In situ Raman detection of gas hydrate in the South China Sea

Abstract

Natural gas hydrate is a great potential energy source in the future, and it also plays a significant roe in the study of global climate change. In past decades, natural gas hydrate is usually studied in laboratory by simulators or studied using the hydrate samples. However, it is a big challenge for the simulating devices to completely recreate field conditions for gas hydrate study. Here we report the first discovery of natural gas hydrates (NGH) exposed on the seafloor in the South China Sea (SCS). Synthetic gas hydrate (SGH) is quickly formed for the first time by the fluids and bubbles erupted from the active cold seeps in the SCS. The NGH and SGH samples are in situ detected by a Raman insertion probe for gas hydrate (RiP-Gh) which is deployed and controlled by the remotely operated vehicle (ROV) Faxian. The in situ Raman spectra of the NGH suggest that the newly formed gas hydrate is Structure I but contains a small amount of gaseous CH <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> , C$_{3}H_{8}$ and H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> S, which are consistent with the results SHG. Authigenic carbonate debris or other debris serving as nucleation particles, and the gas-water interface were proposed as two factors which can promote the formation of synthetic gas hydrate. Overall, our work demonstrates the components of NGH and SGH near the active cold seep vent in the South China Sea, and suggests a new explanation for the quick formation of gas hydrate compared to that in laboratory simulation work.