The Kola superdeep well has been drilled for two whole decades. They started on May 24, 1970, and by 1990 they reached a record depth of 12,262 meters.
At the first stage, drilling was carried out using a serial Uralmash-4E rig. It took 4 years to reach a depth of 7.2 km. After that, a one-year pause was taken - for the installation of a specially designed and manufactured unit for extra deep drilling "Uralmash-15OOO".
The new equipment has increased productivity and improved reliability. The automated format of trips / trips of the drilling tool, bit feed allowed to increase the drilling speed (in comparison with any serial rig).
VNIIBT specialists worked on well drilling technologies. Drilling of the turbine type was used: drilling mud was supplied through the string under pressure. He rotated a multistage turbine with a 214 mm diameter drill head.
V. S. Popov, A. A. Kremenetsky. Deep and superdeep scientific drilling on the continents / Earth Science, 1999, p. 67
This head was ring-shaped, due to which undrilled pillars of rock with a diameter of 60 mm remained in its heart - a core. A core receiver passed through all turbine sections, in which the rock extracted from great depths was collected.
The deeper the Kola superdeep went, the more difficulties and problems appeared. According to theoretical calculations, the temperature in the thickness of our planet by 15 km should have reached 150 degrees. But in fact, already at an 8-kilometer depth it was 170 degrees, and closer to a 12-kilometer depth, it was 230 degrees. Scientists had to invent more heat-resistant, exceptionally strong, but at the same time lightweight pipes, and introduce new devices.
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After 7 km, it became difficult, and then impossible, to maintain an even vertical wellbore. The breeds are no longer strong and relatively uniform. They became fractured, interbedded, with insignificant hard interlayers.
The drill began to deviate from time to time, and the wellbore began to wriggle. An attempt was made to correct this by lowering “diverters” in depth together with the drilling tool, which reduce the angle of inclination of the well.
The column began to be “grabbed” on a regular basis - its sections seemed to stick to the walls of the well.
In September 1984, they reached a depth of 12066 m. After that, they tried to lift the column and could not: 5 km of pipes and turbodrills that had been torn off remained in the depths. We began to drill a bypass shaft nearby, from a depth of 7 km, and then a few more. After 6 years, they again reached 12 km "with kopecks", and again an accident. And so several times. As a result, twelve bypass bores were drilled from the 7-kilometer mark of the well, and it became similar to the root system of a gigantic tree.
In 1992, further attempts were abandoned - officially, due to the exhaustion of the capabilities of modern technology. But in fact - due to the termination of state funding for the project. Now "Object SG-3" is abandoned and is gradually self-destructing. Inside the 70-meter tower, a massive rusty metal cover, bolted to the concrete floor with the same rusty bolts, closes the wellhead.
SG-3 gave scientists a lot of surprises. For example, rock samples from the depths of the Kola borehole coincided with samples of lunar soil delivered from the moon by the Soviet automated space station.
In the strata, which should not contain organic matter, 14 species of fossilized microorganisms were found - in those layers that are more than 2.8 billion years old. At the greatest depths, methane suddenly appeared in colossal concentrations. Which completely destroyed the theory of the biological origin of oil and gas.
Oil drillers are reaching impressive depths these days. In 2008, in Qatar, an exploration well in the Al-Shaheen oil field reached 10,902 m in its horizontal wellbore. And in 2011, Exxon-Neftegaz at the Odoptu field reached a horizontal wellbore depth of 11,475 m. But these are the results achieved not from the earth, but from offshore drilling platforms.