Boring (earth)

Lore & Background

Borehole drilling has a long history, with Han dynasty China (202 BC – 220 AD) using deep borehole drilling for mining and other projects, reaching depths as deep as 600 m. In 1961, the United States began Project Mohole, an ambitious attempt to drill through the Earth's crust into the Mohorovičić discontinuity, but it was discontinued due to high cost. The Kola Superdeep Borehole, a similar project of the USSR in the 1970s and early 1980s, attempted to drill through the crust to sample the Mohorovičić discontinuity. The deepest hole ever drilled failed not because of lack of money or time, but because of rock physics at depth. At approximately 12,000 meters depth, rock begins to act more like a plastic solid than a rigid solid. Rock temperatures of several hundred degrees Celsius required that the drilling fluid be refrigerated before being sent to the cutting face of the drill. As drill bits burnt out and were removed for replacement, the hole simply flowed closed, and the rock had to be re-drilled. The hole was scrapped. Further attempts are planned by American consortia and further Russian attempts in Finland.

Reader's Guide

Boring (earth) is significant for its role in understanding subsurface geology, enabling mineral exploration, foundation engineering, and scientific research. The Kola Superdeep Borehole demonstrated the limits of deep drilling due to rock plasticity at depth, where rock behaves like a plastic solid and temperatures reach several hundred degrees Celsius, requiring refrigerated drilling fluid. This project highlighted the challenges of drilling beyond 12,000 meters, as the hole would flow closed when bits were replaced. The legacy of such projects includes advancing knowledge of Earth's crust and inspiring future attempts by American consortia and Russian efforts in Finland. Additionally, ice boring using hot water drill technology has proven effective for deep holes in Arctic and Antarctic research, as seen in the IceCube Neutrino Detector and Antarctic Muon And Neutrino Detector Array projects, reaching depths of 2,450 meters. The methods developed for boring, including various drill bits for soft, medium, and hard formations, and testing techniques like standard penetration tests and acoustic televiewers, continue to inform geotechnical and hydrological practices.

Did You Know?

• Han dynasty China (202 BC – 220 AD) used deep borehole drilling reaching depths as deep as 600 m.
• The Kola Superdeep Borehole failed because at approximately 12,000 meters depth, rock acts like a plastic solid and the hole flowed closed.
• Hot water drilling has been used to drill as deep as 2,450 meters in ice for the IceCube Neutrino Detector project.
• Drill bits for stone are classified into soft, medium, and hard formations based on the material being drilled.