Enhanced geothermal systems

Also known as EGS, Engineered geothermal, Next-generation geothermal

Enhanced geothermal systems (EGS) engineer flow paths through hot rock that does not let water pass easily, so that water can circulate, pick up heat and return to the surface. A 30-day circulation test at a Utah research site in 2024 was reported by the U.S. Department of Energy as positive initial evidence, but long-term heat output and induced seismicity are not yet established across projects.

Research and prototypesReported, unverifiedReviewed 21 Oct 2026
AI illustration · Illustrative scene, not a photograph of the specific device or experiment.

In plain language

Conventional geothermal power uses hot underground rock where water already flows through natural cracks and pores. Enhanced geothermal systems aim to work where the rock is hot but does not let water pass easily. Engineers drill wells into the hot rock and stimulate it, often by injecting fluid under pressure, to open or improve pathways between an injection well and a production well.

Water is pumped down, travels through the fractures, picks up heat and returns to the surface, where the heat can be used for power or heating. How well this works depends on where the water actually travels, how quickly it comes back and how much heat the rock gives up along the way. Sealed closed-loop designs, which do not rely on fluid moving through fractures, are a different approach and need their own evidence.

Technical explanation

EGS creates or improves a permeable reservoir in low-permeability hot rock by hydraulic stimulation, which opens or extends fractures between an injection well and a production well. Operators then run circulation tests, injecting fluid into one well and recovering it through another while pressure and produced temperature are measured.

At Utah FORGE, a U.S. Department of Energy research site, the Department reports that a 30-day circulation test followed stimulation in August 2024. Cool water was injected at a consistent rate of 10 barrels per minute and produced at about 370°F. The Department describes these results as positive initial indications that significant heat can be extracted from an EGS reservoir, and says a 30-day test cannot provide the same information as an extended test. An extended circulation test was announced on 17 August 2026. It is intended to run for months, to observe pressure and production stability, water recovery and heat extraction. The Department describes the test as just getting under way, with no outcomes reported.

Modelling of a deep closed-loop design, the Eavor-Loop, shows a different set of trade-offs. Kelly and McDermott (2022) used finite element models to test the developer's power output claims, which they found plausible. The upper end of the predictions would likely require production temperatures above 150°C. They also found that adding lateral well arrays makes the design scalable but reduces efficiency through thermal interference. These are model results, not field measurements, and they describe a different design from fracture-based EGS.

What the evidence says

Each statement is typed by the strength of its evidence and linked to the source that supports it.

Reported, unverified Stated by a company or team but not independently confirmed.

The U.S. Department of Energy reports that in August 2024, Utah FORGE ran a 30-day circulation test, injecting cool water at 10 barrels per minute and producing it at about 370°F.

Sources: [1] · Article text on the August 2024 test · medium confidence

The Department of Energy describes the 2024 result as positive initial indications that significant heat can be extracted from an EGS reservoir, and says a 30-day test cannot provide the same information as an extended test.

Sources: [1] · Article text on the August 2024 test · medium confidence

The Department of Energy announced on 17 August 2026 that an extended circulation test at Utah FORGE was starting. It is intended to run for months, and the Department reports no outcomes.

Sources: [1] · Article text on the extended test

In a finite element study of the Eavor-Loop closed-loop design, Kelly and McDermott (2022) concluded that the developer's power output claims are plausible; the upper end of the predictions would likely require production temperatures above 150°C.

Sources: [2] · Abstract · medium confidence

The same study found that adding lateral well arrays makes the closed-loop design scalable but reduces efficiency through thermal interference.

Sources: [2] · Abstract · medium confidence

Zhou and colleagues report that induced seismicity at Basel and Pohang caused ground shaking, building damage or injuries and, in some cases, early project termination. They describe Soultz-sous-Forêts, Helsinki, Blue Mountain and Utah FORGE as having managed induced earthquake risks adequately.

Sources: [3] · Abstract, as shown on the TU Delft repository record (full text not reviewed) · medium confidence

Proposed A design or plan that has not yet been built or tested.

The good practice guideline recommends a seismic risk management framework, seismic risk pre-screening, comprehensive hazard and risk evaluation, traffic light protocol designs, seismic monitoring, and step-by-step communication plans.

Sources: [3] · Abstract, as shown on the TU Delft repository record (full text not reviewed) · medium confidence

Limitations and open problems

  • The best-documented field circulation test in the sources reviewed ran for about a month at a research site. It does not show long-term pressure, production stability, water recovery or heat extraction, which the Department of Energy says need a longer test.
  • The sources checked for this profile do not report water-loss rates, fluid chemistry, scaling or corrosion, so these cannot be judged from them.
  • Hydraulic stimulation can reactivate faults. Basel and Pohang EGS projects caused shaking, damage or injuries and, in some cases, were ended early. The good practice guideline recommends pre-screening, hazard evaluation, traffic light protocols and seismic monitoring (Zhou and colleagues, 2024).
  • Closed-loop modelling suggests that higher output would need production temperatures above 150°C, and that added laterals lose efficiency through thermal interference (Kelly and McDermott, 2022). These are modelled results.
  • The sources reviewed do not give verified drilling costs, well failure rates or levelised cost of heat or electricity for EGS, so commercial viability cannot be judged from them.
  • Heat produced at the wellhead is not electricity delivered to the grid, and net output depends on pumping and plant energy.

Possible future uses

Speculative

Ideas, not predictions. None of these has been demonstrated.

  • Geothermal power in regions that lack naturally permeable hydrothermal reservoirs but have accessible hot rock.
  • Dispatchable heat for district heating or industrial processes, if long-term production proves stable at useful temperatures.
  • Engineered wells that add pressure to existing hydrothermal fields.

Timeline

  1. 23 Feb 2022Kelly and McDermott publish finite element modelling of the Eavor-Loop closed-loop geothermal design in AIMS Geosciences. Sources: [2]
  2. 2024Zhou and colleagues publish a good practice guideline for managing induced seismicity risk from EGS in Reviews of Geophysics. Sources: [3]
  3. Aug 2024Utah FORGE completes a 30-day circulation test, injecting water at 10 barrels per minute and producing it at about 370°F, as reported by the Department of Energy. Sources: [1]
  4. 17 Aug 2026The U.S. Department of Energy reports that Utah FORGE is starting an extended circulation test intended to run for months. Sources: [1]

Futures this could help bring about

AI illustration
How far away?

Geothermal power almost anywhere

Pilots · 3 of 9 steps done

Related breakthroughs

Glossary

Enhanced geothermal system (EGS)
A geothermal system in which wells and engineered permeability help circulate fluid through hot rock that does not provide enough natural flow.
Hydraulic stimulation
Injection of fluid under pressure to create, open or improve underground flow pathways; the method and resulting fracture behaviour vary by geology and design.
Circulation test
A field test that injects fluid into one well and measures its return through another well, including flow, pressure and temperature.
Closed-loop geothermal
A system in which working fluid circulates through sealed underground pipes and exchanges heat with surrounding rock without intentionally flowing through a fracture network.

Sources

  1. government report
    Running Hot, Keeping Cool: FORGE Embarks on Extended Circulation Test
    U.S. Department of Energy, Geothermal Technologies Office, 17 Aug 2026. Accessed 21 Oct 2026.
  2. peer reviewed paper
    Numerical modelling of a deep closed-loop geothermal system: evaluating the Eavor-Loop
    Joseph J. Kelly, Christopher I. McDermott. AIMS Geosciences, 23 Feb 2022. DOI: 10.3934/geosci.2022011. Accessed 21 Oct 2026.
  3. review article
    Managing Induced Seismicity Risks From Enhanced Geothermal Systems: A Good Practice Guideline
    Wen Zhou, Federica Lanza, Iason Grigoratos et al.. Reviews of Geophysics, 2024. DOI: 10.1029/2024RG000849. Accessed 21 Oct 2026.

Revision history

3 changes since this profile was created.

Changes on 21 Oct 2026
Published on owner instruction (content loop iteration 3)9518996
Sources and claims re-checked against originalsfbb434c
Initial profile drafted from Codex research note and primary sources0eba374