Mutual solubility of CH4, CO2, H2S, and their mixtures in brine under subsurface disposal conditions

An accurate thermodynamic predictive model is necessary to calculate mutual solubilities of injected gas and aqueous phases under subsurface disposal conditions. In this work, an accurate model is presented and discussed. The Peng–Robinson equation of state coupled with a non-random mixing rule is used to model sour and acid gas phase. The aqueous phase is modeled by Henry's law approach. Good agreement between this model and experimental data available in the literature was observed. The aqueous phase solubility and water content of pure CH4, CO2, and H2S were represented with absolute average relative deviations of less than 6.3% and 5.6%, respectively. The applicability of this model in calculating the solubility of these components in aqueous NaCl and other salt solutions was evaluated by comparisons between the results of this model, the experimental data, and some other models in the literature. An acceptable accuracy was found in the regeneration of the gas phase water content and the aqueous phase solubility of the mixtures of sour and acid gas in equilibrium with pure water. Furthermore, the model was tested for brine systems with salt concentrations up to 200,000 ppm, and accurate results were obtained.

► Model is developed to calculate acid/sour gas and brine mutual solubility.
► PR-EoS and Henry's law are used to model acid/sour gas and brine phase equilibrium.
► Complex behavior of H2S and CO2 is modeled using non-random mixing rule.
► Results cover operational conditions for the most acid gas disposal scenarios.