Flow and thermal modeling of CO2 in injection well during geological sequestration

A two-dimensional (2D) axisymmetric (radial) model, considering the effects of the fluid in annulus and heat transfer with surrounding rocks is developed to investigate the flow and thermal behavior of CO2 in injection well during its geological sequestration. The mass equation, the momentum equations with turbulent model and energy equation are solved both in the wellbore flow direction and the radial direction using computational fluid dynamics (CFD) method. Real-gas properties are employed to ensure the calculation accuracy. The wellhead pressure and bottomhole temperature behavior with injection time are predicted. The impact of natural convection of water in the annulus on flow and thermal behavior of injected CO2 are also studied. Besides, factors impacting the bottomhole temperature of CO2 are analyzed. It is found that the work done by pressure (compressibility), potential energy loss and the heat exchange with surrounding rocks are three major factors leading to an increase in the bottomhole temperature of CO2 comparing to the injection temperature. With an increase in injection mass flow rate, the wellhead pressure decreases firstly and then increases, and the bottomhole temperature of CO2 decreases nonlinearly. However, both of them increase linearly with an increase in the injection temperature. This study may help deepen our understanding of the mechanisms of CO2 injection and generate quantitative information in support of design, monitoring and risk assessment of the CO2 geological sequestration.