Experimental and Optimization Strategies for Fines Migration–Conductivity Damage Suppression in Hydrate Reservoir Fracturing Proppant-Filled Layer

Hydraulic fracturing has considerable potential for stimulating natural gas hydrate reservoirs (NGHRs). However, hydrate dissociation-induced mechanical weakening of sediments, together with gas–water two-phase flow-driven fine particle migration, poses significant engineering challenges, including proppant embedment and fracture plugging, which severely degrade fracture conductivity. This study employed a visual sapphire reactor to investigate the effects of proppant-filled layers on hydrate formation and dissociation behavior. X-ray computed tomography (X-ray CT) was further utilized to characterize fine particle migration patterns and pore-structure damage within the proppant-filled layer. The results indicate that conductivity impairment predominantly occurs during the constant-pressure stage and the subsequent gas output stage. Increasing proppant concentration and reducing proppant particle size significantly mitigate conductivity damage while enhancing gas production rates. Moreover, a gradient-filling strategy using 20–40 and 40–60 mesh proppants effectively optimized fracture conductivity, yielding total porosity increases of 84.6% and 23.9%, respectively, relative to uniform proppant filling. Additionally, pore-structure damage was found to vary nonlinearly with decomposition pressure, highlighting a coupled relationship between damage severity and gas–water two-phase flow velocity, which in turn influences particle migration intensity and spatial distribution. These findings provide valuable guidance for optimizing proppant gradation and developing effective protective strategies, and offer a useful reference framework for integrating hydraulic fracturing and sand control to support sustainable and stable gas production from hydrate reservoirs.