Commonly used geothermal energy comes from a depth of 150-200 m where temperatures are around 6-8°C. Researchers at NTNU, University of Bergen, the Geological Survey of Norway (NGU) and SINTEF believe it is possible to drill down to 10,000 m where temperatures can reach at least 374°C and the water has a pressure of at least 220 bars.
“If we manage to produce this kind of energy it would clearly be a ‘moon landing’. This is one of the few sources of energy that we really have enough of. The only thing that we need is the technology to harvest it,” says Researchers at SINTEF Materials and Chemistry, Odd-Geir Lademo.
Learning from the oil industry
Oil companies are already drilling down to 5000 m where temperatures reach 170°C. However, deeper drilling becomes a challenge due to the high temperatures.
A 10,000 m pilot
|Norwegian company Rock Energy plans a pilot plant in Oslo that will collect geothermal heat from 5500 m where the temperature is around 90-95°C. The heat would be used in district heating systems.|
Steel becomes brittle and materials such as plastic and electronics will be weakened or melt. Electronic normally only operate a short time at temperatures above 200°C. SINTEF says these problems would have to be overcome.
“We have a strong an innovative oil industry in this country [Norway]. Because the oil industry has wanted to develop oil and gas deposits from inaccessible areas, drilling technology has evolved tremendously over the past 10 years. There are test wells for oil that go 12,000 m into the earth. Knowledge from the oil and drilling industry may be used in the future to capture geothermal energy,” says Lademo and colleague Are Lund, Senior Researchers at SINTEF Materials and Chemistry.
However, precision drilling is still not possible at depths of 10,000-12,000 m.
“We have to have a common commitment. Multidisciplinary expertise is required. Here at Materials and Chemistry, we are working with an internally funded project in which we are assessing SINTEF’s overall ability to contribute. The goal is to work on projects with industry and the Research Council of Norway,” Lunde says.
“If research and industry succeed in developing the materials and technology needed to bring up the most difficult-to-reach oil, in the long run we will be able to replace oil with geothermal energy for heating and electricity.
Geography determines depth
The depth at which one needs to drill to exploit geothermal energy varies around the world as the crust varies in thickness. At more northerly latitudes such as Norway, the temperature increases by about 20°C/km into the earth’s crust. In other parts of the world, the geothermal gradient is 40°C/km. On average, the geothermal gradient is around 25°C/km.
Norway’s government financed energy efficiency agency, Enova, has questioned the cost associated with deep geothermal energy. Senior Adviser Kjell Olav Skjølsvik, says: “Deep geothermal heat from thousands of metres deep could be promising. But the cost picture here is still uncertain.”
Belief in success
Lademo and Lund are nonetheless optimistic about the future for deep geothermal energy.
“The oil and gas industry is conservative. To begin to develop geothermal energy from 10,000 to 12,000 m deep will be expensive. But the benefits will also be enormous. That is why the industry will eventually begin to invest. In the 1960s, we were beginners when it came to pumping oil from the North Sea. Tackling that challenge was a huge boost in many ways. As a nation, we bet and we won,” says Lademo.
Lund adds: “I believe we can develop the knowledge we need about materials to get down to 300°C in 10 years’ time. It might take 25 years or more of research and development to get down to 500°C.”
30 years lifespan
The normal lifespan for a deep geothermal well is around 30 years, after which the rock has cooled down too much from the cold water injected into the well. However, if left for 25-30 years, the geothermal well will have heated up again.