1. vb. [Drilling]

To plug the wellbore around a drillstring. This can happen for a variety of reasons, the most common being that either the drilling fluid is not properly transporting cuttings and cavings out of the annulus or portions of the wellbore wall collapse around the drillstring. When the well packs off, there is a sudden reduction or loss of the ability to circulate, and high pump pressures follow. If prompt remedial action is not successful, an expensive episode of stuck pipe can result. The term is also used in gravel packing to describe the act of placing all the sand or gravel in the annulus.

See: annulus,  circulate,  cuttings,  stuck pipe

2. vb. [Well Completions]

To effect hydraulic isolation, either with a sealing device, such as a packer, or with a specialized plastic or fluid, such as a sealing compound.

See: packer,  seal assembly