Theoretical insight into thermal transport and structural stability mechanisms of triaxial compressed methane hydrate

The heat transfer and stability of methane hydrate in reservoirs have a direct impact on the drilling and production efficiency of hydrate resources, especially in complex stress environments caused by formation subsidence. Herein, we investigated the thermal transport and structural stability of methane hydrate under triaxial compressions using molecular dynamics (MD) simulations. The results suggest that the thermal conductivity of methane hydrate increases with increasing compression strains. Two phonon transport mechanisms were identified as factors enhancing thermal conductivity: At low compressive strains, a low-frequency phonon transport channel was established due to the overlap of phonon vibration peaks between methane and water molecules. At high compressive strains, the filling of larger phonon band gaps facilitated the opening of more phonon transport channels. Additionally, we found that a strain of -0.04 is a watershed point where methane hydrate transitions from stable to unstable. Furthermore, a strain of -0.06 marks the threshold at which the diffusion capacity of methane and water molecules is at its peak. At a higher strain of -0.08, the increased volume compression reduces the available space, limiting the diffusion ability of water and methane molecules within the hydrate. The synergistic effect of strong diffusion ability and high probability of collision between atoms increases the thermal conductivity of hydrates during the unstable period compared to the stable period. Our findings offer valuable theoretical insights into the thermal conductivity and stability of methane hydrates under reservoir stress environments.