Phase equilibrium modeling for CCUS fluids using a modified association equation of state

Accurate derivatives are required for simulating large-scale carbon dioxide (CO 2 ) geological storage using the Cubic-Plus-Association equation of state (CPA EoS). However, due to the mathematical implicitness of cross-association, calculating the correct derivatives of site fractions for cross-association mixtures is extremely difficult and computationally demanding. A general explicit formulation of cross-association for different bonding types is presented. The non-bonded fraction of cross-associating molecules is obtained from the non-bonded fraction of self-associating molecules without cross-association. This approach eliminates the circular iterative process and improves computational efficiency. The overall CPU time decreases by 70 % for flash calculations and compositional simulations . The modeling capability of CPA is extended to H 2 O-CO 2 -H 2 S-N 2 -O 2 -Ar-SO 2 -CH 4 -C 2 H 6 -C 3 H 8 mixtures. Results indicate that CPA can accurately predict the phase behavior of binary CO 2 capture, utilization, and storage (CCUS) mixtures. This study provides a modified CPA EoS, applicable to most of the currently treated CCUS fluids, and discusses its strengths and limitations. • A general explicit formulation of cross-association for different bonding types. • Derived non-bonded fraction of cross-associating molecules from non-bonded fraction of self-associating molecules. • Overall CPU time decreases by 70 % for flash calculations and compositional simulations. • Extended applicability range of CPA model to CCUS mixtures.