Geoscientists view the world’s deepest drill hole

Geoscientists from around the globe caught a once-in-a-lifetime glimpse of the world’s deepest diamond drill hole when they visited the Kola project in the Soviet Union recently.

The drill site, 40 km east of the Norwegian border near Murmansk, is usually closed to foreign visitors because of its proximity to a border and to the Barents Sea.

“The Kola visit was an opportunity comparable to the viewing of rocks from the moon,” said Art Barber, who reported on the visit for CSD News, a publication of the U.S. Continental Scientific Drilling Program. Delegates of the International Seminar on Superdeep Drilling watched as a robot extracted 11,140 metres of drill pipe from the hole, changed the drill bit, and lowered the string back to the bottom of the hole within a speedy 16 hours.

Although the Kola hole reached a record depth of 12,261 metres in 1985, serious deviation, a common problem in deep holes, prevented further drilling. The current hole had reached a depth of just over 11 km with a modest deviation of 1 from vertical when delegates gathered at the end of September. Bottom-of-the-hole temperatures were a searing 190C. The Kola engineers are aiming for a depth of 15 km. By comparison, a mineral exploration hole on the Canadian Shield is considered deep, and potentially problematic, beyond a depth of about 2,000 metres.

Highlights of the report by CSD News, include:

— A 12-km section of the Precambrian continental crust exposed through cores and downhole measurements;

— Significant hydrothermal mineralization, including copper, nickel and gold values evident at depths below five kilometres;

— A variety of liquids and gases occur at unexpected depths. Detailed data of the nine deep holes drilled in the Soviet Union are available, in English, from the publication Models and Cross-Sections of the Earth’s Crust Based on Superdeep Drilling Data of the USSR.