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Abstract

An expandable drill bit for cleaning solidified cement from a well casing used in oil drilling operations. The bit has an initial diameter which allows it to be passed through a permanent restriction in a well casing and thereafter expanded to clean out the casing below the restriction. The bit has three uniformly spaced cutting elements which may be fully retracted within the diameter of the cylindrical outline of the body of the bit and are located at the forwardmost end in a strengthened portion of the body. The cutting elements have projections which are engaged by the forward end of a piston sliding along the axis of the drill body within a cylinder bore and are actuated thereby to their cutting positions, with their cutting edges generally radially extending but slightly forwardly divergent, by the hydraulic pressure on the piston of a fluid forced down through the drilling string which carries the bit. The piston has a central bore and a passage extending therefrom to communicate with an annular recess in the outer surface of the piston body. After the piston is forced to the position in which the cutting elements are actuated to their extended cutting positions, this recess communicates with ports in the wall of the cylinder bore which extend to passages in the tool body having outlet ports at the cutting end of the drill body. Cutting elements in their retracted positions have converging edge portions which guide the drill through restrictions during movement toward a drilling location and which are moved to parallel wall engaging positions to support the tool during drilling. The drill string is lubricated while being retracted from a well for repair or replacement of the drill bit by a device comprising a flat cylindrical annular plate inserted below the blowout preventers of a well head and comprising radial passages surrounding the drill string and forming spray nozzles for controlled pressurized insertion of a lubricating fluid sprayed around the circumference of the drill string. A plurality of spring biased check valves in the passages prevent the escape of pressure from within the well.

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First Claim