Modeling of synthesized hydrate-bearing sands: Effect of hydrate morphology on absolute and relative permeabilities

Abstract

Absolute and relative permeability of hydrate-bearing sediments are crucial flow parameters to hydrate exploitation processes. However, up to now, grain-coating hydrate-bearing sediments (GC-HBS) with high hydrate saturation (Sh) and pore-filling hydrate-bearing sediments (PF-HBS) are still prohibitive to be prepared in laboratory. In this work, three-dimensional pore structures of GC-HBS with high Sh and PF-HBS were numerically synthesized, based on the CT scanning of porous samples. Then, a state-of-the-art quasi-static pore-network model (PNM) was used to study the absolute and relative permeability of these HBS. Results show that the absolute permeability of both of the GC-HBS and PF-HBS declined rapidly with increasing of Sh, they can be well fitted by the Tokyo model with exponential parameter of 3.5 and 5.3, respectively. And the absolute permeability of PF-HBS is smaller than that of GC-HBS with same Sh for a bigger specific surface area of PF-HBS which increases the flow resistance for flows. It shows that the wetting and non-wetting relative permeability of GC-HBS decreases with the increase of Sh. But the gas-water two-phase relative permeability of PF-HBS has nonmonotonic changes with the increase of Sh.