Artificial lift

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Artificial lift system involves the use of artificial means to improve the flow of fluids like crude oil,water and gas to the surface by implementing a mechanical device in or on the well bore, which can be high pressure gas, mechanical pumps or velocity strings. Artificial lift is needed in wells when there is insufficient pressure in the reservoir to lift the fluid to the surface. This fluid can be both oil, water and gas. The artificial lift provides additional energy to the system such that the fluids can be lifted to surface.

The most common methods of achieving this in oil wells is to use pumps. The most recognized type is the rod pump or the "Nodding Donkey" seen in land based oil fields world wide. The rod pump works by creating a reciprocating motion in a sucker-rod string that connects to the downhole pump assembly. The pump contains a plunger and valve assembly to convert the reciprocating motion to vertical fluid movement. This type of pump is used on low rate well producing where 10's to 100's of barrels of oil are produced a day. The other types of commonly used lifting methods are Electric Submersible Pump (ESPs), Jet Pumps, Progressing-Cavity pumps (PCPs) and gas lift. These systems are introduced into the well down hole. They are also accompanied by a ground-level power-supplier device that can be electrical and/or mechanical.

1 Hydraulic Pumping Systems
2 ESP
3 Rod Pumps
- 3.1 Components
4 References

[edit] Hydraulic Pumping Systems

Hydraulic pumping systems, such as Jet Pumps, transmit energy downhole by means of pressurized power fluid that flows in the wellbore tubular. This method of transmitting energy downhole is reasonably efficient. The two methods of converting the energy downhole is to have either a downhole hydraulic pump, which has a set of coupled reciprocating piston, one is powered by the injected fluid while the other pumps the wellbore fluid to surface. The jet pump works by taking the injected fluid and turning it into a high velocity jet that mixes with the wellbore fluid and helps lift it to surface.

These systems are very versatile and have been used in shallow depths (1000ft) to deeper wells (18,000ft), low rate wells with production in the 10’s of barrels per day to wells producing in excess of 10,000 Barrels per day. In addition to this certain fluids can be mixed in with the injected fluid to help deal or control with corrosion, paraffin and emulsion problems. They are also suitable for wells where conventional pumps such as the rod pump are not possible due to crooked or deviated wells.

[edit] ESP

Electric Submersible Pumps consist of three parts, a downhole pump and motor, electric power cable from the pump to the surface and surface controls to operate the pump. The pump it self is located in the tubing string where it is close coupled to a submersible electric motor which is attached to the power cables. ESP’s are very versatile artificial lift methods and can be found in operating environments all over the wells. They are able to handle low rate producing wells to extremely high rate fluid flows up to 90,000 B/d. They can be modified to handle contaminants commonly found in oil, as well as aggressive corrosive fluids such as H2S and CO2 and abrasive contaminants such as sand. Increasing water cut has been shown to have no significant detrimental effect on the ESP performance either. It is possible to locate them in horizontal, deviated or directionally drilled wells however it is recommended for optimum performance they are located in straight section of tubing.

[edit] Rod Pumps

Rod Pumps are large cylinders with fixed and mobile elements inside. The most important components are: the barrel, vales (traveler and fixed) and the piston. It also has

another 18 to 30 components which are called "fitting". The pump is designed to be inserted inside the tubing of a well and its main purpose is to gather fluids from beneath

it and take them to the surface.

[edit] Components

Every part of the pump is important for its correct operation. The most commonly used parts are described below:

- Barrel: The barrel is a large cylinder which can be from 10 to 36 feet long and a diameter from 1.25 to 3.75 inches. After using several materials for its construction, the API (American Petroleum Institute) standardized the use of 2 materials or compositions for this part which are carbon steel and brass, both with an inside coating of chrome. The advantage of brass against carbon steel, weather is a more soft material, is its 100% resistance to corrosion.

- Piston: This is a nickel-metal sprayed steel cylinder, that goes inside the barrel. Its main purpose is to create a sucking effect that lift the fluids beneath it and then, with the help of the valves, take that fluids above it and, progressively, out of the well. It achieves this with a reciprocal up and own movement.

- Valves: The valve has two components - the seat and the ball - which create a complete seal when closed. After trying several materials, the most commonly used seats are made of carbon nitride and the ball is often made of silicon nitride. In the past, balls of iron, ceramic and titanium were used. This last type of balls, made of titanium, are still being used but only where crude oil is extremely dense and/or the quantity of fluids is too much. The most common configuration of a rod pump, requires two valves, called the traveling valve and fixed or static valve.

- Piston Rod: It's a rod that connects the piston with the outside of the pump. Its main purpose is to transfer the engine produced by the "Nodding Donkey" above in a up/down reciprocal movement.

- Fitting: The rest of the parts of the pump is called fitting and is, basically, small pieces designed to keep everything hold together in the right place. Most of these parts, are designed to let the fluids pass uninterrupted.

- Filter: The job of the filter, as guessed, is to stop big parts of rock, rubber or any other garbage that might be loose in the well from going into the pump. There are several types of filters, being a common iron cylinder with enough holes in it to permit the entrance of the amount of fluid the pump needs the most commonly used.