Kola Superdeep Borehole - Could people reach center of Earth?

The Kola Superdeep Borehole is the result of a scientific drilling project of the former USSR. The project attempted to drill as deep as possible into the Earth's crust. Drilling began on 24 May 1970 on the Kola Peninsula, using the Uralmash-4E, and later the Uralmash-15000 series drilling rig. A number of boreholes were drilled by branching from a central hole. The deepest, SG-3, reached 12,261 metres (40,230 ft) in 1989, and remains the deepest hole ever drilled. The longest hole ever drilled is the 12,290 m (40,300 ft) Maersk Oil BD-04A well at Al-Shaheen field in Qatar, but the Maersk hole was primarily horizontal.

The initial target depth was set at 15,000 m (49,000 ft). On 6 June 1979, the world depth record held by the Bertha Rogers hole in Washita County, Oklahoma at 9,583 m (31,440 ft) was broken. In 1983, the drill passed 12,000 m (39,000 ft), and drilling was stopped for about a year to celebrate the event. This idle period may have contributed to a break-down on 27 September 1984: after drilling to 12,066 m (39,590 ft), a 5,000 m (16,000 ft) section of drillpipe twisted off and was left in the hole. Drilling was later restarted from 7,000 m (23,000 ft). The hole reached 12,262 m (40,230 ft) in 1989. In that year the hole depth was expected to reach 13,500 m (44,000 ft) by the end of 1990 and 15,000 m (49,000 ft) by 1993. However, due to higher than expected temperatures at this depth and location, 180 °C (356 °F) instead of expected 100 °C (212 °F), drilling deeper was deemed unfeasible and the drilling was stopped in 1992. With the expected further increase in temperature with increasing depth, drilling to 15,000 m (49,000 ft) would have meant working at a projected 300 °C (570 °F), at which the drill bit would no longer work.

The Kola borehole penetrated about a third of the way through the Baltic continental crust, presumed to be around 35 kilometres (22 mi), exposing rocks 2.7 billion years old at the bottom. The project has been a site of extensive geophysical studies. The stated areas of study were the deep structure of the Baltic Shield; seismic discontinuities and the thermal regime in the Earth's crust; the physical and chemical composition of the deep crust and the transition from upper to lower crust; lithospheric geophysics; and to create and develop technologies for deep geophysical study.

To scientists, one of the more fascinating findings to emerge from this well is that the change in seismic velocities was not found at a boundary marking Jeffreys' hypothetical transition from granite to basalt; it was at the bottom of a layer of metamorphic rock that extended from about 5 to 10 kilometers beneath the surface. The rock there had been thoroughly fractured and was saturated with water, which was surprising. This water, unlike surface water, must have come from deep-crust minerals and had been unable to reach the surface because of a layer of impermeable rock.

Another unexpected discovery was the large quantity of hydrogen gas, with the mud flowing out of the hole described as "boiling" with hydrogen.

The site is currently controlled by the State Scientific Enterprise on Superdeep Drilling and Complex Investigations in the Earth's Interior (GNPP Nedra) as the Deep Geolaboratory. As of 2003, the deepest active bore, SG-5, is 8,578 m (28,140 ft) and with a 214 mm (8.4 in) diameter.

credited to wikipedia