Downhole pumps are commonly used in petroleum industries in order to measure the boosting the productivity of a well by lowering the bottom hole flowing pressure.
Two types of pumps are used: positive-displacement pumps, which include sucker rod pumps and hydraulic piston pumps; and dynamic displacement pumps, the most common of which are electrical submersible centrifugal pumps and jet pumps.
Here we are going to look at the dynamic displacement pump.
Electrical Submersible Pumps:
An electrical submersible pump (ESP) is a multistage centrifugal pump that offers a great deal of flexibility. ESPs are capable of producing very high volumes of fluid, can be used efficiently in deeper wells than sucker rod pumps, and are able to handle some free gas in the pumped fluid.
The pump is driven by an electric motor connected by cables to a three-phase power source at the surface.
The motor is situated so that the produced fluids flow around the motor, providing cooling, either by setting the pump above the producing interval, or by equipping the pump with a shroud that directs the fluids past the motor before entering the pump intake.
Centrifugal pumps do not displace a fixed amount of fluid, as do positive-displacement pumps, but rather create a relatively constant amount of pressure increase to the flow stream. The flow rate through the pump will thus vary, depending on the back pressure held on the system.
Jet Pumps:
Ajet pump is a dynamic-displacement pump that differs dramatically from a centrifugal pump in the manner in which it increases the pressure of the pumped fluid. A power fluid is accelerated through a nozzle and then mixed with the produced fluid in the throat of the pump. As the fluids mix, some of the momentum of the power fluid is transferred to the produced fluid; in the diffuser, some of the kinetic energy of the mixed stream is converted to static pressure.
Jet pumps offer the advantage of having no moving parts, so dirty or gassy fluids can be produced without the wear that will result in positive-displacement pumps. They can also be used at any depth. Drawbacks to jet pumps are their low efficiency (generally in the 20-30% range) and the need for high suction pressure to prevent cavitation in the pump.
