Role of mechanical deformation in the thermal transport of sI-type methane hydrate.

ABSTRACT

Natural gas hydrates (NGHs) are rising as an unconventional energy resource. The fundamental thermal characteristics of NGHs are of importance for natural gas exploitation from permafrost and oceanic sediments that are geomechanically deformed. Here, utilizing classic molecular dynamics simulations with all-atom (AA) and coarse-grained (CG) models of the methane guest molecule, the effects of mechanical strain on the thermal conductivity of sI-type methane hydrate are for the first time examined. Upon triaxial tension and compression, methane hydrate exhibits strong asymmetry in the stress responses. As the triaxial loads go from compression to tension, a reduction trend in the thermal conductivity is revealed for methane hydrate with both AA and CG models of methane, within a maximum reduction of over 44%. This reduction is because triaxial strain from compression to tension softens the phonon modes. Interestingly, there is a sudden rise in thermal conductivity at critical triaxial strain of 0.06, originating from that, at which, the phonon modes are hardened and the peaks of radial distribution functions are shifted back. This study provides important information on the thermal conductivity of methane hydrate, which is helpful for the practical production of natural gas from geo-deformed NGH-bearing sediments via a heating technique as well as evaluating their stability.