An introduction to the next clean energy frontier: Superhot rock geothermal and successes from the Iceland Deep Drilling Project
This blog is part of a series exploring and explaining the science behind next-generation geothermal, with a special focus on Superhot Rock Geothermal, through a curated tour of influential technical and academic papers. This edition highlights key features of the World Geothermal Congress Proceeding by Friðleifsson et al. (2021) The IDDP success story – Highlights. The full blog series, in addition to their reference reports, can be found at the Superhot Rock Resource Library.
After a decade of technological progress, geothermal systems are increasingly recognized as a key solution to growing global demand for clean, firm energy. Previously limited to areas with shallow pockets of hot water, recent advancements in next-generation geothermal technologies suggest that continued innovation could enable geothermal deployment virtually anywhere it is needed. Among these technologies, superhot rock geothermal (SHR) systems stand out for their potential to unlock even hotter, deeper, and more energy-dense geothermal resources. For example, early studies in Iceland found that SHR can generate up to 10x the energy output for a single well when compared to conventional geothermal systems.
Despite this potential, only a handful of wells have encountered the supercritical conditions required for SHR. This is largely due to the technology’s nascency and the need for technological advancements in heat extraction, power production, drilling, well design and construction, and siting and characterization to unlock its full potential. However, given SHR’s higher energy density and the potential for competitive costs at scale, efforts to overcome these technological hurdles appear well worth the effort.
In their proceeding from the 2021 World Geothermal Congress, The IDDP success story – Highlights, Friðleifsson et al. detail the efforts of the Iceland Deep Drilling Project (IDDP) to unlock the potential of SHR. With the growing interest in next-generation geothermal, including SHR, it is worth revisiting the lessons learned from these early efforts, while also highlighting the early successes.
IDDP-1 successes suggest that a bright future is ahead for superhot rock geothermal systems
The IDDP was started in 2000 by a consortium of three Icelandic energy companies — Hitaveita Sudurnesja (now HS Orka), Landsvirkjun, and Orkuveita Reykjavíkur (also known as Reykjavík Energy in English) — and the National Energy Authority of Iceland (Orkustofnun). The project was conceived to study the feasibility and economics of extracting energy and chemicals from conventional geothermal systems (e.g., hydrothermal systems) at supercritical conditions.
IDDP’s first well (IDDP-1) was drilled by Landsvirkjun in Krafla (northeast Iceland) from 2008 to 2009. The plan originally called for drilling to around 4.5 km depth, but work halted when 900°C magma was encountered at 2.1 km. After allowing the magma to cool, the well was completed and flow testing began in 2010. The flow tests assessed fluid movement through fractures in the reservoir and the reservoir’s generation potential, demonstrating that IDPP-1 could have generated up to 36 MWe, or 5-10x the energy output of a typical commercial geothermal well at lower temperatures. Although closed in 2012 due to the failure of several surface valves, it was the world’s hottest production well at 450°C.
Prior to its closure, IDDP-1 drilled into magma three times, got stuck twice, and was sidetracked twice. However, several critical lessons were learned in the process:
- Although drilling was halted by the magma, the surrounding rocks—measuring nearly 500 °C—were successfully fractured thermally by the drilling fluid, as noted through step rate injection tests. This suggests that a potential method for creating fractures exists under similar conditions at other SHR reservoirs.
- The casing was being severely corroded while the well was heating up, but well corrosion decreased substantially once the fluid heated enough to become superheated (i.e., reached its supercritical point). Friðleifsson et al. concluded that this finding indicates that production casings should be placed sufficiently deep and wells should be given sufficient time to reheat following stimulation before flowing the well, allowing the fluid to become superheated and avoiding a two-phase fluid system (i.e., containing both liquid and steam), which could lead to severe corrosion.
- Whether using a two-phase system or superheated steam, all casings, well head valves, and surface flowline equipment should be designed to withstand hostile and hot conditions for long-term operation. This is in addition to the need to prioritize ductility over strength in the well design.
- Acid gas, gaseous sulfur, silica dust, and dissolved silica were all carried with the steam up through the production well, potentially to the power plant, but could be washed out by wet scrubbing. Wet scrubbing allowed the steam to be ready for power production but caused a reduction in the power output due to the drop in pressure.
Taken together, these findings highlight both the challenges and opportunities of drilling into superhot formations. Friðleifsson et al. note that the high energy potential demonstrated by IDDP-1, combined with the technical lessons learned, suggest a promising future for power production from superhot rock geothermal systems.
IDDP-2 provides first data on operating in supercritical hydrothermal conditions
Building on the knowledge gained from IDDP-1, drilling of IDDP-2 was led by HS Orka in the Reykjanes peninsula of southwestern Iceland. Drilling began in August 2016 and concluded in January 2017, when an existing 2.5 km well was deepened to a depth of 4.6 km. This became the deepest well ever drilled in Iceland and the first to successfully encounter supercritical hydrothermal conditions, with a bottom hole temperature approaching 600°C.
The well experienced near total circulation loss of drilling fluids, which is the loss of all the circulating drilling fluid (i.e., mud) to the surrounding rock, from the outset of deepening. Production of IDDP-2 was never initiated due to casing failure, but the project showed that reinjection can stimulate a hydrothermal SHR reservoir.
Although the production portion of the well is no longer accessible, ongoing studies of IDDP-2 continue to provide valuable insights, such as into the chemical composition of the geothermal fluid, which can inform planning and development for future high temperature geothermal wells.
Looking forward to IDDP-3
IDDP-3 is being planned in the Hengill area in southwest Iceland and is being led by Orkuveita Reykjavíkur (Reykjavík Energy), where evidence of superhot formations has been observed at about 2 km depth. The goal for IDDP-3 has been shifted slightly from the initial goal of the IDDP to focus on reaching superhot conditions. Accordingly, IDDP-3 is targeting fluid enthalpy greater than 3,000 kilojoules per kilogram (kJ/kg), rather that strictly achieving supercritical conditions.
What’s next?
Drilling of the IDDP-1 and IDDP-2 wells identified several technical and geologic challenges that must be overcome to enable the success of future superhot rock wells. Many of these challenges, among others, are detailed in Clean Air Task Force’s Bridging the Gaps report series. At the same time, important lessons were learned in the drilling of these wells, and multiple successes were achieved, including the demonstration of increased power capacity and potential strategies for managing the corrosive nature of supercritical geofluids.
By recognizing these remaining challenges, while also building on earlier successes, the field can maintain momentum and direct research and funding toward the breakthroughs needed to commercialize SHR.
Stay tuned for more from CATF as we continue to push forward bold ideas on how to scale superhot rock geothermal as an essential source of reliable and clean electricity.
This blog is part of a series exploring and explaining the science behind next-generation geothermal energy, with a special focus on superhot rock geothermal:
Through a curated tour of influential technical and academic papers, the series aims to provide a fresh perspective from a geoscientist entering the geothermal industry. The goal is to share my learning journey and encourage collaboration around these groundbreaking solutions, which are critical to achieving a clean energy future. Whether you’re new to geothermal or looking to deepen your knowledge, I hope this series offers valuable insights into this fast-evolving field.
