Pore-scale effect on the hydrate variation and flow behaviors in microstructures using X-ray CT imaging

Abstract

Gas-hydrates are natural clean energy resources with significant potentials as the alternative energy resources. Nevertheless, the formation, migration and dissolution of hydrates in microstructures are not still well understood. Hydrate formation in sand-pack specimen and X-ray CT imaging experiments are conducted to elucidate the hydrates changes in microstructures. Color difference phase separation method is proposed to accurately segment the hydrate, pore and grain phases. Pore-scale variables are defined to quantitatively investigate the characteristics of hydrates. Moreover, the pore-scale flow properties in microstructures with hydrates are also studied. Results indicate that relative pore-scale variables significantly affect hydrate behaviors, in which hydrate saturation first increases with decreasing relative pore-scale variables, then keeps constant with relative stable pore-scale variables, and finally decreases with decreasing relative pore-scale variables during the hydrate migration. In the hydrate interaction, hydrate saturation keeps 0 as relative pore-scale variables gradually decrease to 0, caused by interaction between gas-hydrates and water-hydrates. During the hydrate conversion, hydration saturation increases with increasing relative porosity, relative pore size and relative grain size due to the conversion of gas-hydrates to water-hydrates. Hydrates can decrease the permeability in porous sediments due to the occupation of the pore space by hydrates, and the permeability decreases with increasing hydrate phase in porous sediments. The proposed approach gives more insights to the hydrates behaviors and permeability in fine-gained hydrate-bearing sediments.