Abstract: An apparatus for controlling rotation of an outer sleeve member relative to an inner cylindrical duct member is used in a drilling system for controlling steering of a downhole drilling tool. The apparatus includes an annular swash plate pump and a stack of annular brake disks in the space between the members. The pump is driven by the rotation to pump fluid into a supply cylinder driving the brake. An orifice controls escape of the fluid from the chamber at a controlled rate. The rate is controlled to maintain a balance between the pumping rate and the brake pressure to keep the rotation at a required rate. The apparatus is used in the drilling system which includes a shallow bend in the drilling tool and a system for rotating the bent drilling tool slowly about a longitudinal axis of the drilling tool while the drill bit rotates more rapidly. The controlled orifice further allows the slow rotation to be halted at a predetermined orientation of the bend axis so as to effect a change in drilling direction.

Abstract: A method is provided for drilling of a well bore portion including a short radius curved section followed by a straight section. A drilling tool is provided having a first portion on which the drill bit is mounted and a second portion carrying the motor with a knuckle coupling therebetween. The short radius curved section is completed using the drilling tool with the knuckle coupling diverting to one side of the bore to steer the drill bit to the other side. After the curved section is complete the drilling is controlled in an accurately straight orientation by providing an eccentric collar which is attached onto the drilling tool at a position adjacent the knuckle portion. The eccentric collar holds the drilling tool at a slight angle less than that during the curved section. Simultaneously with the rotation of the drill bit, the drill string, the tool and the collar are rotated more slowly about the longitudinal axis so as to constantly vary the angle of attack of the drill bit.

Abstract: A drilling system for controlling steering of a downhole drilling tool includes a shallow bend in the drilling tool and a system for rotating the bent drilling tool slowly about a longitudinal axis of the drilling tool while the drill bit rotates more rapidly. The system further allows the slow rotation to be halted at a predetermined orientation of the bend axis so as to effect a change in drilling direction. The system for rotating and halting this slow rotation comprises a downhole swivel coupling between the drilling tool and the drill string so that torque from the drill bit tends to rotate the drilling tool in the opposite direction. A control device is provided to restrict the amount of torque communicated through the swivel coupling and to halt the swivel coupling as required to control the steering of the drill bit.