Effect of nanoparticles on the flow and heat transfer characteristics of scCO2

Geological carbon dioxide sequestration can help reduce large-scale greenhouse gas emissions. Adding nanoparticles to supercritical carbon dioxide injected into a wellbore alters its physical properties, such as density and viscosity. This study employs computational fluid dynamics methods to establish a numerical model simulating the flow and heat transfer behavior of nanofluids (composed of supercritical carbon dioxide and nanoparticles) during injection into wellbores. The reliability of the developed model is validated through comparison with existing literature data. The study focuses on analyzing the effects of injection rate and injection temperature on fluid pressure and temperature distribution from the wellhead to 100 meters downhole. It further investigates the influence patterns of different types and concentrations of nanoparticles on fluid temperature and pressure within the wellbore. The results revealed that throughout the wellbore, the temperature and pressure distribution trends of the nanofluid were similar to those of pure supercritical carbon dioxide. However, the addition of nanoparticles significantly altered local temperature values, particularly in the downstream region, where the temperature decrease was more pronounced. The effect of nanoparticles on pressure was relatively minor. Higher injection rates enhance convective heat transfer, facilitating fluid cooling. Increasing the volume fraction of nanoparticles enhances the fluid's heat transfer capability, speeding up cooling. Among the nanoparticles, Al?O? provides the best cooling effect due to its high thermal conductivity, while SiO? has the weakest, with TiO? intermediate. This study provides a theoretical basis for selecting optimal types and concentrations of nano-additives tailored to specific reservoir temperature conditions in geological sequestration, offering guidance for optimizing injection process design to mitigate thermal stress risks in wellbores.