An improved cubic model for the mutual solubilities of CO2-CH4-H2S-brine systems to high temperature, pressure and salinity

The phase behavior of CO2-CH4-H2S-brine systems is of importance for geological storage of greenhouse gases, sour gas disposal and enhanced oil recovery (EOR). In such projects, reservoir simulations play a major role in assisting decision makings, while modeling the phase behavior of the relevant CO2-CH4-H2S-brine system is a key part of the simulation. There is a need for an equation of state (EOS) for such system which is accurate, with wide application range (pressure, temperature and aqueous salinity), computationally efficient and easy for implementation in a reservoir simulator. In this study, an improved cubic EOS model of the system CO2-CH4-H2S-brine is developed based on the modifications of the binary interaction parameters in Peng-Robinson EOS, which is widely implemented in reservoir simulators. Thus the new model is suited for numerical implementation in reservoir simulators. The available experimental data of pure gas brine equilibrium and gas mixture solubility in water/brine are carefully reviewed and compared with the new model. From the comparison, the new model can accurately reproduce (1) the CO2-brine mutual solubility data at temperature from 0 degrees C to 250 degrees C, pressure from 1 bar to 1000 bar and NaCl molality (mole number in 1 kg water, molal is used for short) from 0 to 6 molal, (2) CH4-brine mutual solubility data at temperature from 0 degrees C to 250 degrees C, pressure from 1 bar to 2000 bar and NaCl molality from 0 to 6 molal, (3) H2S-brine mutual solubility data at temperature from 0 degrees C to 250 degrees C, pressure from 1 bar to 200 bar and NaCl molality from 0 to 6 molal, and (4) has good accuracy for gas mixture solubility in brine. (C) 2014 Elsevier Ltd. All rights reserved.