| 摘要 |
A subsurface borehole underreamer comprises a tubular body which is adapted at its upper end for coaxial connection to a rotary drill string. A plurality of cutter support arms have upper and lower ends. The upper ends of the arms are pivoted to the body for motion of the lower ends thereof between retracted positions, in which the lower ends are disposed essentially within the diameter of the body, and open positions, in which the arm lower ends are disposed outwardly of the body. Cutters are mounted to the lower end of each arm and are configured to extend essentially to the center of the body when the arm is in its retracted position. An actuator in the body is selectively operable for moving the arms from their retracted to their open positions. The actuator includes an open ended tubular element which is movable downwardly in the body coaxially thereof during operation of the actuator from an upper position, wherein the lower end of the tubular element is disposed in the body above the locations occupied by the cutters in their retracted positions, to a lower position, wherein the lower end of the tubular element is disposed below said cutter location. The body has a fluid flow passage therealong comprised of upper and lower axial passage sections, respectively, above and below the retracted positions of the cutters. When the arms move to their open position, the tubular element moves past the retracted position of the cutters to connect the passage upper and lower sections axially of the body in fluid flow relation.
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