Graded cementing device capable of preventing cement from returning

Abstract

The utility model discloses a graded cementing device capable of preventing cement from returning, which comprises an outer connecting cylinder, a closing sleeve and a closing plug seat, the outer connecting cylinder provided with a first slurry circulating hole and the closing sleeve provided with a second slurry circulating hole are connected through a locking block, and a clamp spring is further arranged between the outer connecting cylinder and the closing sleeve; the closing plug seat which is provided with a locking block withdrawing groove and only allows liquid to flow downwards, the opening sleeve and the baffle ring are all mounted in the closing sleeve, and the closing sleeve is connected with the closing plug seat through a shear pin; the opening sleeve, the baffle ring and the closing sleeve are sequentially connected through shear pins and threads. According to the utility model, the structure is improved, so that the problem that the opening sleeve is opened in advance due to overhigh excitation pressure in the tripping-in process of the device can be effectively prevented, and particularly, the problem of cement return caused by untight closing of the closing sleeve can be effectively prevented after an upper rubber plug collides with the device in the later stage of well cementation.

Description

Technical Field

[0001] This utility model relates to the field of cementing technology in the petroleum industry, and in particular to a staged cement injection device that can prevent cement backflow. Background Technology

[0002] In the horizontal well cementing completion construction of the petroleum industry, the screen pipe is run into the open hole in the oil layer section of the oil well. The top of the screen pipe is cemented using tools such as packers, stage clamps, and blind plates. This can effectively seal off heterogeneous layers and significantly increase oil well production.

[0003] However, current staged cementing devices suffer from structural defects that result in insufficient reliability during construction. Problems such as premature opening of the opening sleeve and incomplete closing of the closing sleeve lead to serious issues like cement plugs returning to the casing and cement solidifying inside the casing (a phenomenon commonly known as "sausage stuffing"). These problems severely affect cementing quality, prolong construction time, increase construction costs, and also impact the service life of oil wells. They also cause numerous inconveniences for subsequent treatment, hindering the progress of oil well construction and making it difficult to meet the requirements of accelerating, improving quality, and increasing efficiency in oilfield development.

[0004] To address the aforementioned issues, on-site technicians have made numerous improvements. Through patent searches, the following relevant patent documents were retrieved: Authorization Announcement No. CN109869114A discloses a sealing-type staged cementing device and its operating method. The invention belongs to the field of oil well cementing tool technology, specifically relating to a staged cementing device, particularly a sealing-type staged cementing device, and a staged cementing method using such a device.

[0005] The invention solves the problem of annular leakage caused by the difficulty in achieving annular mechanical sealing during special operations such as deep wells and staged cementing. It effectively improves the annular sealing effect and pressure bearing capacity during staged cementing, and greatly reduces the risk of leakage during staged cementing of long sections in deep wells.

[0006] However, problems still exist, such as premature opening of the opening sleeve, incomplete closure of the closing sleeve, and cement backflow caused by the return of the cementing plug.

[0007] Application publication number CN116006118A discloses a staged cementing injector, which is suitable for staged cementing. It eliminates the risk of premature shut-in during cementing operations and enables the staged cementing injector to achieve high temperature resistance and long-term sealing after cementing operations.

[0008] The staged cementing device involved in the above invention needs to be grouted in a timely manner during the running-in process. Otherwise, there is a risk of premature opening during the running-in process. After cementing pressure, there is a risk that the closing sleeve of the staged cementing device will not close tightly, which will cause cement backflow, affecting the cementing quality and the service life of the oil well.

[0009] Application publication number CN116181276A discloses a differential pressure type open-hole graded cement injector, comprising a separate hole-closing mechanism and a hole-opening mechanism. The hole-opening mechanism has a hole-opening sleeve threadedly connected to the outside of a cylindrical hole-opening seat. A non-sealed annular space is provided between the hole-opening sleeve and the main body. The upper end face area of ​​the hole-opening mechanism is larger than the lower end face area. Upon pressure, the hole-opening pin is broken, and the hole-opening mechanism opens the cement slurry hole. The hole-closing mechanism has a hole-closing sleeve threadedly connected to the outside of a cylindrical hole-closing seat. A cement plug seals the hole at the upper end of the hole-closing seat. Upon pressure, the hole-closing pin is broken, and the hole-closing mechanism seals the cement slurry hole on the main body. In the locking mechanism, a locking spring presses the locking pin into a groove on the outer surface of the hole-closing sleeve, reliably locking the hole-closing sleeve.

[0010] The above invention further improves the internal structure and orifice closing method of existing cement injectors, and has advantages such as reliable orifice closing and stable locking. However, the problem of cement backflow may still occur.

[0011] Chinese Patent Application No. 202322000409.0 discloses a staged cementing device and tool string for half-stage cementing. The staged cementing device includes: a body assembly, an inner sleeve, and a closing assembly arranged sequentially from the outside to the inside; and a closing slide sleeve and an opening slide sleeve arranged sequentially from top to bottom between the body assembly and the inner sleeve. The opening and closing slide sleeves are axially slidable to allow communication or closure between a first circulation hole on the body assembly and a second circulation hole on the opening slide sleeve. The closing assembly includes a closing plug, a valve, and a basket. The closing plug is connected to the basket, and the valve is positioned between the closing plug and the basket, with its top abutting against the closing plug. A spring is fitted on the valve; under hydraulic pressure, the valve separates from the closing plug to open the closing plug and compress the spring; and after injection, it abuts against the closing plug under the restoring force of the spring to close the closing plug. The structure of the closing assembly forms a single-flow valve core, which can prevent backflow.

[0012] The above-mentioned utility model effectively improves the reliability of the graded cement injection device, but its structure is relatively complex and may cause failure, so it still needs to be improved.

[0013] The above invention effectively solves and prevents the problem of cement slurry backflow, but its structure is relatively complex. Summary of the Invention

[0014] The purpose of this invention is to provide a staged cement injection device that can prevent cement backflow, solving the problems of insufficient reliability in current staged cement injection devices, such as premature opening of the opening sleeve and incomplete closing of the closing sleeve leading to backflow of the cement plug and cement solidification inside the casing. This invention simplifies the structure of the staged cement injection device, reduces manufacturing costs, and decreases its failure rate during operation.

[0015] The technical solution of this utility model is: a graded cement injection device that can prevent cement backflow, including an outer connecting cylinder, a closing sleeve, and a closing plug seat, wherein: the outer connecting cylinder with a first mud circulation hole and the closing sleeve with a second mud circulation hole are connected by a locking block and are also equipped with a retaining spring; the closing plug seat with a locking block exit groove that only allows liquid to flow downward, as well as the opening sleeve and the retaining ring, are all installed in the closing sleeve, and the closing sleeve and the closing plug seat are connected by a shear pin; the opening sleeve, the retaining ring, and the closing sleeve are connected in sequence by a shear pin and a thread.

[0016] Preferably, the inner wall of the outer connecting cylinder is further provided with a backstop ring and a snap ring release groove. The backstop ring is located above the closing sleeve and the closing plug seat. The inner diameter formed by the backstop ring is larger than the outer diameter of the later-added rubber plug and smaller than the outer diameter of the closing sleeve. The snap ring release groove is located in the inner wall of the outer connecting cylinder below the circulation hole.

[0017] Preferably, the outer connecting cylinder has two or more circulation holes, and the outer connecting cylinder is connected to the cementing string through connecting threads in the upper inner circle and the lower outer circle.

[0018] Preferably, the closing sleeve is further provided with a closing sleeve shear pin hole, a sealing ring and a retaining ring mounting groove. The closing sleeve and the closing plug are connected by shear pins installed in the closing sleeve shear pin hole. The sealing ring is installed on both sides of the circulation hole two, and a retaining ring can be installed in the retaining ring mounting groove.

[0019] Preferably, the closing plug seat is provided with an outlet hole, a spring rod, a spring, a float, and an inlet hole. The outlet hole is located in a connecting base connected to the body of the closing plug seat. A spring is installed on the outside of the spring rod connected to the connecting base. The spring is located between the float and the connecting base. The float can block the inlet hole located at the top of the closing plug seat.

[0020] Preferably, the liquid outlet is disposed in two or more connecting bases located on the outer periphery of the spring rod.

[0021] Preferably, the float is hemispherical and has an internal thread in the lower central hole that can be connected to the spring rod; the upper inner cavity of the closing plug is an arched inner cavity, and the liquid inlet hole communicates with the arched inner cavity and is located in the center of the arched inner cavity; the curvature of the arched inner cavity matches the curvature of the float.

[0022] Preferably, the spring rod and float are made of polymer engineering resin material.

[0023] Preferably, the opening sleeve is a non-uniform diameter cylindrical body with the outer diameter of the upper cylinder being larger than that of the lower cylinder; the lower end of the upper cylinder of the opening sleeve is provided with an opening sleeve anti-rotation key / groove, and the lower cylinder of the opening sleeve is provided with an opening sleeve shear pin groove; the opening sleeve shear pin groove can accommodate shear pins that connect with the retaining ring.

[0024] Preferably, the retaining ring is a non-uniform diameter cylindrical body with the outer circles at both ends being larger than the outer circle at the middle. The upper end of the retaining ring is provided with a retaining ring anti-rotation groove / key, which engages with the opening sleeve anti-rotation key / groove in the opening sleeve. The lower outer circle of the retaining ring is provided with an external thread and can be threadedly connected to the closing sleeve.

[0025] Compared with the prior art, this utility model, through structural improvements, can effectively prevent the opening sleeve from opening prematurely due to excessive excitation pressure during the installation process. Especially in the later stages of cementing, after the rubber plug collides with the device, it can effectively prevent cement backflow caused by the closing sleeve not closing tightly. Specifically, this is manifested in: 1. The device has a backflow preventer ring with an inner diameter larger than the outer diameter of the later-installed rubber plug on the inner wall of the outer connecting cylinder. The backflow preventer ring is set to further prevent cement backflow. If cement backflow occurs, the backflow preventer ring can prevent the lower components from pushing upwards and prevent cement from solidifying inside the casing due to the rubber plug returning upwards, which is commonly known as "sausage filling" and other serious problems, thus further preventing the occurrence of the above-mentioned accidents.

[0026] 2. A retaining ring is provided between the outer connecting cylinder and the closing sleeve in this device. When the upper rubber plug is inserted and the closing plug seat and the closing sleeve are pushed down together, the retaining ring can be locked into the retaining ring release groove in the outer connecting cylinder, which can effectively prevent the closing sleeve from moving up and down and causing the problem of incomplete closure.

[0027] 3. The shut-off plug in this device mainly consists of a spring rod, a spring, a float, an inlet hole, and an outlet hole. Under the combined action of the spring rod, spring, and float, the liquid can only flow downwards from the wellhead, and cannot flow upwards from the wellhead.

[0028] 4. The spring rod and float in the closing plug seat of this device are made of high polymer engineering resin material with good drillability, which can reduce the difficulty of drilling and reduce the amount of construction work caused by cement solidification in the casing.

[0029] This invention can be used for staged cementing in deep and ultra-deep wells, as well as cementing the top of the screen pipe in horizontal wells. It has significant effects and good application value. Attached Figure Description

[0030] The accompanying drawings are provided to further illustrate the present invention and form part of the specification. They are used together with the embodiments of the present invention to explain the present invention, but do not constitute a limitation thereof. In the drawings:

[0031] Figure 1 This is a schematic diagram of the structure of this utility model.

[0032] Figure 2 yes Figure 1 A schematic diagram of the structure of the open sleeve.

[0033] Figure 3 yes Figure 1 A schematic diagram of the middle retaining ring.

[0034] In the diagram: outer connecting sleeve 1, anti-reverse ring 1-1, circulation hole 1-2; closing sleeve 2, closing sleeve shear pin hole 2-1, circulation hole 2-2, sealing ring 2-3; closing plug seat 3, locking block exit groove 3-1; opening sleeve 4, opening sleeve shear pin groove 4-1, opening sleeve anti-rotation key / groove 4-2;

[0035] 5. Retaining ring; 5-1. Retaining ring anti-rotation groove / key; 6. Snap ring release groove; 7. Snap ring; 8. Locking block; 9. Liquid outlet hole; 10. Spring rod; 11. Spring; 12. Float; 13. Liquid inlet hole. Detailed Implementation

[0036] The accompanying drawings are for reference and illustration only and are not intended to limit the scope of protection of this utility model. The technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this utility model without creative effort are within the scope of protection of this utility model.

[0037] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present utility model and are not intended to limit the present utility model.

[0038] In the description of this utility model, it should be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this utility model 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 utility model. Furthermore, in the description of this utility model, "a plurality of" means two or more, unless otherwise explicitly specified.

[0039] See Figures 1-3A graded cement injection device capable of preventing cement backflow includes an outer connecting cylinder 1, a closing sleeve 2, and a closing plug seat 3, wherein: the outer connecting cylinder 1, which has a mud circulation hole 1-2, is connected to the closing sleeve 2, which has a mud circulation hole 2-2, by a locking block 8 and is also equipped with a retaining spring 7; the closing plug seat 3, which has a locking block exit groove 3-1 and only allows liquid to flow downward, as well as the opening sleeve 4 and the retaining ring 5, are all installed in the closing sleeve 2, and the closing sleeve 2 and the closing plug seat 3 are connected by shear pins; the opening sleeve 4, the retaining ring 5, and the closing sleeve 2 are connected in sequence by shear pins and threads.

[0040] The structure of this device is simpler, and with further reduction in manufacturing costs, it can improve the working stability of the device, reduce the failure rate during operation, and avoid adverse consequences after a failure occurs.

[0041] In its initial state, this device opens sleeve 4 to block the circulation hole 1-2 in the outer connecting cylinder 1 and closes the circulation hole 2-2 in sleeve 2, forming the mud circulation channel.

[0042] Before using this device for construction, first insert a rubber plug into the well, then connect this device to the cementing work string and lower it into the well.

[0043] In the early stages of construction, pressure is applied from the surface, and pressure-applying fluid enters through the cementing work string and the device. First, the shear pin between the opening sleeve 4 and the retaining ring 5 is cut off. Then, the construction fluid can flow through the fluid channel of the closing plug 3 (which only allows fluid to flow downwards), as well as circulation holes 1-2 and 2-2, to perform cementing and slurry injection operations on the oil well. Because the closing plug 3 (which only allows fluid to flow downwards) is equipped with shear pins between the opening sleeve 4 and the retaining ring 5 located below it, and the retaining ring 5 is threadedly connected to the closing sleeve 2, the opening sleeve 4 is well protected, preventing premature opening caused by excessively high pressure during installation and construction.

[0044] The closing sleeve 2 is connected to the threaded retaining ring 5 and also to the outer connecting cylinder 1 via a locking block 8. Furthermore, a retaining spring 7 is installed between the closing sleeve 2 and the outer connecting cylinder 1, ensuring a stable connection. This guarantees the reliability and stability of this invention, solving the problems of insufficient reliability in current graded cementing devices, such as premature opening of the opening sleeve and incomplete closing of the closing sleeve leading to backflow of the cement plug and cement solidification inside the casing. It demonstrates significant effectiveness in practical use.

[0045] In the later stages of construction, when the inserted rubber plug moves to the position of the closing plug seat 3, the shear pin between the closing plug seat 3 and the closing sleeve 2 is cut off under the action of the rubber plug. The closing plug seat 3 moves down to the position of the locking block exit groove 3-1, and the locking block 8 between the closing sleeve 2 and the outer connecting cylinder 1 is released into the locking block exit groove 3-1. The rubber plug drives the closing plug seat 3 and the closing sleeve 2 to move down together, closing the mud circulation channel formed by mud circulation hole 1-2 and mud circulation hole 2-2, thereby completing the cementing operation.

[0046] Based on the above embodiment one, the present invention also has the following embodiments:

[0047] In a preferred embodiment, the inner wall of the outer connecting cylinder 1 is further provided with a backstop ring 1-1 and a snap ring release groove 6. The backstop ring 1-1 is positioned above the closing sleeve 2 and the closing plug seat 3. The inner diameter of the backstop ring 1-1 is larger than the outer diameter of the later-installed rubber plug but smaller than the outer diameter of the closing sleeve 2. The snap ring release groove 6 is positioned in the inner wall of the outer connecting cylinder 1 below the circulation hole 1-2. When the rubber plug is installed in the later stage of cementing, pushing the closing plug seat 3 and the closing sleeve 2 downward together, the snap ring 7 can be engaged in the snap ring release groove 6, which can effectively prevent the closing sleeve 2 from not closing tightly and ensure the stable connection of the components inside the outer connecting cylinder 1. The backstop ring 1-1 is provided to further prevent cement backflow. If cement backflow occurs, the backstop ring 1-1 can prevent the lower components from pushing upward and prevent the cement from solidifying inside the casing due to the backflow of the lower rubber plug, which is commonly known as "sausage filling" and other serious problems, thus further preventing cement backflow accidents.

[0048] In a preferred embodiment, the outer connecting cylinder 1 has two or more circulation holes 1-2, and the outer connecting cylinder 1 is connected to the cementing string through connecting threads in the upper inner circle and the lower outer circle.

[0049] In a preferred embodiment, the closing sleeve 2 is further provided with a closing sleeve shear pin hole 2-1, a sealing ring 2-3, and a snap ring mounting groove. The closing sleeve 2 and the closing plug seat 3 are connected by shear pins installed in the closing sleeve shear pin hole 2-1. The sealing ring 2-3 is installed on both sides of the circulation hole 2-2, and the snap ring 7 can be installed in the snap ring mounting groove. The closing sleeve 2 is provided with sealing rings 2-3 on both sides of the circulation hole 2-2 to form a seal with the outer connecting cylinder 1. The outer connecting cylinder 1 has a snap ring release groove 6, which cooperates with the snap ring 7 installed in the closing sleeve 2. Combined with the single-flow action of the closing plug seat 3, it forms a double insurance, which is safer and more reliable than the prior art. When the closing sleeve 2 is completed after cementing and well cementing, it moves down to the snap ring release groove 6 in the inner wall of the outer connecting cylinder 1 under the push of the inserted rubber plug and the closing plug seat 3. The snap ring 7 is released and snaps into the snap ring release groove 6, locking the closing sleeve 2 and the outer connecting cylinder 1 together.

[0050] In a preferred embodiment, the shut-off plug 3 is provided with a liquid outlet 9, a spring rod 10, a spring 11, a float 12, and a liquid inlet 13. The liquid outlet 9 is located in a connecting base connected to the body of the shut-off plug 3. A spring 11 is installed on the outside of the spring rod 10 connected to the connecting base. The spring 11 is located between the float 12 and the connecting base, and the float 12 can block the liquid inlet 13 located at the top of the shut-off plug 3. Liquid pressurized from the surface, cement slurry circulating in the well, and mud can all push the float 12 in the shut-off plug 3 downwards and enter the annulus between the casing and the cementing work string through circulation holes 1-2 and 2-2.

[0051] In a preferred embodiment, the liquid outlet 9 is disposed in two or more connecting bases located on the outer periphery of the spring rod 10.

[0052] In a preferred embodiment: the float 12 is hemispherical and has an internal thread in the lower central hole that can connect with the spring rod 10; the upper inner cavity of the closing plug 3 is an arched inner cavity, and the liquid inlet 13 communicates with the arched inner cavity and is located in the center of the arched inner cavity; the curvature of the arched inner cavity matches the curvature of the float 12.

[0053] In a preferred embodiment, the spring rod 10 and float 12 are made of a high-molecular engineering resin material. This material has good drillability, and to prevent mud backflow or entrapment during cementing, the high-molecular engineering resin material used in the spring rod 10 and float 12 reduces drilling difficulty and facilitates subsequent processing.

[0054] In a preferred embodiment: the opening sleeve 4 is a non-uniform diameter cylindrical body with the outer diameter of the upper cylinder larger than that of the lower cylinder; the lower end of the upper cylinder of the opening sleeve 4 is provided with an opening sleeve anti-rotation key / groove 4-2, and the lower cylinder of the opening sleeve 4 is provided with an opening sleeve shear pin groove 4-1; the shear pin connected to the retaining ring 5 can be inserted into the opening sleeve shear pin groove 4-1. During ground compaction, the opening sleeve 4 shears the shear pin between itself and the retaining ring 5 by the difference in cross-sectional area between the upper and lower cross sections of the body. Its design structure is simpler.

[0055] In a preferred embodiment: the retaining ring 5 is a non-uniform diameter cylindrical body with the outer diameters at both ends larger than the outer diameter at the middle. The upper end of the retaining ring 5 is provided with a retaining ring anti-rotation groove / key 5-1, which engages with the opening sleeve anti-rotation key / groove 4-2 in the opening sleeve 4. The lower outer diameter of the retaining ring 5 is provided with external threads and can be threadedly connected to the closing sleeve 2. Through the threaded connection between the retaining ring 5 and the closing sleeve 2, the opening sleeve 4 and the closing sleeve 2 are connected together. After the shear pin between the retaining ring 5 and the opening sleeve 4 is broken, the opening sleeve 4 descends and engages with and rests against the retaining ring 5, resulting in a better, more reliable, and stable effect. Simultaneously, it ensures that when cement backflow requires drilling, the opening sleeve 4 and the retaining ring 5 will not rotate relative to each other, effectively improving drilling efficiency.

[0056] During the use of this device, when the closing plug seat 3 comes into contact with the later-added rubber plug, the closing plug seat 3 is pushed downward by the upper rubber plug and moves the closing sleeve 2 downward together, closing the mud circulation channel formed by the closing sleeve 2 and the circulation hole 1-2 and circulation hole 2-2 in the outer connecting cylinder 1, and the cementing well construction is completed.

[0057] This device reduces structural complexity, improves tool reliability, reduces the risk of subsequent drill plugging, and lowers the cost of subsequent drill plugging operations.

[0058] When using this device, during the initial ground pressurization, the sleeve 4 is opened to cut the shear pin between it and the retaining ring 5 by the difference in cross-sectional area between the upper and lower sections.

[0059] After cementing, the inserted rubber plug presses against the closing plug seat 3, and the shear pin between the closing plug seat 3 and the closing sleeve 2 is cut off by the inserted rubber plug. The closing plug seat 3 and the locking block 8 enter the locking block exit groove 3-1. The rubber plug pushes downward, causing the closing sleeve 2 and the closing plug seat 3 to move down together, closing the circulation holes 1-2 and 2-2 respectively set in the outer connecting cylinder 1 and the closing sleeve 2, thus completing the cementing operation.

[0060] This invention has a simple structure, and the opening and closing of the staged cement injector is safe and reliable, reducing construction risks.

[0061] The embodiments described above are merely typical examples, but the present invention is not limited to these embodiments. Those skilled in the art can make modifications without departing from the spirit and teachings of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the inventive spirit and concept of the present invention should be included within the protection scope of the present invention. Therefore, the protection scope is not limited to the above description.

Claims

1. A graded cement injection device capable of preventing cement backflow, comprising an outer connecting cylinder, a closing sleeve, and a closing plug seat, characterized in that, The outer connecting cylinder with mud circulation hole one is connected to the closing sleeve with mud circulation hole two by a locking block and is also equipped with a snap ring; the closing plug seat with locking block exit groove that only allows liquid to flow down, as well as the opening sleeve and the retaining ring are all installed in the closing sleeve, and the closing sleeve and the closing plug seat are connected by shear pins; the opening sleeve, the retaining ring and the closing sleeve are connected by shear pins and threads in sequence.

2. The graded cement injection device for preventing cement backflow as described in claim 1, characterized in that, The inner wall of the outer connecting cylinder is also provided with a backstop ring and a snap ring release groove. The backstop ring is located above the closing sleeve and the closing plug seat. The inner diameter formed by the backstop ring is larger than the outer diameter of the later-added rubber plug and smaller than the outer diameter of the closing sleeve. The snap ring release groove is located in the inner wall of the outer connecting cylinder below the circulation hole.

3. A graded cement injection device for preventing cement backflow as described in claim 2, characterized in that, The outer connecting cylinder has two or more circulation holes, and the outer connecting cylinder is connected to the cementing string through connecting threads in the upper inner circle and the lower outer circle.

4. A graded cement injection device for preventing cement backflow as described in claim 3, characterized in that, The closing sleeve is also provided with a closing sleeve shear pin hole, a sealing ring and a snap ring mounting groove. The closing sleeve and the closing plug are connected by shear pins installed in the closing sleeve shear pin hole. The sealing ring is installed on both sides of the circulation hole two, and a snap ring can be installed in the snap ring mounting groove.

5. A graded cement injection device capable of preventing cement backflow as described in claim 1, 2, 3, or 4, characterized in that, The closing plug seat is provided with a liquid outlet, a spring rod, a spring, a float, and a liquid inlet. The liquid outlet is located in the connecting base connected to the main body of the closing plug seat. A spring is installed on the outside of the spring rod connected to the connecting base. The spring is located between the float and the connecting base. The float can block the liquid inlet located at the top of the closing plug seat.

6. A graded cement injection device as described in claim 5, characterized in that, The liquid outlet is located in two or more connecting bases on the outer periphery of the spring rod.

7. A graded cement injection device for preventing cement backflow as described in claim 5, characterized in that, The float is hemispherical and has an internal thread in the lower center hole that can connect to the spring rod; the upper inner cavity of the closing plug is an arched inner cavity, and the liquid inlet hole communicates with the arched inner cavity and is located in the center of the arched inner cavity; the curvature of the arched inner cavity matches the curvature of the float.

8. A graded cement injection device for preventing cement backflow as described in claim 7, characterized in that, The spring rod and float are made of polymer engineering resin material.

9. A graded cement injection device for preventing cement backflow as described in claim 5, characterized in that, The opening sleeve is a non-uniform diameter cylindrical body with the outer diameter of the upper cylinder being larger than that of the lower cylinder; the lower end of the upper cylinder of the opening sleeve is provided with an opening sleeve anti-rotation key / groove, and the lower cylinder of the opening sleeve is provided with an opening sleeve shear pin groove; the opening sleeve shear pin groove can accommodate shear pins that connect with the retaining ring.

10. A graded cement injection device for preventing cement backflow as described in claim 9, characterized in that, The retaining ring is a non-uniform diameter cylindrical body with the outer circles at both ends being larger than the outer circle at the middle. The upper end of the retaining ring is provided with a retaining ring anti-rotation groove / key, which engages with the opening sleeve anti-rotation key / groove in the opening sleeve. The lower outer circle of the retaining ring is provided with an external thread and can be threadedly connected to the closing sleeve.

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