Kola Superdeep Borehole

The project attempted to drill as deep as possible into the Earth's crust.

Kola Superdeep Borehole

Superstructure of the Kola Superdeep Borehole, 2007
Location
Kola Superdeep Borehole Location of the borehole in Murmansk Oblast, Russia Show map of Russia Kola Superdeep Borehole Kola Superdeep Borehole (Murmansk Oblast) Show map of Murmansk Oblast
Location	Pechengsky District
Province	Murmansk Oblast
Country	Russia
Coordinates	69°23′47″N 30°36′36″E / 69.3965°N 30.6100°E / 69.3965; 30.6100
Production
Type	Scientific borehole
Greatest depth	12,262 metres (40,230 ft)
History
Opened	1965
Active	1970–1983 1984 1985–1992
Closed	1995

Drilling began on 24 May 1970 using the Uralmash-4E, and later the Uralmash-15000 series drilling rig, and it became the deepest manmade hole in history in 1979. The 23-centimetre-diameter (9 in) boreholes were drilled by branching from a central hole. The deepest reached 12,262 metres (40,230 ft; 7.619 mi) in 1989, the deepest human-made hole on Earth, and remains so as of 2024^[update].

In terms of true vertical depth, it remains the deepest borehole in the world. For two decades, it was also the world's longest borehole in terms of measured depth along the well bore (that is, borehole length) until it was surpassed in 2008 by the 12,289-metre-long (40,318 ft; 7.636 mi) Al Shaheen Oil Well in Qatar.

 

Drilling 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 7,000-metre (23,000 ft) depth. In 1974, the new purpose-built Uralmash-15000 drilling rig was installed onsite, named after the new target depth, set at 15,000 metres (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 metres (31,440 ft), was broken. In October 1982, the first hole reached 11,662 metres (38,261 ft), and the second hole was started in January 1983 from a 9,300-metre (30,500 ft) depth of the first hole.

In 1983, the drill passed 12,000 metres (39,000 ft) in the second hole, and drilling was stopped for about a year for numerous scientific and celebratory visits to the site.

This idle period may have contributed to a breakdown after drilling resumed; on 27 September 1984, after drilling to 12,066 metres (39,587 ft), a 5 metres (16 ft) section of the drill string twisted off and was left in the hole. Drilling was restarted in September 1986, 7,000 metres (23,000 ft) from the first hole.

The third hole reached 12,262 metres (40,230 ft) in 1989. In that year, the hole depth was expected to reach 13,500 metres (44,300 ft) by the end of 1990 and 15,000 metres (49,000 ft) by 1993.^{[failed verification]}

In June 1990, a breakdown occurred in the third hole at 12,262 metres (40,230 ft) of depth. The drilling of the fourth hole was started in January 1991 from 9,653 metres (31,670 ft) of depth of third hole. The drilling of the fourth hole was stopped in April 1992 at 11,882 metres (38,983 ft) of depth. Drilling of the fifth hole started in April 1994 from 8,278 metres (27,159 ft) of depth of the third hole. Drilling was stopped in August 1994 at 8,578 metres (28,143 ft) of depth due to lack of funds and the well itself was mothballed.

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. 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.

During the drilling process, the expected basaltic layers at seven kilometers 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 seven kilometers 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. In fact, in another unexpected finding, water pooled three to six kilometers below the surface, 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 six kilometres (3.7 mi) below the surface.

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.

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 the United Kingdom, the University of Wyoming in the United States, and the University of Bergen in Norway, as well as several Russian earth science research institutions. The experiment was documented in a video recorded by Professor David Smythe, which shows the drilling deck in action during an attempt to recover a tool dropped down the hole.

 

The borehole site in 2012

 

The borehole (welded shut), August 2012

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. In 2007, the scientific team was dissolved and the equipment was transferred to a private company and partially liquidated.

In 2008, the company was liquidated due to unprofitability, 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.

• 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 metres (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.
• In 2023, China embarked on a 10,000 m super-deep borehole in the Tarim Basin in the Xinjiang region for scientific, oil and gas exploration. On 4 March 2024, drilling of the borehole, which is known as Shendi Take 1, reached a depth of 10,000 m.

The Kola Superdeep Borehole was both the longest and deepest borehole in the world from 1989 to 2008. In May 2008, the Kola Superdeep Borehole's record length (but not record depth) was surpassed by a curved borehole of the extended reach drilling well BD-04A in the Al Shaheen Oil Field in Qatar, with a total length of 12,289 metres (40,318 ft) and a horizontal reach of 10,902 metres (35,768 ft). In terms of depth below the surface, the Kola Superdeep Borehole SG-3 retains the world record at 12,262 metres (40,230 ft) reached in 1989 and is still the deepest artificial point on Earth.

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