| 摘要 |
A drill bit and hole opener assembly, comprising a drill bit having a boring diameter D1 and a tubular hole opener connected to the drill bit and having a cutting elements disposed around the outer perimeter of the tubular hole opener, the cutting elements having a cutting diameter D2. The cutting elements are fixed non-rotating cutting elements, D2 is not greater than D1, and preferably D2 is less than D1, the cutting elements are PDC cutting elements and the gauge length of the drill bit and hole opener assembly is greater than the sum of the individual gauge lengths of the drill bit and hole opener. In addition, a method of widening a borehole with a drill bit having a hole opener attached to the drill bit, the method comprising the steps of advancing the drill bit along a bend in a borehole, the bend having an inside and an outside, and the borehole having a bottom end, with the drill. bit engaging rock at the bottom end of the borehole; and cutting rock on the inside of the bend with the hole opener without cutting rock on the outside of the bend with the role opener.
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