| 摘要 |
An under reamer for expanding a borehole through an earthen formation, the under reamer comprising: a mandrel including an end for connection into a drill string and an opposite end; a housing including an inner bore, telescopically disposed over the mandrel and axially moveable relative to the mandrel, the housing being rotationally moveable with the mandrel; and a plurality of under reamer arms carried on t he housing, the under reamer arms formed as blocks including cutter-supporting portions in which poly-crystalline diamond compact cutters are mounted, the under reamer arms being moveable by driving the housing axially over the mandrel between a stored position extending into the bore the housing and an expande d position wherein the under reamers arms are pivoted out of the housing inner bore and support by the mandrel such that the cutter-supporting portions are exposed for use to enlarge a borehole.
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