Mechanical properties of CH4-CO2 hydrate-amorphous water-silica systems

Geological sequestration of carbon dioxide (CO2) in natural gas hydrate (NGH) reservoirs offers a promising strategy for mitigating greenhouse gas emissions while addressing the energy crisis. The mechanical behavior of CH4-CO2 hydrate-sediment system, particularly the amorphous water layer between hydrate and silica, plays a pivotal role in reservoir stability during CO2-CH4 replacement. In this study, we combine non-equilibrium molecular dynamics (MD) simulations with machine learning (ML) techniques to investigate the mechanical behaviors of CH4-CO2 hydrate-amorphous water-silica (HWS) systems. Our results show that water-silica interaction energy is the dominant factor governing the mechanical strength of this interface, followed by CO2-silica interactions and hydrogen bonding between silanol groups and water. In contrast, the silica surface structure exerts minimal influence. Notably, CH4-CO2 hydrates exhibit stronger mechanical stability in the HWS systems than pure CH4 hydrates, enhancing the overall stability of NGH-bearing sediments. The mechanical strength of the amorphous water-mediated interface peaks at a 50 % CO2-to-CH4 ratio, driven by the strongest water-silica interactions at this composition. Our findings clarify the key factors influencing the mechanical stability of CH4-CO2 HWS system and demonstrate that CO2 injection can mechanically reinforce NGH reservoirs, providing a viable path toward safe and sustainable carbon storage.