GEOGRAPHY

The kinetic mechanism of rapid formation of abyssal cold spring hydrates was revealed


Recently, the international academic journal “Ocean and Petroleum Geology” reported the latest research results of the Institute of Oceanology, Chinese Academy of Sciences on the rapid formation kinetics of hydrate in the cold spring environment, which revealed the influence of the seabed cold spring environment on the formation of hydrates, and provided new insights for the kinetic process of hydrate formation in the cold spring area of the South China Sea.

Schematic diagram of hydrate formation kinetics in cold spring environment Courtesy of the research group

Sampling area map and sampling photo Courtesy of the research group

The active cold seep area of the deep sea contains a large amount of natural gas hydrates, forming a wide distribution of autogenic carbonate rocks and unique cold seep biomes, which is a complex deep-sea extreme environment that significantly affects the formation and decomposition of hydrates.

The in-situ synthesis experiment of hydrate carried out by the research group in the active cold spring vent area in the South China Sea showed that the bubble stream ejected by the cold spring vent could quickly generate natural gas hydrate in just a few seconds, while the laboratory results of the in-situ environmental conditions of the cold spring showed that although the temperature and pressure of the cold spring environment were simulated, the hydrate was difficult to be generated quickly. This suggests that the complex environment of cold springs has a unique effect on hydrate formation, but this effect is not well understood.

Zhang Xin’s team, a researcher at the Institute of Oceanology, obtained samples of cold spring vent fluid, bottom seawater and self-generated carbonate rocks through fidelity sampling technology in the cold spring area of Tainan in the northern part of the South China Sea, and simulated the formation process of methane hydrate in the cold spring environment by using the above real samples, and monitored and observed the hydrate formation process by time series Raman spectroscopy and video.

The experimental results show that the hydrate in the cold spring fluid is formed within 2 minutes, and the autogenic carbonate rocks in the cold spring environment show a certain promoting effect on the formation of hydrate. In addition, cold simmer fluids with low salinity and rich in tiny particles significantly promote hydrate formation relative to the inhibition of high salinity bottom seawater. The low salinity of the cold spring fluid may be attributed to the dilution of the water produced by the decomposition of hydrates, which shows a strong promotion effect on the re-formation of hydrates due to the existence of a “memory” of the formation of hydrates in the decomposition of the decomposition.

Thus, the synergy of self-generated carbonate particles, low-salinity cold spring fluids and bubble streams with “memory effect” promotes the rapid formation of cold spring hydrates.

The researchers comprehensively considered the effects of nucleation of self-generated carbonate particles, cold swell fluids and bubble flow with “memory effect” on the rapid formation of hydrates in cold spring environment, and proposed a kinetic model of methane hydrate formation in in-situ cold spring environment. This model elucidates the combined influence of polyphasic environmental factors on hydrate formation in cold swells, and provides new insights into the kinetic process of rapid formation of hydrates in situ cold springs.

It can be seen that the complex environmental conditions of cold springs will have a unique impact on the dynamics of hydrates, and it is expected that in the future, in-situ long-term monitoring experiments of cold spring hydrates will be carried out, so as to deepen the understanding of the formation, evolution and response mechanism of cold spring hydrates and surrounding biomes. (Source: China Science News, Liao Yang, Wang Min)

Related paper information:https://doi.org/10.1016/j.marpetgeo.2023.106401



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