Formation Kinetics and Morphology Characteristics of Fracture-Filling Natural Gas Hydrate under the Influence of Multiple Parameters

To study the effects of multiple physical and chemical parameters on the formation kinetics and morphological characteristics of fracture-filling natural gas hydrate is of great significance for large-scale development and disaster prevention of natural gas hydrate in the South China Sea (SCS). In this study, the effects of the disturbance rate, chemical promoter concentration, silty sediment concentration, and pressure on the induction time, formation kinetics, and growth morphology of fracture-filling natural gas hydrate were studied by conducting formation kinetic experiments and morphological observation using the visualization platform of hydrate in situ formation. The results show that hydrate clusters formed within fractures are stratified into three distinct layers: a dense and hard layer near the gas–liquid interface, a shaggy layer in the upper region of the gas–liquid interface, and a loose layer formed by the agglomeration of hydrate fragments in the lower region. Elevated disturbance rates significantly reduce induction and growth times, enhancing overall hydrate formation, for example, when the disturbance rate was increased from 15 to 50 rpm, the induction time decreased by 69.87% and the yield increased by 148.34%. Optimal sodium dodecyl sulfate (SDS) concentrations (400 ppm) foster the development of a porous, loosely aggregated hydrate structure, improving gas–liquid contact and accelerating growth rates. However, SDS does not alter the fundamental hydrate structure or increase the total yield. The presence of silty sediments significantly boosts hydrate formation rates and yields, with the optimal concentration of 0.5 wt % leading to a remarkable 200% reduction in induction time. Elevated pressures initially reduce induction times and subsequently promote denser hydrate formation, enhancing both growth rates and the total yield. This study is supposed to provide critical insights into the formation kinetics and morphological characteristics of fracture-filling natural gas hydrate.