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Study on the gas hydrates in porous medium has great significance to the formation, accumulation and exploitation of natural gas hydrate (NGH). Consequently, we investigated the formation/dissociation of ethane hydrate in a sub-millimeter sized capillary in this work, and observed the appearance and kinetic rate during the hydrate formation/dissociation process. The dissociation equilibria of ethane hydrate in capillary was measured first, then the influences of hydrate memory effect (dissociation temperature and time) and degree of subcooling on ethane hydrate formation were obtained, respectively. The results demonstrate that hydrate forms more difficultly in capillary than in conventional macro-reactor because of the fluid resistance effect and poor mass transfer of gas-liquid. The appearance and formation kinetics of ethane hydrate are greatly influenced by the memory effect and subcooling degree. The morphology of ethane hydrate formation on the bubble surface in water bulk phase shows that “bridge effect” occurs during the hydrate formation and growth in capillary.

In co-flowing microfluidic device, it is usually thought the droplet size is significantly influenced by the capillary number in dripping flow. However, it was found in this study that when the contact angle of the dispersed fluid with the dispersed fluid channel was sufficiently large, the droplet size would be little affected by the capillary number. To explain this phenomenon, an “interface – shrinkage – driven” breakup mechanism was proposed. Three different systems and six different microfluidic devices were used in the experiment to prove the universality of the mechanism. The critical contact angle of the dispersed fluid with the dispersed fluid channel was finally discussed.

A concrete understanding of hydrate dissociation behavior is crucial for hydrate exploration and oil/gas transportation. A microfluidic chip has been used in this study to visualize cyclopentane (CP) hydrate dissociation. The results showed that during CP-pure water hydrate dissociation, the guest fluid (CP) released from the CP hydrate behaves like small CP microdroplets, forming a stable CP-in-water emulsion. The size and size distribution of the released CP microdroplets are quantified. The mean size of the microdroplets was around 5.3 μm, while the size distribution was within a narrow range of 4 to 9 μm. Fewer and less stable CP microdroplets were released from the CP-brine hydrate dissociation, while more significant coalescences of the CP microdroplets were observed at a higher salt concentration. For the CP-SDS system, a thick and stable emulsion layer was formed by the mass of tiny CP microdroplets released from the CP hydrate during hydrate dissociation.

Accurate calculation of equilibrium formation conditions of hydrates is important for gas storage and separation based on hydrate technology. In this work, the hydrate formation conditions of a synthesized gas mixture in tetra-n-butyl ammonium bromide (TBAB) aqueous solution were measured at temperature ranging from 278.1 to 286.2 K. An inflection point in the P–T curve of hydrate phase equilibria was found. It is suggested that the hydrate structures transformed from semiclathrate hydrates to pure structure I hydrates with an increase in formation temperature. Then a thermodynamic model was proposed for calculating formation conditions of the semiclathrate hydrates formed from the gas mixtures+TBAB aqueous solution. The Patel–Teja equation of state was used to calculate the fugacity of gaseous hydrate former and several correlations were used to calculate the properties of TBAB. Ethylene molecules are supposed not to be able to occupy the dodecahedral small cages in the TBAB semiclathrate hydrates under the experimental P–T conditions. The presented model results show good agreement with the experimental data and the literature data.

In two-phase dispersion processes coupled with interphase mass transfer, the interfacial tension varies with the mass transfer and significantly affects the dispersion. Determination of the transient interfacial tension (TIFT) in such processes could facilitate better understanding and optimization of the existing processes. In this study, a microfluidic device in which a Laplace sensor was used as a pressure probe was developed to determine the TIFT. The developed Laplace sensor was shown to allow accurate measurement of the local pressure in a micro-device, and to be superior to a commercial pressure sensor. The new method can be used to precisely determine the interfacial tension when the dispersion rate was not higher than 1.5 Hz, and to have a measurement range not narrower than 0.17–58.53 mPa·s. The TIFTs of several systems were then determined, and a mathematical model was established to predict the results. The main factors governing the TIFT were analyzed based on both the experimental and theoretical results.

A novel three-dimensional natural gas hydrate physical simulation device, with a capacity of 0.196 m 3 and maximum operating pressure of 32 MPa, was designed and developed to study the accumulation and exploitation of hydrate-bearing sediment in the natural environment. Acoustic, electrical, and thermal properties at different positions can be collected in real-time to analyze the evolution of hydrate-bearing porous media during the accumulation of hydrate or the production of natural gas. A preliminary experiment was performed to investigate the behaviors of hydrate formation and aggregation in sediment in conditions simulating a gas seeping system. The experimental results showed the methane seeping route has a critical effect on hydrate formation and accumulation within the sediment, and the location of hydrate-rich region. The distribution of hydrate in sediment was controlled by fluid flow field, which was also proven by the simulation of FLUENT TM code. A modified