Production

Gas Lift Systems Explained: How Injected Gas Keeps Wells Flowing

Gas lift is a method of artificial lift that uses injected gas to make a well flow again. Compressed gas is sent down the annulus and enters the production tubing through valves, where it aerates the fluid column, lowers its density, and lets reservoir pressure push the lighter mixture to surface. The principle is simple; the equipment and tuning behind it are not.

Typical injection rates run from about 1,000 to 5,000 standard cubic feet of gas per barrel of produced fluid, and gas lift valves are set at depths from about 2,000 to 10,000 feet depending on reservoir pressure and lift requirements. The method is estimated to operate on 30 to 50 percent of wells in mature fields and accounts for roughly 10 percent of artificial lift installations worldwide.

The Principle: Lighter Fluid Flows

A column of oil has density, and that density is what the reservoir pressure has to push against. Inject gas into the column and the gas expands, breaks the liquid into droplets, and cuts the average density of the mixture to a fraction of the oil alone. The well's natural pressure, which was too weak to lift a full column, can now lift a foamy, aerated one. The deeper the gas is injected, the more of the column it lightens, which is why valve placement matters so much.

The System, Top to Bottom

Downhole Hardware

• Gas lift mandrels are installed in the tubing string at planned depths, typically 2,000 to 10,000 feet, and each carries a gas lift valve.
• Valves open when casing pressure exceeds the valve's set pressure, admit gas into the tubing, and close when the pressure differential reverses.
• Multiple valves let the well unload: shallow valves kick the well off initially, and as the column lightens, the operating point moves down to the design valve.
• Completion design determines whether valves are wireline retrievable or part of the tubing string, which affects future intervention cost.

Surface Facilities

• A compressor station or high-pressure gas source supplies lift gas at the required injection pressure.
• Metering and control equipment measures injection rate per well and regulates it, because over-injection wastes gas and under-injection leaves production on the table.
• Produced gas is separated, treated, and either sold or recycled back into the lift system; gas handling capacity is often the real constraint on a field's lift program.

Continuous vs Intermittent Lift

Most gas lift wells run continuous: a steady stream of gas keeps the column light at all times, suited to wells with strong enough pressure and steady inflow. Intermittent lift is the alternative for wells with weak pressure or low productivity: gas is injected in cycles, a slug of liquid is allowed to build, then the gas shoves the slug to surface in one push. Intermittent lift produces in bursts and needs careful timing of valve and surface controls, but it can lift wells that continuous gas lift cannot sustain.

Where Gas Lift Fits

Gas lift earns its place in mature fields, where an estimated 30 to 50 percent of wells run on it, and offshore, where it competes with submersible pumps on reliability and simplicity. It has no moving parts downhole, which removes the most common failure mode of mechanical lift. Deviated and horizontal wells are no problem, because there is no rod string to wear against the tubing. The trade is that it needs a reliable supply of high-pressure gas, so fields without gas infrastructure, or with low gas-oil ratios, usually look elsewhere.

What Limits Performance

• Emulsions: viscous water-oil mixtures resist being aerated and can choke the tubing even with good gas rates.
• Corrosion and scale: valve seats, mandrel ports, and tubing walls degrade, changing the pressure behavior the design assumed.
• Gas supply: injection below the design rate leaves the well under-lifted; injection above it wastes compression capacity and can actually reduce production.
• Valve tuning: a valve set too deep or too shallow shifts the operating point, and the well ends up cycling instead of flowing smoothly.
• High water cut: as water cut climbs, more gas is needed per barrel of oil, and the economics tighten.

Optimizing a Gas Lift Well

Gas lift is a tuning problem, not a set-and-forget installation. Production engineers track injection rate, casing and tubing pressure, and wellhead temperature, then adjust valve settings and surface gas rates as the reservoir depletes. Wells that used to lift at 2,000 SCF/bbl may need different rates at 5,000 a year later, and the wells that get revisited on data are the ones that stay near their design point.

That is where well records matter. OpsFlo's predictive maintenance module flags wells whose lift performance keeps drifting, and the asset intelligence module keeps valve and mandrel history so redesigns start from what is actually downhole, not from memory. For the fundamentals behind lift design, see the basics section, and the equipment reference covers the valves, compressors, and separators this system depends on. The glossary has the terms you will meet on a gas lift design sheet.