Flow and heat transfer for non-Newtonian CO2 mixed fluid injection in the wellbore

CCUS (Carbon capture, utilization, and storage) is a crucial approach to addressing the climate crisis caused by fossil fuels. CO₂ (carbon dioxide) injection is a vital process in both geological CO₂ geological sequestration and utilization. Understanding the flow and heat transfer during CO₂ injection is essential for the technological design and analysis of CO₂ behavior in geological formations. Although the flow and heat transfer of pure CO₂ have been extensively studied, the complex non-Newtonian properties of fluids caused by the interaction of CO₂ with the additives remain underexplored. This study developed a rheological model of non-Newtonian CO₂ mixed fluid by performing experiments at various temperatures and pressures. The friction factor and flow mechanisms of non-Newtonian CO₂ mixed fluid were then analyzed using the finite volume method. Finally, the transient temperature and pressure during different injection operations were numerically simulated. The findings indicate that non-Newtonian CO₂ mixed fluid exhibits shear-thinning properties, which intensify under high temperatures and pressures. The frictional resistance to the flow of non-Newtonian CO₂ mixed fluid is reduced due to a slippage effect that creates a more uniform velocity profile. The field injection case demonstrates that our model can accurately predict the variations and magnitudes of pressure and temperature. Optimizing the injection rate, duration, and shutdown time proved feasible for managing BHT (bottomhole temperature), which provides insights for optimizing injection design and CO₂ utilization efficiency.