Apparatus and method for directional drilling of boreholes

A method for directional drilling of a borehole defined by a borehole wall, the method comprising the steps of:

• (a) positioning an apparatus within the borehole, the apparatus located between an uphole drill string defining a drill string bore and a downhole drill bit defining a drill bit opening, the apparatus comprising:
• (i) a bent tubular housing for orienting the drill bit at a predetermined angle, wherein the drilling fluid is pumped through the bent tubular housing and exits the drill bit opening at the predetermined angle into an outer annular space defined between an outer wall of the housing and the borehole wall;
• (ii) a drive shaft within the housing for coupling rotation of the drill string to the drill bit, wherein the drive shaft is disposed within the housing, wherein the drilling fluid flows through the drill string bore into an inner annular space defined between an inner wall of the housing and the drive shaft and exits the drill bit opening;
• (iii) at least one piston positioned within a piston chamber attached to the housing, the drilling fluid flows from the inner annular space into the piston chamber to move the piston relative to the housing to, in use, apply force to the borehole wall and thereby limit rotation of the housing within the borehole;
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• (iv) a biasing means, wherein the piston, the piston chamber and the biasing means are arranged such that either a drilling fluid pressure in the piston chamber urges the piston in a first direction towards the borehole wall, and the biasing means urges the piston in a second direction away from the borehole wall, or the drilling fluid pressure in the piston chamber urges the piston in a first direction away from the borehole wall, and the biasing means urges the piston in a second direction towards the borehole wall;
• (v) at least one valve for selectively controlling drilling fluid flow between the outer annular space and the piston chamber, relative to drilling fluid flow between the inner annular space and the piston chamber and thereby, in use, controlling the drilling fluid pressure in the piston chamber;
• and
• (vi) a clutch for selectively coupling the housing to the drive shaft for rotation with the drive shaft and for adjusting the tool face of the housing;
• (b) flowing the drilling fluid from the drill string bore to the outer annular space via the inner annular space and the drill bit opening to establish a drilling fluid pressure differential between the inner annular space and the outer annular space;
• (c) actuating the clutch for selectively coupling the housing to the drive shaft for rotation with the drive shaft and for adjusting the tool face of the housing;
• and
• (d) actuating the at least one valve to selectively control drilling fluid flow between the outer annular space and the piston chamber, relative to drilling fluid flow between the inner annular space and the piston chamber, and thereby control drilling fluid pressure in the piston chamber to urge the piston to press against the borehole wall and thereby limit rotation of the housing within the borehole.