CO₂ leakage and seepage coupled with hydration in sub-sea sediment

In order to explore the CO₂ leakage and seepage coupled with hydration in sub-sea sediment, a mathematical model describing the influence of hydrate formation upon CO₂ leakage and seepage was established based on the Darcy's law and kinetics of hydrate formation, and the effect of hydrate formation on the CO₂ seepage in porous media and the dynamic evolution of sub-sea sediment' characteristic parameters at different temperatures were studied. The results show that the CO₂ hydrate formed rapidly at the leakage outlet. For 15 years, the CO₂ hydrate formed, grew, and accumulated near the leakage outlet which led to the two-order-magnitude decrease in the sediments permeability, from the initial value 1.0^-12 m² to 6.5^-14 m². The effective porosity dropped by 30%, from the initial value 0.3 to 0.2095, and an ultra-low-permeability CO₂ hydrate cover layer formed. The saturation of the CO₂ hydrate near the leakage outlet decreased with the temperature in sub-sea sediment. The influence of leakage on the far field was relatively small and the CO₂ saturation was lowest at 281 K.