Gas lift is a method used in the oil and gas industry to enhance oil flow from a well. This technique involves injecting high-pressure gas into the production tubing to assist natural forces. As an artificial lift method, gas lift helps maintain or increase production rates when natural reservoir pressure is insufficient to push fluids to the surface.
The Need for Artificial Lift in Oil Production
Oil wells initially often possess sufficient natural pressure to drive hydrocarbons to the surface. However, as production continues over time, the pressure within the reservoir naturally declines. This reduction in reservoir pressure eventually makes it difficult for oil to flow to the surface on its own, leading to a decrease in production rates.
To counteract this natural decline and maintain economic production, artificial lift methods become necessary. These techniques supplement or replace the reservoir’s natural energy to bring fluids to the surface.
How Gas Lift Enhances Oil Flow
The fundamental mechanism of gas lift involves injecting high-pressure gas into the production tubing of an oil well. This gas typically enters the well through the annular space between the production tubing and the casing. Downhole, the injected gas mixes with the oil and other produced fluids within the tubing.
Mixing the gas with the fluid column significantly reduces the overall density of the fluid mixture. This aeration effect lightens the hydrostatic column. With a lighter fluid column, the natural reservoir pressure, even if diminished, becomes more effective at pushing the less dense mixture to the surface. The expanding gas bubbles also contribute to propelling the oil upwards, thereby enhancing the flow rate.
Essential Equipment for Gas Lift Operations
A gas lift system relies on several primary components to function effectively. Compressors are surface equipment responsible for taking gas and increasing its pressure to the required injection level. This high-pressure gas is then delivered to the wellhead through surface injection lines.
Downhole, gas lift valves are installed within mandrels integrated into the production tubing. These valves precisely control the entry of the high-pressure gas from the casing annulus into the production tubing. The mandrels provide a means to position these valves at specific depths, ensuring gas injection occurs at optimal points to maximize lift efficiency.
Different Approaches to Gas Lift Systems
Gas lift systems are primarily categorized into two main operational approaches: continuous flow and intermittent flow. Continuous flow gas lift involves a steady injection of high-pressure gas into the well. This method is typically employed for high-volume wells with sufficient reservoir pressure, where it helps maintain a consistent and stable flow of fluids to the surface.
Intermittent gas lift, on the other hand, operates by injecting gas in pulses or timed cycles. This approach is often chosen for wells with lower production rates or declining reservoir pressures, where a continuous injection might not be efficient. The pulsed gas creates slugs of liquid that are pushed to the surface, allowing the well to build up a fluid column before the next injection cycle.
When Gas Lift is the Preferred Method
Gas lift is a suitable artificial lift technique in several specific scenarios. It is often preferred when a readily available source of injection gas exists. The system’s robustness also makes it a viable option for wells producing corrosive fluids or sand, as its downhole components are generally more resilient compared to some mechanical pumping systems.
Gas lift is also well-suited for wells with high gas-oil ratios, where the natural gas present can be supplemented to enhance lift. Its relatively compact surface footprint also makes it advantageous for remote locations or offshore platforms where space is limited. While flexible, gas lift may become less efficient if reservoir pressure or liquid production rates become very low, potentially leading operators to consider other artificial lift methods.