Underreamer with large cutter elements and axial fluid passage

A borehole underreamer comprising a tubular body adapted at an upper end thereof for coaxial connection to a rotary drill string, a plurality of cutter means support arms having upper and lower ends, the arms being disposed at selected locations around the circumference of the body at a selected point therealong and being mounted at their upper ends for pivotal motion relative to the body between (a) retracted positions in which the arms are disposed essentially within the outer diameter of the body and (b) opened positions in which the arm lower ends are disposed a selected distance outwardly of the exterior of the body, cutter means mounted to the lower end of each arm and configured to extend essentially to the center of the body when the arm is in its retracted position, actuator means in the body selectively operable for moving the arms from their retracted to their opened positions, the actuator means including an open-ended tubular element movable downwardly in the body coaxially thereof during operation of the actuator means from (a) an upper position wherein the lower end of the element is disposed above the locations occupied by the cutter means in the retracted positions of the arms to (b) a lower position wherein the lower end of the element is disposed below said cutter means locations, the body having a fluid flow passage therealong comprised of upper and lower axial passage sections respectively above and below said cutter means retracted positions, the lower passage means including means cooperable with the lower end of the tubular element in the lower position of the element for connecting the passage upper and lower sections in fluid flow relation, the tubular element carrying an annular piston circumferentially of the exterior thereof in a piston chamber defined by the body circumferentially of the tubular element, the tubular element having an upper end a selected distance above the piston which in all positions of the element axially relative to the body is slidably sealed to the body above the piston chamber, and including duct means in the body in parallel flow relation to the underreamer axial fluid flow passage, the duct means having outlet ends to the piston chamber above the piston and inlet ends above the upper end of the tubular element in the upper position thereof communicating to fluid pressure presented to the underreamer via a drill string.

A borehole underreamer comprising a tubular body adapted at an upper end thereof for coaxial connection to a rotary drill string, a plurality of cutter means support arms having upper and lower ends, the arms being disposed at selected locations around the circumference of the body at a selected point therealong and being mounted at their upper ends for pivotal motion relative to the body between (a) retracted positions in which the arms are disposed essentially within the outer diameter of the body and (b) opened positions in which the arm lower ends are disposed a selected distance outwardly of the exterior of the body, cutter means mounted to the lower end of each arm, actuator means in the body selectively operable for moving the arms from their retracted to their opened positions, the actuator means including an open-ended tubular element movable downwardly in the body coaxially thereof during operation of the actuator means, the body having an axial fluid flow passage at least partially therealong from the upper end of the body and opening from the body at the upper end thereof, the tubular element carrying an annular piston circumferentially of the exterior thereof in a piston chamber defined by the body circumferentially of the tubular element, the tubular element having an upper end a selected distance above the piston which in all positions of the element axially relative to the body is slidably sealed to the body above the piston chamber, and including duct means in the body in parallel flow relation to the underreamer axial fluid flow passage, the duct means having outlet ends to the piston chamber above the piston and inlet ends above the upper end of the tubular element in the upper position thereof communicating to fluid pressure presented to the underreamer via a drill string.

A borehole underreamer comprising a tubular body adapted at an upper end thereof for coaxial connection to a rotary drill string, a plurality of cutter means support arms having upper and lower ends, the arms being disposed at selected locations around the circumference of the body at a selected point therealong and being mounted at their upper ends for pivotal motion relative to the body between (a) retracted positions in which the arms are disposed essentially within the outer diameter of the body and (b) opened positions in which the arm lower ends are disposed a selected distance outwardly of the exterior of the body, cutter means mounted to the lower end of each arm and configured to extend into the body when the arm is in its retracted position, actuator means in the body selectively operable for moving the arms from their retracted to their opened positions, the actuator means including an elongate actuator element movable downwardly in the body coaxially thereof from an upper position to a lower position during operation of the actuator means, the actuator element being operable in moving from its upper position to its lower position in the body to move the cutter support arms from their retracted to their opened positions, the upper position of the actuator element corresponding to a closed state of the underreamer and the lower position of the element corresponding to an opened state of the underreamer, means resiliently biasing the actuator element in the body to its upper position, means for mechanically holding the underreamer in its opened state, and means for mechanically operating the underreamer from its opened to its closed state.

A borehole underreamer comprising a tubular body adapted at an upper end thereof for coaxial connection to a rotary drill string, a plurality of cutter means support arms having upper and lower ends, the arms being disposed at selected locations around the circumference of the body at a selected point therealong and being mounted at their upper ends for pivotal motion relative to the body between (a) retracted positions in which the arms are disposed essentially within the outer diameter of the body and (b) opened positions in which the arm lower ends are disposed a selected distance outwardly of the exterior of the body, cutter means mounted to the lower end of each arm and configured to extend essentially to the center of the body when the arm is in its retracted position, actuator means in the body selectively operable for moving the arms from their retracted to their opened positions, the actuator means including an open-ended tubular element movable downwardly in the body coaxially thereof during operation of the actuator means from (a) an upper position wherein the lower end of the element is disposed above the locations occupied by the cutter means in the retracted positions of the arms to (b) a lower position wherein the lower end of the element is disposed below said cutter means locations, the body having a fluid flow passage therealong comprised of upper and lower axial passage sections respectively above and below said cutter means retracted positions, the lower passage means including means cooperable with the lower end of the tubular element in the lower position of the element for connecting the passage upper and lower sections in fluid flow relation, fluid discharge nozzles carried by the body below the cutter means support arms and directed toward the locations of the cutter means in the opened positions of the arms, and duct means for communicating the nozzles to the lower section of the underreamer fluid flow passage when the tubular element is in its lower position.

A borehole underreamer comprising a tubular body adapted at an upper end thereof for coaxial connection to a rotary drill string, a plurality of cutter means support arms having upper and lower ends, the arms being disposed at selected locations around the circumference of the body at a selected point therealong and being mounted at their upper ends for pivotal motion relative to the body between (a) retracted positions in which the arms are disposed essentially within the outer diameter of the body and (b) opened positions in which the arm lower ends are disposed a selected distance outwardly of the exterior of the body, cutter means mounted to the lower end of each arm and configured to extend essentially to the center of the body when the arm is in its retracted position, actuator means in the body selectively operable for moving the arms from their retracted to their opened positions, the actuator means including an open-ended tubular element movable downwardly in the body coaxially thereof during operation of the actuator means from (a) an upper position wherein the lower end of the element is disposed above the locations occupied by the cutter means in the retracted positions of the arms to (b) a lower position wherein the lower end of the element is disposed below said cutter means locations, the body having a fluid flow passage therealong comprised of upper and lower axial passage sections respectively above and below said cutter means retracted positions, the lower passage means including means cooperable with the lower end of the tubular element in the lower position of the element for connecting the passage upper and lower sections in fluid flow relation, the flow passage lower section comprising a bore axially in the body below the positions occupied in the body by the cutter means when the cutter means support arms are in their retracted positions, the bore having a diameter corresponding to the outer diameter of the tubular element at and closely adjacent to its lower end, the upper end of the bore being spaced below the lower end of the tubular element in its upper position by an amount less then the distance through which the tubular element moves in moving from its upper to its lower position.