Rotary steerable drilling apparatus and method

Abstract

The present invention relates to drilling apparatus which includes a steerable bottom hole assembly for use in a well bore. The steerable bottom hole assembly includes a bent sub assembly connectable to a distal end of a drill string. It also has a control bias unit connected to the bent sub assembly and a drill bit connected to the control bias unit. The bent sub assembly may have an adjustable angle.

1 . A steerable bottom hole assembly for use in a well bore comprising:
 a bent sub assembly connectable to a distal end of a drill string;   a control bias unit connected to the bent sub assembly; and,   a drill bit connected to the control bias unit.   
   
   
       2 . The steerable bottom hole assembly of  claim 1  wherein the bent sub assembly provides a low bending stiffness relative to the control bias unit. 
   
   
       3 . The steerable bottom hole assembly of  claim 1  wherein the bent sub assembly has an adjustable angle. 
   
   
       4 . The steerable bottom hole assembly of  claim 1  wherein the control bias unit comprises a control unit providing a signal output to steer the bit along a given path in the well and a bias unit for converting such signal into movements of one or more bias pads against an adjacent face of the well bore. 
   
   
       5 . A rotary steerable bottom hole assembly comprising:
 a drill bit;   means for biasing the drill bit in a particular direction in response to signals received from a control unit; and,   means for coupling to a drill string allowing rotation in three planes.   
   
   
       6 . A method of drilling a well bore comprising the steps of:
 attaching a bent sub assembly to a drill string;   attaching a control bias unit to the bent sub assembly;   attaching a drill bit to the control bias unit; and,   rotating the drill bit while actuating the control bias unit to move the drill bit in a desired direction.   
   
   
       7 . The method of  claim 5  wherein the drill member is a drill string. 
   
   
       7 . The method of  claim 5  wherein the bent sub assembly is mounted above the top of a downhole motor. 
   
   
       8 . The method of  claim 7  wherein the bent sub assembly is part of the assembly between the mud motor and its bearing section. 
   
   
       9 . The method of  claim 5  wherein the bent sub assembly may be adjusted while down hole.