At present, CNPC is using more than 120,000 conventional beam pumping units for oil production. The average efficiency of this conventional pumping system is only about 24%, so the energy consumption is very high. For energy-efficient, two types of long stroke pumping unit based on permanent magnet synchronous motor (PMSM) were developed: direct-drive pumping unit (DDPU) and chain transmission pumping unit (CTPU).
For DDPU, the driving wheel is directly connected to a low-speed high-torque PMSM and drives the belt by friction to achieve oil pumping. The maximum polished rod load of DDPU is below 200kN. The CTPU is another version of DDPU: a chain transmission was added between the PMSM and driving wheel. CTPU is mainly larger type pumping unit, the maximum polished rod load of which is above 200kN.
A DDPU is tested on X9-4 well in Jianghan oilfield and a CTPU is tested on Dugu-4 well in Liaohe oilfield. Test results show that both pumping units run smoothly and have low noise, and the stroke is stepless adjustable. Compared with the replaced conventional beam pumping units, the energy consumption for DDPU is 21 percent lower and for CTPU is 28 percent lower. Fewer pumping cycles result in decreased sucker rod vibration and higher pump filling factor. The dynamic indicator diagrams are much closer to the static indicator diagram.
Now the two types of pumping unit have been deployed on more than 40 wells - mainly in Tarim oilfield for deep or viscous oil wells, and will be a new energy-saving and cost-reducing means of oil production.