Abstract: A chain saw for cutting slots in a wellbore casing and the surrounding formation comprises a pair of cutting chain assemblies (37) rotatably mounted on a body and moveable from a storage position in which the axis of the cutting chain assemblies are parallel to the axis of the tool to a position at right angles to the storage position. The chains are driven by a mud-motor, step-up gearbox, drive shaft (20) and bevel gear (34). The position of the chain arms is controlled by a mud operated piston (44) which is connected by rods (41A) to racks (41) which mesh with pinions provided on the arms of the chain assemblies (37). Pressurization of the drillstring upon which the tool is mounted will cause rotation of the motor to drive the cutting chains and simultaneous downward displacement of the piston (44) to bring the cutting chains into engagement with the casing.

Abstract: A drill string component for preventing chafing of a drill casing as a result of contact between the drill casing and a rotating drill string comprises a central mandrel (2) having rotatably mounted thereon a sleeve (11). The sleeve (11) is retained between shoulders defined on the mandrel to prevent accidental loss of the sleeve in the event of excessive wear in the supporting bearings. Axial thrust loads are transferred from the outer sleeve (11) to the mandrel by way of thrust bearings supported on the mandrel shoulders. Seals (24A, 24B) located between the outer sleeve seal bodies (23) and an inner sleeve (9) prevent the ingress of contaminants to the zone of bushings (12, 13) which rotatably support the outer sleeve.

Abstract: A tool for use in an oil or gas well to retrieve a drilling or production string from the well, said tool comprising an assembly which can be mounted on a supporting string, a driven member carried by the assembly and responsive to vertical movement of the assembly, to be driven in a predetermined rotational direction, said driven member being provided with or supporting a self-tapping thread provided at the lowermost end of the assembly, the self-tapping thread having the same sense as said predetermined direction of rotation.