The largest geothermal power station in the world, the Geysers in Northern California, once produced 2000 MW of power but due to lack of water to feed the high enthalpy high temperature steam geothermal project and other factors have led to a decline in power production to 630 MW, still quite high, but less than a third of its original output. The Geysers use up 15 million gallons of water per day. It is not a single power plant but a series of 18 power plants spread over 45 miles of geography. Treated municipal wastewater is the water source for the plants, but even with that resource, there is often not enough water. The region as a whole is dry, and water is usually at a premium.
Canadian firm GreenFire
Energy has a project in progress and just announced a pilot demonstration at
one well in the field to test their closed-loop conductive geothermal
technology which uses an Organic Rankine Cycle (ORC) with working fluids that
heat up when they reach the bottom of the hole and cool down after they are at
the surface in a closed loop. The working fluids do not actually touch the
hydrothermal system water and steam. The working fluid boils at a temperature
much lower than the boiling point of water. Thus, it can produce steam to spin
a turbine at a lower temperature than water.
The goal of the project is to
revitalize the power station with the new technology. While conductive
geothermal will produce less power than recirculating large quantities of water
with significant losses, the technology is much less prone to the significant
problems of conventional geothermal. According to the press release:
“Early test results, using an existing geothermal well
are extremely positive, providing a potential foundation for what’s possible
using next-gen geothermal technology in steam dominated reservoirs. The
demonstration project’s early performance marks a meaningful leap in geothermal
recovery efficiency, highlighting GreenFire Energy’s ability to boost output in
mature fields like The Geysers. By matching technology to geology and combining
patented systems with field-optimized practices, the project demonstrates a
proven path to accelerate geothermal development using next-gen solutions.”
“The system installed in a low-output well nearing idle
status is now fully operational–initial results show sustained flow rates
between 300-350 gpm with higher-than-expected output temperatures at 310 F in a
stable closed-loop system. GreenFire Energy enhances heat recovery by
leveraging natural convection and optimizing saturation pressure within the
reservoir, while maintaining a closed-loop flow in the liquid phase to bring
heat to the surface. This approach enables efficient energy transfer, potentially
unlocking more power from existing well infrastructure in places like The
Geysers and other geothermal fields while still preserving water mass in the
reservoir. Two seven-day production tests have already been completed,
step-change testing is complete in both forward- and reverse-flow
configurations, and an industry-standard duration steady-state test is nearly
complete. These series of high-flow tests are designed to validate performance
across multiple operating conditions and applicability in other low-output
wells showing the scalability in geothermal fields. This California Energy
Commission-funded demonstration project is expected to be completed in June.”
GreenFire Energy has been
developing its closed-loop advanced geothermal system (AGS) for use in
steam-dominated and high-enthalpy two-phase reservoirs. The new technology
benefits from a downhole heat exchange system (DBHX) that utilizes a siphon
effect and pressure to circulate the working fluids. According to GreenFire’s
website:
“In Steam and 2-Phase, a downhole tube-in-tube heat
exchanger circulates large volumes of a variety of working fluids. The working
fluid returns to the surface hot through an insulated tube and can be flashed
to produce power at an existing power plant, used for the direct power
production by an integrated Organic Rankine Cycle power-generating system, or
used for direct use geothermal heating and cooling. Downhole steam condenses on
the surface of the heat exchanger transferring its latent heat of vaporization
to the working fluid. The condensed steam produces a flow of geofluid
condensate towards the bottom of the well, where it builds up to produce the
hydrostatic head required to force the liquid deep back into the reservoir. The
effect of the downbore closed-loop heat exchanger is to extract heat, rather
than mass (or water), from the resource, thereby preserving mass and pressure
in the geothermal resource and ensuring the long-term sustainability of the
resource.”
GreenFire’s Steam Dominated GreenLoop (SDGL)
A 2021 paper published in GRC
Transactions describes the technology in detail. According to the abstract:
“This application of closed-loop geothermal (CLG) is
called Steam Dominated GreenLoop (SDGL). In SDGL a downhole tube-in-tube heat
exchanger is used to circulate large volumes of a working fluid (e.g., water,
supercritical CO2, iso-pentane). The working fluid returns to the surface hot
through a vacuum insulated tube and can be flashed to produce power at an
existing power plant, used for the direct production of power by an integrated
Organic Rankine Cycle (ORC) power-generating system, or used for district
heating. Downhole, steam condenses on the surface of the heat exchanger,
transferring its latent heat of vaporization to the working fluid. The
condensed steam produces a flow of liquid condensate towards the bottom of the
well, where it builds up to produce the hydrostatic head required to force the
liquid deep into the reservoir. Non-condensable gases are allowed to slowly
rise to the surface, where they are collected and treated. The effect of the
down-hole closed-loop heat exchanger is to extract heat, rather than mass, from
the steam dominated resource, thereby conserving water and maintaining pressure
in the geothermal resource.”
The paper gives a full
description of the closed-loop process:
“The closed-loop process flow can be simply described as
follows: a pump is used as the motive force within the DBHX. Generally, the
flow is down the annular portion of the DBHX on the outside of the VIT. At the
bottom of the DBHX, the flow reverses direction and returns up the center of
the VIT. Outside the DBHX, the steam enters the wellbore and interacts with the
cold surface of the DBHX. This causes the steam to quickly condense to liquid.
The liquid (by virtue of having ~1000x the density of steam) will flow
downwards, while the uncondensed steam and NCGs {non-condensable gases} will
slowly flow upwards. The DBHX working fluid flows counter to the
NCGs, which are vented at the surface. Due to the counter flow, as the NCGs
approach the surface, they cool and lose humidity until they are produced
relatively dry at the surface. NCGs may be treated (e.g., H2O2 for H2S
abatement) and then vented or reinjected. Power production occurs by
using a heat exchanger with an ORC binary power plant. Other alternatives
include flashing water to an existing power plant or using an ORC fluid (e.g.,
CO2 or iso-pentane) in the DBHX to generate power directly at the
surface. GreenFire Energy’s proprietary models can analyze and
design systems tailored to each specific resource. The selection of a site with
the correct geothermal geological properties is important to optimize
performance. There should be sufficient reservoir pressure, enthalpy, and
permeability to provide a good flow of steam to the wellbore. Ideally this occurs
from a feed zone that is relatively shallow (e.g., a steam cap). Additionally,
there should be a lower feed zone or resource permeability that is near the
bottom of the well. These features are evaluated using drilling logs, well
surveys, injectivity and productivity tests, and other geothermal techniques.”
The advantages of closed-loop
geothermal over conventional open-loop geothermal are given as:
a) there is no separate reinjection of fluids that can
cause seismic or subsidence events,
b) there is no mixing of subsurface fluids with the working
fluids or interference with natural flows in the resource that would negatively
impact nearby landowners or their businesses (e.g., farming or hot springs
resorts), and
c) there are no waste streams associated with
mineralization (e.g., H2S) in the geothermal brine.
It should be interesting to track this project to see what power production results are obtained and to evaluate whether it will be a cost-effective and technologically feasible way to re-power and revitalize power output from steam-dominated and two-phase high-enthalpy geothermal reservoirs. The company noted that it will report results to the California Energy Commission at project completion.
References:
Pilot
project seeks to fix Achilles’ heel of geothermal power. Saul Elbein. The Hill.
May 8, 2025. Pilot
project seeks to fix Achilles’ heel of geothermal power
The
Geysers: Produce Steam from Existing Production Wells. GreenFire Energy. The Geysers -
GreenFire Geothermal Projects
Closed-Loop
Geothermal in Steam Dominated Reservoirs. Brian Higgins, Joseph Scherer, Alvaro
Amaya, and Harish Chandrasekar, GreenFire Energy. September 2021. GRC
Transactions, Vol 45, 2021. (PDF)
Closed-Loop Geothermal in Steam Dominated Reservoirs
GreenFire
Energy Launches First Commercial Next-Gen Demonstration Geothermal System at
The Geysers. Business Wire. May 8, 2025. GreenFire
Energy Launches First Commercial Next-Gen Demonstration Geothermal System at
The Geysers
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