Abstract: Gas hydrates are one of the significant offshore petroleum resources. The exploration of hydrates using combined
porewater geochemistry and fluid reaction-transport modelling has become an important proxy in researches of recent years.
Based on the data of GMGS-1 drilling project from the Shenhu area of the South China Sea, the advection velocity of porewater
during the Holocene was fitted by the molar ratio of bromine to iodine, and a two-stage non-steady state multiphase fluid transport
model of the gas hydrate zone was constructed. We found that the hydrate accumulation in the study area, i.e. Site SH7, was in
decline since the Pleistocene. Through sensitivity analysis of model parameters, it was learned that the parameter weights affecting
the output were sediment porosity, organic matter content and sediment burial rate in descending order. Further numerical
analysis shows that in the hydrate accumulation system, hydrate saturation is proportional to organic matter content, but shows
a non-monotonic dependence on other main parameters. Besides, it is the external methane from deep below dominates the
methane source in the hydrate stability zone. The multiphase fluid transport model of this study provides theoretical basis for the
exploration of hydrate resources.

Key words: gas hydrate, fluid transport model, hydrate saturation, porewater, multiphase flow, the South China Sea