초록 ▼

A modulated bias unit is provided for controlling the direction of drilling of a rotary drill bit when drilling boreholes in subsurface formations. The unit comprises a plurality of hydraulic actuators spaced apart around the periphery of the unit and having movable thrust members hydraulically disp

A modulated bias unit is provided for controlling the direction of drilling of a rotary drill bit when drilling boreholes in subsurface formations. The unit comprises a plurality of hydraulic actuators spaced apart around the periphery of the unit and having movable thrust members hydraulically displaceable outwardly for engagement with the formation of the borehole being drilled. Each actuator has an inlet passage for connection to a source of drilling fluid under pressure and an outlet passage for communication with the annulus. A selector control valve connects the inlet passages in succession to the source of fluid under pressure, as the unit rotates, and a choke is provided to create a pressure drop between the source of fluid under pressure and the selector valve. A further choke is provided in the outlet passage from each actuator unit. The actuators and control valve arrangements may take a number of different forms.

대표청구항 ▼

A modulated bias unit, for controlling the direction of drilling of a rotary drill bit when drilling boreholes in subsurface formations, comprising: a body structure having an outer peripheral surface; at least one cavity located at and facing outwardly of said outer peripheral surface; a movable th

A modulated bias unit, for controlling the direction of drilling of a rotary drill bit when drilling boreholes in subsurface formations, comprising: a body structure having an outer peripheral surface; at least one cavity located at and facing outwardly of said outer peripheral surface; a movable thrust member partly projecting outwardly of said cavity for engagement with the surrounding formation of the borehole being drilled; means for supplying fluid under pressure to said cavity from a source of fluid under pressure to displace said movable member outwardly and thereby displace the bias unit away from the region of the formation which the movable member engages; and means for modulating the pressure of fluid supplied to the cavity in synchronism with rotation of the body structure, and in selected phase relation thereto, whereby said movable member is displaced outwardly at a selected rotational orientation of the body structure; and a controllable input element coupled to said pressure modulating means, the condition of said input element determining the phase relation of the modulation of the fluid pressure to the rotation of the body structure, whereby said phase relation, and hence said rotational orientation at which said movable member is outwardly displaced, may be selected to any desired value by adjustment of the condition of said input element.