The release connector includes an upper connector, a ball seat inner sleeve, a shear pin, and a locking ball; the ball seat inner sleeve is inserted into the upper connector, and the shear pin passes through the side wall of the upper connector and is inserted into the ball seat inner sleeve; a through hole is provided on the side wall of the upper connector, the locking ball is installed in the through hole, and a groove is provided at the top of the self-sealing plug; the locking ball is configured to abut against the outside of the ball seat inner sleeve and embed into the groove at the top of the self-sealing plug to lock the upper connector and the self-sealing plug; the self-sealing plug includes a piston assembly and a sealing assembly fitted under the piston assembly, the sealing assembly including a rubber sleeve and slips. Under the pressure inside the wellbore, the release connector and the self-sealing plug are separated, and anchoring and sealing are completed.

Description

Technical Field

[0001] This invention relates to the field of downhole tool technology for oil and gas field development, and in particular to a device that can automatically temporarily close the casing and change the wellhead. Background Technology

[0002] When a leak occurs in the main gate valve switch plate of a casing-fracturing well, it is usually necessary to run a casing plug under pressure using coiled tubing. After the casing plug is set and verified as sealed, the main gate valve can be installed or replaced. Coiled tubing is a crucial piece of equipment for downhole operations, and due to its limited quantity, more important processes must be prioritized during production activities. Other processes requiring pressurized operation must be scheduled for a later date. On the other hand, using cryogenic temporary plugging to replace the wellhead requires injecting a temporary plugging agent into the pressure isolation area, which is then frozen to form a cryogenic temporary plug bridge, achieving pressure isolation. Both of these wellhead replacement processes have long construction cycles and high costs. Summary of the Invention

[0003] The purpose of this invention is to provide a device that can automatically temporarily close the casing to replace the wellhead, so as to shorten the replacement time and reduce the replacement cost.

[0004] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows:

[0005] An automatic casing replacement device includes a release connector and a self-sealing plug. The release connector includes an upper connector, a ball seat inner sleeve, a shear pin, and a locking ball. The ball seat inner sleeve is inserted into the upper connector, and the shear pin passes through the side wall of the upper connector and is inserted into the ball seat inner sleeve. A through hole is provided on the side wall of the upper connector, and the locking ball is installed in the through hole. A groove is provided at the top of the self-sealing plug, and the locking ball is configured to abut against the outside of the ball seat inner sleeve and be embedded in the groove at the top of the self-sealing plug to lock the upper connector and the self-sealing plug. The self-sealing plug includes a piston assembly and a sealing assembly fitted under the piston assembly. The sealing assembly includes a rubber sleeve and slips.

[0006] Under the pressure inside the wellbore, the inner sleeve of the ball seat moves down and shears off the shear pin. After the inner sleeve of the ball seat moves down, it no longer abuts against the locking ball. The self-sealing plug disengages from the locking ball under the action of gravity. After the self-sealing plug disengages from the locking ball, it falls down. At the same time, driven by the pressure inside the wellbore, the piston assembly moves up to drive the rubber sleeve to expand and seal with the inner wall of the wellbore. At the same time, it drives the slips to expand and anchor to the inner wall of the wellbore.

[0007] Furthermore, a bypass hole is provided on the side wall of the upper connector. The bypass hole is higher than the inner sliding sleeve of the ball seat. The size of the bypass hole can control the speed at which the high-pressure fluid in the wellbore enters the upper connector, so that the pressure in the upper connector gradually increases to the time required to push the inner sliding sleeve of the ball seat and shear the shear pin. The diameter of the bypass hole and the pressure value required for the shear pin to be sheared together control the release time.

[0008] Furthermore, the piston assembly includes a piston and a piston rod; the upper part of the piston rod is inserted into the piston, the piston rod is a hollow tube, and a piston communication hole is provided on the side wall of the piston rod, which is located below the piston.

[0009] Furthermore, the piston assembly also includes a hollow guide cone, which is located at the lower end of the piston rod. A throttle valve is installed inside the hollow guide cone. The size of the annulus between the outer diameter of the throttle valve and the hollow guide cone can control the flow rate of high-pressure fluid in the wellbore into the self-sealing plug, thereby controlling the upward movement time of the piston assembly and achieving a delay effect to ensure that the self-sealing plug falls smoothly into the wellbore and sets below the wellhead.

[0010] Furthermore, the valve core of the throttle valve is made of ceramic material; after setting, as the fluid in the wellbore continues to pressurize, the fluid pressure in the wellbore increases, and the pressure of the fluid in the wellbore continuously pressurizing will crush the valve core of the throttle valve.

[0011] Furthermore, the self-sealing plug also includes a rupture disc; the rupture disc is positioned above the piston to seal the space above the piston, preventing high-pressure fluid in the wellbore from hindering the piston's upward movement; the pressure required for the rupture disc to break is greater than the pressure of the fluid continuously accumulating pressure in the wellbore.

[0012] Furthermore, the outer wall of the inner sliding sleeve of the ball seat is provided with a ball-locking release groove. After the inner sliding sleeve of the ball seat moves down, the position of the ball-locking release groove is consistent with the position of the locking ball.

[0013] Furthermore, the self-sealing plug also includes a retrieval head, the upper part of which is fitted onto the lower part of the upper connector; the inner wall of the retrieval head is provided with an annular groove, into which the locking ball is embedded.

[0014] Furthermore, the self-sealing plug also includes a piston cylinder, the upper end of which is threadedly connected to the lower end of the retrieval head; the piston assembly is inserted into the piston cylinder and moves along the axial direction of the piston cylinder.

[0015] Furthermore, the self-sealing plug also includes a pusher, which is inserted into the lower part of the piston cylinder; the lower side of the piston rod passes through the pusher, and the piston communication hole is located above the pusher.

[0016] In summary, the technical effects achieved by this invention are as follows:

[0017] This invention provides an automatic casing replacement device, comprising a release connector and a self-sealing plug. The release connector includes an upper connector, a ball seat inner sleeve, a shear pin, and a locking ball; the ball seat inner sleeve is inserted into the upper connector, and the shear pin passes through the side wall of the upper connector and is inserted into the ball seat inner sleeve. A through hole is provided on the side wall of the upper connector, and the locking ball is installed in the through hole. A groove is provided at the top of the self-sealing plug, and the locking ball is configured to abut against the outside of the ball seat inner sleeve and embed into the groove at the top of the self-sealing plug to lock the upper connector and the self-sealing plug. The self-sealing plug includes a piston assembly and a sealing assembly fitted under the piston assembly; the sealing assembly includes a rubber sleeve and slips.

[0018] Under the pressure inside the wellbore, the inner sleeve of the ball seat moves downward and shears off the shear pin. After moving downward, the inner sleeve of the ball seat no longer abuts against the locking ball, and the self-sealing plug disengages from the locking ball under the action of gravity. After the self-sealing plug disengages from the locking ball, it falls. At the same time, driven by the pressure inside the wellbore, the piston assembly moves upward to drive the rubber sleeve to expand and seal with the inner wall of the wellbore. Simultaneously, it drives the slips to expand and anchor to the inner wall of the wellbore.

[0019] The automatic casing replacement device provided by this invention can detach the release connector and self-sealing plug under the pressure and gravity inside the wellbore. After detachment, it anchors and sets the self-sealing plug using the pressure inside the wellbore, achieving temporary closure of the wellhead. This invention eliminates the need for running the casing plug under pressure using coiled tubing, avoiding the waiting time and relatively cumbersome construction process associated with coiled tubing, effectively shortening the construction cycle and reducing construction costs. Furthermore, compared to the construction method of generating a frozen temporary plug bridge through freezing, it also offers advantages such as faster construction and lower cost. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art 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.

[0021] Figure 1 A schematic diagram of the main structure of the device for automatically temporarily closing the casing and changing the wellhead provided in an embodiment of the present invention;

[0022] Figure 2 A schematic diagram of the installation of the device for automatically temporarily closing the casing and changing the wellhead provided in an embodiment of the present invention;

[0023] Figure 3 This is a cross-sectional view of the drop-off connector;

[0024] Figure 4This is a schematic diagram of a self-sealing plug.

[0025] Icons: 100 - Drop-off connector; 200 - Self-sealing plug; 300 - Short section; 400 - Blowout preventer; 500 - Pressure relief valve; 600 - Wellhead main gate valve; 110 - Upper connector; 120 - Ball seat inner sleeve; 130 - Shear pin; 140 - Locking ball; 210 - Piston assembly; 220 - Sealing assembly; 230 - Retrieval head; 240 - Piston cylinder; 250 - Pusher; 260 - Rupture disc; 11 1-Bypass hole; 121-Lock ball release groove; 211-Piston; 212-Piston rod; 213-Hollow guide cone; 214-Plug; 221-Slipper; 222-Rubber sleeve; 223-Slipper seat; 224-Upper cone; 225-Setting pin; 226-Shoulder; 227-Lower cone; 231-Annular groove; a-Throttle valve; b-Piston connecting hole; c-Limited movement area; d-Drive space. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments 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, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0027] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0028] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0029] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. 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, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0030] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0031] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0032] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0033] When a leak occurs in the 600 main gate valve switch plate of a casing-fracturing well, it is usually necessary to run a casing plug under pressure using coiled tubing. After the casing plug is set and verified as sealed, the installation or replacement of the 600 main gate valve can be carried out. Coiled tubing is a crucial piece of equipment for downhole operations, and due to its limited quantity, more important processes must be prioritized during production activities. Other processes requiring pressurized operation must be scheduled for a later date. On the other hand, using cryogenic temporary plugging to replace the wellhead requires injecting a temporary plugging agent into the pressure isolation area, which is then frozen to form a cryogenic temporary plug bridge, achieving the effect of pressure isolation. Both of these wellhead replacement processes have long construction cycles and high costs.

[0034] In view of this, the present invention provides a device for automatically temporarily closing the casing and changing the wellhead, including a release connector 100 and a self-sealing plug 200. The release connector 100 includes an upper connector 110, a ball seat inner sleeve 120, a shear pin 130, and a locking ball 140; the ball seat inner sleeve 120 is inserted into the upper connector 110, and the shear pin 130 passes through the side wall of the upper connector 110 and is inserted into the ball seat inner sleeve 120. A through hole is provided on the side wall of the upper connector 110, the locking ball 140 is installed in the through hole, and a groove is provided at the top of the self-sealing plug 200. The locking ball 140 is configured to abut against the outside of the ball seat inner sleeve 120 and be embedded in the groove at the top of the self-sealing plug 200 to lock the upper connector 110 and the self-sealing plug 200. The self-sealing plug 200 includes a piston assembly 210 and a sealing assembly 220 fitted under the piston assembly 210. The sealing assembly 220 includes a rubber sleeve 222 and a slip 221.

[0035] Under the pressure inside the wellbore, the inner sleeve 120 of the ball seat moves downward and shears the shear pin 130. After moving downward, the inner sleeve 120 no longer abuts against the locking ball 140, and the self-sealing plug 200 disengages from the locking ball 140 under the action of gravity. After the self-sealing plug 200 disengages from the locking ball 140, it falls. At the same time, driven by the pressure inside the wellbore, the piston assembly 210 moves upward to drive the rubber sleeve 222 to expand and seal with the inner wall of the wellbore. Simultaneously, it drives the slip 221 to expand and anchor to the inner wall of the wellbore.

[0036] The automatic casing replacement device provided by this invention can detach the release connector 100 and the self-sealing plug 200 under the pressure and gravity inside the wellbore. After detachment, the self-sealing plug 200 is anchored and set by the pressure inside the wellbore, achieving temporary closure of the wellhead. This invention eliminates the need for pressurized tubing to insert the casing plug, avoiding the waiting time and relatively cumbersome construction process associated with using tubing, effectively shortening the construction cycle and reducing construction costs. Furthermore, compared to the construction method of generating a frozen temporary plug bridge through freezing, it also has the advantages of rapid construction and low cost.

[0037] The following combination Figures 1-4 The structure and shape of the device for automatically temporarily closing the casing and changing the wellhead provided in this embodiment are described in detail:

[0038] In an optional embodiment, the device for automatically temporarily closing the casing and changing the wellhead also includes a short section 300. For example... Figure 1 , Figure 2 As shown, the lower side of the short section 300 is inserted into the upper side of the upper connector 110 and threadedly connected to the upper connector 110, thus closing the upper end of the upper connector 110.

[0039] In this embodiment, the device for automatically temporarily closing the casing and changing the wellhead also includes a blowout preventer (BOP) 400 and a wellhead main gate valve 600. The BOP 400 is sealed to the wellhead main gate valve 600 via a flange. The BOP 400 contains a release connector 100 and a self-sealing plug 200. The upper side of the short section 300 is connected to the upper end of the BOP 400, fixing the release connector 100 and the self-sealing plug 200, with the self-sealing plug 200 positioned above the wellhead main gate valve 600. Furthermore, a pressure relief valve 500 is provided on the BOP 400 for depressurizing the BOP 400.

[0040] In the optional solutions of this embodiment, such as Figure 1As shown, a bypass hole 111 is provided on the side wall of the upper connector 110. The bypass hole 111 is higher than the inner sleeve 120 of the ball seat. The high-pressure fluid in the wellbore enters the upper connector 110 through the bypass hole 111 and acts on the inner sleeve 120 of the ball seat, causing the inner sleeve 120 of the ball seat to shear the shear pin 130 and move downward. Specifically, a step is provided on the outer side of the inner sleeve 120 of the ball seat, and a step is provided on the inner wall of the upper connector 110, so that the inner sleeve 120 of the ball seat and the upper connector 110 form a limiting movement area c, so as to ensure the space for the inner sleeve 120 of the ball seat to move downward, and at the same time prevent the inner sleeve 120 of the ball seat from disengaging from the upper connector 110 after moving downward.

[0041] It should be noted that the size of the bypass hole 111 can control the speed at which high-pressure fluid enters the upper connector 110 in the wellbore, so that the pressure in the upper connector 110 gradually increases to the time it takes to push the inner sliding sleeve 120 of the ball seat and shear the shear pin 130; the diameter of the bypass hole 111 and the pressure value required for the shear pin 130 to be sheared together control the release time.

[0042] In this embodiment, as Figure 3 As shown, the outer wall of the inner sliding sleeve 120 of the ball seat is provided with a ball locking release groove 121. After the inner sliding sleeve 120 of the ball seat moves down, the position of the ball locking release groove 121 is consistent with the position of the locking ball 140. At this time, the locking ball 140 can move towards the inner sliding sleeve 120 of the ball seat.

[0043] In this embodiment, the self-sealing plug 200 also includes a retrieval head 230, the upper part of which is fitted onto the lower part of the upper connector 110; the inner wall of the retrieval head 230 is provided with an annular groove 231, and the locking ball 140 is embedded in the annular groove 231, so that the retrieval head 230 is connected to the upper connector 110, thereby connecting the release connector 100 and the self-sealing plug 200.

[0044] In this embodiment, the self-sealing plug 200 also includes a piston cylinder 240, the upper end of which is threadedly connected to the lower end of the retrieval head 230; the piston assembly 210 is inserted into the piston cylinder 240 and moves along the axial direction of the piston cylinder 240.

[0045] In this embodiment, the self-sealing plugger 200 also includes a pusher 250, which is inserted into the lower part of the piston cylinder 240; the lower part of the piston assembly 210 passes through the pusher 250.

[0046] In this embodiment, the piston assembly 210 includes a piston 211, a piston rod 212, and a plug 214. For example... Figure 4As shown, piston 211 is inserted into piston cylinder 240 and positioned above push cylinder 250. The upper part of piston rod 212 is inserted into piston 211, and the lower part of piston rod 212 passes through push cylinder 250. Piston rod 212 is a hollow tube, and a piston communication hole b is provided on the side wall of piston rod 212, which is located between piston 211 and push cylinder 250. Plug 214 is inserted into the upper end of piston rod 212 to close the upper end of piston rod 212 and cooperates with the step at the upper end of piston rod 212 to connect piston 211 and piston rod 212. Piston 211, piston cylinder 240, piston rod 212, and push cylinder 250 form a driving space d, and piston communication hole b communicates with driving space d. High-pressure fluid in the wellbore enters driving space d through piston rod 212 and piston communication hole b, driving piston assembly 210 to move upward. It should be noted that a limit ring is provided on the piston rod 212. The lower end face of the limit ring abuts against the upper end face of the push cylinder 250, so that the piston 211 and the push cylinder 250 maintain a certain distance, preventing the piston connecting hole b from disengaging from the drive space d.

[0047] Furthermore, the piston assembly 210 also includes a hollow guide cone 213, which is located at the lower end of the piston rod 212. A throttle valve a is installed inside the hollow guide cone 213. The size of the annular space between the outer diameter of the throttle valve a and the hollow guide cone 213 controls the flow rate of high-pressure fluid entering the self-sealing plug 200 from the wellbore, thereby controlling the upward movement time of the piston assembly 210 and achieving a delay effect. This ensures that the self-sealing plug 200 smoothly falls into the wellbore and sets below the wellhead.

[0048] High-pressure fluid inside the wellbore enters the piston rod 212 through the annulus between the throttle valve a and the hollow guide cone 213, and finally enters the drive space d. The speed at which the fluid enters the self-sealing plug is controlled by the throttle valve a, preventing the self-sealing plug from setting prematurely.

[0049] In this embodiment, a sealing ring is provided between the piston 211 and the piston cylinder 240, and sealing rings are provided on the upper and lower sides of the connection between the piston rod 212 and the hollow guide cone 213 to prevent high-pressure fluid leakage.

[0050] In this embodiment, the valve core of the throttle valve a is made of ceramic material. When the pressure reaches a certain value, the valve core of the throttle valve a is crushed, increasing the cross-section of the self-sealing plug 200 and the wellbore, preventing the high-pressure fluid in the drive space d from being blocked by the throttle valve a and making it difficult to discharge, thus causing the piston 211 to be obstructed from moving downward.

[0051] In this embodiment, the sealing component 220 also includes a locking seat 223. For example... Figure 4As shown, the slip seat 223 is located below the push cylinder 250 and is used to install the slip 221. Further, the sealing assembly 220 also includes an upper cone 224, a lower cone 227, and a setting pin 225. The lower side of the upper cone 224 is fitted onto the upper side of the lower cone 227. The setting pin 225 passes through the side wall of the lower cone 227 and inserts into the upper cone 224, connecting the upper cone 224 and the lower cone 227. The slip 221 is fitted onto the upper side of the upper cone 224; the slip 221 is fitted onto the lower side of the lower cone 227, and the lower end face of the slip 221 fitted onto the lower side of the lower cone 227 abuts against the hollow guide cone 213.

[0052] In this embodiment, the rubber sleeve 222 is fitted onto the upper side of the lower cone 227. Shoulders 226 are provided at both the upper and lower ends of the rubber sleeve 222. One side of the shoulder 226 engages with the end of the rubber sleeve 222, and the other side engages with grooves on the upper cone 224 and the lower cone 227, respectively. This ensures a tight seal between the rubber sleeve 222 and the lower cone 227 after the rubber sleeve 222 is deformed by compression, thus guaranteeing a sealing effect.

[0053] In an optional embodiment, the self-sealing plugger 200 further includes a rupture disc 260, which is disposed inside the retrieval head 230. The pressure required for the rupture disc 260 to break is greater than the pressure of continuous pressure build-up in the wellbore after setting, preventing the rupture disc 260 from breaking prematurely and causing high-pressure fluid in the wellbore to enter the piston cylinder 240 from the retrieval head 230, affecting the upward movement of the piston assembly 210.

[0054] The working process of the device for automatically temporarily closing the casing and changing the wellhead provided in this embodiment is as follows:

[0055] First, install the short section 300, the release connector 100, and the self-sealing plug 200 in sequence inside the blowout preventer 400. Then, install the blowout preventer 400 onto the wellhead main gate 600 to form a sealed space with the wellhead main gate 600.

[0056] Then, the main gate valve 600 is opened, and the high-pressure fluid in the wellbore enters the blowout preventer 400 and passes through the bypass hole 111 into the upper connector 110. Under the pressure of the high-pressure fluid, the inner sleeve 120 of the ball seat shears the shear pin 130 and moves downward, causing the locking ball release groove 121 to move downward. Under its own weight, the self-sealing plug 200 pushes the locking ball 140 to move towards the locking ball release groove 121 and downward, realizing the release of the release connector 100 and the self-sealing plug 200. The self-sealing plug 200 then passes through the main gate valve 600 and falls to a suitable position in the wellbore. The release time is jointly controlled and determined by the diameter of the bypass hole 111 and the pressure value required for the shear pin 130 to be sheared.

[0057] During the release process, high-pressure fluid inside the wellbore slowly enters the drive space d through the throttle valve a, hollow guide cone 213, piston rod 212, and piston connecting hole b. After the release is completed, the self-sealing plug 200 begins to fall. When the high-pressure fluid inside the wellbore fills the drive space d, the piston assembly 210 moves upward. At this time, the hollow guide cone 213 drives the slip 221 fitted on the lower cone 227 to move upward and expand outward. The upper cone 224 moves upward with the lower cone 227 and squeezes the slip 221 fitted on the upper cone 224. As the piston assembly 210 continues to move upward, the upper cone 224 and lower cone 227 shear off the setting pin 225. The lower cone 227 continues to move upward with the piston assembly 210, starting to squeeze the rubber sleeve 222 and forming a seal with the inner wall of the wellbore. During this process, the slip 221 continues to expand outward and finally anchors on the inner wall of the casing as the piston assembly 210 moves upward, completing the automatic setting. It should be noted that the falling time is determined by the flow rate of throttle valve a and the size of the annulus between throttle valve a and hollow guide cone 213.

[0058] After the self-sealing plug 200 is set, under the action of the high-pressure fluid in the wellbore, the pressure in the drive space d continues to rise, continuously acting on the piston 211 to maintain the set state. Simultaneously, the valve core of the throttle valve a breaks under the continuous pressure of the high-pressure fluid in the wellbore, increasing the cross-sectional area connecting the drive space d and the wellbore. At this time, the air in the space above the piston 211 and below the rupture disc 260 is compressed, and the pressure increases. It should be noted that the setting time of the self-sealing plug 200 can be adjusted by regulating the diameter of the piston connecting hole b to regulate the speed at which the high-pressure fluid enters the drive space d, thereby regulating the descent time of the self-sealing plug 200, ensuring a delay effect, and ultimately controlling the setting position of the self-sealing plug 200 to ensure it falls smoothly into the wellbore and sets below the wellhead. Simultaneously, the setting time can be controlled by adjusting the shear force required to cut the setting pin 225, in conjunction with the piston connecting hole b. It should be noted that the flow rate of throttle valve a and the size of the annulus between throttle valve a and hollow guide cone 213 are the main factors controlling the setting of the seal.

[0059] After the self-sealing plug 200 sets, the casing above the rubber sleeve 222 will gradually depressurize to zero due to inlet leakage. Alternatively, open the gate valve on the wellhead four-way valve and observe for an extended period for any overflow. If there is no overflow, it indicates that the self-sealing plug 200 is properly set. Afterward, open the pressure relief valve 500 to release the pressure inside the blowout preventer 400 and the release connector 100, then close the wellhead main gate valve 600, remove the blowout preventer 400, and replace the wellhead valve.

[0060] After changing the wellhead, coiled tubing is run in, with the bottom end connected to the fishing tool. When the coiled tubing encounters resistance, pressure is applied to engage the fishing tool with the fishing head 230. Pressure is then applied into the fishing head 230, exceeding the pressure continuously accumulated in the wellbore, causing the rupture disc 260 to break and pushing the piston assembly 210 downwards, expelling the high-pressure fluid from the drive space d. After the piston assembly 210 moves downwards, the slips 221 lose support and reset, and the lower cone 227 also moves downwards, no longer compressing the rubber sleeve 222, which resets, thus completing the unsealing process. After unsealing, the fishing tool is pulled up, and the self-sealing plug 200 is removed.

[0061] During the setting process, no coiled tubing is required; setting and wellhead replacement can be completed solely based on the pressure within the wellbore. This avoids dependence on coiled tubing, simplifies operation, and allows for timely inlet replacement, effectively shortening the construction cycle and reducing construction costs. After replacement, the coiled tubing can be used for unsealing when it becomes available, without affecting other processes.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A device for automatically temporarily closing the casing and changing the wellhead, characterized in that, Includes a drop-off connector (100) and a self-sealing plug (200); The drop-off connector (100) includes an upper connector (110), a ball seat inner sleeve (120), a shear pin (130), and a locking ball (140). The ball seat inner sleeve (120) is inserted into the upper connector (110), and the shear pin (130) is inserted into the ball seat inner sleeve (120) after passing through the side wall of the upper connector (110). The upper connector (110) has a through hole on its side wall, the locking ball (140) is installed in the through hole, the top of the self-sealing plug (200) has a groove, the locking ball (140) is configured to abut against the outside of the inner sleeve (120) of the ball seat, and be embedded in the groove at the top of the self-sealing plug (200) to lock the upper connector (110) and the self-sealing plug (200). The self-sealing plug (200) includes a piston assembly (210) and a sealing assembly (220) fitted under the piston assembly (210), the sealing assembly (220) including a rubber sleeve (222) and a slip (221). A bypass hole (111) is provided on the side wall of the upper connector (110). The bypass hole (111) is higher than the inner sliding sleeve (120) of the ball seat. The fluid in the wellbore enters the upper connector (110) through the bypass hole (111) and acts on the inner sliding sleeve (120) of the ball seat. Under the pressure inside the wellbore, the inner sleeve (120) of the ball seat moves down and shears the shear pin (130). After the inner sleeve (120) of the ball seat moves down, it no longer abuts against the locking ball (140). The self-sealing plug (200) disengages from the locking ball (140) under the action of gravity. After the self-sealing plug (200) disengages from the locking ball (140) and falls, the piston assembly (210) moves upward under the pressure inside the wellbore to drive the rubber sleeve (222) to expand and seal with the inner wall of the wellbore, while driving the slip (221) to expand and anchor to the inner wall of the wellbore. The size of the bypass hole (111) can control the speed at which high-pressure fluid enters the upper connector (110) in the wellbore, so that the pressure in the upper connector (110) gradually increases to the time it takes to push the inner sliding sleeve (120) of the ball seat and cut off the shear pin (130); The diameter of the bypass hole (111) and the pressure required for the shear pin (130) to be sheared together control the release time. The piston assembly (210) includes a piston (211) and a piston rod (212). The upper part of the piston rod (212) is inserted into the piston (211). The piston rod (212) is a hollow tube, and the side wall of the piston rod (212) is provided with a piston communication hole (b), which is located below the piston (211). The piston assembly (210) also includes a hollow guide cone (213), which is disposed at the lower end of the piston rod (212); A throttle valve (a) is installed inside the hollow guide cone (213). The fluid in the wellbore enters the piston rod (212) through the throttle valve (a) and the annulus between the throttle valve (a) and the hollow guide cone (213). Finally, it acts on the piston assembly (210) through the piston connecting hole (b) and drives the piston assembly (210) to move upward. The size of the annulus between the throttle valve (a) and the hollow guide cone (213) can control the flow rate of the high-pressure fluid in the wellbore into the self-sealing plug (200) so as to control the time of the piston assembly (210) moving upward, thereby achieving a delay effect and ensuring that the self-sealing plug (200) falls smoothly into the wellbore and sets below the wellhead.

2. The device for automatically temporarily closing the casing and changing the wellhead according to claim 1, characterized in that, The valve core of the throttle valve (a) is made of ceramic material; After setting, as the fluid in the wellbore continues to pressurize, the fluid pressure in the wellbore increases, and the pressure of the fluid in the wellbore continues to pressurize, crushing the valve core of the throttle valve (a).

3. The device for automatically temporarily closing the casing and changing the wellhead according to claim 2, characterized in that... The self-sealing plug (200) also includes a rupture disc (260); The rupture disc (260) is located above the piston (211) to block the space above the piston (211) and prevent the high-pressure fluid in the wellbore from hindering the piston (211) from moving upward; The pressure required for the rupture disc (260) to break is greater than the pressure required for the fluid in the wellbore to continue to hold.

4. The device for automatically temporarily closing the casing and changing the wellhead according to claim 3, characterized in that... The inner sleeve (120) of the ball seat has a ball release groove (121) on its outer wall. After the inner sleeve (120) of the ball seat moves down, the position of the ball release groove (121) is consistent with the position of the ball (140).

5. The device for automatically temporarily closing the casing and changing the wellhead according to claim 4, characterized in that, The self-sealing plug (200) also includes a retrieval head (230), the upper part of which is fitted onto the lower part of the upper connector (110); The inner wall of the retrieval head (230) is provided with an annular groove (231), and the locking ball (140) is embedded in the annular groove (231).

6. The device for automatically temporarily closing the casing and changing the wellhead according to claim 5, characterized in that, The self-sealing plug (200) also includes a piston cylinder (240), the upper end of which is threadedly connected to the lower end of the retrieval head (230); The piston assembly (210) is inserted into the piston cylinder (240) and moves along the axis of the piston cylinder (240).

7. The device for automatically temporarily closing the casing and changing the wellhead according to claim 6, characterized in that, The self-sealing plug (200) also includes a pusher (250) inserted into the lower part of the piston cylinder (240); The lower side of the piston rod (212) passes through the push cylinder (250), and the piston connecting hole (b) is located above the push cylinder (250).

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