Fluid pressure locked well drilling tool

摘要

A telescopic bumper jar is made up in a string of drill collars in a well drilling pipe string, and fluid pressure holds the tool in a telescopically contracted condition with opposing shoulders abutting to prestress the tool to prevent fatigue during drilling. In one form the tool is locked by a fluid pressure expanded locking sleeve coengaged between the telescopic bodies. In another form a differential piston responsive to pressure in the tool and to hydrostatic pressure in the drill pipe prestresses the tool. In both forms, the pressure is relieved by a tripping plug dropped through the drill pipe.