Drilling 3-4 km

I’m watching a BBC Horizon documentary on Lake Vostok in Antarctica, and they mention how scientists have so far been able to get ice core samples that go 3.5 km into the arctic ice.

How, exactly?

It doesn’t seem possible to have a drill bit that’s 3.5 km long, so my best guess is that it is somehow built in sections as it drills. This French engineer just said that “From a technical point of view there is no problem to drill 4 km down.” Anyone know how they do it?

How do you think they drill Oil that deep?

The drill bit is only the bit on the end. Beyond that, it’s only a matter of adding pipe sections as it goes.

They can go much farther than that.

http://www.sitnews.us/0607news/061207/061207_shns_deepwater.html

I think the OP is trying to say that you can’t transport a drill that is several kilometers long and then stick it upright. Sections are mentioned, and sections are the answer. That technology has been used since forever. It just gets harder the more sections that are needed. That’s where the high tech comes in.

And pulling the whole mess out every so often to change the bit at the end, then stuffing the whole thing back down the hole, drilling aways farther then pulling …

Everyone has seen pictures of oil derricks – it’s iconic of the industry. The purpose of the derrick is to handle the 30-foot long sections of drill pipe as they are being inserted or withdrawn from the drill hole. This page at Howstuffworks gives you an idea of what’s going on at the surface and below a derrick, and subsequent pages the drilling process itself.

This picture shows some workers standing on the turntable either adding a section of drill pipe so they can go deeper, or removing one because they are withdrawing the bit. I’m not enough of an expert to tell which. The clampy things hold the pipe in place while they do the screwing and unscrewing.

The point is, oil workers routinely drill thousands of feet down thirty feet at a time.

Don’t the pipe segments twist? Or does that matter?

“Twist” or “rotate”? They rotate. There was a drilling project on Russia’s Kola Peninsula where they drilled to a record 7 miles. They had to invent a special rig that had stationary shafts with a rotating drill on the end because it was so deep and any normal rig would have twisted itself to death.

Over the length of a drill string, the pipe does indeed twist somewhat when it is rotated to turn the bit, but the steel of the pipe body and connections has enough ‘give’ to tolerate this without immediate damage. Excessive twisting (described as ‘torque’ in the industry) or more importantly, excessive variations (especially harmonic vibrations) of this torque can cause the drill string to break apart. This is known as a ‘twist-off’, and requires that so-called fishing tools be run in the hole to recover the lost sections of pipe.

I suspect that twist-offs would be rare in an ice-drilling operation, however. Don’t have a figure for the compressive strength of water ice handy, but I would think it is lower than for consolidated rocks at the same depths. Thus the stresses on the drill string should be relatively low compared to hard-rock drilling.