Kola Ultra-deep Well

The Kola Experimental Ultra-deep Corehole (SG-3) is the world’s deepest underground working of scientific significance. It was part of a system of ultra-deep wells in the USSR.

In 1997, it was entered in the Guinness Book of World Records as the deepest human intrusion into the Earth’s crust, and remains so until now. It was also the world’s longest drillhole, to be only surpassed in 2008 by the Maersk Oil BD-04A oil well drilled at a sharp angle to the Earth’s surface.

According to the Director of the Geological Institute of the RAS Kola Research Centre, as of 2010 the well was mothballed and gradually deteriorating.