Petroleum Operations Practice Test

In a multi-stage separator, what is the purpose of a third stage?

To vent gases to atmosphere.

To remove remaining liquids (water) from the gas after primary separation.

A multi-stage separator uses successive stages to progressively remove liquids from gas, giving more residence time and gravity-driven settling so droplets can drop out at each step. The third stage specifically targets what slips through the first two stages—the remaining liquids, especially water, that are still entrained in the gas after primary separation. By providing extra separation area and time, it pulls out this residual liquid, producing drier gas for downstream equipment and reducing issues like corrosion, hydrate formation, and compressor trouble.

Venting to atmosphere is not the purpose, as it would waste hydrocarbons and create environmental concerns. Increasing contact between gas and oil would work against separation, potentially keeping droplets suspended. Compressing the oil isn’t the role of a separator stage either; separation is about removing liquids from gas, not compressing them.

To increase the contact between gas and oil for better separation.

To compress the oil for storage.