1. n. [Drilling]

A brief influx of gas that is introduced into the drilling fluid when a pipe connection is made. Before making a connection, the driller stops the mud pumps, thereby allowing gas to enter the wellbore at depth. Gas may also be drawn into the wellbore by minor swabbing effects resulting from short movements of the drillstring that occur during the connection. Connection gas usually occurs after one lag interval following the connection. On a mud log, it will appear as a short peak above background levels. This peak often appears at 30-foot intervals, depending on the lengths of drillpipe being connected as the well is drilled.

See related terms: equivalent circulating density,  trip gas