Dissociation Conditions and Influencing Factors of Methane Hydrate in Chloride Salt Solution under High Pressure

A method that can be used for gas hydrate exploitation is the injection of a brine solution into hydrate reservoir, therefore, the hydrate dissociation conditions and the influencing factors in brine solution should be investigated under reservoir pressure. In this paper, methane hydrate dissociation conditions in NaCl, MgCl(2), and CaCl(2) solutions were investigated. The results show that the dissociation temperature depressions are (4.8, 2.4, 1.0 K (NaCl)), (5.3, 1.5 K (MgCl(2))), (4.3, 1.8 K (CaCl(2))) in NaCl (2.0, 1.0, 0.5 mol . L(-1)), MgCl(2) (1.0, 0.5 mol . L(-1)), and CaCl(2) (1.0, 0.5 mol . L(-1)) solutions, respectively, relative to those in pure water. The experimental values were in good agreement with the calculated values based on the van der Weals and Platteeuw thermodynamic model and the Pitzer-Mayorga equation for the water activity of electrolyte solution. In chloride salt solution the water molecule solvent effect and the salting-out effect that is caused by an electrostatic field decreases the water activity resulting in a depression of the hydrate dissociation temperature.