How does drilling into Earth's crust work?

[arabianights]

i knew during geology survey, they can drill into Earth thousands of meters below the surface. just curious how did they accomplish that?

 

[billy_joule]

With very large drills

Drill, add extension shaft ('drill string' apparently),drill again. Repeat ad naseum.

http://science.howstuffworks.com/environmental/energy/oil-drilling4.htm

wiki has this interesting note about the deepest hole ever drilled:

In the 1970s and early 1980s the USSR attempted to drill a hole through the crust, to sample the Mohorovicic Discontinuity. The deepest hole ever drilled failed not because of lack of money or time, but because of the physics of rocks within the crust. The hole achieved approximately 12,000 metres depth, a depth at which rock begins to act more like a plastic solid than a rigid solid. The rock also approached temperatures of several hundred degrees Celsius, requiring that the drilling fluid be refrigerated before being sent to the cutting face of the drill. As the drill bits burnt out and were removed for replacement, the hole simply flowed closed, and the rock had to be re-drilled. Due to the temperature, the drill bits burnt out before achieving any headway. The hole was scrapped.

https://en.wikipedia.org/wiki/Boring_(earth)

https://en.wikipedia.org/wiki/Kola_Superdeep_Borehole