A comparative analysis of flow channeling and heat extraction behavior between water- and ScCO2-based Enhanced Geothermal Systems considering fracture aperture heterogeneity

The selection of working fluid critically influences the heat extraction performance of Enhanced Geothermal Systems (EGS). Water and supercritical carbon dioxide (ScCO2), as two representative fluids, exhibit distinct thermophysical properties that result in different flow behaviors and thermal performance. These differences may be further affected by the fracture aperture heterogeneity commonly observed in real-world EGSs. We develop a field-scale EGS model to compare the flow and thermal behaviors of water and ScCO2, for both homogeneous and heterogeneous aperture scenarios. Under a constant injection mass rate, ScCO2 exhibits more severe flow channeling than water due to its lower and less temperature-sensitive viscosity, and this difference is further intensified by aperture heterogeneity. Therefore, water demonstrates better thermal performance in these injection conditions. Under constant pressure injection, the thermal performance of water and ScCO2 is aperture-sensitive. ScCO2 demonstrates better performance than water in homogeneous aperture scenarios, while water outperforms ScCO2 in heterogeneous aperture scenarios. In addition, aperture heterogeneity limits the sensitivity of the comparative thermal performance between the two fluids to most injection parameters and reservoir properties. These findings highlight the critical role of working fluid selection and fracture aperture heterogeneity in optimizing flow channeling control and heat extraction efficiency in EGSs.