Imagine a hole more than 12 kilometers below the surface of the earth, so almost 38 stacked Eiffel Towers. This is the record held by the “experimental super-deep reference well Kola” (also called SG-3) in the Murmansk region of Russia.
This hole is the deepest ever dug by man and it was the result of an ambitious project started by the Soviet Union in 1970. Originally, the goal was to go to a depth of 15 km and study the structure and composition of the earth’s crust, we explain to colleagues from Ouest France.
However, drilling ceased in 1992 after the collapse of the USSR and the site was completely abandoned. Finally, in 2005, the hole was sealed, ending an extraordinary scientific and technological adventure.
A challenge started after conquering space
As a reminder, the SG-3 project arose in the context of the Cold War, which faced the United States and the USSR on several fronts. After the Soviets saw the Americans set foot on the moon in 1969, they wanted to differentiate themselves in another area: that of ultra-deep drilling.
They weren’t the first to try the experiment. Between 1961 and 1966, the Americans dug a 3,653 meter deep hole off Mexico as part of the Mohole Project. But the Soviets had higher goals, or rather: lower goals: they had set themselves the goal of reaching a depth of 15 kilometers with a diameter of only 23 kilometers cm.
On May 24, 1970, they began drilling in the Kola Peninsula, an area of ​​northwestern Russia near the borders of Finland and Norway. The site was chosen for its geological stability and proximity to industrial infrastructure.
© Western France / Open Street Map
scientific discoveries
For more than two decades, scientists will then tirelessly dig using innovative techniques. They will break several depth records, including that of the Bertha Rogers well, drilled to search for oil in Oklahoma (USA), which reached a depth of 9,583 meters. The world record was broken on June 6, 1979, when Russian drilling finally drilled beyond 10 km.
But the SG-3 project is not just a competition: it is also a unique opportunity to explore the interior of the Earth and learn more about its structure, composition and even its history. Scientists will thus make several surprising discoveries.
© Yuri Yakovlev / Wikimedia Commons / CC.BY.SA.4.0
In particular, they will find microscopic fossils of unicellular plankton that are several million years old and reach depths of 4 miles. These organisms were trapped in sedimentary rocks during their formation.
You can also find water made from minerals in the deep earth’s crust that could never reach the surface due to an impermeable layer. This water could be very old, reflecting the extreme conditions that existed on Earth billions of years ago.
Insurmountable technical difficulties
But drilling is not without its difficulties. As scientists delve deeper into the earth, they encounter technical problems related to pressure and temperature. In fact, the heat increases with depth, reaching higher levels than expected.
While they thought they would find rock with a temperature of about 100 °C at a depth of 12 km, they found rock with a temperature of 180 °C. This makes drilling very difficult and leads to accidents, breakage and loss of equipment.
Another example from 1984: after reaching 12,066 meters, a 5,000 millimeter section of drill string twisted and became stuck in the hole. Recovery will take several months. Incidents of this type are repeated several times and significantly slow down drilling operations.
In 1991 the project received the final blow. The USSR collapses and the research center begins to decay. The then 12,262 meter deep well was officially stopped in 1992. The goal of 15 km was never reached. Since then, work has never resumed and the site has fallen into disuse. In 2005 the hole was finally sealed with a welded metal plug (see photo). All that remains is a small, almost invisible opening that marks the entrance to the deepest hole in the world.
Nevertheless, the SG-3 project remains a scientific and technological achievement that has made it possible to gain unprecedented knowledge of the Earth and its mysteries. It has also inspired other deep drilling projects, such as Japan’s Chikyu project, which aims to reach the Earth’s mantle at a depth of around 30 km.
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