World's deepest hole

My patient today is 84 and said he helped drill the deepest oil well in Texas at the time - since superseded. It was 18,000 feet. He said it took 12 hours to pull the pipe out to change the drill head, and 8 hours to put it back in. (That would be very frustrating!)  He also said the pipe would come out far too hot to touch.

Found an interesting article, which distinguishes between length of drill pipe versus actual vertical depth. 

https://www.google.com/amp/s/oilprice.com/Energy/Energy-General/The-Truth-About-The-Worlds-Deepest-Oil-Well.amp.html

I would suspect that there are some physical principles at work when you have a pipe of 15km length that you are torquing where a significant amount of it has changing metallurgic characteristics due to high basal temperatures, and then friction-heating on top.  In spite of them being Russian and broke I would suspect there were some physical limitations placed upon them as well.

... I'll copy my father, who is always moderate of opinion, and see what his thoughts are on this!  You know, since he's a engineer in the oil patch and has been involved in one or two drilling projects (although usually through ice...)

 http://en.m.wikipedia.org/wiki/Kola_Superdeep_Borehole

The subject is very complex and perhaps intractable. Realize that a drill string that long will twist significantly more than  360 degrees from the rotary table to the bit. Just one thing to consider. Also, the weight of the string and drill collars (drill collars are heavy pieces of steel connected into the string to keep it from floating out of the hole and to assist in maintaining sufficient weight on the bit to ensure penetration) will require a huge rig with a massive draw works and accompanying horsepower. The drill string itself is a piece of spaghetti in the hole.

https://dspace.lib.cranfield.ac.uk/handle/1826/7752

To picture the drill string as a long piece of spaghetti suspended in a hole is very different than how I pictured it. I pictured rigid steel supported by the drill mud but I can see that wouldn't be the case as you lower it most of the way down. 

I still think they were speaking politically when they said conditions were "too hot" to drill deeper. I think there were many other constraints, that prevented  drilling deeper. 

 Also, in this video at 13:27, he says that above 400 Celsius the logging, and diagnostics systems to monitor the drilling process fail. 

https://youtu.be/J0Zk6sVxKbI