APPARATUS AND METHOD FOR DRILLING AND REAMING A BOREHOLE

摘要

A drilling assembly (100) and an eccentric, adjustable diameter reamer (10) are disclosed. The reamer includes cutter elements mounted on at least a fir st fixed blade (30) for reaming a previously-formed borehole or for forming a borehole of increased diameter beneath an existing cased borehole. The metho d and apparatus provide for stabilizing the drilling assembly so that the ream er may be used in back reaming the hole. Retainer means, such as shear pins (42 6) or spring-biased reciprocating latch members (650, 680), are provided to prevent premature extension of the reamer's moveable members (40), including blades and pistons. The shear pins are preferably accessible from the outer surface of the reamer housing so as to expedite field replacement of the she ar pins without requiring disassembly of the reamer. The spring-biased latching members repeatedly latch and unlatch so that field replacement is not requir ed.