E - Fixed Constructions – 21 – B
Patent
E - Fixed Constructions
21
B
E21B 7/04 (2006.01) E21B 4/00 (2006.01) E21B 7/06 (2006.01) E21B 17/10 (2006.01)
Patent
CA 2150731
A modulated bias unit, for controlling the direction of drilling of a rotary drill bit when drilling boreholes in subsurface formations, comprises a number of hydraulic actuators spaced apart around the periphery of the unit, each having a movable thrust member which is hydraulically displaceable outwardly for engagement with the formation of the borehole being drilled. A selector control valve modulates the fluid pressure supplied to each actuator in synchronism with rotation of the drill bit so that, as the drill bit rotates, each movable thrust member is displaced outwardly at the same selected rotational position so as to bias the drill bit laterally and thus control the direction of drilling. Each thrust member is connected to a surrounding wall by a flexible rolling diaphragm having an annular portion of U-shaped cross-section between the thrust member and the wall. A further flexible annular diaphragm is connected between the thrust member and the wall outwardly of said rolling diaphragm, to shield the rolling diaphragm from debris in drilling fluid flowing past the bias unit.
Marks & Clerk
Thorp Richard Edward
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