Unveiling the role of residual structure in hydrate secondary formation through molecular dynamics simulations

The rapid secondary formation of gas hydrate is a potential cause of flowline blockage in deepwater oil and gas production systems, posing serious flow assurance challenges. However, its microscopic formation mechanism remains an area of active research. Recently, the residual structure hypothesis has gained significant attention in explaining the rapid secondary formation of hydrates. In this study, massive molecular dynamics simulations are conducted to investigate the secondary formation of methane hydrates in solutions containing hydrate residual structures of varying sizes. The results indicated that residual structures, owing to their hydrate-like characteristics, facilitate the adsorption and capture of methane molecules, leading to the formation of local gas supersaturation regions. Residual structures promote hydrate formation through two key mechanisms: acting as nucleation sites and supplementing methane concentrations. Particularly, a synergy between residual structures and gas concentration was identified: high gas concentrations stabilize small residual structures, allowing them to serve as nucleation sites, while large stable structures can enrich methane even under low gas concentration.

This work not only provided a detailed understanding of the mechanisms of hydrate secondary formation but also provided valuable insight for hydrate blockage prediction and control in subsea oil and gas pipelines, contributing to improved flow assurance strategies.