Modulated bias units for steerable rotary drilling systems

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;
• a plurality of cavities spaced substantially equally apart around the outer peripheral surface of the body structure;
• a movable thrust member partly projecting outwardly of each cavity for engagement with the surrounding formation of the borehole being drilled;
• means for supplying fluid under pressure to said cavities from a source of fluid under pressure to displace said movable members outwardly;
• and
• means for modulating the pressure of fluid supplied to each cavity in synchronism with rotation of the body structure, and in selected phase relation thereto, whereby each said movable member is displaced outwardly at a selected rotational orientation of the body structure, said pressure modulating means comprising valve means operable to increase the pressure of fluid supplied to each cavity in succession, as the unit rotates.

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 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
• 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 rotation orientation of the body structure;
• at least part of said cavity being defined by a flexible sealing element connected between the movable thrust member and the body structure of the unit, which cavity increases in volume as fluid under pressure is delivered thereto, so as to urge the movable thrust member outwardly with respect to the cavity;
• said flexible sealing element comprising a metal bellows, one end of which is connected to an inner face of the movable thrust member and the opposite face of which is connected to a surface of the body structure around an inlet and outlet for fluid under pressure, whereby said cavity is defined by the metal bellows, said inner face of the movable thrust member and said surface of the body structure.

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;
• a plurality of cavities located at said outer peripheral surface;
• a movable thrust member partly projecting outwardly of each cavity for engagement with the surrounding formation of the borehole being drilled;
• means for supplying fluid under pressure to said cavities from a source of fluid under pressure to displace said movable member outwardly;
• and
• means for modulating the pressure of fluid supplied to each 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;
• there being provided at least one pair of cavities and movable thrust members diametrically oppositely disposed with respect to the central longitudinal axis of the bias unit, the movable thrust members of each said pair being mechanically coupled together by connecting means extending through the body structure of the bias unit whereby as one thrust member moves outward the other thrust member moves inwardly by an equal amount and vice versa.

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 periphery;
• a plurality of hydraulic actuator units spaced apart around the periphery of the body structure and having movable thrust members hydraulically displaceable outwardly with respect to the body structure for engagement with the formation of the borehole being drilled;
• each actuator unit having an inlet passage for connection to a source of fluid under pressure and an outlet passage for communication with a lower pressure zone;
• selector valve means for connecting said inlet passages in succession to said source of fluid under pressure, as the unit rotates;
• choke means to create a pressure drop between the source of fluid under pressure and said selector valve means;
• and
• further choke means in the outlet passage from each actuator unit.

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 periphery;
• a plurality of hydraulic actuator units spaced apart around the periphery of the body structure and having movable thrust members hydraulically displaceable outwardly with respect to the body structure for engagement with the formation of the borehole being drilled;
• each actuator unit having an inlet passage for connection to a source of fluid under pressure and an outlet passage for communication with a lower pressure zone;
• valve means in one of the inlet and outlet passages of each actuator unit;
• choke means in the other of the inlet and outlet passages of each actuator unit;
• and
• means for selectively operating said valve means in succession as the bias unit rotates, to place the hydraulic actuators successively in communication with the source of fluid under pressure.

A drill bit for drilling boreholes in subsurface formations comprising a bit body having an outer peripheral surface and a shank for connection to a drill string, an inner passage for supply drilling fluid under pressure to the bit, and a plurality of cutting elements mounted on the bit body, the bit body including a modulated bias unit comprising:

• a plurality of hydraulic actuator units spaced apart around the peripheral surface of the body and having movable thrust members hydraulically displaceable outwardly with respect to the bit body for engagement with the formation of the borehole being drilled;
• each actuator unit having an inlet passage for connection to said inner passage and an outlet passage for communication with the annulus between the bit body and the borehole being drilled;
• selector valve means for connecting said inlet passages in succession to said inner passage as the drill bit rotates;
• choke means to create a pressure drop between the inner passage and said selector valve means;
• and further choke means in the outlet passage from each actuator unit.

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 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
• 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;
• said pressure modulating means comprising valve means operable by a shaft which extends at least partly into a region providing said source of fluid under pressure, a flowpath leading from said region to the valve means including an annular choke to effect a pressure drop in fluid flowing along said flowpath, and said shaft extending through said choke.

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 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;
• 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
• means to constrain the movable thrust member to reciprocate linearly inwardly and outwardly with respect to said cavity, the movable thrust member being constrained to reciprocate along an axis which is parallel to a radius of the bias unit but is spaced rearwardly from said radius with respect to the direction of rotation of the unit during drilling, whereby said axis does not intersect the axis of rotation of the bias unit.

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 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
• 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;
• at least part of said cavity being defined by a flexible sealing element connected between the movable thrust member and the body structure of the unit, which cavity increases in volume as fluid under pressure is delivered thereto, so as to urge the movable thrust member outwardly with respect to the cavity;
• said flexible sealing element comprising an annular element of generally c-shaped cross-section, one face of which is connected to an inner face of the movable thrust member and the opposite face of which is connected to a surface of the body structure, around an inlet and outlet for fluid under pressure, whereby said cavity is defined by the annular element, said inner face of the movable thrust member and said surface of the body structure.

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 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 outward;
• 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;
• at least part of said cavity being defined by a flexible sealing element connected between the movable thrust member and the body structure of the unit, which cavity increases in volume as fluid under pressure is delivered thereto, so as to urge the movable thrust member outwardly with respect to the cavity;
• said flexible sealing element comprising a diaphragm connected between the movable thrust member and a surrounding wall of a recess in the body structure.

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 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;
• 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;
• an inlet flowpath leading from said source of fluid under pressure to said cavity, said means for modulating the pressure of fluid supplied to the cavity, said means for modulating the pressure of fluid supplied to the cavity comprising rotary valve means in said inlet flowpath operable in synchronism with rotation of the unit to modulate the pressure of fluid supplied to said cavity from said source;
• and
• a valve control input shaft coupled to said rotary valve means so that said selected phase relation is determined by the rotational orientation of said input shaft.

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;
• a plurality of cavities spaced substantially equally apart around the outer peripheral surface of the body structure;
• a movable thrust member partly projecting outwardly of each cavity for engagement with the surrounding formation of the borehole being drilled;
• means for supplying fluid under pressure to said cavities from a source of fluid under pressure to displace said movable members outwardly;
• and
• means for modulating the pressure of fluid supplied to each cavity in synchronism with rotation of the body structure, and in selected phase relation thereto, whereby each said movable member is displaced outwardly at a selected rotational orientation of the body structure, said pressure modulating means comprising valve means operable to increase the pressure of fluid supplied to each cavity in succession, as the unit rotates, said valve means comprising a single selector valve adapted to connect an inlet, leading from said source of fluid under pressure, to each one in succession of a plurality of outlets, each of which outlets leads to a different one of said cavities.

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;
• said movable thrust member being pivotally mounted on the body structure for pivotal movement about a pivot axis located to one side of said cavity;
• 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;
• 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.

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 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;
• said movable thrust member including a piston portion which is slidable within a cylinder portion communicating with said cavity;
• means for supplying fluid under pressure to said cavity from a source of fluid under pressure to displace said movable member outwardly;
• 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;
• said cylinder portion constraining the piston portion of the movable thrust member to reciprocate linearly inwardly and outwardly with respect to said cavity, the movable thrust member being constrained to reciprocate along an axis which is parallel to a radius of the bias unit but is spaced rearwardly from said radius with respect to the direction of rotation of the unit during drilling, whereby said axis does not intersect the axis of rotation of the bias unit.

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 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
• 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;
• at least part of said cavity being defined by a flexible sealing element connected between the movable thrust member and the body structure of the unit, which cavity increases in volume as fluid under pressure is delivered thereto, so as to urge the movable thrust member outwardly with respect to the cavity;
• said flexible sealing element comprising a diaphragm connected between the movable thrust member and a surrounding wall of a recess in the body structure, said diaphragm being a rolling diaphragm having an annular portion of elongate U-shaped cross-section between the movable thrust member and said surrounding wall of said cavity.

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;
• said movable thrust member being formed in two pans comprising an outer part pivotally mounted on said body structure for pivotal movement about a pivot axis located to one side of said cavity, and for engagement with the surrounding formation of the borehole being drilled, and an inner part which is subjected to the pressure of fluid in said cavity and is movable outwardly under the action of said pressure, the inner pan being operatively engaged with the outer part whereby outward movement of the inner part is accompanied by outward movement of the outer part.