Regulation of Structure II Hydrate Nucleation Characteristics by Marine Sediment Particles in the South China Sea

Abstract Elucidating the nucleation kinetics of structure II (sII) hydrates in authentic marine clay environments is essential for gas hydrate resource evaluation and safe exploitation in the South China Sea. Using in-situ marine clay sediments as porous media, we conducted high-pressure visual hydrate formation experiments at five loading gradients (0–10 g) coupled with multi-scale characterizations, to quantify variations in induction time and gas conversion rate. Marine clay exhibits a pronounced dual concentration-dependent effect: moderate dosage (≤ 2 g) reduces induction time by 192.67 min compared with the blank system, while excessive clay prolongs it by 11.67 min relative to the optimal group. The gas conversion rate follows a non-monotonic trend, peaking at 2–5 g and declining sharply at 10 g. Dispersed clay particles at low concentrations furnish abundant heterogeneous nucleation sites to lower the energy barrier, whereas excess clay triggers aggregation and pore clogging, elevates mass transfer resistance, and inhibits nucleation. This work clarifies the concentration-dependent nucleation mechanism of sII hydrates in natural marine sediments, providing a reliable experimental basis for hydrate development.