To start the mud pump for restoring circulation of the mud column.
Because the stagnant drilling fluid has thickened or gelled during the period of no circulation, high pump pressure is usually required to break circulation.
To establish circulation of drilling fluids after a period of static conditions.
Circulation may resume after a short break, such as taking a survey or making a mousehole connection, or after a prolonged interruption, such as after a round trip.
The operation is of more concern to drillers and well planners with longer static intervals, since immobile drilling mud tends to become less fluid and more gelatinous or semisolid with time.