A General Multiphase Equilibrium Calculation Framework for H2O/Brine-CO2-Dimethyl Ether-Hydrocarbon Systems

Summary Increasing oil recovery technology is crucial for the sustainable growth of the petroleum industry and the assurance of energy security. Dimethyl ether (DME) has emerged as a potential candidate to further enhance the efficiency of water/CO2 flooding processes. However, developing a reliable and accurate multiphase equilibrium calculation package that meets the high efficiency and robustness standards required for reservoir simulation in DME-enhanced water/CO2 flooding remains a significant challenge. This study presents a comprehensive multiphase equilibrium calculation framework specifically designed for H2O/brine-CO2-DME-hydrocarbon systems. The Peng-Robinson (PR) equation of state (EOS) combined with the Huron-Vidal (HV) mixing rule is used to predict phase behavior accurately. The framework incorporates several key components: (1) an improved model for saline systems to enhance computational efficiency; (2) innovative stability analysis strategies to ensure robustness; (3) a salt precipitation module to address water vaporization scenarios; and (4) a numerical solver that integrates successive substitution iteration (SSI) with the trust region (TR) method to secure computational efficiency. Extensive testing involving millions of data points has demonstrated the accuracy, robustness, and efficiency of our algorithm. This framework serves as a powerful tool for phase equilibrium calculations in complex reservoir systems, facilitating more effective simulation and optimization of DME-enhanced water/CO2 flooding operations.