The researchers from Moscow Polytechnical University, Tomsk Polytechnical University and K.I. Satpaev Kazakhstan National Research Technical University developed the engineering solution to improve reliability of subsurface sucker-rod pumps — the key equipment at mature oil fields. This development allows for eliminating the main reason of pumps failures — leakages in the valves.
Subsurface sucker-rod pumps remain the most widely used equipment for artificial oil lift. For example, at Uzen oilfield in Kazakhstan 917 out of 927 operating wells are equipped with such pumping units. At the same time, in 2022 only, 2,794 repairs were performed at these wells, i.e., about 3 times a year at one well. One of the key reasons of failures was wear and tear of valve couplings (a ball and a seating) leading to loss of sealing capacity and shutdown of pumps.
The engineering task was to eliminate the wear and tear emerging due to the fact that at each stroke the valve ball strikes into one and the same position on the seating. With time, sand, rust and paraffin deposits are accumulating in this nod aggravating the wear and tear due to abrasive forces.
To resolve this task, Russian and Kazakhstan scientists proposed to install a specialized inlet piece under the seating — a turbulator creating the swirl flow and making the ball to pivot. Due to this, the contact between the ball and the seating becomes more equable, and the wear and tear signs are evenly distributed across the entire surface.
To test their solution, the scientists made several turbulators prototypes different from each other by the axis deviation angle (0°, 5°, 10°, 15°) and the width of the spiral plate (5, 7.5 and 10 mm). They printed the prototypes on the 3D-printer using the FDM technology. The tests were performed at the lab unit with visualization of the ball movement via a high-speed camera (up to 4,800 frames per second). The set-up with the vertical axis and the 7.5 mm spiral plate demonstrated the best results: the ball was pivoting in a sustained way — up to 30 rotations per 7 seconds without significant increase of pulsatory oscillation and pressure losses.
The field tests at Uzen oilfield were the key stage. Ten turbulators made of aluminum alloy Al-Si-Mg (aluminum-silicium-magnesium) were installed into the valves of five pumps operating at the depth from 400 to 912 meters in the environment of high water cut (up to 98%) and significant mechanical impurities. In four out of five cases the upgraded valves operated much longer — from 77 to 101 days, while as the standard valves failed after 52 days on average.
Nevertheless, in one of the pumps (in well № 6356) the turbulator made of aluminum alloy broke prematurely due to abrasive damage: sand, rust and solid impurities quickly damaged the spiral plate. It showed that more wear-resistant materials are needed for operating in the aggressive medium. As an alternative, the scientists proposed to switch to the stainless steel, grade 316L featuring high durability, corrosion resistance and proved wear-resisting properties. In terms of durability, this grade exceeds the used aluminum alloy almost 1.5 times, and its life span is confirmed in several industries including healthcare and nuclear power generation.
