Experimental determination and prediction of methane hydrate stability in alcohols and electrolyte solutions

In petroleum exploration and production operations, gas hydrates pose serious flow assurance, economic and safety concerns. Thermodynamic inhibitors are widely used to reduce the risks associated with gas hydrate formation. In this communication, in order to establish the effects of salts and thermodynamic inhibitors on the locus of incipient hydrate-liquid water-vapour (H-L_W-V) curve, we report new experimental dissociation data for various quaternary systems, methane/water/thermodynamic inhibitor/salts for a pressure range of 6.89-29 MPa. The investigated systems include alcohols such as methanol and ethylene glycol and common salts such as sodium chloride, potassium chloride and calcium chloride. The freezing points of all the aqueous solutions were also measured to check the validity of a previously developed correlation for the prediction of hydrate equilibrium conditions in the presence of salts and alcohols. A thermodynamic approach in which the well-proven Valderrama modification of the Patel-Teja (VPT) equation of state combined with a modified Debye-Hückel electrostatic term was employed to model the phase equilibria. The hydrate-forming conditions are modelled by the solid solution theory of Van der Waals and Platteeuw. The Langmuir constants have been calculated using the Kihara potential model. The results show that the agreement for both model and correlation are very good. © 2008 Elsevier B.V. All rights reserved.