1. n. [Drilling]
A small-diameter channel worn into the side of a larger diameter wellbore. This can be the result of a sharp change in direction of the wellbore (a dogleg), or if a hard formation ledge is left between softer formations that enlarge over time. In either case, the diameter of the channel is typically similar to the diameter of the drillpipe. When larger diameter drilling tools such as tool joints, drill collars, stabilizers, and bits are pulled into the channel, their larger diameters will not pass and the larger diameter tools may become stuck in the keyseat. Preventive measures include keeping any turns in the wellbore gradual and smooth. The remedy to keyseating involves enlarging the worn channel so that the larger diameter tools will fit through it.