Pore-scale investigation of hydrate morphology evolution and seepage characteristics in hydrate bearing microfluidic chip

Abstract

Abstract The efficiency and safety of natural gas hydrate exploitation is significantly affected by the occurrence and distribution of hydrate and the seepage behaviors of gas and water in hydrate bearing sediments. We present the results from xenon hydrate formation and dissociation experiments with different salinities using quartz etching microfluidic chips. Direct visualization of hydrate growth morphology is obtained with the help of industrial grade charge coupled device (CCD) camera coupled with a microscope module. The results show that the hydrate growth process in microfluidic chip can be divided into four stages, which are the hydrate inducing stage, the primary hydrate nucleation stage, the rapid hydrate nucleation stage and the hydrate nucleation maturation stage, respectively. Different hydrate morphologies (dendritic, intestine-like) and aggregation patterns (grain-coating, grain-cementing) are observed during the different stage of hydrate formation. The average value of all 219 contact angles of water phase on gas-hydrate interface is 44.03°, which indicates the hydrate surface is hydrophilic. And the hydrophilicity of the hydrate surface is impaired by the increase of brine salinity, owing to the loss of attraction between the molecules caused by the salt-removing effect during the hydrate formation process. The effective water permeability in hydrate bearing microfluidic chip decreases with the decrease of the pore size and is further affected by the heterogeneity. The permeability reduction caused by the hydrate formation is more pronounced in the microfluidic chips with larger initial pores. The hydrate formation kinetics is significantly inhibited by the coupling effect of the tortuosity, the pore size and the salinity and resulted in drastic reduction in hydrate saturation.