Pore-scale morphology and wettability characteristics of xenon hydrate in sand matrix - Laboratory visualization with micro-CT

The properties of gas hydrate bearing sediments (GHBS) depend on their changing morphology and wettability characteristics, which are in turn important for efficiency and safety issues during production. We present the results of xenon hydrate formation experiments using quartz sand packs at different salinities. Direct 3D visualization of hydrate distribution in the pore space was obtained with the help of high-resolution micr-ocomputed tomography (CT). Four phases, xenon hydrate, xenon gas, brine and quartz sands were segmented and labelled in the raw micro-CT scanned images. A 3D reconstruction reveals typical pore-scale patterns of hydrate occurrence (pore-filling, grain-coating) and shows that hydrate preferentially aggregates at the gas-water interface, reflecting greater local access to xenon gas molecules. The hydrate cluster shape factor ranges from 2 to 10, indicating that xenon hydrate forms with a complex and irregular microstructure, consistent with random growth nature of hydrate. The hydrate saturation is found to decrease with salinity under excess-gas condition, which we interpret in terms of the hydrate formation kinetics to indicate that gas hydrate prefers to grow into the gas phase at the gas-water interface. A total of 270 local contact angles of water at the gas and hydrate interfaces in pores were measured with a micro-CT image analysis method to obtain information on the wettability variation of hydrate surfaces. The average was calculated to be 47.6 degrees, indicating that xenon hydrate surface is hydrophilic. Our analysis of the xenon hydrate morphology provides a new method for revealing hydrate growth behavior at pore-scale. The wettability characterization offers key parameters for accurate numerical simulation of multiphase flow prediction and seepage behavior in GHBS.