Dissociation mechanism of methane hydrate by CaCl₂: an experimental and molecular dynamics study

The formation of gas hydrate is a serious threat to the safe and effective completion of deepwater drilling and transportation operations, although it is considered as a potential energy resource. The inorganic salts are generally used as thermodynamic inhibitors; CaCl₂ as a common additive in drilling fluids exhibits unique properties. In this study, we explored the dissociation mechanism of CH₄ hydrate in CaCl₂ solutions at the macroscopic and microscopic scale using experiment and molecular dynamics (MD) simulation. The experimental results showed that CaCl₂ accelerated the dissociation rate of CH₄ hydrate. The dissociation rate of CH₄ hydrate increased with the increase of CaCl₂ concentration at large depressurization pressure and was mainly affected by pressure when the depressurization pressure was lower. MD simulations were used to give an atomic scale interpretation of the macroscopic results obtained from the experiment. The results showed that the addition of CaCl₂ destroyed the resistance liquid film formed during CH₄ hydrate dissociation, thus accelerating the dissociation process, in good agreement with experimental results. HIGHLIGHTS: • The amount of CaCl₂ affects CH₄ hydrate dissociation at large depressurization pressure. • The dissociation of CH₄ hydrate at low depressurization pressure is dependent on pressure. • Ca²⁺ destroys effectively the resistance liquid film produced during hydrate dissociation. • MD simulation results are in agreement with those of the experiment.