Lift Gas is used for increasing oil production. Gas is injected into the well casing, and infuses with the oil at different well depths depending on valve placement. The gas bubbles reduce the fluid column’s hydrostatic pressure and allow the reservoir liquids in the welll-bore to flow faster.
The lift gas comes up as associated or entrained gas in the oil. Lift gas applications can recover the “produced” gas and re-use it for continued lift.
Gas is not introduced to the reservoir itself.
Gas Injection is an Enhanced Oil Recovery (EOR) method. Gas is pumped into the reservoir and raises the pressure to “push” liquids towards the production well, or lower the viscosity to allow easier flow. In both cases, the reservoir composition is changed.