Drilling into the earth is done for a number of reasons. Some are exploratory, many are for oil, some for water, some for mining purposes, and others for various reasons. As we explore the layers of the earth, we uncover many things and have a need to dig deeper into the earth into uncharted regions, not knowing what we will find.
The deepest drilling ever done by mankind is the drilling that has taken place on the Kola Peninsula in Russia. This drilling started in 1970 and had reached a depth of 12,262 meters, in 1994. The drilling itself was done differently in the Kola Peninsula. The entire drill itself was not rotated; only the drill bit was turned by the flow of drilling mud.
It is not oil or natural resources that are being sought at the Kola Peninsula, but an understanding of the layers and nature of the Earth's crust, including seismic discontinuities, the physical and chemical compositions of the earth's crust, and improving upon the techniques of deep geophysical sound interpretation.
Some interesting things have been discovered within the earth's crust, as this drill made its way approximately halfway through the earth's crust at that point, exposing rocks 2.7 billion years old on a 4.6 billion year old planet. One interesting thing found along the way was a fractured area of rock 3 to 6 miles beneath the surface that had been thoroughly saturated with water. This occurrence has never been observed anywhere. This most likely means that water, which was part of the chemical composition of the rock minerals, had been forced out of the crystals and could not ascend due to an overlying cap of impermeable rock.
The Kola Peninsula drill's goal drilling depth is 15,000 meters. At this depth it is expected to be 300 degrees Celsius or higher, too high of a temperature for the drill to operate at. Another drilling worth mentioning has been started in the Caspian Sea. This drill also shares the same goal depth as the drilling at the Kola Peninsula. Aside from drillings for research, a noteworthy drilling is the Bertha Rogers well in Oklahoma, which is a 9,583 m (31,441 ft) deep gas well. This was the previous world record holder prior to the drilling in the Kola Peninsula. The well was started in 1974 and continued until it struck molten sulfur at its final depth.
