Kola Superdeep Borehole


The Kola Superdeep Borehole SG-3 is the deepest human-made hole on Earth, 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 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 and Biyikzhal SG-2, 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

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 1983, the drill passed 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, a section of the drill string twisted off and was left in the hole. Drilling was restarted in September 1986, from the first hole.
The third hole reached in 1989. 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.

Research

The stated areas of study of the Kola Superdeep Borehole 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. Drilling penetrated about a third of the way through the Baltic Shield of the continental crust, estimated to be around deep, reaching Archean rocks at the bottom. 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.
  • Water pooled 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.
  • The drilling mud that flowed out of the hole was described as "boiling" with an unexpected level of hydrogen gas.
  • Microscopic plankton fossils were found below the surface.
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 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. 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.

Similar projects

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.