Technology advances could multiply geothermal output five-fold

Far below the Earth’s surface is an energy source with huge and perpetual potential: geothermal heat. But the forces in its scorching and inhospitable depths must be tamed. Now scientists know what that will take.

“Deep underground we find temperatures of more than 1,000°C, which can be converted into energy that is renewable and almost CO₂-free. This geothermal heat is also independent, available and stable 24 hours a day.”

These are the words of Hieu Nguyen Hoang, a senior research scientist at SINTEF. He is one of the technologists who has set out to tame the inhospitable conditions deep within the Earth.

Geothermal energy could become a critically important energy source that the world desperately needs more of, as we accelerate the shift towards greener and more renewable energy. However, currently it produces a lot of greenhouse gas emissions.

So far, the potential of geothermal energy has been relatively untapped, with less than 3% of global energy currently coming from geothermal heat. High costs and the high energy production associated with drilling are the main reasons for this.

We need to be able to drill down to temperatures that are high enough for profitable electricity production, because the closer to the Earth’s core we get, the hotter it gets.

At least a five-fold efficiency increase

New technological advances are bringing us ever closer to the goal.

Iceland is already well on its way to taking advantage of the country’s unique geological conditions. Today, 99% of Icelanders’ electricity comes from renewable sources, and geothermal energy is an important part of the energy mix.

The Iceland Deep Drilling Project (IDDP) is a research and development project that has been investigating how to create wells that can withstand both the high temperatures and porous geological formations of Iceland for several years.

The goal is to drill down to “supercritical water”—a state of water that occurs when the temperature exceeds 374°C and the pressure increases to 218 times the air pressure at the surface. These extreme conditions produce five to ten times more electricity than traditional geothermal energy.

“Supercritical water, with its higher energy density, offers a unique opportunity for producing electricity. Unleashing this resource could revolutionize geothermal power and make it one of the most efficient renewable energy sources,” says Hoang at SINTEF.

IDDP partners come from several countries, including Equinor, Norway’s international energy company. They have been working to find solutions through two previous projects. So far, they have not been successful.

“The first well achieved superheat conditions, and the second one attained supercritical conditions at a depth of 4650 meters. However, both wells experienced failures due to inadequate casing systems in the outer wall of the well,” says Hoang.

New super well

Now a new IDDP project is underway: The COMPASS project is picking up where its predecessor, HotCaSe, left off. The goal is to construct a new well that can withstand both high temperatures and the porous geological formations. At the same time, costs must be kept as low as possible, so that the project is profitable and more sustainable.

“Corrosive fluids, extreme pressures and geothermal stresses are tough challenges for well design. Innovative solutions are essential to ensure the integrity and longevity of geothermal wells,” says Hoang.

SINTEF is responsible for developing the simulation tool for the well. Reykjavik Energi is responsible for drilling what will be the IDDP project’s third well. With its subsidiary On Power, they have prepared for the task through several research projects. The goal is to set new standards for well design with the help of an international team of experts.

Has to withstand ‘everything’

Extracting geothermal energy occurs by the water in the reservoir flowing into the well and up to the surface. The porous formations with their natural cracks enable the water to move in the formations. The challenge is to ensure the well’s integrity over time and under the extreme temperature and pressure conditions that exist in these geothermal environments.

The researchers in the COMPASS project will be developing technology to provide a stronger and more flexible well that can handle the extreme conditions. This includes the development of stronger and more flexible outer walls, called casings, to reduce thermal stress. The project will also focus on innovative, corrosion-resistant well designs.

“Using a laser, we’ll apply a protective layer to the pipe that resists corrosion and can withstand the high pressure and corrosive liquids,” says Tèrence Coudert, a researcher and SINTEF colleague.

A technological crystal ball

SINTEF has developed an advanced simulation tool called Casinteg, and this technology could completely change geothermal well design, according to the researchers behind it.

By simulating and extracting data from wells, the tool makes it possible to identify what kinds of physical phenomena occur in the depths of the Earth. The simulation also provides information about chemical reactions and which materials are needed to create a flexible structure.

“The tool is absolutely key and is an important result of the previous HotCaSe project and the ongoing COMPASS project. It provides us with quick calculations of the forces in the well and what the structure can withstand, so that we can keep developing the technology and reduce costs,” says Coudert.

In the previous project, the casing system quickly suffered damage in the super-hot conditions. The result was that the researchers were not able to measure the conditions in the well nor carry out the planned tests.

“Our experience from the first IDDP wells shows how important the casing system is, so that the outer wall can hold up,” says Hoang.

Possible reuse of previous wells

According to the researchers, geothermal energy could play an important role in the global energy transition and become a reliable and versatile alternative to traditional renewable energy.

However, geothermal energy is more than a renewable energy source: it also has the potential to play a key role in a circular energy economy. By reusing wells for carbon capture, thermal energy storage or hydrogen production, geothermal projects can extend their life cycle and minimize their environmental impact.

“Our goal is to create wells with a lifespan of 30-plus years that can be adapted to future applications and conditions,” says Lilja Tryggvadóttir at Reykjavik Energy.

“We are also exploring the possibilities of reusing and refurbishing old wells, and extracting energy from deeper resources,” she says.