The oil industry is a developed industry with many innovations over the years aimed at improving efficiencies, increasing production and accessing previously hard to reach oil and gas deposits. In addition, the oil industry also experiences external pressures. As the oil price also fluctuates significantly, the economics of oil production also fluctuates.
These pressures have helped focus innovations in the industry and have led to significant breakthroughs. One of these breakthrough technologies is known as the gas lift method.
History of the Gas Lift Method
The principle of the gas lift method goes all the way back to the 18th century where it was used in mining to lift water out of mine shafts. Initial applications used air as the gas lift medium. This was also true in the oil industry when it was first used in the 1860s. However, air and hydrocarbon gas is not a good mixture and could easily result in explosions.
The process soon shifted to using hydrocarbon gas for oil well production, which is the basis for the gas lift methods we use today.
How the Gas Lift Method Works
The basic principle of the gas lift method is the expansion of gas as its pressure is reduced. Gas is compressed and injected into the well production tubing as low as possible without interfering with the bottom hole production. At the point where the gas is injected, the pressure is high as it is far below the surface of the earth and the production tubing is full of oil.
However, the gas expands as it enters the production tubing, lowering the pressure at that point.
Gas will automatically rise towards the surface up the production tubing due to the pressure gradient. As the gas rises, the pressure in the production tubing decreases because it is getting closer to atmospheric pressure at the top. The reduction in pressure causes the gas to expand more, thus creating even more upward lift in the production tubing. The net effect is that the flowing pressure gradient from the point of gas injection to the surface is reduced.
The pressure drop at the point of gas injection also helps oil production because it creates a pressure gradient from the bottom hole to the gas injection point. This means that the flow out of the well will actually increase. Once the gas has escaped from the production tubing at the surface, the column of oil would collapse back down into the well, unless more gas is injected at the bottom.
Both continuous and intermittent gas injection models are used in the gas lift method. Continuous gas injection supplies a steady flow of gas into the production tubing and maintains a steady oil production from the well. Intermittent gas injection only injects a burst of gas when needed to assist the flow of oil up the production tubing.
10 Important Factors for Using the Gas Lift Method
Gas injection pressure
Gas injection pressure can never exceed the rock pressure of a producing well, otherwise the flow of oil will stop completely.
Operating Parameters of a Well
The more detail about the operating parameters of a well, the more effective the design of a gas lift system will be. Some key parameters are:
- Viscosity of oil.
- Gas/liquid ration of the production stream from the well.
- Rock pressure.
- Specific gravity of the production stream.
- The amount of sand and consistency of sand carried through during production.
Production Oil Temperature
The temperature of production oil is also important from a safety perspective. High temperatures cause the gas to expand quickly, which could cause damage to mechanical equipment. Temperatures above 130F or 54C are not suitable for the gas lift method for this reason.
Continuous Gas lift Best Suited to Wells with High Volumes
The continuous gas lift method is ideally suited to wells with high volumes and high bottom hole pressure.
Consistency in Gas Pressure and Quality
Consistency in gas pressure and quality are important to maintain a consistent and reliable gas lift for the well.
Copes Well with Sand that Carries Through With the Oil
The gas lift method copes well with sand that carries through with the oil, whereas most other pumping methods do not.
Single Gas lift System Effectiveness
A single gas lift system can be used across a number of wells in close proximity. This is one of the ways to reduce the operating costs of using the gas lift method.
Gas lift systems are dependent on the design, operation and maintenance of the gas compressor. Skilled resources are needed for successful implementation of the gas lift method and must be considered as part of the planning process.
Intermittent Gas Lift High-Pressure Surges
Intermittent gas lift has limitations in wells that carry through a large amount of sand. The high pressure surges at the bottom hole will exacerbate this problem.
Intermittent Gas Lift Best Suited for Wells With Low Bottom-Hole Pressure
Intermittent gas lift is ideally suited for wells with a low bottom hole pressure and low volumes of oil production.
What We've Learned
Gas lift is one of the methods that has been developed in order to maximize oil production and improve efficiencies. It is a method that has been proven over many years of use and is widely accepted in the industry.
Gas lift systems are very effective when applied in the right circumstances. Knowledge of the well parameters helps designers and engineers to identify whether the well could benefit from gas lift and also to design the best system for the circumstances.