Hydrate growth in granular materials: Implication to hydrate bearing sediments

It is often assumed that the properties of hydratebearing sediments are affected by hydrate growth habits in pores. We test this hypothesis by stochastically simulating hydrate growth in pore space of a simple cubic packing of mono-sized spherical sediment grains, and assume three extreme nucleation preferences in the absence of heat or mass transport limitations, and without interfacial surface tension: (1) Homogeneous nucleation produces isolated nuclei and a highly porous hydrate mass; (2) Heterogeneous nucleation results in combined surface coating and framebuilding hydrate structures; and (3) Preferential heterogeneous nucleation on pre-existing hydrate surfaces leads to hydrate growth into the pore space. Spatial distribution of hydrate is analyzed to investigate the surface coating density, grain connectivity and mass density of hydrate cluster. Results show that surface coating density is predominant for heterogeneous nucleation and grain connectivity by hydrates is lower than the hydrate volume fraction in all cases. Therefore, a slow increase in stiffness is anticipated at low hydrate volume fraction. The highly porous hydrate structure formed by homogeneous nucleation and dense hydrate cluster are discussed with the relevance to the geomechanical and physical properties of hydrate-bearing sediments.