Molecular dynamics study on the dissociation of methane hydrate via inorganic salts

ABSTRACT

Hydrate plugging is a hidden threat to the safe exploitation of oil and gas. Inorganic salts are widely used as thermodynamic inhibitors to effectively prevent the hydrate formation. This study uses a molecular dynamics method to explore the mechanism of the hydrate dissociation via inorganic salts on the micro-scale. We simulated the dissociating process of methane hydrate under different concentration series of NaCl, KCl and CaCl₂ solutions at 273 K, and analysed the changes of ionic structure, transport parameters and kinetic energy in the system of inorganic salt/hydrate. The simulation results successfully revealed the step-by-step dissociation of hydrate, and the differences in dissociation rates among the different inhibitors. The energy needed for hydrate dissociation alters for different inorganic solutions; the energy reaches maximum when KCl is the inhibitor, and lowest when the concentration of CaCl₂ exceeds 30% w/w. We calculated the coordination numbers of all components, including oxygen atoms, cations and anions, and also their diffusion coefficients; analysed the effects of the three inorganic salts on the simulated hydrate structure and its transport; in addition, investigated the mechanism of hydrate dissociation via inorganic salts.

KEYWORDS:

• Methane hydrate
• dissociation
• inorganic salts
• molecular dynamics simulation

Acknowledgements

The authors gratefully acknowledge assistance with the modelling in molecular dynamics from Prof. Jun Zhang at China University of Petroleum.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Basic Research Program of China [grant number 2015CB251200], and the Fundamental Research Funds for the Central Universities [grant number 15CX02008A], [grant number 14CX06030A].