Controllable deflection housing, downhole steering assembly and method of use

1. A controllable deflection tool having a first end and a second end, the tool having:

a conduit for a working fluid;

a rotary element configured to rotate within the tool;

a deflection member;

a vane motor configured to rotate the deflection member relative to the rotary element, the vane motor comprising an eccentric housing within which is located a body carrying at least three vanes, the body being connected to the rotary element to rotate with the rotary element, the body being rotatable relative to the eccentric housing, the vanes being movably mounted upon the body so that they remain in contact with the eccentric housing during relative rotation of the body; and

a valve for controlling the flow of working fluid to the vane motor,

in which the deflection member is a bent housing.

2. The controllable deflection tool according to claim 1 in which the rotary element is an annular sleeve.

3. The controllable deflection tool according to claim 2 in which the annular sleeve surrounds a part of a rotatable shaft.

4. The controllable deflection tool according to claim 3 in which there is a gap between the sleeve and the shaft, the gap providing a part of the conduit.

5. The controllable deflection tool according to claim 1 in which the vane motor has at least three channels, each channel being configured to locate a vane, the vanes being movable relative to their respective channel.

6. The controllable deflection tool according to claim 5 in which the conduit is in communication with each of the channels, the pressure of the working fluid in use acting to drive the vanes into engagement with the eccentric housing.

7. The controllable deflection tool according to claim 1 in which the valve controls the flow of working fluid from the conduit to the vane motor.

8. The controllable deflection tool according to claim 1 in which the working fluid passes around a closed hydraulic loop.

9. A downhole steering assembly adapted for connection to a rotatable drill string, the assembly comprising:

a drill bit,

a downhole motor and

a controllable deflection tool having:

a first end and a second end;

a conduit for a working fluid;

a rotary element configured to rotate within the tool;

a deflection member;

a positive displacement motor configured to rotate the deflection member relative to the rotary element; and

a valve for controlling the flow of working fluid to the positive displacement motor,

the controllable deflection tool being configured to be located between the downhole motor and the drill bit,

the downhole motor having a stator and a rotor, the stator being adapted for connection to the drill string and to rotate with the drill string, the rotary element being connected to the stator to rotate with the stator, the rotor being configured to be connected to the drill bit.

10. The downhole steering assembly according to claim 9 in which the controllable deflection tool includes a rotatable shaft which communicates rotation of the rotor to the drill bit.

11. A method of steering a downhole drilling assembly comprising the steps of:

{i} connecting a downhole motor, a drill bit, and a controllable deflection tool to a rotatable drill string, the controllable deflection tool having a first end and a second end, the tool having:

a conduit for a working fluid;

a rotary element configured to rotate within the tool;

a deflection member;

a positive displacement motor configured to rotate the deflection member relative to the rotary element; and

a valve for controlling the flow of working fluid to the positive displacement motor,

the downhole motor having a stator and a rotor, the stator being connected to the drill string to rotate with the drill string, the controllable deflection tool being located between the downhole motor and the drill bit, the drill bit and the rotor being connected to rotate together, the rotary element being connected to the stator to rotate with the stator;

{ii} operating the drilling assembly to rotate the drill bit and drill a length of borehole;

{iii} determining a curved path for the drill bit;

{iv} operating the valve whereby to rotate the positive displacement motor relative to the drill string; and

{v} modulating the valve whereby to maintain a chosen orientation of the deflection member.