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The sucker rod serves as the slender component of a pumping well, connecting the polished rod above and the lower portion of the pump itself to transmit power. Typically, each section of the sucker rod measures around 7.62 or 8 meters, sometimes extending to 9.14 meters, and is usually made from low-carbon alloy steel that undergoes heat treatment. These rods are joined end-to-end using threaded couplings and extend all the way down to the piston located in the oil-bearing formation. The reciprocating motion of these rods helps extract oil from beneath the ground. In modern oil wells, the total length often reaches approximately two kilometers, with some reaching depths exceeding three kilometers, as seen in the case of Shengli Oilfield.
The sucker rod is a critical element in rod-pumping equipment, transferring the energy generated by the surface pumping unit to the downhole pump. A typical sucker rod string consists of dozens or even hundreds of individual rods linked together by couplings. During operation, the sucker rod string experiences asymmetrical cyclic loading, while simultaneously being exposed to well fluids like oil and saline water, which may contain corrosive agents. As a result, the primary modes of failure for sucker rods tend to involve fatigue fractures or corrosion fatigue fractures. When these rods fail, it significantly impacts oil production, increases maintenance costs, and raises operational expenses.
Sucker rods have a rich history spanning nearly a century. Initially crafted from natural materials like rattan, the first metal sucker rod patent was granted to Samuel M. Jones of Ohio on October 30, 1894. Over the last twenty years, both domestic and international manufacturers have embraced innovative approaches in producing sucker rods, including the utilization of multi-element alloy steels and fiberglass, along with advancements in forging techniques such as induction heating systems, infrared temperature measurement tools, non-rotating sucker rod heads, automated coupling assembly lines, and sophisticated die designs. These innovations have dramatically enhanced the quality and manufacturing standards of sucker rods.
To cater to specific requirements such as high-capacity pumping, deep-well operations, heavy oil extraction, wax-laden wells, corrosive environments, and slanted boreholes, numerous specialized sucker rods have been developed. Examples include ultra-high-strength sucker rods, FRP (Fiber-Reinforced Plastic) oil pumps, hollow sucker rods, KD-grade sucker rods, continuous sucker rods, electrically heated sucker rods, wire-rope sucker rods, and aluminum-alloy sucker rods. Additionally, various auxiliary components for sucker rod strings, such as long-stroke polished rods, toothless polished rod clamps, rotating rod devices, shock absorbers, graphite-adjustable center polished rod seals, roller couplings, centralizers, wax scrapers, weighted rods, anti-drop mechanisms, disconnecting tools, and magnetic wax inhibitors, have been introduced to extend the lifespan and broaden the application scope of sucker rods.
One notable innovation involves high-strength sucker rod nipples, which boast superior tensile strength and feature couplings equivalent to or surpassing those of standard sucker rods. These nipples ensure direct contact with the tubing while employing sacrificial anode electrochemical corrosion protection to mitigate electrochemical corrosion caused by localized wear. By providing a cathodic current through the electrolyte to the protected structure, this method achieves effective cathodic protection. To prevent the anode material from being dislodged or eroded by fluid flow, stainless steel sleeves encase the inner and outer wire joints of the sucker rod and the anode body. Furthermore, the coupling is constructed using high-nickel alloys, ensuring a smooth surface and significantly enhancing the longevity of the sucker rod coupling.
Technical specifications for these improved sucker rods include diameters of 1", 7/8", 3/4", and 5/8". Supporting rod diameters range from 25mm to 16mm, with centralizer outer diameters reaching up to φ56mm. The sacrificial anode's spontaneous potential protection spans 50m, with an effective power output of ≥1.1 A.h/g. The anode consumption rate remains below 12.36 kg/A.a, and the current efficiency exceeds 65%.
Field installations require careful consideration during sucker rod deployment. When lowering the rods into the well, they must be securely fastened using sucker rod screws. The installation interval depends on the degree of corrosion and eccentric wear present in the oil well, typically spaced every 80-100 meters. For optimal results, the sucker rod anti-corrosion and anti-wear devices should be used alongside KXY-2 tubing cathodic protectors and standard nylon centralizers.
In addition to these technical improvements, ongoing research focuses on optimizing sucker rod performance under increasingly challenging conditions. Recent studies emphasize integrating advanced materials science with traditional engineering practices to create more resilient and efficient sucker rods capable of enduring prolonged exposure to harsh environments. This commitment to innovation ensures that sucker rods remain a vital component in maximizing oil production efficiency while minimizing operational disruptions and costs.