Evolution of Marine Gas Venting System and Impact on Gas Hydrate Crystallization
CHEN Duo-fu ~(1, 2) FENG Dong~1 CHEN Guang-qian ~1 CHEN Xian-pei ~1 Lawrence M Cathles~3 1(Key Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry and South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510640) 2(Guangzhou Center for Gas Hydrate Resaerch, Guangzhou 510640) 3(Department of Earth & Atmospheric Sciences, Cornell University, Ithaca, New York 14853-1504, USA)
Based on the kinetic model of hydrate crystallization from venting gas in gas vent system, the evolvement characteristics and the impacts on gas hydrate crystallization in the Bush Hill gas vent system in GC 185 of Gulf of Mexico were studied. The venting rates are fast (gas flux q 18.4 kg/m~-a) in the earlier stage of the gas vent system, mud volcano occurred on the seafloor, the vent gas has almost the same composition as the source gas, and the heaviest possible hydrates are crystallized near the surface. The venting rates are slow (gas flux q 0.55 kg/m~-a) in the later stage, hydrate crystallization will not reach the sea floor, seep carbonate will be occurred on the seafloor. Between these extremes gas hydrate and seep community is developed on the seafloor of the gas vent system, and the vent and hydrate gas compositions, and the mass fraction of venting gas crystallized hydrate depend strongly on venting rate. Changes in vent and hydrate gas chemistry observed at multiple submersible visits to the Bush Hill vent system suggest the variations of venting rates between different submersible visiting time and different locations over the last 10 years.