Development and application of smooth rod seal at

2022-05-26
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At present, in China's oilfields, the sucker rod pumping system is the main force of oil well production. Among the surface equipment of the sucker rod pumping system, the wellhead sucker rod sealing device is an essential equipment, and its overall performance directly affects the working quality of the surface equipment. According to the field statistics, the failure rate of wellhead polished rod sealing device in the whole system is quite large, which seriously restricts the normal production of the oilfield. According to the investigation on the field use of the conventional polished rod sealing device in Shengli Oilfield, the total loss caused by the failure of the device is huge. According to incomplete statistics, it is more than 40 million yuan per year (only compared with some new devices and calculated according to the discount part). Therefore, for the later development of the oilfield, the research on the polished rod sealing device and its sealing materials has become very important. According to the requirements of the development of oilfield oil production technology, Shengli Oilfield has put forward a variety of practical schemes through comprehensive investigation, analysis, research and demonstration, developed and popularized several new devices and seals, and achieved good economic and social benefits. 1 factors affecting the sealing effect and the service life of the sealing ring 1.1 external factors (relative to the sealing ring itself)

① due to the new design and packaging of the oil and the thinning of the wall thickness, the production status of the well, such as the oil-water ratio in the well fluid, etc. Practice has proved that the reduction of oil content worsens the lubrication conditions between the polished rod and the sealing ring, intensifies the wear, shortens the service life of the sealing ring and reduces the effect

② the well fluid contains corrosive media, such as sulfide. As a result, the polished rod is corroded, the surface quality is reduced, the sealing wear of the sealing ring is intensified, the effect becomes worse and the service life is reduced

③ structure and function of sealing device. The wellhead sealing devices with different structures have an important impact on the working conditions and effect of the sealing ring. For example, the sealing effect and service life have been greatly improved after the new packing box structure with adjustable deviation and inclination is adopted in some wells. 1.2 internal factors

① shape of sealing ring. The shape of the sealing ring is different from the working effect and service life of the sealing ring with the same working condition, the same device structure, the same material but different shape; For example, the working performance of octagonal conventional seal ring is obviously better than that of conventional rectangular seal ring

② material of sealing ring. The sealing effect and service life of sealing rings made of different materials are different under the same working condition and the same device

③ the storage, installation and use of sealing ring [1] affect its effect and service life. 2 shape and material of sealing ring 2.1 conventional rectangular sealing ring

the sealing ring is made of oil resistant nitrile rubber, and its structure is shown in Figure 1. From the perspective of sealing mechanism, its sealing function is realized by filling the whole sealing cavity. However, from the field application, the anti extrusion and anti-wear ability of the sealing ring is poor, the elastic compensation performance is not good, and its sealing effect and working performance are not ideal. Figure 1 conventional rectangular sealing ring 2.2 octagonal conventional sealing ring

octagonal conventional sealing ring is made of oil resistant nitrile rubber (as shown in Figure 2), which has a certain improvement in structure compared with conventional sealing ring. From the perspective of sealing mechanism, the sealing ring can not only realize the filling sealing function, but also play a certain role of liquid self sealing and better self lubrication due to the formation of multi-stage liquid ring between multi-stage sealing rings in work, and also remove the deformation layer. The field application shows that the sealing effect of the sealing ring is significantly improved compared with the conventional rectangular sealing ring, and the service life is relatively prolonged by 1 ~ 2 times compared with the conventional rectangular sealing ring. Figure 2 octagonal conventional seal ring 2.3 conical seal ring

2.3.1 monomer conical seal ring

this type of seal ring is made of oil resistant nitrile rubber (as shown in Figure 3), and the sealing tear performance (nail rod method) GB/t328 (2) 007 sealing ring solves the disadvantages of troublesome disassembly and assembly of conventional rectangular sealing ring and the prominent problem of serious extrusion damage of upper packing. Compared with conventional rectangular sealing ring, the compression degree between each sealing ring is similar, and the extrusion damage of upper sealing ring is not very prominent; However, the field application shows that its comprehensive performance is not improved much, and new requirements are put forward for the packing box; Therefore, it has not been popularized and applied. Fig. 3 single conical sealing ring 2.3.2 integral conical spiral sealing ring

integral conical spiral sealing ring is the most commonly used sealing ring form in the new polished rod sealing device at present. It is made of oil-resistant nitrile rubber with cloth, and its structure is shown in Fig. 4. It has high strength, good anti extrusion, anti aging and strong compensation performance. Because the overall structure adopts a cone, it has the characteristics of easy assembly and disassembly, convenient and labor-saving, good sealing effect, long service life and so on. Fig. 4 integral conical spiral seal ring 2.4 conventional polytetrafluoroethylene (P.T.F.E) seal ring

conventional polytetrafluoroethylene

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