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Comment by CorrectHorseBat | Hacker News Reader

Well, where are the used up drill bits supposed to go to in a hole just as wide as the bits itself except for up and out?

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Why don’t they just retract the bits and change them like I would on a regular drill that needs a new bit?

Is the failure mode they always or often fall off the shank into the hole and they can’t be extracted?

That's exactly what they do. It just takes a while since there's tens of thousands of feet of drillstring.

Then what’s the jive about needing to drill around the old bits?

Removing many miles of pipe to swap out a drill bit at the end is slow and seems rather inefficient.

Which suggests just leaving the old drill bit somewhere in the ground. But currently doing that would also involve removing the pipe, as to why: https://news.ycombinator.com/item?id=43371776

That was answering silly speculation about intentionally leaving worn-out drill bits behind. There are actually workable procedures for drilling around things, but it's far more cumbersome and time-consuming than replacing a bit normally. Those procedures used for things like the drillstring getting stuck due to hole collapse; nobody would do that just for a worn-out drill bit.

The actual way to avoid the problem is by using bits whose design lifetime in the formation you're drilling is at least as long as the hole section you're planning to drill.

Again going for obvious solution, drop it, back up a few meters and drill around. Alternatively, have pre drilled side paths for drill bit drop off.

How do you pre-drill side paths ? Isn't being able to drill the hard part ? I am not saying it's dumb but from what I know about the industry (almost nothing) it does not seem simple at all

They need to be able to steer drills for all kinds of reasons: https://www.youtube.com/watch?v=JAhdb7dKQpU

Actual answer seems to be drilling side holes also involves removing the pipe. https://news.ycombinator.com/item?id=43371776

The drill is on the end of what amounts to a several km long rope. I’m pretty sure a side hole would introduce friction with the side that wasn’t there before, making it easy to stick going in and out. I think if the obvious solution worked then people would already be doing it, cause they’d save multiple millions of dollars.

They can do side drills, but apparently that also requires removing the pipe which is the bit I was missing.

https://news.ycombinator.com/item?id=43371776

Ah yep that does explain it well.

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