Pressure stabilizing device for cementing plug and cementing plug system

Abstract

The utility model provides a pressure stabilizing device for a cementing plug and a cementing plug system, and belongs to the technical field of well packing. The pressure stabilizing device for the cementing plug comprises a buffer container used for storing liquid and a connecting pipe communicated with the buffer container, and the connecting pipe is provided with an installation connector used for being connected with a wellhead device so that the connecting pipe can be communicated with an annular space between a sleeve and an oil pipe. The buffer container is provided with a driving device used for squeezing liquid in the buffer container into the connecting pipe when the pressure in the connecting pipe is lower than balance pressure for preventing the unsolidified cement plug from moving upwards. The cement plug injection system comprises the pressure stabilizing device for cement plug injection. The pressure stabilizing device for the cementing plug is used for stabilizing the pressure in a well in the construction process of the cementing plug, so that the situation that the stability of the cement plug is affected by unbalanced pressure on the upper side and the lower side of the cement plug when the pressure in the well fluctuates is prevented.

Description

Technical Field

[0001] The utility model belongs to the technical field of wellbore isolation, in particular to a pressure stabilizing device for cementing plugs and a cementing plug system. Background Art

[0002] There are differences in water content and pressure in various strata of multi-layer oil fields. During the development process, especially in the later stage of water injection development, the contradictions between layers become more and more prominent. For the high-water-content strata in the lower part that are temporarily unused or abandoned, it is necessary to inject cement plugs in the oil and water wells for sealing.

[0003] The general process of cement plugging is: lower the tubing into the casing and place its lower end above the formation to be sealed, then inject clean water from the tubing for positive circulation well washing to clean the wellbore and cool the wellbore, then inject cement slurry from the tubing into the well and use clean water to displace it, so that the cement slurry in the tubing is sent to the set position in the wellbore, then lift the tubing 1-2m, and inject clean water into the well from the annulus between the tubing and the casing for reverse circulation well washing to wash out the excess cement slurry in the wellbore and tubing, and finally wait for the cement slurry to solidify to form a cement plug.

[0004] In actual projects, there is overflow in the stratum below the cement plug. On the one hand, the injected cement slurry is easily diluted by the overflow before solidification, which affects the normal solidification of the cement slurry. On the other hand, the overflow will push the cement slurry upward, so that the injected cement slurry cannot stay in the preset position.

[0005] The existing Chinese utility model patent with authorization announcement number CN217176567U discloses an anti-overflow ash pipe column, which includes an oil pipe and an anti-overflow ash valve arranged on the oil pipe. The anti-overflow ash valve includes a valve body and an upper joint and a lower joint arranged at both ends of the valve body. The valve body is provided with a first channel and a second channel that pass through the valve body from top to bottom in parallel. The first channel is provided with a first one-way valve structure for controlling the one-way conduction of liquid from top to bottom, and the second channel is provided with a second one-way valve structure for realizing the one-way conduction of liquid from bottom to top. The anti-overflow ash pipe column in the utility model patent is applied to oil wells where the formation above the cement plug is prone to overflow, which can prevent the upper overflow from continuously flowing upward from the oil pipe through the cement plug and carry away the cement slurry on the upper layer of the unsolidified cement plug, but the upper overflow will not pass through the cement plug in the process of flowing upward from the annulus between the oil pipe and the casing, so it will not affect the cement plug.

[0006] When the above-mentioned anti-overflow ash pipe column cement plug is used for construction and overflow occurs in the lower formation of the cement plug, the upper part of the annular space between the oil pipe and the casing can be closed and the return liquid can be discharged by the pressure relief valve during reverse circulation well washing to keep the pressure in the oil and water well above the cement plug balanced with the overflow pressure below the cement plug, thereby maintaining the stability of the cement plug. However, in actual use, the pressure of cement slurry and the liquid used for well washing will fluctuate due to the influence of pumping equipment, and the opening and closing action of the pressure relief valve will also cause instantaneous pressure fluctuations, resulting in a short-term imbalance in the pressure on the upper and lower sides of the cement plug, thereby affecting the stability of the cement plug. Utility Model Content

[0007] One of the purposes of the utility model is to provide a pressure stabilizing device for cement plugging, so as to solve the technical problem in the prior art that the pressure in the well is prone to fluctuate during the cement plugging construction process, thus affecting the stability of the cement plug.

[0008] One of the purposes of the utility model is to provide a cement plug system to solve the above-mentioned technical problems.

[0009] In order to achieve the above-mentioned purpose, the technical solution of the pressure stabilizing device for cementing plug provided by the utility model is:

[0010] A pressure stabilizing device for cement plug injection comprises a buffer container for storing liquid and a connecting pipe connected to the buffer container, the connecting pipe having a mounting interface for connecting to a wellhead device so as to communicate the connecting pipe with the annular space between the casing and the oil pipe, and the buffer container is provided with a driving device for squeezing the liquid in the buffer container into the connecting pipe when the pressure in the connecting pipe is lower than the equilibrium pressure for preventing the unsolidified cement plug from moving upward.

[0011] As a further improvement, the connecting pipe also has a pumping interface for connecting a pumping device to pump liquid into the buffer container.

[0012] As a further improvement, a first stop valve is provided on the connecting pipe, the first stop valve is located between the buffer container and the installation interface, and the first stop valve is closed before the liquid is pumped into the buffer container by using the pumping equipment.

[0013] As a further improvement, a safety valve is provided on the connecting pipe to prevent the liquid in the connecting pipe from flowing back to the pumping interface, and the safety valve is located between the pumping interface and the buffer container.

[0014] As a further improvement, at least two safety valves are provided, and at least one of them is a one-way valve.

[0015] As a further improvement, the driving device is a gas storage tank for storing pressurized gas, and a conducting pipe is provided between the gas storage tank and the buffer container for connecting the two.

[0016] As a further improvement, a control valve for controlling whether the gas in the gas storage tank flows out is provided on the conducting pipe.

[0017] As a further improvement, the connecting pipe is provided with a pressure relief valve for discharging the liquid in the connecting pipe when the pressure in the connecting pipe is higher than the equilibrium pressure.

[0018] As a further improvement, the connecting pipe includes a main pipe and a branch pipe, the pressure relief valve is arranged on the branch pipe, one end of the main pipe constitutes an installation interface, and the other end constitutes a pumping interface for connecting a pumping device to pump liquid into the buffer container, and a second stop valve is arranged on the branch pipe upstream of the pressure relief valve.

[0019] The beneficial effect is that the utility model provides a pioneering pressure stabilizing device for cementing plugs. The buffer container in the pressure stabilizing device for cementing plugs can be connected to the annular space between the casing and the oil pipe through a connecting pipe, and a certain amount of liquid is pre-stored in the forward buffer container. When the pressure in the well fluctuates, especially when the pressure in the well decreases, the liquid in the buffer container will enter the connecting pipe under the drive of the driving device, and then be supplemented into the annular space between the casing and the oil pipe, so as to slow down the pressure fluctuation in the well, so that the cementing plug will not move up due to the pressure fluctuation.

[0020] To achieve the above purpose, the technical solution of the cement plug system provided by the utility model is:

[0021] A cementing plug system comprises a casing and an oil pipe arranged in the casing, a wellhead device is arranged at the upper end of the casing, the oil pipe is provided with an anti-overflow ash valve, the wellhead device is connected to a pressure stabilizing device for cementing plugs, the pressure stabilizing device for cementing plugs comprises a buffer container for storing liquid and a connecting pipe connected to the buffer container, the connecting pipe has a mounting interface for connecting to the wellhead device so that the connecting pipe is connected to the annular space between the casing and the oil pipe, and the buffer container is provided with a driving device for squeezing the liquid in the buffer container into the connecting pipe when the pressure in the connecting pipe is lower than the equilibrium pressure for preventing the unsolidified cement plug from moving upward.

[0022] As a further improvement, the connecting pipe also has a pumping interface for connecting a pumping device to pump liquid into the buffer container.

[0023] As a further improvement, a first stop valve is provided on the connecting pipe, the first stop valve is located between the buffer container and the installation interface, and the first stop valve is used to close before the liquid is pumped into the buffer container by using the pumping equipment.

[0024] As a further improvement, a safety valve is provided on the connecting pipe to prevent the liquid in the connecting pipe from flowing back to the pumping interface, and the safety valve is located between the pumping interface and the buffer container.

[0025] As a further improvement, at least two safety valves are provided, and at least one of them is a one-way valve.

[0026] As a further improvement, the driving device is a gas storage tank for storing pressurized gas, and a conducting pipe is provided between the gas storage tank and the buffer container for connecting the two.

[0027] As a further improvement, a control valve for controlling whether the gas in the gas storage tank flows out is provided on the conducting pipe.

[0028] As a further improvement, the connecting pipe is provided with a pressure relief valve for discharging the liquid in the connecting pipe when the pressure in the connecting pipe is higher than the equilibrium pressure.

[0029] As a further improvement, the connecting pipe includes a main pipe and a branch pipe, the pressure relief valve is arranged on the branch pipe, one end of the main pipe constitutes an installation interface, and the other end constitutes a pumping interface for connecting a pumping device to pump liquid into the buffer container, and a second stop valve is arranged on the branch pipe upstream of the pressure relief valve.

[0030] The beneficial effect is that the utility model provides a pioneering cement plug system. The buffer container in the cement plug system can be connected to the annular space between the casing and the oil pipe through a connecting pipe, and a certain amount of liquid is pre-stored in the forward buffer container. When the pressure in the well fluctuates, especially when the pressure in the well decreases, the liquid in the buffer container will enter the connecting pipe under the drive of the driving device, and then be supplemented into the annular space between the casing and the oil pipe, so as to slow down the pressure fluctuation in the well and prevent the cement plug from moving up due to the pressure fluctuation. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a structural schematic diagram of a cement plug system in one embodiment of the utility model;

[0032] Figure 2 It is a schematic structural diagram of a pressure stabilizing device for cement plugging in one embodiment of the utility model.

[0033] Description of reference numerals:

[0034] 1. Casing; 2. Oil pipe; 3. Wellhead large cross-joint; 4. Self-sealing well sealer; 5. Anti-overflow ash valve; 6. Pressure stabilizing device for cement plug; 601. Gas storage tank; 602. Buffer tank; 603. Connecting pipe; 6031. Installation interface; 6032. Pumping interface; 604. Pressure relief valve; 605. Conducting pipe; 606. Control valve; 607. Inspection branch pipe; 608. Pressure gauge; 609. Third stop valve; 610. One-way valve; 611. Manual valve; 612. First stop valve; 613. Second stop valve; 7. First gate valve; 8. Second gate valve; 9. Cement plug; 10. Bakelite plug; 11. Upper formation; 12. Lower formation. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below in conjunction with the embodiments.

[0036] In view of the problems in the prior art, the basic concept of the utility model is to utilize a pressure stabilizing device for cement plugging to stabilize the pressure in the well during the cement plugging construction process, thereby preventing the pressure imbalance on the upper and lower sides of the cement plug from affecting the stability of the cement plug when the pressure in the well fluctuates.

[0037] Specific embodiments of the cementing plug system provided by the utility model:

[0038] A cement plug system, see attached Figure 1 , including a casing 1 arranged in an oil and water well, an oil pipe 2 arranged in the casing 1, a wellhead device arranged on the top of the casing 1, and the wellhead device specifically including a wellhead big four-way 3 connected to the casing 1 and a self-sealing well sealer 4 for sealing the annular space between the casing 1 and the oil pipe 2. The oil pipe 2 is provided with an anti-overflow ash valve 5, the structure of which is the same as that of the anti-overflow ash valve 5 in the Chinese utility model patent with the authorization announcement number CN217176567U, which can realize the unidirectional conduction of the liquid in the oil pipe 2 from top to bottom under a certain pressure, and can also realize the unidirectional conduction of the liquid in the oil pipe 2 from bottom to top under a certain pressure, and when the anti-overflow ash valve 5 is unidirectionally conducted from bottom to top, its opening pressure can be set according to actual conditions.

[0039] The cementing plug system also includes a pressure stabilizing device 6 for cementing plugs, see attached Figure 2 The pressure stabilizing device 6 for cementing plugs includes a gas storage tank 601, a buffer container and a connecting pipe 603. The connecting pipe 603 includes a main pipe and two branch pipes arranged on the main pipe, and the two ends of the main pipe are respectively an installation interface 6031 and a pumping interface 6032, wherein the installation interface 6031 is connected to the wellhead big four-way 3 and a first gate valve 7 is arranged between the wellhead big four-way 3, and the pumping interface 6032 is connected to a pumping device for pumping liquid into the connecting pipe 603. A second gate valve 8 is arranged at another interface of the wellhead big four-way 3.

[0040] In this embodiment, the buffer container is a buffer tank 602, and in other embodiments, it can also be a buffer cylinder or a buffer bottle. One branch of the connecting pipe 603 is connected to the buffer tank 602 so that the inner cavity of the buffer tank 602 is connected to the inner cavity of the connecting pipe 603, and the branch is connected to the bottom of the buffer tank 602. A pressure relief valve 604 is installed on the other branch of the connecting pipe 603, and the opening pressure of the pressure relief valve 604 can be adjusted as needed.

[0041] A conducting pipe 605 is provided between the gas storage tank 601 and the buffer tank 602 to connect the two, and the conducting pipe 605 is connected to the top of the buffer tank 602. A control valve 606 is provided on the conducting pipe 605, and the conducting pipe 605 is also connected to a detection branch pipe 607, a pressure gauge 608 is installed at the end of the detection branch pipe 607, and a third stop valve 609 is also provided on the detection branch pipe 607.

[0042] A safety valve is provided on the main pipe of the connecting pipe 603 to prevent the liquid in the connecting pipe 603 from flowing back to the pumping interface 6032. There are two safety valves and both are located between the pumping interface 6032 and the branch pipe connected to the buffer tank 602. One of the safety valves is a one-way valve 610 and the other is a manual valve 611.

[0043] A first stop valve 612 is provided on the main pipe of the connecting pipe 603, and the first stop valve 612 is located between the branch pipe connected to the buffer tank 602 and the installation interface 6031. A second stop valve 613 is provided on the installation pipe, and the second stop valve 613 is located upstream of the pressure relief valve 604. The second stop valve 613 is provided to improve reliability and facilitate maintenance after the pressure relief valve 604 fails. In other embodiments, the second stop valve 613 may not be provided.

[0044] The construction process using the cement plug system in this embodiment is as follows:

[0045] (1) Lower the oil pipe 2 and use the lower end of the oil pipe 2 to push the rubber plug 10 to the position of the cement plug 9. The position of the cement plug 9 is between the upper stratum 11 and the lower stratum 12. Connect the anti-overflow ash valve 5 to the oil pipe 2 and lower it into the well. Adjust the opening pressure of the anti-overflow ash valve 5 for unidirectional conduction from bottom to top and make the difference between it and the stable wellhead pressure when shutting in the well greater than 0MPa and less than or equal to 5MPa. The difference is preferably 2MPa. The stable wellhead pressure when shutting in the well is the equilibrium pressure when the pressure above and below the unsolidified cement plug 9 is balanced. The depth of the anti-overflow ash valve 5 = the depth of the oil pipe 2 - the depth of the oil pipe 2 when backwashing the well + 110 meters.

[0046] (2) Install the self-sealing well sealer 4.

[0047] (3) Connect the installation interface 6031 to the first gate valve 7 on the wellhead large four-way 3.

[0048] (4) Clean water is used for positive circulation well washing. Clean water enters the well from the oil pipe 2 from top to bottom, and then returns to the wellbore from the annular space between the oil pipe 2 and the casing 1 from bottom to top. The clean water returned from the wellbore can be directly discharged by opening the second gate valve 8, without passing through the pressure stabilizing device 6 for cementing plugs. In other embodiments of positive circulation well washing with clean water, the clean water returned from the oil well can also pass through the pressure stabilizing device 6 for cementing plugs 9 and be discharged from the pressure relief valve 604. In this embodiment, step (5) needs to be performed in advance.

[0049] (5) Before using the pressure stabilizing device 6 for cementing plugs, adjust the opening pressure of the pressure relief valve 604 and make the difference between it and the stable wellhead pressure when the well is shut in greater than 0 MPa and less than or equal to 5 MPa, and the difference is preferably 2 MPa. Close the first stop valve 612, open the second stop valve 613 and the manual valve 611, connect the pumping equipment to the pumping interface 6032, and pump clean water into the buffer tank 602. Then open the control valve 606 to allow the pressurized nitrogen stored in the gas storage tank 601 to enter the buffer tank 602. At this time, the upper part of the buffer tank 602 is nitrogen and the lower part is clean water. Initially, the pressure value in the buffer tank 602 is slightly greater than the opening pressure value of the pressure relief valve 604, and the pressure relief valve 604 will discharge a certain amount of clean water, and finally the pressure value in the buffer tank 602 is equal to the opening pressure value of the pressure relief valve 604.

[0050] (6) The second gate valve 8 is closed and the first gate valve 7 is opened to connect the pressure stabilizing device 6 for cementing plug to the annular space between the oil pipe 2 and the casing 1.

[0051] (7) Replace cement slurry and clean water according to the designed amount. During this process, a certain amount of clean water in the wellbore returns from the annulus between the oil pipe 2 and the casing 1 and is discharged through the pressure relief valve 604.

[0052] (8) The pumping equipment connected to the pressure stabilizing device 6 for cementing plugs continuously pumps clean water into the connecting pipe 603, keeps clean water flowing out of the pressure relief valve 604, and then lifts the oil pipe 2 to the position of reverse circulation well washing. In this process, since the pumping equipment continuously pumps clean water, it can compensate for the decrease in well pressure caused by lifting the oil pipe 2, and keep the pressure on the upper and lower sides of the cement plug 9 always balanced.

[0053] (9) Close the first gate valve 7, open the second gate valve 8, and connect another pumping device to the second gate valve 8 to pump clean water into the annular space between the oil pipe 2 and the casing 1 to perform reverse circulation well washing. The clean water flows from top to bottom in the annular space between the oil pipe 2 and the casing 1, then flows from the oil pipe 2 from bottom to top, and finally is discharged from the oil pipe 2 through the anti-overflow ash valve 5, and the excess cement slurry is washed out in the process. In other embodiments of reverse circulation well washing, it is also possible not to connect another pumping device to the second gate valve 8. In this case, the pumping device connected to the pressure stabilizing device 6 for cementing plugs continues to be used to pump clean water, but the second stop valve 613 needs to be closed at this time.

[0054] (10) Close the second gate valve 8, open the first gate valve 7, and continue to pump clean water through the pumping equipment connected to the pressure stabilizing device 6 for cementing the cement plug, keep the pressure relief valve 604 draining clean water, lift the oil pipe 2, and the lifting height is 100 meters. Finally, close the first gate valve 7, shut in the well and wait for solidification.

[0055] During the construction process, the upper part of the annular space between the casing 1 and the oil pipe 2 is closed, and the pressure relief valve 604 can be used to discharge the excess liquid in the annular space between the casing 1 and the oil pipe 2, and the pressure in the well can be maintained to prevent the cement plug 9 from being pushed upward by the overflow of the lower formation 12 after the pressure on the upper and lower sides of the cement plug 9 is unbalanced, and the cement plug 9 cannot be formed between the upper formation 11 and the lower formation 12. Continuously pumping liquid into the well while lifting the oil pipe 2 can keep the pressure of the liquid in the well stable, ensure that the pressure on the upper and lower sides of the cement plug 9 is always balanced during the process of lifting the oil pipe 2, and prevent the cement plug 9 from being pushed upward by the overflow of the lower formation 12, and the cement plug 9 cannot be formed between the upper formation 11 and the lower formation 12.

[0056] In response to the instantaneous fluctuation of the well pressure during the construction process, the buffer tank 602 can effectively buffer and reduce the fluctuation amplitude of the well pressure. For example, when the well pressure starts to drop from the equilibrium pressure, the liquid in the buffer tank 602 will be discharged from the buffer tank 602 and enter the connecting pipe 603 under the impetus of nitrogen to make up for the pressure loss; when the well pressure increases, part of the liquid will re-enter the buffer tank 602; if the well pressure continues to increase, part of the liquid will be leaked from the pressure relief valve 604 to avoid the continuous increase of the well pressure and ensure the pressure stability. Therefore, the pressure stabilization device 6 used for cementing plugs can ensure the stability of the well pressure during the entire construction process, and the cement plug 9 will not move up due to pressure fluctuations.

[0057] In the above embodiments, the pressure relief valve is arranged on one of the branches of the connecting pipe, on the one hand, in order to facilitate the reservation of a pumping interface for connecting the pumping equipment on the main pipe, and on the other hand, to make the cementing plug system more compact. In other embodiments, the pumping equipment may not be connected to the pressure stabilizing device for cementing plugs, but the pumping equipment may be connected to other interfaces of the wellhead large four-way. In this case, it is not necessary to reserve a pumping interface for connecting the pumping equipment on the main pipe, so the pressure relief valve can be installed at the end of the main pipe, and no branch pipe for installing the pressure relief valve is reserved. In this embodiment, a filling port for filling liquid into the buffer tank can be set on the buffer tank to facilitate the pre-storage of liquid; the function of the first stop valve is to close before the pumping equipment injects liquid into the buffer tank to prevent the liquid from entering the well, but in this embodiment, since it is not necessary to use the pumping equipment to inject liquid into the buffer tank, the first stop valve may not be set. In other embodiments, the pressure relief valve may also be installed on other interfaces of the wellhead large four-way, and no branch pipe for installing the pressure relief valve is reserved.

[0058] In the above embodiments, the safety valve is used to prevent the liquid from flowing back to the pumping interface during the process of replacing cement slurry and replacing clean water, and one of them is set as a one-way valve for easy operation. In other embodiments, only one safety valve can be set and the safety valve is a manual valve. The safety valve is closed when replacing cement slurry and replacing clean water, and opened when injecting liquid into the buffer tank or lifting the oil pipe. When replacing cement slurry and replacing clean water, if the liquid is discharged through the pressure relief valve installed at other interfaces of the wellhead large four-way, the safety valve may not be set. In this case, the first gate valve can be directly closed.

[0059] In the above embodiments, the gas tank is used as a driving device and a control valve and a pressure gauge are arranged on the conducting pipe, which can facilitate control and use, and facilitate the acquisition and storage of pressurized gas. In other embodiments, the control valve may not be arranged. In this embodiment, the gas tank only provides storage space for pressurized air. Before construction, the gas tank is filled with pressurized gas using an air pump.

[0060] In the above embodiments, the pressurized gas stored in the gas storage tank is nitrogen because nitrogen has better stability and is safer for oil and water well field construction than air. In other embodiments, air can also be stored in the gas storage tank.

[0061] In other embodiments, the driving device may also have other forms. For example, the buffer container may also be a rubber bag, which expands when the pressure in the well is stable, and contracts when the pressure in the well decreases, so that part of the liquid in the rubber bag is injected into the connecting pipe and enters the well.

[0062] In the above embodiments, the liquid for washing the well is clean water. In other embodiments, a specially configured well washing liquid may also be used.

[0063] Specific embodiments of the pressure stabilizing device for cementing plugs provided by the utility model:

[0064] The pressure stabilizing device for the cementing plug is the pressure stabilizing device for the cementing plug in the embodiment of the cementing plug system, which will not be described in detail here.

[0065] Finally, it should be noted that the above is only a preferred embodiment of the utility model and is not intended to limit the utility model. Although the utility model is described in detail with reference to the above embodiments, those skilled in the art can still modify the technical solutions recorded in the above embodiments without creative work, or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the utility model shall be included in the protection scope of the utility model.

Claims

1. A pressure stabilizing device for cementing plugs, characterized in that: It comprises a buffer container for storing liquid and a connecting pipe connected to the buffer container. The connecting pipe has a mounting interface for connecting to a wellhead device so as to communicate the connecting pipe with the annular space between the casing and the oil pipe. The buffer container is provided with a driving device for squeezing the liquid in the buffer container into the connecting pipe when the pressure in the connecting pipe is lower than the equilibrium pressure for preventing the unsolidified cement plug from moving upward.

2. The pressure stabilizing device for cementing plugs according to claim 1, characterized in that: The connecting pipe also has a pumping interface for connecting a pumping device to pump liquid into the buffer container.

3. The pressure stabilizing device for cementing plugs according to claim 2, characterized in that: A first stop valve is arranged on the connecting pipe, and the first stop valve is located between the buffer container and the installation interface. The first stop valve is closed before the liquid is pumped into the buffer container by using the pumping equipment.

4. The pressure stabilizing device for cementing plugs according to claim 2 or 3, characterized in that: The connecting pipe is provided with a safety valve for preventing the liquid in the connecting pipe from flowing back to the pumping interface, and the safety valve is located between the pumping interface and the buffer container.

5. The pressure stabilizing device for cementing plugs according to claim 4, characterized in that: At least two safety valves are provided, and at least one of them is a one-way valve.

6. The pressure stabilizing device for cementing plugs according to any one of claims 1 to 3, characterized in that: The driving device is a gas storage tank for storing pressurized gas, and a conducting pipe for connecting the gas storage tank and the buffer container is arranged between the gas storage tank and the buffer container.

7. The pressure stabilizing device for cement plugging according to claim 6, characterized in that: The conducting pipe is provided with a control valve for controlling whether the gas in the gas storage tank flows out.

8. The pressure stabilizing device for cementing plugs according to any one of claims 1 to 3, characterized in that: The connecting pipe is provided with a pressure relief valve for discharging the liquid in the connecting pipe when the pressure in the connecting pipe is higher than the equilibrium pressure.

9. The pressure stabilizing device for cement plugging according to claim 8, characterized in that: The connecting pipe includes a main pipe and a branch pipe, the pressure relief valve is arranged on the branch pipe, one end of the main pipe constitutes a mounting interface, and the other end constitutes a pumping interface for connecting a pumping device to pump liquid into the buffer container, and a second stop valve is arranged on the branch pipe upstream of the pressure relief valve.

10. A cement plug system, comprising a casing and an oil pipe arranged in the casing, a wellhead device is arranged at the upper end of the casing, and an anti-overflow ash valve is arranged on the oil pipe, wherein: The wellhead device is connected to a pressure stabilizing device for cementing plugs according to any one of claims 1 to 9.

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