Exploring the world’s hottest hole

Materials World magazine
,
30 Apr 2017

Iceland is tapping into hot magma to create a natural wealth of energy. Natalie Daniels looks at how the country is benefitting from exploring geothermal wells. 

Located on the Mid-Atlantic Ridge, Iceland’s unique natural landscape attracts tourists from around the world. But, the country’s geographical position also means that today it obtains more of its electricity and heat from renewable sources than any other country. Iceland was once considered one of Europe's poorest countries, dependent upon peat and imported coal for its energy – far from current reliance on renewable resources. Geothermal power plants in Iceland produced around 26.2% of the nation's electricity in 2015. In addition, geothermal heating meets the heating and hot water requirements of approximately 87% of its buildings. Approximately 73.8% of the nation’s electricity is generated by hydropower, and 0.1% from fossil fuels. Geothermal energy harnesses the heat of the Earth’s mantle to turn water to steam, which is then used to drive turbines.

Lauren Boyd, Enhanced Geothermal Systems Programme Manager at the Office of Energy Efficiency and Renewable Energy's Geothermal Technologies Office, USA, explained its benefits, ‘Geothermal is unique in that it is a baseload renewable energy source, meaning that electricity can be produced consistently, running 24 hours per day/seven days a week, regardless of weather conditions. Geothermal development is also advantageous because it requires only a small land footprint.’ 

Iceland has five major geothermal power plants – two produce electric and thermal energy and the other three electricity. The first geothermal pipeline is believed to date back to the 13th Century, when it was constructed to heat the outdoor bath of Icelandic historian, poet and politician, Snorri Sturlusson, tapping into the power lurking in the ground to warm a pool in his garden. That pool, located in the village of Reykholt, has been restored and remains a tourist attraction today.

The main use of geothermal power in Iceland is for space heating. In 1970, around 43% of the population was served by geothermal district heating systems. After the oil crisis in the 1970s, priority was given to replacing imported coal with natural energy sources – both hydro and geothermal. Today, around 87% of heating is powered by geothermal energy, the rest by electricity (11.5%) and oil (1.5%). The economic savings gained by switching from oil to geothermal energy – an estimated US$8.2bln over a period of 30 years – has contributed significantly to Iceland’s prosperity, transforming it from one of the poorest countries in the European Economic Area to one of the most successful in terms of GDP per capita and quality of life. ‘Iceland’s unique geological conditions have afforded that nation unparalleled geothermal resources. Its resources are extremely hot, shallow and widespread – ideal conditions for power production. As a result, Iceland derives the majority of its power from prolific hydrothermal resources,’ explained Boyd. As well as the cost savings, geothermal fields also produce only one-sixth of the CO2 equivalent to a natural gas-fuelled power plant. 

Deep drilling  

The Iceland Deep Drilling Project (IDDP) was founded in 2000 to investigate the economic feasibility of producing electricity from supercritical geothermal reserves. The consortium was formed by Orkustofnun, the National Energy Authority of Iceland, and three Icelandic energy companies – Hitaveita Sudurnesja (now known as HS Orka) Landsvirkjun and Orkuveita Reykjavíkur. It set out to drill a deep well in three different geothermal fields located in Krafla, Hengill and Reykjanes in southwest Iceland. In 2009, the group explored the roots of a conventional high-temperature hydrothermal system in Krafla (IDDP-1) to produce water at super critical conditions and bring it to the surface as 400–600oC superheated steam at subcritical press (less than 220 bar). Following a number of unsuccessful trials, the drilling was terminated at 2.1km when they discovered 900oC glass-like, silica-rich rock, rhyolite magma had flowed into the well 2,104m below ground. Engineers cemented a perforated steel casting into the well. The hole was then allowed to heat slowly and flow superheated steam for the next two years until July 2012, when it was closed to replace some of the surface equipment. Wilfred Elders, Professor Emeritus of Geology at the University of California, USA, commented in Geothermics, ‘The IDDP-1 created the world’s first magma-enhanced geothermal system.’ With the number of drilling problems encountered in IDDP-1, costs of the Krafla site reached around US$20 million, and the HS Orka team began re-evaluating the drilling programme during 2013–14. 

Drilling into the country’s hot rocks to tap geothermal energy is not unusual but reaching deep enough to tap the energy from magma ejected by volcanoes was a greater challenge. The consortium took lessons learnt from the Krafla site and began exploring the Reykjanes Peninsula, located above a major heat source with a depth of 10km, in the second stage of the project (IDDP-2) between 2014–15. The geothermal fluid at Reykjanes area contains modified seawater, which the researchers hoped would determine the root zone of a magma-hydrothermal system. 

Reaching new depths

The project reached a milestone in January 2017. After 176 days of drilling, the researchers reached a depth of 4.65km, exceeding its proposed target to drill beyond 3.08km, extract cores, measure temperatures and search for permeability. Temperatures at the bottom measured 427oC at a pressure of 340 bars, with drilling cores still retrievable following extraction. The new exploration site is now the deepest hole in Iceland – encased within a 2mm steel casting at 2.940m, and following cementing, the casting was deepened with a 215mm rotary drill part. The IDDP-2 hopes to produce up to 10 times more electricity than traditional geothermal energy sources. Boyd believes that these results prove vital for future research, ‘This unprecedented access has important implications for energy production from what are called "supercritical resources" not only in Iceland, but worldwide. Supercritical systems are significantly hotter than a typical hydrothermal system, so energy production would be exponentially higher if it is feasible to exploit these resources.’  

To extract the magma, the IDDP-2 researchers used a rig named ‘Thor’, using a 152mm polycrystalline diamond that cuts a 67mm-diameter core to drill 5km into the Earth’s crust. Unsurprisingly, the team faced challenges exploring such great depths. According to the IDDP-2, ‘Drilling becomes more complicated as the well gets deeper and in this project we went deeper than before. In the beginning, we had difficulties extracting drill cores, but in the end we managed to extract 27.3m in 13 attempts and the last core was from the bottom of the well at 4.65km from the surface. Using conventional drilling methods was not an option for many aspects of the project, so new methods had to be developed to ensure its progress.’

However, the biggest problem remained unsolved when a complete loss of circulation below 3.06km depth could not be cured with lost circulation materials, or by sealing the loss zone with cement. ‘At 3,180m, we gave up cementing below that depth and no drill cuttings were returned to the surface. Consequently, the drill cores were the only deep rock samples recovered. We attempted as many coring runs as the budget allowed,’ as stated by the IDDP project. The loss of circulation beyond 3km depth was unexpected, but despite this, the team is still determined that deep geothermal harnessing will become the fastest growing part of the Icelandic energy market. 

While Iceland continues to benefit from geothermal energy, other countries including the USA and the UK are also looking to follow in its footsteps (see Materials World, March 2017, page 4). But even with its environmental credentials, geothermal energy has its flaws. One concern is the release of hydrogen sulphide, a gas that smells like rotten eggs at low concentrations. Another concern is the disposal of some geothermal fluids, containing low levels of toxic materials. Although geothermal sites are capable of providing heat for many decades to come, eventually specific locations may cool down. Nevertheless, based on the estimated pressure levels in the well, the IDDP-2 project could produce up to 50MW of power, substantially more than regular geothermal wells. ‘Iceland’s abundant supercritical resources are of interest, especially considering the recent success of the IDDP-2 project, which brings the community one step closer to understanding if power production from supercritical systems is feasible and at what cost,’ adds Boyd. However, potential use of this magma will not be known until the end of 2018 when all the research has been conducted.