A literature review of using supercritical CO2 for geothermal energy extraction: Potential, methods, challenges, and perspectives

In order to achieve the goal of carbon neutrality in the energy sector and promote sustainable economic development, it is critical to expand the depth of geothermal exploitation and accelerate the development of mid-deep geothermal energy. However, traditional hydrothermal geothermal systems are hindered by water scarcity, low heat extraction efficiency and so on. The solution may lie in using supercritical CO₂ (SCCO₂) instead of water for geothermal extraction, which not only enables efficient geothermal exploitation but also allows for additional CO₂ sequestration. This paper begins by introducing the current status and characteristics of geothermal resources, including hot dry rock, deep saline aquifers, and depleted oil–gas reservoirs, along with a review of related engineering cases in the world. Additionally, the advantages of SCCO₂ compared to water in heat extraction are examined, and progress in the development of CO₂ geothermal systems, CO₂-enhanced geothermal system (CO₂-EGS) and CO₂ plume geothermal system (CPGS), is summarized, highlighting the challenges they face. Furthermore, the paper explains the additional benefits of CO₂ geothermal systems. In the end, future research trends and development strategies are presented. For CO₂-EGS, reservoirs artificial fracturing technology should be the focus of future research. For CPGS, it is vital to improve the efficiency of heat extraction, with special attention given to the geothermal resources in depleted oil–gas reservoirs, particularly depleted gas reservoirs. The practical application of CO₂ geothermal systems requires the efforts of governments, research institutions, enterprises, and other stakeholders to work together.