Patent ID: 7287605
Filing Date: 2007-10-30
Classification: E21B

Abstract:
1. An apparatus for steerable rotary drilling of a borehole having a wall in the earth comprising: a) a longitudinally axially extending mandrel, having a central opening there through for the passage of drilling fluids, b) said mandrel having a lower connection for operatively connecting to a drill bit structure, c) said mandrel having an upper connection for operatively connecting to a drill string above said apparatus, and the mandrel having an intermediate portion, d) an outer generally cylindrical housing surrounding longitudinal extent of said mandrel intermediate portion, e) a differential displacement drive within the outer housing, f) one or more pairs of radially-extensible, opposed side-force exerting elements controlled by said differential displacement drive to provide for side force exertion against the said borehole wall, g) said drive including a pair of pistons for activating each pair of radially-extensible opposed side-force elements, said pistons movable longitudinally in parallel relation to the mandrel, there being actuators movable longitudinally by the pistons, between the mandrel and said outer housing, and there being camming surfaces interengageable between the actuators and said side-force exerting elements for displacing said elements generally radially away from the mandrel in response to said piston longitudinal movement, each piston being in longitudinal alignment with an actuator and a pair of camming surfaces, h) one or more displacement transducers for said pair of pistons, i) control valves within said outer housing for fluid pressure control of said differential displacement drive, and j) sensing, control and power supply elements to control operation of said control valves, to steer drilling in a desired direction by selective operation of said side force exerting elements.