What is the concept of a gas lift?

• A. Gas acts to increase the hydrostatic head
• B. Increase gas-liquid ratio resulting in a reduction to bottomhole pressure
• C. Gas heats the fluid to reduce viscosity
• D. Gas-liquid ratio decreases with depth

Answer: (B)

Gas lift works by injecting gas into the produced fluid so the upward flow becomes a gas–liquid mixture with a lower effective density. By increasing the amount of gas relative to liquid (the gas–liquid ratio), the hydrostatic pressure in the wellbore drops, meaning the bottomhole pressure needed to push fluids to surface is reduced. As the gas expands while rising in the well, the mixture becomes even lighter, making it easier to lift production to surface. This is why the statement about increasing the gas–liquid ratio resulting in a reduction of bottomhole pressure best captures the concept of gas lift. The other ideas—heating to reduce viscosity, or depth-driven changes in the gas–liquid ratio, or gas adding pressure instead of reducing it—do not describe how gas lift actually facilitates lifting.