Gas Hydrate Equilibria in the Presence of Monoethylene Glycol, Sodium Chloride and Sodium Bromide at Pressures up to 150 MPa

Hydrate dissociation data for single hydrate formers are widely available, however there is a clear gap for multicomponent systems over a wide range of pressures and in presence of inhibitor or electrolytes. This data is required to validate thermodynamic models being used to predict hydrate inhibitor (monoethylene glycol (MEG)) requirements in pipelines transporting unprocessed well streams with highly concentrated formation waters and, in the case of sodium bromide, drilling fluids. In this work, hydrate dissociation temperature measurements at pressures up to 150 MPa were conducted for a multicomponent synthetic gas mixture in equilibrium with deionised water, an aqueous sodium chloride solution, mixed aqueous MEG/sodium chloride and MEG/sodium bromide solutions using the isochoric step heating method.

The Soave-Redlich and Kwong – Cubic-Plus-Association equation of state combined with a modified Debye Hückel electrostatic term 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 has been evaluated using these new generated hydrate data. The thermodynamic model (as implemented in our in-house software HWPVT 1.1) and experimental data are in good agreement, supporting the reliability of the developed model.