A spiral packing for wellhead sealing of an oil pumping unit and its preparation method

Abstract

This invention provides a spiral packing for wellhead sealing of an oil pumping unit and its preparation method, relating to the field of oil and gas exploration equipment technology. It addresses the problems of high friction coefficient, short service life, and poor resistance to wear in existing packing technologies. The invention forms a double-helix structure by nesting the rectangular helixes of a first packing between the rectangular helixes of a second packing. The first packing has a higher hardness and lower elasticity than the second packing. This double-helix structure, with its different hardness and elasticity, forms a spiral-sealed chamber with the polished rod during axial compression. This prevents continuous impact of oil and gas pressure on the packing, ensuring a sufficient seal between the packing and the polished rod while reducing the friction coefficient and improving the packing's service life. Furthermore, in cases of misalignment during pumping unit installation, the second packing extends further in the direction of wear, thus maintaining the packing's sealing performance.

Description

Technical Field

[0001] This invention relates to the field of oil and gas exploration equipment technology, and in particular to a wellhead sealing spiral packing for an oil pumping unit and its preparation method. Background Technology

[0002] Most oilfields in my country have entered the mechanical oil production stage, primarily using rod-type pumping units, with wellhead seals being an essential component. One of the weakest links in rod-type pumping systems is the wellhead packing seal, whose overall performance directly impacts the operational quality of surface equipment. Existing packings, based on material properties, can be categorized into natural fiber packings, mineral fiber packings, synthetic fiber packings, ceramic packings, and metal fiber packings, all belonging to the elastic material category. The sealing condition of a packing seal system requires the contact pressure at the sealing surface to exceed the fluid pressure. Therefore, the contact pressure at the sealing surface significantly affects the sealing effect. To increase the contact pressure, the pressure between the packing and the polished rod needs to be increased, leading to continuous friction between them. This causes the packing to quickly fail due to wear, especially when the pumping unit is misaligned, resulting in uneven wear between the packing and the polished rod, accelerating packing wear and necessitating frequent packing replacements. This not only significantly increases production costs but also disrupts normal oil and gas production. Summary of the Invention

[0003] In view of the above problems, the present invention proposes a spiral packing for wellhead sealing of oil pumping units and its preparation method, which is used to solve the technical problems of high friction coefficient and short service life between packing and polished rod in the prior art.

[0004] One technical solution adopted in this invention is: a spiral packing for sealing the wellhead of an oil pumping unit, comprising a first packing and a second packing, wherein the first packing and the second packing are both spirals with equal pitch and equal diameter extending along the axial direction, the cross-section of the spiral is rectangular, and the height, diameter, pitch and helix angle of the spiral of the first packing and the spiral of the second packing are the same.

[0005] The height of the rectangular cross-section of the first packing helix is ​​equal to the axial clearance distance of the second packing helix, and the width of the rectangular cross-section of the first packing is equal to the width of the rectangular cross-section of the second packing.

[0006] The wellhead sealing spiral packing of the pumping unit has a double helix structure formed by the rectangular spiral of the first packing nested between the rectangular spirals of the second packing.

[0007] The first packing has a higher hardness than the second packing; the first packing has a lower elasticity than the second packing.

[0008] Furthermore, the axial thickness of the rectangular helix of the first packing is less than or equal to the axial thickness of the rectangular helix of the second packing.

[0009] Furthermore, the main body of the first and second packings is made of hydrogenated nitrile rubber.

[0010] The hydrogenated nitrile rubber contains aramid pulp and polytetrafluoroethylene powder.

[0011] The surfaces of the first packing and the second packing have a polytetrafluoroethylene film.

[0012] The components and weight parts of the first packing are as follows: 100 parts of hydrogenated nitrile rubber raw rubber; 6 parts of aramid pulp; 10 parts of polytetrafluoroethylene powder; 1 part of stearic acid; 30 parts of silica; 5 parts of dicumyl peroxide; 0.5 parts of 2-mercaptomethylbenzimidazole zinc; and 2 parts of magnesium oxide.

[0013] The components and weight parts of the second packing are as follows: 100 parts of hydrogenated nitrile rubber raw rubber; 4 parts of aramid pulp; 20 parts of polytetrafluoroethylene powder; 1 part of stearic acid; 25 parts of silica; 5 parts of dicumyl peroxide; 0.5 parts of 2-mercaptomethylbenzimidazole zinc; and 1 part of magnesium oxide.

[0014] The thickness of the polytetrafluoroethylene film of the first packing is less than the thickness of the polytetrafluoroethylene film of the second packing.

[0015] Based on the above technical solution, the present invention also proposes a method for preparing a spiral packing for sealing the wellhead of an oil pumping unit. Aramid pulp, polytetrafluoroethylene powder and additives are added to hydrogenated nitrile rubber raw rubber, mixed and extruded under pressure to generate pre-crosslinked raw rubber. The additives include: dicumyl peroxide, silica, stearic acid, 2-mercaptomethylbenzimidazole zinc and magnesium oxide.

[0016] The components and their weight parts of the first packing are as follows: 100 parts hydrogenated nitrile rubber raw rubber; 6 parts aramid pulp; 10 parts polytetrafluoroethylene powder; 1 part stearic acid; 30 parts silica; 5 parts dicumyl peroxide; 0.5 parts 2-mercaptomethylbenzimidazole zinc; and 2 parts magnesium oxide.

[0017] The components and their weight parts for the second packing are as follows: 100 parts hydrogenated nitrile rubber raw rubber; 4 parts aramid pulp; 20 parts polytetrafluoroethylene powder; 1 part stearic acid; 25 parts silica; 5 parts dicumyl peroxide; 0.5 parts 2-mercaptomethylbenzimidazole zinc; 1 part magnesium oxide.

[0018] The pre-crosslinked raw rubber is mixed and extruded into cylindrical rubber tubes;

[0019] The cylindrical rubber hose is subjected to high-temperature vulcanization. The vulcanization temperature is 175-180 degrees Celsius, the vulcanization pressure is 0.5-1.0 MPa, and the vulcanization time is 10-15 minutes.

[0020] The cylindrical rubber tube is spirally cut, and the spirally cut cylindrical rubber tube is shaped to form a spiral packing body;

[0021] The spiral packing body is immersed in polytetrafluoroethylene emulsion;

[0022] The soaked spiral packing body is subjected to secondary high-temperature vulcanization to produce the first packing and the second packing respectively. The vulcanization temperature of the secondary high-temperature vulcanization is 175-180 degrees Celsius, the vulcanization pressure is 0.5-1.0 MPa, and the vulcanization time is 5-10 minutes.

[0023] Nest the first packing ring between the rectangular spirals of the second packing ring and adjust their alignment;

[0024] Cutting and grinding make the two ends of the packing flat, thus forming the wellhead sealing spiral packing of the oil pumping unit.

[0025] Furthermore, during the high-temperature vulcanization of the cylindrical rubber hose, the high-temperature vulcanization time of the first packing is longer than that of the second packing.

[0026] Furthermore, the polytetrafluoroethylene emulsion is a mixture comprising polytetrafluoroethylene powder, acetone, and low-activity magnesium monoxide.

[0027] The components of the polytetrafluoroethylene emulsion and the weight parts of each component are as follows: 100 parts water; 10 parts polytetrafluoroethylene powder; 5 parts acetone; and 2 parts low-activity magnesium monoxide.

[0028] The present invention provides a wellhead sealing spiral packing for oil pumping units and its preparation method. The wellhead sealing spiral packing for oil pumping units is formed by nesting the rectangular helixes of a first packing between the rectangular helixes of a second packing to create a double-helix structure. The first packing has a higher hardness than the second packing, and the first packing has a lower elasticity than the second packing. This double-helix structure, with its different hardness and elasticity, forms a spiral-sealed chamber with the polished rod during axial compression. This prevents continuous impact of oil and gas pressure on the packing, ensuring sufficient sealing between the packing and the polished rod while reducing the coefficient of friction and improving the packing's service life. Furthermore, in cases of misalignment during oil pumping unit installation, the second packing will extend further in the direction of wear, thus maintaining the packing's sealing performance.

[0029] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0030] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0031] Figure 1 The diagram shows the installation structure of the spiral packing for sealing the wellhead of the oil pumping unit according to the present invention.

[0032] Figure 2 A flowchart illustrating the preparation process of the spiral packing for wellhead sealing of the oil pumping unit according to the present invention is shown.

[0033] Among them, 1. First packing; 2. Second packing; 3. Bare trunk. Detailed Implementation

[0034] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0035] Packing is a type of soft packing seal, a compression sealing device that fills circumferential gaps. In a typical packing seal structure, the packing is housed within a packing box. The gland, through the axial preload of the gland bolts, causes axial compression deformation of the packing, simultaneously inducing radial expansion. This expansion is constrained by the inner wall of the packing box and the shaft surface, resulting in tight contact between the packing and the two surfaces, filling the gaps and achieving a seal. The sealing condition of a packing seal system is that the contact pressure of the sealing surface must be greater than the fluid pressure. Therefore, the contact pressure of the sealing surface has a significant impact on the sealing effect. To increase the contact pressure, the pressure between the packing and the polished rod needs to be increased. This leads to continuous friction between the packing and the polished rod, causing the packing to wear down quickly and fail. This exacerbates packing wear, shortens the packing replacement cycle, increases material consumption, and necessitates frequent packing replacements, significantly increasing production costs and impacting normal oil and gas production. To ensure a leak-proof wellhead, the packing clamping force is typically high, causing the surface of the sucker rod to heat up. This increases the energy consumption of the pumping unit and also increases the friction between the sucker rod and the packing box, accelerating packing wear, shortening the packing replacement cycle, and increasing material consumption. If the pumping unit is misaligned, causing uneven wear, the friction between the sucker rod and the packing box will increase exponentially.

[0036] The wellhead sealing spiral packing and its preparation method provided in this invention involve forming a double-helix structure by nesting the rectangular helixes of a first packing between the rectangular helixes of a second packing. The first packing has a higher hardness than the second packing, and its elasticity is lower than that of the second packing. Under axial compression, the packing with higher elasticity expands radially, forming a small spiral-sealed chamber with the polished rod. This allows pressure to be transferred over a larger area, preventing continuous impact of oil and gas pressure on the packing. This ensures a sufficient seal between the packing and the polished rod while reducing the coefficient of friction and improving the packing's service life. Furthermore, it prevents uneven wear of the packing in case of misalignment during pumping unit installation.

[0037] The specific implementation includes the following:

[0038] Example 1: Refer to Appendix Figure 1This embodiment of a pumping unit wellhead sealing spiral packing includes a first packing 1 and a second packing 2. Both the first packing 1 and the second packing 2 are axially extending spirals with equal pitch and equal diameter. The cross-section of the spiral is rectangular, and the height, diameter, pitch, and helix angle of the spirals of the first packing 1 and the second packing 2 are the same. The height of the rectangular cross-section of the spiral of the first packing 1 is equal to the axial clearance distance of the spiral of the second packing 2. The width of the rectangular cross-section of the first packing 1 and the rectangular cross-section of the second packing 2 are equal. The rectangular spirals of the first packing 1 are nested between the rectangular spirals of the second packing 2 to form a double-helix structure for the pumping unit wellhead sealing spiral packing. The hardness of the first packing 1 is greater than that of the second packing 2. The elasticity of the first packing 1 is less than that of the second packing 2. With the above structure, the double-helix packing composed of two packings with different hardness and elasticity expands radially when axially compressed. It forms a small spiral-sealed chamber with the polished rod 3. The small chamber is naturally filled with water or oil. The water or oil will conduct pressure along the small chamber, so that the pressure is transferred to a larger area. This prevents the oil and gas pressure from continuously impacting the packing. At the same time, the water or oil in the small chamber has a certain viscosity and compressibility, which buffers the pressure. This ensures that a sufficient seal is formed between the packing and the polished rod 3, while also reducing the coefficient of friction between the packing and the polished rod 3, thus improving the service life of the packing.

[0039] Furthermore, because the highly elastic second packing 2 can expand radially under pressure, and the extent of this expansion is related to the contact pressure between the packing and the polished rod, the second packing 2 will extend further in the direction of wear when the pumping unit is misaligned, thus maintaining the packing's sealing performance. In contrast, existing packings, due to their uniform axial mechanical properties, will only expand and extend axially under pressure when wear occurs, but the extent of expansion is limited. The packing's sealing performance gradually weakens as wear intensifies. Therefore, the technical solution of this embodiment can also effectively avoid the problem of polished rod wear, further increasing the packing's sealing performance and service life.

[0040] To achieve a hardness greater than that of the second packing 2 and an elasticity less than that of the second packing 2, this embodiment employs the following method:

[0041] The first method: The axial thickness of the rectangular helix of the first packing is less than or equal to the axial thickness of the rectangular helix of the second packing. Specifically, for example... Figure 1As shown, the axial thickness of the rectangular helix of the first packing is less than or equal to the axial thickness of the rectangular helix of the second packing. This arrangement saves on packing material. Since both helical packings cut from a cylindrical tubing have the same thickness, they can both be used in the subsequent production of helical packings for pumping unit wellhead sealing, preventing material waste. Furthermore, when the axial thickness of the rectangular helix of the first packing is less than that of the second packing, the thicker second packing is more prone to radial deformation under pressure, giving it greater flexibility.

[0042] In the second embodiment, the main body of the first packing 1 and the second packing 2 is made of hydrogenated nitrile butadiene rubber (NBR). The NBR contains aramid pulp and polytetrafluoroethylene (PTFE) powder. The surfaces of the first and second packings have a PTFE film. Specifically, the aramid pulp content in the first packing is greater than that in the second packing; the PTFE powder content in the first packing is less than that in the second packing; and the thickness of the PTFE film in the first packing is less than that in the second packing. Filling with aramid pulp increases the tensile stress of the hydrogenated NBR and reduces its permanent deformation, while filling with PTFE powder reduces the coefficient of friction and improves its wear resistance. Because the aramid pulp content in the first packing is greater than that in the second packing, the elasticity of the second packing 2 is greater than that of the first packing 1. Furthermore, since the second packing 2 is the one primarily in contact with the polished rod, its internal and surface PTFE content is relatively high.

[0043] Hydrogenated nitrile rubber is filled with polytetrafluoroethylene (PTFE) powder, and a PTFE film is formed on its surface. The PTFE film reduces the coefficient of friction. During use, the PTFE continuously migrates and penetrates to the surface of the smooth rod, significantly reducing the coefficient of friction. After prolonged use, the PTFE film within the packing's inner bore wears away. At this point, the film layer between the spirals continues to function, migrating and penetrating into the smooth rod. Simultaneously, the PTFE powder inside the packing further reduces the packing's coefficient of friction. Furthermore, due to the double-helix structure used in this invention, the two packings have different hardness and elasticity, resulting in inconsistent wear. After the PTFE in the second packing 2 wears to a certain extent, increasing axial pressure causes the first packing 1 to deform more, initiating friction with the smooth rod and continuing to migrate PTFE towards it. This results in a longer migration time for the PTFE, making the packing more durable. In contrast, the wear of the inner bore of a traditional single-helix packing is axially uniform. Once one section of the inner bore fails, other sections will also fail or nearly fail, leading to relatively poor durability. In summary, the above-described technical solution of this embodiment can significantly reduce the friction coefficient of the packing and improve its service life.

[0044] Example 2: Refer to Appendix Figure 2 This embodiment provides a method for preparing a spiral packing for sealing the wellhead of an oil pumping unit as described in Embodiment 1. The specific preparation method is as follows:

[0045] S1: Add aramid pulp, polytetrafluoroethylene powder and additives to hydrogenated nitrile rubber raw rubber, mix and extrude under pressure to generate pre-crosslinked raw rubber.

[0046] In step S1, the additives added to the hydrogenated nitrile rubber raw rubber include reinforcing agents, plasticizers, antioxidants, vulcanizing agents, activators, and pre-crosslinking agents, which are used to improve the rubber's weather resistance, mechanical properties, oil resistance, and other indicators.

[0047] Specifically, the pre-crosslinking agent is dicumyl peroxide; the reinforcing agent is silica; the plasticizer is stearic acid; the antioxidant is zinc 2-mercaptomethylbenzimidazole; the activator is magnesium oxide or zinc oxide; and the vulcanizing agent is dicumyl peroxide.

[0048] In this embodiment, adding dicumyl peroxide to hydrogenated nitrile butadiene rubber (NBR) raw rubber and extruding it using a screw extruder allows for pre-crosslinking of the NBR. A twin-screw extruder is used for this process. Pre-crosslinking effectively increases the Mooney viscosity of the NBR, and the rubber compound forms a crosslinked network or clusters before vulcanization, resulting in higher stability and increased oil resistance and strength. Inorganic activators such as magnesium oxide or zinc oxide can increase the polarity of the rubber, forming ionic bonds and enhancing the strength of the NBR. The use of 2-mercaptomethylbenzimidazole zinc as an antioxidant effectively improves the weather resistance of the NBR, enabling it to adapt to the complex environmental changes in oil wells and preventing cracking during use.

[0049] To ensure that the hardness of the first packing 1 is greater than that of the second packing 2, and the elasticity of the first packing 1 is less than that of the second packing 2, the method used in this embodiment is as follows: In step S1 above, the content of aramid pulp added to the first packing 1 is greater than the content of aramid pulp added to the second packing 2; the content of polytetrafluoroethylene powder added to the first packing 1 is less than the content of polytetrafluoroethylene powder added to the second packing 2.

[0050] In one embodiment, in step S1, the rubber formulation for preparing the first packing 1 includes the following components and their mass fractions: 100 parts of hydrogenated nitrile rubber raw rubber; 6 parts of aramid pulp; 10 parts of polytetrafluoroethylene powder; 1 part of stearic acid; 30 parts of silica; 5 parts of dicumyl peroxide; 0.5 parts of 2-mercaptomethylbenzimidazole zinc; and 2 parts of magnesium oxide.

[0051] The rubber formulation for making the second packing 2 includes the following components and their mass fractions: 100 parts hydrogenated nitrile rubber raw rubber; 4 parts aramid pulp; 20 parts polytetrafluoroethylene powder; 1 part stearic acid; 25 parts silica; 5 parts dicumyl peroxide; 0.5 parts 2-mercaptomethylbenzimidazole zinc; and 1 part magnesium oxide.

[0052] All of the above-mentioned formulation materials can be purchased or ordered on the market. For example, the main rubber chain of the hydrogenated nitrile rubber raw rubber specifically used contains epoxy groups, the epoxy degree is 30%, the ring-opening rate of the epoxy groups is 45%, the acrylonitrile content is 25%, and the degree of hydrogenation is greater than 90%.

[0053] It should be noted that the above formula and component content are only one specific embodiment and do not limit the implementation of other embodiments of the present invention.

[0054] S2: The pre-crosslinked raw rubber is mixed and extruded into a cylindrical tube, the wall thickness of which is equal to the radial thickness of the packing in Example 1.

[0055] In step S2, the mixing in this embodiment adopts high-temperature mixing to facilitate the formation of a filler network of polytetrafluoroethylene powder, so that the polytetrafluoroethylene powder in the packing can slowly migrate to the smooth rod during the wear process, thereby improving the wear resistance of the rubber. The high-temperature mixing can effectively improve the physical properties of the packing, such as strength and elasticity. Specifically, the mixing temperature can be above 90 degrees Celsius.

[0056] S3: The cylindrical rubber hose is vulcanized at high temperature.

[0057] To achieve the technical effect in Example 1 where the hardness of the first packing 1 is greater than that of the second packing 2, and the elasticity of the first packing 1 is less than that of the second packing 2, in step S3 above, during the high-temperature vulcanization of the cylindrical tubing, the high-temperature vulcanization time of the first packing 1 is longer than that of the second packing 2. This results in a more thorough cross-linking reaction and a greater degree of cross-linking in the first packing 1, leading to greater hardness of the packing colloid. Conversely, the degree of cross-linking in the second packing 2 is relatively smaller, resulting in relatively greater elasticity. In this step, the vulcanization temperature is 175-180 degrees Celsius, the vulcanization pressure is 0.5-1.0 MPa, and the vulcanization time is 10-15 minutes; specifically, the high-temperature vulcanization time for the first packing 1 is 15 minutes, and the high-temperature vulcanization time for the second packing 2 is 10 minutes.

[0058] S4: The cylindrical rubber tube is spirally cut, and the cylindrical rubber tube after spiral cutting is shaped to form a spiral packing body.

[0059] This step is used to manufacture the main body of the first packing 1 and the second packing 2. During the helical cutting process, after determining the pitch and helix angle, existing machine tools can be used. The cylindrical rubber tube after helical cutting is shaped, including deburring the cut and grinding the inner surface. Deburring the cut facilitates the uniform coating of polytetrafluoroethylene emulsion in the subsequent S5 soaking step, while grinding the inner surface increases the contact area of ​​the inner surface of the packing, which is beneficial to the vulcanization and crosslinking of polytetrafluoroethylene in the polytetrafluoroethylene emulsion with the polytetrafluoroethylene inside the polytetrafluoroethylene emulsion.

[0060] S5: Immerse the spiral packing body in polytetrafluoroethylene emulsion.

[0061] In step S5, the polytetrafluoroethylene emulsion is a mixture containing polytetrafluoroethylene powder, acetone, and low-activity magnesium monoxide. The main function of acetone is as a crosslinking agent, while the low-activity magnesium monoxide can improve the mechanical properties of the polytetrafluoroethylene film. The components of the polytetrafluoroethylene emulsion and the weight parts of each component are as follows: 100 parts water; 10 parts polytetrafluoroethylene powder; 5 parts acetone; and 2 parts low-activity magnesium monoxide.

[0062] S6: The soaked spiral packing body undergoes a second high-temperature vulcanization to produce the first and second packings. During the second high-temperature vulcanization process, the PTFE emulsion on the packing surface is vulcanized and tightly adheres to the spiral packing body. Furthermore, the PTFE in the PTFE emulsion cross-links with the PTFE inside the packing body, resulting in a PTFE film with better mechanical properties and greater wear resistance. This PTFE film significantly reduces the coefficient of friction between the packing and the smooth rod, thus improving the packing's service life. In this step, the vulcanization temperature for the second high-temperature vulcanization is 175-180 degrees Celsius, the vulcanization pressure is 0.5-1.0 MPa, and the vulcanization time is 5-10 minutes, with 5-8 minutes being optimal.

[0063] S7: Nest the first packing root 1 between the rectangular spirals of the second packing root 2 and adjust the alignment.

[0064] S8: Cut and grind to make the two ends of the packing flat, thus forming the wellhead sealing spiral packing of the pumping unit.

[0065] Cutting and grinding the ends of the packing to make them flat is to ensure that the ends of the packing are in line with the shape of the packing box, so that the packing can be better installed in the packing box.

[0066] The above preparation steps produce the first packing 1 and the second packing 2 according to different ratios, and then assemble them into the wellhead sealing spiral packing of the actual oil pumping unit according to the structure of Example 1.

[0067] Unless otherwise specified, the equipment and processes used in the above process are all existing equipment and processes. For example, the equipment and processes used in the extrusion, cutting, and grinding processes in this embodiment are not specifically limited here.

[0068] The spiral packing for wellhead sealing of oil pumping units, manufactured using the technical solution of this invention, was applied to laboratory and field tests. Laboratory tests were conducted on a dedicated test bench. Based on the pressure of the medium, the frictional torque, compressive force, expansion and contraction, and leakage between the packing and the polished rod were calculated. After the tests, optical inspection was performed on the packing to assess damage, and comparative tests were conducted with existing products to obtain test data and results. Field tests involved installing the test piece on an oil well. After the oil pumping unit had accumulated a set operating period (15 days), the test piece was removed for observation, including the degree of cracking and uneven wear. The packing was then reinstalled on the oil pumping unit for further testing.

[0069] After testing and comparison with existing single-spiral packing, it can be seen that the spiral packing for wellhead sealing of the present invention meets the well sealing requirements of the oil well. Existing packing generally needs to be replaced once a month, while the product of this application can be used continuously for more than three months, increasing the service life by more than 2 times. No packing wear failure was found during normal shutdown inspection. The continuous working time of the oil pumping unit is increased by about 4 times, and the production efficiency of the oil pumping unit is increased by more than 20%, which significantly improves the production efficiency and economic benefits of the enterprise.

[0070] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of the invention and form different embodiments. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A spiral packing for sealing the wellhead of an oil pumping unit, comprising a first packing and a second packing, characterized in that: Both the first packing and the second packing are helical shapes with equal pitch and equal diameter extending along the axial direction. The cross-section of the helix of the helix is ​​rectangular, and the height, diameter, pitch and helix angle of the first packing and the second packing are the same. The height of the rectangular cross-section of the first packing helix is ​​equal to the axial clearance distance of the second packing helix, and the width of the rectangular cross-section of the first packing is equal to the width of the rectangular cross-section of the second packing. The pumping unit wellhead sealing spiral packing has a double-helix structure formed by the rectangular helix of the first packing nested between the rectangular helixes of the second packing. The first packing has a higher hardness than the second packing; the first packing has a lower elasticity than the second packing. The main body of the first packing and the second packing is made of hydrogenated nitrile rubber; The hydrogenated nitrile rubber contains aramid pulp and polytetrafluoroethylene powder. The surfaces of the first packing and the second packing have a polytetrafluoroethylene film. The components and weight parts of the first packing are as follows: 100 parts hydrogenated nitrile rubber raw rubber; 6 parts aramid pulp; 10 parts polytetrafluoroethylene powder; 1 part stearic acid; 30 parts silica; 5 parts dicumyl peroxide; 0.5 parts 2-mercaptomethylbenzimidazole zinc; 2 parts magnesium oxide. The components and weight parts of the second packing are as follows: 100 parts of hydrogenated nitrile rubber raw rubber; 4 parts of aramid pulp; 20 parts of polytetrafluoroethylene powder; 1 part of stearic acid; 25 parts of silica; 5 parts of dicumyl peroxide; 0.5 parts of 2-mercaptomethylbenzimidazole zinc; and 1 part of magnesium oxide.

2. The spiral packing for sealing the wellhead of an oil pumping unit according to claim 1, characterized in that: The axial thickness of the rectangular helix of the first packing is less than or equal to the axial thickness of the rectangular helix of the second packing.

3. The spiral packing for sealing the wellhead of an oil pumping unit according to claim 1, characterized in that: The thickness of the polytetrafluoroethylene film of the first packing is less than the thickness of the polytetrafluoroethylene film of the second packing.

4. A method for preparing a spiral packing for sealing the wellhead of an oil pumping unit, used to prepare the spiral packing for sealing the wellhead of an oil pumping unit as described in claim 1, characterized in that: Aramid pulp, polytetrafluoroethylene powder, and additives are added to hydrogenated nitrile rubber raw rubber, mixed, and extruded under pressure to generate pre-crosslinked raw rubber. The additives include: dicumyl peroxide, silica, stearic acid, 2-mercaptomethylbenzimidazole zinc, and magnesium oxide. The components and their weight parts of the first packing are as follows: 100 parts hydrogenated nitrile rubber raw rubber; 6 parts aramid pulp; 10 parts polytetrafluoroethylene powder; 1 part stearic acid; 30 parts silica; 5 parts dicumyl peroxide; 0.5 parts 2-mercaptomethylbenzimidazole zinc; and 2 parts magnesium oxide. The components and their weight parts for the second packing are as follows: 100 parts hydrogenated nitrile rubber raw rubber; 4 parts aramid pulp; 20 parts polytetrafluoroethylene powder; 1 part stearic acid; 25 parts silica; 5 parts dicumyl peroxide; 0.5 parts 2-mercaptomethylbenzimidazole zinc; 1 part magnesium oxide. The pre-crosslinked raw rubber is mixed and extruded into cylindrical rubber tubes; The cylindrical rubber hose is subjected to high-temperature vulcanization. The vulcanization temperature is 175-180 degrees Celsius, the vulcanization pressure is 0.5-1.0 MPa, and the vulcanization time is 10-15 minutes. The cylindrical rubber tube is spirally cut, and the spirally cut cylindrical rubber tube is shaped to form a spiral packing body; The spiral packing body is immersed in polytetrafluoroethylene emulsion; The soaked spiral packing body is subjected to secondary high-temperature vulcanization to produce the first packing and the second packing respectively. The vulcanization temperature of the secondary high-temperature vulcanization is 175-180 degrees Celsius, the vulcanization pressure is 0.5-1.0 MPa, and the vulcanization time is 5-10 minutes. Nest the first packing ring between the rectangular spirals of the second packing ring and adjust their alignment; Cutting and grinding make the two ends of the packing flat, thus forming the wellhead sealing spiral packing of the oil pumping unit.

5. The method for preparing a spiral packing for sealing the wellhead of an oil pumping unit according to claim 4, characterized in that: When the cylindrical rubber hose is vulcanized at high temperature, the vulcanization time of the first packing is longer than that of the second packing.

6. The method for preparing a spiral packing for sealing the wellhead of an oil pumping unit according to claim 4, characterized in that: The polytetrafluoroethylene emulsion is a mixture containing polytetrafluoroethylene powder, acetone, and low-activity magnesium monoxide. The components of the polytetrafluoroethylene emulsion and the weight parts of each component are as follows: 100 parts water; 10 parts polytetrafluoroethylene powder; 5 parts acetone; and 2 parts low-activity magnesium monoxide.

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