Parece que hay por lo menos dos acepciones. 1. Descargar para reducir presión (podría ser despresurizar), y 2. inicio de flujo de hidrocarburos en un pozo terminado. La cita es: http://www.glossary.oilfield.slb.com/Display.cfm?Term=swab

swab
1. vb. [Drilling] ID: 1617
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.

See: kick, swabbing, volumetric efficiency, well control

2. vb. [Well Completions] ID: 2847
To unload liquids from the production tubing to initiate flow from the reservoir. A swabbing tool string incorporates a weighted bar and swab cup assembly that are run in the wellbore on heavy wireline. When the assembly is retrieved, the specially shaped swab cups expand to seal against the tubing wall and carry the liquids from the wellbore.

Alternate Form: swabbing