Surface Wettability Governs CO ₂ Hydrate Formation Dynamics: Insights from In Situ NMR Studies

Surface wettability in geological sediments critically influences gas hydrate formation, yet the combined effects of wettability on gas migration and hydrate growth remain poorly understood. This study examines how surface wettability governs the dynamics of CO2 hydrate formation constrained through in situ nuclear magnetic resonance (NMR) spectroscopy and imaging across a spectrum of hydrophilic to hydrophobic conditions. Our experiments reveal that distinct hydrate formation patterns vary systematically with pore surface wettability. In hydrophobic pores, a hydrate shell forms rapidly at gas–water interfaces and restricts the diffusion of CO2, ultimately limiting the final hydrate saturation. Conversely, hydrophilic pores exhibit extended induction times, enabling sustained CO2 dissolution and, consequently, higher hydrate saturation. Time-resolved T2 relaxation profiles reveal greater heterogeneity in gas–water–hydrate distribution within hydrophobic samples, where hydrates preferentially develop in a pore-filling morphology, while in hydrophilic samples, they predominantly exhibit a grain-coating morphology. These wettability-dependent formation patterns substantially influence sediment permeability, with hydrophobic pores showing a more pronounced reduction compared with hydrophilic conditions. We propose a conceptual model that explains these observations through the dynamic interplay among surface wettability, gas–water interface distribution, and subsequent hydrate growth patterns. These findings enhance our understanding of hydrate formation mechanisms in natural sediments, with important implications for the inhibition of secondary hydrate formations and geological carbon storage strategies, where formations are ubiquitous and intrinsically heterogeneous, in terms of structure and mineral surface properties.