Steerable rotary drilling systems
First Claim
1. A modulated bias unit, for use in a steerable rotary drilling system, of the kind including at least one hydraulic actuator, at the periphery of the unit, having a movable thrust member which is hydraulically displaceable outwardly for engagement with a wall of a borehole being drilled, and a control valve operable to bring the actuator alternately into and out of communication with a source of fluid under pressure, as the bias unit rotates so that, in use, the fluid pressure to the actuator may be modulated in synchronism with rotation of the bias unit, and in selected phase relation thereto, whereby the movable thrust member can be displaced outwardly at the same rotational position of the bias unit, the bias unit being characterized by the provision of auxiliary valve means, operable between a first position where it permits the control valve to pass a maximum supply of fluid under pressure to the hydraulic actuator, and a second position where it prevents the control valve from passing said maximum supply of fluid under pressure to the hydraulic actuator.
2 Assignments
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Accused Products
Abstract
A modulated bias unit, for use in a steerable rotary drilling system, 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, and a control valve operable to bring the actuators alternately in succession into and out of communication with a source of fluid under pressure, as the bias unit rotates. The fluid pressure supplied to each actuator may thus be modulated in synchronism with rotation of the drill bit, and in selected phase relation thereto, so that each movable thrust member is displaced outwardly at the same rotational position of the bias unit so as to apply a lateral bias to the unit for the purposes of steering an associated drill bit. To enable the biasing action to be neutralized or reduced there is provided an auxiliary shut-off valve in series with the control valve, which is operable to prevent the control valve from passing the maximum supply of fluid under pressure to the hydraulic actuators.
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Citations
15 Claims
- 1. A modulated bias unit, for use in a steerable rotary drilling system, of the kind including at least one hydraulic actuator, at the periphery of the unit, having a movable thrust member which is hydraulically displaceable outwardly for engagement with a wall of a borehole being drilled, and a control valve operable to bring the actuator alternately into and out of communication with a source of fluid under pressure, as the bias unit rotates so that, in use, the fluid pressure to the actuator may be modulated in synchronism with rotation of the bias unit, and in selected phase relation thereto, whereby the movable thrust member can be displaced outwardly at the same rotational position of the bias unit, the bias unit being characterized by the provision of auxiliary valve means, operable between a first position where it permits the control valve to pass a maximum supply of fluid under pressure to the hydraulic actuator, and a second position where it prevents the control valve from passing said maximum supply of fluid under pressure to the hydraulic actuator.
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15. A method of operating a modulated bias unit which includes at least one hydraulic actuator, at the periphery of the unit, having a movable thrust member which is hydraulically displaceable outwardly for engagement with a wall of a borehole being drilled, and a control valve operable to bring the actuator alternately into and out of communication with a source of fluid under pressure, as the bias unit rotates so that, in use, the fluid pressure to the actuator may be modulated in synchronism with rotation of the bias unit, and in selected phase relation thereto, whereby the movable thrust member can be displaced outwardly at the same rotational position of the bias unit, the bias unit including auxiliary valve means, operable between a first position where it permits the control valve to pass a maximum supply of fluid under pressure to the hydraulic actuator, and a second position where it prevents the control valve from passing said maximum supply of fluid under pressure to the hydraulic actuator, the method comprising subjecting the auxiliary valve means, over a period of time during operation of the bias unit, to a succession of temporary operations from its first position to its second position.
Specification