Kola Superdeep Borehole

Kola Superdeep Borehole, commemorated on a 1987 USSR stamp

The main 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, United States, at 9,583 m (31,440 ft)[3] was broken. In 1983, the drill passed 12,000 m (39,000 ft), and drilling was stopped for about a year for numerous scientific and celebratory visits to the site.[4]

This idle period may have contributed to a breakdown after drilling resumed; on 27 September 1984, after drilling to 12,066 m (39,587 ft), a 5,000 m (16,000 ft) section of the drill string twisted off and was left in the hole. Drilling was later restarted from 7,000 m (23,000 ft).[4]

The hole reached 12,262 m (40,230 ft) in 1989. In that year, the hole depth was expected to reach 13,500 m (44,300 ft) by the end of 1990 and 15,000 m (49,000 ft) by 1993.[5][6] Because of higher-than-expected temperatures at this depth and location, 180 °C (356 °F) instead of the expected 100 °C (212 °F), drilling deeper was deemed unfeasible. The unexpected decrease in density, the greater porosity, and the unexpectedly high temperatures, caused the rock to behave somewhat like a plastic, making drilling nearly impossible.[7] Drilling was terminated in 1992.[4]

The Kola Superdeep Borehole penetrated about a third of the way through the Baltic Shield continental crust, estimated to be around 35 kilometres (22 mi) deep, reaching Archean rocks at the bottom.[8] The project has been a site of extensive geophysical examinations. 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 no transition from granite to basalt was found at the depth of about 7 km (4.3 mi), where the velocity of seismic waves has a discontinuity. Instead the change in the seismic wave velocity is caused by a metamorphic transition in the granite rock. In addition, the rock at that depth 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.[9]

Microscopic plankton fossils were found 6 kilometers (4 mi) below the surface.[1]

Another unexpected discovery was a large quantity of hydrogen gas. The drilling mud that flowed out of the hole was described as "boiling" with hydrogen.[10]

In 1992 an international geophysical experiment obtained a reflection seismic crustal cross-section through the well. The Kola-92 working group consisted of researchers from the Universities of Glasgow and Edinburgh in Scotland, the University of Wyoming in the United States and the University of Bergen in Norway as well as several Russian earth science research institutions.[11] The experiment was documented in a video recorded by Professor David Smythe,[12] which shows the drilling deck in action during an attempt to recover a tool dropped down the hole.

The borehole in 2012

The borehole (welded shut), August 2012

The project was officially terminated in 1995, due to the dissolution of the Soviet Union, and the site has since been abandoned.[13] In 2008 the Russian InfoCentre announced that the borehole was to be destroyed.[14] The site is still visited by curious sightseers, who have reported that the structure over the borehole has been partially destroyed or removed.[7]

• 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 of 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 9,101 m (29,859 ft) reaching temperatures of more than 260 °C (500 °F). Its ambitious measuring program used high-temperature logging tools that were upgraded specifically for KTB.[15]

The Kola Superdeep Borehole was the longest and deepest borehole in the world for 19 years.

In May 2008, a record for borehole length was established by the extended reach drilling (ERD) well BD-04A, which was drilled by Transocean for Maersk Oil in the Al Shaheen Oil Field in Qatar. Transocean drilled a total length of 12,289 m (40,318 ft), with a record horizontal reach of 10,902 m (35,768 ft) in only 36 days.[16][17]

In terms of depth below the surface, the Kola Superdeep Borehole SG-3 retains the world record at 12,262 metres (40,230 ft) in 1989, and is still the deepest artificial point on Earth.[18]

• Chikyū – Japanese scientific drilling ship, deep oceanic drilling ship, which achieved a subsea drilling record in 2012
• Denman Glacier, deepest natural point on land
• Earthscope
• Extreme points of Earth – List of geographical locations that extend farther in one direction than any other location
• Lake Vostok – Antarctica's largest known subglacial lake
• List of deepest mines – Wikipedia list article
• Mohorovičić discontinuity – Boundary between the Earth's crust and the mantle
• San Andreas Fault Observatory at Depth
• USArray
• Well to Hell hoax – Urban legend observed since 1995

• Fuchs, K.; Kozlovsky, E.A.; Krivtsov, A.I. & Zoback, M.D. (1990). Super-Deep Continental Drilling and Deep Geophysical Sounding. Berlin: Springer Verlag. p. 436. ISBN 978-0-387-51609-7.
• Kozlovsky, Ye.A (1987). The Superdeep Well of the Kola Peninsula. Berlin: Springer Verlag. p. 558. ISBN 978-3-540-16416-6.

Wikimedia Commons has media related to Kola Superdeep Borehole.

• Official Kola Superdeep Borehole website (in Russian)
• 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 (in Russian)
• Photo report on a trip to the Kola superdeep well in 2017. Many photos of the current state. (in Russian)