Phase equilibria for petroleum reservoir fluids containing water and aqueous methanol solutions: Experimental measurements and modelling using the CPA equation of state

Thermodynamic inhibitors, such as methanol, are widely used to reduce the risks associated with gas hydrate formation. The work presented in this communication is the result of a study on the phase equilibria of petroleum reservoir fluids in the presence of aqueous methanol solutions. Experimental hydrate dissociation data, for systems composed of methane/water/methanol and natural gas/water/methanol, in addition to experimental freezing point depression data for aqueous methanol solutions, are reported. A statistical thermodynamic approach, with the cubic-plus-association equation of state (CPA-EoS), is employed to model the phase equilibria. The hydrate-forming conditions are modelled by the solid solution theory of van der Waals and Platteeuw. The thermodynamic model was used to predict the hydrate dissociation conditions of methane and natural gases in the presence of distilled water or methanol aqueous solutions. Predictions of the developed model are validated against independent experimental data and the data generated in this work. A good agreement between predictions and experimental data is observed, supporting the reliability of the developed model.