Steerable drilling system

Abstract

A steerable system comprises a fluid powered motor 10 having a rotor 16 and a stator 18 , and a bias arrangement having a plurality of bias pads 34 connected to the stator 18 so as to be rotatable therewith, the bias pads 34 being moveable to allow the application of a side load to the steerable system.

1 . A steerable system comprising a fluid powered motor having a rotor and a stator, and a bias arrangement having at least one bias pad connected to the stator so as to be rotatable therewith, the at least one bias pad being actuatable to allow the application of a side load to the steerable system. 
     
     
         2 . A system according to  claim 1 , wherein each bias pad is moveable by an actuator. 
     
     
         3 . A system according to  claim 2 , wherein each actuator comprises a piston to which fluid can be supplied to move the associated bias pad from its retracted position towards its extended position. 
     
     
         4 . A system according to  claim 3 , further comprising a control arrangement for controlling the operation of the actuators. 
     
     
         5 . A system according to  claim 4 , wherein the control arrangement includes a plurality of solenoid actuated valves. 
     
     
         6 . A system according to  claim 5 , wherein each solenoid actuated valve includes a bistable actuator. 
     
     
         7 . A system according to  claim 4 , wherein the control arrangement comprises a control unit and the fluid powered motor is located between the drill bit and at least part of the control unit. 
     
     
         8 . A system according to  claim 7 , wherein the control unit includes at least one sensor arranged to sense a drilling parameter. 
     
     
         9 . A system according to  claim 1 , wherein the at least one pad of the bias arrangement is mounted directly upon the stator. 
     
     
         10 . A system according to  claim 1 , wherein the at least one pad of the bias arrangement is mounted upon a separate housing rotatable with the stator. 
     
     
         11 . A system according to  claim 10 , wherein the separate housing is connected to the stator by a flexible drive connection to transmit rotary motion of the stator to the separate housing, but to allow the separate housing to be angularly displaced relative to the axis of the stator. 
     
     
         12 . A steerable drilling system comprising a fluid driven downhole motor having an upstream region and a downstream region, a fluid pressure drop occurring in use, between the upstream and downstream regions, and a bias unit having an actuator piston, one end surface of which is exposed to the fluid pressure within a chamber which is communicable through a valve arrangement with the upstream region, wherein the fluid driven downhole motor rotates a drill bit. 
     
     
         13 . A system according to  claim 12 , wherein the bias unit and motor are integral with one another. 
     
     
         14 . A system according to  claim 12 , wherein at least one passage is provided in the motor to allow the supply of fluid from the upstream region to the said chamber. 
     
     
         15 . A system according to  claim 12  claims, wherein the valve arrangement is located at the upstream region. 
     
     
         16 . A system according  claim 12 , further comprising a control unit for controlling the operation of the valve arrangement, wherein the control unit is located at the upstream region. 
     
     
         17 . A steerable drilling system comprising a fluid driven downhole motor having an upstream region and a downstream region, a fluid pressure drop occurring in use, between the upstream and downstream regions, and a bias unit controlled using a valve arrangement, wherein the valve arrangement is located at the upstream region, wherein the fluid driven downhole motor powers a drill bit. 
     
     
         18 . A system according to  claim 17 , further comprising a control unit arranged to control the operation of the valve arrangement, wherein the control unit is located at the upstream region. 
     
     
         19 . A system according to  claim 17 , wherein the control unit is a roll-stabilised control unit and the valve arrangement comprises a rotary valve. 
     
     
         20 . A system according to  claim 17 , wherein the valve arrangement includes a plurality of individually actuable valves.