Steering component, steering assembly and method of steering a drill bit in a borehole

1. A steering component adapted for connection to a drill string, the drill string carrying a drill bit and a motor for rotating the drill bit relative to the drill string, the steering component comprising:

a rotatable driveshaft adapted for connection between the drill bit and the motor;

a first drive mechanism; and

an offsetting component;

the first drive mechanism providing a rotatable connection between the drill string and the offsetting component whereby the drill string can rotate relative to the offsetting component, the first drive mechanism utilizing relative rotation between the driveshaft and drill string to drive the offsetting component to rotate in an opposed direction to the driveshaft, wherein the steering component further comprises a second drive mechanism adapted to drive the offsetting component to rotate in the same direction as the driveshaft.

2. A steering component according to claim 1 wherein the first drive mechanism operates cyclically, and drives the offsetting component to rotate in the opposed direction during only part of each cycle.

3. A steering component according to claim 1 wherein the offsetting component has at least one borehole-engaging element adapted to engage the wall of a drilled borehole.

4. A steering component according to claim 3 wherein the offsetting component locates a part of the driveshaft, with the driveshaft being eccentric to the borehole-engaging element(s).

5. A steering component according to claim 4 wherein the offsetting component is a stabilizer.

6. A steering component according to claim 1 wherein the first drive mechanism comprises a gearbox and clutch mechanism.

7. A steering component according to claim 6 wherein the gearbox provides the rotatable connection.

8. A steering component according to claim 6 wherein the clutch mechanism has an engaged condition and a disengaged condition, and wherein the drive mechanism drives the offsetting component to rotate in the opposed direction to the driveshaft when the clutch mechanism is in its engaged condition.

9. A steering component according to claim 1 wherein the first drive mechanism comprises a sun and planet gearset and a clutch mechanism, the sun and planet gearset comprising a sun gear, at least one planet gear rotatably mounted upon a planet carrier, and a ring gear.

10. A steering component according to claim 9 wherein the sun gear is connected to the driveshaft by way of the clutch mechanism, the planet carrier is connected to the drill string, and the ring gear is connected to the offsetting component.

11. A steering component according to claim 1 wherein the offsetting component is adapted to provide a variable offset.

12. A steering component according to claim 11 wherein the minimum offset is zero.

13. A steering component according to claim 1 in which the motor is a mud motor.

14. A steering assembly adapted for connection to a drill string, the assembly comprising a steering component, a drill bit and a motor to rotate the drill bit relative to the drill string, the steering component being located between the motor and the drill bit, the steering component comprising:

a rotatable driveshaft connected between the drill bit and the motor;

a first drive mechanism; and

an offsetting component;

the first drive mechanism providing a rotatable connection between the drill string and the offsetting component whereby the drill string can rotate relative to the offsetting component, the first drive mechanism utilizing relative rotation between the driveshaft and drill string to drive the offsetting component to rotate in an opposed direction to the driveshaft

wherein the steering assembly further comprises a second drive mechanism adapted to drive the offsetting component to rotate in the same direction as the driveshaft.

15. A method of steering a drill bit in a borehole with a steering component connected to a drill string, the steering component comprising a rotatable driveshaft, a drive mechanism and an offsetting component, the drive mechanism utilizing relative rotation between the driveshaft and the drill string to drive the offsetting component to rotate in an opposed direction to the driveshaft, the method comprising the steps of:

providing the drill string with a downhole motor for rotating the drill bit relative to the drill string;

connecting the downhole motor and the drill bit to opposed ends of the rotatable driveshaft;

operating the motor to drive the driveshaft and drill bit and drill a length of borehole;

determining a desired direction of curvature for the borehole and thereby determining a desired angular orientation for the offsetting component; measuring the rotation of the offsetting component induced by rotation of the driveshaft;

operating the drive mechanism to counter the induced rotation.

16. A method according to claim 15 wherein the drive mechanism is operated cyclically, whereby the offsetting component undergoes induced rotation in the direction of rotation of the driveshaft for a part of each cycle, and undergoes driven rotation in the opposed direction for the remaining part of each cycle, and whereby the offsetting component is caused to oscillate around its desired angular orientation.