Gas lift
A gas lift or bubble pump is a type of pump that can raise fluid between elevations by introducing gas bubbles into a vertical outlet tube; as the bubbles rise within the tube they cause a drop in the hydrostatic pressure behind them, causing the fluid to be pulled up. Gas lifts are commonly used as artificial lifts for water or oil, using compressed air or water vapor.
Gas lifts have been used for a variety of applications:
- Coffee percolators and electric drip coffeemakers use vaporized water to lift hot water
- Airlift pumps use compressed air to lift water
- Pulser pumps use a subterranean air chamber to lift underground water
- Suction dredges use a variety of the gas lift called an airlift pump to vacuum mud, sand and debris
- Mist lifts use vaporized water to draw seawater in ocean [thermal energy conversion] systems
Petroleum industry uses
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 is measured. Alternatively, mathematical models can be used to estimate the optimum gas injection rate. Such models offer significant economic benefit, since they allow one to simulate the performance of an actual or planned gas-lifted well using a digital replica of the well.
Although the gas is recovered from the oil at a later separation stage, the process requires energy to drive a compressor 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 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.
Gas lift operation can be optimized in different ways. The newest way is using risk-optimization which considers all aspects for gas lift allocation.