Dynamic mechanisms of gas hydrate evolution in hydrophobic sediments: Wall-climbing and secondary formation

Understanding the dynamic evolution of gas hydrates within hydrophobic fine-grained sediments remains a significant challenge for predicting natural hydrate heterogeneity and for improving production strategies. However, the mechanism controlling the hydrate spatial heterogeneity and temporal evolution during phase changes are poorly understood. To address this, we investigated the formation and dissociation dynamics of gas hydrates in hydrophobic porous media using in situ X-ray computed tomography (X-CT). We observed a distinct boundary-driven growth mode, termed “wall-climbing”, in which hydrates preferentially accumulated as massive aggregates with isolated pores at the upper region of the sediment, rather than forming uniform pore-filling hydrates within the internal matrix. During depressurization-induced dissociation, the decomposition of boundary-localized hydrate triggers fluid redistribution and substantial secondary hydrate formation in the lower sediment pores, highlighting a non-equilibrium self-organization pathway during decomposition. We elucidate the dynamic mechanism of gas hydrates in hydrophobic sediments by linking the wall-climbing effect and secondary formation to coupled effects of wettability-controlled capillary redistribution, preferential migration pathways, gravity, and boundary-localized heat transfer. We further propose a field-relevant conceptual analogy in which similar interface-driven accumulation and redistribution may occur at natural high-contrast boundaries, such as fractures, seep conduits, sediment-carbonate interfaces. These findings provide mechanistic insights into hydrate heterogeneity and dynamic redistribution, with implications for gas recovery, flow assurance, and interpretation of cold seep hydrate architectures.