Molecular dynamics simulations of the mechanisms of thermal conduction in methane hydrates

Abstract

The thermal conductivity of methane hydrate is an important physical parameter affecting the processes of methane hydrate exploration, mining, gas hydrate storage and transportation as well as other applications. Equilibrium molecular dynamics simulations and the Green-Kubo method have been employed for systems from fully occupied to vacant occupied sI methane hydrate in order to estimate their thermal conductivity. The estimations were carried out at temperatures from 203.15 to 263.15 K and at pressures from 3 to 100 MPa. Potential models selected for water were TIP4P, TIP4P-Ew, TIP4P/2005, TIP4P-FQ and TIP4P/Ice. The effects of varying the ratio of the host and guest molecules and the external thermobaric conditions on the thermal conductivity of methane hydrate were studied. The results indicated that the thermal conductivity of methane hydrate is essentially determined by the cage framework which constitutes the hydrate lattice and the cage framework has only slightly higher thermal conductivity in the presence of the guest molecules. Inclusion of more guest molecules in the cage improves the thermal conductivity of methane hydrate. It is also revealed that the thermal conductivity of the sI hydrate shows a similar variation with temperature. Pressure also has an effect on the thermal conductivity, particularly at higher pressures. As the pressure increases, slightly higher thermal conductivities result. Changes in density have little impact on the thermal conductivity of methane hydrate.