- https://doi.org/10.1016/j.marpetgeo.2020.104340
- 10.1016/j.marpetgeo.2020.104340
Abstract — Hydrate-bearing sediments constitute complex hydrological systems. The presence of gas hydrates in pores affects the physical properties of sediments significantly. The pore habit of hydrate in sediments is crucial to all physical properties. However, there is scarce pore-scale evidence of the evolution of hydrate growth in porous media and the influence of water salinity in the micro-morphology of hydrate. In this paper, we monitored -through X-ray computed micro-tomography (CT)- three experiments of methane hydrate growth in sand partially saturated with either NaBr or KI brine under excess-gas conditions. The experiments show coexistence of gas, brine and hydrate at the pore-scale and their evolution of hydrate pore-habit towards three-phase equilibrium. The experiments and data analysis reveal that (1) hydrate forms as a porous medium mixed with inclusions of brine and gas, where hydrate and brine evolve gradually into separate phases as hydrate cages exclude salt ions, (2) hydrate growth mobilizes water over fairly long distances resulting in heterogeneous hydrate distribution, and (3) hydrate can exhibit interconnected pore-habit at local hydrate saturations higher than ~50%, even if grown under excess-gas conditions. The results imply that hydrate micro-morphology and pore habit evolve during hydrate formation and, we suggest that so do the physical properties of hydrate-bearing sediments. The results are relevant to explain the micro-morphology of hydrate and evolution of the properties of hydrate-bearing sediments synthetized in the laboratory and in natural systems.