A BOREHOLE CUTTING ASSEMBLY FOR DIRECTIONAL CUTTING

摘要

A borehole cutting assembly for directional cutting in a borehole, the assembly comprising an input pipe (1) and a cutting head (3) rotatably mounted on the input pipe (1) such that the orientation of the cutting head (3) relative to the input pipe (1) can be altered to determine the direction of cutting of the borehole. A cutting tool (9) and cutting tool motor (11) are mounted on the cutting head (3) to enable the cutting tool (9) to be rotatably driven relative to the cutting head (5) so that when the cutting tool (9) is loaded in use the cutting head (3) is subject to a tool reaction torque that acts to rotate the cutting head (3) to change the orientation of the cutting head (3). The cutting head (3) is rotatably mounted on the input pipe (1) by a controlled torque coupling (13) comprising a progressive cavity pump (21) having a rotor (15) and a stator (19) each provided with drive formations arranged to define a fluid flow cavity (27) therebetween. Rotation of the rotor (15) relative to the stator (19) forces fluid flow through the cavity (27) to counteract the tool reaction torque. Fluid flow control means (45) is provided to resist the flow of fluid through the cavity (27) in use and thus to control the magnitude of the counteraction generated by the progressive cavity pump (21) to the tool reaction torque.