Drilling the deepest hole on the planet

Currently, there are only 32 countries in the world with geothermal power plants in operation. But not every country is as lucky as Iceland, where hot water reserves at temperatures of about 120 – 240 degrees Celsius are easily accessible close to the ground. One reason geothermal power is not popular is the high initial investment costs to harness that energy. For more parts of the world to be able to use geothermal power, deeper drilling will be needed to reach the temperatures needed to produce electricity or provide large-scale heat to nearby areas, according to National Geographic.

In most places on Earth, the temperature increases 25 – 30 degrees Celsius with each kilometer deeper you go. For example, in the UK, the temperature near the ground at a depth of about 5 km is about 140 degrees Celsius, according to the British Geological Survey. If drilled deep enough, it is possible to reach water temperatures above 374 degrees Celsius at a pressure of more than 217 atmospheres. This is where water enters a supercritical state, being neither liquid nor gas. The greater the temperature and pressure, the more energy it contains.

In fact, a super-hot geothermal well can produce 5 to 10 times more energy than today’s commercial geothermal wells, according to the US National Renewable Energy Laboratory (NREL). However, a major obstacle is that conventional rotary drills, even those fitted with diamond drill bits, are not powerful enough to dig to the depths needed to reach these temperatures. In geological conditions that are difficult to predict with certainty, extreme temperatures and enormous pressures, drilling components can frequently fail, and preventing the borehole from being sealed is a constant battle.

For example, in 2009, a team working on the Iceland Deep Drilling Project encountered supercritical conditions while drilling into the magma chamber at Krafla volcano about 2 km above ground. The super-hot steam emitted from this well has a high acid concentration, so it is difficult to use. High temperatures and pressures also make it difficult to control. Finally, a valve failure forced authorities to seal the hole.

Deep drilling is also a time- and money-consuming activity. The deepest hole humans have ever dug was born during the Cold War. The Soviet Union drilled through 12.2 km of rock, creating the Kola super-deep borehole on the Kola Peninsula in the Arctic Circle. It took them nearly 20 years to reach that depth and the record still stands today. NREL estimates the cost of drilling a well one kilometer deep at about $2 million, while a depth four times that could cost $6-10 million with current technology.

Still, deep underground geothermal energy can offer significant cost savings compared to conventional geothermal, due to the access to higher temperatures and pressures. Therefore, some researchers and companies are pioneering new types of drills and drilling technology to dig the deepest holes ever.

Quaise Energy, a startup from the Massachusetts Institute of Technology, aims to drill holes 12 kilometers deep to reach temperatures of 500 degrees Celsius or more. To do that, they used a tool based on years of fusion energy research. Company co-founder Matt Houde and his collaborators experiment with millimeter wave energy beams that vaporize even the hardest rock. The device focuses a beam of high-energy radiation similar to microwaves but at a higher frequency onto a piece of rock, heating it to 3,000 degrees Celsius so that it melts and evaporates. By aiming the energy beam directly to drill through rock, the team was able to create deep holes without creating debris and friction like traditional drilling techniques. “Millimeter wave drilling is a process that can operate regardless of depth. Millimeter wave energy can travel through dusty environments,” Houde said.

The technology grew out of fusion plasma experiments conducted by Paul Woskov, an engineer at MIT’s Center for Fusion and Plasma Science. Millimeter wave energy has been exploited as a way to heat plasma in fusion reactors since the 1970s, but a few years ago, Woskov developed another use. He began using millimeter wave beams created by a device called a gyrotron to melt rock.

However, until now, the technology has only been tested in the laboratory, drilling shallow holes in relatively small rock samples. Quaise Energy says it can drill through rock at a speed of 3.5 meters per hour. Although this speed is quite slow compared to traditional drilling techniques, there are many other benefits such as the drill bit does not crush rock so it does not wear out and does not need to be replaced. Currently, Quaise Energy is in the final stages of testing millimeter wave technology in the lab with a view to starting field trials in early 2025. But taking millimeter wave drilling technology from the lab to scale drilling Large scale remains a challenge.

Meanwhile, GA Drilling in Slovakia is exploring another high-energy drilling technology to dig through the Earth’s crust. They use pulsed plasma drills, which rely on very short high-energy electrical discharges to shatter rock without causing melting. This helps avoid creating any slimy molten rock that can be difficult to remove and prevent the drill bit from going deeper. “Due to the extremely fast process with short electric shocks that break the rock, there is no time for the rock to melt, which largely reduces the need to pull up and replace drill bits,” said Igor Kocis, president and CEO GA Drilling, said. “The target in our current development program is a depth of 5 – 8 km, later more than 10 km. Such a depth will allow access to geothermal energy almost anywhere.”

Research on plasma pulse drills, which use very short pulses of energy to shatter rock with ionized gas hot up to 6,000 degrees Celsius, is also the direction of a European consortium led by the Geothermal Energy and Geofluids (GEG) group. top, along with partners in Germany and Switzerland. GA Drilling is collaborating with Konstantina Vogiatzaki, associate professor of engineering science at the University of Oxford, to adapt advanced algorithms to examine how supercritical fluids can be controlled to exploit subcritical energy sources. deep underground through plasma drilling.

Many other units are looking for new solutions for deep drilling through technology developed for exploration missions on the surface of Venus, where temperatures can reach 475 degrees Celsius. For example, Ozark Integrated Circuits, manufacturer electrical equipment manufacturer in Fayetteville, Arkansas, USA, is adapting circuit boards that can withstand extreme temperatures used on geothermal drilling rigs deep inside the Earth. NREL is also relying on AI to analyze complex underground environments to find the best locations for supercritical water drilling, as well as predict and detect faults in drills before they cause serious problems.

Geothermal company Eavor said it has reached a depth of 5 km with two vertical wells in Gerestried, Bavaria, Germany. They used two of Europe’s largest land-based drilling rigs to create a commercial-scale plant at Geretsried, bringing geothermal heat to the surface through circulating water in a closed loop called the Eavor Loop. That system looks like a giant radiator, with cold water heated underground, then returned to the surface and used to produce electricity and pump it into neighboring homes through the central heating system. heart. Eavor hopes to begin on-site energy production in the first half of 2025, according to John Redfern, Eavor’s chief executive officer and president. Jeanine Vany, a geologist and co-founder of Eavor, said their technology could drill up to 11 km deep in the future.

Their closed circuit method also helps avoid the pollution problem that occurs when superheated water is extracted from deep geothermal wells and reduces emissions of harmful gases such as hydrogen sulfide.