Steerable drill string

Abstract

A rotatable steerable drill string in which guidance module controls the direction of the drilling. A magnetorheological fluid in the module supplies pressure to pistons that apply forces to the wall of the bore and thereby alter the direction of the drilling. The pressure applied by the magnetorheological fluid is regulated by valves that apply a magnetic field to the fluid so as to increase or decrease its fluid shear strength thereby controlling the actuation of the pistons and the direction of the drilling.

What is claimed:  
     
         1 . A guidance apparatus for steering a rotatable drill string through a bore hole, comprising: 
 a) a housing for incorporation into said drill string;    b) a movable member mounted in said housing so as to be capable of extending and retracting in the radial direction, said movable member having a distal end projecting from said housing adapted to engage the walls of said bore hole;    c) a supply of a magnetorheological fluid;    d) means for pressurizing said magnetorheological fluid;    e) means for supply said pressurized rheological fluid to said movable member, the pressure of said rheological fluid generating a force urging said movable member to extend radially outward, the magnitude of said force being proportional to the pressure of said rheological fluid supplied to said movable member; and    f) a valve for regulating the pressure of said magnetorheological fluid supplied to said movable member so as to alter said force urging said movable member radially outward, said valve comprising means for subjecting said magnetorheological fluid to a magnetic field so as to change the shear strength thereof.    
     
     
         2 . The guidance apparatus according to  claim 1 , wherein said movable member is a piston slidably mounted in said housing.  
     
     
         3 . The guidance apparatus according to  claim 1 , wherein said pressurized fluid supply means comprises a passage placing said pressurizing means in fluid flow communication with said movable member, and wherein said valve is disposed in said passage.  
     
     
         4 . The guidance apparatus according to  claim 1 , further comprising: 
 g) a second movable member mounted in said housing so as to be capable of extending and retracting in the radial direction, said second movable member having a distal end projecting from said housing that is adapted to engage the walls of said bore hole, said second movable member being circumferentially spaced from said first movable member;    h) means for supply said pressurized rheological fluid to said second movable member; and    i) a second valve for regulating the pressure of said magnetorheological fluid supplied to said second movable member so as to alter said force urging said second movable member radially outward, said second valve comprising means for subjecting said magnetorheological fluid to a magnetic field so as to change the shear strength thereof.