Coso Project

First Field-Scale Demo of GreenLoop

Geothermal power generation in California is severely restricted with conventional hydrothermal technology which must have the necessary combination of porosity, heat, and fluids to produce a developable geothermal resource. At the Coso geothermal field in California, USA, GreenFire Energy Inc. demonstrated the first field-scale use of closed-loop geothermal technology using a grant from the California Energy Commission (CEC).


Geothermal power generation in California is severely restricted with conventional hydrothermal technology. Closed-loop geothermal technology has the potential to generate power and restore idle wells but had not been demonstrated at field-scale before this project.


GreenFire’s GreenLoop® is a novel Down Bore Heat Exchanger (DBHX) technology that typically requires a single well and no injection well nor surface facilities to dispose of any effluent. The GreenLoop system circulates a selected working fluid through the DBHX to absorb and transport heat from the geothermal fluids entering the wellbore. As the technology extracts thermal energy only, reservoir mass and pressure are conserved thus ensuring long-term sustainability of the resource. The produced fluid from the GreenLoop system can be used for either electricity production, space heating and cooling or some industrial applications.

A GreenLoop system consisting of a 7” outer casing and 3-½” vacuum insulated tubing (VIT) was installed in an idle well at Coso that produces a high concentration of non-condensable gas (NCG) with the objective of making this stranded well useful again. Due to budget limitations, the GreenLoop system was set at 330 m only below the ground.

  • Design, build, and operate a closed-loop demonstration plant
  • Determine the power generation potential of an underperforming geothermal well using closed-loop technology
  • Model the heat transfer process
  • Co-produce brine and steam to the surface through the DBHX to increase convective heat flow
  • Use water and supercritical CO2 (sCO2) as working fluids for the system
  • Varied flow rate of the working fluid (water and sCO2) to understand heat transfer conditions and identify the best strategy for long-term sustainability
  • Build dataset using the demonstration plant to guide development of field-scale CLG projects across the globe


By using water as working fluid for the GreenLoop system, the extracted heat energy was estimated to generate 1 – 1.2 MWe of net electric power through Coso’s double-flash turbines. The produced GreenLoop fluids were not directly piped to the existing steam flash plant and net power was estimated using the steam usage rate of the power plant. If the produced GreenLoop fluids were used in an Organic Rankine Cycle (ORC) binary power plant, the estimated generation would be >1.9 MWe.

This demonstration project has confirmed the validity of GreenFire Energy’s closed-loop modeling and provided the geothermal industry with the basis for considering well-retrofit projects and new field-scale geothermal projects using closed-loop geothermal technology. Results indicate that both water and sCO2 were proven to be effective heat transfer fluids during this field test. The project aided the quantification of field-scale closed-loop projects. It is expected that these results will enable the geothermal industry to expand beyond its current constraints, use a much greater portion of the global geothermal resource, and more extensively and efficiently harvest energy from geothermal locations.

Summary Results

  • Closed-loop geothermal technology could be run at field-scale
  • The energy can produce 1.2MWe using existing surface turbine or 1.9MWe with new ORC units
  • Potential production could be 10 times greater
  • The DBHX provided sufficient surface area for condensation of geothermal brine
  • Both water and sCO2 can be effectively used as a transfer fluid
  • The project helped validate GreenFire Energy’s modeling approach which enables the quantification of field-scale closed-loop projects