Patent ID: 6059050
Filing Date: 2000-05-09
Classification: E21B

Abstract:
Apparatus for drilling a well bore comprising:a drilling tool and a drill tubing mounted for rotation of the drilling tool relative to the drill tubing about an axis of rotation;the drilling tool including a main tool body and a rotary drill bit mounted on the main body for rotation relative to the main body such that rotation of the drill bit causes a torque to be developed between the main body of the drilling tool and the drill tubing;and an apparatus for controlling rotation of the main body of the drilling tool relative to the drill tubing in response to said torque comprising:a hydraulic pump having a first pump part a first member connected to one of the drilling tool and the drill tubing and a pump second part a second member connected to the other of the drilling tool and the drill tubing and arranged such that said relative rotation of the drilling tool and the drill tubing causes relative rotation of said first and second pump parts and thereby pumping of a hydraulic fluid from a first chamber to a second chamber within which the hydraulic fluid is under pressure;a hydraulically actuated brake having a first brake part on the first member and a second brake part on the second member and arranged such that application of the hydraulic fluid under pressure from the second chamber causes actuation of the brake to resist said relative rotation of the drilling tool and the drill tubing;a duct for releasing the hydraulic fluid under pressure from the second chamber for return to the first chamber for pumping by the pump arranged such that flow of the hydraulic fluid from the second chamber tends to release the brake to allow said relative rotation while said relative rotation causes pumping of further fluid to the second chamber to apply said brake;and an orifice for controlling flow of fluid through the duct, the orifice being operable to maintain said flow of fluid at a required rate to maintain the relative rotation at a required rate.