The Kola Superdeep Borehole is the result of a scientific drilling project of the Soviet Union in the Pechengsky District, on the Kola Peninsula. The project attempted to drill as deep as possible into the Earth's crust. With a depth of, it has been since 1989 the deepest artificial point on Earth. Drilling began on 24 May 1970 using the Uralmash-4E, and later the Uralmash-15000 series drilling rig. Boreholes were drilled by branching from a central hole. The deepest, SG-3, reached in 1989 and is the deepest artificial point on Earth. The borehole is in diameter. In terms of true vertical depth, it is 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, until it was surpassed in 2008 by the Al Shaheen oil well in Qatar.
Drilling
The main target depth was set at. On 6 June 1979, the world depth record held by the Bertha Rogers hole in Washita County, Oklahoma, United States, at was broken. In 1983, the drill passed, 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 on 27 September 1984: after drilling to, a section of the drill string twisted off and was left in the hole. Drilling was later restarted from. The hole reached in 1989. In that year, the hole depth was expected to reach by the end of 1990 and by 1993. Because of higher-than-expected temperatures at this depth and location, instead of the expected, drilling deeper was deemed unfeasible and the drilling was stopped in 1992.
Research
The Kola borehole penetrated about a third of the way through the Baltic Shieldcontinental crust, estimated to be around 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. 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, 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. Microscopic plankton fossils were found 6 kilometers below the surface. Another unexpected discovery was a large quantity of hydrogen gas. The mud that flowed out of the hole was described as "boiling" with hydrogen. In 1992 an international geophysical experiment took place to obtain 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. The experiment was documented in a video recorded by Professor David Smythe, which includes unique footage of the drilling deck in action during a fishing trip.
Status
The project ended in 1995 due to the dissolution of the Soviet Union, and the site has since been abandoned. The ruins of the site, however, are frequently visited by curious sightseers. The superstructure tower was destroyed at some point between 2007 and 2012.
The KTB superdeep borehole 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.
Records
The Kola Superdeep Borehole was the longest and deepest borehole in the world for nearly 20 years. In May 2008, a new record for borehole length was established by the extended reach drilling 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, with a record horizontal reach of in only 36 days. In terms of depth below the surface, the Kola Superdeep Borehole SG-3 retains the world record at in 1989, and is still the deepest artificial point on Earth.
