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Spotlight

Electrical Submersible Pump

Wed, 01/22/2014 - 16:19

The electrical submersible pump (ESP) is a system that enables users to stimulate fluids from wellbores. The device has a hermetically sealed motor close-coupled to the pump body. Unlike jet pumps, which pull fluids, submersible push pumps press the fluids upwards, making this instrument a more efficient solution. The main advantage of using an ESP is that it prevents pump cavitation, a problem associated with a high elevation difference between the pump and the fluid surface. The submersible pumps used in ESP installations are multi-stage centrifugal pumps operating in a vertical position. After being subjected to significant centrifugal forces caused by the high rotational speed of the impeller, produced liquids lose their kinetic energy in the diffuser. In consequence, kinetic energy is converted into pressure. The pump shaft is connected to the gas separator by a mechanical coupling at the bottom of the pump. Well fluids enter the pump and are lifted by the pump’s stages. Radial bearings are distributed along the length of the shaft providing support to the pump shaft as this spins at high rotational speeds.

More oil can be produced by decreasing pressure at the bottom of the well either by lowering bottom hole flowing pressure or increasing drawdown. ESP systems consist of surface components, housed in oil platforms or other facilities, and subsurface components that can be found in the well hole. Surface components include the motor controller, surface cables, and transformers. Subsurface elements include a multi-staged centrifugal pump, a three phase induction motor, a seal chamber section, and cables. Submersible pumps can be connected to various types of pipes and hoses according to the task and the fluid being pumped.

Until recently, the installation of ESPs had been rather costly due to the need of an electric cable downhole. Advancements in coiled tubing umbilicals now allow for both the piping and electric cable to be deployed with a single conventional coiled tubing unit to supply energy to the motors. The powering of ESP systems can be tricky, as these perform better with alternate current sources needed to drive a special motor that can work under high temperatures of up to 300°F and high pressures of up to 5,000psi. Another problem with ESP units is that given their high rotational speed of up to 4000rpm and tight clearances, they have very low tolerance to solids, such as sand. However, special pumps with hardened surfaces and bearings to minimize wear and increase run life are available. New varieties of ESPs even include a water-oil separator which enables the reinjection of the extracted water into the reservoir without the need to lift it to the surface.