Prediction of CO2-CH4-H2S-N2 gas mixtures solubility in brine using a non-iterative fugacity-activity model relevant to CO2-MEOR

Abstract

Numerical simulations of carbon dioxide-microbial enhanced oil recovery (CO2-MEOR) would require computationally rigorous iterative methods to solve resulting system of flow, transport and kinetic reaction equations. This includes additional iterative procedures to account for the solubility of gas mixtures in the aqueous phase. This work proposes a new non-iterative fugacity-activity thermodynamic model to predict the solubility of CO2-CH4-H2S-N2 gas mixtures in brine. This model can readily be implemented in MEOR simulation programs to account for mass transfer and kinetics of microbial reactions in CO2-MEOR operations. Fugacity coefficients (ϕi) in the proposed model were calculated using Predictive Peng-Robinson 78 (PPR78) and Peng-Robinson (PR) equation of state (EOS). The proposed model was successful in predicting CO2 solubility in the aqueous phase with ϕi calculated either using PPR78 EOS or PR EOS. Comparison showed that at temperature and pressure conditions relevant to MEOR, using calibrated binary interaction parameters (PR EOS) leads to more accurate predictions than binary interaction parameters estimated from the group contribution expression (PPR78 EOS). Comparison of predicted CO2-CH4-H2S gas mixtures solubility in the aqueous phase obtained with the proposed non-iterative fugacity-activity model and an iterative fugacity-activity model, confirmed that proposed model with ϕi calculated using PR EOS can be used as substitute for iterative fugacity-activity models that relies on the solution of Rachford-Rice equation.