Gas lift
Encyclopedia
Gas lift is one of a number of processes used to artificially lift oil
or water from wells where there is insufficient reservoir pressure to produce the well. The process involves injecting gas through the tubing-casing annulus
. Injected gas aerates the fluid to reduce its density
; the formation pressure is then able to lift the oil column and forces the fluid out of the wellbore. Gas may be injected continuously or intermittently, depending on the producing characteristics of the well and the arrangement of the gas-lift equipment.
The amount of gas to be injected to maximize oil production varies based on well conditions and geometries. Too much or too little injected gas will result in less than maximum production. Generally, the optimal amount of injected gas is determined by well tests, where the rate of injection is varied and liquid production (oil and perhaps water) is measured.
Although the gas is recovered from the oil at a later separation stage, the process requires energy to drive a compressor
in order to raise the pressure of the gas to a level where it can be re-injected.
The gas-lift mandrel
is a device installed in the tubing string of a gas-lift well onto which or into which a gas-lift valve
is fitted. There are two common types of mandrels. In a conventional gas-lift mandrel, a gas-lift valve is installed as the tubing is placed in the well. Thus, to replace or repair the valve, the tubing string must be pulled. In the side-pocket mandrel
, however, the valve is installed and removed by wireline
while the mandrel is still in the well, eliminating the need to pull the tubing to repair or replace the valve.
A gas-lift valve is a device installed on (or in) a gas-lift mandrel, which in turn is put on the production tubing
of a gas-lift well. Tubing and casing pressures cause the valve to open and close, thus allowing gas to be injected into the fluid in the tubing to cause the fluid to rise to the surface. In the lexicon of the industry, gas-lift mandrels are said to be "tubing retrievable" wherein they are deployed and retrieved attached to the production tubing. See gas-lift mandrel.
Other typical examples of equipment also used in connection with gas-lift production may be found at: http://www.slb.com
Petroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...
or water from wells where there is insufficient reservoir pressure to produce the well. The process involves injecting gas through the tubing-casing annulus
Annulus (oil well)
The annulus of an oil well refers to any void between any piping, tubing or casing and the piping, tubing, or casing immediately surrounding it. It is named after the corresponding geometric concept...
. Injected gas aerates the fluid to reduce its density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
; the formation pressure is then able to lift the oil column and forces the fluid out of the wellbore. Gas may be injected continuously or intermittently, depending on the producing characteristics of the well and the arrangement of the gas-lift equipment.
The amount of gas to be injected to maximize oil production varies based on well conditions and geometries. Too much or too little injected gas will result in less than maximum production. Generally, the optimal amount of injected gas is determined by well tests, where the rate of injection is varied and liquid production (oil and perhaps water) is measured.
Although the gas is recovered from the oil at a later separation stage, the process requires energy to drive a compressor
Gas compressor
A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas...
in order to raise the pressure of the gas to a level where it can be re-injected.
The gas-lift mandrel
Mandrel
A mandrel is one of the following:* an object used to shape machined work.* a tool component that grips or clamps materials to be machined.* a tool component that can be used to grip other moving tool components.- Variants :...
is a device installed in the tubing string of a gas-lift well onto which or into which a gas-lift valve
Valve
A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...
is fitted. There are two common types of mandrels. In a conventional gas-lift mandrel, a gas-lift valve is installed as the tubing is placed in the well. Thus, to replace or repair the valve, the tubing string must be pulled. In the side-pocket mandrel
Mandrel
A mandrel is one of the following:* an object used to shape machined work.* a tool component that grips or clamps materials to be machined.* a tool component that can be used to grip other moving tool components.- Variants :...
, however, the valve is installed and removed by wireline
Wireline
In the oil and gas industry, the term wireline usually refers to a cabling technology used by operators of oil and gas wells to lower equipment or measurement devices into the well for the purposes of well intervention and reservoir evaluation....
while the mandrel is still in the well, eliminating the need to pull the tubing to repair or replace the valve.
A gas-lift valve is a device installed on (or in) a gas-lift mandrel, which in turn is put on the production tubing
Production tubing
Production tubing is a tube used in a wellbore through which production fluids are produced .Production tubing is run into the drilled well after the casing is run and cemented in place. Production tubing protects wellbore casing from wear, tear, corrosion, and deposition of by-products, such as...
of a gas-lift well. Tubing and casing pressures cause the valve to open and close, thus allowing gas to be injected into the fluid in the tubing to cause the fluid to rise to the surface. In the lexicon of the industry, gas-lift mandrels are said to be "tubing retrievable" wherein they are deployed and retrieved attached to the production tubing. See gas-lift mandrel.
Other typical examples of equipment also used in connection with gas-lift production may be found at: http://www.slb.com
See also
- PumpjackPumpjackA pumpjack is the overground drive for a reciprocating piston pump in an oil well....
- Progressive cavity pumpProgressive cavity pumpA progressive cavity pump is a type of positive displacement pump and is also known as a progressing cavity pump, eccentric screw pump or even just cavity pump. It transfers fluid by means of the progress, through the pump, of a sequence of small, fixed shape, discrete cavities, as its rotor is...
- Submersible pumpSubmersible pumpA submersible pump 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...