A submersible pump (or sub pump, electric submersible pump (ESP)) is a device which has a hermetically sealed motor close-coupled to the pump body. The whole assembly is submerged in the fluid to be pumped. The main advantage of this type of pump is that it prevents pump cavitation, a problem associated with a high elevation difference between pump and the fluid surface. Submersible pumps push fluid to the surface as opposed to jet pumps having to pull fluids. Submersibles are more efficient than jet pumps.
Ca. 1928 Russian oil delivery system engineer and inventor Armais Arutunoff successfully installed the first submersible oil pump. In 1929, Pleuger Pumps pioneered the design of the submersible turbine pump, the forerunner of the modern multi-stage submersible pump. In the mid 1960s the first fully submersible deep-well water pump was developed by Poul Due Jensen who later went on to start Grundfos.
The submersible pumps used in ESP installations are multistage centrifugal pumps operating in a vertical position. Although their constructional and operational features underwent a continuous evolution over the years, their basic operational principle remained the same. Produced liquids, after being subjected to great centrifugal forces caused by the high rotational speed of the impeller, lose their kinetic energy in the diffuser where a conversion of kinetic to pressure energy takes place. This is the main operational mechanism of radial and mixed flow pumps.
The pump shaft is connected to the gas separator or the protector by a mechanical coupling at the bottom of the pump. When fluids enter the pump through an intake screen and are lifted by the pump stages.Other parts include the radial bearings (bushings) distributed along the length of the shaft providing radial support to the pump shaft turning at high rotational speeds. An optional thrust bearing takes up part of the axial forces arising in the pump but most of those forces are absorbed by the protector’s thrust bearing.
Submersible pumps are found in many applications. Single stage pumps are used for drainage, sewage pumping, general industrial pumping and slurry pumping. They are also popular with pond filters. Multiple stage submersible pumps are typically lowered down a borehole and most typically used for residential, commercial, municipal and industrial water extraction (abstraction), water wells and in oil wells.
Other uses for submersible pumps include sewage treatment plants, seawater handling, fire fighting (since it is flame retardant cable), water well and deep well drilling, offshore drilling rigs, artificial lifts, mine dewatering, and irrigation systems.
Special attention to the type of submersible pump is required when using certain types of liquids. Pumps used for combustible liquids or for water that may be contaminated with combustible liquids must be designed not to ignite the liquid or vapors.
Use in oil wells
Submersible pumps are used in oil production to provide a relatively efficient form of "artificial lift", able to operate across a broad range of flow rates and depths. By decreasing the pressure at the bottom of the well (by lowering bottomhole flowing pressure, or increasing drawdown), significantly more oil can be produced from the well when compared with natural production. The pumps are typically electrically powered and referred to as Electrical Submersible Pumps (ESP).
ESP systems consist of both surface components (housed in the production facility, for example an oil platform) and sub-surface components (found in the well hole). Surface components include the motor controller (often a variable speed controller), surface cables and transformers. Subsurface components typically include the pump, motor, seal and cables. A gas separator is sometimes installed.
The pump itself is a multi-stage unit with the number of stages being determined by the operating requirements. Each stage consists of a driven impeller and a diffuser which directs flow to the next stage of the pump. Pumps come in diameters from 90mm (3.5 inches) to 254mm (10 inches) and vary between 1 metre (3 ft) and 8.7 metres (29 ft) in length. The motor used to drive the pump is typically a three phase, squirrel cage induction motor, with a nameplate power rating in the range 7.5 kW to 560 kW (at 60 Hz).
New varieties of ESP can include a water/oil separator which permits the water to be reinjected into the reservoir without the need to lift it to the surface. There are at least 15 brands of oilfield esps used throughout the world. Until recently, ESPs had been highly costly to install due to the requirement of an electric cable downhole. This cable had to be wrapped around jointed tubing and connected at each joint. New coiled tubing umbilicals allow for both the piping and electric cable to be deployed with a single conventional coiled tubing unit.
The ESP system consists of a number of components that turn a staged series of centrifugal pumps to increase the pressure of the well fluid and push it to the surface. The energy to turn the pump comes from a high-voltage (3 to 5 kV) alternating-current source to drive a special motor that can work at high temperatures of up to 300 °F (149 °C) and high pressures of up to 5,000 psi (34 MPa), from deep wells of up to 12,000 feet (3.7 km) deep with high energy requirements of up to about 1000 horsepower (750 kW). ESPs have dramatically lower efficiencies with significant fractions of gas, greater than about 10% volume at the pump intake. Given their high rotational speed of up to 4000 rpm (67 Hz) and tight clearances, they are not very tolerant of solids such as sand.
A submersible pump cable is a specialized product to be used for a submersible pump in a deep well, or in similarly harsh conditions. The cable needed for this type of application must be durable and reliable as the installation location and environment can be extremely restrictive as well as hostile. As such, submersible pump cable can be used in both fresh and salt water. It is also suitable for direct burial and within well castings. A submersible pump cable's area of installation is physically restrictive. Cable manufacturers must keep these factors in mind to achieve the highest possible degree of reliability. The size and shape of submersible pump cable can vary depending on the usage and preference and pumping instrument of the installer. Pump cables are made in single and multiple conductor types and may be flat or round in cross section; some types include control wires as well as power conductors for the pump motor. Conductors are often color-coded for identification and an overall cable jacket may also be color-coded.
Major types of cable include:
In 3&4 Core cable as per right side SPC types image shown, Plain Copper/Tinned Copper used as conductor.
- PVC 3&4 Core Cable
- Flat Cable
- Round Cable
- Rubber 3&4 Core Cable
- Flat Cable
- Round Cable
- Flat Drincable
- HO7RN-F Cable
- A Historical Perspective of Oilfield Electrical Submersible Pumps
- World Pumps: A Brief History of Pumps
- Grundfoss Museum- Youtube
- Lyons (ed), Standard Handbook of Petroleum & Natural Gas Engineering", p. 662
- Other forms of artificial lift include Gas Lift, Beam Pumping, Plunger Lift and Progressive cavity pump.
- "Submersible pump cable", The Pump Book, pp. 67–74, ISBN 978-0-615-18509-5
- Ray C. Mullin, Phil Simmons (2011), "Submersible Pump Cable", Electrical Wiring Residential, pp. 423–424, ISBN 978-1-4354-9826-6
- Robert J. Alonzo (19 January 2010). Electrical Codes, Standards, Recommended Practices and Regulations: An Examination of Relevant Safety Considerations. Elsevier. pp. 317–. ISBN 978-0-8155-2045-0. Retrieved 16 November 2012.
- Lyons, William C., ed. (1996). Standard Handbook of Petroleum & Natural Gas Engineering. 2 (6 ed.). Gulf Professional Publishing. ISBN 0-88415-643-5.
- Operation, applications and advantages of electric submersible pumps
- Versatile Pump Works Under Water, July 1947, Popular Science excellent cutaway drawing of large public water works submersible pump design
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