Modeling of Transient Pressure Response for CO2 Flooding Process by Integrating Convection and Diffusion Driven Mass Transfer

Abstract Traditional well test models for CO2 flooding neglect dynamic mass transfer and over-simplify transient viscosity in a transition zone, making them unable to deal with more complicated and heterogeneous field situations. To eliminate this restriction/limitation, this study proposes a comprehensive transient pressure model that incorporates a convection– diffusion mass transfer process. It actually is an enhanced three-region composite model that includes CO2 bank, transition zone, and oil zone. Type curves are plotted and four flow regimes are identified: early radial flow, transition flow, pseudo-radial flow, and boundary-dominated flow. In addition, it is found that mass transfer mainly leads the transition flow regime to slower slope change, and pseudo radial flow regime with lower straight line compared with a case neglects the mass transfer in a transition zone. Moreover, it shows that a smaller injection rate and a longer injection period are better for viscosity reduction than a larger injection rate and a shorter injection period.