Study on the Promotion of Methane Hydrate Formation by Surface Modification of Quartz Sand

Natural gas hydrates, with their vast reserves and high gas storage density, have emerged as a highly promising alternative energy source and technology for gas storage and transportation. Wettability, as a core surface property of porous media, directly influences hydrate nucleation, growth, occurrence morphology, and flow behavior. In this study, quartz sand with varying surface properties was prepared with the octyltrimethoxysilane (OTMS) silane coupling agent via surface chemical reactions. The methane hydrate (MH) equilibrium conditions as well as the formation kinetics in silica sand were measured, and the mechanism and potential of the surface modification for enhancing methane hydrate storage capacity were analyzed. The experimental results indicate that surface modification of quartz sand has no significant effect on the MH equilibrium condition. Hydrophobic modification of quartz sand provides more gas–liquid interfaces, increases the contact area, and thereby significantly enhances mass transfer under high-water-saturation conditions and accelerates the MH formation rate. However, excessively high surface hydrophobicity may reduce the effective gas–liquid interfacial area and limit the overall hydrate formation rate. Due to the influences of the hydrate distribution and aggregation, as well as gas diffusion on hydrate formation, the effect of the initial formation pressure on MH formation is only observed during the early stages of MH formation, while the temperature effect is less pronounced than that of formation pressure. It is suggested to further consider combining stirring with continuous gas injection to enhance gas–liquid flow and improve gas–liquid contact, thereby increasing the formation rate of hydrates.