Chinese scientists reveal the evolution of the South China Sea deep-sea cold seep system

Recently, Wang Jiliang, an associate researcher at the Institute of Deep-sea Science and Engineering of the Chinese Academy of Sciences, and colleagues from several domestic research institutions systematically analyzed the structural characteristics and evolution of a methane seep system in an active cold seep in the Qiongdongnan Deepwater Basin in the northern South China Sea. This research provides new insights into the enrichment mechanisms of natural gas hydrates (combustible ice) and the carbon cycle of deep-sea cold seeps. The findings have been published in the international journal Earth and Planetary Science Letters.

In deep-sea shallow strata dominated by fine-grained mud deposits, "mud-encased sand" sedimentary structures often develop, which has an important impact on the activity patterns of cold seeps and the exploration of natural gas hydrate resources, but there have been many gaps in our understanding of its specific mechanism.

A research team discovered a 12.5-meter-thick sand layer rich in natural gas hydrates in an active methane seep area in the southeastern Qiongdongan deepwater basin. The study found that the sand layer plays a triple role in the cold seep system: first, it captures methane transported by the underlying gas chimney through its pore structure, forming and enriching natural gas hydrates under high pressure and low temperature conditions; second, the differential aggregation of hydrates leads to pore blockage, creating a "self-sealing" effect that continuously accumulates gas pressure below; finally, when the overpressure breaks through the overlying mudstone caprock, secondary hydraulic fracturing is triggered to form new gas channels, initiating a new round of gas escape.