Morphological and hydrodynamic properties of hydrates during dissociation in sediment

Abstract

The formation and dissociation of hydrate at the pore scale can be observed qualitatively using μ-CT X-ray imaging. However, a quantitative criterion for hydrate pattern is not currently available in the literature. To fill this research gap, we generated numerically-simulated sediments with specific hydrate formation patterns and accurate hydrate saturation levels, by integrating X-ray computed tomography techniques, morphological operation algorithm, and quartet structure generation set method. Using the topological information extracted from the generated hydrate-bearing sediments, we proposed a quantitative criterion for the microscopic classification of hydrates (namely pore-floating, cementing, and bridging) based on the complexity of pore topology (Tp) and hydrate topology (Th). In this work, we visualized 3D distribution of hydrate utilizing μ-CT imaging technology, as well as analyzed the topology of hydrate and its dynamic evolution through extracted dual-network models and proposed classification method. Our findings demonstrate that when the hydrate saturation exceeds 30%, the dominating hydrate patterns are bridging and pore-floating, while sediment is more likely to exhibit cementing and pore-floating patterns when the hydrate saturation is below this threshold. Additionally, we applied the lattice Boltzmann method to numerically analyze the variation of normalized permeability and tortuosity under different hydrate saturation levels. The permeability monotonically increases as hydrate dissociates from the sediments, while the behaviour of tortuosity is non-monotonic.