Enhanced phonon transport in sI-type methane hydrate under uniaxial compression strain: Unveiling the opening of an advantageous channel

Abstract

Unveiling the thermal transport mechanisms of natural gas hydrate under strain conditions is fundamental to the heat transfer of the hydrate reservoir during drilling and production. This work investigated the structural stability and phonon transport mechanisms of methane hydrate using equilibrium molecular dynamics simulations subjected to uniaxial compression strain. The results indicate that the stability of large cages within methane hydrates weakens under strain. However, the presence of methane molecules effectively stabilizes the cage structure, enabling it to remain intact even under significant deformation. Furthermore, the thermal conductivity of methane hydrate demonstrates non-linear behavior, characterized by an initial increase followed by a subsequent decrease with increasing uniaxial compression strain. Particularly, the thermal conductivity of methane hydrate attains a maximum value of 0.87±0.018 W⋅m−1⋅K−1 at a strain of -0.04. The results suggest that the elevated spectral energy density and the prolonged phonon lifetime contribute to the enhanced thermal conductivity of methane hydrate. Interestingly, it was observed that the overlapping of phonon vibration modes between water and methane molecules results in the suppression of the peaks and valleys when the strain reaches -0.04. This overlap eliminates the gap and opens up an advantageous channel for phonon transport, thereby enhancing the heat transport capability of methane hydrate. The opening of an advantageous channel for phonon transport results in an extended phonon lifetime and a subsequent increase in thermal conductivity. This study presents a novel perspective for comprehending the unusual thermal conductivity of methane hydrate under strain conditions.