The Kola Superdeep Borehole SG-3 () is the deepest human-made hole on Earth (since 1979), which attained maximum true vertical depth of in 1989. It is the result of a scientific drilling effort to penetrate as deeply as possible into the Earth's crust conducted by the Soviet Union in the Pechengsky District of the Kola Peninsula, near the Russian border with Norway.

SG (СГ) is a Russian designation for a set of superdeep () boreholes conceived as part of a Soviet scientific research programme of the 1960s, 1970s and 1980s. Aralsor SG-1 (in the Pre-Caspian Basin of west Kazakhstan) and Biyikzhal SG-2 (in Krasnodar Krai), both less than deep, preceded Kola SG-3, which was originally intended to reach deep. Drilling at Kola SG-3 began in 1970 using the Uralmash-4E, and later the Uralmash-15000 series drilling rig. A total of five boreholes were drilled, two branching from a central shaft and two from one of those branches.

In addition to being the deepest human-made hole on Earth, Kola Superdeep Borehole SG-3 was, for almost three decades, the world's longest borehole in measured depth along its bore, until surpassed in 2008 by a hydrocarbon extraction borehole at the Al Shaheen Oil Field in Qatar.

Drilling

thumb|upright|Kola Superdeep Borehole, commemorated on a 1987 USSR stamp

Drilling at Kola SG-3 began on 24 May 1970 using the Uralmash-4E, a serial drilling rig used for drilling oil wells. The rig was slightly modified to be able to reach a depth. In 1974, the new purpose-built Uralmash-15000 drilling rig was installed onsite, named after the new target depth, set at .

On 6 June 1979, Kola SG-3 broke the world depth record then held by the Bertha Rogers hole in Washita County, Oklahoma, United States, at . In October 1982, Kola SG-3's first hole reached .

The second hole was started in January 1983 from a depth of the first hole. In that year, the hole depth was expected to reach by the end of 1990 and by 1993. In June 1990, a breakdown occurred in the third hole at of depth.

The drilling of the fourth hole was started in January 1991 from of depth of the third hole. The drilling of the fourth hole was stopped due to higher-than-expected temperatures of in 1992 at of depth.

Drilling of the fifth hole started in April 1994 from of depth of the third hole. Drilling was stopped in August 1994 at of depth due to lack of funds, and the well itself was mothballed. Numerous unexpected geophysical discoveries were made:

  • During the drilling process, the expected basaltic layers at down were never found, nor were basaltic layers at any depth. There were instead more granites, deeper than predicted. The prediction of a transition at 7 kilometres was based on seismic waves indicating discontinuity, which could have been caused by a transition between rocks, or a metamorphic transition in the granite itself. having percolated up through the granite until it reached a layer of impermeable rock. This water did not naturally vaporize at any depth in the borehole.
  • Microscopic plankton fossils were found below the surface.

The experiment was documented in a video recorded by David Smythe,

which shows the drilling deck in action during an attempt to recover a tool dropped down the hole.

Status

The drilling ended in 1995 due to a lack of funding. The scientific team was transferred to the federal state unitary subsidiary enterprise "Kola Superdeep," downsized, and given the new task of thoroughly studying the exposed section. and the site was abandoned. It is still visited by sightseers, who report that the structure over the borehole has been partially destroyed or removed.

Similar projects

  • The United States had embarked on a similar project in 1957, dubbed Project Mohole, which was intended to penetrate the shallow crust under the Pacific Ocean off Mexico. After initial drilling, the project was abandoned in 1966 when funding was cut off. This program inspired the Ocean Drilling Program, Integrated Ocean Drilling Program, and the present International Ocean Discovery Program.
  • The KTB superdeep borehole (German Continental Deep Drilling Programme, 1987–1995) at Windischeschenbach in northern Bavaria was drilled to a depth of , reaching temperatures of more than . Its ambitious measuring program used high-temperature logging tools that were upgraded specifically for KTB.
  • In 2023, China embarked on a super-deep borehole in the Tarim Basin in the Xinjiang region for scientific, oil and gas exploration. In March 2024, drilling of the borehole, which is known as Shendi Take 1, reached a depth of 10,000 metres.

Records

The deep Kola Superdeep Borehole has been the world's deepest borehole since 1979. It was also the longest borehole in the world from 1979 to 2008. Its record length was surpassed in May 2008 by the curved extended reach drilling bore of well BD-04A in the Al Shaheen Oil Field in Qatar, which attained a total length of but depth of just .

See also

  • , set at Kola Borehole
  • , deep oceanic drilling ship, which achieved a subsea drilling record in 2012
  • , covers the lowest point on land
  • Vertical seismic profile — relevant seismic measurements

References

Further reading

  • Official Kola Superdeep Borehole website
  • The World's Deepest Hole – Alaska Science Forum – July 1985
  • The Deepest Hole 20 June 2006
  • Kola Superdeep – Scientific research results and experiences by PhD A. Osadchikh 1984
  • Photo report on a trip to the Kola superdeep well in 2017. Many photos of the current state.