Migration characteristics of fine clay particles under the influence of pore water during production in marine clayey silt hydrate reservoirs

Marine clayey silt hydrate sediments are highly susceptible to fines migration during production, which strongly influences reservoir seepage behavior. Hydrate dissociation modifies pore structure and pore water salinity, triggering clay particle detachment, transport, and pore throat clogging. This study investigates pore-water-driven migration behaviors of illite and montmorillonite under hydrate depressurization, focusing on the coupled effects of flow rate, salinity, pore throat evolution, clay content, and production pressure. The results show that illite migrates preferentially ahead of silt particles and is controlled by distinct critical flow rate and salinity. Particle detachment is governed by torque imbalance induced by increasing flow rate. Salinity reduction exhibits a dual control mechanism: above the critical salinity, pore throat expansion associated with hydrate dissociation dominates illite migration, whereas below this value, thickening of the electric double layer and enhanced electrostatic repulsion markedly increase particle concentration, promoting clogging even at low flow rates. Migration mechanisms also depend on production pressure, shifting from flocculation-induced pore clogging at low pressures to bridging-dominated clogging at higher pressures. Montmorillonite exhibits a substantially stronger impact on seepage characteristics due to the combined effects of swelling, dispersion, and migration. Low salinity and high montmorillonite content significantly enhance particle availability, while low Reynolds number conditions favor rolling detachment, re-adsorption, and pore throat clogging. The results provide critical insights for optimizing hydrate production strategies and mitigating permeability damage and associated geohazard risks.