Influence of cold-seep environments on the kinetics of methane hydrate formation

Methane hydrate (MH) is widely distributed in active deep-sea cold-seep areas. The complex environment of cold seeps influences MH formation. Investigating the effects of cold-seep environments on MH formation can provide an in-depth understanding of the formation mechanism of MH and kinetic process of cold-seep development and evolution. In this study, multiple MH formation experiments were conducted in the laboratory to investigate the effects of a cold-seep environment on the kinetics of hydrate formation. Considering the cold-seep fluid and bottom seawater as the samples, MH was formed in the capillary under the same pressure-temperature conditions as those in cold-seep environments. The entire process of MH formation was recorded by time-series Raman spectra and video, and the results demonstrated the promotion of MH formation by solid particles, especially authigenic carbonates. Compared to 20 min in seawater, the induction time of 2 min in cold-seep fluids indicated promotion of hydrate formation by tiny particles and by its lower salinity. Notably, the reduction in salinity in the cold-seep fluid may be attributed to the dilution effect of pure water produced by hydrate decomposition, indicating the presence of a hydrate memory effect. Overall, our results are in agreement with those of the in situ hydrate formation experiment in a cold-seep environment. A model of hydrate formation in a cold-seep environment has been proposed, which can aid in understanding the kinetics of hydrate formation.