Pressure slow-release ball seat for well cementation and pressure slow-release method for well cementation operation

Abstract

The invention provides a pressure slow-release ball seat which comprises a ball seat shell and a pressure slow-release ball seat, the locking seat is arranged in the ball seat shell and is fixedly connected with the ball seat shell; the compression sleeve is arranged in the locking seat, and a liquid cavity is formed between the compression sleeve and the locking seat; the valve mechanism is arranged between the compression sleeve and the locking seat and comprises a rupture disc; and the ball seat body is arranged in the compression sleeve. In the initial state, the ball seat body and the compression sleeve are mutually locked through the check block, and the liquid cavity is filled with pressure liquid. The rupture disc is configured to rupture in the first pressure building state, so that the pressure liquid in the liquid cavity can flow out. The compression sleeve is configured to move downstream in the second pressure building state, locking of the check block on the ball seat body is released, and therefore the ball seat body can independently move downstream. The invention further provides a pressure slow-release method for well cementation operation by using the pressure slow-release ball seat.

Description

Technical Field

[0001] The invention relates to cementing technology in the petroleum engineering industry, and more particularly to a pressure-releasing ball seat and a pressure-releasing method for cementing operations. Background Art

[0002] The liner hanging cementing process is a commonly used cementing process in petroleum engineering, in which the liner hanger is connected mainly through the drill pipe to send the liner downhole, thereby completing the liner hanging and liner cementing.

[0003] In the liner cementing technology, in order to reduce the length of the plug and reduce the drilling time, the ball seat is generally located at the bottom of the liner, 30-100m away from the bottom of the well. The conventional liner hanger is a hydraulically activated suspension mechanism, that is, a ball is thrown into the ball seat in the pipe to form a pressure in the pipe, which activates the suspension mechanism of the hanger. After the liner is suspended, the pressure is continued to destroy the ball seat pressure device, and the liner cementing operation is carried out after a circulation channel is formed. In order to improve the reliability of the liner hanger and its supporting tools, it is necessary to open the pump multiple times during the liner lowering process to circulate and unblock, so as to reduce the pressure after the liner is lowered into place.

[0004] In order to avoid the accident of premature seating of the liner hanger due to the top circulation of the pump during the liner lowering process, the seating pressure of the liner hanger is generally designed to be relatively high, and the shear pressure of the corresponding ball seat is also designed to be relatively high, generally in the range of 16-23MPa. Since the instantaneous release of the pressure of the ball seat will generate instantaneous pressure on the bottom of the well, it directly acts on the bottom of the well. Therefore, in the case of weak formations prone to leakage in the well, it is easy to compress the formation and cause the loss of drilling fluid, making it impossible to carry out liner cementing. In this case, it is necessary to carry out circulation plugging or remove the liner string and then plug the leak, which greatly increases the construction risk and economic investment.

[0005] To this end, Chinese patent CN 202788755U proposes a solution. In order to reduce the initial pressure when the ball seat is detached, a bipolar pressure holding method is adopted, that is, a primary ball seat and a secondary ball seat are provided, and they and the outer cylinder are provided with circumferentially evenly arranged and mutually corresponding through holes. Although this structure can reduce the probability of the ball seat penetrating the formation to a certain extent, it cannot guarantee that the initial pressure applied to the ball seat during the secondary pressure holding cannot penetrate the formation.

[0006] Therefore, there is a need in the art to improve the liner suspension cementing pressure holding system to reduce formation leakage caused by instantaneous pressure release. Summary of the invention

[0007] In view of the above technical problems existing in the prior art, the present invention provides a pressure release ball seat for cementing and a pressure release method for cementing operation. Through the pressure release ball seat, after the tail pipe is suspended after the pressure is held in the pipe, the high pressure in the pipe can be slowly released, thereby effectively avoiding the impact of the instantaneous release of high pressure on the formation.

[0008] According to a first aspect of the present invention, a pressure-release ball seat is proposed, which includes: a ball seat shell; a locking seat arranged in the ball seat shell and fixedly connected thereto; a compression sleeve arranged in the locking seat, a liquid cavity is formed between the compression sleeve and the locking seat; a valve mechanism arranged between the compression sleeve and the locking seat, the valve mechanism including a rupture disk; and a ball seat body arranged in the compression sleeve. Wherein, in the initial state, the ball seat body is locked with the compression sleeve by a stopper, and the liquid cavity is filled with pressurized liquid. The rupture disk is configured to rupture in a first pressure-holding state, so that the pressurized liquid in the liquid cavity can flow out. The compression sleeve is configured to move downstream in a second pressure-holding state, releasing the lock of the stopper on the ball seat body, so that the ball seat body can move downstream independently.

[0009] In a preferred embodiment, the pressure-release ball seat proposed in the present invention also includes an emergency shear sleeve arranged between the compression sleeve and the locking seat and downstream of the valve mechanism. The emergency shear sleeve is connected to the locking seat through a first shear pin, and the first shear pin is configured to be sheared when the pressure is greater than the pressure in the second pressure-holding state.

[0010] In a preferred embodiment, the liquid chamber is formed upstream of the valve mechanism, and the emergency shear sleeve has a first through hole, so that after the rupture disk ruptures, the pressure liquid in the liquid chamber can flow through the valve mechanism and the first through hole to the downstream of the pressure relief ball seat.

[0011] In a preferred embodiment, a second through hole is formed on the wall of the compression sleeve, and the stopper is arranged in the second through hole, so that the radial outer end of the stopper abuts against the emergency shear sleeve, and the radial inner end extends into a blind groove formed in the wall of the ball seat body.

[0012] In a preferred embodiment, the emergency shear sleeve includes a step portion arranged in its inner cavity, and a limit sleeve is provided on the step portion, wherein the axial upper end of the limit sleeve abuts against the valve mechanism, and the radial inner end abuts against the radial outer end of the stop block.

[0013] In a preferred embodiment, the outer diameter of the upper end of the limiting sleeve is smaller than the inner diameter of the emergency shear sleeve, so that an outflow channel communicating with the first through hole is formed between the emergency shear sleeve and the limiting sleeve.

[0014] In a preferred embodiment, the lower end of the emergency shear sleeve has a limiting portion for limiting the downward movement stroke of the compression sleeve, and a pressure relief port is provided on the limiting portion.

[0015] In a preferred embodiment, an injection hole is provided on the wall of the locking seat for injecting pressurized liquid into the liquid cavity.

[0016] In a preferred embodiment, the valve mechanism further comprises a throttle valve, so that the flow rate of the pressure liquid flowing out of the liquid chamber is controlled by the wellhead pressure and the throttle valve.

[0017] According to the second aspect of the present invention, a pressure relief method for cementing operations is also proposed, comprising: step S1, placing a pressure-holding ball into the above-mentioned pressure relief ball seat for cementing and forming a joint with the ball seat body; step S2, holding the pressure to rupture the rupture disk, thereby allowing the pressure liquid in the liquid cavity to flow to the downstream of the pressure relief ball seat, and immediately releasing the pressure after the rupture disk ruptures, and then only maintaining the pressure in the pipe string that allows the pressure liquid in the liquid cavity to flow out normally; step S3, holding the pressure again, so that the compression sleeve moves downstream and releases the lock of the block on the ball seat body, so as to allow the ball seat body to move independently downstream.

[0018] In a preferred embodiment, in step S2, when the holding pressure is greater than the rupture pressure of the rupture disk for a period of time, it is considered that the rupture disk has been ruptured and the pressure is relieved.

[0019] In a preferred embodiment, when the pressure liquid in the liquid chamber cannot flow to the downstream of the pressure release ball seat due to a malfunction in step S2, the following steps are performed: step S3', the pressure is held again to shear the first shear pin, so that the emergency shear sleeve, compression sleeve and ball seat body move downstream together.

[0020] In the pressure release ball seat proposed according to the present invention, the high pressure in the pipe is slowly released by means of the throttle valve, the rupture disk and the pressure relief hole. The mechanical structure is simple and can effectively prevent the high pressure in the pipe from being released instantly and leaking into the formation. At the same time, the emergency shear nails and emergency shear sleeves provided in the pressure release ball seat prevent the normal cementing operation from being unable to be carried out due to special circumstances, which may cause the pressure relief work to fail to proceed smoothly.

[0021] In the present invention, after meeting the high-pressure sealing requirements of the tail pipe suspension and sitting operation, the pressure can be slowly released during the pressure holding process to reduce the pressure when the ball seat is detached, and prevent the ball seat from instantly holding the pressure to cause leakage accidents in weak formations, thus solving the leakage problem caused by the high-pressure holding of the ball seat in weak formations. At the same time, the pressure-release ball seat has an emergency shearing function to ensure that the mechanism can still perform cementing operations under special circumstances. The pressure-release ball seat has a simple structure, is safe and reliable, and has the advantages of easy operation and low risk during construction; at the same time, it ensures the smooth progress of the tail pipe suspension pressure holding and pressure relief process, and has high working reliability and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be described below in conjunction with the accompanying drawings. In the accompanying drawings:

[0023] Figure 1 A schematic diagram showing the structure of a pressure-release ball seat for cementing in a sealed state according to an embodiment of the present invention is shown;

[0024] Figure 2 A schematic diagram showing the structure of the pressure relief ball seat in a normally open state;

[0025] Figure 3 Shows Figure 1 The schematic diagram of the structure of the pressure relief ball seat shown is in the emergency open state.

[0026] The drawings of the present invention are all schematic drawings, which are only used to illustrate the structural principles of the present invention and are not necessarily drawn according to the actual scale.

[0027] In the accompanying drawings, the meanings of the reference numerals are as follows:

[0028] 1-ball seat shell; 2-locking seat; 3-compression sleeve; 4-liquid chamber; 5-injection hole; 6-throttle valve; 7-valve; 8-gasket; 9-rupture disk 10-outflow channel; 11-first shear pin; 12-first through hole; 13-stopper; 14-limiting sleeve; 15-emergency shear sleeve; 16-limiting part; 17-ball seat body; 18-second shear pin; 19-flower basket; 20-second through hole; 21-blind groove; 22-step part; 23-pressure relief port. DETAILED DESCRIPTION

[0029] In order to make the technical solutions and advantages of the present invention more clearly understood, the exemplary embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. The described embodiments are only part of the embodiments of the present invention, rather than an exhaustive list of all the embodiments. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0030] For convenience, in this document, the direction toward the wellhead is described as "above", "upstream", "upper end" or similar terms, and the direction away from the wellhead is described as "below", "downstream", "lower end" or similar terms. In addition, the length direction along the pressure relief ball seat is described as "longitudinal" or "axial", and the direction perpendicular to the "longitudinal" or "axial" is described as "radial", wherein the direction toward the formation in the radial direction is described as "radially outside", and the direction away from the formation is described as "radially inside".

[0031] The present invention will be further described below in conjunction with the accompanying drawings.

[0032] The pressure release ball seat for cementing according to the present invention can be used in conjunction with a liner hanger for cementing operations. Figure 1As shown, the pressure slow-release ball seat 100 for cementing according to the present invention comprises a ball seat shell 1 in the shape of a hollow cylinder. A locking seat 2 is connected to the inner cavity of the ball seat shell 1. The locking seat 2 is also constructed as a hollow cylinder, and an external thread is provided on its outer wall. Through the cooperation between the external thread and the internal thread formed on the inner surface of the ball seat shell 1, the locking seat 2 and the ball seat shell 1 are fixedly connected to each other.

[0033] The pressure-releasing ball seat also includes a compression sleeve 3 disposed in the inner cavity of the locking seat 2. As shown in the figure, the outer surface of the compression sleeve 3 is configured as an L-shaped structure, wherein the upper end portion of the outer surface has a surface structure adapted to the inner cavity of the locking seat 2, so that they are sealed and engaged with each other. To this end, a sealing member (not shown) can be provided in the contact area between the outer surface of the compression sleeve 3 and the inner surface of the locking seat 2.

[0034] The main part of the outer surface of the compression sleeve 3 has a smaller size than the inner diameter of the locking seat 2, so that a radial space is formed between the compression sleeve 3 and the locking seat 2. A valve mechanism 7 is arranged in the space. In this way, a liquid chamber 4 is formed in the radial space between the compression sleeve 3 and the locking seat 2, which is axially limited by the valve mechanism 7 and the upper end portion of the compression sleeve 3. Figure 1 In the sealing state (also referred to as the initial state) shown, the liquid chamber 4 is filled with a pressurized liquid. In this regard, a through-injection hole 5 may be formed on the side wall of the locking seat 2, so that the pressurized liquid can be injected into the liquid chamber 4 through the injection hole. According to a preferred embodiment of the present invention, the pressurized liquid is an incompressible hydraulic oil. However, it is understood that other forms of pressurized liquid may also be used.

[0035] According to the present invention, the valve mechanism 7 includes a sleeve-shaped main body, which is arranged between the compression sleeve 3 and the locking seat 2. It is easy to understand that sealing members (not shown) are arranged on the inner and outer surfaces of the main body of the valve mechanism 7 to prevent leakage of the pressurized liquid in the liquid chamber 4. A throttle valve 6 and a rupture disk 9 are arranged in the main body of the valve mechanism. Among them, the throttle valve 6 is arranged at the front end of the valve mechanism 7 and is connected to the liquid chamber 4. The rupture disk 9 is arranged at the rear end of the valve mechanism 7, and is made of a material that can rupture under a certain pressure. It is easy to understand that the material of the rupture disk 9 can be easily determined by a technician in this field according to actual conditions.

[0036] For easy installation, the valve mechanism 7 further includes a gasket 8 disposed between the throttle valve 6 and the rupture disk 9. An emergency shear sleeve 15 is disposed downstream of the valve mechanism 7. In this way, the valve mechanism 7 is axially limited by the pressure liquid in the liquid chamber 4 and the emergency shear sleeve 15, thereby maintaining stability in the axial direction. The specific structure and function of the emergency shear sleeve 15 will be described in detail below.

[0037] A ball seat 17 is also provided in the compression sleeve 3. The lower end of the ball seat 17 is connected to a flower basket 19 (such as Figure 2 The structure and function of the flower basket 19 and the connection between the flower basket 19 and the ball seat body 17 are well known to those skilled in the art, and a detailed description thereof will be omitted here.

[0038] According to the present invention, the ball seat body 17 is releasably locked with the compression sleeve 3 through the stopper 13. Specifically, a through hole 20 is provided on the outer wall of the compression sleeve 3, and the stopper 13 is installed in the through hole 20. At the same time, a blind groove 21 is provided on the outer wall of the ball seat body 17. The radial outer end of the stopper 13 is defined by the emergency shear sleeve 15, and the radial inner end extends into the blind groove 21. In this way, the stopper 13 locks the ball seat body 17 and the compression sleeve 3 together.

[0039] For the convenience of manufacturing and assembly, the emergency shear sleeve 15 includes a step portion 22 arranged in its inner cavity, and a limit sleeve 14 is installed on the step portion 22. The limit sleeve 14 is arranged so that its axial upper end surface abuts against the lower end of the valve mechanism 7, and its axial lower end surface abuts against the step portion 22. At the same time, the radial inner surface of the limit sleeve 14 abuts against the radial outer surface of the stopper 13, thereby pressing the stopper 13 into the blind groove 13.

[0040] According to the present invention, the outer diameter of the upper end of the limiting sleeve 14 is smaller than the inner diameter of the emergency shear sleeve 15, so that the outflow channel 10 is formed between the emergency shear sleeve 15 and the limiting sleeve 14. In addition, a through hole 12 is formed on the outer wall of the emergency shear sleeve 15, and the through hole 12 is connected to the outflow channel 10.

[0041] In the initial state, the ball seat body 17 is locked with the compression sleeve 3 through the stopper 13, and the stopper 13 is limited by the limiting sleeve 14 in the second through hole 20 on the compression sleeve 3 and the blind groove 21 of the ball seat body 17. The limiting sleeve 14 is located on the step 22 on the emergency shear sleeve 15 and abuts against the lower end of the valve mechanism 7, so that the valve mechanism 7 remains stable in the axial direction under the joint action of the pressure liquid (which is incompressible) in the liquid chamber 4 and the limiting sleeve 14.

[0042] When the liner hanger is lowered to the designed well depth and needs to be hung, the pressure-holding ball is put in to form a sealed joint with the ball seat body 17. At this time, the pressure in the pipe string increases with the injection of the upper fluid, and enters the first pressure-holding state. In this state, the pressure-holding pressure achieved will be greater than the rupture pressure of the rupture disk 9. In this case, the rupture disk 9 in the valve mechanism 7 is squeezed and broken by the upstream pressure, so that the liquid chamber 4 and the outflow channel 10 are connected. In this way, the pressure liquid in the liquid chamber 4 can flow through the throttle valve 6 to the outflow channel 10 formed between the limit sleeve 14 and the emergency shear sleeve 15, and continue to be discharged downstream through the through hole 12 connected to the outflow channel 10. In addition to being controlled by the wellhead pressure, the outflow speed of the pressure liquid in the liquid chamber 4 is also controlled by the throttle valve 6. In other words, the outflow speed of the pressure liquid in the liquid chamber 4 can be conveniently controlled by adjusting the opening of the throttle valve 6.

[0043] After the holding pressure is greater than the rupture pressure of the rupture disk 9, the holding pressure is maintained for a short period of time, such as 2-5 seconds (this time can be determined by a person skilled in the art based on experience), and then it can be determined that the rupture disk 9 has ruptured. At this time, the pressure can be immediately relieved at the wellhead, and then a lower pressure can be maintained in the pipe string. The pressure can be selected to enable the pressure liquid in the liquid chamber 4 to flow out normally, which can be easily determined by the technology in the art. In this way, the instantaneous pressure generated by the high-pressure seal when the ball seat is set in the prior art will no longer exist, and thus will not be transmitted to the formation to cause formation leakage.

[0044] As the pressure liquid in the liquid chamber 4 gradually flows out, the volume of the liquid chamber 4 gradually decreases. At this time, the pressure is held again and the second pressure holding state is entered. In this case, due to the loss of the incompressible pressure liquid in the liquid chamber 4, the compression sleeve 3 will move axially downward under the action of the upstream pressure, driving the stopper 13 to move downstream together. Since the limit sleeve 14 prevents the radial outward movement of the stopper 13, the upstream pressure will force the stopper 13 to disengage from the blind groove 21 on the ball seat body 17. It is easy for those skilled in the art to understand that a chamfer is provided on the inner surface of the stopper 13 to facilitate the movement of the stopper 13 out of the blind groove 21.

[0045] After the stopper 13 is separated from the blind groove 21, the locking effect of the stopper 13 on the compression sleeve 3 and the ball seat body 17 is released. In this case, the ball seat body 17 is separated from the compression sleeve 3, so that it can move freely downstream together with the flower basket 18, such as Figure 2 At this point, the circulation can be re-established and normal cementing operations can be carried out.

[0046] In addition, in order to prevent the compression sleeve 3 from excessively moving downward due to the upstream pressure, a limiter 16 is provided below the emergency shear sleeve 15. Thus, the axial movement stroke of the compression sleeve 3 can be limited. In addition, a pressure relief port 23 can be provided on the limiter 16 to prevent locking due to pressure.

[0047] In this article, Figure 2 The state in which the ball seat body 17 is separated from the compression sleeve 3 is called the normal open state. However, in actual production, the pressure liquid may not be discharged normally due to the blockage of the through hole 12 or other reasons, resulting in the compression sleeve 3 not being able to move downstream normally and releasing the locking effect of the block 13. In this case, the ball seat body 17 and the flower basket 19 cannot fall off normally.

[0048] Therefore, according to the present invention, a method for re-establishing circulation under abnormal circumstances is also provided. Specifically, the emergency shear sleeve 15 is connected to the locking seat 2 through the emergency shear pin 11. The shear stress of the emergency shear pin 11 is selected to be greater than the pressure in the first and second pressure-holding states. In this way, when the locking effect of the block 13 cannot be released due to abnormal reasons in the second pressure-holding state, the upstream pressure continues to be held until the first shear pin 11 connecting the locking seat 2 and the emergency shear sleeve 15 is sheared. In this case, the compression sleeve 3, valve mechanism 7, emergency shear sleeve 15, ball seat body 17, flower basket 19 and other parts located inside the locking seat 2 all fall off the locking seat 2 and move downstream. This state is Figure 3 After this, the circulation can be re-established and normal cementing operations can be carried out.

[0049] It is easy to understand that the specific pressure values ​​in the first and second pressure holding states can be obtained by those skilled in the art according to actual conditions during actual work.

[0050] Therefore, the pressure-release ball seat for cementing of the present invention can prevent the risk of the ball seat body being unable to fall off due to abnormal reasons and thus being unable to re-establish circulation, thereby enhancing the safety and reliability of the device according to the present invention.

[0051] According to another aspect of the present invention, a pressure relief method for cementing operation is also proposed.

[0052] The method begins with step S1, wherein a pressure-holding ball is put into a pipe string so as to engage with the ball seat body 17 in the pressure-release ball seat 100 for cementing as described above.

[0053] Then, step S2 is performed, in which the pressure is held and made greater than the rupture pressure of the rupture disk 9, so that the rupture disk 9 explodes. In this case, the pressure liquid in the liquid chamber 4 will flow to the downstream of the pressure-release ball seat via the outflow channel 10 and the first through hole 12. After the rupture disk 9 ruptures, the pressure is immediately released at the wellhead, and then a lower pressure is maintained in the pipe string. The pressure can be selected to enable the pressure liquid in the liquid chamber 4 to flow out normally, which can be easily determined by the technology in the field. In this way, the instantaneous pressure generated by the high-pressure seal when the ball seat is set in the prior art will no longer exist, and thus will not be transmitted to the formation to cause formation leakage.

[0054] Then, step S3 is performed, wherein the compression sleeve 3 is moved downstream again, thereby releasing the locking of the ball seat body 17 by the stopper 13. In this case, the ball seat body 17 (together with the flower basket 19 connected thereto) can move downstream independently. After this, the circulation can be reestablished and normal cementing operation can be performed.

[0055] In step S2, if the pressure liquid in the liquid chamber 4 cannot flow to the downstream of the pressure relief ball seat due to a fault, step S3' is performed, in which the pressure is held again to shear the emergency shear pin 11, so that the emergency shear sleeve 15, the compression sleeve 3 and the ball seat body 17 move downstream together. After this, the circulation can be re-established and normal cementing operations can be carried out.

[0056] In step S2, when the pressure is greater than the rupture pressure of the rupture disk 9 and is maintained for a period of time, it is considered that the rupture disk 9 has ruptured. The period of time can be, for example, 2-5 seconds, which can be easily selected by a person skilled in the art.

[0057] It is easy to understand that, although the pressure relief ball seat is introduced above by taking cementing as an example, it is understandable that the pressure relief ball seat can also be used for other downhole operations.

[0058] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic creative concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and / or modifications that fall within the scope of the present invention, and changes and / or modifications made according to the embodiments of the present invention should be included within the scope of protection of the present invention.

Claims

1. A pressure-release ball seat for cementing, comprising: Ball seat housing (1), A locking seat (2) is arranged in the ball seat housing (1) and fixedly connected thereto, A compression sleeve (3) is arranged in the locking seat (2), and a liquid cavity (4) is formed between the compression sleeve (3) and the locking seat (2). a valve mechanism (7) disposed between the compression sleeve (3) and the locking seat (2), the valve mechanism (7) comprising a rupture disk (9), and A ball seat body (17) is arranged in the compression sleeve, Wherein, in the initial state, the ball seat body (17) and the compression sleeve (3) are locked with each other through the stopper (13), and the liquid chamber (4) is filled with pressurized liquid. The rupture disk (9) is configured to rupture in the first pressure-holding state, thereby allowing the pressurized liquid in the liquid chamber (4) to flow out. The compression sleeve (3) is configured to move downstream in the second pressure-holding state, releasing the locking of the ball seat body (17) by the stopper (13), thereby enabling the ball seat body (17) to move downstream independently.

2. The pressure-release ball seat for cementing according to claim 1, characterized in that: It also includes an emergency shear sleeve (15) arranged between the compression sleeve (3) and the locking seat (2) and located downstream of the valve mechanism (7), the emergency shear sleeve (15) is connected to the locking seat (2) via a first shear pin (11), and the first shear pin is configured to be sheared when the pressure is greater than the pressure in the second pressure holding state.

3. The pressure-release ball seat for cementing according to claim 2, characterized in that: The liquid chamber (4) is formed upstream of the valve mechanism (7), and the emergency shear sleeve (15) has a first through hole (12), so that after the rupture disk (9) ruptures, the pressure liquid in the liquid chamber (4) can flow through the valve mechanism (7) and the first through hole (12) to the downstream of the pressure release ball seat.

4. The pressure-release ball seat for cementing according to claim 3, characterized in that: A second through hole (20) is formed on the wall of the compression sleeve (3), and the stopper (13) is arranged in the second through hole (20), so that the radial outer end of the stopper (13) abuts against the emergency shear sleeve (15), and the radial inner end extends to a blind groove (21) formed in the wall of the ball seat body (17).

5. The pressure-release ball seat for cementing according to claim 4, characterized in that: The emergency shear sleeve (15) comprises a step portion (22) arranged in its inner cavity, and a limit sleeve (14) is provided on the step portion, wherein the axial upper end of the limit sleeve (14) abuts against the valve mechanism (7), and the radial inner end abuts against the radial outer end of the stop block (13).

6. The pressure-release ball seat for cementing according to claim 5, characterized in that: The outer diameter of the upper end of the limiting sleeve (14) is smaller than the inner diameter of the emergency shear sleeve (15), thereby forming an outflow channel (10) in communication with the first through hole (12) between the emergency shear sleeve (15) and the limiting sleeve (14).

7. The pressure-release ball seat for cementing according to any one of claims 2 to 6, characterized in that: The lower end of the emergency shear sleeve (15) has a limiting portion (16) for limiting the downward movement stroke of the compression sleeve (3), and the limiting portion (16) is provided with a pressure relief port (23).

8. The pressure-release ball seat for cementing according to any one of claims 1 to 6, characterized in that: An injection hole (5) is provided on the wall of the locking seat (2) for injecting pressurized liquid into the liquid cavity (4).

9. The pressure-release ball seat for cementing according to any one of claims 1 to 6, characterized in that: The valve mechanism (7) also includes a throttle valve (6), so that the flow rate of the pressure liquid flowing out of the liquid chamber (4) is controlled by the wellhead pressure and the throttle valve.

10. A pressure relief method for cementing operations, comprising: Step S1, putting a pressure-holding ball into a pressure-release ball seat for cementing according to any one of claims 1 to 9 and forming a connection with the ball seat body (17); Step S2, holding the pressure to rupture the rupture disk (9), thereby allowing the pressure liquid in the liquid chamber (4) to flow to the downstream of the pressure relief ball seat, and immediately releasing the pressure after the rupture disk ruptures, and then only maintaining the pressure in the pipe string to allow the pressure liquid in the liquid chamber (4) to flow out normally; Step S3, re-pressurizing to make the compression sleeve (3) move downstream and release the locking of the ball seat body (17) by the stopper (13), so as to allow the ball seat body (17) to move downstream independently.

11. The pressure release method according to claim 10, characterized in that: In step S2, when the holding pressure is greater than the rupture pressure of the rupture disk (9) for a period of time, it is considered that the rupture disk (9) has been ruptured and the pressure is released.

12. The pressure release method according to claim 10 or 11, characterized in that: In step S2, when the pressure liquid in the liquid chamber (4) cannot flow to the downstream of the pressure relief ball seat due to a fault, the following steps are performed: Step S3', holding the pressure again to shear the first shear nail (11), so that the emergency shear sleeve (15), the compression sleeve (3) and the ball seat body (17) move downstream together.

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