Patent ID: 9322218
Filing Date: 2016-04-26
CPC Classification: E21B

Claim Text:
1. A borehole cutting assembly for directional cutting in a borehole, the assembly comprising an input pipe and a cutting head rotatably mounted on the input pipe such that the orientation of the cutting head relative to the input pipe can be altered to determine the direction of cutting of the borehole, the cutting head comprising a cutting tool and a cutting tool motor operable to rotate the cutting tool relative to the input pipe so that when the cutting tool is loaded in use the cutting head is subject to a tool reaction torque that acts to rotate the cutting head to change the orientation of the cutting head, the cutting head being rotatably mounted on the input pipe by a controlled torque coupling comprising a progressive cavity pump having a rotor and a stator each provided with drive formations arranged to define a fluid flow cavity therebetween, rotation of the rotor relative to the stator forcing fluid flow through the cavity to counteract the tool reaction torque, fluid flow control means being provided to control the flow of fluid through the cavity in use and thus to control the magnitude of the counteraction generated by the progressive cavity pump to the tool reaction torque, the fluid flow control means comprising a hydraulic circuit comprising the progressive cavity pump, a valve and a tank from which the progressive cavity pump draws and returns fluid, the valve being arranged in the hydraulic circuit in series with the progressive cavity pump such that a pressure head generated at the progressive cavity pump in use is contained within the circuit branch between the progressive cavity pump and the valve.