The different types of oil pumping
If the fluid extracted from oil wells does not have sufficient energy to reach the surface, the wells are said to be "non-eruptive".
A pumping device adapted to the well’s producing conditions is then lowered into the well, in order to raise the fluid up to the surface. The pumping system itself is also adapted to the well’s flow.
Wells can be equipped with 2 pumping systems:
- Pumping unit (PU), (or stem pumps or "horse heads"). The double-acting piston pump lowered to the bottom of the well is connected by a small diameter rod string (approximately 20 mm) to the surface-mounted rock pump unit, thus giving it a reciprocating motion. This device does not allow pumping in heavily deviated wells as is often the case today, and it is limited in flow (maximum 100 m3 approximately).
- Electric Submersible Pump (ESP): A small diameter centrifugal pump (120 to 130 mm), with a very large number of stages (200 to 300), is powered by a powerful electric motor (100 to 300 HP). Located at the bottom of the well, the motor is connected to a high voltage electrical cable (about 1800 V) and suspended from the production casing through which the fluid will be produced. This makes it possible to put into production sidetracked wells, with flows that can be significant (more than 1 000 m3 /d). On the surface, only a small wellhead and a current transformer station will remain, making this pumping mode particularly discreet.
For larger flows, ESPs is used. For flow rates of less than 50 m3 /day, PUs are preferred. This means that the pumping system can change during the life of a well.
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