Page 334 - Drilling Technology in Nontechnical Language

Chapter 13 – DRILLING PROBLEMS AND SOLUTIONS 325

A simple washover tool can be made on the rig from a piece of small-
diameter casing or liner. This tool is set on bottom, weight is applied, and
the string is rotated. This causes the fingers to bend and twist so as to close

the fingers below the bits of junk. It is useful for catching rock bit cones or
other small bits that are lying on the bottom of the hole.

Drilling, milling, and smashing junk

In surface holes where formations are soft, smaller bits of loose junk
can be drilled with a steel tooth bit. Often what happens is that the bits of
junk get pushed into the side of the hole and are never seen again. Steel
tooth bits are also capable of breaking up small bits of junk—no other drill
bit can do this.

Mills can be used when junk is in the hole. Mills work well on junk that
is not loose—that is, it is cemented in place or otherwise prevented from
rolling around. Rolling junk can damage the mill, although mills can deal
with this kind of junk also. It might take more than one mill to do the job.

Mills used for cutting up junk (and especially junk that might be loose)
have chips of tungsten carbide brazed to the bottom of a steel body to cut

as in figure 13–9.

Fig. 13–9. Flat-bottomed mill

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