The Kola super hole at 40,502 feet remains the deepest point drilled into earth till now. The Russians who bored the hole stopped it because the temperature at that point reached 356 degrees Fahrenheit (180 degrees centigrade) and there was equipment breakdown. High temperature, high pressure, technological insufficiency and funding shortages faced by the several boring teams all over the world, has ensured that this record holds for the last 20 years.
The chief factor that hinders the drilling is the increasing temperature, which increases rapidly and unpredictably as we drill into the earth. The geothermal temperature gradient is the major source of the temperature distribution through the crust and the other layers. The drilling equipment also produces significant friction heat from the drill bit grinding the earth.
To prevent the drilling column and other component failure from the temperature, the entire drilling column, including the drill bit, is cooled by using drilling fluids. It is normally used in every oil and natural gas drilling rigs to provide the necessary cooling and lubricating effect on the drill bits. Even as they partially eliminate the temperature issues, they exert a staggering amount of pressures when the borehole gets deeper. As the hydrostatic pressure increases along with an increasing lithostatic pressure, the borehole’s walls are subjected to very high vertical stresses. If the hole collapses and closes itself, it could be fatal to the drilling equipment. To avoid such collapses, drillers use casings like the PVC to protect the hole and continue drilling to a point where the diameter of the hole shrinks down due to the casing. By using the improved versions of existing technologies we could overcome the factors that constrain the drill operations beyond a certain depth, and we could very well drill beyond the Kola’s mark of 40502 feet. Experts opine that with industrial diamond drill bits and well-reamed casing, the borehole can be maintained very well to eliminate the lithostatic stresses from affecting the drill column and the borehole.
New technologies are being developed with which drilling would be continuous with a constant borehole diameter. Plasma deep drilling technology is being talked about a lot. However, it is far from industrial deployment. BP, one of the major oil companies is developing deep water drilling technologies that could withstand up to 20,000 PSI. There are other new drilling ideas being floated. Researchers from England propose a new idea to use cobalt-60, a radioactive element, inside a tungsten capsule to melt away itself though the earth’s crust. The temperature of the mantle graduates from 500 °C at the crust boundary to 4000 °C at the core boundary. Tungsten has the highest melting point among all metals. The 3422 °C melting point of tungsten will protect the cobalt-60, as the immense heat from the decay could melt the rocks in its way down. They have estimated that it would take three years for the capsule to sink to a depth of 20 kilometers. Compare this to the current achievement with conventional technology of 7.6 miles at Kola Super hole, to get an idea of the exciting potential,
David J. Stevenson, a professor at California Institute of Technology, suggests that pouring molten iron into a crack, made by a TNT or nuclear explosion, would be feasible for a grapefruit-size probe to go all the way into the crust and beyond that.
Though ideas are aplenty, the governments who should be the primary funding agencies in such knowledge-oriented billion dollar ventures which do not bring in immediate commercial profits, aren’t convinced why such explorations matter. This might be the greatest barrier today. The depth we can drill into the earth is not a matter of technology anymore. The major drilling corporations already have the technology to break the earlier records. The current researches in composites and materials bestow such great hope that we could break the crust and explore the deepest parts of our planet early.
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