The Impact of Gas Flow on Hydrate Reformation and Reservoir Seepage Characteristics in Clayey Silt Sediments

Natural gas hydrate is a promising clean and efficient energy source, but reformation during mining can impede commercial utilization. The impact of gas flow on hydrate reformation and reservoir seepage characteristics has not been extensively researched despite being a crucial parameter in hydrate mining processes. This study employs a core holder to simulate the formation and dissociation of hydrate in clayey silt sediments from the South China Sea (SCS). Differential gas pressure gradients were manipulated to simulate reformation under varying gas flow conditions, during which the water content and pore distribution were quantified with a low-field nuclear magnetic resonance (NMR) spectrometer. Meanwhile, the gas permeabilities k(S h) concerning different hydrate saturation (S h) were measured under constant effective stress. Results indicated that gas flow effectively enhances hydrate reformation, resulting in an increase of the maximum hydrate saturation from 9.44% to 21.15% and an increase of the average reformation rate from 0.15 cm3/h to 0.26 cm(3)/h with an escalating gas pressure differential from 0 to 1 MPa. Hydrate growth primarily occurs laterally along the gas-water interface under low saturation conditions (Delta S h < 10%), while vertical growth dominates at high hydrate saturations (Delta S h > 10%). Notably, the gas flow encourages hydrates to occupy capillaries with a smaller radius under high saturation conditions.