The World’s Deepest Well
Supercritical fluid is neither liquid nor evaporated, and it includes lots of energy. In Iceland, a company has drilled down to the vapour of an underground magma chamber to try to take advantage of the extreme water.
Liquid magma from Earth’s interior rises to heat the rock to a temperature of up to 500 degrees. The ground water is heated and compressed into redhot, liquid gas. The extreme water rises towards the surface, where its huge energy content is used: supercritical fluid powers a power plant, which lights lamps, charges smartphones, and keeps the cookers of 50,000 Icelandic homes going.
In February 2017, Icelandic engineers finished the drilling of a 4,659 m hole into the area above a magma chamber. A hole, which is to be the world’s hottest geothermal well and generate unprecedented quantities of eco-friendly electricity harvested directly from the heat in Earth’s interior.
At this depth, the temperature and pressure are so high that the ground water is converted into a state, in which the water contains much more energy than ordinary warm underground water and vapour. So, scientists believe that this one well can generate 10 times as much electricity as an ordinary geothermal well – approximately 50 megawatts per year.
The deep well has been drilled as part of the Iceland Deep Drilling Project (IDDP), which was initiated in 2000 by three Icelandic energy companies aiming to drill much deeper than the existing geothermal wells, of which the deepest is almost 3 km.
ICELANDIC VAPOUR BEAT WORLD RECORD
Iceland is the obvious place to experiment with geothermal energy, as the country is located on the Mid-Atlantic Ridge, where the North American and Eurasian tectonic plates meet. In between the plates, magma rises to heat the underground, and the Icelandic population has long taken advantage of the phenomenon.
Today, 90 % of all Icelandic homes are heated via geothermal energy. Power generation is not as common as direct heating, but Iceland is still the second to none world leader. One third of the electricity consumed by Icelandic households derives from geothermal power plants.
Hot water and vapour extracted from the ground have their limitations, however. Ideal drilling locations are hard to find, drilling is expensive, and lots of wells are required to operate a geothermal power plant. The Krafla plant, which is the smallest geothermal plant in Iceland, pumps up vapour from 33 wells to generate 60 megawatts of power, i.e. only 10 megawatts more that the IDDP expects to generate from the new Reykjanes well.
The deep drilling idea originated by accident. In 2009, engineers drilled a geothermal well in the Krafla region. About 2 km into the ground, they accidentally drilled a hole into a magma chamber. The hole was sealed with a plug made of steel and concrete. The plug was full of microscopic holes, allowing the water vapour from the
Geothermal energy could provide 20 per cent of the world's power by 2050.
ground to slowly seep up from the hole. The vapour was more than 450 degrees hot – a new world record for a geothermal well and much warmer than the about 300 degrees of a typical geothermal well.
The scientists behind the project made measurements of the energy potential of the red-hot well and got extremely promising results: the well could generate 36 megawatts of electricity – more than half of the Krafla plant’s 33 holes combined. At Krafla, scientists were surprised that the drill reached into a magma chamber. And when the well was to be linked with the Krafla plant, a valve broke, forcing scientists to stop their work to seal the hole.
The people behind the IDDP decided to try again in the Reykjanes region in SouthWestern Iceland. This time, the well was to be 5 km deep to get both the high temperatures of the Krafla drilling and ensure high pressure. At temperatures above 374 degrees and a pressure of 220+ bar, water does not only turn into vapour, but rather into supercritical fluid, which becomes much more high-energy at rising temperatures than if ordinary water vapour were heated further.
This is due to the laws of thermodynamics. When water is 100+ hot, all other heat is used to convert water into vapour (boiling). At a higher pressure, the boiling point increases, and the water will not bubble until at a higher temperature. On the other hand, less energy is lost in the boiling process and in the transition from water into vapour. When the temperature exceeds the critical point, and the pressure is sufficiently high, the water will no longer boil, but rather be converted from water into vapour without any energy consumption. In this state, the water is known as super-critical vapour.
Due to its qualities, supercritical fluid includes more energy per drop than subcritical vapour. One litre of supercritical fluid of 400 degrees under a pressure of 250 bar contains five times as much energy as ordinary vapour of 225 degrees.
In a geothermal power plant, the difference is key. The more energy the vapour contains, the more it can make a powergenerating turbine move, before the vapour cools and condensates.
BRIGHT FUTURE
Now that the IDDP drilling has been completed, a period of about two years of efficiency studies follows. Scientists must find out how the supercritical fluid affects the stainless steel, nickel, titanium, and concrete which make up the well and the plug at the bottom. Supercritical fluid is highly corrosive, i.e. it breaks down other materials in the same way as acid, etc. Moreover, scientists have not yet powered a turbine by supercritical fluid. So, a turbine which can efficiently convert the extreme vapour into energy must be developed.
Once the different challenges have been solved, the future potential is huge. Iceland has almost covered its own electricity requirement, but scientists are trying to find out, if it is possible to place a live cable on the ocean floor to carry surplus electricity to Scotland or Scandinavia, where it can be distributed via local electricity grids.
Geothermal energy researchers are optimistic concerning the future of geothermal heat. Right now it provides just 1% of the world’s energy demand, but according to scientists, it could rise to as much as 20% by 2050.