GreenFire Energy is involved in developing closed-loop geothermal technology and methods to efficiently and economically extract thermal energy from various geothermal and oil and gas resources. Initial analysis and projects often involve the retrofitting of existing underperforming/depleted geothermal and oil-and-gas wells with the longer term goal being the technology for use in new purpose drilled wells to create large projects in similar resources. Numerous process simulations have been carried out since the inception of the firm in 2014 using a variety of downbore working fluids in the closed-loop system. In particular, in 2019, at GreenFire Energy’s test project at the Coso geothermal site in southern California, two such working fluids, namely water and supercritical carbon dioxide (sCO2) were tested in GreenFire’s GreenLoop™ down bore heat exchanger (DBHX) system installed in an existing geothermal well. These fluids were benign by nature, and therefore, any accidental thru-well leakage isn’t considered an environmental issue. Over the years with significant advancements in manufacturing technologies, casing manufacturers have guaranteed their zero-leakage premium joint designs paving the way for the use of organic hydrocarbon working fluids (eg, cyclopentane, isopentane or isobutane). To validate this, a test with water is planned for 2023, with support from the California Energy Commission at GreenFire Energy’s proof of concept project at The Geysers geothermal site. By using organic fluids for the technology, it is possible to directly hook up an expansion machine (turbine or expander) straight from the wellhead outlet flange. Heat exchangers at the surface to transfer heat from the produced fluid to the ORC fluid will no longer be required resulting in substantial cost savings. Other advantages include the absence of scaling in, and other issues arising from the injection wells since injection wells are typically not required where the technology is used, long-term sustainability, and compatibility with non-flowing and sub-par producing wells. This paper compares water, sCO2, and an organic fluid (n-pentane) as working fluids, baselined to one common well using the DBHX for heat extraction and thus electricity generation.