Swab:

To reduce pressure in a wellbore by moving pipe, wireline tools or rubber-cupped seals up the wellbore.

If the pressure is reduced sufficiently, reservoir fluids may flow into the wellbore and towards the surface.

Swabbing is generally considered harmful in drilling operations, because it can lead to kicks and wellbore stability problems.

In production operations, however, the term is used to describe how the flow of reservoir hydrocarbons is initiated in some completed wells.

antonym: surge.