Research Progress on CO₂ as Geothermal Working Fluid : A Review

With the continuous increase in global greenhouse gas emissions, the impacts of climate change are becoming increasingly severe. In this context, geothermal energy has gained significant attention due to its numerous advantages. Alongside advancements in CO₂ geological sequestration technology, the use of CO₂ as a working fluid in geothermal systems has emerged as a key research focus. Compared to traditional water-based working fluids, CO₂ possesses lower viscosity and higher thermal expansivity, enhancing its mobility in geothermal reservoirs and enabling more efficient heat transfer. Using CO₂ as a working fluid not only improves geothermal energy extraction efficiency but also facilitates the long-term sequestration of CO₂ within reservoirs. This paper reviews recent research progress on the use of CO₂ as a working fluid in Enhanced Geothermal Systems (EGS), with a focus on its potential advantages in improving heat exchange efficiency and power generation capacity. Additionally, the study evaluates the mineralization and sequestration effects of CO₂ in reservoirs, as well as its impact on reservoir properties. Finally, the paper discusses the technological developments and economic analyses of integrating CO₂ as a working fluid with other technologies. By systematically reviewing the research on CO₂ in EGS, this study provides a theoretical foundation for the future development of geothermal energy using CO₂ as a working fluid.