Subsurface safety valve with bimetal sealing structure

Abstract

The invention relates to the technical field of subsurface safety valves of oil and gas wells, and provides a subsurface safety valve with a bimetal sealing structure, which comprises a piston assembly, a central pipe, a spring barrel, a reset spring, a valve plate assembly and a middle joint with a piston cavity, an upper metal sealing seat is arranged at the upper end of the piston assembly, and a lower metal sealing seat is arranged at the lower end of the piston assembly; when the safety valve is opened, the metal upper sealing seat and the metal stop seat form a sealing pair; and when the safety valve is closed, the metal lower sealing seat and the metal stop seat form a sealing pair. Metal sealing can be achieved in the opening state and the closing state of the safety valve, a double-metal sealing structure is formed, the sealing reliability is improved through the double-metal sealing structure, and the problem that due to the fact that solid impurities such as fracturing sand enter a piston cavity, the safety valve cannot work normally is effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of downhole safety valves for oil and gas wells, and more particularly, to a downhole safety valve with a bimetallic seal structure. Background Art

[0002] A downhole safety valve is a downhole tool placed in a wellbore, connected to a tubing string, which can prevent blowouts and ensure production safety. A downhole safety valve generally includes a central tube assembly (including a central tube, a return spring, etc.), a valve plate assembly (including a valve plate, a return torsion spring, a valve plate mounting structure, etc.), a piston assembly (including a piston rod, a sealing assembly, etc.) and a hydraulic control line. The hydraulic control line extends to the ground and is connected to a ground pressure control system. When the oil well is in normal production, the ground pressure control system transmits pressure to the piston assembly through the hydraulic control line. The piston rod pushes the central tube and compresses the return spring. As the pressure in the hydraulic control line increases, the central tube gradually pushes open the valve plate, opening the downhole safety valve and thus connecting the production channel. When the pressure of the downhole fluid is abnormal, the pressure in the hydraulic control line is cut off through the ground pressure control system. The central tube resets under the action of the return spring, and the valve plate resets under the action of the return torsion spring, closing the downhole safety valve and thus disconnecting the production channel.

[0003] There is usually a sealing measure between the piston rod and its installation cavity. Usually, a non-metallic sealing ring is used to achieve sealing. This sealing method is only suitable for operation in a conventional environment and is mainly used to block gas-liquid impurities. However, for operations in a fracturing environment with other solid impurities such as fracturing sand, the above sealing method has poor effects and is also prone to premature failure due to factors such as the torsion generated when the return spring is compressed. Once other solid impurities such as fracturing sand enter the piston cavity, scratching the piston rod, there is a risk of the piston rod getting stuck, making the central tube unable to reset, and further causing the safety valve to malfunction. Summary of the Invention

[0004] The purpose of the present invention is to provide a downhole safety valve with a bimetallic seal structure to solve the above-mentioned defects of the prior art.

[0005] The present invention is achieved by the following technical solutions: A downhole safety valve with a bimetallic seal structure includes a piston assembly, a central tube, a spring cylinder, a return spring, a valve plate assembly and a middle joint with a piston cavity. The piston cavity is provided with a metal stop seat. The upper end of the piston assembly is provided with a metal upper seal seat, and the lower end of the piston assembly is provided with a metal lower seal seat. When the safety valve is opened, the metal upper seal seat and the metal stop seat form a sealing pair. When the safety valve is closed, the metal lower seal seat and the metal stop seat form a sealing pair.

[0006] Optionally, the return spring includes an upper spring and a lower spring with end faces abutted against each other. The upper spring and the lower spring have the same diameter and length, and the winding directions of the upper spring and the lower spring are opposite.

[0007] Optionally, the surfaces where the upper spring and the lower spring abut against each other are planes.

[0008] Optionally, an annular gasket is provided between the upper spring and the lower spring.

[0009] Optionally, a plane bearing is provided at one end of the return spring.

[0010] Optionally, the valve plate assembly is threadedly connected to the lower end of the spring barrel, the inner edge of the lower end of the spring barrel forms a sealing pair with the valve plate assembly, and the lower end of the spring barrel is provided with an annular groove to make the inner side of the lower end of the spring barrel elastic.

[0011] Optionally, the valve plate assembly includes a valve plate chamber, a valve plate seat, a connecting sleeve, a sealing valve plate and a reset torsion spring. One end of the sealing valve plate is hinged to the valve plate chamber and maintains a closing tendency under the action of the reset torsion spring. The valve plate chamber is sleeved on the lower end of the valve plate seat, the upper end of the valve plate seat is threadedly connected to the lower end of the spring tube, and the lower end of the valve plate seat forms a sealing pair with the sealing valve plate; both ends of the connecting sleeve are provided with threads with opposite rotation directions, wherein the thread at one end is connected to the valve plate seat, and the thread at the other end is connected to the valve plate chamber, and a limiting structure for limiting relative rotation is provided between the valve plate seat and the valve plate chamber.

[0012] Optionally, the limiting structure includes a limiting groove provided on the valve plate seat, and a limiting block provided on the valve plate chamber, and the limiting block cooperates with the limiting groove.

[0013] Optionally, an O-ring is provided on the sealing surface between the sealing valve plate and the valve plate seat.

[0014] Optionally, the piston assembly is provided with at least one pair, and each pair of piston assemblies is symmetrically arranged.

[0015] The technical solution of the present invention has at least the following advantages and beneficial effects: 1. In the present invention, a sealing pair is formed between the metal upper sealing seat and the metal stop seat when the safety valve is opened, and a sealing pair is formed between the metal lower sealing seat and the metal stop seat when the safety valve is closed, that is, metal sealing can be achieved in both the open and closed states of the safety valve, forming a bimetallic sealing structure. The bimetallic sealing structure has a better barrier effect on solid impurities such as fracturing sand, and is not easily failed prematurely (i.e., not easily damaged) due to factors such as the torque generated when the return spring is compressed, thereby improving the sealing reliability and effectively solving the problem that the safety valve cannot work normally due to solid impurities such as fracturing sand entering the piston cavity.

[0016] 2. Since the return spring is a spiral structure, for a large-volume downhole safety valve, a strong torque will be generated when compressed, which will not only easily cause the sealing structure of the piston rod to fail prematurely, but also easily cause damage (deformation, bending) to the piston assembly. In the present invention, the return spring includes an upper spring and a lower spring with the same diameter and length. The two springs are installed against each other and the threads of the two springs are rotated in opposite directions. In this way, the torque generated by the upper spring and the lower spring can offset each other, avoiding damage to the piston assembly and the above-mentioned bimetallic sealing structure.

[0017] 3. In the present invention, a plane bearing is provided at one end of the return spring. When the return spring is compressed and has a tendency to twist, the provision of the plane bearing can cause one end of the return spring to twist in the opposite direction, thereby avoiding torque generated when the return spring is compressed as much as possible.

[0018] 4. The valve plate assembly is connected to the lower end of the spring barrel by threads. After the connection, the inner edge of the lower end of the spring barrel forms a sealing pair with the valve plate assembly. At the same time, an annular groove is provided at the lower end of the spring barrel so that the sealing part on the spring barrel forms a cantilever beam structure. In this way, on the one hand, by controlling the thickness of the inner side of the lower end of the spring barrel, the spring barrel can be made elastic. After the threads are tightened, the inner side of the lower end of the spring barrel can be elastically deformed to achieve effective sealing of metal-to-metal contact (i.e., a tighter seal), thereby preventing solid impurities such as fracturing sand from entering the spring barrel from here and causing damage to the reset spring and the above-mentioned bimetallic sealing structure. On the other hand, the annular groove can accommodate solid impurities such as fracturing sand. After the annular groove is filled, it can block the wear of the sealing surface by the solid impurities, thereby greatly improving the reliability and durability of the seal.

[0019] 5. In the present invention, threads with opposite rotation directions are provided at both ends of the connecting sleeve, the threads at one end are connected to the valve plate seat, and the threads at the other end are connected to the valve plate chamber, that is, a positive and negative buckle connection is adopted, and the relative rotation between the valve plate seat and the valve plate chamber is limited by a limiting structure. In this way, after the connecting sleeve, the valve plate seat and the valve plate chamber are installed in place, the axial relative position of the valve plate seat and the valve plate chamber can be effectively limited to avoid the formation of a gap between the valve plate seat and the sealing valve plate, which may cause sealing failure.

[0020] 6. In the present invention, the sealing valve plate and the valve plate seat are in contact with each other to form a sealing pair. At the same time, an O-ring is provided on the sealing surface between the sealing valve plate and the valve plate seat. The O-ring is squeezed to form another sealing pair, thereby forming a double seal and improving the sealing effect.

[0021] 7. In the present invention, at least one pair of piston assemblies is provided, and each pair of piston assemblies is arranged symmetrically. In this way, for a large-volume downhole safety valve, the thrust exerted on the central pipe can be balanced, and dual power can be provided, which is convenient for reducing the hydraulic control output pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the structure of a downhole safety valve with a bimetallic seal structure provided by the present invention; Figure 2 Schematic diagram of the structure of the middle joint; Figure 3 For Figure 2 Enlarged view at D in Figure 4 For Figure 2 Enlarged view at E in Figure 5 Schematic diagram of the structure of the piston assembly; Figure 6 For Figure 1 Enlarged view at A in Figure 7 For Figure 1 Enlarged view at B in Figure 8 For Figure 1 Enlarged view at C in Figure 9 Exploded schematic diagram of the valve plate seat and the valve plate chamber; Reference numerals: 1 - piston assembly, 101 - piston rod, 102 - metal upper seal seat, 103 - metal lower seal seat, 2 - metal stop seat, 201 - upper sealing surface, 202 - lower sealing surface, 3 - central tube, 4 - spring cylinder, 401 - annular groove, 5 - return spring, 501 - upper spring, 502 - lower spring, 6 - valve plate assembly, 601 - valve plate chamber, 6011 - limit block, 602 - valve plate seat, 6021 - limit groove, 603 - connecting sleeve, 604 - sealing valve plate, 7 - middle joint, 701 - piston cavity, 702 - oil inlet ring groove, 8 - plain bearing, 9 - elastic circlip, 10 - bearing seat. Detailed implementation manners

[0023] Refer to Figure 1A downhole safety valve with a bimetallic sealing structure comprises a piston assembly 1, a center tube 3, a spring cylinder 4, a return spring 5, a valve plate assembly 6 and a middle joint 7 with a piston cavity 701. It is easy to understand that this part is the component structure of the existing downhole safety valve. The middle joint 7 and the upper end of the spring cylinder 4 are usually fixed by threaded connection, and the lower end of the spring cylinder 4 and the valve plate assembly 6 are usually fixed by threaded connection. The piston assembly 1 is installed in the piston cavity 701 of the middle joint 7, the center tube 3 is clamped with the lower end of the piston assembly 1, the return spring 5 is installed in the spring cavity between the spring cylinder 4 and the center tube 3, and the ground hydraulic control pipeline (not shown) is connected to the upper end of the piston cavity 701. The downhole valve safety valve is opened and closed according to the working principle recorded in the background technology. It should be understood that the above-mentioned structure is only the main part of the downhole safety valve. Other components and their connection methods that are not described in detail (such as the sealing sliding method of the center tube 3, the method of clamping the center tube 3 and the piston assembly 1, the composition of the piston assembly 1, and the pressure balancing mechanism for balancing the internal and external pressures when opening the downhole safety valve, etc.) can be implemented by technical personnel in this field based on the existing technology and common knowledge in the field.

[0024] It should be noted that the "upper end" and "lower end" in the present invention are defined according to the posture of the downhole safety valve when in use, and the "upper end" and "lower end" appearing in the context are interpreted in this way. It is easy to understand that if the downhole safety valve is taken out separately, the "upper end" and "lower end" appearing in the text will have different specific positions depending on the placement posture.

[0025] The present invention is improved on the above basis, referring to Figures 2 - 6 One of the improvements of the present invention is to improve the sealing measures for isolating external impurities from entering the piston cavity 701 and contacting the piston rod 101. Specifically, a metal stopper 2 is provided in the piston cavity 701 on the middle joint 7, and a metal upper sealing seat 102 is provided at the upper end of the piston assembly 1, and a metal lower sealing seat 103 is provided at the lower end of the piston assembly 1; when the safety valve is opened, the metal upper sealing seat 102 forms a sealing pair with the metal stopper 2; when the safety valve is closed, the metal lower sealing seat 103 forms a sealing pair with the metal stopper 2, that is, metal sealing can be achieved in both the open and closed states of the safety valve, forming a bimetallic sealing structure, which has a better barrier effect on solid impurities such as fracturing sand, and is not easily prematurely failed (i.e., not easily damaged) due to factors such as the torsion generated when the return spring 5 is compressed, thereby improving the sealing reliability and effectively solving the problem that the safety valve cannot work normally due to solid impurities such as fracturing sand entering the piston cavity 701. In addition, the metal stopper 2 also limits the upper and lower limit positions of the piston assembly 1, that is, constrains the stroke of the piston assembly 1.

[0026] As an option, the metal stop seat 2 is arranged at the lower end of the piston chamber 701 and is threadedly connected to the side wall of the piston chamber 701, which is convenient for replacement and disassembly. The metal upper seal seat 102 and the metal lower seal seat 103 are installed on the piston rod 101 of the piston assembly 1. In practical applications, steps can be provided at both ends of the piston rod 101, and the metal upper seal seat 102 and the metal lower seal seat 103 are sleeved on the stepped part. The connection structure between the shoulder of the step and the end of the piston rod 101 limits the positions of the metal upper seal seat 102 and the metal lower seal seat 103. The metal stop seat 2 is provided with an upper seal surface 201 and a lower seal surface 202. The upper seal surface 201 is used to contact the metal upper seal seat 102, and the lower seal surface 202 is used to contact the metal lower seal seat 103. The materials of the metal stop seat 2, the metal upper seal seat 102, and the metal lower seal seat 103 are not limited. For example, stainless steel, nickel-based alloy, copper alloy, cemented carbide, etc. can all be used. In addition, in practical applications, the contact surfaces between the metal stop seat 2 and the metal upper seal seat 102, and between the metal stop seat 2 and the metal lower seal seat 103 can be tapered surfaces to ensure the sealing effect.

[0027] Reference Figure 1 , the second improvement of the present invention lies in the improvement of the structure of the return spring 5. Specifically, the return spring 5 includes an upper spring 501 and a lower spring 502. The upper spring 501 and the lower spring 502 have the same diameter (i.e., the outer diameter, inner diameter, and wire diameter are all the same), and the upper spring 501 and the lower spring 502 also have the same length, that is, to ensure that the torsional forces generated by the two during compression are equal. The upper spring 501 and the lower spring 502 have opposite helix directions, which is convenient for the torsional force directions generated by the two to be opposite. When installed, the end faces of the upper spring 501 and the lower spring 502 are in contact with each other. In this way, the torsional forces generated by the upper spring 501 and the lower spring 502 can cancel each other out, avoiding damage to the piston assembly 1 and the above-mentioned bimetallic seal structure.

[0028] In this embodiment, the surfaces of the upper spring 501 and the lower spring 502 in contact with each other are flat surfaces, which better ensure axial compression. Further, an annular gasket (not shown in the figure) can be provided between the upper spring 501 and the lower spring 502 to better ensure that the upper spring 501 and the lower spring 502 are in a flat surface against each other. It should be understood that the inner diameter of the annular gasket is larger than the outer diameter of the central tube 3, and the outer diameter of the annular gasket is smaller than the inner diameter of the spring cylinder 4 to avoid jamming during movement. In addition, positioning sinking grooves can be provided on the inner edges on both sides of the annular gasket. Preferably, the diameter of the positioning sinking grooves is equal to the outer diameters of the upper spring 501 and the lower spring 502, and the ends of the upper spring 501 and the lower spring 502 are installed in the positioning sinking grooves to limit the radial position of the annular gasket.

[0029] It should be noted that in the prior art, although there are some applications of balancing spring torque, for example, a double-spring structure safety valve is disclosed in the prior art with the publication number "CN208107249U", which uses two coaxial springs arranged inside and outside with opposite winding directions to cancel the torque. However, this method cannot be applied to downhole safety valves. The reason is that in a downhole safety valve, the piston rod 101 and the above-mentioned bimetallic seal structure are arranged on a circumference with a definite radius, so the installation space of the return spring 5 is limited. If the method of using two springs inside and outside in the prior art is adopted to cancel the torque, there is no installation space; moreover, the diameters of the two springs inside and outside are different, and theoretically, the torque generated by the outer spring is larger than that generated by the inner spring, and the torque cannot be effectively canceled.

[0030] Reference Figure 7 , the third improvement of the present invention lies in that a plain bearing 8 is provided at one end of the return spring 5. When the return spring 5 compresses and has a tendency to twist, the setting of the plain bearing 8 can make one end of the return spring 5 twist in the opposite direction, thereby avoiding the generation of torque when the return spring 5 compresses. Preferably, the plain bearing 8 is installed at the end of the return spring 5 away from the piston assembly 1. In practical applications, the plain bearing 8 is installed in the bearing seat 10, and the bearing seat 10 abuts against the inner step of the spring cylinder 4. Further, the position of the bearing seat 10 is restricted by an elastic snap ring 9.

[0031] Reference Figure 8 , the fourth improvement of the present invention lies in the improvement of the connection and sealing structure between the valve plate assembly 6 and the lower end of the spring cylinder 4. Specifically, the valve plate assembly 6 is threadedly connected to the lower end of the spring cylinder 4, and the inner edge of the lower end of the spring cylinder 4 and the valve plate assembly 6 form a sealing pair. The lower end of the spring cylinder 4 is provided with an annular groove 401, so that the sealing part on the spring cylinder 4 forms a cantilever beam structure. In this way, on the one hand, by controlling the thickness of the inner side of the lower end of the spring cylinder 4, it can have elasticity, and the inner side of the lower end of the spring cylinder 4 can elastically deform after the thread is tightened, realizing effective sealing of metal-to-metal contact (that is, the sealing is tighter), and preventing solid impurities such as fracturing sand from entering the spring cylinder 4 from here and damaging the return spring 5 and the above-mentioned bimetallic seal structure; on the other hand, the annular groove 401 can accommodate solid impurities such as fracturing sand. After the annular groove 401 is filled, it can block the wear of the solid impurities on the sealing surface, greatly improving the reliability and durability of the sealing.

[0032] Reference Figure 8, The fifth improvement of the present invention lies in the improvement of the connection method of some components in the valve plate assembly 6. The valve plate assembly 6 includes a valve plate chamber 601, a valve plate seat 602, a connecting sleeve 603, a sealing valve plate 604, and a return torsion spring (not shown in the figure). One end of the sealing valve plate 604 is hinged to the valve plate chamber 601 and tends to remain closed under the action of the return torsion spring. It should be noted that the installation method of the sealing valve plate 604 is not improved, and any existing installation method can be adopted. Therefore, how to install the return torsion spring to realize the reset of the sealing valve plate 604 will not be elaborated.

[0033] In this improvement, the connection method of the valve plate chamber 601, the valve plate seat 602, and the connecting sleeve 603 is mainly improved. Specifically, the lower end of the valve plate seat 602 is provided with a step, and the valve plate chamber 601 is sleeved on the step at the lower end of the valve plate seat 602; the upper end of the valve plate chamber 601 abuts against the step shoulder at the lower end of the valve plate chamber 601. The upper end of the valve plate seat 602 is threadedly connected to the lower end of the spring cylinder 4. The lower end of the valve plate seat 602 and the sealing valve plate 604 form a sealing pair; both ends of the connecting sleeve 603 are provided with threads with opposite helix directions. One end of the thread is connected to the valve plate seat 602, and the other end of the thread is connected to the valve plate chamber 601. At the same time, a limiting structure for restricting relative rotation is provided between the valve plate seat 602 and the valve plate chamber 601. That is, in the present invention, the connecting sleeve 603 connects the valve plate chamber 601 and the valve plate seat 602 in a positive and negative buckle manner, and the relative rotation between the valve plate seat 602 and the valve plate chamber 601 is restricted. In this way, after the connecting sleeve 603, the valve plate seat 602, and the valve plate chamber 601 are installed in place, the axial relative positions of the valve plate seat 602 and the valve plate chamber 601 can be effectively restricted, and the gap between the valve plate seat 602 and the sealing valve plate 604 can be avoided, resulting in sealing failure.

[0034] Reference Figure 9 , As an option, in this embodiment, the limiting structure includes a limiting groove 6021 provided on the valve plate seat 602 and a limiting block 6011 provided on the valve plate chamber 601, and the limiting block 6011 cooperates with the limiting groove 6021. During installation, the circumferential rotation of the valve plate seat 602 and the valve plate chamber 601 is restricted, and the limiting block 6011 and the limiting groove 6021 are aligned. By screwing the connecting sleeve 603, the valve plate seat 602 and the valve plate chamber 601 can be made to approach each other until the limiting block 6011 and the limiting groove 6021 cooperate, that is, the connection is in place. In other embodiments, of course, other structures can be used to realize the restriction of the relative rotation between the valve plate seat 602 and the valve plate chamber 601, such as through a connection key.

[0035] The sixth improvement of the present invention lies in that an O-ring seal is provided on the sealing surface between the sealing valve plate 604 and the valve plate seat 602. In this way, when the sealing valve plate 604 and the valve plate seat 602 come into contact, a sealing pair will be formed. At the same time, the O-ring seal is compressed, and another sealing pair will be formed, constituting a double seal to improve the sealing effect. In practical applications, a sealing ring groove is provided on the valve plate seat 602, and the O-ring seal is installed in the sealing ring groove.

[0036] Reference Figures 1 - 3 , The seventh improvement of the present invention lies in that there are at least a pair of piston assemblies 1, and each pair of piston assemblies 1 is symmetrically arranged. As an option, only one pair of piston assemblies 1 is provided in this embodiment (of course, multiple pairs can also be provided in other embodiments), that is, two piston assemblies 1, and the two piston assemblies 1 are symmetrically arranged. In this way, for a large-volume downhole safety valve, the thrust on the central pipe 3 can be balanced, and double power can be provided, which is convenient for reducing the hydraulic control output pressure. In practical applications, an oil inlet ring groove 702 is provided at the upper end of the piston cavity 701 of the middle joint 7. The oil inlet ring groove 702 communicates with the two piston cavities 701 at the same time. The hydraulic oil input by the hydraulic control pipeline first enters the oil inlet ring groove 702 and then enters the piston cavity 701 to push the piston rod 101.

[0037] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A downhole safety valve with a bimetallic seal structure, comprising a piston assembly, a central tube, a spring cylinder, a return spring, a valve plate assembly, and a middle joint having a piston chamber, characterized in that, The piston chamber is provided with a metal stop seat. The upper end of the piston assembly is provided with a metal upper sealing seat, and the lower end of the piston assembly is provided with a metal lower sealing seat. When the safety valve is opened, the metal upper sealing seat and the metal stop seat form a sealing pair. When the safety valve is closed, the metal lower sealing seat and the metal stop seat form a sealing pair.

2. The downhole safety valve with a bimetallic seal structure according to claim 1, characterized in that, The return spring includes an upper spring and a lower spring with their end faces abutted against each other. The upper spring and the lower spring have the same diameter and length, and their helix directions are opposite.

3. The downhole safety valve with a bimetallic seal structure according to claim 2, characterized in that, The surfaces of the upper spring and the lower spring that abut against each other are flat surfaces.

4. The downhole safety valve with a bimetallic seal structure according to claim 3, characterized in that, An annular gasket is provided between the upper spring and the lower spring.

5. The downhole safety valve with a bimetallic seal structure according to claim 1, characterized in that, A plain bearing is provided at one end of the return spring.

6. The downhole safety valve with a bimetallic seal structure according to claim 1, characterized in that, The valve plate assembly is threadedly connected to the lower end of the spring cylinder. The inner edge of the lower end of the spring cylinder forms a sealing pair with the valve plate assembly. The lower end of the spring cylinder is provided with an annular groove to make the inner side of the lower end of the spring cylinder elastic.

7. The downhole safety valve with a bimetallic seal structure according to claim 1, characterized in that, The valve plate assembly includes a valve plate chamber, a valve plate seat, a connecting sleeve, a sealing valve plate and a return torsion spring. One end of the sealing valve plate is hinged to the valve plate chamber and tends to remain closed under the action of the return torsion spring. The valve plate chamber is sleeved on the lower end of the valve plate seat. The upper end of the valve plate seat is threadedly connected to the lower end of the spring cylinder. The lower end of the valve plate seat forms a sealing pair with the sealing valve plate. The two ends of the connecting sleeve are provided with threads with opposite helix directions. One end of the threads is connected to the valve plate seat, and the other end of the threads is connected to the valve plate chamber. And a limiting structure for restricting relative rotation is provided between the valve plate seat and the valve plate chamber.

8. The downhole safety valve with a bimetallic seal structure according to claim 7, characterized in that, The limiting structure includes a limiting groove provided on the valve plate seat and a limiting block provided on the valve plate chamber. The limiting block cooperates with the limiting groove.

9. The downhole safety valve with a bimetallic seal structure according to claim 7, characterized in that, An O-ring seal is provided on the sealing surface between the sealing valve plate and the valve plate seat.

10. The downhole safety valve with a bimetallic seal structure according to any one of claims 1-9, characterized in that, There are at least a pair of piston assemblies, and each pair of piston assemblies is symmetrically arranged.

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