Beyond gas supersaturation: Dissecting the secondary formation of methane hydrate

Rapid secondary formation of gas hydrate is a critical issue in gas transportation and at the same time has foreseeable potential in future gas storage. Despite the devoted research in the past decade, the intrinsic mechanism of the secondary formation of gas hydrate, is still an on-going subject of debate. Because the secondary formation of gas hydrate is commonly observed under conditions with extraordinarily high content of gas, gas supersaturation is hypothesized as one crucial mechanism. To dissect the gas supersaturation hypothesis, Molecular Dynamics simulations were conducted systematically with hydrate secondary formation in solutions with various gas concentrations covering supersaturation conditions. The effects of key parameters influencing the secondary formation of hydrate, including system temperature and local methane concentration, were explored. The results revealed for the first time a U-shape-like trend in the induction time of hydrate formation with the increase of gas concentration, pinpointing an optimal gas content with the given environmental temperature and pressure. Importantly, the findings highlighted the needed revision of the current gas supersaturation hypothesis in both methane hydrate mitigation and application. This work not only advanced the current understanding of the secondary formation of methane hydrate but also contributed to the fundamental knowledge essential for future gas storage by gas hydrates.