A fully non-iterative technique for phase equilibrium and density calculations of CO2+brine system and an equation for CO2

Carbon sequestration is a big environmental issue these days. For geologic sequestration of CO2 accurate and time-efficient estimation of phase equilibrium between CO2 and brine is an important concern. As we know any phase equilibrium or mutual solubility calculations require iterations in order to attain desired convergence in fugacity measurements from which equilibrium compositions are obtained. In this paper a fully non-iterative technique is proposed for calculating phase equilibrium compositions of CO2 in brine water and that of H2O in CO2 rich phase for the temperature and pressures ranges of 20–40 °C, 1–400 bar, respectively. Brine salinity is tested up to 4 molality. As an essential part of this computation process, an empirical volume explicit equation for CO2 having only 8 parameters is presented. The volumetric data and calculated results of phase compositions using this equation are compared with the literature values. They exhibit good agreement with less than 2% deviation. A modified scheme of CO2+brine density calculation is also shown. More so, computational efficiency following the non-iterative technique against using Equation of State (EoS) in reservoir simulation is compared. This shows that the proposed technique can be even more than 1000 times faster than conventional phase equilibrium computation after integrating with numerical simulation of CO2 flow in reservoir.